Capacitor-Current PID Feedback Control Method for Grid-Connected Inverter to Improve System Stability and Harmonic Rejection Ability

The wide variation of the grid impedance can easily cause system resonance or even system instability of LCL-type grid-connected inverter in weak grid, and the injected grid current is severely distorted due to grid voltage harmonics. To address this issue, a capacitor-current PID feedback control method is proposed in this paper to correct inverter system impedance. It makes the output impedance of inverter and the equivalent virtual impedance of the filter capacitor in parallel have a nonnegative real part within the Nyquist frequency, while increasing the inverter output impedance’s low-frequency gain. Then, the design guideline for the parameters of capacitor-current PID feedback coefficient is given. The proposed method has the ability to significantly enhance system stability and harmonic suppression capability, simultaneously enhancing system robustness to variation in grid impedance. Finally, simulation results verify the effectiveness of the proposed method and parameter design.