Switching trajectory improvement of SiC MOSFET devices using a feedback gate driver

The trend in power electronic applications is to reach higher power density and higher efficiency. Currently, the wide band-gap devices such as silicon carbide MOSFET (SiC MOSFET) are of great interest because they can work at higher switching frequency with low losses. The increase of the switching speed in power devices leads to high power density systems. However, this can generate problems such as overshoots, oscillations, additional losses, and electromagnetic interference (EMI). In this paper, a novel active gate driver (AGD) for improving the SiC MOSFET switching trajectory with high performance is presented. The AGD is an open-loop control system and its principle is based on gate energy decrease with a gate resistance increment during the Miller plateau effect on gate–source voltage. The proposed AGD has been designed and validated through experimental tests for high-frequency operation. Moreover, an EMI discussion and a performance analysis were realized for the AGD. The results show that the AGD can reduce the overshoots, oscillations, and losses without compromising the EMI. In addition, the AGD can control the turn-on and turn-off transitions separately, and it is suitable for working with asymmetrical supplies required by SiC MOSFETs.

Silicon carbide (SiC) MOSFET features low switching loss and it is advantageous in high switching frequency application, but the manufacture per Ampere cost is approximately five times higher than the silicon (Si) IGBT. Therefore, by paralleling Si IGBT and SiC MOSFET together, a trade-off between cost and loss is achieved. In this paper, a four control freedoms active gate driver (AGD) including turn-on delay, turn-off delay, and two independent gate voltages, is proposed to optimize the performance of the paralleled device. By adjusting these four control freedoms, optimal operation for paralleled device can be obtained. Moreover, the proposed AGD can dynamically adjust the current ratio between two paralleled devices, which can help achieve thermal balance between two devices and improve system reliability. Double pulse test (DPT) experimental results are presented and analyzed to validate the effectiveness of the proposed AGD for paralleled Si IGBT and SiC MOSFET application.

The trend in the development of power converters is focused on efficient systems with high power density, reliability and low cost. The challenges to cover the new power converters requirements are mainly concentered on the use of new switching-device technologies such as silicon carbide MOSFETs (SiC). SiC MOSFETs have better characteristics than their silicon counterparts; they have low conduction resistance, can work at higher switching speeds and can operate at higher temperature and voltage levels. Despite the advantages of SiC transistors, operating at high switching frequencies, with these devices, reveal new challenges. The fast switching speeds of SiC MOSFETs can cause over-voltages and over-currents that lead to electromagnetic interference (EMI) problems. For this reason, gate drivers (GD) development is a fundamental stage in SiC MOSFETs circuitry design. The reduction of the problems at high switching frequencies, thus increasing their performance, will allow to take advantage of these devices and achieve more efficient and high power density systems. This Thesis consists of a study, design and development of active gate drivers (AGDs) aimed to improve the switching performance of SiC MOSFETs applied to high-frequency power converters. Every developed stage regarding the GDs is validated through tests and experimental studies. In addition, the developed GDs are applied to converters for wireless charging systems of electric vehicle batteries. The results show the effectiveness of the proposed GDs and their viability in power converters based on SiC MOSFET devices. La tendencia en el diseño y desarrollo de convertidores de potencia está enfocada en realizar sistemas eficientes con alta densidad de potencia, fiabilidad y bajo costo. Los retos para cubrir esta tendencia están centrados principalmente en el uso de nuevas tecnologías de dispositivos de conmutación tales como, MOSFETs de carburo de silicio (SiC). Los MOSFETs de SiC presentan mejores características que sus homólogos de silicio; tienen baja resistencia de conducción, pueden trabajar a mayores velocidades de conmutación y pueden operar a mayores niveles de temperatura y tensión. A pesar de las ventajas de los transistores de SiC, existen problemas que se manifiestan cuando estos dispositivos operan a altas frecuencias de conmutación. Las rápidas velocidades de conmutación de los MOSFETs de SiC pueden provocar sobre-voltajes y sobre-corrientes que conllevan a problemas de interferencia electromagnética (EMI). Por tal motivo, el desarrollo de controladores de puertas es una etapa fundamental en los MOSFETs de SiC para eliminar los problemas a altas frecuencias de conmutación y aumentar su rendimiento. En consecuencia, aprovechar las ventajas de estos dispositivos y lograr sistemas más eficientes y con alta densidad de potencia. En esta tesis, se realiza un estudio, diseño y desarrollo de controladores activos de puerta para mejorar el rendimiento de conmutación de los MOSFETs de SiC aplicados a convertidores de potencia de alta frecuencia. Los controladores son validados a través de pruebas y estudios experimentales. Además, los controladores de puerta desarrollados son aplicados en convertidores para sistemas de carga inalámbrica de baterías de vehículos eléctricos. Los resultados muestran la importancia de los controladores de compuerta propuestos y su viabilidad en convertidores de potencia basados en carburo de silicio.

Silicon carbide (SiC) devices have the benefit of low energy losses and high operation temperature. The fast switching speed of SiC may result in serious electromagnetic interference (EMI) noise, overshoot voltage, and even false triggering. To address these issues, an intelligent cascaded multi-level active gate driver (AGD) topology is proposed to control the switching trajectory of the power device dynamically. It can flexibly adjust the switching speed by either speeding up or slowing down. Its slow turn-off mode has the advantage of short turn-off delay compared with a two-stage turn-off. The circuit has the benefits of simple-realization and cost-effectiveness. Also, a switching behavior trajectory-based model predictive control (MPC) strategy is introduced for this gate driver circuitry. The MPC strategy balances the switching energy losses, EMI noise, and switching process duration. The experimental results reveal that the proposed intelligent AGD can provide desirable performance for controlling the slew rate of the semiconductor device

The series connection of silicon carbide (SiC) MOSFETs and the cascaded system allows operating at a higher voltage than the rated voltage of devices. However, the unbalancing voltage problem occurs in the series-connected devices. The main reason for the unbalancing voltage problem is the parasitic capacitance of the device's gate to the ground. There are several methods for balancing the series-connected device voltage. The snubber circuits, active clamp circuits and the active gate driver. In this paper, the active gate driver method is proposed to control the unbalanced device voltage. Also, the device voltage sensing circuit and the feedback controller are designed in detail. Finally, the proposed active gate driver is verified with the simulation.

Featuring higher switching speed and lower losses, the silicon carbide MOSFETs (SiC MOSFETs) are widely used in higher power density and higher efficiency power electronic applications as a new solution. Due to the limited current capability of a single module, more modules parallel-connected are necessary for higher power application. However, current sharing is the key obstacle. In this article, an active gate driver (AGD) for high-power SiC MOSFETs is presented to balance the currents of parallel-connected SiC MOSFET modules. The principle of the AGD is based on dynamic gate drive voltage adjustment to synchronize current edges and current slopes among parallel-connected SiC MOSFET modules automatically. Each AGD measures and controls the current of its SiC MOSFET module individually. No extra supervising control circuit is needed. In addition, the hardware and software configurations are independent of the system design and no restrictions on the number of SiC MOSFET modules connected in parallel exist. Finally, the switching performance of the AGD was experimentally verified on two parallel-connected SiC MOSFET modules in a multipulse test under constant and variable load currents. In addition, the effectiveness of AGD under different control topologies has been studied with simulation and verified using three parallel-connected SiC MOSFET modules.

Silicon Carbide (SiC) MOSFET devices exhibiting several advantages, including high blocking voltage, lower conduction losses, and lower switching losses, when compared to silicon-based devices have become commercially available, enabling their adoption into power supply products. This paper presents a novel approach to designing a cycloconverter using SiC MOSFETs as opposed to the conventional usage of IGBT. A comparative study is attempted between the two with respect to distortion and system efficiency. MATLAB/Simulink models and simulations are used to analyze the results for the above.

This paper investigates an active gate driver (AGD) for an SiC-MOSFET. The source current feedback type active gate driver utilizes the reactive voltage of the source wire inductance as a negative feedback signal to regulate the source current di/dt. Recently, the improvement of the switching performance of the AGD is limited due to the feedback system bandwidth. In this paper, a high bandwidth current feedback type power operational amplifier is applied as the gate drive circuit. Switching characteristics of the conventional resistive gate driver and the active gate driver are experimentally investigated by a double pulse test setup. The switching setup condition is 700 V / 80 A. This paper describes the construction of the AGD circuit and the experimental results. The over-shoot and ringing of the Vds and Is are reduced by using the active gate driver. In addition, the switching loss is simultaneously reduced.

This paper investigates an active gate driver for a large capacity multi-chip SiC-MOSFET power module. The active gate driver utilizes the reactive voltage of the source wire inductance as the negative feedback signal of the gate voltage. In addition, the feedback stabilization design is included in the circuit. The switching characteristics of the conventional resistive gate driver and the active gate driver are experimentally investigated by a double pulse test setup. The switching setup condition is 800 V / 300 A. This paper describes the construction of the active gate driver circuit and the experimental results. The over-shoot and ringing of the Vds and Is are reduced by using the active gate driver. In addition, the switching loss is simultaneously reduced.

The Silicon Carbide (SiC) MOSFET is considered to be the leading candidate for future 1.7 kV and 3.3 kV switches in 2-level voltage source converters (VSC) up to 2 MW. For those converters, short circuit (SC) in the dc-link loop can occur due to a number of reasons, e.g. faulty semiconductor modules, faulty gate drivers (GDs), or electro-magnetic interference (EMI). Termination of such SCs is important in order to protect components and reduce the damage in the converter box. This paper presents a new short circuit protection scheme based on a universal current-source GD principle without dedicated hardware components. The performance of the design is evaluated for SC in the dc-link loop under load conditions, called type II and type III. Moreover, measurement results are presented using the proposed GD connected to a 1700 V 300 A SiC MOSFET tested during SC type II and III at two different dc-link stray inductances, 30 nH and 100 nH, and at two different temperatures, 25 °C and 125 °C. The conclusions are that the proposed scheme is able to terminate both SC type II and III with fast reaction time, with low energy dissipation, with a margin of about 15 times below the destructive level for dc-link voltages and load currents up to 1050 V and 300 A respectively.

With the development of silicon carbide devices, the use of low-voltage Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) in series has become an option in medium/high voltage applications, but it introduces voltage imbalance problem and SiC MOSFETs suffer the great voltage peak stresses as well as the extremely high dv/dts. This brings great challenges to the insulation design of the gate driver circuit. In this study, based on the strategy of adjusting the driving signal time delay, an active gate driver is designed, it can not only reduce the design of sampling isolation through the ‘floating ground’ but also reduce the requirement for the coupling capacitance of the isolated power supply. Finally, the proposed active gate driver circuit is verified through experiments.

The short-circuit capability of Silicon Carbide (SiC) MOSFETs is much worse than the Si IGBT counterparts. There are two kinds of commercially available SiC MOSFET devices (trench MOSFETs and planar MOSFETs), and their short-circuit capability is not exactly the same. At present, there is a lack of comparative study on the short-circuit capability of these two kinds of devices. To solve this problem, this paper carries out a comparative study of the short-circuit capability of the two devices. Experiment results show that in the case of short circuit tests, it takes more time for planar MOSFETs to reach their peak currents because of their lower channel mobility and higher trap density. The DC voltage has little impact on the peak current which is mainly affected by the gate voltage. At the low DC voltage, such as 400V, 500V and 600V, planar MOSFETs have better short-circuit indexes no matter the short circuit withstand time (SCWT) or the short-circuit energy. However, at 800V DC voltage, trench MOSFETs have a better performance in short-circuit tests. Considering the factor of different areas, the short-circuit energy density of trench MOSFETs is higher than that of planar devices, especially under the condition of 800V high DC voltage.

The acceptance of Wide band Gap devices is partially dependent on the ease of retrofitting existing designs of power converter. Standard power modules are inherently ill-suited to the fast switching behavior of Silicon Carbide power transistors. Active gate drivers can manage the switching dynamics of power devices by means of feedback and control on the gate. This paper proposes a low cost yet effective di/dt-based active gate driver using a sensor made on a printed circuit board (PCB) and an analog feedback loop.

The traditional heatsink design technologies for forced air-cooling and power semiconductors with low junction temperatures have constrained the converters to be designed with massive heatsinks. The low power losses of WBG device technology and higher junction temperature operation over a wide operating range of power have not been fully utilized with liquid-cooled systems. The other major limitation has also been the traditional power module packaging “stack” approach with baseplate. This paper presents a novel power stage design which involves 1.7 kV silicon carbide (SiC) MOSFETs, a heatsink design with Genetic Algorithm (GA) and built using 3D printing technology, and a novel integrated modular power module for high power density. The air-cooled module assembly has a SiC MOSFET phase leg module with split high-side and low-side switches and a gate driver with cross-talk and short circuit protection functions. The heatsink design was modeled using a co-simulation environment with finite element analysis software and GA in MATLAB and COMSOL. The proposed concepts were verified and validated through experiments at each stage of development. The power stage was evaluated at 800V, 900 V, and 1kV for 20 kHz switching frequency and 50-kW load. The experimental results show that the CEC efficiency is 98.4 %. In addition to the efficiency, a power density of 75 W/in 3 was also achieved.

Silicon carbide (SiC) MOSFETs feature salient characteristics such as higher breakdown voltage, lower losses and higher switching speed when compared to Silicon (Si) MOSFETs. However, due to the high switching speed and parasitic parameters, the SiC MOSFET turn-on and turn-off dynamics lead to overvoltage, overcurrent and electromagnetic interference (EMI) issues. This paper proposes a SiC MOSFET switching speed control concept based on a gate driver that features dynamically changeable gate resistance allowing microcontroller-based adjustment of the SiC MOSFET switching speed. This function therefore enables a closed-loop SiC MOSFET switching speed control, which is suited to device safety and EMI control. The configuration and operation of the proposed concept are presented. Both simulation and experimental results are provided to verify the proposed circuit.