A Resonance Suppression Strategy for LCL-Type Photovoltaic Grid-Connected Inverters

To solve the resonant suppression problem of grid-connected photovoltaic inverters, an efficient active resonant suppression strategy is proposed. When converting the direct current power supply to alternating current power supply, photovoltaic inverter is prone to resonance problems due to fluctuations in grid impedance, resulting in a decline in output current quality. Based on the analysis of inverter control structure, transfer function and resonance phenomenon, a method of harmonic suppression by capacitor voltage is proposed. The power grid voltage fundamental wave is extracted through phase-locked loop and root mean square loop, and the power grid voltage fundamental wave is subtracted from the real-time sampling value of the power grid voltage to separate the power grid voltage harmonics. Virtual impedance control of these harmonics can reduce the use of sampling equipment and avoid the influence of low frequency current control. Finally, the effectiveness of the proposed method is verified by experiments, and the practicability of the virtual impedance algorithm for harmonic separation is proved.