Ruirui Chen

10 kV silicon carbide (SiC) MOSFETs have been receiving increasing research attention in medium voltage (MV) applications. Compared with silicon (Si) IGBT counterparts, 10 kV SiC MOSFETs exhibit shorter short-circuit withstand time (SCWT), which requires fast and reliable short-circuit protection (SCP) circuits. The di/dt-based SCP circuit is a promising solution because of its fast response and simple implementation without additional current sensors. However, a major limitation of the di/dt-based method is its inability to detect the dc component of the current, resulting in prolonged detection time during a fault-under-load (FUL) event. This paper proposes a novel di/dt-based SCP circuit with decoupled SCP thresholds for hard-switching-fault (HSF) and FUL of 10 kV SiC MOSFETs. The proposed circuit differentiates HSF and FUL states by monitoring the gate voltage and automatically adjusts the SCP threshold voltage for FUL, thereby accelerating short-circuit (SC) detection for FUL events. In addition, a simple constant-current soft-turn-off (STO) circuit is proposed to minimize the SC turn-off overvoltage. Experimental results with a 10 kV SiC MOSFET module verified the effectiveness of the proposed circuits.

This letter proposes an indirect power detection based short-circuit protection (SCP) method for gallium nitride high-electron-mobility transistors (GaN HEMTs). The proposed method requires sensing only v_ds of a GaN HEMT, similar to the widely used desaturation protection method. However, unlike desaturation protection, the proposed method directly monitors v_ds after a predefined delay without a diode, enabling faster short circuit detection and improved noise immunity. Experimental results show that the short-circuit detection time is significantly shorter than that of the desaturation protection. In addition, the proposed method is evaluated over a wide temperature range, from room temperature to cryogenic temperatures, verifying its effectiveness for GaN HEMTs in cryogenic applications.

High-power transient voltage suppression (TVS) diodes serve as the primary energy-absorbing elements in solid-state circuit breakers (SSCBs), providing rapid clamping of over voltages that threaten main interrupting devices. This paper presents a coaxial packaging solution for stacked TVS diodes, which achieves a dramatic reduction in commutation loop inductance from 95 nH to 3.8 nH, resulting in an approximately 96% reduction. Experimental validation, which demonstrates a substantial decrease in turn-off overvoltage from 950 V to 300 V, shows an approximate 68% reduction. A derived modular design is further proposed to achieve higher voltage ratings, enabling scalable deployment across different SSCB applications. The package performance is evaluated through finite element analysis (FEA) of inductance and electric field distribution and experimentally confirmed in a 1.7 kV/100 A SSCB. Results verify that the proposed coaxial package effectively mitigates loop inductance and overvoltage, enhancing both reliability and operational safety of high-power SSCBs.

Emerging 10 kV silicon carbide (SiC) MOSFET based medium voltage (MV) converters have attracted increasing research interest due to their significantly improved performance compared with silicon (Si) IGBT based converters. The success of such MV converter design requires an accurate model of 10 kV SiC MOSFETs, which is proposed in this paper. The impact of high voltage on the transconductance and the dynamic gate charge characteristics of the 10 kV SiC MOSFET is first characterized. Based on these results, an improved switching model considering high voltage impact is proposed and experimentally verified. The developed model is then applied to aid the design of a 5-level MV flying capacitor converter (FCC). A low-cost decoupling capacitor solution for FCC switching cell is proposed. Challenges posed by high switching speed are examined using the developed model, with a gate resistances selection strategy proposed. Finally, a prototype of the 10 kV SiC device based MV 5L-FCC phase-leg is developed. Its reliable operation under high voltage (e.g., 23 kV) and very fast switching speed (e.g., >100 V/ns) are demonstrated.

Enabled by the fast switching capability of emerging 10 kV SiC mosfets, medium voltage (MV) power converters can achieve significantly reduced power loss. However, high dv/dt of 10 kV SiC mosfets also poses challenges for MV converter design. This letter proposes a simple method to reduce turn-on switching loss of 10 kV SiC mosfet without increasing dv/dt. The proposed circuit employs a widely used desat short-circuit protection circuit to determine the dv/dt stage of the turn-on switching transient and adjust the gate resistance to accelerate current rise period, while maintaining voltage fall period unchanged. The proposed circuit can achieve switching loss reduction under various dc voltages and load currents similar to a closed-loop active gate driver, but the circuit required is quite simple. Experimental results with a 10 kV SiC mosfet are demonstrated to verify the effectiveness of the proposed circuit.

A four-wire modular multilevel converter (MMC) with the split dc-link capacitor topology is a promising solution for a power conditioning system (PCS) of an asynchronous microgrid (ASMG). In an ASMG, the PCS is applied to connect two distribution-level systems with a transformerless structure, which has numerous challenges in the design and control of the MMC. However, in the existing literature, MMCs have been mainly applied in transmission systems with isolation transformers or serve as static compensators in distribution systems. The design and control methods of MMCs for these applications cannot be directly applied to an ASMG. Therefore, in this article, considering the impacts of the unbalanced load, transformerless structure, and different operation modes on the MMC-based PCS, the corresponding control and hardware design are conducted. The proposed MMC-based PCS solution can limit the microgrid (MG) voltage unbalance caused by the load unbalance, eliminate the harmonic zero-sequence current impacts on the main grid, and compensate for the unbalanced load current of local sources in the M. Moreover, a medium voltage testing setup is developed to verify the analysis and demonstrate the proposed control algorithms on a 10 kV SiC mosfet-based MMC at 13.8 kV ac voltage.

Solid-state circuit breaker (SSCB) with high efficiency and high gravimetric power density is required for electrified aircraft propulsion (EAP). A cryogenically cooled gallium nitride (GaN) device-based SSCB module is developed for the EAP system to achieve a higher power density than existing SSCBs. The SSCB module is suitable for medium voltage direct current (MVdc) applications and is designed with low-weight modular cold plates. Each module is rated for 750 V, 100 A, and can interrupt a fault current of 1 kA at cryogenic temperature. The SSCB module structure design, thermal interface design, modular cold plate design, and insulation design are discussed. The developed SSCB module prototype achieves a power density of 329 kW/kg and an efficiency of 99.93%. Experimental results of interrupting a fault of 1 kA and insulation test of the SSCB module are provided to validate its operation.