A 99.74% Efficient Capacitor-Charging Converter Using Partial Power Processing for Electrocalorics

This work combines a 99.2% efficient gallium nitride (GaN)-based low-voltage fast-switching half-bridge converter with an Si-based high-voltage slow-switching and almost lossless switched capacitor multiplexer using a partial power processing approach to a six-level prototype with 99.74% efficiency. A loss breakdown shows how the ideal partial power processing efficiency is theoretically increased to 99.84% by using four additional voltage levels but then reduced to the measured efficiency by the additional static and dynamic losses of the multiplexer. For electrocaloric heat pumps, an emerging technology for cooling and heating applications with zero global warming potential, such high charging efficiencies enable a high heat-pump system coefficient of performance (COP). Based on available data of electrocaloric lead magnesium niobate (PMN)-based samples and a first-principle and best-case analysis for Carnot-like cycles, it is predicted that the 99.74% electrical charging efficiency in combination with the electrocaloric material data enables to surpass 50% of the thermal Carnot limit (for cooling with a heat pump). Ultrahigh efficiency of power converters, thus, paves the way toward future electrocaloric heat pumps of competitive system performance.