ISSN Vol.07,Issue.13, September-2015, Pages:

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1 ISSN Vol.07,Issue.13, September-2015, Pages: Simulation of Photo Voltaic System with Boost Converter based APF for Power Quality Improvement B. RENUKA 1, P. VARAPRASAD REDDY 2 1 PG Scholar, Dept of EEE, VBIT Engineering College, Ghatkesar, RR. (Dt), TS, India. 2 Assistant Professor, Dept of EEE, VBIT Engineering College, Ghatkesar, RR. (Dt), TS, India. Abstract: In this paper, a three-phase three-wire Active Power Filter(APF) which is fed by Photovoltaic (PV) array or battery operated DC-DC boost converter is proposed for power quality improvement in the distribution system. The proposed APF consists of a three-leg Voltage Source Converter (VSC) with a DC bus capacitor. The PV array or battery operated boost converter is proposed to maintain the DC link voltage of the DC bus capacitor for continuous compensation for the load. The control of APF is achieved by using P-Q theory which is used to generate the reference currents. The switching of VSC will occur by comparing the source current with the reference current using Hysteresis based Pulse Width Modulation (PWM) current controller. The performance of the APF is validated using MATLAB software with its Simulink and Power System Block set(psb) toolboxes. Keywords: Distribution Static Compensator, Photo Voltaic Array, Boost Converter, Voltage Source Converter, P-Q Theory. I. INTRODUCTION Electricity is a convenient form of energy for lightning, heating, cooling and also produces motive power for various types of loads and power for a number of applications. Hence, the annual consumption of electricity has been increasing rapidly throughout the world. Thus, the increased usage of electricity in the modern day world challenges the economic co-operations of a power system with a greater focus on power quality. Many researchers have focused on renewable energy source based power quality improvement in the power distribution system. Power quality has caused a great concern to electric utilities with the growing use of sensitive and susceptive electronic and computing equipment such as personal computers, computer-aided design work stations, fax machines, uninterruptible power supplies, printers, etc. and other nonlinear loads such as fluorescent lighting, adjustable speed drives, heating and lighting control etc. Hence, in the deregulated power market, the power quality is becoming a major issue for the competing power distribution utilities. These nonlinear loads of switching converters and other power electronic devices create major power problem in the distribution system which tends to power quality problem. The various power electronic based devices called custom power devices used to mitigate the power quality problems have been proposed in the literature survey. Among these, APF is the most effective device. The Active Power Filter (APF) is one of the shunt connected custom power device which injects current through the interface inductor at the Point of Common Coupling (PCC) so that the reactive power compensation, source current harmonic reduction and load current compensation can be achieved. The different topologies of APF are reported in the literature such as a 3-leg VSC (Voltage Source Converter), three single phase VSC and 3-leg VSC with split capacitor APF etc. The proposed APF consists of three-leg VSC with a dc bus capacitor. The operation of VSC is supported by a DC bus capacitor with proper dc voltage across it. For controlling APF, and hence to generate the reference currents there are number of controllers reported in the literature survey such as instantaneous reactive power theory, adaptive neural network, synchronous frame theory and power balance theory. All the above mentioned algorithms have slow response. Here, the P- Q Theory is proposed for generating the reference currents. Since, after tracking the reference currents with the help of controller and by comparing it with source currents, the switching of VSC will occur and hence cancel out the disturbances caused by the nonlinear loads. In this paper, the Photo Voltaic (PV) module or battery with boost converter is connected to the dc bus capacitor of VSC which is used to provide the desired voltage across the dc bus for providing continuous reactive power compensation, source harmonic reduction and load compensation throughout the day. The proposed system is simulated under MATLAB environment using SIMULINK and sim power system tool boxes. II. SYSTEM CONFIGURATION Fig.1 shows the basic circuit diagram of the three phase three-wire system which is used to feed the non-linear load continuously. The nature of the nonlinear Load is to cause distortion in the current. After connecting the nonlinear load, suddenly there will be a distortion in the distribution system. In order to eliminate these distortions, the control of APF is achieved by using the IcosΦ algorithm IJATIR. All rights reserved.

2 B. RENUKA, P. VARAPRASAD REDDY arrays. The rating of a solar module is given by the maximum output or maximum power it can deliver. The output of a solar module depends on the number of cells in the module, type of cell and the total surface area. The output of a module changes depending on the amount of solar irradiance, the angle of the module with respect to the sun, the temperature of the module and the voltage at which the load is drawing power from the module [3]. The current-voltage (I-V) curve of a typical solar cell under Standard Test Condition (STC; 1000 W/m2, 25 C) is shown in Fig. 2. Fig.1. Circuit diagram of proposed APF. The load currents, source voltages and the dc bus voltage are given as an input to the IcosΦ controlling algorithm. The controlling algorithm is used to generate the reference currents. Then the Hysteresis based PWM current controller compares the reference and source currents and gives a switching pulse to the APF. The APF consists of six Insulated Gate Bipolar Transistor's (IGBT) with antiparallel diode based three leg VSC connected in shunt with the dc bus capacitor. The PV module with the DCDC boost converter is connected with the dc bus capacitor, which is used to give a desired voltage across the capacitor for continuous compensation. According to the gate pulse given, the switching of VSC will occur which injects a currents at the PCC through the interface inductor L r. B. Boost Converter Boost converter is DC-DC converter which converts lower voltage to higher voltage. A typical boost converter is composed of an inductor, switching device, diode, capacitor, load and gate signal for switching device as shown in Fig. 3. The boost converter with MPPT algorithm is used in solar PV system to generated maximum power at different weather condition and constant voltage across the load so that it can be converted to AC power easily by using inverter. The inductor is used to store the energy. By switching MOSFET on and off, the stored current from the inductor is transformed to load through the diode. The output voltage is kept continuous and constant by using large capacitor. Fig. 3. Boost converter with MPPT. Fig. 2. I-V Curve of PV Module. A. PV Array Solar energy is generally present in the form of solarir radiance. The PV cell works in the principle of Photoelectric effect; light striking on solar cell is converted to electric energy. These cells are made by silicon or other semiconductor materials. A typical silicon solar cell generates about 0.5 volts in normal operation. Large number of solar cells is connected in series, forming a module to meet the voltage requirement of the system. Large number of solar modules is connected to make III. CIRCUIT MODEL OF PV MODULE The voltage and current generated by a single PV cell is very low. So, solar cells are interconnected in a series-parallel combination to achieve the desired power. Desired voltage is generated by connecting the solar cells in series and the desired current is generated by connecting the cells in parallel. The series connection of cells known as PV modules usually has 28, 36 or 54 cells in it and array is the parallel connection of modules. The equivalent circuit of an ideal PV cell consists of a current source and a diode connected in anti-parallel with it[7-9]. A general model of the solar cell is the combination of current source (I pv ) connected in anti-parallel to a diode D, series resistance (R se ) and parallel resistance (R p ). Fig.4 shows the general model of solar cell. The PV system has nonlinear I-V and P-V characteristics. The two main factors which affect the output of PV system are temperature and irradiation level. The change of temperature and irradiation level results in change of voltage and current generated by PV system. The nominal operating condition of the solar module is 250C temperature, 1000 W/m 2 (G=1)irradiation at AM of 1.5.I-V and P-V characteristics of PV cell are shown in Fig.5 Open circuit voltage (Voc) is the maximum voltage a cell can generate under open circuit condition at I=0 and the short circuit current (ISC) is the current corresponds to short circuit at V=0. Through the operation, the PV cell generates

3 Simulation of Photo Voltaic System with Boost Converter based APF for Power Quality Improvement maximum power at only one point and this point is called Based on the general model, the equation for the output as Maximum Power Point (MPP). current of solar cell can be defined as (4) Fig.4. General Model of solar cell. I m, V m and Pm in the graph are maximum current, maximum voltage and the maximum power of the solar cell respectively. (5) The value of parallel resistor R p in equation (5) is extremely high and it is generally neglected for analysis of PV. The equivalent circuit of PV without R p is the called as the simplified model. The appropriate model of solar cell [11] is shown in fig.6. Based on the appropriate model, the output current defined in equation (5) is re-written as (6) Fig.5. I-V and P-V Characteristics of Solar Cell. The mathematical equation for output current of ideal cell is [8-10]. (1) Where, I pv is the light generated current which is directly proportional to the solar irradiation and Id is the Shockley equation. The light generated current of the solar cell is mainly depends on the solar irradiation level and its working temperature, which is expressed as (2) Where, I sc is the short-circuit current of cell at 25 C temperature and G=1, KI is the short-circuit current temperature co-efficient of cell, T c and T rare the operating temperature of cell and reference temperature respectively. The temperatures are in o K The Shockley equation can be expressed as (3) Where, Isis the saturation or leakage current of the diode, q is the electron charge [1.60 x o C], k is the Boltzmann constant [1.38x10-23J/K], and A is the ideality factor of diode. The values of k and T c should be taken into account with same unit as either in ocor in ok. The diode ideality factor A differs with respect to PV technology adopted [11]. Mono crystalline Si and the poly crystalline Si are most commonly used to technologies to produce PV modules. The ideality factors of those PV technologies are 1.2 and 1.3 respectively. Fig.6.Appropriate model of solar cell. bb The solar cells must be connected in series-parallel combination to obtain the desired output power. The mathematical equation for the PV array of the simplified model with (Ns) number of modules connected in series and (Np) number of modules connected in parallel can be described as The diode saturation current of the cell varies with the cell temperature, which is expressed in [10] as, Where, I rs is the reverse saturation current of a cell at a reference temperature and a solar irradiation, Egis the band gap energy of the semiconductor used in the cell. E g is approximately equal to 1.12 ev for the polycrystalline Si at 25 oc [12-13]. Using equation (9), the reverse saturation current of a cell I rs at reference temperature of 250C can be calculated. (9) IV. DC-DC BOOST CONVERTER MODELING DC-DC converters are used in PV systems to regulate the voltage generated by the PV modules. DC-DC boost converters are used in grid connected applications to step up the module voltage. The circuit diagram of DC-DC boost converter is shown in fig.7. (7) (8)

4 B. RENUKA, P. VARAPRASAD REDDY V. CONTROL OF GRID INTERACTIVE PV SYSTEM The grid interactive PV system configuration used for simulation study is shown in Fig.8. It consists of two power processing stages: DC-DC boost converter as first stage and three-phase voltage source inverter as second stage. The boost converter stage provides not only the boosting of PV output voltage for grid connectivity but also used as MPP tracker. Fig. 7. DC-DC Boost Converter. The DC-DC boost converter circuit consists of Inductor (L), Diode (D), Capacitor (C), load resistor (RL), the control switch (S). These components are connected in such a way with the input voltage source (Vin) so as to step up the voltage. The output voltage of the boost converter depends on the duty cycle of the control switch. So, the output voltage can be varied by varying the ON time of the switch. Thus, for the duty cycle D the average output voltage can be calculated using (10) Where V in, V o are the input and output voltage of the converter respectively and D is the duty cycle of the control switch. In an ideal circuit, the output power of the converter is equal to input power which yields. (11) The inductor value and the capacitor value are calculated using the formulas given. A. Selection of Inductor The inductor value of the Boost converter are calculated using (12) Where f s is the switching frequency and I L is the input current ripple. Current ripple factor (CRF) is the ratio between input current ripple and output current. For good estimation of inductor value CRF should bound within 30%. i.e., (13) The current rating of inductor should be always higher than that of the maximum output current. B. Selection of Capacitor The capacitor value can be obtained from (14) Where V o is the output voltage ripple which is usually considered as 5% of output voltage which yields (15) Fig.8. Grid connected PV system configuration. By controlling the duty ratio of boost converter using the proposed fuzzy based MPPT controller described in section- III, the current corresponding to maximum power is injected into the grid. The second inverter stage is used for multiple functions: (i) active power injection (ii) harmonic compensation of nonlinear load connected with the grid and (iii) reactive power compensation of the load. The additional functionality of the PV inverter as a shunt active power filter increases the overall efficiency of the system. The inverter switching signals are generated using the current control technique based on hysteresis current controller. A. Reference Current Generation The reference current generator block generates the reference current to be injected into the grid upon sensing the voltage at the Point of Common Coupling (VPCC) and load currents using instantaneous active and reactive power (p-q) theory. For the computation of p and q, the three phase voltages at the point of common coupling (PCC) and load currents must first be transformed to the stationary two axis (α-β) co-ordinates. The instantaneous real and reactive power p and q are determined using equations (9) Both instantaneous power quantities p and q consists of dc and ac components. While the dc components p and q arise due to the fundamental, the ac components p and q are a result of harmonic components. In order to inject active power generated by PV obtained using the proposed MPPT controller and also to provide harmonic as well as reactive power compensation as per the load demand, the reference for active and reactive power are generated. The ac component is determined by first extracting using a very low cut off low pass filter and then subtracting it from p (8)

5 Simulation of Photo Voltaic System with Boost Converter based APF for Power Quality Improvement obtained using. Finally, the reference currents are generated as per (10) and (11). (10) (11) B. Hysteresis Current Controller The hysteresis current controller compares the three phase reference currents (i ca *, i cb *, i cc *) generated using with the actual inverter currents (i ca, i cb, i cc ) and generates the switching pulses as per the logic given below: Leg-a upper switch is OFF and lower switch is ON. Fig.10. I-V characteristic curves of PV module obtained from the simulation under various irradiation levels. Leg-a upper switch is ON and lower switch is OFF. Where, hb is the hysteresis band around the reference current which is usually 5 % of the maximum current to be injected by the inverter. Similarly, control signals for leg-b and leg-c of the inverter switches are generated. C. Ripple Filter The ripple filter as shown in Fig.6 is used to absorb the switching frequency ripples. The switching ripples are generated due to switching of the inverter using the hysteresis current controller because of practical limitation in minimizing the hysteresis band and also due to switching of the boost converter. The ripple filter is a series R-C filter whose component values are so chosen as to absorb the high frequency components in multiple of switching frequency with the constraint that the fundamental current drawn by ripple filter should not exceed 5 % of the maximum load current. Fig.11. P-V characteristics of Solar module at different irradiation level and constant temperature (Tc=25 0 C). VI. MATLAB/SIMULINK RESULTS Simulation results of this paper is as shown in bellow Figs. 9 to 27. Fig.9. MATLAB/SIMULINK model of photo voltaic panel for I-V and PV characteristics. Fig.12. I-V characteristics at different temperature and constant irradiation level (G=1).

6 B. RENUKA, P. VARAPRASAD REDDY Fig.13. DC-DC Boost Converter simulation circuit. Fig.17. Output Voltage of Boost Converter constant DC input supply. Fig.14. PWM Pulse generation. Fig.18. Output current of Boost Converter constant DC input supply. Fig.15. PWM Pulse generation. Fig.19. Output voltage waveform of PV fed converter. Fig.16.Mat lab/simulink model of boost converter. Fig.20. Output current waveform of PV fed converter.

7 Simulation of Photo Voltaic System with Boost Converter based APF for Power Quality Improvement Fig.25.Shows the waveform for the source current Fig.21.MATLAB/SIMULATION model of the proposed APF with PV cell and boost converter. Fig.26. shows the power factor waveform for the circuit with fuzzy. Fig.22. Subsystem of the control circuit. Fig.27.THD for source current. Fig.23.Activepower filters circuit. VII. CONCLUSION The simulation of the Photovoltaic (PV) array or battery operated DC-DC boost converter fed three-leg VSC based APF has been carried out for reactive power compensation, source harmonic reduction and load current compensation in the distribution system. The APF was controlled by P-Q algorithm. The boost Converter is used to step up the voltage so as to match the dc link voltage of the three-leg VSC based APF for continuous compensation. The comparison of THD values of APF before and after compensation. The THD value is below the permissible limit of 5% (IEEE ). The MATLAB software with its Simulink and Power System Block set (PSB) toolboxes has been used to validate the proposed system. Fig.24. Shows The Waveform for The Source Current. VIII. REFERENCES [1] J.A.Gow, C.D.Manning, Development of photovoltaic array model for the use in power electronic simulation studies, IEE Proceedings Electric power applications, Vol. 146, No.2, March, 1999.

8 [2] Jee-Hoon Jung, and S. Ahmed, Model Construction of Single Crystalline Photovoltaic Panels for Real-time Simulation, IEEE Energy Conversion Congress & Expo, September 12-16, 2010, Atlanta, USA. [3] T. F. Elshatter, M. T. Elhagry, E. M. Abou-Elzahab, and A. A. T. Elkousy, Fuzzy modeling of photovoltaic panel equivalent circuit, in Proc. Conf. Record 28th IEEE Photovoltaic Spec. Conf., pp , [4] M. Balzani and A. Reatti, Neural network based model of a PV array for the optimum performance of PV system, in Proc. Ph.D. Res. Microelectron.Electron., vol. 2, pp , [5] S. Sheik Mohammed, Modeling and Simulation of Photovoltaic module using MATLAB/Simulink International Journal of Chemical and Environmental Engineering, [6] Francisco M. González-Longatt, Model of Photovoltaic Module in Matlab 2do congresoiberoamericano de estudiantes de ingenieríaeléctrica, electrónica y computación (ii cibelec 2005). [7] Huan-Liang Tsai, Ci-Siang Tu, and Yi-Jie Su Development of Generalized Photovoltaic Model Using MATLAB/SIMULINK WCECS 2008, October 22-24, 2008, San Francisco, USA [8]S. W. Angrist,, Direct Energy Conversion, Allyn and Bacon, Inc., 4th edition, 1982, pp [9] O. Wasynczuk, Modeling and dynamic performance of a line commutated photovoltaic inverter system, IEEE Transactions on Energy Conversion, vol. 4, no. 3, 1989, pp [10] R. Messenger and J. Ventre, Photovoltaic Systems Engineering, CRC Press, 2000, pp [11] C. C. Hua and C. M. Shen, Study of maximum power tracking techniques and control of dc-dc converters for photovoltaic power system, Proceedings of 29th annual IEEE Power Electronics Specialists Conference, vol. 1, 1998, pp [12] W. De Soto, S. A. Klein, and W. A. Beckman Improvement and validation of a model for photovoltaic array performance Solar Energy, 80(1):78 88, January [13] Geoff Walker. Evaluating MPPT converter topologies using a Matlab PV model Journal of Electrical & Electronics Engineering, Australia, 21(1), [14] Brigitte Hauke, Basic Calculation of a Boost Converter's Power Stage Application Report, SLVA372B November 2009 Revised July B. RENUKA, P. VARAPRASAD REDDY Author s Profile: P. Varaprasad Reddy was born on Received his B.Tech degree from JNTU, Hyderabad, India in 2009 and M.Tech degree in Power Electronics and Electrical Drives in 2012 from J.N.T.University, Anantapur, India. He has the teaching experience of 4 years. His areas of interests are Power Electronic Drives and Renewable Energy Sources. B.Renuka was born on 1992.She received her B.Tech Degree in Electrical and Electronics from JNTU, Hyderabad, in 2013 and M.Tech degree in Power Electronics and Electrical Drivesin 2015 from JNTU, Hyderabad.