Control of electrolyte-free microinverter with improved MPPT performance and grid current quality

This paper presents a control technique to improve the MPPT performance and grid current quality for two-stage electrolyte-free microinverter. The proposed method rejects the PV-side double-line frequency oscillation and reduces the grid current distortion with the PV dc-dc converter controlled with a high loop gain while intermediate dc bus voltage loop of grid-tie dc-ac inverter controlled with a low loop gain both at the double-line frequency. The dc-bus film capacitors with the small capacitance allow to have high ripple voltage to buffer the double-line energy while the PV-side could not see this doubleline frequency oscillation due to the control of dc-dc converter with high double-line frequency ripple rejection capability. As a result of high reduction of double-line frequency of dc bus voltage loop, the distortion of grid current reference is reduced and the total harmonic distortion (THD) of the grid current is improved. The PV-side capacitance can also be greatly reduced because it is only required to filter the high-frequency transistor switching ripple. Experimental results justify the effectiveness of the proposed control method.