Passivity Enhancement and Grid-Current Distortion Mitigation for Inverter-Side Current Controlled LCL-Type Grid-Connected Inverters

Abstract

Inverter-side current (ISC) control has been widely used in LCL-type grid-connected inverters due to its cost-effectiveness. However, the ISC-controlled inverters suffer from instability and injected grid current distortion under weak grid conditions, such as grid impedance variations and background harmonics. To solve these problems, this article presents an admittance shaping scheme based on capacitor voltage feedforward (CVF) for ISC-controlled LCL-type grid-connected inverters. A delay compensated proportional CVF method is used to shape the inverter output admittance to be passive almost up to the Nyquist frequency. Then, another high-pass filter-based CVF method is employed to shape the grid harmonic admittance to greatly reduce the admittance magnitude at the harmonic frequencies. Thanks to the proposed admittance shaping scheme, the ISC-controlled inverter system can operate stably regardless of the grid impedance and has excellent grid-current harmonic suppression capability. The effectiveness of the proposed admittance shaping scheme is verified by detailed simulation and experimental results.INDEX TERMS Grid-connected inverter, capacitor voltage feedforward, harmonic suppression, passivity.