Resonant mechanism of multi grid-connected inverters in distribution power systems

With increasing penetration of grid-connected photovoltaic (PV) power generation in distribution network, the equivalent impedance of the distribution network and the distribution capacitance of the interconnection cables are changed. The changed impedance network may be excited by the harmonic current of inverters or the harmonics of the grid voltage, which will affect the power quality and stable operation of the distribution network. The frequency characteristic of the grid current is given firstly. Then a Norton equivalent model of grid-connected inverter with LCL filter is established. Basing on the inverter model, the Norton model of distribution network considering the cable distribution capacitance is proposed. By analyzing of the series and parallel resonant characteristics, the resonant mechanism is demonstrated. Simulative results verify the validity of theoretical analysis.