Passivity enhancement for LCL-filtered grid-connected inverters using the dominant-admittance-based controller

LCL filters are widely used for power quality improvement. However, its resonance complicates the design process. Although the single-loop filter-based control reduces the cost, it is not reliable because of the grid impedance variation at the point of common coupling (PCC). This study proposes a dominant-admittance-based controller to improve the passivity of the inverter. Meanwhile, no extra hardware cost increases. It first offers a single-loop damping method using a low-pass filter, which frees inverter from the conventional limitation (f(res)>f(s)/6). A graphical procedure is applied to coordinate the current loop design to mitigate the low-pass filter's negative effects on bandwidth. Then it introduces the dominant admittance concept for the inverter with PCC voltage feedforward control, which provides a new starting point for the admittance reshaping of the filter-based damping inverter. Based on this concept, a PCC voltage feedforward control using a second-order low-pass filter is presented. The inverter output admittance is passive up to the Nyquist frequency with the feedforward control. Although the additional control loop is introduced, the controller requires no extra sensors because the PCC voltage measurement has already existed for the grid synchronisation. Experimental results validate the proposed scheme.