Injected Grid Current Quality Improvement Method for Grid-Connected Inverters Considering Inductor Nonlinearity

Given that the photovoltaic (PV) output is usually intermittent and fluctuating, the grid-connected PV inverter may often operate at half load or even light load conditions, and the distortion of injected grid current deteriorates. Considering that the inductor made of magnetic powder core material behaves soft saturation and nonlinear characteristics, its inductance value can change with the current. Then, the current controller which is usually designed according to the rated power inductor value is relatively conservative and is not beneficial to the grid current quality when the inverter power changes. Therefore, this paper proposes an adaptive grid current quality improvement method for grid-connected inverter considering the inductor nonlinearity, which adaptively adjusts the current controller parameters at different power values on the premise of ensuring system stability. The inverter achieves better current harmonics suppression by increasing the system loop gain during power changes especially under low power conditions. The effectiveness of the improved method is verified through simulations and experiments.