international journal of pure and applied mathematics volume … · 2018. 7. 15. · improved power...

IMPROVED POWER SHARING OF WIND-DIESEL PENETRATED

MICROGRID

Mrs.P.Rathidevi1, Dr.P.Sivakumar

2, Mr.A.Rajapandiyan

3 1Assistant Professor, Department of Electrical & Electronics Engineering,

J.J. College of Engineering & Technology, Trichy, INDIA 2Professor, Department of Electrical & Electronics Engineering,

Rajalakshmi Engineering College, Chennai, INDIA 3 Assistant Professor, Department of Electrical & Electronics Engineering,

Er. Perumal Manimekalai College of Engineering, Hosur, INDIA Abstract: This paper proposes a power sharing between the wind and diesel generator based micro

grid. The aggravated increase in energy demand has posed a serious problem for the power system’s

stability and reliability, and hence has become of major concern. Wind diesel hybrid systems (WDHS)

obtain maximum contribution by the wind resource while providing continuous high quality electric

power. An active power control strategy has been developed such that when the wind alone is not able

to meet the energy demand, without compromising the frequency, a transition occurs to wind diesel

mode so that the energy demand is met. The idea proposed in this paper is to maximize the wind energy

and minimize the amount of fuel consumed by the diesel generator. The simulation results confirm the

smooth operation of the proposed concept for disturbances from main grid as well as due to the

intermittent wind and diesel power plants.

Key Words: Wind-diesel system, controlled bus, grid connected and islanded operation.

1. Introduction

The renewable power plants are mostly implemented in rural areas

as they cover large surface area. The rural areas are far away from the main grid network and connection is possible through a weak transmission line. The concept of microgrid is proposed as effective solution for such weak systems.

Smart Grid will be the future electricity distribution system. This intelligent system consists of advanced digital meters, distribution automation, communication systems and distributed energy resources. Self-healing, high reliability and power quality, providing accommodations to a wide variety of distributed generation and storage options are some of the functionalities for a desired smart grid. If photovoltaic generations, fuel cells, wind turbines and gas co-generations are installed into utility grids directly

International Journal of Pure and Applied MathematicsVolume 119 No. 16 2018, 4213-4224ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

4213

then they can cause a variety of problem such as voltage rise and protection problem in the utility grid. In order to avoid these problems, the new concept in power system has been introduced and that is called micro grid. Renewable “Distributed Energy Resources” (DERs) can consist of small Photovoltaic (PV) generators and small wind turbines that can be installed anywhere such as customer’s place. Microgrid consists of DER, including Distributed Generation (DG) and Distributed Storage (DS) [1]. In disasters, current distribution systems can face challenges to provide the required energy supply. Using the proposed micro grid in parallel with the grid, the distribution system can recover faster. Micro grids have the ability to be switched in and out of the transmission system i.e., standalone [2] [3] and grid connected capability. They can also operate independently from the system for a period of time.

2. Existing Microgrid Technologies

Hybrid energy systems are a combinations of two or more energy conversion devices (e.g., electricity generators or storage devices), or two or more fuels for the same device , that when integrated , overcome limitations that may be useful because it includes a wide range of possibilities and the essential feature of the multiplicity of energy conversion.

Micro-grid is defined as a cluster (typically two to three) of DG units

and loads which operates in a coordinated and independent manner as a single entity that can be integrated into a distribution system or stand-alone system. In a more advanced MG, energy storages such as super capacitors, super conducting magnetic energy storage (SMES), Flywheel and batteries are also integrated along with generating units and loads. MG appears to the main grid as a single load or source depending on whether load is higher than the generating sources in the area. MG architecture ensures that it follows grid and/or distribution codes and does no harm to existing consumers and the rest of the grid. MG concept will allow a higher penetration of renewable energy in the form of DG units without requiring re-design and re-engineering of distribution system. However, control aspect of MG is critical for allowing maximum penetration of desirable energy without hampering the grid integrity.

Power control strategies of a grid connected hybrid system or MG for versatile power transfer have been proposed [4].

3. Proposed Microgrid Technologies

A model is developed to study the operations of integrated Wind-Diesel generators in a MG. Simplified active and reactive power controllers [5] are developed to the wind and diesel generator. A supervisory control that regulates power generation of generating elements has been used for the system to operate in the various operation modes. Finally the system's

International Journal of Pure and Applied Mathematics Special Issue

4214

operations are studied with grid connected modes with intermittent power from renewable plants.

In this system, as the hybrid system cannot always provide stable

output with weather conditions, an auxiliary generation apparatus that uses elastic of energy is used to form energy storage. Rotary energy in the spring was used to power a small scale generator. However, the auxiliary generator output was limited to a maximum of 240 W. Relatively larger Wind-diesel hybrid generation system design, experimental as well as simulation results have been presented.

Wind diesel hybrid systems (WDHS) obtain maximum contribution

from wind and rest by diesel generators. An active power control strategy has been developed such that when the wind alone is not able to meet the energy demand, without compromising the frequency a transition occurs to wind diesel mode so that the energy demand is met. The idea proposed in this paper is to maximize the wind energy and minimize the amount of fuel consumed by the diesel generator.

The hybrid generation that consists of 9 MW of wind turbine and of

13.8 KV diesel power as auxiliary source was designed to supply power to private houses in the island and far away from utility. The wind energy generation system is based on fixed speed induction generator and its input torque is applied with fluctuation to reflect the intermittent nature of wind speed. Whenever an Induction generator is connected to the power grid, the frequency is regulated by the grid. The wind generator is connected to a three phase transformer of 25 KV/575 V and from the main grid with 120KV equivalent is also connected with another transformer of 120 KV/25 KV. The load with the filters is connected with the controlled bus. For wind, a Fixed Speed Induction Generator is considered; hence no special control is described.

The diesel generator system is modeled by the synchronous

generator. The generator frequency is a function of rotational speed. The diesel generator is also connected with the three phase transformer of 13.8 KV/120 KV. The load with filters is also connected with the controlled bus. The wind and diesel generator system is connected with a 25 KV transmission line.

The proposed system has reported several modes of operations

similar to what is presented. Though the MG configuration has been verified with test results, the hybrid system is relatively small and the islanded mode of operation is not covered in the system. Based on the above, in this system relatively large MG, in few MW range, with Wind-Diesel hybrid system has been proposed.


4215

Fig.3.1 Schematic Diagram of proposed system

Fig.3.2 Block Diagram of proposed system

i) Diesel Subsystem The diesel generator is then assumed to consist of three main

components: the diesel engine, the synchronous generator and the excitation system (see Fig 3.3)

Fig.3.3 Block diagram of diesel generator

a) Model of Diesel Engine System The general structure of the diesel engine model is shown in Fig 3.4.

It can be seen that it is assumed to consist of four main sub-models: the controller, the actuator, the engine and the flywheel. The model of each component is briefly described in [7].

WT IG Load

SG DE


4216

Fig.3.4 Block diagram of a diesel engine system

b) Synchronous Generator Model The equations of synchronous generator are obtained from Park

Transformation, after per unit representation and some simplifications. Consider a salient pole synchronous generator with the rotor consists

of three windings. A field and a damping winding are considered on the direct axis in order to take into account the transient and sub transient behavior respectively in this axis. Meanwhile, a damping winding is considering on the quadrature axis.

The terminal voltage phasor is determined by,

Vt = Vd + jVq ……………………. (1) Vd =Ed

**-RsId+Xq

**Iq ……………………. (2)

Vq=Eq**-RsIq+Xd

**Id ……………………. (3)

where, Rs is the armature resistance, Iq and Id are the currents flowing in

the stator winding, the X**d,q are the so-called sub-transient d and q-axis reactance and E**d,q are given by,

…………………… (4)

…………………… (5)

Where, Xd,q and X*d,q are the synchronous and transient reactance, the

T**dqo are the open circuit sub transient time constants and E*q is given by

…………………… (6)


4217

Where, Efd is the exciter field voltage and T*do is the open circuit transient time constant.

As it can be seen in Fig 3.2, there is an additional feedback term from

the generator to the diesel engine given by the electromagnetic torque that in flywheel mode can be evaluated from:

…………………… (7)

ii) Wind Subsystem

a) Wind Turbine Model

The mechanical power and the aerodynamic torque developed by a wind

turbine are given by,

…………………… (8)

where Pw is the mechanical output power captured from the turbine (W), is the air density (kg/m3), r is the radius of the turbine (m), vwind is the wind

speed (m/s), Cp is the power coefficient of the wind turbine, β is the pitch angle and λ is the tip speed ratio. Where the tip speed ratio is defined as

…………………… (9)

where ωm is the angular speed of turbines (rad/s). One of the methods

used to calculate the power coefficient Cp by using a generic equation is,

…………………… (10)

b) Generator Model for Wind System According to a standard per-unit notation [9], in the synchronously

rotating frame, the induction generator can be represented by the detailed differential equations of the flux linkages. All stator and rotor quantities are in the arbitrary two-axis reference frame (d–q frame). The used subscripts are defined as follows: d: d-axis quantity, q: q-axis quantity, r: rotor quantity, s: stator quantity.

…………………… (10)

…………………… (11)


4218

…………………… (12)

…………………… (13)

where ωs is the synchronous speed(in per unit, ωs=1); ωb is the system

base frequency i.e, 2πf. Electromagnetic Torque Te,

…………………… (14)

The constitutive flux linkage equations are,

…………………… (15)

…………………… (16)

…………………… (17)

…………………… (18)

where Lss is the summation of leakage inductance Ll and mutual

inductance Lm.

4. Modes of Operation

i) Mode 1: (PWind>=PLoad) When the wind power alone is sufficient to meet the load

requirement, the diesel engine is cut off. (PDiesel=0)

PWind = PLoad …………………. (20)

Fig.4.1 Mode 1: (PWind>=PLoad)

PWin

d PLoa

d

PDies

el


4219

ii) Mode 2: (PWind < PLoad)

When the load demand exceeds the wind power, it should be meet

with the help of diesel generator.

PWind+P Diesel=PLoad ………………….. (21)

Fig.4.2 Mode 2: (PWind < PLoad)

5. Simulation Results `The network with two generator technologies of Wind-Diesel is shown in

Fig 5.1 was modeled in MATLAB / SIMULINK environment. The simulations are carried out to check the operation of the system with proposed controllers.

Fig.5.1 Simulink Model of Proposed System.

PWin

d PLoa

d

PDies

el


4220

Fig.5.2 Output waveform of wind power

Fig.5.3 Simulation results of the synchronous machine with excitation system.(a) Mechanical Power (b) Field Voltage (c) Terminal Voltage (d)

Rotor Speed


4221

Fig.5.4 Simulation results of wind farm and diesel generator

6. Simulation Results

Wind – Diesel system is used in the proposed Micro grid. This

system obtains a maximum contribution from wind and rest by the diesel generators. An active power control strategy is developed such that when the wind alone is not able to meet the energy demand, without compromising the frequency, a transition occurs to wind -diesel mode so that the energy demand is met. The idea proposed in this paper is to maximize the wind energy and reduce the fuel consumption. Operations of the proposed system were studied for the intermittent nature of wind – diesel plants. The results confirm the smooth operation of the Micro grid.

References

[1] R. Lasseter, A Akhil, C. Marnay, J. Stephens, J. Dagle, R. Guttromson, AS. Meliopoulos, R.

Yinger and J. Eto, "White paper on integration of distributed energy resources -the CERTS

MicroGrid concept", Office of Power Technologies of the US Department of Energy, Contract

DEAC03-76SFO0098, 2002.

[2] S.J. Park, B.B. Kang, J.P. Yoon, I.S. Cha, and J. Y Lim, "A study on the standalone operating or

photovoltaic/wind power hybrid generation system", IEEE 35" Annual Power Electronics

Specialists Conf (PESC 04), vol. 3, 20th -25th June 2004, pp. 2095 -2099.

[3] N.A Ahmed and M. Miyatake, "A stand-alone hybrid generation system combining solar

photovoltaic and wind turbine with simple maximum power point tracking control", Proc. IEEE

5th Int. Cont on Power Electronics and Motion Control (IPEMC 2006), vol. 1,14 -16th Aug.

2006, pp. I -7.


4222

[4] S.K. Kim, J.H. Jeon, C.H. Cho, J.B. Ahn, and S.H. K won, "Dynamic modeling and control of a

grid-connected hybrid generation system with versatile power transfer", IEEE Trans. Industrial

Electronics, vol. 55, no. 4, April 2008, pp. 1677 -1688.

[5] M. Meiqin, S. Jianhui, L. Chang, Z. Guorong, and Z. Yuzhu, "Controller for I kW-5kW wind-

solar hybrid generation systems", Proc. Canadian Conf Electrical and Computer Engineering

(CCECE 2008), 4th - 7th May 2008, pp. 1175 -1178.

[6] T. Tadokoro, K. Taira, and M. Asaoka, "A photovoltaic-diesel hybrid generation system for small

islands", Proc. 24t h IEEE Photovoltaic Specialists Conf, vol. I, 5th -9th Dec. 1994, pp. 708 -715.

[7] J. Salazar, F. Tadeo, Prada, C," Modelling Of Diesel Generator Sets That Assist Off- Grid

Renewable Energy Microgrids", Journal of Renewable Energy and Sustainable Development

(RESD) June 2015, pp-72-80.

[8] A. Omar Noureldeen, A. Mahmoud Rihan , B. Barkat Hasanin "Stability improvement of fixed

speed induction generator wind farm using STATCOM during different fault locations and

durations", Ain Shams Engineering Journal (2011) 2, 1–10.

Biographies

Mrs.P.Rathidevi was born in Tiruchirapalli, India on April 11, 1984. She

did her Bachelor of Engineering at Annai Teresa College Engineering in 2005 at Thirunavallur, Villupuram (Dt), India. She did her Master of Engineering in Power Electronics and Drives at J.J. College of Engineering and Technology in 2010 at Tiruchirapalli, India. She is currently pursuing Ph.D degree at Anna University, Chennai, India. She is presently working as an Assistant Professor (Senior Grade) at J.J. College of Engineering and Technology, Tiruchirapalli, India.

Dr.P.Sivakumar was born in Tiruchirapalli, India on July 3, 1975. He did

his U.G. and P.G. at Regional Engineering College, Trichy, India and SASTRA University, Tamil Nadu, India. He is presently working as an Associate Professor at Rajalakshmi Engineering College, Chennai, India. His current research interests include dispersed power generators based on PV and wind power generations, DG sourced power system optimization and power electronics control.

Rajapandiyan A received the B.E., degree from Mount Zion College of

Engineering and Technology, Pudukkottai, Tamil Nadu, India in 2011. He received the M.E., degree from J.J College of Engineering and Technology, Tiruchirapalli, Tamil Nadu, India. Currently, he is working as a Assistant Professor in Er. Perumal Manimekalai College of Engineering, Hosur, Tamil Nadu, India. His current research interests include power system planning, operation and control; application of artificial intelligence techniques to power system; and renewable energy systems. E-mail ID: [email protected].


4223

international journal of pure and applied mathematics volume … · 2018. 7. 15. · improved power...

Documents