A novel series dynamic voltage restorer for distribution systems

This paper describes how a series dynamic voltage restorer (DVR), based on the use of a Cryo-MOSFET PWM inverter and energy storage system, can be used to protect sensitive power customers from voltage sags/swells. The proposed DVR restores the end-user voltage to its normal level by rapidly injecting a compensating voltage onto the line against the upstream power disturbances. The control strategy has adopted the concept of reference voltage tracking control. A control law is derived to maintain the downstream voltage in a pure sinusoidal waveshape with constant amplitude, no matter what kind of upstream power disturbances occur. Test results on 230 V mains are presented to demonstrate that the Cryo-MOSFET can be used as the power switching device for the converter, and to validate the control strategy. Furthermore, it would also be possible to employ the DVR in a distribution network with a radial structure to improve the downstream power quality.