Control strategies of dynamic voltage restorer
LI Hui-xun · Dianli zidonghua shebei · 2007
As voltage compensation strategy is the main part of DVR(Dynamic Voltage Restorer),several compensation methods,such as pre-sag compensation,in-phase compensation and minimum-energy compensation,are introduced and their principles are analyzed in phasor diagram.Pre-sag compensation ensures the continuity of load voltage before and after voltage sag,but the amplitude and power of output voltage are out of control.In-phase compensation is simple in calculation and its output voltage amplitude is the smallest,but the phase angle of output voltage is offset and the power out of control.Minimum-energy compensation optimizes the output power,but the amplitude of output voltage is bigger and the phase angle offset.The optimal compensation method is proposed,which integrates the advantages of three methods above-mentioned to find the optimal compensation point according to different sag conditions.DVR applying the optimal compensation method saves the energy stored at DC side,extends the compensation time and avoids the danger of over-voltage at DC side caused by the energy feedback to DVR when system voltage rises.Simulation results verify the effectiveness of the presented compensation method.