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Bonfring International Journal of Power Systems and Integrated Circuits, Vol. 9, No. 1, March 2019 1 Power Quality Improvement Using Dynamic Voltage Restorer K. Sureshkumar, S. Vasanthamani, M. Mariammal, S. Raj, R.L. Vinodkumar Abstract--- One of the important in a power system study is a power quality improvement. It will be important now due to preface the discrete industrial devices and sensitive loads. The main issues in a power quality are voltage sags and swells at the distribution side. There are many different methods available to defect voltage sags and swells; the most popular methods is DVR (Dynamic Voltage Restorer). The DVR is a series compensating device, it is mainly used in low voltage and medium voltage application. The new configuration of DVR has been proposed using PI (Proportional Integral) controller and PID (Proportional Integral Derivative) controller and also THD values of PI (Proportional Integral) and PID (Proportional Integral Derivative) controllers are compared and it is conclude that total THD in PID (Proportional Integral Derivative) controller is better than PI (Proportional Integral) controller, which compensates voltage sags and swells during a single phase fault. Simulation results are carried out with MATLAB/SIMULINK to verify the performance of the proposed model. Keywords--- DVR, Single-Phase Faults, Voltage Sags, Voltage Swells. I. INTRODUCTION W E know the quality of power is facing discrete problems such as voltage sags, swells, surges, flicker, voltage imbalance, interruption and harmonic distortion. Among that voltage sags and swells are more frequent and acute than others. The DVR is one of the most custom power devices used for the progress of power quality performance. The DVR maintains the load side voltage at a real magnitude and phase by compensating the voltage sags and swells. Therefore any variety of voltage unbalance at the point of common coupling (PCC) can be eliminated. The DVR compensates voltage sags by increasing voltage in series with the supply side, hence overcomes the losses of power. The DVR injects sufficient amount of voltage to restore the voltage to its real value. The amount of power injection by the DVR can be decided by choosing an appropriate amplitude and phase angle.The SVC pre-dates the DVR, but the DVR is still favored because the SVC has no capability to control the active power flow. The DVR is small in size and price is less compared to DSTATCOM and other custom power devices.Most of the HVDC systems in operation today are based on linecommutated converters. With line commutated converters, the converter has only one degree of freedom – the firing angle, which represents the time delay between the voltage across a valve becoming positive (at which point the valve would start to conduct) and the thyristors being turned on.PID (Proportional Integral Derivative) is not heavy on hardware, therefore it can be implemented on cheap hardware also. For e.g. arduino Uno can run a couple of PID (Proportional Integral Derivative) loops very efficiently.PID(Proportional Integral Derivative) controller once designed, then its further tuning doesn't require a skilled personnel. According to IEEE 519 1992 and IEEE 1159 1995 standards voltage sag generally ranges from 10%-90% of the real operating voltage and lasts for a duration of half cycle to 1minute. On the other hand voltage swells are defined as an increase in RMS voltage for durations 0.5 cycles to 1 minute with magnitude 1.1pu to 1.8pu. The Fig.1 below shows the voltage sags and swells of IEEE 1159 1995 standard. As voltage swells are less common in distribution side so they do not need much more attention as voltage sags. Voltage sags and swells can create large current unbalance, causes shutdown or failure to sensitive equipments. Figure 1: Voltage Reduction II. K. Sureshkumar, UG Student, Department of Electrical and Electronics Engineering, SCAD Institute of Technology. S. Vasanthamani, UG Student, Department of Electrical and Electronics Engineering, SCAD Institute of Technology. M. Mariammal, UG Student, Department of Electrical and Electronics Engineering, SCAD Institute of Technology. S. Raj, UG Student, Department of Electrical and Electronics Engineering, SCAD Institute of Technology. R.L. Vinodkumar, Asst Professor, Department of Electrical and Electronics Engineering, SCAD Institute of Technology. DOI:10.9756/BIJPSIC.9002 LITERATURE SURVEY In 2016, R.Kalaivani, Voltage sag disturbances are the most frequently occurring Power Quality problems in the distribution system. This concept explains modeling and simulation of a dynamic voltage restorer as a voltage sag and swell mitigation device in electrical power distribution networks. A Dynamic Voltage Restorer (DVR) is proposed to handle deep voltage sags, swells and outages on a low voltage single phase residential distribution system. ISSN 2277-5072 | © 2019 Bonfring Bonfring International Journal of Power Systems and Integrated Circuits, Vol. 9, No. 1, March 2019 In 2015, S.Manmadha Rao, S.V.R.LakshmiKumari, B.Srinivasa Rao, Power quality is the most important aspect in the present power system environment. Among all the power quality problems most frequently occurring disturbances, affecting the quality of power are voltage sags and swells. Custom power device, Dynamic Voltage Restorer (DVR) connected in series with a goal to protect the loads from source side voltage disturbances. Here single phase DVR is adopted for each phase instead of using three phase DVR to compensate unbalanced sags/swells. 2 The change in phase angle is obtained by comparing the per-unit faulted voltage with the reference voltage 1P.U. Then the error signal so obtain is given to PI (Proportional Integral)controller and PID (Proportional Integral Derivative) controller, which generates the required change in phase angle. Then the reference voltage is generated by using new changed phase angle which are summarized in equation. The MATLAB representation of the control strategy of DVR is shown in Fig.4. DYNAMIC VOLTAGE RESTORE III. L. Gyugyi in 1994 proposed a methodology for dynamic voltage restoration at the distribution end. This method enables the use of real power to be injected at the faulted supply voltage side and is known as dynamic voltage restorer. In this study, the DVR structure basically consists of a voltage source converter (VSC), a line injection transformer between the supply AC voltage side and the sensitive load, a dc energy source in parallel with a DC link capacitor and a control technique as shown in Fig.2. Figure 4: Simulink Model for the Control Strategy of DVR The flow chart for the control strategy of DVR for injecting the voltage to a test system during fault condition is shown in Fig.5. As the DVR is a series compensating device, so it is connected in series between the source voltage side and the sensitive load through the line injection transformer. In order to inject active and reactive power several types of energy storage are used. Such as battery bank, DC link capacitor, super conductors. For the switching action of the DVR during fault duration controller is an important part. The VSI converts DC to AC and makes it sure that only the sag and swell voltage will be injected through the line transformer at the PCC. Figure 2: Basic Topology of a DVR IV. CONTROL STRATEGY For fast response action the control strategy of the DVR plays an important role. When the voltage sags and swells are detected, the DVR should react as fast as possible. It can be implemented using SPWM control technique per unit reference voltage and instantaneous value of load voltage in per unit. The basic rules of control strategy are as follows:detection of voltage sags and swells, calculating the amount of compensation required, generating pulses through SPWM generator and stop the pulse triggering after passing of fault duration. Figure 5: Flow Chart for the Control Strategy of DVR It is then given to SPWM generator to produce singlephase pulse that controls the switching of VSI and hence the DVR. The Fig.6 below shows the control strategy for generating reference voltage. ISSN 2277-5072 | © 2019 Bonfring Bonfring International Journal of Power Systems and Integrated Circuits, Vol. 9, No. 1, March 2019 Figure 6: Control Strategy for Reference Voltage Generator The complete schematic diagram of DVR with proposed system is shown in Fig.7. Figure 7: Simulation of DVR Connected System V. SIMULATION RESULTS 3 Figure 8 (b): Load side voltage after sagCompensation with PI controller Figure 8 (c): Load Voltage after sag Compensation with PID Controller The Fig.8 (a) represents the duration of three-phase voltage sag. The result shows about 80% drop in voltage during the sag duration within the interval 0.1sec to 0.2sec. With a total sag duration for 0.1sec. (b)Shows the line voltage after sag compensation with PI (Proportional Integral) controller. Shows the line voltage after sag compensation with PID (Proportional Integral Derivative)controller. Figure 8(d): THD with PI Controller Figure 8 (a): Load Bus Voltage During Sag Figure 8(e): THD with PID Controller ISSN 2277-5072 | © 2019 Bonfring Bonfring International Journal of Power Systems and Integrated Circuits, Vol. 9, No. 1, March 2019 The THD for PI controller in DVR having 1% with the fundamental frequency 50HZ as shown in figure-8(d). The THD for PID controller in DVR having 0.9% with the fundamental frequency 50HZ as shown in figure-8(e). [14] R. Mihalic, P. Zunko and D. Povh, “Improvement of transient stability using unified power flow controller power delivery”, IEEE Transactions, Vol. 11, Pp. 485–492, 1996. [15] A.A. Edris, “Proposed terms and definitions for flexible AC transmission systems (FACTS)”, IEEE Transactions, Vol. 2, Pp. 1848– 1853, 1997. The THD for PID controller is better than PI controller. VI. CONCLUSION A comprehensive study of a DVR as a powerful custom power device has been studied with use of MATLAB/SIMULINK. The main advantages of DVR are low cost, simpler implementation; require less computational efforts and its control is simple as compared to other methods. The control system is based on PI(Proportional Integral) and PID(Proportional Integral Derivative) based SPWM technique which scaled error between load side of the test system and its reference for compensating sags and swells. The simulation results show that the DVR performance is efficient in mitigation ofvoltage sags and swells. The DVR handles both overvoltage and under voltage situations without any difficulties. It injects an appropriate voltage component to correct any abnormality rapidly in the voltage waveform; in addition, it keeps the load voltage balanced and constant at the nominal value. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] 4 R. Pal and S. Gupta, “Simulation of Dynamic Voltage Restorer (DVR) to Mitigate Voltage Sag During Three-Phase Fault”, International Conference on Electrical Power and Energy Systems (ICEPES), 2016. Y. Prakash and S. Sankar, “Mitigation of Voltage SAG Problem Using Dynamic Voltage Restorer (DVR)”, International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering, Vol. 4, No. 10, 2015. D. Francis, “Mitigation of Voltage Sag and Swell Using Dynamic Voltage Restorer”, International Conference on Magnetics, Machines & Drives, AICERA, 2014. M. Venmathi and L. Ramesh, “The Impact of Dynamic Voltage Restorer on Voltage Sag Mitigation”, IET Chennai 3rd International on Sustainable Energy and Intelligent Systems (SEISCON 2012), Pp. 1-7, 2012. C. Benachaiba and B. Ferdi, “Power Quality Improvement Using DVR”, American Journal of Applied Sciences, Vol. 6, No. 3, Pp. 396-400, 2009. H. Kim, S.J. Lee and S.K. 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Iyer, “Dynamic Voltage restorer three dimensional space vector PWM control algorithm”, 9 th International, Conference Electrical Power Quality and Utilization, 2007. L. Sarıbulut, “Performance analysis of unified power flow controller (UPFC) by using different controllers”, M.Sc. thesis, Department of Electrical and Electronic Engineering, Cukurova University, 2008. Y.H. Song and A.T. Johns, Flexible AC Transmission Systems (FACTS), IEE Power and Energy Series, 1999. ISSN 2277-5072 | © 2019 Bonfring