| Popis: |
For the grid-connected inverter which acts as the key interface in renewable energy power generation systems, the gird current quality and the robustness are important indicators of the system behaviors. The low-frequency voltage harmonics existed in the grid voltage are mainly responsible for the current distortion, and the feedforward of the voltage at the PCC (point of common coupling) can effectively suppress low-order current harmonics. However, in the weak grid, the voltage feedforward may amplify the low-order current harmonics and endanger the robustness due to the high grid impedance. During the last decade, some studies have indeed discussed some improved feedforward methods; however, the comparative study is still lacking and it is not easy for engineers to choose suitable feedforward methods for the application. Therefore, based on the impedance-based modelling and stability criterion, this study deeply discusses the impact of different feedforward strategies (including proportional feedforward, full feedforward, fundamental feedforward, bandpass filter-based feedforward, and low-pass filter feedforward) on the system robustness and grid current quality, while the behavior of SOGI-PLL is considered. The features and merits of different feedforward strategies are reviewed, and the applicable occasions are discussed. |
