Boundary control of dynamic voltage restorers in voltage harmonic compensation

Abstract

Dynamic voltage restorer (DVR) is used to provide load voltage support and protect sensitive load during voltage sags situation. However, voltage sags do not appear frequently and hence the utilization of the DVR is low. In order to increase the utilization of the DVR, the DVR should operate to compensate any load voltage instability especially the load voltage harmonics and source voltage variations in steady-state operation. A boundary controller using a second-order switching surface is proposed for DVR application for both voltage sags and power quality control under steady-state condition. The switching surface is derived to estimate the state trajectory movement of the DVR after a hypothesized switching action. It results in a high state trajectory velocity along the switching surface. This phenomenon accelerates the trajectory moving towards the target operating point. The dynamic performance of the DVR is verified experimentally with distorted supply voltages, non-linear loads and distorted voltage sag situation. Experimental results confirm that the proposed boundary control scheme can achieve better harmonic compensation performance than some other control methods.