Double feed-forward control strategy for dynamic voltage restorer

In open-loop utility voltage feed forward control,DVR(Dynamic Voltage Restorer) has fast dynamic response,but the load voltage is always greatly distorted by the load current.Closed-loop PI(Proportional-Integral) controller can reduce this effect,but the dynamic response speed is slowed down and the load voltage influenced by the utility voltage.Regarding the load voltage as the control object,the duty ratio of power devices as control variables,and the utility voltage and load current as interferences,it is found from the mathematic model of DVR that the system performance is always disturbed by these two interferences.Transfer functions of different system control strategies are derived and conclusion is drawn that,the system steady state error is caused by these two interferences.An open-loop double feed forward controller adopting both utility voltage and load current feed forward is thus proposed,which guarantees the fast dynamic response of open-loop control and eliminates influen-ces of both utility voltage and load current.To avoid the noise caused by differential section in load current feed forward,estimation of load current with load voltage only is designed.