A Passivity-Based Weighted Proportional-Derivative Feedforward Scheme for Grid-Connected Inverters With Enhanced Harmonic Rejection Ability

To suppress the effect of the point of common coupling (PCC) voltage on the grid current, the unit PCC voltage feedforward scheme is commonly applied to the grid-connected inverters. However, this method results in a negative real part of the inverter output impedance both in a wide low-frequency band and around the Nyquist frequency ( f(s)/2) ( f(s) is the sampling frequency), which degrades the passivity and leads to a risk of system instability in weak grid. This article proposes a weighted proportional-derivative (PD) PCC voltage feedforward scheme. By properly tuning the weighted coefficients of the two feedforward elements, the real part of the inverter output impedance becomes nonnegative in the frequency range up to 0.47 fs, harvesting satisfying passivity. Meanwhile, compared with the unit PCC voltage feedforward scheme, the proposed feedforward scheme also gains superior harmonic rejection ability, guaranteeing high-quality injected current. Experiments are performed on a 6-kW prototype and the results validate the effectiveness of the proposed feedforward scheme.