Silicon-carbide (SiC) transistors with growing readiness for the power converter market have raised an emerging need for high-performance gate driver (GD) units to maximize their remarkable characteristics. In particular, the GD units for the SiC devices that experience extremely fast commutations at the medium-voltage level require powerful driving capability, effective short-circuit (SC) protection, and superb common-mode transient immunity. Thereby, this article presents a systematic enhanced GD (eGD) solution that incorporates three scalable features compatible with almost all the SiC mosfet modules. First, a BJT-based multicell current booster is proposed to attain balanced high driving current, low losses, gate-loop inductance less than 1 nH, and great cross-talk immunity. Second, a nonintrusive Rogowski switch-current sensor with high bandwidth and fair accuracy is developed, capable of detecting SC fault in 86 ns and softly turning off 5 kA SC current in 1  $\mu$ s. Third, two noise-free isolation architectures are proposed to mitigate common-mode noise-admittance by more than 100 dB. Fundamentals, analytical designs, experimental validations, and scalability discussions of the three techniques are elaborated, respectively. Finally, a 6-kV, 84-A, and 102-V/ns continuous pump-back test is demonstrated, for the first time, to verify the eGD's excellent performance.

High-Scalability Enhanced Gate Drivers for SiC MOSFET Modules With Transient Immunity Beyond 100 V/ns

This article presents the cryogenically cooled application for wide bandgap (WBG) semiconductor devices. Characteristics of silicon carbide (SiC) and gallium nitride (GaN) at cryogenic temperatures are illustrated. SiC MOSFETs exhibit increased on-state resistance and slower switching speed at cryogenic temperatures. However, cryogenic cooling provides low ambient temperature environment and thus enables the SiC converter to operate at lower junction temperature to achieve higher efficiency compared to room temperature cooling. A cryogenically cooled MW-level SiC inverter prototype is developed and demonstrated the feasibility of operating high-power SiC converter with cryogenic cooling. GaN HEMTs exhibit more than five times on-state resistance reduction and faster switching speed at cryogenic temperatures which makes GaN HEMTs an excellent candidate for cryogenic power electronics applications. The significantly reduced on-state resistance of GaN devices provides the possibility to operate them at a current level much higher than rated current at cryogenic temperatures. A GaN double pulse test (DPT) circuit is constructed and demonstrated that GaN HEMTs can operate at nearly four times of rated current at cryogenic temperatures. Challenges of utilizing WBG device with cryogenic cooling are discussed and summarized.

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SiC and GaN Devices With Cryogenic Cooling

A unique three-step short-circuit protection method is proposed for the 650-V enhancement mode (E-mode) gallium nitride high-electron mobility transistor (GaN HEMT). This method can quickly detect the short-circuit event, reduce gate voltage to enhance the device short-circuit capability, and turn off the device under fault after confirmation. Experimental results prove that with this method, the short-circuit fault detection time for E-mode GaN HEMT is shortened from 2  μ s to several tens of nanoseconds, and the device can be successfully protected from fatal failure under high dc bus voltage without mistriggering.

A Reliable Ultrafast Short-Circuit Protection Method for E-Mode GaN HEMT

The efficiency and power density improvement of power switching converters play a crucial role in energy conversion. In the field of motor control, this requires an increase in the converter switching frequency together with a reduction in the switching legs’ dead time. This target turns out to be complex when using pure silicon switch technologies. Gallium Nitride (GaN) devices have appeared in the switching device arena in recent years and feature much more favorable static and dynamic characteristics compared to pure silicon devices. In the field of motion control, there is a growing use of GaN devices, especially in low voltage applications. This paper provides guidelines for designers on the optimal use of GaN FETs in motor control applications, identifying the advantages and discussing the main issues. In this work, primarily an experimental evaluation of GaN FETs in a low voltage electrical drive is carried out. The experimental investigation is obtained through two different experimental boards to highlight the switching legs’ behavior in several operative conditions and different implementations. In this evaluative approach, the main GaN FETs’ technological aspects and issues are recalled and consequently linked to motion control requirements. The device’s fast switching transients combined with reduced direct resistance contribute to decreased power losses. Thus, in GaN FETs, a high switching frequency with a strong decrease in dead time is achievable. The reduced dead time impact on power loss management and improvement of output waveforms quality is analyzed and discussed in this paper. Furthermore, input filter capacitor design matters correlated with increasing switching frequency are pointed out. Finally, the voltage transients slope effect (dv/dt) is considered and correlated with low voltage motor drives requirements.

Low-Voltage GaN FETs in Motor Control Application; Issues and Advantages: A Review

Short-circuit capability is essential for the adoption of GaN power devices in motor drives for industrial and automotive applications. In this work, we report an innovative solution for GaN power switches to achieve short-circuit withstanding time (SCWT) equal to or greater than 3 micro-seconds with limited increase in on-resistance. We discuss the technology, referred to as Short-Circuit Current Limiter (SCCL) and show the experimental results including static and dynamic Ron, 400-V short-circuit, inductive switching, off-state leakage and 1000-hour high-temperature reverse-bias stress. Thanks to extended SCWT, the SCCL technology allows the industry to adopt conventional short-circuit protection schemes, with sufficient immunity to noise and switching transients.

Short-Circuit Capability Demonstrated for GaN Power Switches

The Enhancement-mode (E-mode) Gallium Nitride High-Electron Mobility Transistor (GaN HEMT) has proven excellent electrical performance in various applications. Meantime, multiple comprehensive studies on the short circuit behavior show that GaN HEMTs has much shorter short circuit withstand time compared to conventional silicon (Si) devices. In this paper, the GaN HEMT short circuit capability is first introduced. Based on the testing results, the voltage dip on the phase-leg dc voltage under short circuit condition is proposed to be the short circuit detection signal, and the corresponding detection circuit and ultra-fast short circuit protection method is depicted. Finally, experimental results prove that with the proposed protection method, soft turn-off can be initiated within 200 ns and the short circuit current can be terminated in 281 ns.

An Ultra-Fast Short Circuit Protection Solution for E-mode GaN HEMTs

The Enhancement-mode (E-mode) Gallium Nitride High-Electron Mobility Transistor (GaN HEMT) has several hundred nanosecond level short circuit withstand time, much shorter than that of the silicon (Si) devices. Reliable ultra-fast protection solutions for the GaN HEMTs are in great demand. In this paper, a three-step GaN HEMT short circuit protection solution is proposed, including ultra-fast detection, active gate clamping and de-saturation circuit confirmation. First, the GaN HEMT short circuit capability under various gate voltages has been explained. Based on the safe protection boundary, the three- step protection solution is proposed. Experimental results prove that with the proposed protection method, the short circuit fault can be detected within 36 ns, and the short circuit energy is reduced with the ultra-fast detection and gate voltage clamping. Eventually, the GaN HEMT can be successfully protected from fatal failure up-to 400 V dc bus.

A Reliable Ultra-Fast Three Step Short Circuit Protection Method for E-mode GaN HEMTs

This paper presents a new short-circuit protection method developed for Gallium Nitride (GaN) gate injection transistors (GITs). The proposed protection method is based on ultra-fast detection of the voltage dip on the phase leg of the converter, active current clamping of the gate drive, and fault confirmation with a low pass filter based de-saturation fault detection. Thus, it achieves an ultra-fast reaction and reliable protection for GaN GIT devices. The proposed protection method was experimentally validated with a 600 V rated commercial GaN GIT under single and repetitive short- circuit operations at 400 V. The total short-circuit fault response time was recorded within 224 ns, and the short-circuit energy is reduced with the ultra-fast detection and the active gate current clamping.

A Reliable Short-Circuit Protection Method with Ultra-Fast Detection for GaN based Gate Injection Transistors

This paper proposes a high temperature design of an integrated three phase inverter using direct drive GaN HEMT devices and metal clad PCBs (MCPCB). The inverter features a modular design approach, utilizing a 600 V direct drive GaN device with integrated overcurrent and overtemperature protection. Aluminum based PCBs with high thermal conductivity are also used to achieve a natural cooling solution with only air convection at an ambient temperature of up to 95°C Thermal . simulations are performed to verify the thermal performance of the system. The inverter was built and experimentally tested in a thermal chamber to verify the drive performance at high temperatures. The design achieves a continues power of 1.8 kW. Peak efficiencies of 99.8% and 99.45% are achieved at room temperature and 95°C respectively

Ke Wang

Papers

A Reliable Ultrafast Short-Circuit Protection Method for E-Mode GaN HEMT

An Ultra-Fast Short Circuit Protection Solution for E-mode GaN HEMTs

A Reliable Ultra-Fast Three Step Short Circuit Protection Method for E-mode GaN HEMTs

A Reliable Short-Circuit Protection Method with Ultra-Fast Detection for GaN based Gate Injection Transistors

High Temperature Design of a GaN Based Modular Integrated Drive with Natural Cooling Using Metal Clad PCBs