Fast transient control of single-phase dynamic voltage restorer (DVR) without external DC source

Abstract

This paper presents a fast dynamic control scheme for the capacitor-supported single-phase dynamic voltage restorer (DVR). The scheme consists of two main control loops as inner and outer control 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 first loop. It has three control modes for achieving two different functions, including 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 serves for the same purpose as the second mode. However, it will be activated when the capacitor voltage is reduced to a level that starts distorting the output voltage. 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 500VA, 110V, 60Hz prototype has been built and tested with nonlinear loads. The dynamic behaviors of the prototype under different voltage dip depths will be investigated.