Index Terms |
| Photo Voltaic Active Power Filter, Shunt Active Power Filter, Power Quality. |
INTRODUCTION |
| Due to increasing air pollution, global warming concerns, diminishing fossil fuels and their increasing cost have made
it necessary to look towards Renewable Energy Sources (RES) as a future energy solution. In finding solutions to overcome a
global energy crisis, the Photo Voltaic (PV) system has attracted significant attention in recent years. The government is
providing incentives for further increasing the use of grid-connected PV systems. Renewable Energy Sources are increasingly
integrated at the distribution level due to increase in load demand which utilize power electronic converters. Due to the
extensive use of power electronic devices, disturbances occur on the electrical supply network. These disturbances are due to
the use of non-linear devices. These will introduce harmonics in the power system thereby causing equipment
overheating ,damage devices ,EMI related problems etc. Active Power Filters (APF) is extensively used to compensate the
current harmonics and load unbalance. This will result in additional hardware requirements. So, in this paper, the existing PV
inverter acts as Shunt Active Power Filter (SAPF) that is capable of simultaneously compensating problems like current
unbalance, current harmonics and also of injecting the energy generated by RES. The shunt active filter is a voltage source
inverter (VSI), which is connected in parallel with load. Shunt Active Power Filter has the ability to keep the mains current
balanced and sinusoidal after compensation for various Load conditions. |
ORGANIZATION OF THE PAPER |
| The paper has been divided into five sections for easy understanding. Each section has got its own importance and relevance in
the project. |
| An overview of the individual sections is presented below. |
| Section-1: This gives the introduction to the project constituting overview of the work. |
| Section-2: This section gives the details of topology and components of the proposed system. |
| Section-3: This section displays the simulation and tabular results of the whole work done. |
| Section-4: This section gives the references on which this work is done. |
| Section-5: This section comprises of bibliography of the authors, which gives brief introduction of them. |
SYSTEM DESCRIPTION |
| A. TOPOLOGY |
| Active power filters are power electronic devices that cancel out unwanted harmonic currents by injecting a compensation
current which cancels harmonics in the line current. Shunt active power filters compensate load current harmonics by injecting equal-but opposite harmonic compensating current. Generally, four-wire APFs have been conceived using fourleg converters
[5]. This topology has proved better controllability [6] than the classical three-leg four-wire .In this paper, it is shown that using
an adequate control strategy, even with a three phase four-wire system, The topology of the investigated APF and its
interconnection with the grid is presented in Fig. 1. It consists of a three-leg four-wire voltage source inverter. In this type of
applications, the VSI operates as a current controlled voltage source. The proposed system is Three Phase Four wire which
consists of Photovoltaic system connected to the dc-link of a grid-interfacing inverter as shown in Fig. 1. The voltage source
inverter is a key element of a PV system as it interfaces the renewable energy source to the grid and delivers the generated
power. The Photovoltaic system is connected to grid with an inverter coupled to dc-link. The dc-capacitor decouples the
Photovoltaic system from grid and also allows independent control of converters on either side of dc-link. |
 |
| B.VOLTAGE SOURCE CONVERTER (VSC) |
| A Voltage Source Converter (VSC) is a power electronic device that connected in shunt or parallel to the system. It can
generate a sinusoidal voltage with any required magnitude, frequency and phase angle. It also converts the DC voltage across
storage devices into a set of three phase AC output voltages. It is also capable to generate or absorbs reactive power. If the
output voltage of the VSC is greater than AC bus terminal voltages, is said to be in capacitive mode. So, it will compensate the
reactive power through AC system. The type of power switch used is an IGBT in anti-parallel with a diode. The three phase
four leg VSI is modeled in Simulink by using IGBT. |
| C.CONTROLLER FOR APF |
| The dc link voltage, Vdc is sensed at a regular interval and is compared with its reference counterpart Vdc*.The error signal is
processed in a PI-controller. The output of the pi controller is denoted as Im.The reference current templates (Ia*,Ib*,and Ic*)
are obtained by multiplying this peak value (Im) by the three-unit sine vectors (Ua , Ub and Uc) in phase with the three source
voltages. Theseunit sine vectors are obtained from the three sensed line to neutral voltages. The reference grid neutral current
(In*) is set to zero, being the instantaneous sum of balanced grid currents. Multiplication of magnitude Im with phases (Ua ,Ub,
and Uc) results in the three phase reference supply currents (Ia*,Ib*,and Ic*). |
| The grid synchronizing angle (Ѳ) obtained from phase locked loop (PLL) is used to generate unity vector template as |
 |
 |
 |
HYSTERESIS CURRENT CONTROL |
| The hysteresis current control (HCC) is the easiest control method to implement; it was developed by Brod and
Novotny in 1985 . The shunt APF is implemented with three phase current controlled VSI and is connected to the ac mains for
compensating the current harmonics. The VSI gate control signals are brought out from hysteresis band current controller.
A hysteresis current controller is implemented with a closed loop control system and waveforms are shown in Fig .3. An error
signal is used to control the switches in a voltage source inverter. This error is the difference between the desired current and
the current being injected by the inverter . If the error exceeds the upper limit of the hysteresis band, the upper switch of the
inverter arm is turned off and the lower switch is turned on. As a result, the current starts decaying. |
 |
| If the error crosses the lower limit of the hysteresis band, the lower switch of the inverter arm is turned off and the upper
switch is turned on. As a result, the current gets back into the hysteresis band. The minimum and maximum values of the error signal are eminand emax respectively. The range of the error signal e max -emin directly controls the amount of ripple in the output
current from the VSI. |
SIMULATION RESULTS |
| The performance of the proposed structure is assessed by a computer simulation that uses MATLAB Software. The
parameters of the proposed system are given in the tables below. The performance of the system with proposed control scheme
is discussed, which includes the following case studies. |
 |
| Fig. 4 shows the source current, load current, inverter compensating current respectively. The inverter is turned on at
0.09 seconds. Fig. 4 (a) : it clearly indicates the source current from 0 to 0.09 sec represents the non-sinusoidal nature due to the
presence of nonlinear load .At 0.09 seconds the nature of waveform is sinusoidal this represents the inverter compensated the
non sinusoidal wave to balanced sinusoidal wave. The load current waveform is shown in Fig. 4 (b) .The inverter supplies the
compensating current that is shown in Fig. 4 (c). THD analysis for NON LINEAR LOAD is shown in figure (5) and (6) below. |
| THD OF SOURCE CURRENT BEFORE COMPENSATION |
 |
| Total Harmonic Distortion of Source Current Before Compensation = 30.13% |
| THD OF SOURCE CURRENT AFTER COMPENSATION |
 |
| Total Harmonic Distortion of Source Current after Compensation = 3.20%. |
| After compensation, THD of the source is reduced from 30.13% to 3.20% which is well below the recommended 5% limit. |
| CASE 2 : UNBALANCED LOAD |
 |
| From Fig. 7, it clearly indicates the source current from 0 to 0.1 sec represents the unbalance nature due to the presence of
unbalance load. At 0.1 seconds the nature of waveform is sinusoidal this represents the inverter compensated the unbalance
wave to balanced sinusoidal wave. The load current waveform is shown in Fig .7(b). The inverter supplies the compensating
current that is shown in Fig. 7 (c). |
| CASE 3: BALANCED NONLINEAR LOAD |
 |
| From Fig.8, it clearly indicates the source current from 0 to 0.1 sec represents the balance nonlinear nature due to the
presence of balance nonlinear load. At 0.1 seconds the nature of waveform is sinusoidal this represents the inverter
compensated the balanced nonlinear wave to balanced sinusoidal wave. |
| CASE 4: UNBALANCED NONLINEAR LOAD |
 |
| CASE 5 : THD ANALYSIS FOR DIFFERENT HYSTERESIS BANDS |
 |
| From the above table 1 it can be observed that as the hysteresis bands increase the THD valves of source current increased. |
| CASE 6: THD ANALYSIS FOR DIFFERENT PERCENTAGE OF UNBALANCED NONLINEAR LOAD |
 |
| From the above table 2 it can be observed that for different percentage of Unbalanced Nonlinear load the to eliminate
harmonics for various load. |
 |
References |
- Mukhtiar Singh, Student Member, IEEE, VinodKhadkikar, Member, IEEE, Ambrish Chandra, Senior Member, IEEE and Rajiv K. Varma, Senior Member, IEEE "Grid Interconnection of Renewable Energy Sources at the Distribution Level With Power−Quality Improvement Features."IEEE Transactions On PowerDelivery, Vol. 26, No. 1, January 2011.
- Y. Jaganmohan Reddy, K. Padma Raju, Y. VenkataPavan Kumar, "Use of DC Motor−Generator Set for Power Quality Improvement in a Renewable Energy Based Hybrid Power System." International Journal on Recent Trends in Engineering & Technology, Vol. 05, No. 02, Mar 2011.
- Hung−Cheng Chen, Jian−Cong Qiu, and Chia−Hao Liu "Dynamic Modeling and Simulation of Renewable Energy Based Hybrid Power Systems" DRPT 2008, pp. 2803−2809.
- D.M. Brod and D.W. Novotny, "Current Control of VSI PWM Inverters", IEEE Transactions Industrial Application, Vol. IA−21,no.4.pp.562 570,1985.
- M.takeda et al, "Harmonic Current Compensation With Active Filter", in IEEEIIAS Ann. Meeting,1987,pp,808.
- KaruppananP ,KamalaKantaMahapatrab"PLL Synchronization With PID Controller Based on Shunt Active Power Line FILTER." International Journal of Computer and Electrical Engineering ,Vol.3,No.1,February 2011.
- AswathyB.Raj , B. Shyam, Robins Anto"Simulation of Distributed Generation Power Inverter as Active Power Filter using MATLAB/Simulink." International Journal on Recent Trends in Engineering and Technology ,Vol.6, No.2,Nov 2011.
- R. C. Dugan, M. F. McGranaghan, S. Santoso, H. W. Beaty, "Electrical Power Systems Quality", Second Edition, McGraw−Hill.
- M. Aiello, A. Catalioti, S. Favuzza, G. Graditi, "Theoretical and Experimental Comparison of Total Harmonic Distortion Factors for the evaluation of Harmonic and Inter harmonic Pollution of Grid−Connected.''IEEE Transactions On Power Delivery, Vol. 21, No. 3, July 2006
- .J. M. A. Myrzik, and M. Calais, Member, IEEE "String and Module Integrated Inverters for Single−Phase Grid Connected Photovoltaic Systems – A Review".Power Technical Conference Proceedings, 2003 IEEE Bologna
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