CONTROL OF SQUARE-WAVE INVERTERS IN HIGH-POWER HYBRID ACTIVE-FILTER SYSTEMS

This paper presents a new control scheme for a hybrid parallel active filter (HPAF) system intended for high-power applications-up to 100-MW nonlinear loads-to meet IEEE 519 recommended harmonic standards. The active filter inverter is realized with small-rated (1%-2% of the load rating) square-wave inverters operating at the dominant harmonic freq uencies. The proposed system achieves harmonic isolation at desired do minant harmonic frequencies, such as the fifth and seventh, even in th e presence of supply voltage harmonic distortions. A novel method of a ctive filter inverter de-bus control, as proposed here, achieves power balancing by exchanging energy at the fundamental frequency and at th e dominant harmonic frequency (such as the fifth). The proposed square -wave inverter-based HPAF system provides improved filtering character istics as compared to the conventional passive filter and is expected to be cost effective for high-power nonlinear loads compared to the co nventional passive filter or other active filtering solutions. The con cept of harmonic isolation at dominant harmonic frequencies by square- wave inverters with the proposed control scheme is validated by simula tion results.