Dynamic Modelling Based Reference Current Extraction Technique for the Control of Shunt Active Power Filter

Abstract

In the recent decades, use of power electronic loads have increased because of their better control and reduced cost. However, these loads draw non-sinusoidal currents from the utility which affects the power quality of the system. This has led to the use of passive filters. Though the passive filters have addressed the issues concerning the power quality, they are encountered with problems such as resonance, single frequency compensation, system parameter dependency and bulkiness. This has motivated the researchers to use active power filter as an alternative to the existing passive filters. Recent studies have shown that the use of shunt connected active power filter not only solves the power quality issues, it also solves the generic problems associated with passive filters. Shunt active power filter (SAPF) works efficiently for power quality improvement and reactive power compensation. The performance of the shunt active power filter depends on the method of reference current extraction. Though the conventional extraction methods have shown good results for balanced load conditions, they have failed to accurately determine harmonic and reactive currents, in cases of (a) distorted and unbalanced supply and (b) unbalanced load. This study presents a method to estimate the harmonic component and the unbalanced and reactive current components having fundamental frequency, based on adaptive interference cancellation theory. An adaptive PI control based DC-link voltage regulator is developed to avoid the effect of continuous change of load in the distribution end. Simulations are performed in MATLAB/SIMULINK environment to verify the feasibility of the proposed method. The results show that the Total Harmonic Distortion (THD) of utility current from this method falls well below the prescribed IEEE-P519 limit of 5%.