Minimum Energy and Capacitance Requirements for Single-Phase Inverters and Rectifiers Using a Ripple Port

Converters with a dc port and a single-phase ac port must store energy to buffer the inherent double-frequency power flow at the ac port. The minimum energy storage required to isolate the power ripple from the dc port is presented, and leads to the minimum capacitance required for converters that use capacitive energy storage. This paper presents a ripple power port to manage energy storage and decouple capacitor ripple from power ripple. A ripple power port allows the designer to make a choice of capacitor voltage independent of other system voltages. A combination of an ac link converter and a ripple power port leads to a dramatic increase in reliability: it is shown that converters with nominal ratings up to 200 W can be designed with expected mean-time-between-failure ratings on the order of 1.4 × 10⁶ h-sufficient for hundred-year operation in long-life applications such as photovoltaic converters and LED lamps. This large increase in life is achieved with minimal extra cost.