A GaN-based DC-DC Converter with Zero Voltage Switching and Hysteretic Current Control for 99% Efficient Bidirectional Charging of Electrocaloric Capacitive Loads
A switched-mode power converter for highly efficient charging and discharging of electrocaloric capacitors is presented. A GaN-based half-bridge is controlled by analog hysteretic current control with zero-voltage switching and adjustable dead-time, implemented on a programmable system-on-chip. Optimization of control parameters results in up to 99.3% efficiency in continuously alternating charging and discharging cycles. Arbitrary voltage waveform generation is demonstrated, while maintaining a high efficiency. Electrocaloric PMN-2PT ceramic samples are driven by the converter, and from the measured reversible temperature change and total power loss, the relative heat pump coefficient of performance is estimated for Carnot-like refrigeration cycles. An offset voltage is used to avoid the high permittivity at low bias of the ceramic material, which improves the performance. While electrocaloric heat-pump system prototypes were previously limited by around 80% charging efficiency of resonant-type circuits, this work’s approach with 20-fold reduced losses contributes to significantly increase the performance of electrocaloric heat pumps, an emerging solution with zero global warming potential for a future sustainable energy system.