Study of double feedforward controller for dynamic voltage restorer

To guarantee the fast dynamic response, open-loop controller is always adopted with the utility voltage as feedforward variable. The main drawback of this controller is that the load voltage is always distorted by load current. Closed-loop PI controller can reduce this effect, but the dynamic response is slowed down. Regarding the load voltage as control object, the duty ratio of the power devices as control variable, and the utility voltage and load current as interferences, it can be concluded that the load voltage is always distorted by the two interferences. An open-loop double feedforward controller is thus proposed. The open-loop structure guarantees the fast dynamic response, and the double feedforward eliminates the influences of both the utility voltage and the load current. To avoid the noises caused by differential section in the load current feedforward, an estimation method is designed.