Ultraefficient Voltage Doubler Based on a GaN Resonant Switched-Capacitor Converter

Resumen

In this paper, we present a highly efficient and compact voltage doubler based on a resonant switched-capacitor converter implemented with GaN FETs. Two possible approaches for its implementation are analyzed and compared. In the first approach, the resonant inductor is placed in series with a resonant capacitor, conducting a sinusoidal current, while in the second, it is placed in series with the input source, conducting rectified sinusoidal current. Both resonant converters have the same voltage gain, and although the change in the position of the resonant inductor is, at the first glance, of minor importance, the analysis and results show that it has huge impact on the capability to achieve zero-voltage switching (ZVS) transitions at low output power. The experimental results clearly show that at low loads when the resonant inductor is in series with the resonant capacitor, the switching frequency can be significantly higher than the resonant frequency and that it is, practically, impossible to achieve ZVS transitions, forcing the implementation of cycle skipping. The prototype implemented for the experiments can provide up to 4.5-kW losing between 20 and 22 W. In the case of light load (500 W), the power losses were only 2-3 W. Its power density is higher than 65 kW/dm3. The same resonant converter was tested with Si CoolMOS devices as well and the impact of the semiconductor technology on the overall power losses was verified. Due to higher Coss capacitance, the Si-based converter has 40% higher power losses at full power than its GaN-based counterpart. The components of the GaN-based converter occupy only 65 cm3, which opens a possibility to obtain a design with extremely high power density.