25-09-2012, 12:48 PM
A Technical Survey on Control Strategies of Active Filter for Harmonic Suppression
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Abstract
In modern era, the tradition of non-linear loads in Electrical power system has sparked the research in
power quality (PQ) concern like voltage flicker, voltage sag and swell, harmonics, etc., Among all the other concerns,
one of the the majority significant of PQ problem is Harmonics .Active Power Filter (APF) is one of most
challenging filter for the mitigation of harmonics. The heart of the Active power Filter is the controller part. In this
study, a wide-ranging review of various controllers have been projected ,Which mitigate harmonics, reactive power
and unbalanced load currents originating from load side, and also the advantages and disadvantages of presented
techniques are presented. The study also helps the researchers to select the optimum control strategies and power
circuit configuration for APF applications.
Introduction
To reduce the harmonics conventionally passive L–C filters were used and also capacitors were
employed to improve the power factor of the ac loads .But the passive filters have several drawbacks like
fixed compensation, large size and resonance problem. To mitigate the harmonics problem [6][7], many
research work development are developed on the active power (APF) filters or active power line
conditioners [1]-[5] .Active filters appear to be a viable solution for power quality conditioning [7]-[9].
Control techniques for active power filters
Advancement in Microelectronics has motivated new directions for APF design starting from the use
of analog and digital components to microprocessors, microcontrollers, digital signal processors
(DSP’s)[27] and FPGA[34] implementation. From fig 1 it shows that control part plays important role in
filtering. Further, these developments have made it possible to use different control algorithm, the
controller of active power filter mainly divided into two parts i.e. reference current generation and PWM
current controller. The PWM current controller is principally used for providing gating pulse to the active
power filter. In reference current generation scheme, reference current is generated by using the distorted
wave form. Many control schemes are there for reference current generation, such as p-q theory[9][10],
Dead Beat controller[19] ,Adaptive control[18][23], Neuro[22-26],Fuzzy[27][28],wavelet control[29-33]
,sliding mode control [29]-[33],delta-sigma modulation[14][15] vector control[13] , SFX control[18],
repetitive control[17], etc. for improving the steady state and dynamic performance of APFs. By
implementing this performance, response as well as the cost is efficient compare to the analog one.
Fixed Frequency Control
The fixed frequency control [6] has been shown in figure 2 in which the error between the reference
and actual current is fed through a PI controller which integrates the error between the feedback and
reference current to generate a variable voltage value then, this value is fed into a triangle pulse-width
modulator to produce gate signal. The output V control of the amplifier is compared with a fixed
frequency (switching frequency fs) triangular waveform