Cooperative Interharmonics Control Scheme for Parallel Photovoltaic Inverters with Particle Swarm Optimization and Phase-Shifting

The perturbation and observation maximum power point tracking (P&O MPPT) is widely applied in photovoltaic (PV) system, which can introduce interharmonics problem, posing a threat to power quality. If multiple PV inverters are connected in parallel, it may induce further exacerbation of power quality by the interaction between interharmonics. To address this issue, a cooperative interharmonics control scheme is proposed in this paper. According to the steady state MPPT reference voltage function obtained from the Fourier transform and phase-angle function, the functional of the effective value of the total DC-link perturbations voltage and the phase angle of the MPPT perturbations is established. Mitigating the effective value of the total DC-link perturbations voltage is taken as the optimization target, particle swarm optimization (PSO) intelligence algorithm is applied to calculate the properly shifting phase-angle of MPPT perturbations. By shifting the phase-angel of MPPT perturbations of each inverter based on the calculated shifting phase-angle, the total DC-link voltage oscillation can be effectively mitigated. With the proposed scheme, interharmonics can be effectively suppressed and further power quality can be improved. Simulation results have validated the effectiveness of the proposed scheme.