动态电压恢复器的双前馈控制策略研究

采用基于电网电压前馈的开环控制时,动态电压恢复器(DVR)动态响应速度快,但负载电压受负载电流影响较大;用比例积分(PI)调节器实现闭环控制可以减小这一影响,但动态响应速度变慢,且负载电压受电网电压影响变大。提出把负载电压看作DVR的控制对象,桥式电路中开关器件的占空比看作控制量,电网电压和负载电流看作干扰量,根据数学模型分析出被控对象不仅受控制量控制,而且受2个干扰量的影响。结合不同控制策略中控制量的计算方法,推导出各种控制策略下系统的传递函数,分析可知系统存在稳态误差的原因在于2个干扰量的影响。基于此,提出同时利用电网电压前馈和负载电流前馈的双前馈开环控制方法,既保持了开环控制动态响应速度快的优点,也可基本消除电网电压和负载电流对负载电压的影响。为避免电流前馈微分环节噪声影响,设计了用负载电压估计负载电流的估算方法。仿真结果验证了理论分析的正确性。

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.