Improved grid voltage feedforward for strengthening the inverter's adaptability to utility

Grid-connected inverters with the proportional grid voltage feedforward usually achieve satisfied output impedance, which contributes to the low order harmonic elimination. However, a potential positive feedback link is introduced, which decreases the phase margin significantly or even trigger instability when inverters are connected to utility with the non-negligible grid impedance. To maintain the stability and high quality of the injected current for inverters connected to utility with a large set of grid impedance, this study proposes the proportional weighted with partial fundamental grid voltage feedforward. With the aid of the proportional weighted feedforward, the influence of the positive feedback link related to the grid impedance is mitigated. Besides, the steady-state performance is guaranteed by the partial fundamental grid voltage feedforward compensation. Therefore, with the proposed feedforward, the grid-connected inverter can stably operate and achieve high current quality in the weak utility. Then the inverter's adaptability to utility is strengthened. Experiments validate the effectiveness of the proposed method.