Decoupling capacitor minimization in HF-link single-phase cycloconverter based microinverter

This paper presents a technique to reduce the value of the decoupling capacitor in a single-phase PV microinverter system, allowing its implementation through long-lifetime high reliability film capacitors. Single-phase system inherently requires the handling of energy variation at twice the output frequency through an energy buffer, referred to as decoupling capacitor; such buffer traditionally consists of an electrolytic type capacitor which presents limited lifetime, reducing system reliability. The presented technique makes use of the impedance reflection effect in the high-frequency link transformer through an additional ripple-power converter, an adequate commutation scheme is proposed for the switches of the additional converter to manage the energy variation; without adding extra circuitry for modulation and control of the added converter. An analysis and estimation of losses in the proposed system are presented showing that the inclusion of the ripple-port converter, with proper switching devices selection, in comparison with conventional electrolytic decoupling solution allows to extract the available input power and does not significantly affects the efficiency of the system. (C) 2014 Elsevier Ltd. All rights reserved.