An improved grid-connected photovoltaic power generation system with low harmonic current in full power ranges

An improved grid-connected photovoltaic (PV) power generation system is proposed to solve the problem that the total harmonic distortion (THD) of grid-connected current generally exceeds 5% under the condition of low output power of PV array in this paper. The system includes a larger capacity master inverter with an LCL filter and a smaller capacity slave inverter with an L filter. Two inverters are connected in parallel with the utility grid via an isolated line-frequency transformer. Two inverters can operate in one of three working modes according to output power of the PV array to reduce the grid-connected harmonic current in full power ranges. Moreover, an active harmonic compensation circuit and its control method are presented to eliminate the harmonic current generated by the inverter. Design process of the system is studied. Control strategies of the different working modes are discussed. Simulation results verify that the system and its control strategies are feasible.