For power converters with inductive loads, a freewheeling path is needed for the current due to reactive power. The MOSFET synchronous rectification (SR) is widely used to reduce the conduction loss during the freewheeling period. Due to the wide band gap of silicon carbide (SiC), the intrinsic body diode of SiC MOSFET exhibits a high voltage drop. Hence, an antiparallel SiC Schottky diode is normally implemented to eliminate its conduction. However, the external SiC Schottky diode is not fully utilized as it only works during the dead time. In this paper, the hard-switching SR is investigated in an SiC three-phase inverter and compared with a conventional inverter using freewheeling diode (FWD). An improved power loss model for the two inverters has been developed. It is found that the inverter using SR has higher efficiency due to the smaller switching loss. A 7-kW prototype of SiC three-phase inverter is built, which achieves a peak efficiency of 98.8% (±0.15%) and 98.5% (±0.15%) at 40 kHz using SR and FWD, respectively. This paper confirms that the SiC MOSFET is an ideal candidate for the SR.

As the most popular wide bandgap (WBG) power device, the silicon carbide (SiC) MOSFET has been widely adopted in the power electronics applications, and brings in the benefits including reduced switching losses, enhanced switching frequency, and improved power density. However, the switching oscillation and the electromagnetic interference (EMI) become more serious due to the rapid switching speed of SiC MOSFET. Thus, adding RC snubber branch is considered as an effective method to suppress such unwanted oscillation in the early works. In this paper, the switching transient of SiC MOSFET with RC snubber is investigated with an analytical model based on finite state machine (FSM). The accuracy of proposed analytical model can be verified by comparisons between calculated and measured waveforms during the switching transition. In addition, the impacts of the RC snubber on switching oscillation, switching loss and high-frequency (HF) EMI noise have been comprehensively investigated based on the model, which shows that the added RC snubber can effectively avoid the switching oscillation, and reduce the level of HF EMI without increasing switching loss.

In this article, we have carried out a comprehensive study on the wireless power transfer (WPT) concept from the rectifier circuit construction and state-of-art GaN Schottky barrier diode (SBD) device technology to the WPT system demonstration. Benefited from the wide bandgap, high mobility, and saturation velocity of the gallium nitride (GaN) two-dimensional electron gas, engineered lateral GaN SBD with low turn- on voltage ( V _on ) of 0.47 V, on -resistance ( R _on ) of 4 Ω, breakdown voltage of 170 V, and junction capacitance $(C_{j})$ of 0.32 pF at 0 V bias are achieved, which satisfy the fundamental requirements for microwave power rectification. After incorporating the high-performance GaN SBD into the optimized rectifier circuit, high radio frequency (RF)/dc conversion efficiency of 79% is achieved, and the input power of per single GaN SBD is increased by 10X when compared with that of a commercially available silicon (Si) SBD at the same efficiency of 50% and frequency of 2.45 GHz. Based on the rectifier circuit, a microwave power transfer system is constructed with 400 light emitting diodes lighted up, verifying the great promise of adopting high-power GaN SBD for the wireless high-power transfer as an alternative energy-harvesting technique for future WPT application.

A gallium nitride (GaN)-based resonant step-up converter is proposed for the application in the satellite electric propulsion (EP) system. This converter consists of a full-bridge inverter, a resonant tank, and a multistage Cockcroft–Walton voltage multiplier to provide a high voltage gain. Additionally, the air-core transformer is introduced due to the megahertz switching frequency allowed by the GaN device. Thus, the limited magnetizing inductance of transformer and the remarkable junction capacitance of diode have to be carefully considered in the resonant tank design, especially after considering that this converter normally operates at the light load in the EP system. In this work, the fourth-order $ LCLC$ resonant converter is investigated. The recommended parameter selection for the fourth-order resonant tank is also provided. A 1.2-MHz, 23-V/2.5-kV, and 6-W prototype is demonstrated. It achieves a low harmonics distortion and a low power loss with the zero voltage switching.

The trend to move toward the solid-state and repetitive pulsed power supply requires the high-voltage, high-current, and high-speed semiconductor devices, which makes an insulated gate bipolar transistor (IGBT) preferred for this application. However, as a bipolar device, the IGBT is limited by the switching speed and switching loss. In this paper, the potential of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) for the pulsed power application is investigated. The surge current capabilities of 1.2-kV, 30-A commercial Si IGBT and SiC MOSFET are characterized and compared by the capacitor discharge experiment. In addition, the effects of various circuit parameters, including gate resistance, dc-link voltage, and dc-link capacitance, on the capacitor discharge process are investigated. It is found that the pulse current of SiC MOSFET is around two times of Si IGBT, which achieves good agreement with the datasheet. Using $di/dt$ to represent the discharging speed, the SiC MOSFET is 10 times faster than the Si IGBT. It is because the SiC MOSFET shows a lower ON-resistance in the saturation region resulted from the short-channel effect. This paper confirms the high-speed and high-current advantages of SiC MOSFET in the pulsed power application.

The conventional Z-Source inverter (ZSI) has the following disadvantages: unidirectional power flow, high start-up inrush current, presence of undesirable mode operation, and low boost factor. To solve aforementioned shortcomings, an enhanced-boost bi-directional Quasi-ZSI (QZSI) with novel active switched inductor (SL) cells (named as Active-SLs QZSI) is proposed. The proposed active SL cell replaces three diodes in the conventional SL cell of the QZSI with two capacitors and one active switch, thus allowing bi-directional power flow and achieving higher boost factor. Besides, the Z-Source Network (ZSN) diode is also replaced by an active switch. Compared with existing ZSIs, the proposed Active-SLs QZSI has less current stress of ZSN, higher efficiency and higher boost factor. A modified Space Vector Modulation (MSVM) is introduced to reduce the switching frequency of active switches of ZSN. Both simulation and experimental results validate theoretical analysis of the proposed Active-SLs QZSI.