- Energy storage requirements for converters with a dc port and a single-phase grid-connected port are evaluated, based on the unavoidable double-frequency power requirement. The minimum energy storage requirement is linked to a minimum capacitance requirement for converters that use capacitance energy storage. It is shown how to employ a ripple power port to manage energy storage and decouple capacitor ripple from power ripple. A ripple power port allows a designer to make a choice of capacitor voltage independent of system voltages. This in turn allows film capacitors of modest size to be used for energy storage in these applications. A combination of ac link converter and 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 million hours-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. 2009 IEEE.