Active Mitigation Method of Harmonic Currents for Photovoltaic Converter Considering Multi-frequency Coupling Characteristics

Distributed photovoltaic (PV) exacerbates waveform distortion of the point of common coupling (PCC). Multi-frequency coupling characteristics are obvious between grid voltage and PV grid-connected current, but the traditional harmonic suppression methods fail to consider the impact on the coupled frequency harmonics, resulting in harmonic currents at the coupled frequency being amplified due to the grid background harmonic changes. Therefore, the mitigation of photovoltaic coupled harmonic currents in distorted grids is an urgent technical challenge to be overcome. This paper first constructs a harmonic coupling matrix model (HCMM) of the (photovoltaic converter, PVC) to describe the harmonic coupling characteristics, which can represent the influence of topology and control parameters simultaneously. Secondly, the effect of the positive and negative sequence virtual impedance on the coupled harmonic admittance of the HCMM is analyzed. Finally, an adaptive virtual impedance tuning method based on repetitive control and dual bandpass filters is proposed, which can reduce more than 80% of coupled harmonics in a grid with single or multiple voltage distortions. Comparative experiments of a three-phase PVC are provided by a MATLAB/Simulink simulation and the physical experiments with a DSP controller. The results verify the validity of the coupled harmonic analysis and the effectiveness of the proposed method.