A novel control of a current-source active filter for AC power system harmonic compensation

A novel control strategy for an active power filter that consists of a current-source PWM (pulse width modulation) converter and LC filters to eliminate the PWM carrier frequency components is proposed in order to obtain good harmonic compensation characteristics. The PWM converter is controlled with feedback loops of filter input currents and their derivatives to suppress the transient oscillations caused by the LC filters without inserting damping resistors. Optimum values of feedback gains are investigated. The cut-off frequency of the optimum design is about one seventh of the PWM carrier frequency, and the compensation delay time is two times as large as the carrier period. The performance of the active power filter with the proposed control strategy was confirmed by experiments in which the harmonic currents generated by a phase-controlled bridge converter were compensated. Input current after compensation was essentially sinusoidal, and the harmonic content was reduced to less than 4%