Improved repetitive controller for active power filter

In order to eliminate a certain type of harmonics in power grid, this paper presents a novel compound controller to improve the performance of active power filter (APF) based on synchronous frame. The proposed controller can work effectively with the help of a proportional-integral (PI) control and an advanced repetitive controller. By optimizing the internal model of the repetitive controller, the controller can deal with the current from grid directly, which simplifies the APF system dramatically. Because there is no need to add extra sensors and the APF system does not require a harmonic detector. Moreover, the proposed controller which has a shorter convergence time for its smaller repetitive period can eliminate the harmonics faster than the traditional one. And its repetitive cycle is only one-sixth as that of the traditional. In addition, thanks to an advanced voltage phase collector, the voltage phase collected from the grid becomes more accurate, which improves the compensation performance of APF. The controller design algorithm is also given in detail. Theoretical analysis and results obtained by simulations validate the superiority of the proposed controller.