High Frequency, High Efficiency, and High Power Density GaN-Based LLC Resonant Converter: State-of-the-Art and Perspectives

Abstract

Soft switching for both primary and secondary side devices is available by using LLC converters. This resonant converter is an ideal candidate for today’s high frequency, high efficiency, and high power density applications like adapters, Uninterrupted Power Supplies (UPS), Solid State Transformers (SST), electric vehicle battery chargers, renewable energy systems, servers, and telecom systems. Using Gallium-Nitride (GaN)-based power switches in this converter merits more and more switching frequency, power density, and efficiency. Therefore, the present paper focused on GaN-based LLC resonant converters. The converter structure, operation regions, design steps, and drive system are described precisely. Then its losses are discussed, and the magnets and inductance characteristics are investigated. After that, various interleaved topologies, as a solution to improve power density and decrease current ripples, have been discussed. Also, some challenges and concerns related to GaN-based LLC converters have been reviewed. Commercially available power transistors based on various technologies, i.e., GaN HEMT, Silicon (Si) MOSFET, and Silicon Carbide (SiC) have been compared. Finally, the LLC resonant converter has been simulated by taking advantage of LTspice and GaN HEMT merits, as compared with Si MOSFETs.

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“…Since the design of the broadband rf amplifier with an output of 600 V p‑p over a frequency range of 1 MHz to 200 kHz, remarkable developments have occurred in semiconductor technology. One such advancement is the commercialization of Gallium Nitride (GaN) devices, which has enabled the design and development of circuits with enhanced voltage, power, and speed performance characteristics. , In this work, a high-field rf amplifier incorporated these state-of-the-art technologies, which could amplify signals from 130 to 700 kHz with a maximum output voltage of 900 V p‑p was upgraded. Although the bandwidth is greater than 1 MHz for higher frequencies, the slew rate reaches its limit (4000 V/μs), necessitating voltage reduction to prevent distortion caused by insufficient slew rate.…”

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“…Despite the fact that for applications requiring high-power, the switching frequencies are not as high compared to applications requiring low-power, EMI still remains notable since the amplitude of switching voltages and currents are high. On the contrary, for low-power applications, the magnitude of switching currents and voltages can be smaller than those in high-power, however, since the devices operate at a high frequency EMI's presence is significant [84]. EMI propagation paths and EMI noise source characteristics are key to compare the EMI performance of Si devices and WBG devices.…”