A soft-switching modular three-phase AC voltage regulator

This paper presents a soft-switching modular three-phase ac voltage regulator which can solve the abnormal voltage problems such as under-voltage, over-voltage, voltage sag and voltage swell. The proposed scheme is the combination of three single-phase modules while each one of the single-phase module is a serial compensation ac voltage regulator. Besides, each one of the single-phase module is composed of a three-arm topology which operates as a rectifier and an inverter. Rather than the conventional four-arm topology, the proposed three-arm topology not only reduces the number of main switches but also increases the system reliability and simplifies the control circuits. Using simple resonant units, all main switches of high frequency arm are operated at zero-voltage-switching (ZVS) turn-on, while all auxiliary switches are operated at zero-current-switching (ZCS) turn-off. Moreover, the proposed feed forward control, based on the energy balance concept, is proposed to control the voltage of energy-storage capacitors. Finally, some simulation results are presented for verification.