Passivity enhancement in RES based power plant with paralleled grid-connected inverters

Harmonic instability is threatening the operation of power plants with multiple grid connected converters in parallel. To analyze and improve the stability of the grid connected converters, the passivity of the output admittance converters is first analyzed in this paper. It is shown that the non-passivity of the output admittance of the converters will make the system unstable under certain grid conditions. Based on the stability analysis, this paper proposes a new method to cancel the nonpassivity of the power plant by using inverters with different power rating and control strategies. Three specific cases, where the LCL parameters, sampling frequency and current control strategies of the paralleled inverters are different, are studied. The results suggest that the grid connected converters with different power ratings and control strategies improve the stability of the power plant as a whole.