Operation of unified constant-frequency integration controlled three-phase active power filter in unbalanced system

In recent years, the power quality of the AC system has become a great concern due to the rapidly increased numbers of electronic equipment. In order to reduce harmonic contamination in power lines and improve the transmission efficiency, active power filter research has become a hot topic. Many control methods for the active power filter (APF) were proposed. The theory and experiments have demonstrated that unified constant-frequency integration (UCI) controller features excellent performance, simple circuitry, and low cost control methods for three-phase APF under three-phase balanced conditions. In this paper, a three-phase APF working in an unbalanced condition with a UCI controller are studied. Analysis and simulation show that with UCI control sinusoid input current can be realized, whether the input voltages are balanced or unbalanced.