A soft-switching three-phase five-arm ac voltage regulator

This paper presents a soft-switching three-phase five-arm ac voltage regulator. It can solve the unusual voltage situations such as under-voltage, over-voltage, voltage sag, voltage swell and three-phase unbalanced source and load. Also, the proposed voltage regulator not only maintains a stable output voltage but corrects the input current to achieve a unity power factor. The proposed scheme combines a three-phase rectifier with a three-phase inverter in a common dc-link. Besides using simple resonant units, all main switches are operated at zero-voltage-switching (ZVS) turn-on. Furthermore, all auxiliary switches are operated at zero-current-switching (ZCS) turn-off. Rather than the conventional three-phase ac voltage regulator, which uses twelve main switches to construct a six-arm topology, the proposed soft-switching five-arm ac voltage regulator can reduce the number of main switches. Moreover, the reduction in the number of main switches not only can simplify the control circuit but also can increase the system reliability. In addition, a simple feed forward controller, based on the energy balance concept, is proposed to control the voltage of energy-storage capacitors. Since the energy change in the energy-storage capacitors can be fast compensated, the transient performance of the proposed voltage regulator can be improved. After all, some experimental results are presented to verify the feasibility of the proposed soft-switching three-phase five-arm ac voltage regulator.