Sag mitigation of voltage by Dynamic voltage restorer using Fuzzy controller

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International Journal of Electrical, Electronics and Computer Systems (IJEECS)

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ISSN (Online): 2347-2820, Volume -4, Issue-7, 2016 25

Sag mitigation of voltage by Dynamic voltage restorer using Fuzzy controller

1Meghana S, ²Faheem Ahmed Khan

Department of Electrical and Electronics Ghousia College of Engineering

Abstract : Increase in the use of electronic equipment results in power quality problem such as voltage sag. This is one of the important parameter in the present era.

Dynamic voltage restorer (DVR) is a tool for compensating the voltage sag. This paper presents the closed loop control method of DVR using fuzzy controller and it is verified using MATLAB simulations.

Index terms: power quality, Voltage sag, Dynamic voltage restorer, Fuzzy controller

I. INTRODUCTION

Electric utilities are experiencing the demand of power quality by industrial power consumers. There are various power quality problems that occur, one of which is voltage sag. This is mainly caused due to the faults on parallel transmission/distribution feeders. The solution to this problem at large power levels has been commonly called dynamic voltage restorer (DVR). The main function of DVR is to mitigate the voltage sag, although sometimes, additional functions such as harmonics compensation and reactive power compensation are also integrated to the device. The main component of the DVR are 1) Injected transformer 2) Filter unit 3) Voltage source converter 4) Energy storage device 5) Control and protection system.

Fig 1: Block diagram of DVR

Open loop feed-forward technique is commonly used for the control of DVR. This generally results in poor damping of the output harmonic filter. Closed loop control method is employed for DVR due to its strong dynamic behavior compared to open loop. Fuzzy controller is used in the closed loop control method in order to reduce the disturbances of the system and also it gives faster and smoother response. Multilevel

converter gives best solution at high power application that is at distribution voltage levels. It can be realized by using high power and high voltage semiconductor switches. Multilevel converter can reduce the harmonic content and also can synthesize the output voltage leads to the lower electromagnetic interference.Open loop feed-forward technique is commonly used for the control of DVR. This generally results in poor damping of the output harmonic filter.

II. METHODOLOGY

Fig 2: H-bridge converter applied to DVR Three phase source is used to give the supply for each of the H-bridgeconverter through the three phase transformer for the purpose of power transfer. H-bridge converteris connected in series with the transformer, which is made as subsystem and the combination of these are connected in parallel. Each H-bridge consists of four semiconductor devices (MOSFET) and voltage level can be increased by increasing the number of switches. The voltage obtain on the load side is ranges from 300-400V for supply voltage 0f 50V for each phase. Energy storage unit such as battery is used across which capacitor is connected for storing purpose. Boost converter is used to increase the voltage in the ratio of 1:2. Three phase VI measurement is used on the output side for measuring the voltage and the current of three phase balanced resistive load.

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Fig 3: Overall system structure illustrating controller

Overall system controller of PRSRF and NRSRF is as shown in fig 2. The three phase voltages (a, b, c) are sensed and it is converted in to orthogonal equivalent two phase system (α, β).The positive and negative supply voltages are separated by using complex co- efficient filter. The positive and negative supply voltage is compared with the load voltage and the difference between them becomes injected voltage.

The controller generates the correct voltage references and it is given to PWM in order to generate the positive sequence component and extraneous negative sequence component. Gating signal for nine H-bridge may be generated from command voltage.

The controller consists of inner current loop and outer voltage loop structure. The proportional regulator is designed to yield necessary bandwidth for the inner current loop. The outer voltage loop is fuzzy controller, which generates the current command for the inner current loop.

III. RESULTS

The simulation has been carried out using Matlab- Simulink to verify the proposed control scheme.

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Fig 4: Simulation results for voltage sag (a) Supply voltage (b) Load voltage

The figure shows the simulated results of voltage sag of supply voltage and load voltage for H-bridge converter with fuzzy controller. From the figure (a), it can be observed that the voltage sag occurs between 0.5-1.

The H-bridge converter consists of 4 switches (3 level).So that the voltage range obtain on the load side is 300-400V and also the voltage sag is compensated as shown in the figure (b).

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Fig 5: Simulation results of load voltage (c) With PI controller (d) With Fuzzy controller

The figure shows the simulated results of load voltage.

From the figure (c), it can be observed that the disturbances is more on the load side with PI controller

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and it can be reduce with the use of fuzzy controller as shown in figure (d).

IV. CONCLUSION

This paper presented the closed loop control of DVR using fuzzy controller. Based on the simulation carried out, it is clear that the voltage sag is compensated with DVR using fuzzy controller. This controller gives best results as it reduces the disturbances, easy to modify and cheaper to implement than the PI controller.

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