Extended Application of Improved D-D- Current Control in Synchronous Inverter Cluster Considering N Times Equivalent Impedance

Photovoltaic (PV) power station is an inverter cluster with a single grid connected inverter as the unit. The resonance frequency shift caused by the grid impedance of the inverter cluster under weak grid is more serious. In this paper, Dual-Division-Summation (D-D-Sigma) current control strategy is extended to inverter cluster to solve the more serious problem of resonant frequency offset. A derivative curve of logarithmic amplitude frequency characteristic curve is used to analyze the resonance characteristics, and the change of resonance characteristics caused by equivalent grid impedance is analyzed mathematically. Aiming at the resonance characteristics after the equivalent impedance is enlarged by N times, a resonance suppression strategy of inverter cluster under weak grid is proposed. The control gain of the resonance suppression strategy is obtained through the Routh Criterion, which can consider the wider range of resonance frequency offset. The experimental results verify the correctness of the above analysis.