Multirate Resonant Controllers for Grid-Connected Inverters With Harmonic Compensation Function

Resonant controller (RSC) is one of the most popular approaches for ac current/voltage control due to the high performance of zero steady-state tracking error. However, it suffers from heavy computational burden issue when multiple RSCs are demanded to control multiple harmonics. To alleviate this issue, a down-sampled multirate RSCs (MRRSCs) scheme is proposed for controlling power inverters, e.g., grid-connected inverters and active power filters. The proposed control scheme is composed of an inner control loop with a fast sampling rate, which is identical to the switching frequency, and an array of paralleled MRRSCs-based external control loop with a reduced sampling rate. With the reduced sample rate, the MRRSCs can be executed alternatively in the dq-frame, such that the computational burden can be significantly reduced per cycle. Moreover, to reinforce the wide frequency adaptability of the MRRSC, its central resonant frequency is online updated according to the output of the phase-locked loop. In the paper, the equivalent single-rate closed-loop model of the overall system is developed, based on which the controller parameters are designed employing the Nyquist diagram and root locus. Finally, experiments are performed on a grid-connected inverter to validate the superiority of the proposed scheme.