Harmonic suppression and stability improvement for aggregated current-controlled inverters

For LCL-filtered grid-connected inverters, classical control methods such as the proportional grid voltage feedforward, the harmonic quasi resonant (HQR) control etc., are widely utilized to achieve low current distortion. However, the system stability is easily challenged by the grid impedance and the increased number of the paralleled inverters. Therefore, this paper orients to guarantee the harmonic suppression and the system stability, simultaneously. The impedance-based approach is employed for modeling the multiple-inverter system. The control strategy which consists of the proportional weighted grid voltage feed-forward and HQR with phase compensation is proposed. Moreover, the relationship between the proportional weighted value and the number of the improved HQR controllers is clearly clarified. With the help of the proposed control strategy, the magnitude of the inverter output impedance is maximized as much as possible and the phase across -90 degree is avoided to improve the system stability. The effectiveness of the method is verified with experimental results on a two-inverter-parallel system.