Implementing synchronous DC link voltage control with phase skipping on a three-phase microinverter using minimum DC link capacitance

To improve light load efficiency, a three-phase photovoltaic (PV) based microinverter may operate in single-phase, two-phase or three-phase mode depending on the available input power. Therefore, its DC link capacitor may be subjected to large peak-to-peak voltage ripple when operating in phase skipping mode. This paper determines the minimum value of the DC link capacitor by allowing the maximum acceptable voltage ripple on the DC link. This allows for the use of film capacitors instead of electrolytic capacitors in order to improve the microinverter reliability. It is proposed that a simple synchronous control method can be used to regulate the DC link voltage with the presence of large voltage ripple. The DC link voltage controller is synchronized with the phase-locked loop and samples the average value of DC link voltage without introducing unwanted harmonics into the voltage sense path. A 300-W three-phase microinverter prototype was built to verify the proposed DC link voltage control performance. Inverter output current total harmonic distortion of 1.6% was achieved even though the DC link peak-to-peak voltage ripple reached as high as 87 V with 219 V split DC link voltage. Dynamic response is fast enough to easily track the most extreme ramp change in input PV power.