Synchronous DC link voltage control for microinverters with minimum DC link capacitance

This paper investigates DC link capacitor optimization for three-phase photovoltaic (PV) based microinverters. This concept minimizes the storage capacitance by allowing greater voltage ripple on the DC link. Therefore, the microinverter reliability can be significantly increased by replacing electrolytic capacitors with film capacitors. However, this intentionally increased voltage ripple can introduce harmonic distortion on the output current of the inverter stage if it is not mitigated by the DC link voltage controller. For this purpose, a robust and accurate DC link voltage control is proposed to filter this ripple while regulating the DC link voltage without using any additional circuit components. The experimental results on a 400-W three-phase half-bridge microinverter prototype validate the theoretical analysis of the DC link capacitor optimization and show that a significant reduction of the DC link capacitor requirement can be achieved. The proposed high accuracy DC link voltage controller is also implemented on this prototype to demonstrate very low harmonic distortion of the inverter output current while tightly regulating the DC link voltage even during transients.