In this paper, an implementation of shunt active filter for current harmonics compensation in order to achieve power quality improvement under non linear load condition is proposed. Shunt active filter makes the source current almost sinusoidal under non linear load condition by eliminating current harmonics. Controller generates the reference current and it is compared with actual current. PWM current controller controls the switch of the shunt active filter circuit. Shunt active filter eliminates the undesired current harmonics by injecting current into the system thereby reduces total harmonic distortion and improves power factor. The main objective of the project is to find the most suitable control method that is capable of reducing total harmonic distortion in the source current under non linear load condition. Fast and precise control loop is needed in order to assure the desired power quality. Three control techniques have been proposed: PI controller, Hysteresis current controller, Fuzzy logic controller. The system is modeled using Matlab/Simulink and simulation results prove that the source current harmonics can be reduced and power factor can be improved. The comparative performance of the proposed three controllers is also presented.

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Comparison of Controllers for Power Quality
Improvement Employing Shunt Active Filter
ABSTRACT:
In this paper, an implementation of shunt active filter for current harmonics compensation in
order to achieve power quality improvement under non linear load condition is proposed. Shunt
active filter makes the source current almost sinusoidal under non linear load condition by
eliminating current harmonics. Controller generates the reference current and it is compared with
actual current. PWM current controller controls the switch of the shunt active filter circuit. Shunt
active filter eliminates the undesired current harmonics by injecting current into the system
thereby reduces total harmonic distortion and improves power factor. The main objective of the
project is to find the most suitable control method that is capable of reducing total harmonic
distortion in the source current under non linear load condition. Fast and precise control loop is
needed in order to assure the desired power quality. Three control techniques have been
proposed: PI controller, Hysteresis current controller, Fuzzy logic controller. The system is
modeled using Matlab/Simulink and simulation results prove that the source current harmonics
can be reduced and power factor can be improved. The comparative performance of the proposed
three controllers is also presented.

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KEYWORDS:
1. Power Quality
2. Shunt Active Filter
3. Voltage Source Inverter
4. PI
5. Hysteresis Current Controller
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.1. Block diagram of shunt active power filter

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EXPECTED SIMULATION RESULTS:
Fig. 2 Simulated waveforms for uncontrolled diode bridge rectifier with RC load using PI controller (a) Supply
voltage (b) Load current (c) APF Injected current (d) Source current after injection
Fig.3 Simulated waveforms for uncontrolled diode bridge rectifier with RC load using hysteresis controller (a)
Supply voltage (b) Load current (c) APF Injected current (d) Source current after injection
Fig. 4 Simulated waveforms for uncontrolled diode bridge rectifier with RC load using fuzzy logic controller (a)
Supply voltage (b) Load current ( c) APF Injected current (d) Source current after injection

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Fig. 5 Simulated waveforms for uncontrolled diode bridge rectifier with buck converter load using PI controller (a)
Supply voltage (b) Load current (c) APF Injected current (d) Source current after injection
Fig. 6 Simulated waveforms for uncontrolled diode bridge rectifier with buck converter load using hysteresis
controller (a) Supply voltage (b) Load current (c) APF Injected current (d) Source current after injection
Fig. 7 Simulated waveforms for uncontrolled diode bridge rectifier with buck converter load using fuzzy logic
controller (a) Supply voltage (b) Load current (c) APF Injected current (d) Source current after injection

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Fig.8 Simulated waveforms for uncontrolled diode bridge rectifier AC voltage controller load using PI controller (a)
Supply voltage (b) Load current (c) APF Injected current (d) Source current after injection
Fig. 9 Simulated waveforms for uncontrolled diode bridge rectifier with AC voltage controller load using hysteresis
controller (a) Supply voltage (b) Load current (c) APF Injected current (d) Source current after injection
Fig. 10 Simulated waveforms for uncontrolled diode bridge rectifier with AC voltage controller load using fuzzy
logic controller (a) Supply voltage (b) Load current (c) APF Injected current (d) Source current after injection

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CONCLUSION:
In this paper, the design of shunt active filter to compensate harmonics in the power system
based on three control techniques were presented and compared. All the control techniques make
the source voltage and source current to be in phase. In the first control scheme the capacitor
voltage is regulated based on reference voltage and provides compensation for the reduction of
harmonics in the source current, the second one provides compensation based on reference
current generated from the fourier transform of load current, while the third one considers the
active filter controlled by fuzzy logic controller which is suitable for uncertainty condition.
Among the three proposals the fuzzy logic control technique [7] doesn' t need any mathematical
model, reduces total harmonic distortion in a better way and provides good performance and
robust to the parameter uncertainties compared with other strategies.
REFERENCES:
[1] David A .Torrey, Adel M. A . M. AI-Zamel "Single-phase active power filters for multiple
nonlinear loads" IEEE Transactions on Power Electronics, Vol. 1 0, No. 3, May 1 995, pp 263-2
72.
[2] B.Singh ,K.Ai-Haddad, and A.chandra , " A review of active filters for power quality
improvement" IEEE Transaction on Industrial electronics, vol 46,Issue no. 5, Oct-1999, pp 960-
971.
[3] Fabiana Pottker de Souza, and Ivo Barbi, " Single-phase active power filters for distributed
power factor correction", Power Electronics Specialists Conference 2000, PESC 00, Vol.l ,
pp500-505.
[4] M. EI- Habrouk, M.K. Darwish and P. Mehta "Active filter - A review" Electric Power
Applications, lEE Proceedings, Vol 1 4 7, Sep 2000, Issue 5, pp 403-413.