I und J

This paper presents a 15kV silicon carbide (SiC) MOSFET gate drive, which features high common-mode (CM) noise immunity, small size, light weight, and robust yet flexible protection functions. To enhance the gate-drive power reliability, a power over fiberbased isolated power supply is designed to replace the traditional design based on isolation transformer. It delivers the gate-drive power by laser light via optical fiber over a long distance (>1 m), so a high isolation voltage (>20 kV) is achieved, and the circuit size and weight are reduced. More importantly, it eliminates the parasitic CM capacitance coupling the power stage and control stage, and thus eradicates the control signal distortion caused by high dv/dt in switching transients of the high-voltage SiC devices. In addition, the gate-drive circuit design integrates comprehensive protection functions, including the overcurrent protection, undervoltage/overvoltage lockout, active miller clamping, soft turn off, and fault report. The overcurrent protection responds within 400 ns. The experimental results from a 15kV double-pulse tester are presented to validate the design.

A Gate Drive With Power Over Fiber-Based Isolated Power Supply and Comprehensive Protection Functions for 15-kV SiC MOSFET

This paper proposes a new method for the investigation of the short-circuit safe operation area (SCSOA) of state-of-the-art SiC MOSFET power modules rated at 1.2 kV based on the variations in SiC MOSFET electrical parameters (e.g., short-circuit current and gate–source voltage). According to the experimental results, two different failure mechanisms have been identified, both reducing the short-circuit capability of SiC power modules with respect to discrete SiC devices. Based on such failure mechanisms, two short-circuit safety criteria have been formulated: 1) the short-circuit-current-based criterion; and 2) the gate-voltage-based criterion. The applicability of these two criteria makes possible the SCSOA evaluation of SiC MOSFETs with some safety margins in order to avoid unnecessary failures during their SCSOA characterization. SiC MOSFET power modules from two different manufacturers are experimentally tested in order to demonstrate the procedure of the method. The obtained results can be used to have a better insight of the SCSOA of SiC MOSFETs and their physical limits.

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A Short-Circuit Safe Operation Area Identification Criterion for SiC MOSFET Power Modules

In this paper, the short-circuit (SC) performance of two different SiC MOSFETs is experimentally investigated for different input voltages, biasing voltages and case temperatures. The measurement results are compared to simulations, and a good agreement is achieved. For fault handling, two different overcurrent protection (OCP) circuits are designed and applied to the SiC MOSFETs. The desaturation method is successfully tested with a hardware solution substituting the blanking time delay. The second method is based on sensing the voltage drop across the parasitic inductance at the source pin. The experimental and simulation results show that both OCP methods have the capability to detect a short circuit condition in the SiC MOSFET within safe SC time avoiding device failure.

Short-circuit evaluation and overcurrent protection for SiC power MOSFETs

This paper presents the characterization of the temperature-dependent short-circuit performance of a Gen3 10 kV/20 A silicon carbide (SiC) mosfet . The test platform consisting of a phase-leg configuration and a fast speed 10-kV solid state circuit breaker, with temperature control, is introduced in detail. A novel FPGA-based short-circuit protection circuit having a response time of 1.5  μ s is proposed and integrated into the gate driver. The short-circuit protection is validated through the platform. The short-circuit characteristics for both the hard switching fault and fault under load (FUL) types at various dc-link voltages (from 500 V to 6 kV) are tested and discussed. The saturation current increases with dc-link voltage and achieves 360 A at 6 kV. Different from low voltage SiC devices, there is no current spike in FUL type of fault. The temperature-dependent short-circuit performance is also presented from 25 to 125 °C. The difference of short-circuit waveforms at various initial junction temperatures can be neglected. A thermal model of the 10-kV SiC mosfet is built for the junction temperature estimation during the short circuit and for analysis of the initial junction temperature impact on the short-circuit performance.

Short-Circuit Characterization and Protection of 10-kV SiC mosfet

A short-circuit e.g. in a half-bridge converter is a severe and potentially destructive operation condition for a power transistor and needs to be turned-off quickly and safely. In order to define strategies how to improve the reliability of a power device, it is necessary to understand the failure dynamics during a short-circuit. In this paper, an experimental study focussing on the short-circuit capability of different types of 600V power transistors based on Si, SiC and GaN is presented. Usually, a 10μ8 short-circuit withstand time at 400V is required for 600V power transistors. Measurement results show that the investigated Si and SiC MOSFETs can withstand short-circuit times up to 13μs at 400V and 150°C, while the normally-off and cascode GaN devices demonstrate considerably less withstand capability.

Robustness in short-circuit mode: Benchmarking of 600V GaN HEMTs with power Si and SiC MOSFETs

In this work, the static and dynamic characteristics of a new double-trench SiC MOSFET are experimentally investigated and compared to two different available commercial SiC MOSFETs. The SiC devices are applied in a ZVZCS Phase-Shifted Full-Bridge converter which uses the parasitic leakage inductance of the transformer to achieve soft switching. A practical method to break down the converter losses based on separating the measured semiconductor and magnetic losses is proposed and compared to an analytical loss model. The experimental results show several advantages of using SiC MOSFETs as well as ZVZCS in the converter. The main results can be summarized as elimination of the freewheeling circulating current mode, clamping the overshoot voltage across the rectifier diodes and achieving soft switching in a wide power load range without additional auxiliary circuits or resonant inductor. Experimental results for a 10kW, (100–250) kHz prototype show an efficiency of up to 98,1% for the whole converter.

Efficiency analysis of a high frequency PS-ZVS isolated unidirectional full-bridge DC-DC converter based on SiC MOSFETs

The reverse recovery characteristics of the body diodes of planar and double-trench SiC MOSFETs are experimentally analyzed in switching tests and compared. The body diode of the trench SiC MOSFET shows improved performance, so that using an anti-parallel SBD to suppress the reverse recovery behavior becomes unnecessary. Following the switching tests, the devices are operated in continuous mode in a 10kW / 100–250 kHz buck converter. The measured efficiency of the whole converter is up to 98.9% in synchronous rectification mode. Parallel operation of the considered planar MOSFETs is needed in the converter. Therefore, the impact of parameter mismatch on the static and dynamic current sharing of the transistors is evaluated, showing that paralleling of SiC MOSFETs is feasible. The performance of the parallel connection is temperature dependend. Based on the measured and analytically calculated losses, the junction temperature is estimated to ensure the safe operation area of the parallel SiC devices in continuous operation mode.

Operation of planar and trench SiC MOSFETs in a 10kW DC/DC-converter analyzing the impact of the body diode

In this paper, current silicon carbide (SiC) MOSFETs from two different manufacturers are evaluated including static and dynamic characteristics for different gate resistances, different load currents and at various temperatures. These power semiconductors are operated continuously at a high switching frequency of 1MHz comparing a hard- and a soft-switching converter. A calorimetric power loss measurement method is realized in order to achieve a good measurement accuracy, and the results are compared to the electrical measurements.

Abdullah Eial Awwad

Papers

Short-circuit evaluation and overcurrent protection for SiC power MOSFETs

Robustness in short-circuit mode: Benchmarking of 600V GaN HEMTs with power Si and SiC MOSFETs

Efficiency analysis of a high frequency PS-ZVS isolated unidirectional full-bridge DC-DC converter based on SiC MOSFETs

Operation of planar and trench SiC MOSFETs in a 10kW DC/DC-converter analyzing the impact of the body diode

Investigation of 1.2 kV SiC MOSFETs for hard- and soft-switching converters