An independent control approach for three-phase four-wire shunt active filter based on three H-bridge topology under unbalanced load conditions

This paper presents a simple scheme to compensate the load reactive power, current harmonics, load unbalance, and neutral current in a three-phase four- wire (3P4W) system. The shunt active power filter (APF) consists of three H-bridge single-phase voltage source inverters (VSI) supported by a common DC bus voltage. Thus each phase of 3P4W system can be viewed and controlled as independent phase and/or in conjunction with other phases, and hence it improves the overall system controllability. The 3H-bridge topology also results in the reduction of required DC bus voltage by a maximum factor of radic3 , which indeed helps to reduce the inverter rating and thus promises an effective topology for high power applications. In this paper, the single-phase p-q theory based controller is realized to achieve - i) proposed independent phase control approach and ii) load unbalance compensation approach. The 3P4W shunt APF system with both the approaches is first simulated by using MATLAB/ Simulink, and then developed, implemented, and tested in the laboratory using the digital signal processor (DSP) DS1104 of dSPACE. The developed shunt APF system is able to reduce the current total harmonics distortion (THD) up to 2.1%, and the current unbalance factor from 40% to 4.76%.