A Single-Phase Grid-Connected PV Microinverter With Very Low DC Bus Capacitance, Low THD, and Improved Transient Response

Abstract

Harmonics and decrease in power factor occur in single-phase photovoltaic microinverters because the DC bus voltage exhibits a double frequency ripple. In order to reduce this ripple, large electrolytic capacitors which have short lifetimes are often used at the DC bus. To increase the lifetime of microinverters, it is necessary to replace electrolytic capacitors with thin film capacitors which have long lives and low capacitance. The trade-off between the output current THD and the bus voltage overshoot cannot be addressed with the ordinary bus voltage controller (PI) as reduction in bus capacitance leads to increase in the amplitude of the double frequency ripple on the bus voltage. In this paper, by using the proposed control method, a microinverter is designed and simulated so that this trade-off has been solved without using additional hardware. This microinverter is connected to the grid (220 V, 50 Hz). It has a very small 20 μF bus capacitor. The bus voltage has a negligible overshoot in response to an input power step of 200 W. THD of the injected current into the grid is 0.44% at 250 W output power. The outcomes of simulation conducted with Matlab-Simulink software confirm that the proposed method is effective.