POWER MANAGEMENT AND POWER FLOW CONTROL

OF THE MICROGRID CONNECTED PV-FC HYBRID

SYSTEM

* S Yogendra Reddy S Bharat

Electrical Engineering. PNC & VIET Electrical Engineering. PNC & VIET

Guntur, India Guntur, India

s.yogendra.eee@gmail.com s.bharat.eee@gmail.com

Abstract— This paper proposes a method for Power Generation

in the Smart Grid will be based on Photovoltaic (PV) array and

a Proton Exchange Membrane Fuel Cell (PEMFC) mainly due to

the high penetration level of distributed renewable power

generators. Starting from electricity generation to its

transmission and storage with the ability to respond to dynamic

changes in energy supply through cogeneration and demand

adjustments. Decentralized Generation, storage and intelligence

are key components of a smart microgrid. In this paper, we

examine the significant role that build to play in energy use and

its management in a Smart Microgrid. We discuss how can be

enhanced and interfaced with the smart microgrid. The impact of

DC side Voltage fluctuation of the DGs and DG tripping on

power sharing is also investigated. The efficacy of the proposed

control arrangement has been validated through simulation for

various operating conditions. The model of the microgrid power

system is simulated in MATLAB.

Keywords- Photovoltaic array, Proton Exchange Membrane Fuel

Cell, & DC side Voltage Fluctuation.

I. INTRODUCTION

The ever increasing energy consumption, the soaring cost

and the exhaustible nature of fossil fuel, and the worsening

global environment have created increased interest in green

[renewable and/or fuel cell (FC)-based energy sources] power

generation systems. The growth of wind and photovoltaic

(PV) power generation systems has exceeded the most

optimistic estimation. FCs also show great potential to be

green power sources of the future because of many merits

they have (such as high efficiency, zero or low emission of

pollutant gases, and flexible modular structure) and the rapid

progress in FC technologies.

A new control strategy based on optimal usage of FC systems.

Different works have done to show the dynamic behavior and

power management of hybrid power generation. The effect of

dynamic behavior of FC system in transient event such as step

load and variation of load demand in hybrid power generation

in long duration of time.

In this paper, power management and power flow control of

hybrid system is proposed .The proposed system comprise PV

and FC system. The main goal of this paper is to show the

dynamic behavior of PV/FC System.

The paper is organized as follows. The system configuration is

discussed in Section II. The system component characteristics

are given in Section III. Section IV discusses the overall power

management strategy for the system. Section V gives the

simulation results. Section VI concludes the paper.

II. SYSTEM CONFIGURATION

Overall system configuration of proposed hybrid

renewable power generation and storage system are shown in

Fig.1. The studied system includes PV/FC as power generate-

on. Each system is connected to the DC link with appropriate

power electronics devices.

Fig .1. System configuration of the hybrid system

III. SYSTEM COMPONENT CHARACTERISTICS

To develop an overall power management strategy for the

system and to investigate the system performance, dynamic

models for the main components in the proposed hybrid

system have been developed using MATLAB/Simulink. The

models are for the following: PV and FC.

A. Photovoltaic

PV effect is a basic physical process through which solar

energy is converted directly into electrical energy. The

physics of a PV cell, or a solar cell, is similar to the classical

p-n junction diode .The relationship between the output

voltage V and the load current I of a PV cell or a module

can be expressed as

…………………(1)

where IL is the light current of the PV cell (in amperes),

I0 is the saturation current, I is the load current, V is the

PV output voltage (in volts), Rs is the series resistance of

the PV cell (in ohms), and α is the thermal voltage timing

completion factor of the cell (in volts).

The I–V characteristic curves of the PV model used in

this study under different irradiances (at 25 ◦ C) are given in

Fig. 2. It is noted from the figure that the higher the

irradiance, the larger are the short-circuit current (Isc) and

the open-circuit voltage (Voc). As a result, the larger will be

the output PV power. Temperature plays an important role in

the PV performance because the four parameters (IL, I0,

Rs, and α) in (1) are all functions of temperature. The

effect of the temperature on the PV model performance is

illustrated in Fig. 2. It is noted from the figure that the lower

the temperature, the higher is the maximum power and the

larger the open circuit voltage.

Fig.2. The I-V & P-V CURVES.

Decentralized configuration as show in Fig.3., the PVs are arranged in smaller modules independent of each other

and each connected to a common bus. The common bus

could be of different types: DC, low voltage AC or the

grid. The result has shown, not surprisingly, that one

central inverter gives the highest energy efficiency and

lowest cost, provided no shading effects are taken into

account.

Fig.3. Decentralized configuration

B. FC Power Generation System

Fuel cell power generation system is used as reliable

alternative power generation. To solve this problem different

form of renewable power generation such as FC system are

used as hybrid system to enhance the reliability of whole

system.

Among different types of FC systems, PEMFC has some

advantages such as high power density, high efficiency and

also have lower temperature. The PEMFC models have been

presented in different based on relationship between output

voltage and partial pressure of hydrogen, oxygen and water.

Fig. 4 shows the chemical reaction of PEMFC system that

occurred inside the cell.

Fig.4. Schematic diagram of a PEMFC

However, FC system have different and effective problem

such as slow dynamic and need hydrogen as fuel

continuously. In the previous works, the dynamic behavior of

FC system is neglected and FC system is simulated without

its slow dynamic. In this paper a new control strategy based

on FC system protection is proposed. The proposed control

Strategy has two important advantages. First it can simulate

the actual dynamic behavior of FC system. Second, this

control strategy is simple and economical way for protection

of FC system. This control strategy is based on coordination

of FC system and the dynamic behavior of utilization factor.

This control strategy can keep the utilization factor in its

optimal value by synchronizing of between FC system and

power electronic interfacing. The proposed control strategy is

implemented in hybrid power management.

The dynamic behavior of fuel valve is simulated as first

order lead-lag transfer function and is applied to the power

electronic interfacing through reference power of FC system.

With this control strategy, the hydrogen consumed by FC

stack is equal to the hydrogen that is injected by hydrogen

fuel valve.

The overall control strategy that is used for FC system is

shown in Fig.5.

Fig.5. Overall control strategy used for FC system

IV. POWER MANAGEMENT

An overall control strategy for power management among

different energy sources in a multisource energy system is

needed. Fig.6. shows the block diagram of the overall

control strategy for the proposed hybrid alternative energy

system. PV electricity generation unit, controlled by a

maximum power point tracking (MPPT) controller are the

main energy sources of the system. The power difference

between the generation sources and the load demand is

calculated as

Pne t = PPV − Pload − Psc ………… (2)

where PPV is the power generated by the PV energy

conversion system, Pload is the load demand, and Psc is

the self-consumed power for operating the system. The

system self-consumed power is the power consumed by the

auxiliary system components to keep it running, for example,

the power needed for running the cooling systems, the control

units, and the gas compressor. For the purpose of

simplification, only the power consumed by the compressor

(Pcomp) is considered in this study.

The governing control strategy is that, at any given time, any excess wind and PV-generated power (Pne t > 0) is supplied to the electrolyzer to generate hydrogen that is delivered to the hydrogen storage tanks through a gas compressor. Therefore, the power balance equation given in (2) can be written as

PPV = Pload + Pelec + Pco m p , Pne t >0…………..(3)

Where Pelec is the power consumed by the electrolyzer to

generate H2 a n d Pcomp is the power consumed by the gas

compressor. When there is a deficit in power generation

(Pne t < 0), the FC stack begins to produce energy for the

load using hydrogen from the storage tanks. Therefore, the

power balance equation for this situation can be written as

PPV + PFC = Pload, Pne t < 0 …..(4)

Where PFC is the power generated by the FC stack.

Fig.6. Overall control strategy and power management

of the hybrid power generation system

Dynamic models have been used for all the components

of the system shown in Fig.6.

V. SIMULATION RESULTS

The simulation of grid connected PV-FC hybrid system is done

in MATLAB/Simulink toolboxs. The MATLAB/Simulink

model of proposed system is depicted in Fig. 7.

Fig.7. Simulation model of proposed system

Using the component models discussed Section IV; a

simulation system test bed for the proposed PV/FC energy

system has been developed using MATLAB/Simulink. In

order to verify the system performance under different

situations, situation studies have been carried out using

practical load demand data.

The output power from the PV array in the system over

the 20 hour simulation is shown in Fig .8.

Fig.8. PV Power generated

Due to slow dynamic in FC system actuator, the FC

system cannot change its power to desired value as fast as

the load variation. In the proposed system, the dynamic

respond of fuel valve is simulated as first lead-lag transfer

function and this delay time is applied to the power

reference to keep the utilization factor of FC system at its

optimal value to improve FC system lifetime. The behavior

of the FC system in transient events such as step load

demand is shown in Fig.9 for a specified zoom.

Fig.9. FC stack system output power

VI. CONCLUSION

In this paper, an PV/FC alternative energy system is

proposed. The system configuration and unit-sizing are

discussed; the characteristics of the main components in the

system, namely, the PV, FC, and electrolyzer are given; and

the overall control and power management strategy for the

proposed hybrid energy system is presented. The PV

generation systems are the main power generation devices,

and the electrolyzer acts as a dump load using any excess

power available to produce H2 . The FC system is the

backup generation and supplies power to the system when

there is power deficit. The simulation model of the hybrid

system has been developed using MATLAB/Simulink.

Simulation studies have been carried out to verify the

system performance under different scenarios using the

practical load.

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