mgt literature review

ABSTRACT

Nowadays there is a great interest for the use of microturbines as sources of

distributed generation, particularly in areas where demand is both electricity and heat. In

these areas microturbines reach very high efficiency rates.

Microturbines can operate both stand-alone and grid connected. The second one of

the mentioned possibilities is which deserves a much deeper study, to analyse the

interaction of the microturbine with the distribution network it is connected to.

This project deals with the theory, modeling, simulation, mathematical analyses and

analysis of load following behavior of a micro turbine (MT) as a distributed energy

resource (DER).

In this project a dynamic model of a microturbine is developed with

Matlab/Simulink/Sim power systems. The model has been included The model has been

mathematical verified and several dynamic simulations have been performed to study the

response to step changes in the power control references. Also, the performance of the

microturbine to faults in the network has been analyzed.

Index Terms:

Distributed energy resources (DERs), load following Performance, micro turbine

(MT), recuperator, speed control, Synchronous generator (SG), Dynamic model.

DYNAMIC PERFORMANCE ANALYSIS OF A MICROTURBINE BASED DISTRIBUTED ENERGY RESOURCE

INTRODUCTION

DISTRIBUTED energy resources (DERs) are a variety of small-scale, modular

distributed generation (DG) technologies that can be combined with energy management

and storage systems. DERs have received significant attention as a means to improve the

performance and reliability of electrical power system. They can provide low-cost energy

and increase energy efficiency through combined heat and power (CHP) mode of

operation. Moreover, their application can also reduce transmission and distribution (T&D)

losses, relieve T&D assets, reduce constraints, and improve overall power quality and

reliability. Literature review shows that there is extensive thrust on the application of MT

for DG. Research areas include simulation, offline/real-time studies, and development of

inverter interfaces for MT applications. Peirs et al. Report the development of a single-

stage axial flow MT for power generation. Nichols and Loving highlight the facilities of

MT technology through relevant test results.Suter reports the development of an active

filter for MT operations.Jurado and Saenz describe an adaptive control mechanism of a

hybrid power system with fuel cell and MT.Gaonkar and coworkers demonstrate a

simulation model developed from the dynamics of each part of the MT and discuss its

operation in islanded and grid-connected modes

Most MT’s use a permanent-magnet synchronous generator (PMSG) or asynchronous

generator for power generation. The system model in considers bidirectional power flow

between the grid and MT system using PMSG.PMSG is also used in and the operation of

MT is considered in islanded connected mode. However, very little is reported on

development and load following performance analysis of MT models with a synchronous

generator (SG) in islanded connected mode. This area needs to be extensively investigated

to resolve the technical issues for integrated operation of an MT with the utility grid.

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In this project, we describe the modeling and simulation of an MT–generator

(MTG) system consisting of an MT coupled with an SG followed by its load

following performance analysis. We have analyzed the performance in islanded connected

mode. Simulation is done in MATLAB–Simulink platform. Simulation results have been

compared with other existing results as well as typical real MT data. The proposed model is

also suitable for studying the dynamic behavior of the MTG system connected with other

types of DG in micro grid and grid applications.

1.1 Background

Nowadays, the need of energy production to be used for either industrial or

several transportations is in great demand. The type of power generation has become the

major concern because of its widespread need. For the concern of recent time needs, the

suitable power generation type is one which achieves a relatively better efficiency, low in

cost, and satisfied the demanding criteria.

For those needs the gas turbine system is the answer. Gas turbines are internal

combustion engines that they use a rotating shaft or rotor instead of "reciprocating" in

cylinders. It has the advantages of small dimensions, light weight, easy to be serviced

(resulting to low maintenance cost), and most of all it can produce more power (relative to

the power produced-to-weight ratio) and faster speed spin. They became practical sixty

years ago; today gas turbines are one of the keystone technologies of the civilization.

Because of its critical role, it is understandable that innovation to a step further is

needed. In a field where the major role needed and development costs both 2 are the

major concerns, it was thought to build the smallest possible gas turbine, and to explore

whether the device could be made into smaller size. The microturbine is actually the

scale-down of the large ordinary gas turbine system.

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This is what gave birth to this project – since the advantages of gas turbines are

already known compare to the others, in this thesis, I have simulated gas based microturbine

and analyzed its performance for different loads. The behavior of torque and speed for slow

dynamic conditions is care fully examined. Also I have connected the MT generator to low

voltage and high voltage grids. Analysis is made for voltages and currents at different points

in the networks in the event of faults.

1.3. Objective of Study

The objective of this study to simulated gas based microturbine and analyzed its

performance for different loads. The behavior of torque and speed for slow dynamic

conditions is care fully examined. Also I have connected the MT generator to low voltage

grid with and with out fault. Analysis is made for voltages and currents in the networks in the

event of faults.

1.4 Outline of Report

This project is divided into ten chapters.

Chapter 1 presents the Introduction, the background of the study, which gave birth

to this project. It also covers the objective of study, and this project’s outline report.

Chapter 2 describes the literature review of the project.

Chapter 3 describes the Generally, the term Distributed or Distributed Generation

refers to any electric power production technology that is integrated within distribution

systems, close to the point of use. Distributed generators are connected to the high voltage

or low voltage grid

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Chapter 4 discussed a number of micro turbines generators have recently been

announced as currently commercially available for sale to customers, such as end users,

utilities, and energy service providers. Manufacturers and others are reporting certain

performance capabilities of the turbines; however, no consistent third-party

independent testing as been done to confirm or discredit such performance claims

Chapter 5 discussed a gas turbine is a rotating engine that extracts energy from a

flow of combustion gases that result from the ignition of compressed air and a fuel (either

a gas or liquid, most commonly natural gas). It has an upstream compressor module

coupled to a downstream turbine module, and a combustion chamber(s) module in

between.

On chapter 6 discussed a Micro turbines are small high-speed gas turbines. The

three main components of a micro turbine are compressor, combustor, and the turbine.

The compressor is used to pressurize the air before entering the combustor. Injected fuel

is mixed with the compressed air in the combustor and the mixture is ignited. Mechanical

energy is produced when the hot combustion gases flow and expand through the turbine.

The turbine drives a synchronous generator.

On chapter 7 discussed the microturbine model description. Usually, an MT

consists of turbine, synchronous machine, power electronics, recuperator, control and

communication. And also discussed mt, controller, turbine model and parameters of all

models used in this project.

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On chapter 8 discussed the simulation model for MT model and Simulation

Results of Islanded mode and connected to fault.

On chapter 9 discussed the Mathematical analysis of micro turbine.

In this project, modeling and simulation of MT coupled with SG are performed and

reported. Its load following performance is thoroughly tested and validated for different

operating conditions, with and without speed controllers. The model has been simulated

working in grid connected mode and different operation conditions have been analysed

(Step change, fault,…). The simulation results have showed that the microturbine works

properly connected to a low voltage distribution grid.

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LITERATURE REVIEW

Nowadays there is a great interest for the use of microturbines as sources of

distributed generation, particularly in areas where demand is both electricity and heat. This

project deals with the theory, modeling, simulation, and analysis of load following behavior

of a micro turbine (MT) as a distributed energy resource (DER). In these areas

microturbines reach very high efficiency rates. Also, the performance of the microturbine

to faults in the network has been analysed. In this project a dynamic model of a

microturbine is developed with Matlab/Simulink/Sim power systems.

A Development of models for analyzing the load-following performance of

microturbines and fuel cells, Y. Zhu, K. Tomsovic, [1] presents Deregulation has begun to

allow for the provision of various ancillary services, such as load-following. This paper

presents simplified slow dynamic models for microturbines and fuel cells. Their stand-

alone dynamic performances are analyzed and evaluated. A distribution system embedded

with a microturbine plant and an integrated fuel cell power plant is used as an example.

The control strategy and load-following service in this distribution system are simulated. It

is illustrated that microturbines and fuel cells are capable of providing load-following

service, significantly enhancing their economic value. a simplified slow dynamic model of

a split-shaft microturbines is developed.

A Dynamic model of microturbine generation system for grid connected/islanding

operation, D. N. Gaonkar, R. N. Patel, and G. N. Pillai. [2] presents the performance of

microturbine generation systems their efficient modeling is required. This paper presents a

dynamic model of a MTG system, suitable for grid connection/islanding operation. The

presented model allows the bidirectional power flow between grid and MTG system. The

components of the system are built from the dynamics of each part with their

interconnections. At first the mathematical modeling of the microturbine along with the

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control systems is given and following that the detailed simulation model of the MTG

system is developed using MATLAB's SimPowerSystems library. The simulation results

demonstrate that the established model provides a useful tool suitable to study and to

perform accurate analysis of most electrical phenomena that occur when a micro turbine is

connected to the grid or is operated in islanded mode. The simulation results show that the

developed model of the MTG system has the ability to adjust the supply as per the power

requirements of the load within MTG's rating.

A Modeling and Performance Analysis of a Microturbine as a Distributed Energy

Resource, A. K. Saha, [3] presents modeling, simulation, and analysis of load following

behavior of a microturbine (MT) as a distributed energy resource (DER). The MTG model

also incorporates a speed controller for maintaining constant speed at variable loads.

Performance is studied both with and without the speed controller. The paper also

compares the simulation results with already reported results and with real life load

following data for a typical islanded MT of similar rating. modeling and simulation of MT

coupled with SG are performed and reported for both islanded and gridconnected modes of

operation. The results are compared with already reported results and with typical real life

load following data for a similar system in islanded mode. This model is quite useful for

studying the dynamic performances of MTs in microgrid and hybrid power system

environment.

A Novel Power Conversion System for Distributed Energy Resources, R. Esmaili

et, al., [4] presents a novel approach to developing a power conversion system (PCS) for

Distributed Energy Resources (DER). Many DER require the use of a PCS to develop

useable electricity from an energy source. The paper discusses various aspects of the design

including inverter topology, power, control and power supply circuit designs, switching

and protection equipment and thermal considerations. Experimental and analytical results

indicate that losses associated with a three-level inverter topology are compatible with

design concepts. Immersing the power circuit in transformer oil can dissipate the heat

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generated by a three-level inverter, when utilizing a heat sink designed by Heat Technology

Inc. to optimize heat transfer.

A Modeling and Simulation of the Electric Part of a Grid Connected Micro

Turbine, O. Fethi, L.-A. Dessaint, [5] presents a simulation model of the electric part of a

grid connected micro turbine (MT). The simulation results obtained with the model using

Sim Power Systems software were compared with experimental results obtained with a

Capstone 30 kW micro turbine. The simulation results demonstrate that the established

model provides a useful tool suitable to study and to perform accurate analysis of most

electrical phenomenon that occurs when a micro turbine is connected to the grid. The

model has been validated through several experiments preformed on a 30 kW Capstone

unit. The simulation results obtained for utility voltage unbalances as well as for utility

voltage distortions show the usefulness of the model and its accuracy.

An Assessment of Microturbine Generators, D. K. Nichols and Kevin P. Loving,

[6] discusses microturbine technology , those facilities and present test results.

Microturbine generators hold promise to efficiently meet energy demand while lowering

associated environmental impact. As with any new technology, application of the

technology will occur only after thorough assessment and demonstration , To accomplish

that assessment test facilities have heen developed to assess performance, system

compatibility , and efiiciency and emission issues.

Adaptive Control of a Fuel Cell-Microturbine Hybrid Power Plant, Francisco

Jurado, and José Ramón Saenz, [7] presents The composition of natural gas may vary

significantly, and load power varies randomly. Traditional control design approaches

consider a fixed operating point in the hope that the resulting controller is robust enough to

stabilize the system for different operating conditions. An adaptive minimum variance

controller is developed in this paper. Conventional control depends on the mathematical

model of the plant being controlled. This paper develops the control system with an

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adaptive minimum variance controller and based on the simulation study, the resulting

controller is robust enough to stabilize the system for different disturbances affecting the

plant (load power variation) or a change in the plant model parameters (gas composition).

Dynamic Performance of a Microturbine Connected to a Low Voltage Network, E.

Torres1 et,al., [8] presents a dynamic model of a microturbine is developed with

Matlab/Simulink/Simpowersystems. The model has been included within a low voltage

network model and several dynamic simulations have been performed to study the response

to step changes in the power control references. The model has been simulated working in

grid connected mode and different operation conditions have been analysed (Step change,

fault,…). The simulation results have showed that the microturbine works properly

connected to a low voltage distribution grid. Next developments in this field will be the

improvement and optimization of the microturbine model as well as the analysis of

multiple operation conditions, mainly related to different fault situations and the definition

of the settings of protection relays.

A Simulink-Based Microturbine Model for Distributed Generation Studies,

Sreedhar R. Guda, C. Wang, [9] presents the modeling and simulation of a microturbine

generation system suitable for isolated as well as grid-connected operation. The system

comprises of a permanent magnet synchronous generator driven by a microturbine.

Simulation studies have been carried out in MATLAB/Simulink under different load

conditions. The modeling of a single-shaft microturbine generation system suitable for

power management in DG applications is presented in this paper. Simulation results show

that the developed model has the ability to meet the requirements of the load, maintaining

prescribed values of voltage and frequency with the help of the power electronic controls.

Modeling and Performance Analysis of a Microturbine as a Distributed Energy

Resource, A. K. Saha, [10] presents modeling, simulation, and analysis of load following

behavior of a microturbine (MT) as a distributed energy resource (DER). The MTG model

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also incorporates a speed controller for maintaining constant speed at variable loads.

Performance is studied both with and without the speed controller. The paper also

compares the simulation results with already reported results and with real life load

following data for a typical islanded MT of similar rating. The results are compared with

already reported results and with typical real life load following data for a similar system in

islanded mode. This model is quite useful for studying the dynamic performances of MTs

in microgrid and hybrid power system environment.

An Educational Guide to Extract the Parameters of Heavy Duty Gas Turbines

Model in Dynamic Studies Based on Operational Data, Mohammad Reza Bank Tavakoli

et, al., [11] presents of Rowen’s model for heavy duty gas turbines in dynamic studies are

estimated by use of available operational and performance data. The way of obtaining the

parameters and sole physical laws are explained to some extents to make it useful for

students of electrical engineering and trainers who are involved in dynamic studies. The

paper provides background knowledge for the students who want to know more about the

building blocks of HDGT dynamic model. Among a lot of parameters and data which are

provided by manufacturer, the useful and most straight forward ones for deriving the model

parameters are used here which can be invoked in any similar case.

Pwm inverters in decentralized generation systems: characterization of the dynamic

behavior under utility fault conditions, S. Nguefeu et,al., [12] presents the concept of

dispersed generation and its impact on the utility distribution network, focusing on four

energy sources : solar energy, fuel cells, wind power and micro turbines. Specific models

for each type of source as well as coupling interfaces are developed. Finally, an example of

the utilization of the models is given : it shows the simulation results obtained in the micro

turbine case for a few faults occurring on the utility low voltage grid.

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In this thesis, I have simulated gas based microturbine and analyzed its performance

for different loads. The behavior of torque and speed for slow dynamic conditions is care

fully examined. Also I have connected the MT generator to low voltage grid. Analysis is

made for voltages and currents at different points in the networks in the event of faults.

DISTRIBUTED ENERGY RESOURCES (DER)

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3.1Distributed Generation Background

Generally, the term Distributed or Distributed Generation refers to any electric

power production technology that is integrated within distribution systems, close to the

point of use. Distributed generators are connected to the medium or low voltage grid. They

are not centrally planned and they are typically smaller than 30 MWe (DTI 2001). The

concept of DG contrasts with the traditional centralised power generation concept, where

the electricity is generated in large power stations and is transmitted to the end users

through transmission and distributions lines (see figure 1.1). While central power systems

remain critical to the global energy supply, their flexibility to adjust to changing energy

needs is limited. Central power is composed of large capital-intensive plants and a

transmission and distribution (T&D) grid to disperse electricity. A distributed electricity

system is one in which small and micro generators are connected directly to factories,

offices, and households and to lower voltage distribution networks. Electricity not

demanded by the directly connected customers is fed into the active distribution network to

meet demand elsewhere. Electricity storage systems may be utilised to store any excess

generation.

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Figure 3-1. An electric power system

Large power stations and large-scale renewable, e.g. offshore wind remain connected

to the high voltage transmission network providing national back up and ensure quality of

supply. Again, storage may be utilised to accommodate the variable output of some forms

of generation. Such a distributed electricity system is represented in figure 1-2 below.

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Figure 3-2. A Distributed Electricity System

The non-traditional operating model of DG has drawn strong interest because

of its potential to cost effectively increase system capacity while meeting the industry

restructuring objective of market driven, customer-oriented solutions. These distributed

generation systems, capable of operating on a broad range of gas fuels, offer clean,

efficient, reliable, and flexible on-site power alternatives. This emerging portfolio of

distributed generation options being offered by energy service companies and independent

power producers is changing the way customers view energy.

Both options require significant investments of time and money to increase

capacity. Distributed generation complements central power by providing in many cases a

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relatively low capital cost response to incremental increases in power demand, avoiding

T&D capacity upgrades by where it is most needed, and having the flexibility to put power

back into the grid at user sites. Significant technological advances through decades of

intensive research have yielded major improvements in the economic, operational, and

environmental performance of small, modular gas-fuelled power generation options.

Forecasts predict a total 520GW from newly installed DG around the globe by 2030.

3.2 Advantages of DER:

DERs have received significant attention as a means to improve the performance

and reliability of electrical power system. They can provide low-cost energy and increase

energy efficiency through combined heat and power (CHP) mode of operation. Moreover,

their application can also reduce transmission and distribution (T&D) losses, relieve T&D

assets, reduce constraints, and improve overall power quality and reliability.

Fig 3.3 distributed energy resources

3.2 Small Distributed Generation Technologies:

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Recent DER technologies include micro turbine (MT), fuel cells, photovoltaic,

wind energy, Solar Thermal, Small Reciprocating Engines etc. Under the current electric

utility restructuring and public environmental policy, there is ample scope for large-

scale integration of DERs into utility grid distribution system .

Micro turbines:

Micro turbines are composed of a generator and small gas turbine mounted

on a single shaft. The turbine technology is based on a refinement of automotive turbo

chargers and military engines. Micro turbines rotate at high speeds, some at nearly 100,000

rpm. A permanent magnet generator spinning at this high shaft speed produces the power

in the form of high-frequency AC, which is converted to DC and then to standard 60-Hz

AC using an inverter. Most micro turbines are fueled by natural gas but can also use liquid

fuels such as diesel or jet fuel. These units currently range in size from 30 to about 100

kW; larger units are under development. Most micro turbines also have a recuperator to

recycle some exhaust heat back to the combustor. A micro turbine with recuperator

typically has 20-30 percent efficiency. Utilization of waste heat can increase overall system

efficiency (electricity and heat) to 70- 80 percent. Because the combustion process is

closely controlled and relies on relatively clean burning fuels, micro turbines typically

produce few emissions

Fuel Cells:

A number of fuel cell technologies are either under development or

currently being used to generate power. The attraction of fuel cells is their potential for

highly efficient conversion to electrical power (35 to 55 percent without heat recovery).

The only technology in general use today is the phosphoric acid fuel cell, which is

available in the 200-kW size range. This fuel cell operates at about 40 percent conversion

efficiency. Because this device operates at 400 degrees F, waste heat is available as steam,

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which boosts the overall fuel conversion efficiency. A number of other fuel cell

technologies are being developed. For the power industry, these include: proton exchange

membrane (low-temperature, hydrogen fueled), molten carbonate (high- temperature), and

solid oxide (high-temperature).

Photovoltaic Cells:

Photovoltaic (PV) devices have been in existence for many years since

their early use in the U.S. space program. They rely on sunlight to produce DC voltage at

cell terminals. The amounts of voltage and current that PV cells can produce depend on the

intensity of sunlight and the design of the cell. PV systems use cell arrays that are either

fixed or track the sun to capture additional energy. Because solar energy is a diffuse

resource, it takes a large area of PV cells to produce significant power. At a typical cell

conversion efficiency of 10 percent, about 10 m2 of panels are needed to provide a peak

power of 1 kW. To reduce the number of costly PV devices used, mirrors or lenses can be

used to concentrate sunlight on to the cells. This increases the PV cell output but requires

tracking devices to insure that the array is aligned with the sun.

Solar Thermal:

Although there are a number of large-scale (several-megawatt) generation

technologies in the solar thermal field, the main technology for small-scale generation is

the sterling dish. This technology is being tested in the 10- to 25-kW range. In this system,

light is concentrated on a small receiver by a sun-tracking array of mirrors. The heat

collected by the receiver is transferred to the hot end of a sterling engine. The sterling

engine uses working fluid in a closed cycle to push pistons and generate shaft rotation. In a

sterling dish, shaft rotation is used to spin an induction generator that is connected to the

electric grid.

Wind:

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Wind generation has been commercially available for many years. The main push

has been in large wind farms where wind turbines from 700 kW to 1.5 MW are available

and in use. Several smaller wind turbines (<250 kW) are available for use in MicroGrids.

These machines typically use an induction generator driven by a rotor with blades. As is

true for the solar options, the wind generators’ power output is determined by the

availability of their energy source. When the turbine is operating in stand-alone mode, any

power requirement in excess of the wind energy available must be supplied by storage

systems or other generation.

Small Reciprocating Engines:

Reciprocating engines that run on various fuels are available in small sizes and up

to several megawatts. Currently available engines are typically intended for stand-alone or

back-up use. These engines, especially the larger ones, have good efficiencies (30 to 40

percent). They operate in stand-alone applications like scaled-down generation plants with

synchronous generators capable of controlling voltage and frequency. Waste heat from

these units can help boost overall system efficiencies.

MICRO TURBINE GENERATOR

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A number of micro turbines generators have recently been announced as currently

commercially available for sale to customers, such as end users, utilities, and energy

service providers. Manufacturers and others are reporting certain performance capabilities

of the turbines; however, no consistent third-party independent testing as been done to

confirm or discredit such performance claims.

4.1 Overview

There are several manufacturers of Micro turbine generators (MTGs) announcing

their products as currently commercially available. Their potential customers are end-users,

utilities, and energy service providers. The chart shows some of the MTG Manufacturers

and current MTG operating features. To be competitive with existing technology, most

MTG manufacturers rely on enhanced reliability and lower maintenance costs. MTG

manufacturers expect to achieve greater reliability and lower costs by using fewer moving

parts and lower manufacturing costs. Manufacturers thus expect economy of manufacturing

of microturbines to replace economics of scale for central plants. For MTGs to be

competitive in the marketplace, minimum customers’ expectations are:

_ 40,000 hour “wheel life”

_ Heat rate of 12,000 to 16,000 BTU/kWh

_ Good part load performance

_ Emissions < 9ppm

_ Noise < 70 dB

_ Cheap and easy installation and maintenance

There is a tremendous potential market for MTGs if the MTG manufacturers can

make their products competitive with the other forms of energy available at the meter.

Using turbo-charger technology, the cost of producing an MTG can become lower and

lower -- depending on the manufacturer’s expertise in economy of manufacturing.

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This is especially true if the manufacturer can use a casting process versus a

machined process. The MTG manufacturers realize that with an adequate volume of sales,

relying on low cost economics of manufacturing, MTGs have a stronger potential to

compete well at the meter with large central power plants. Additionally, on site power

maybe able to pick off other markets within niches to provide for future product

development. MTGs are intended to provide the energy industry with dispersed power

generation assets that may be located close to the loads they serve. For utilities, interest in

MTGs is based on deferred central power plant construction, deferred distribution line

upgrades, and improved reliability. End use customers may view MTGs as an alternative to

other small generators, an environmentally acceptable power generation device, and a

reliability improvement mechanism. There is speculation that MTGs may be an integral

part of the future utility infrastructure. In such as speculation, numerous, small generators

are scattered throughout a utility's traditional distribution network working in parallel with

central power plants. Some believe this will emulate what personal computers and local

area networks did by working in parallel to mainframes. MTG manufacturers and others

are reporting certain performance capabilities of the turbines; however, no consistent,

independent, third party independent testing has been done to confirm or discredit such

performance claims. However, MTGs will only be considered if they perform acceptably

and meet customers’ requirements for power quality, reliability, availability, environmental

considerations, cost effectiveness, usability and system efficiency. As a part of the overall

testing program, MTGs are purchased, installed, operated and tested to assess their

performance. Data was collected electronically and manually. Ultimately results, as

applicable for each unit, include the following performance measures:

_ Starts/stops

_ Overall unit efficiency

_ Net power output

_ Operability

_ Emissions level monitoring

_ Power quality monitoring

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_ Endurance testing

4.2 Technical Backgrounds:

MTGs are small, high-speed power plants that usually include the turbine,

compressor, generator, and power electronics to deliver the power to the grid. These small

power plants typically operate on natural gas. Future units may have the potential to use

lower energy fuels such as gas produced from landfill or digester gas.

Figure 4.1. MTG Components

MTGs have a high-speed gas turbine engine driving an integral electrical generator that

produces 20-100 kW power while operating at a high speed, generally in the range of

50,000-120,000 rpm. Electric power is produced in the 10,000s of Hz, converted to high

voltage DC, and then inverted back to 60 Hz, 480 VAC by an inverter. Most of MTG

engine designs typically have one or several power producing sections, which include the

turbine, compressor, and generator on a single shaft. During engine operation, engine air is

drawn into the unit and passes through the recuperator where temperature is increased by

hot exhaust gas. The air flows into the combustor where it is mixed with fuel, ignited and

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burned. The ignitor is used only during startup, and then the flame is self-sustaining. The

combusted gas passes through the turbine nozzle and turbine wheel, converting thermal

energy of the hot expanding gases to rotating mechanical energy of the turbine. The turbine

drives the compressor and generator. The gas exhausting from the turbine is directed back

through the recuperator, and then out the stack.

4.3 MTG Testing Program

This MTG test program is expected to provide valuable insight, both qualitative and

quantitative, into the installation, performance and maintenance requirements of units

presently available to the market. Test results are based on actual operating conditions at

the test site in

Irvine, California. In addition to the results and experiences derived from installing and

operating these units, performance data are collected to trend and profile operating

characteristics via a Data Acquisition System and manually.

4.3.1 Data Acquisition System (DAS)

The Data Acquisition System (DAS) installed at the MTG test site provides interval

sampling of MTGs in operation. Raw data is collected in 5-minute intervals from various

measurement sensors that feed a datalogger with either pulse or analog signals. The raw

data is collected nightly, and processed once a month. Each MTG is retrofitted with sensors

at various locations. Additionally, environmental parameters are collected for the entire

site. Data parameters collected are described in Table4.1.

Table 4.1. MTG DAS Monitoring Parameters

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Parameter Instrument

Electrical Energy

Produced3-phase electrical meter

with pulse output module

Fuel Consumed (Gas

Flow)

Gas flow meter

Water Flow* Water flow meter

Fuel Temperature RTD

Boiler Air

Temperature – Inlet

and Outlet*

Thermocouple

Relative Humidity Solid State IC

Gas Pressure Pressure transducer

Ambient Temperature Temperature Probe

Water Temperature –

Inlet and Outlet*Resistance Thermal

Detector (RTD)

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Power Quality

Snapshots

BMI 7100 and BMI

8010 power quality

meters

4.3.2 Test Procedures

To fully evaluate the MTGs, a series of tests were developed. Testing of MTGs is

categorized into three phases:

_ Installation and Startup

_ Operation and Maintenance

_ Performance

4.3.3 Installation and Startup

Each MTG delivered to the test site is inspected and noted to include operating

instructions, repair parts or a recommended spare parts list, consumable supplies, trouble-

shooting and maintenance procedures/guides, and a drawings and diagrams to sufficient to

support maintenance Once installed, the MTGs start and stop capabilities are tested. Units

are expected to withstand the wear of daily starts and stops. Operators at the test site

manually shut down the units several times per month. At other times, the units shut down

(e.g. loss of grid) and/or were manually restarted.

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Figure4. 2. Bowman MTGs Bowman 60 kW rated MTG (left) and a Bowman 35 kW

rated MTG (right) are shown installed at test location.

4.4. Machine Performance Test Criteria

4.4.1 Endurance

For the test program, MTGs will be operated for as long as practicable at nominal

load. Daily operating parameters: fuel flow, ambient air pressure, temperature and

humidity, energy (kWh), operating temperatures and pressures will be recorded. Critical

MTG parameters will be recorded with the intent of correlating degradation with factors

other than wear and tear.

4.4.2 Transient Response

MTGs should be able to respond adequately to load changes. Units that are not

capable of isolated bus operation will operate in parallel with the system grid. Changes in

26


system load will be picked up by the grid and not by MTG units. Load changes on these

MTG units will be accomplished by manually setting load using the control system.

4.4.3 Harmonic Distortion

The power output will be measured with a BMI or equivalent recorder, which will

measure total harmonic distortion (THD). The BMI will also be used to determine the

power factor of the fully loaded unit during the endurance test. The measured power factor

will be used to verify that the package achieves rated output when connected to the utility

grid.

4.4.4 Noise Measurement

Ambient noise levels will be measured using a handheld noise meter. Each unit will

be operated independently to acquire the noise measurements during operations.

4.4.5 Emissions Measurement

For each MTG type tested, one certified test will be conducted to determine

compliance with South Coast Air Quality Management District Rule 2005 for NOx

emissions. Additionally, periodic measurements with available handheld equipment would

be made to determine trends and any condition of degradation that may occur with

operating hours.

4.4.6 Peak Load Gross and Net

Peak load gross and net measurements will be taken with a BMI meter or

equivalent recorder that measures power. For units without compressors, or compressors

that are externally powered, the net output must be determined by subtracting the external

27


power requirements to sustain MTG operation. Results of this test will yield performance

characteristics such as efficiency, heat rate, fuel consumption and operating hours.

Comparisons will be made to manufacturer specifications.

Figure 4.3.Capstone 28 kW MTG

If current technology proves itself; the next hurdles are those of specific application

such as power quality, standby power, and peak shaving. Advancing technology that

proves itself in specific applications will grow in value by offering customers new options.

GAS TURBINE

28


5.1 Gas Turbine

A gas turbine is a rotating engine that extracts energy from a flow of combustion

gases that result from the ignition of compressed air and a fuel (either a gas or liquid, most

commonly natural gas). It has an upstream compressor module coupled to a

downstream turbine module, and a combustion chamber(s) module in between.

Energy is added to the gas stream in the combustor, where air is mixed with

fuel and ignited. Combustion increases the temperature, velocity, and volume of the gas

flow. This is directed through a nozzle over the turbine’s blades, spinning the turbine

and powering the compressor. Energy is extracted in the form of shaft power,

compressed air, and thrust, in any combination, and used to power aircraft, trains, ships,

generators, and even tanks.

5.2 Types of Gas Turbine

There are different types of gas turbines. Some of them are named below:

1. Aero derivatives and jet engines

2. Amateur gas turbines

3. Industrial gas turbines for electrical generation

4. Radial gas turbines

5. Scale jet engines

6. Micro turbines

The focus of this project is the modeling of micro turbine.

5.3 Gas Turbine Cycle

29


The simplest gas turbine follows the Brayton cycle (Figure 1.1). In a closed

cycle (i.e., the working fluid is not released to the atmosphere), air is compressed

isentropically, combustion occurs at constant pressure, and expansion over the

turbine occurs isentropically back to the starting pressure. As with all heat engine

cycles, higher combustion temperature (the common idustry reference is turbine inlet

temperature) means greater efficiency. The limiting factor is the ability of the steel,

ceramic, or other materials that make up the engine to withstand heat and pressure.

Considerable design/manufacturing engineering goes into keeping the turbine parts cool.

Most turbines also try to recover exhaust heat, which otherwise is wasted

energy. Recuperators are heat exchangers that pass exhaust heat to the

compressed air, prior to combustion. Combined-cycle designs pass waste heat to

steam turbine systems, and combined heat and power (i.e., cogeneration) uses waste

heat for hot water production. Mechanically, gas turbines can be considerably less

complex than internal combustion piston engines. Simple turbines might have one

moving part: the shaft/compressor/ turbine/alternator-rotor assembly, not counting

the fuel system. More sophisticated turbines may have multiple shafts (spools),

hundreds of turbine blades, movable stator blades, and a vast system of complex

piping, combustors, and heat exchangers.

Figure 5.1- Idealized Brayton Cycle

30


The largest gas turbines operate at 3000 (50 hertz [Hz], European and Asian power

supply) or 3600 (60 Hz, U.S. power supply) RPM to match the AC power grid.

They require their own building and several more to house support and auxiliary

equipment, such as cooling towers. Smaller turbines, with fewer compressor/turbine

stages, spin faster. Jet engines operate around 10,000 RPM and micro turbines around

100,000 RPM. Thrust bearings and journal bearings are a critical part of the design.

Traditionally, they have been hydrodynamic oil bearings or oil- cooled ball bearings.

5.4 Advantages of Gas Turbine

1. Very high power-to-weight ratio, compared to reciprocating engines.

2. Smaller than most reciprocating engines of the same power rating.

3. Moves in one direction only, with far less vibration than a reciprocating engine.

4. Fewer moving parts than reciprocating engines.

5. Low operating pressures.

6. High operation speeds.

7. Low lubricating oil cost and consumption.

31


MICROTURBINE

6.1 Definition:

Micro turbines are small high-speed gas turbines. The three main components of a

micro turbine are compressor, combustor, and the turbine. The compressor is used to

pressurize the air before entering the combustor. Injected fuel is mixed with the

compressed air in the combustor and the mixture is ignited. Mechanical energy is produced

when the hot combustion gases flow and expand through the turbine. The turbine drives a

synchronous generator. A portion of power produced in the turbine is utilized for driving

the air compressor while the rest is converted to electric power in the generator.

The outputs of the MTs range typically from around 25 to 300 kW. Performance

improvement techniques incorporated in MTs include recuperation, low NOx emission

technologies, and the use of advanced materials, such as ceramic for the hot section parts.

MTs are available as single-shaft or split-shaft units. Single-shaft unit is a high-speed

synchronous machine with the compressor and turbine mounted on the same shaft. For

these machines, the turbine speed ranges from 50 000 to 120 000 r/min. On the contrary,

the split-shaft design uses a power turbine rotating at 3000 r/min and a conventional

generator connected via a gearbox for speed multiplication. Unlike traditional backup

generators, MTs are designed to operate for extended periods of time and require little

maintenance. They can supply a customer’s base-load requirements or can be used for

standby, peak shaving, and cogeneration applications.

32


Fig 6.1 micro turbine

The micro turbine took in place because of the emerging need of innovation to the

existing large gas turbine power plant, especially for the application of remote and limited

area to be placed. In 1994, when a MIT turbine engineer named Alan Epstein found

himself sitting in a jury pool and started to think about what it would take to build the

smallest possible jet engine. Then conclusion made that in theory the device could be

shrunk a lot. The idea was then started to make realization for a humungous application to

appear. By attaching a micro generator to the turbine, essentially creating a tiny power

plant, the combination would act like a battery, making power of twenty to fifty times or

even more to the rate of anything could be get on batteries (because there is much more

energy per ounce in burning hydrocarbons than in the electrochemical that usually goes in

batteries). For example: Current Li-ion batteries have energy densities up to 0.5 MJ/kg, but

33


fuel offers a much higher energy density of about 45 MJ/kg. It gives the insatiable appetite

to our needs for batteries; the micro turbine project suddenly became very interesting. For

comparison micro turbines are operated at lower pressure ratios (3 to 4) than larger gas

turbines (10 to 15). Micro turbine usually implemented the recuperated system, which

function is as the air-to-air heat exchanger (regenerator). The heat collected from the

turbine exhaust gas temperature. In a recuperated system, pressure ratio is in direct

proportion to temperature spread between inlet and exhaust. This allows heat (from

exhaust) to be introduced to the recuperator, increasing net cycle efficiency to as much as

30%. Unrecuperated micro turbines average to 17% net cycle efficiency. So it is clear that

the non-recuperated cycle micro turbine configuration would have difficulty competing on

an operating cost basis unless coupled with some form of waste heat recovery.

Micro turbine costs include the heat engine assembly itself, the recuperator, and

the generator. On the other hand, micro turbine engine accessory and control costs tend to

remain nearly constant, i.e., independent of size. Engine control costs also do not follow

scalar relationships, since control dynamic relationships (apart from inertial effects) are

relatively independent of size. Typical micro turbine system cost percentages are of the

order:

• Power head 25%

• Recuperator 30%

• Electronics 25%

• Generator 5%

• Accessories 5%

• Package 10%

Micro turbine efficiency and electrical (and thermal) output are basically functions

of peak cycle temperature (turbine inlet temperature, TIT), recuperator inlet temperature

(i.e., turbine exhaust gas temperature, EGT), compressor pressure ratio, and component

efficiencies and size effects (recuperator effectiveness, turbine isentropic efficiency,

compressor isentropic efficiency) . The TIT is essentially determined by the limits of

34


turbine rotor alloy stress rupture and low cycle fatigue strengths, duty cycle, and rotor

cooling options. Likewise, the recuperator inlet temperature, i.e., EGT, is also determined

by recuperator matrix material life limitations. The pressure ratio is dictated by the

compressor type and material.

6.2 single-shaft configuration:

Single shaft design typically employs metallic radial turbo machinery components.

They operate using one stage of compression and one turbine stage attached in one shaft.

The shaft connects the compressor, the turbine, and the unit generator (figure 2.2). Those

components thus have the same rotational speed. The air flowing into the compressor,

essential to the mass flow through the engine depends on the power turbine condition; the

turbine delivers more torque as it spins faster.

Fig 6.2 single shaft configuration

35


The main advantage of using single-shaft configuration with a PMSG or

asynchronous generator is that it is simpler in design. Moreover, there is no need for a

gear reducer as power electronics rectifier–inverter is used to supply standard

voltage/frequency power to the load A bidirectional inverter can be used to facilitate power

flow from electric grid to drive the generator at the start-up. The system is also small and

light. The disadvantage of the method is that the power electronics system causes some

conversion loss. Also, the complex conversion system is not robust enough. Moreover, the

disadvantages of using high-speed PMSG are thermal stress, demagnetization phenomena,

centrifugal forces, rotor losses because of fringing effects, high cost, etc. Rare earth

permanent magnets are more expensive than the electrical steel used in electromagnets.

They also need to be contained using additional supporting rings. PMSG requires special

machining operations. Handling of recharged permanent magnets is generally difficult in

production shops. These requirements increase the cost of labor for PMSG. The PMSG

produces raw ac power with unregulated voltage. Depending upon the changes in load and

speed, the voltage variation can be wide. When an internal failure occurs in a PMSG, the

failed winding will continue to draw energy until the generator is stopped. For high-speed

generators, this may lead to a long-enough duration during which further damage to

electrical and mechanical components may occur. It could also lead to safety hazards

for the operating personnel. Zhu and Tomsovic used an induction generator with

GAST model. Though induction generators are cheaper and robust, their speed is

load-dependent and they have to be interfaced to the grid only through expensive

power converter systems. For induction generators, self-excitation capacitance is of great

concern. The output voltage and frequency vary with the self-excitation capacitance

when all other parameters are constant. The value of this capacitance should lie between a

minimum and a maximum limit depending upon the combination of load, rotor speed, and

magnetizing reactance. If this capacitance value is not chosen properly, the machine fails to

self-excite.

36


6.3 Split-shaft configuration:

Split-shaft micro turbines follow an industrial equipment design philosophy. They

are built to meet utility grade reliability and durability standards while producing electricity

as efficiently as central generation and distribution technologies currently in use. Split-shaft

micro turbines are designed exclusively for rugged, industrial quality stationary

applications; they fit right in on the plant floor or utility room and include no design

compromises inherited from vehicle or aerospace ancestries. Like single-shaft micro

turbine engines, two-shaft designs typically employ metallic radial Like single-shaft micro

turbine engines, two-shaft designs typically employ metallic radial turbo machinery

components. They use strengthened turbocharger components featuring pressurized lube-

oil systems consistent with industrial best practice. They operate at relatively low pressure

ratios in the 3:1 range using one stage of compression and two turbine stages. The first

turbine (the gasifier turbine) drives the compressor and the second free-power turbine

drives the load generator.

Fig 6.3 Split-shaft configuration

37


Split-shaft configuration is more suitable for machine drive applications because

it does not require an inverter to convert the frequency of the ac power. The main

advantage of coupling an SG with a split-shaft MT is that it eliminates the use of

the rectifier and power converter. In this case, the generator is connected to the turbine

via a gearbox to generate standard 50/60 Hz power. These generators are robust and less

costly as compared to PMSG, and all other problems with high-speed PMSG are

eliminated. The use of power electronic interfaces for power conversion introduces

harmonics in the system to reduce the output power quality. These harmonics are

eliminated if SG is used with a gearbox. Also, there are less chances of failure as the

gearbox is much robust as compared to complex power electronics devices. However, the

main drawback of a gearbox is that it requires maintenance along with its supporting

lubricating system. The dimension and weight of the system increase with respect to the

single-shaft configuration. Some manufacturing companies like Ingersoll Rand Energy

Systems, Ballard, Bowman, and Elliott are using synchronous machines with their MT for

both stand-alone and grid-connected operations

6.4 Synchronous Machine:

Model the dynamics of a three-phase round-rotor or salient-pole synchronous

machine.

The Synchronous Machine block operates in generator or motor modes. The operating

mode is dictated by the sign of the mechanical power (positive for generator mode,

negative for motor mode). The electrical part of the machine is represented by a sixth-order

state-space model and the mechanical part is the same as in the Simplified Synchronous

Machine block.

The model takes into account the dynamics of the stator, field, and damper windings.

The equivalent circuit of the model is represented in the rotor reference frame (qd frame).

38


All rotor parameters and electrical quantities are viewed from the stator. They are identified

by primed variables. The subscripts used are defined as follows:

• d,q: d and q axis quantity

• R,s: Rotor and stator quantity

• l,m: Leakage and magnetizing inductance

• f,k: Field and damper winding quantity

The electrical model of the machine is

Note that this model assumes currents flowing into the stator windings. The measured

stator currents returned by the Synchronous Machine block (Ia, Ib, Ic, Id, Iq) are the

currents flowing out of the machine.

6.5 Necessity of Micro Turbine:

Under the current electric utility restructuring and public environmental policy,

there is ample scope for large-scale integration of DERs into utility grid distribution

system . Nowadays, there is growing interest in deploying MTs in DG application, because

of their quick start capability and easy controllability useful for efficient peak shaving.

39


6.6 SPECIFICATIONS:

The current generation MTs have the following specifications.

1) Size: relatively smaller in size as compared to other DERs.

2) High efficiency: fuel-to-electricity conversion can reach the range of 25%–30%.

However, if the waste heat recovery is used for CHP applications, energy efficiency levels

are greater than 80%.

3) Environmental superiority: NOx emissions are lower than 7 ppm for natural gas

machines in practical operating ranges.

4) Durability: designed for 11 000 h of operation between major overhauls with a service

life of at least 45 000 h.

5) Economy of operation: system costs lower than $500/kW. Cost of electricity is

competitive with alternatives including grid power for market applications.

6) Fuel flexibility: capable of using alternative fuels like natural gas, diesel, ethanol,

landfill gas, and/or other biomass-derived liquids and gases.

7) Noise level: reduced noise and vibrations.

8) Installation: simpler installation.

MODEL DESCRIPTION

40


7.1 MICROTURBINE MODEL

Usually, an MT consists of the following parts as listed next

1) Turbine: High-speed single-shaft or split-shaft gas turbines.

2) Alternator: In single-shaft units, the alternator is directly coupled to the turbine. The

rotor is either two-pole or four-pole permanent design. The stator is of conventional copper

wound design. In split-shaft units, a conventional induction machine or synchronous

machine is mounted on the turbine through the gearbox.

3) Power electronics: In single-shaft machines, the high- frequency (1500–4000 Hz) ac

voltage generated by the alternator is converted to standard power frequency voltage

through the power electronic interfaces. However, in the split-shaft design, these are not

required due to the presence of the gearbox.

4) Recuperator: The recuperator recovers the waste heat to improve the energy efficiency

of the MT. It transfers heat from the exhaust gas to the discharge air before it enters the

combustor. This reduces the amount of fuel needed to raise the discharge air temperature to

that required value.

5) Control and communication: Control and communication systems include the entire

turbine control mechanism, Inverter interface, start-up electronics, instrumentation and

signal conditioning, data logging, and diagnostics and user control communications.

41


Fig. 7.1.MT model.

In this I focused their attention on slow dynamic performance of the system and not on the

transient behaviors. MT

Modeling is based on the following assumptions.

1) System operation under normal conditions: This paper considers normal operating

conditions of the system. Hence, start-up and shut down of MT along with fast

dynamics (faults, loss of power, etc.) are omitted from the model as they do not

affect the operating conditions under normal load. The we would like to work in future for

developing an advanced MT model to include the aforesaid fast dynamics.

2) Omission of the recuperator model: The electromechanical behavior of MT is of main

interest, and hence, the recuperator model is not included as it is only a heat exchanger to

raise engine efficiency. Also, due to the recuperator’s very slow response time, it has little

influence in the timescale of dynamic simulations.

3) Omission of temperature and acceleration control models: The temperature and

acceleration controls have no impact on the normal operating conditions. Temperature

control acts as an upper output power limit. At normal operating conditions, the turbine

temperature remains steady, and hence, it is omitted from the model. Acceleration control

is used primarily during turbine start-up to limit the rate of the rotor acceleration prior to

reaching operating speed. If the operating speed of the system is closer to its rated speed,

42


the acceleration control is of no significance in the modeling. However, without the

temperature control block, the model does not represent turbine operations accurately

at higher load levels when the control is to be done based on exhaust gas temperature

rather than machine speed to prevent the damage of the turbine blades. Besides, if a load

rejection occurs, the speed accelerates at a higher rate than the normal as the acceleration

control block is omitted. The nonlinearities appearing due to this could not be taken care

of. In this respect, the we would include these blocks in the advanced MT model.

4) Omission of governor model: The governor model is omitted as the MT does not use

any governor. Instead, a speed controller is incorporated in the model to keep the speed

constant. The simplified MT model is shown in Fig 3.1

7.2 CONTROLLER MODEL

As the main emphasis is on active power control, therefore the entire control system is

simplified as an active power proportional–integral (PI) control function.

The controlled active power is applied to the turbine. Active power control is represented

as a conventional PI controller, as illustrated in fig 7.2

Fig. 7.2 Controller model.

43


The controller model variables are:

Pin active power control variable applied to the input of MT;

Pde m actual load demand;

Pre f preset power reference;

Kp proportional gain of PI controller;

Ki integral gain of PI controller.

As MTs work on the similar principle as gas turbines, their dynamic models are

evolved from the concept of gas turbine dynamics. Gaonkar and Patel used an MT model

that consists of fuel control, turbine dynamics, temperature control, speed governor,

and acceleration control blocks. Speed control acts when there is a difference between the

reference speed and rotor speed. It is the primary method of speed control when the turbine

is operating under part-load conditions. Temperature control sets the upper limit of the

output power. Acceleration control is used primarily during turbine start-up to limit the rate

of the rotor acceleration prior to reaching operating speed. Gaonkar et al. also used the

same model but excluded the temperature and acceleration control blocks as they have no

impact in normal operating conditions. Recuperator was not included in the both the

models as only electromechanical behavior was of interest. The model used in consists of

transfer function representing fuel system with actuator, turbine, and compressor dynamics

along with heat recovery exchanger. Zhu and Tomsovic sed GAST model for simulation of

a split-shaft MT system. The single-shaft MT model in consists of turbine, PMSG, rectifier,

and inverter with their dynamics and interconnections.

44


7.3 TURBINE MODEL

The turbine or prime mover model for GAST model consists of two fuel systems

and a temperature control feedback. However, the temperature control feedback has

been eliminated in this project.

Fig. 7.3 Block diagram of prime-moverlturbine model

The prime mover model in Fig. 7.3 shows that there are two fuel system lag time

constants to represent the turbine of the GAST model as a prime mover. The first fuel

system lag time constant, Tfl characterizes the k e l valve position time constant. Whilst

the second fuel system lag time constant, Tn describes the fuel injection before being

burned in order to produce hot gas at high pressure and high velocity that go through the

turbine blades for spinning.

The model also includes the limiter due to the fact that there is a maximum and

minimum limit of fuel to be injected in the combustion chamber. This will affect the

mechanical power output from the turbine in terms of its maximum and minimum limit.

The input of the turbine model is the change in valve position from nominal

value, APVa,,,. The turbine model takes into account the turbine damping to obtain the

mechanical power output performance of the turbine. Thus, mechanical power output

from the prime mover is expressed by:

45


(7.1)

The MT does not use any speed regulator. In this project, we have used the widely

accepted GAST turbine model, as shown in Fig. 3.3 for representing the dynamic behavior

of a gas turbine. The advantages of GAST model are that it is simple and follows typical

modeling guidelines.

The following swing equation describes the machine speed and power relationship of the

GAST model:

(7.1)

It is a Western System Coordinating Council (WSCC) compliant model that can

directly be used in specific commercial simulation programs. The model does not represent

turbine operations accurately at higher load levels when the control is to be done based on

exhaust gas temperature rather than machine speed to prevent the damage of the turbine

blades. Hence, the model cannot provide adequate representation of the temperature control

loop. The GAST model also does not account for the nonlinearities that play a major role in

over speed conditions following a sudden load rejection. Moreover, the model parameters

could not be adjusted accurately to reproduce the hunting phenomena around the final

settling frequency.

46


Fig 7.4 Turbine model.

The alternator coupled to the MT is modeled as a standard MATLAB–Simulink

synchronous machine block.

The parameters used for simulation of the MT, the alternator are based on work

reported by Zhu and Tomsovic and are illustrated in Tables 7.1 and 7.2 respectively.

47


7.4 Synchronous Machine:

Model the dynamics of a three-phase round-rotor or simplified synchronous

machine.The Simplified Synchronous Machine block models both the electrical and

mechanical characteristics of a simple synchronous machine. The electrical system for each

phase consists of a voltage source in series with an RL impedance, which implements the

internal impedance of the machine. The value of R can be zero but the value of L must be

positive.

The Simplified Synchronous Machine block implements the mechanical system described

by

Where

Although the parameters can be entered in either SI units or per unit in the dialog

box, the internal calculations are done in per unit. The following block diagram illustrates

how the mechanical part of the model is implemented. Notice that the model computes a

deviation with respect to the speed of operation, and not the absolute speed itself

These expressions represent, in summary, the electrical component of the model

implemented in Matlab/Simulink[MathWorks,2007]. The mechanical equations,

significantly simpler than previous ones, are represented by:

48


MODEL PARAMETERS

7.1 MT PARAMETERS

7.2 ALTERNATOR PARAMETERS

49


7.2 THREE-PHASE SOURCE PARAMETERS

Parameter Value

Phase to phase voltage 440Frequency 60hz3-phase short-circuit level

at base voltage

3.73e3

Base voltage 440

x/r ratio 5

SIMULATION AND RESULTS

8.1 ISLANDED MODE

50


Following cases have been simulated in MATLAB–Simulink environment. Total

simulation time for this case is 120s.The output powers and loads are expressed as per units

with 3.73 kw and the rated line voltage is 440V. the parameters of this microturbine modal

are listed in above table.

2

Tm

1

Pm

1

3.0s+1

Transfer Fcn3

1

0.1s+1

Transfer Fcn2

1

10s+1

Transfer Fcn1

1

sTransfer Fcn

Saturation

min

MinMax

1.0

Gain3

-K-

Gain2

1

Gain1

0.1

Gain

Divide

1.2Constant2

2

Wr

1

Pref

Fig 8(A) Turbine MATLAB–Simulink model.

Fig 8(B) MICROTURBINE MATLAB–Simulink model.

Case 1:

51


In this case, the islanded MTG system is running with a load of 3.73 kW (1 p.u.)

applied to the generator bus up to t = 120 s. The load on the MTG system is shown in Fig.

8.1, Fig 8.2 shows the mechanical power output of MT. It is observed that MT power

output takes about 55 s to match the load demand. Which shows that the MTG system

takes almost the same time to reach the new steady-state speed at the constant load. The

electrical power output of the generator is shown in Fig. 8.4 .It is seen to closely follow

change in load demand.

Fig. 8.1 Load on the MT (Islanded mode).

52


Fig. 8.2 Mechanical power output of MT.

Fig 8.4 Generator electrical power output (Islanded mode).

Case 2:

53


In this case there is a step increase of the power demand from 0.7 p.u.(2.6 kW) to 1

p.u. (3.73 kW) as shows in figure 8.5. Figure 8.7 shows the dynamic response of the

mechanical power, Pm, and the total three-phase electrical power output, Pe Figure 8.8

shows .


54




55


Case 3:

In this case there is a step decreasing of the power demand from 0.7 p.u. (2.6 kW)

to 0.4 p.u.(1.5 kW) as shows in figure 8.8. Figure 8.9 shows the dynamic response of the

mechanical power, Pm, and the total three-phase electrical power output, Pe Figure 8.10

shows .


56




57


Simulation results analysis

From simulation results, the following points are observed:

The initial response time for the step change is around 10 sec; this delay mainly

due to the turbine response time.

The oscillations in Pm and Pe is significant with a time period around 20 sec; this

is mainly due to the small inertia and damping of the Micro Turbine.

A Micro Turbine is the most suitable micro source for dealing with the load

changing in the micro grid.

This microturbine model appears suitable for the time scale to be used in our

dynamic simulation.

58


Case 4: MICROTURBINE WITH OUT FAULT



with 3.73 kw and the rated line voltage is 440V.

Fig 8.11 MICROTURBINE WITH OUT FAULT MATLAB–Simulink model.

In this case, the islanded MTG system is running with a load of 3.73 kW (1 p.u.)

applied to the generator bus up to t = 120 s. The load on the MTG system is shown in Fig.

8.11, Fig 8.12 shows the mechanical power output of MT. It is observed that MT power

output takes about 55 s to match the load demand. Which shows that the MTG system

takes almost the same time to reach the new steady-state speed at the constant load. The

electrical power output of the generator is shown in Fig. 8.13 .It is seen to closely follow

change in load demand. The voltage and current output wave forms as shown in fig

8.14&8.15.

59


Fig. 8.11 Load on the MT .


60


Fig 8.13 Generator electrical power output .

Fig 8.14 Generator voltage output

61


Fig 8.15 Generator current output

62


Case 5: MICROTURBINE WITH FAULT



with 3.73 kw and the rated line voltage is 440V.

Fig 8.16 MICROTURBINE WITH FAULT MATLAB–Simulink model.

In this case, the islanded MTG system is running with a load of 3.73 kW (1 p.u.) applied

to the generator bus up to t = 120 s and connected with a three phase fault. This fault of

duration of 60 to 90 s of duration of run time. The load on the MTG system is shown in

Fig. 8.17, Fig 8.18 shows the mechanical power output of MT. The electrical power output

of the generator is shown in Fig. 8.19 .It is seen to closely follow change in load demand.

The voltage and current output wave forms as shown in fig 8.20&8.21.

63


Fig. 8.17 Load on the MT


64


Fig 8.19 Generator electrical power output

Fig 8.20 Generator voltage output

65


Fig 8.21 Generator current output

66


Simulation results analysis

From simulation results, the following points are observed:

The initial response time for the step change is around 10 sec; this delay mainly due

to the turbine response time.

The oscillation in Pm and Pe is significant with a time period around 20 sec; this is

mainly due to the small inertia and damping of the Micro Turbine.

A Micro Turbine is the most suitable micro source for dealing with the load

following in the micro grid.

When fault period of 60 to 100 sec of duration the power is decreased, when fault

period is over again power will reaches its original values. These are observed from

the above wave forms.

When fault occurs voltage becomes zero and current will be increased as shone in

the wave forms.


dynamic simulation

67


MATHEMATICAL ANALYSIS

Introduction

Gas turbine plants are used for isolated and standalone operations. They are mainly

used in oil fields, desert areas, off shore installations and bio gas plants.

An effective control strategy is required to keep the system stable under

disturbance. The Transfer function model of heavy duty gas turbine has been developed by

Rowen [37] based upon his field experience and the tests he conducted in the gas turbine

plants. This model has been used in many works such as, the dynamic analysis of

combined cycle plant [38], twin shaft gas turbine model [39], and combustion turbine

model [40] and even in micro turbine power generation [41]. The transfer function

simplification has been validated [42]. After tuning the parameters, the response of the gas

turbine plant shows steady state error.

To improve the transient and steady state response, PID controller is required.

Mathematical Model of Micro Turbine :

The Transfer function model developed by Rowen [1] with the following

implifications is considered for the simulation of the response of an isolated micro turbine.

2

Tm

1

Pm

1

3.0s+1

Transfer Fcn3

1

0.1s+1

Transfer Fcn2

1

10s+1

Transfer Fcn1

1

sTransfer Fcn

Saturation

min

MinMax

1.0

Gain3

-K-

Gain2

1

Gain1

0.1

Gain

Divide

1.2Constant2

2

Wr

1

Pref

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i. If the frequency variation is not greater than [+ or -]1%, the acceleration control will become inactive. It can be eliminated.

ii. The turbine output is predominantly controlled by the set point so the need for temperature control is significantly diminished, thereby allowing elimination of temperature control.

iii. The multiplier used in the transfer function can be neglected for small speed variations

The simplified block diagram of micro turbine is shown

A unit step load disturbance has been given to the gas turbine using MATLAB

Simulink and the response is obtained.

The response shows that there is a steady state error. An appropriate secondary

controller has to be included to improve both the steady state and transient response.

Let the PID controller be implemented as

PID Controller:

Proportional--Integral--Derivative (PID) controllers are widely used in many

control applications because of their simplicity and robustness [10]. It is well known that if

the control law employs integral control, the system has no steady state error. However, it

increases the type of the system by one. Therefore the response with integral control is

slow during the transient period. In the absence of the integral control, the gain of the

closed loop system can be increased significantly thereby improving the transient response.

69


Similarly the closed loop system stability can be improved by the differential control, and

therefore PID controller will improve the static and dynamic accuracy.

PID controller consists of Proportional Action, Integral Action and Derivative

action. It is commonly refer to Ziegler-Nichols PID tuning parameters.PID controllers

algorithm are mostly used in feedback loops. PID controllers can be implemented in many

forms. It can be implemented as a stand-alone controller or as part of Direct Digital Control

(DDC) package or even Distributed Control System (DCS). The latter is a hierarchical

distributed process control system which is widely used in process plants such as

pharceumatical or oil refining industries.

It is interesting to note that more than half of the industrial controllers in use today utilize

PID or modified PID control schemes. Below is a simple diagram illustrating the schematic

of the PID controller. Such set up is known as non-interacting form or parallel form.

Figure 11.1. Schematic of The PID Controller – Non-Interacting Form

PID Controller

In proportional control,

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Pterm = KP X Error

It uses proportion of the system error to control the system. In this action an offset is

introduced in the system.

In Integral control,

It is proportional to the amount of error in the system. In this action, the I-action will

introduce a lag in the system. This will eliminate the offset that was introduced earlier on

by the P-action.

In Derivative control,

It is proportional to the rate of change of the error. In this action, the D-action will

introduce a lead in the system. This will eliminate the lag in the system that was introduced

by the I-action earlier on.

3.3 Continuous PID

The three controllers when combined together can be represented by the following transfer

function.

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This can be illustrated below in the following block diagram

Figure11.2. Block diagram of Continuous PID Controller.

What the PID controller does is basically is to act on the variable to be manipulated

through a proper combination of the three control actions that is the P control action, I

control action and D control action. The P action is the control action that is proportional to

the actuating error signal, which is the difference between the input and the feedback

signal. The I action is the control action which is proportional to the integral of the

actuating error signal. Finally the D action is the control action which is proportional to the

derivative of the actuating error signal. With the integration of all the three actions, the

continuous PID can be realized.

This type of controller is widely used in industries all over the world. In fact a lot of

research, studies and application have been discovered in the recent years.

Optimizing Of PID Controller

72


For the system under study, Zieger-Nichols tuning rule based on critical gain Ker

and critical period Per will be used. In this method, the integral time Ti will be set to

infinity and the derivative time Td to zero. This is used to get the initial PID setting of the

system. This PID setting will then be further optimized using the “steepest descent gradient

method”.

In this method, only the proportional control action will be used. The Kp will be

increase to a critical value Ker at which the system output will exhibit sustained

oscillations. In this method, if the system output does not exhibit the sustained oscillations

hence this method does not apply.

it will be shown that the inefficiency of designing PID controller using the classical

method. This design will be further improved by the optimization method such as “steepest

descent gradient method” as mentioned earlier.

Designing PID Parameters

From the response below, the system under study is indeed oscillatory and hence

the Z-N tuning rule based on critical gain Ker and critical period Per can be applied.

73

1

1


Figure 11.3. Illustration of Sustained Oscillation with Period Per.

The transfer function of the PID controller is

Gc(s) = Kp(1 + Ti S + T ds )

In this project there was only PI controller so there was no D block in the controller, so the

block diagram is

Figure 11.4. Schematic of The PI Controller – Non-Interacting Form

The transfer function of the PI controller is

Gc(s) = Kp(1 + Ti S )

The objective is to achieve a unit-step response curve of the designed system that exhibits a

maximum overshoot of 25 %. If the maximum overshoot is excessive says about greater

than 40%, fine tuning should be done to reduce it to less than 25%.

74


The system under study above has a following block diagram

Figure 10.4. Block Diagram Of Controller And Plant.

Since the Ti = ∞ and Td = 0, this can be reduced to the transfer function of

The value of Kp that makes the system marginally stable so that sustained oscillation

occurs can be obtained by using the Routh’s stability citerion. Sincethe characteristic

equation for the closed-loop system is

S2 + 10.1s + 1 + K p = 0

From the Routh’s Stability Criterion, the value of Kp that makes the system marginally

stable can be determined.

The table below illustrates the Routh array.

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s² 1 1

s¹ 10.1 Kp

sº 10.1-Kp/10.1 0

Table11.1. Routh Array

By observing the coefficient of the first column, the sustained oscillation will occur

if Kp=10.1.

Hence the critical gain Ker is

Ker = 10.1

Thus with Kp set equal to Ker, the characteristic equation becomes

S2 + 10.1s + 11.1 = 0

The frequency of the sustained oscillation can be determined by substituting the s terms

with jω term. Hence the new equation becomes

( jω )² + 10.1ω ) + 11.1=0

This can be simplified to

11.1 ( jω – 1)² + jω ( jω – 1 ) = 0

From the above simplification, the sustained oscillation can be reduced to

ω² = 1

Or

ω = √1

The period of the sustained oscillation can be calculated as

Per = 2π/√1

76

1


= 2.8099

The transfer function of the PID controller with all the parameters is given as

Gc(s) = Kp(1 + Ti S )

From the above transfer function, we can see that the PID controller has pole at the origin

and double zero at s = -1.4235. The block diagram of the control system with PID

controller is as follows.

Figure 11.5. Illustrated the Close Loop Transfer Function.

Using the MATLAB function, the following system can be easily calculated. The

above system can be reduced to single block by using the following MATLAB function.

Below is the Matlab codes that will calculate the two blocks in series

% calculation of series system response using matlab

num1=[0 1.08 1];

den1=[0 1.08 0];

num2=[0 0 1];

den2=[1 10.1 1];

[num,den]=series(num1,den1,num2,den2);

77


printsys(num,den)

This will gives the following answer

num/den =

1.08 s + 1

------------------------------

1.08 s^3 + 10.908 s^2 + 1.08 s

Hence the above block diagram is reduced to

Figure 11.6. Simplified System.

Using another MATLAB function, the overall function with its feedback can be calculated

as follow

% calculation of feedback system response using matlab

num1=[0 0 1.08 1];

den1=[1.08 10.908 1.08 0];

num2=[0 0 0 0 1];

den2=[0 0 0 0 1];

78


[num,den]=feedback(num1,den1,num2,den2);

printsys(num,den)

Hence the above block diagram is reduced to

This will result to

num/den =

1.08 s + 1

----------------------------------

1.08 s^3 + 10.908 s^2 + 2.16 s + 1

Therefore the overall close loop system response of

The unit step response of this system can be obtained with MATLAB.

%MATLAB script of the Designed PID Controller System.

num=[0 0 1.08 1];

den=[1.08 10.908 2.16 1];

79


step(num,den);

grid;

title('Unit Step Response of The Design System');

The unit step response is

0 10 20 30 40 50 600

0.2

0.4

0.6

0.8

1

1.2

1.4Unit Step Response of The Design System

Time (sec)

Am

plitude

Figure 11.7. Unit Step Response Of The Designed System

The figure above is the system response of the designed system. From the above response it

is obvious that the system can be further improved

Justification

From simulation and mathematical results, the following points are observed:

80


The initial response time for the step change is around 10 sec; this delay mainly

due to the turbine response time.

The oscillations in Pm and Pe is significant with a time period around 20 sec; this

is mainly due to the small inertia and damping of the Micro Turbine.


dynamic simulation.

CONCLUSION

In this project, modeling, simulation and mathematical analysis of MT coupled with

SG are performed and reported. Its load following performance is thoroughly tested and

validated for different operating conditions, with and without speed controllers. It has been

observed that the MTG system can be effectively used to supply fixed and time-varying

load demands. This model is quite useful for studying the dynamic performance.

A microturbine simplified model has been developed by using Matlab/ Simulink/

Sim power systems software. The model has been mathematically analysis and different

operation conditions have been analyzed (Step change, fault,…). The simulation results

have showed that the microturbine works properly connected to a low voltage distribution

grid. Next developments in this field will be the improvement and optimization of the

microturbine model as well as the analysis of multiple operation conditions, mainly related

to different fault situations and the definition of the settings of protection relays.

81


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