STATCOM WITH POD CONTROLLER FOR REACTIVE POWER COMPENSATION Vijai Jairaj 1, Vishnu.J 2 and Sreenath.N.R 3

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1 STATCOM WITH POD CONTROLLER FOR REACTIVE POWER COMPENSATION Vijai Jairaj 1, Vishnu.J 2 and Sreenath.N.R 3 1 PG Student [Electrical Machines], Department of EEE, Sree Buddha College of Engineering Pattoor, Kerala, India 2 Assistant professor, Department of EEE, Sree Buddha College of Engineering Pattoor, Kerala, India 3 PG Student 3 [Electrical Machines], Department of EEE, Sree Buddha College of Engineering Pattoor, Kerala, India Abstract The main problem faced by the industrial and commercial load is the power quality issues during the fault. This is an undesirable phenomenon. The main aim is to introduce STATCOM as a solution for reactive power. It is connected in shunt for necessary compensation on its load side. To remove the power quality problems it should be compensated by injecting a current so that it can provide necessary compensation. For that purpose we are using reactive power compensative devices (FACTS devices). Among the FACTS devices STATCOM is more preferred. It consists of a voltage source inverter (VSI). The shunt VSI is connected via a DC link, which includes a DC capacitor. The modeling of Transmission line is completed using MATLAB SIMULINK. At that time active power is reduced and power quality problems will dominate. This problem can be eliminated by placing a STATCOM which will supply shortage of reactive power. This paper utilizes a POD Controller for providing necessary control and thus for mitigation of power quality problems and hence reactive power compensation can be done which is the main objective. Keywords- FACTS, STATCOM, VSI, POD I. INTRODUCTION Voltage control is one of the most important aspects in the Transmission line. The main problem with transmission line is its voltage sag during the fault which is harmful for the equipments connected to the line. So it is necessary to compensate such voltage variations. When a fault occurs there will be a sudden dip in voltage at that. This is an undesired phenomenon, can be solved using reactive power compensation devices like FACTS devices. The shunt devices which can be used for reactive compensation are SVC and STATCOM. A Static Var compensator (SVC) is a fast acting shunt device which will regulate voltage, reduce harmonics and stabilize the system. It is also connected near industrial loads to improve power quality. But STATCOM is more preferred than SVC because it provides more reactive power support at low voltages. Dc link capacitor will act as a source for compensation. Different types of controller can be employed. They are proportional controller, proportional plus integral controller. proportional plus integral plus derivative controller and power oscillation damping controller. The STATCOM is additionally equipped with a Power Oscillation Damping (POD) control function. The controller parameters are optimized using parameter identification. Design of current and voltage controllers has a significant role in modeling of STATCOM. The STATCOM is applied with the DC link voltage with the help of designed controllers and depending on spikes and overshoot responses a suitable DC link voltage is applied. Based on the values of DC link voltage passive components are designed [1]. There are large number of sub modules which are connected in series to build up a controllable voltage source in a multi-level converter technology. It reduces the number of harmonics generated compared to SVC devices and also there is no need to install additional fixed harmonic filter bank All rights Reserved 147

2 substation which is the main advantage of multi-level converter technology over redundant modular converter design [2]. The UPFC system has many advantages like it has the ability to control both real and reactive power phase angle and reduced maintenance. [3] Shows the ability of UPFC to control both real and reactive power. With increase in real and reactive power there will be an increase in angle of injection. It explains how power quality can be improved by the control and performance of UPFC. This paper utilizes a model of STATCOM to study about stability phenomenon and the performance of power system. The STATCOM is equipped with a Power Oscillation Damping (POD) control function. Parameter identification is used for optimization of controller parameters. II. STATCOM STATCOM consist of a shunt converter with a dc storage capacitor which is used for compensation. It will inject current to the transmission line thus it can provide necessary compensation. Fig.1. STATCOM single line diagram The major power quality issues [7] faced by domestic and commercial loads are voltage sag and swell. About 80 % of power quality issues is due to this phenomenon. According to definition, Voltage sag is the reduction in the AC rms voltage from half of a cycle at power frequency to a few seconds duration. Similarly Voltage swell is the increase in the rms AC voltage at power frequency from half cycles to a few seconds. In this paper, STATCOM is based on three phase voltage source converter. It produces both capacitive and inductive reactive power internally. By controlling the gate pulses of inverter switches are being controlled, this voltage source can modify the compensating reactive power and making voltage smooth. So, by injecting reactive power voltage sag can be mitigated and by absorbing reactive power voltage swell can be improved. Fig. 2 shows the three basic operation modes of the STATCOM output current, I, which depends on varying values of Vi. If Vi = Vs, the reactive power is zero and at that time it does not absorb or supply reactive power. The STATCOM exhibits a capacitive reactance, when the injecting voltage (Vi) is greater than the supply voltage (Vs), and it is said to be in capacitive mode of operation. Hence in this mode, the device supplies capacitive reactive power to the ac system. On the contrary, when the supply voltage (Vs) is greater than the injecting voltage (Vi), the STATCOM exhibits inductive reactance and hence it is in the inductive mode of operation. In this mode, the device absorbs inductive reactive power from the ac system. Fig.2. Basic modes of operation of All rights Reserved 148

3 III. POD CONTROLLER Fig.3. POD controller A POD controller is developed and is tuned to provide an additional damping to stabilize the power system after severe disturbances. The STATCOM controller parameters are shown in Table 1. The POD controller constitutes a transfer function which is composed of a transducer with a gain which is followed by a washout filter. The signal obtained at the output is limited. The transfer function which constitutes lead-lag filters which can be used for phase compensation of POD controllers Table.1. POD Parameters PARAMETER VALUE UNIT K PU T Sec T Sec T Sec IV. Modeling of transmission Line Fig.4. transmission line model The above figure shows the modelling of transmission line in MATLAB/SIMULINK. A 3 phase source provides which is generally a generator provides the supply for transmission line the input voltage will be 11kV and in order to transmit it need to be step-up, step-up transformer is used here. The voltage is stepped up to a desired voltage and a RL load is connected as load this is modelled to know the variation of voltage with respect to fault which is applied on the load side. V. MODELLING OF TRANSMISSION LINE WITH STATCOM The figure shows the modelling of transmission line with STATCOM. STATCOM consist of voltage source converter with a DC link capacitor. It will inject current to the line to provide necessary compensation [2]. There is a controller provided to control the firing of Voltage source All rights Reserved 149

4 Fig.5. Modeling of transmission line with STATCOM STATCOM is an important device among FACTS family. It is connected in shunt with transmission line, also it has a superior performance in lot of aspects such as fast responding speed, voltage stabilization, power loss is reduced and it also limits the transient voltage. Fig.6. Modeling of STATCOM VI. PWM Generator Fig.7. PWM Generator The PWM generator generates the gate pulses for the IGBTs of the VSC. Here, the sine and the triangular waveforms are generated. The sine wave which is of 50Hz is compared with the triangular wave of 20 khz. Thus on comparison, the PWM pulses are produced and these pulses are given to gates of the IGBTs.. Modulation index is defined as the ratio of the magnitude of modulating wave to carrier wave. By varying the modulation index, the magnitude of the converter output will vary and as well as by varying the phase angle of the modulating wave, the converter output voltage phase angle will also All rights Reserved 150

5 VII. RESULT A transmission system is modeled using MATLAB/ SIMULINK software. A fault is applied and it has a resistance of 0.1 ohm and fault transition time between 0.05 and 0.1sec.During the time of fault voltage sag will occur and there will be a decrease in active power and increase in reactive power during this time. Results obtained during the simulation shown below so we need to compensate this by using a STATCOM so the voltage can be improved and the power is also improved. Here for better understanding simulation time is taken as 0.7. From the voltage waveform at instant of fault STATCOM will inject current in to the system and thus necessary compensation occurs. Fig.8. Voltage without STATCOM Fig.9. Active power without STATCOM Fig.10. Reactive power without All rights Reserved 151

6 Fig.11. Voltage with STATCOM VIII. CONCLUSION Fault is one of the problems faced by power system. During fault the voltage will decrease and there is a sudden increase in reactive power so we need to compensate this using STATCOM which will inject current in to the system and hence necessary compensation can be obtained. A POD controller is used for controlling the gate pulse of IGBT. Thus by POD controller serves a major role in improving power quality. Hence the compensation is done with STATCOM in SIMULINK platform. REFERENCES [1] S.K.Sethy, J.K.Moharana Design, Analysis and Simulation of Linear Model of a STATCOM for Reactive Power Compensation with Variation of DC-link Voltage International Journal of Engineering and Innovative Technology (IJEIT) Volume 2, Issue 5, November 2012 [2] M. Pereira, D. Retzmann, J. Lottes, M. Wiesinger, G. Wong, SVC PLUS: An MMC STATCOM for network and grid access applications, IEEE PowerTech Conference, Trondheim, Norway, 2011 [3] Parvej khan, Himmat singh Power Flow Control In A Transmission Line Through UPFC International Journal of Emerging Technology and Advanced Engineering Website: (ISSN , ISO 9001:2008 Certified Journal, Volume 2, Issue 12, December 2012) [4] M. Rama Sekhara Reddy and M.Vijaya Kumar. "Power Quality Improvement in DFIG based Wind Energy Conversion System using UPFC." IOSR Journal of Engineering (IOSRJEN), vol. 3, no. 1, pp , Jan [5] S.Divya, U.Shyamala, Power Quality Improvement In Transmission Systems Using DPFC IEEE sponsored 2nd international conference on electronics and communication system (icecs 2015). [6] Ch.Chengaiah, R.V.S.Satyanarayana power flow assesment in transmission lines using simulink model with upfc 2012 International Conference on Computing, Electronics and Electrical Technologies [ICCEET]. [7] R. C. Dugan, M. F. McGranaghan and H. W. Beaty, Electric Power Systems Quality. 2nd Edition, McGraw Hill, New York, All rights Reserved 152