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

Abstract

In this paper, we present a highly efficient and compact voltage doubler based on a resonant S'\\itched-capacitor converter implemented with GaN FF.Ts. Two possible approad1es for its implementation are analy:red 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 Roth 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 dearly show that at low loads when the resonant inductor is in series with the resonant capacitor, the S'\\itching 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 tight load (500 W), the power losses were only 2-3 W. Its power density ls higher than 6S kW/dm 3 . The same resonant converter was tested '\\ith Si CoolMOS devices as well and the impact of the semiconductor tedmology 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 cm 3 , which opens a possibility to obtain a design '\\ith extremely high power density. Index Ten11s-Resonant converters, switched capacitors, zero voltage S'\\itching (ZVS ).

Analysis and Design of a Charge-Pump-Based Resonant AC–DC Converter With Inherent PFC Capability

“…Thus, the results go in accordance with the analysis in section IV and the calculated values in section V-B. and verified with simulation results, where the peak current amplitude and the inductance specifications are obtained from (27) and (34) respectively. When handling high-frequency AC currents, a key factor to the inductor design is choosing the right core material.…”

“…The figures show that high power factor and low THD are achieved with different input voltages, as the charge pump circuit works in the same manner. Yet, to achieve the full-load operation for the low line voltage, the resonant tank needs to be redesigned for the high current that will result from (27), while the current prototype was designed for the 230 V rms mains input as given in the design specifications in Table I. Even though the inherently achieved power factor and THD figures fall within the reported ranges, it is noted that the proposed solution has lower efficiency compared to several reported ones.…”

“…First, the resonant tank needs to be designed for the worst-case conditions, with respect to the input rms voltage and output power. More specifically, the resonant tank inductor needs to be designed to handle the worst-case current, which comes with the minimum input rms voltage and maximum output power, as can be seen from (27). Second, in order to satisfy the first condition for obtaining high power factor, given in section III-A, which entitles the class-DE stage to operate near resonance with a near-unity gain, the output voltage will change across the range of the input rms voltage.…”

“…The DC capacitor is then designed for the specified low-frequency ripple according to (29). Eventually, the class-DE stage design takes place according to the procedure given in section IV-C, using (30)(31)(32)(33)(34)(35)(36)(37)(38), where the resonant tank current stress is calculated from (27).…”

“…It is worth mentioning that a higher Q L value would not affect the power factor, as it guarantees a more sinusoidal resonant tank current with lower harmonic content. However, it can complicate the magnetic devices design, see (34), which is a challenge for this topology with the high current stress in the inductor, as shown by (27), and can result in low efficiency. On the other hand, a lower value for Q L can result in mismatch between the proposed design flow and the realized values, as the current in the tank is no longer sinusoidal, and an accurate model taking into account the high-order harmonics in the resonant tank and the pump circuit is then needed, which complicates the design.…”