Stability Margin Analysis of Multi-inverter Grid-connected System Considering Asynchronous Control Period Under High Penetration

With the growth of renewable energy, grid-connected inverter as the interface has gradually increased its application. However, with the large-scale connection of inverters, resonance and stability problems have also been brought to distributed systems. Aiming at this issue, in this paper, a multi-parallel equivalent small signal model based on the structure of the multi-inverter grid-connected system is established firstly, and the expression of the output current of each inverter is obtained. According to the phase characteristics of the inverter’s output at different frequency bands, the output current expressions for synchronized and interleaved control period are further obtained. On this basis, influences of penetration, control gain and delay on harmonic or resonance are analyzed. Finally, a platform of four 30kW inverters is setup, and "resonance stability margin" method is proposed to verify the harmonic resonance characteristics of the inverter output current under high penetration.