Fast DC Bus Voltage Regulation for a Low Cost Single-Phase Grid-Connected PV Microinverter With a Small DC Bus Capacitor

Double-frequency ripples occurring on the voltage of the DC-bus in single-phase photovoltaic microinverters lead to a considerable amount of harmonics and reduce the power factor. A commonly used method to reduce these ripples is the use of large electrolytic capacitors at the DC-bus. Replacing the electrolytic capacitors with thin film capacitors can be used to increase the lifetime of microinverters because thin film capacitors have longer lifetimes. They also have low capacitance, and this leads to large double frequency ripples on the bus voltage and as a result, high distortion in the output current. In this paper, to reduce the output current distortion, an FIR digital notch filter is employed in the bus control system. In this case, the bus controller has a low cost implementation due to the very low sampling frequency. The FIR filter successfully eliminates the distortion, but its dynamic performance is not good. To improve the dynamic performance, an input power feed-forward is proposed. In this method, no additional hardware is required. The proposed microinverter, which has a small 100 μF bus capacitor, is simulated and connected to the grid (220 V, 50 Hz). The output current THD at 250 W is 0.18%. The evaluation of the proposed method is conducted using simulation results in Matlab-Simulink software.