Research On Average Current Control Of Three-phase DC Link Parallel Active Power Filter

Power harmonic pollution produced by power electronic equipments is a large threat for power system running steadily, safely, and economically. Thus, research on power harmonic suppression becomes the focus of power electronics. The main source of power harmonic is the rectifier of equipments, especially the three-phase uncontrolled rectifier, which widely applied in the situation of high or medium power. Three-phase DC link parallel APF is a novel power harmonic compensating method for three-phase uncontrolled rectifier, and has large technologic and cost advantage comparing with the conventional three-phase AC side APF and PFC. Research on three-phase DC link APF just begins and has many problems need to be solved, and the content of this thesis is based on the control strategy.Research on the control strategy of three-phase DC link APF all focus on one-cycle method at present, while this method has not been maturely applied. On the other hand, digital control has been widely used in active power filter. Thus, average current control is applied into three-phase dc link parallel active power filter for digital control in this thesis. The key of average current control is the bandwidth of current loop, which determines the compensation performance of DC link APF. In order to design the current loop bandwidth, the relationship between compensation performance of three-phase dc link active power filter and the current loop bandwidth is investigated in this paper. And compensation performance of three-phase DC link APF is researched in this paper at the frequency-domain to prove its technologic advantage.Consulting the single phase boost PFC, the voltage and current loop model of three-phase DC link APF is developed to design the controller parameter of each loop. Duty feedforward is added in the current loop to eliminate the disturbance of input voltage. Then, the proposed design method and theory analysis are verified by simulation.A test prototype of three-phase DC link parallel APF with digital control is designed to verify the proposed control method, and detailed designed method of hardware and software is given. This prototype is tested at the situation of steady working, load changing and three-phase source unbalance. Experimental results are presented to verify the correctness of the research.