Design and Implementation of a Fast Dynamic Control Scheme for Capacitor-Supported Dynamic Voltage Restorers

Abstract

This paper presents a fast dynamic control scheme for capacitor-supported single-phase dynamic voltage restorers (DVRs) for inductive loads. The scheme consists of two main control loops as inner and outer loops. The inner loop is used to dictate the gate signals for the switches in the DVR. It is based on the boundary control method with the second-order switching surface. The load voltage can ideally be reverted to the steady state in two switching actions during a supply voltage dip. The outer loop is used to generate the DVR output reference for the inner loop. It has three control modes for achieving two different functions, including the output regulation and output restoration. The first mode is for regulating the capacitor voltage on the dc side of the inverter, so that the output of the DVR is regulated at the nominal voltage. The second mode is for restoring the output with the near minimum energy injection by the DVR during a voltage dip. The third mode is in maximum voltage injection and will be activated when the capacitor voltage is reduced to a level that starts distorting the output voltage in the second mode. The mode boundaries will be derived in this paper. By studying the small-signal characteristics of the control loops, a set of design procedures will be derived. A 500 VA, 110 V, 60 Hz prototype has been built and tested with nonlinear inductive loads. The dynamic behaviors of the prototype under different voltage dip depths will be investigated.