Modeling and Simulation of Small Scale Microgrid System

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Australian Journal of Basic and Applied Sciences, 6(9): 412-421, 2012

ISSN 1991-8178

Corresponding Author: Alias Khamis, Department of Industrial Power, Faculty of Electrical Engineering, Universiti

Teknikal Malaysia, Melaka, Malaysia

E-mail: [email protected]

Modeling and Simulation of Small Scale Microgrid System

1Alias Khamis, 2A. Mohamed, 3H. Shareef, 4A. Ayob

1Department of Industrial Power, Faculty of Electrical Engineering, Universiti Teknikal Malaysia,

Melaka, Malaysia2,3,4

Department of Electrical, Electronics and System Engineering Faculty of Engineering and BuiltEnvironment Universiti Kebangsaan Malaysia Bangi, Malaysia

Abstract:A microgrid systems is a new technology for improving reliability and providing alternativeenergy supplies to the grid system. Low voltage faults in the system are one of the critical issues that

require distributed generating sources to disconnect from grid provide energy to the load. Therefore the

techniques used in the microgrid system with microsoures can be important in reducing the problemsin the grid system. In this paper two different microsources photovoltaic (PV) and wind turbine (WT)

with battery storage for a small scale microgrid system are simulated. The aim is to observe the effect

of microsources parameter on the outputs at the point of common coupling. Most of the results can be

used for develop a small scale microgrid system for practical applications.

Key words:Battery Storage, Inverter, Microgrid, Photovoltaic, PSCAD, Wind Turbine.

INTRODUCTION

A small scale microgrid system is a low voltage grid connected to the network that can improve the power

system failure and power quality in the system. Low voltage single phase AC generating units in a small scalemicrogrid system become abundant in recent year. This system includes the combination of distribution

generation or microsouces to connect to the load and grid system. The microsources such as PV and WTcomprising of battery storage are designed to perform in both islanded and grid mode of operation (Yang, Z., et

al., 2009; Georgakis, D., et al. 2004). A typical PV and WT need to optimize design with specific parameters.

Effect of wind speed fluctuation and irradiance for both microsources effect the result from dynamic

performance of microgrid (Rashad, M. et al., 2010). The stability and the performance hybrid WT, PV andbattery system have to be studied for the variable voltage, frequency and loading effect (Li, W. and L. Tsung-

Jen, 2007). Therefore the microgrid system need to be modelled and controlled in grid connected system to

show the capability of - WT and PV hybrid generation system (Seul-Ki, K., et al., 2006). To ensure stableoperation during network disturbances, maintaining stability and power quality in the islanding mode operation

require the sophisticated control strategies for microgrid inverters in order to provide stable frequency andvoltage in the presence of arbitrarily varying load (Kanellos, F.D., et al., 2005). Modelling and simulation of

microgrid power system is an important first step to any sort of physical experimentation or field

implementation. Models can be used to predict performance issues and simulate anomalous condition (LaurentiuNastac, et al., 2009). Modeling of a commonly used microsources an a small scale microgrid system is studied

using PSCAD (Hossienzadeh, H., et al., 2009). Therefore the objective of this paper is to model and simulation

a small scale microgrid system included each of microsources PV, WT and battery storage with inverter aresimulated by PSCAD. The simulation showed the grid connected and islanding mode performance varying by

load and effect of PV and WT microsources with battery capacity storage.

Ii. Small Scale Microgrid System:

A. System Description:.

Grid Connection System:

A small scale microgrid system architecture is as shown in Figure 1. It is a single phase 60Hz, 240V AC

system connected to grid. It comprises of PV, WT and battery storage microsources. Where the DC output

voltage from PV is connected to inverter to change into AC voltage before connected to the grid system. While

AC voltage output from WT and generator are connected to a bridge rectifier change to DC voltage before

converting to AC again through an inverter. Finally the battery storage is connected to bidirectional inverter tomaintain output in AC voltage charge and charging the battery.

2. The Load System:

The load system are divided in three categories that the first load are connected with PV where when

islanding mode this load are supplies from PV microsources. Then the second load are connected with WT also


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when islanding happen this load are supplies from WT microsources. Finally the third load are connected to the

system where if islanding happen this load are supplies from the microsources also battery storage.

Fig. 1:Single diagram small scale microgrid system

B. Distributed Generators:

1. The PV system:The PV microsource is shown in Figure 2. Solar radiation and cell temperature are input source to PV to

convert in current and voltage by PV panel then connected with series diode and parallel capacitor. The functionof the diode is to block output from reverse side and capacitor is used for charge the output from PV then

generate to the load.

Fig. 2:PV system electrical circuit

For calculating current output from PV, the mathematical equation below is used [9]:

Is= IphIo[exp(V+IsRs)/NsVt](V+IsRs)/Rsh (1)

Where, Iph- the photo generated current (A)

Io- the dark saturation current (A)Rs- the panel series resistance ()

Rsh- the panel parallel resistance ()

Ns number of cell in the panel connected in seriesVt = AkT/q junction thermal voltage (A is diode ideality factor, k is Boltzmanns constant, T is

temperature and q is charge of electron)


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TABLE 1 show the PV module characteristic is used in this system. All of the parameter will be calculate

by equation (Yang, Z., et al., 2009) to get the output current and voltage from PV module.

Table1:PV module characteristic

The outputs from PV in DC voltage need to change to AC voltage by inverter as shown in Figure 3. The

circuit have four gates that convert DC voltage from PV to AC voltage and connected the system. This circuitare control by PWM circuit where the square wave graph injects to the gates in sine wave for AC voltage. AC

voltages out from inverter are used for generation to the load and synchronies with the grid system.

Fig. 3:DC/AC inverter circuit

2. The Wind Energy System:

The microsources of WT are shown in Figure 4. The wind speed fluctuations is the wind sources inputpower to the WT. The WT has there blade that is attached to the rotor before connect to the induction generator.

DC voltage output from WT turbine and the induction generator are used for changed to AC voltage.

Fig. 4:WT system electrical ciruit


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For calculating output power from WT, the WT model represents the mechanical mechanism as equation

below (Shi, S.S., et al., 2009):

P = 1/2CpA3 (2)

Where - the air density which around 1.25 kg/m3

Cp- the coefficient performance of the turbine

A = R

2

- the turbine swept area (R is the rotor blade radius)- the wind speed

Then for the calculating of the mechanical torque of WT, the mathematical equation below is used(Bunlung Neammanee, 2007):

T = 1/2CpA3/ (3)

For calculating the tip speed ratio as the WT operating point for extracting maximum power the

mathematical equation below is used (Engr, G., et al., 2008):

= R/ (4)

Where is the rotor angular speed in rad/sec. Generator output from WT in there phase AC voltage change

to DC voltage by bridge rectifier before change to AC voltage again by inverter as shown in Figure 5. DCvoltages from bridge rectifier are single phase input of inverter.

Fig. 5:AC/DC bridge rectifier and DC/DC inverter circuit

C. Energy Storage System:

The battery storage is used in this microgrid system as shown in Figure 6. The electrical circuit show the

battery source connected with series diode and parallel capacitor. The DC/DC converter is used to convert from

small voltage to large voltage before change to AC voltage by inverter (Chong, M.Y., et al., 2010).

Fig. 6:Battery storage and DC/DC converter circuit


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The output from battery storage in DC voltage as a input for inverter as shown in Figure 7. This

bidirectional inverter can comprise with AC voltage in microgrid system for backup when the operation systemin grid connected or islanding mode.

Fig. 7:DC/DC inverter circuit

III. Simulation Result:

A. Grid Connected Mode:

The grid connected mode is the microgrid system with PV, WT and battery storage microsources areconnected to grid AC system. The simulations result of the microgrid system on grid connected mode are shown

in Figure 8. The voltage at the grid system showed 240V AC voltage while the current output from PV, WT and

battery are Ia, Ib and Ic.

Fig. 8:Voltage and current microgrid system

The plots in Figure 9 shows the load power in three types for this microgrid system. P1 and Q1 is the activepower and reactive power for load connected with PV system. While P2 and Q2 is the active power and reactive

are load connected to the WT system. P3 and Q3 is the Active power and reactive power for the load in this

system.


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Fig. 9:Active power and reactive power microgrid load system

PV system:

Figure 10 shows the supply and load voltage and current from PV system. Both of the voltage and current

from PV are variables that effect from solar irradiance and temperature from the source. While the voltage andcurrent at the load or out from inverter is in the sinusoidal waveform.

Fig. 10:Supply and load voltage and current PV system

WT system:

Figure 11 shows the supply and load voltage and current from WT system. Both of the voltage and current

from WT also are variables that effect from speed fluctuation from the source. While the voltage and current atthe load or out from inverter is in the sinusoidal waveform.

Fig. 11:Supply and load Voltage and current WT system


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3. Battery Storage:

Figure 12 shows the supply and load voltage and current from PV system. Both of the voltage and currentfrom PV is variable that effect from charge and discharge from the bidirectional source. While the voltage and

current at the load or out from inverter is in the sinusoidal waveform.

Fig. 12:Supply and load voltage and current battery storage system

B. Islanding Mode:

The islanding mode is the microgrid system with PV, WT and battery storage microsources are not

connected to grid AC voltage system. The simulations result of the microgrid system on islanding mode areshown in Figure 13. The voltage at the grid system showed 240V AC voltage while the current out from PV,

WT and battery are Ia, Ib and Ic.

Fig. 13:Voltage and current microgrid system

The polts in Figure 14 shows the load power in three types for this microgrid system. P1 and Q1 is theactive power and reactive power for load connected with PV system. While P2 and Q2 is the active power and


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reactive are load connected to the WT system. P3 and Q3 is the Active power and reactive power for the load in

this system.

Fig. 14:Active power and reactive power microgrid load system

PV system:


from PV are variables that effect from solar irradiance and temperature from the source. While the voltage andcurrent at the load or out from inverter is in the sinusoidal waveform.

Fig. 15:Supply and load voltage and current PV system

WT system:

Figure 16 shows the supply and load voltage and current from WT system. Both of the voltage and currentfrom WT also are variables that effect from speed fluctuation from the source. While the voltage and current at

the load or out from inverter is in the sinusoidal waveform.


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Fig. 16:Supply and load Voltage and current WT system

Battery Storage:


from PV are variables that effect from charge and discharge from the bidirectional source. While the voltage and

current at the load or out from inverter is in the sinusoidal waveform.

Fig. 17:Supply and load voltage and current battery storage system

Conclusions:In this paper two different microsources photovoltaic (PV) and wind turbine (WT) with battery storage for a

small scale microgrid system are simulated. Simulation is focus on the parameter of the each microsources to

consider the outputs and effectiveness of inverter. Most of the results can be used for develop a small scalemicrogrid system for practical applications.

REFERENCES

Bunlung Neammanee, 2007. Somporn Sirisumrannukul and Somchai Chatratana. Development of a Wind

Turbine Simulator for Wind Generator Testing in International Energy Journal, 8: 21-28.


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Chong, M.Y., A.A. Rahman, N.A. Aziz, A. Khamis, M.F.M. Basar, 2010. Performance Comparison of

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Dezso Sera Teodorescu and Pedro Roddriguez, 2007. PV panel model based on datasheet values in

Industrial Electronics, ISIE 2007. IEEE International Symposium, pp: 2392-2396.Engr, G., Ofualagba and E.U. Dr. Ubeku., 2008. Wind Energy Conversion System Wind Turbine

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Seul-Ki, K., K. Eung-Sang, and A. Jong-Bo, 2006. Modeling and Control of a Grid-connected Wind/PV

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