Fast Transient Control for Three-Phase Capacitor-Supported Dynamic Voltage Restorer (DVR)

A fast transient control scheme for three-phase capacitor-supported dynamic voltage restorers (DVR) is presented in this paper. Instead of using a separate service supply feeder, a capacitor bank is used on the dc side of the series inverters in the DVR to provide the ride-through function during voltage dips. The capacitor voltage is regulated by adjusting the relative phase shift of the inverter output with respect to the mains voltage. The control scheme is based on using the boundary control with a second-order switching surface to dictate the states of the switches. The DVR can also maintain limited voltage restoration and balancing functions. A 1.5kVA, 220V prototype has been built and tested. The transient responses of the DVR during the voltage dip have been studied. Theoretical prediction has been favorably compared with the experimental results. The DVR output can be reverted to the steady state in two switching actions during the voltage dip and swell conditions.