Control Synthesis of a Buck-Derived Active Energy Storage System in PV Microinverter

Solar photovoltaic (PV) microinverters traditionally implement passive electrolytic capacitor (EC) banks as an energy storage medium in the DC link for mitigating the double-line frequency power ripple arising from mismatched DC and AC port power. Such an energy storage medium reduces the magnitude of the resultant DC link voltage ripple. An EC bank solution, however, is severely detrimental to the realizable microinverter power density and reliability. To address this issue, this paper proposes an alternative solution for DC link energy storage in the form of a buck-derived pulsating power buffer (PPB) circuit which enables improvement both in power density and reliability of the microinverter system. Furthermore, this paper focuses on modeling the PPB power stage dynamics and thereby development of a cascaded control scheme featuring grid frequency tracking. The proposed methodology in this work is validated by simulation and hardware prototype for a PPB installed a the front-end of a single-stage PV microinverter system rated for 40VDC to 120VAC nominal voltage conversion at 400W rated load. It is found that the proposed PPB has 98.79% rated load efficiency which reduces the overall system efficiency by 0.57%, exhibits small steady-state error, and reacts rapidly to properly regulate reactive power over inverter load variation.