A Paralleled Current and Voltage Control Strategy With Compound PI Controllers for Three-Phase Active Power Filters

The conventional control strategy for active power filters (APF) is essentially a nested structure, where the output of the outer voltage loop will affect the command current of the inner loop, inevitably impairing the performance in harmonic compensation. In this paper, to enhance the harmonic-compensation performance, the output of the dc-link voltage loop has been modified and added as a disturbance to the current loop, which forms a paralleled structure. Thus the pure command current can be achieved and not affected by the output of the voltage loop. Parameters of the proposed paralleled strategy are designed considering both stability and dynamic responses, and larger phase and gain margins are achieved. In addition, a compound PI controller has been designed to avoid the integral overflow problem. Finally, experimental results verify that, though with a relatively slow the dc-link voltage response, the proposed paralleled strategy can achieve a faster and more precious current control, and a better performance in harmonic compensation compared with the conventional nested strategy.