Zero-voltage Switching Transitions Research Articles

Analysis of ZVS Realization with Consideration of Secondary Parasitic Capacitance for High Frequency GaN-based LLC Resonant Converter under DCM Mode

LLC resonant converter can achieve zero voltage switching (ZVS) for primary side devices and zero current switching (ZCS) for secondary side rectifiers while operating in discontinuous conduction mode (DCM). However, the parasitic capacitance significantly affects the ZVS realization of primary side switches for high frequency GaN-based LLC converter. In order to reveal the influence, this paper analyses ZVS transition process with consideration of secondary parasitic capacitance in a high frequency GaN-based LLC resonant converter under DCM mode. Then, an accurate model during ZVS transition is derived. To verify the analysis and the derived model, a 250V rating input and 270V/6.6A rating output GaN-based LLC converter prototype operating at 500 kHz is built. The experimental results are consistent with the theoretical analysis.

Complete ZVS Analysis in Dual Active Bridge

Zero-voltage-switching (ZVS) has been widely applied in widebandgap devices based on high-switching-frequency converters, for instance, dual-active-bridge isolated dc-dc converter, which consists of two H-bridges. To secure ZVS for all eight switches, previous literature mostly focuses on half-bridge to analyze switching transitions, which, however, is rather incomplete due to ignoring the impact of modulation strategies and cannot fulfill all circumstances. In this letter, the whole H-bridge is used as a unit to analyze the ZVS transient process, addressing the ZVS setting in different modulation strategies. The minimal initial inductor energy to complete the ZVS process is also quantified, which in return can reduce the transformer current, thereby enhancing the efficiency. Furthermore, the accurate ZVS transition time is derived incorporating with the nonlinearity of switch output capacitance, which can be further used to set the dead-band time. An H-bridge prototype with SiC devices is built up to verify the theory proposed in this letter.

Modeling of ZVS Transitions for Efficiency Optimization of the Phase-Shifted Full-Bridge Topology

The emergence of wide bandgap semiconductors paved the way for integration of high-efficiency, high-power-density converters into industrial applications. Key to achieving these performance goals is operation at high switching frequencies, which requires mitigation of switching losses by schemes, such as zero-voltage switching (ZVS). The phase-shifted full-bridge (PSFB) converter is a very appealing converter for such industrial applications. However, the mechanisms that underlie the operation of ZVS within this topology are complex, as they depend on the coupled influence of multiple system parameters. This article aims to provide a detailed analytical treatment of the ZVS mechanisms within this topology, along with a detailed study of the interdependence of the associated critical system parameters. A prototype 10-kW, SiC-based PSFB converter is employed to aid this discourse and provide empirical validations. The outcome of these studies is leveraged to identify a set of practical guidelines for tuning the ZVS mechanisms. These guidelines also consider the impact of practical nonidealities, which are often neglected in the literature. Overall, the theoretical formulations, parametric trade studies, and practical implementation suggestions presented in this article constitute a set of tools that designers can utilize to obtain the full performance entitlement of this topology in practice.

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

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/dm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\mathrm {oss}}$ </tex-math></inline-formula> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which opens a possibility to obtain a design with extremely high power density

A 1-MHz Zero-Voltage-Switching Asymmetrical Half-Bridge DC/DC Converter: Analysis and Design

The asymmetrical half-bridge (AHB) topology discussed in this paper is one of the complementary driven pulse-width modulated converter topologies, which presents an inherent zero-voltage switching (ZVS) capability. In the previous work, the ideal operation of the converter and the ZVS realization process have been analyzed. However, the influence of the circuit parasitics on the output voltage drop and the design constraints of the circuit parameters to ensure the ZVS operation have not been investigated. The minimum load needed to ensure the ZVS operation is also not readily available. This paper presents a detailed and practical design for a 1-MHz AHB converter. A revised voltage transfer ratio of the converter is derived considering the influence of circuit parasitics and the ZVS transition. Two circuit parameters responsible for maintaining the ZVS operation are the transformer leakage inductance and the interlock delay time between the gate signals of two switches. A design method of the two parameters is proposed, which can ensure the ZVS transition. The possible ZVS range of the load variation is also investigated. A 50-W AHB converter with 1-MHz switching frequency was constructed, and a maximum efficiency of 91% was achieved.