A Novel Active Gate Driver for Improving SiC MOSFET Switching Trajectory

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.

In this paper, a feedback active gate driver (AGD) based on a multistage technique for improving the switching trajectory of silicon carbide (SiC) MOSFET devices is presented. The main purpose of this technique is to reduce the oscillations and overshoot in high-frequency with low switching losses. Besides, the gate driver is designed considering the current load variations with simple circuit structure. An AGD validation has been developed by using simulations. The results have shown the behaviour of the AGD and feasibility. Therefore, the AGD can reduce the oscillations to avoid electromagnetic interference (EMI) and also decrease the overshoots caused by high di/dt current and dv/dt voltage slopes. In addition, the tests showed that the proposed AGD can be developed with low switching losses in high-frequency applications and medium power.

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.

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.

1200V SiC MOSFETs have superior characteristics compared to silicon (Si) IGBTs. However due to parasitic inductances in the converter layout, one to one replacement of Si IGBT with SiC MOSFET may result in higher overshoot in the device voltage and current. Active gate driving mechanism can control these unwanted stresses on the device without compromising its switching speed. The limited bandwidth of OP-AMP used in a conventional closed loop active gate driver poses a major hindrance to drive fast switching SiC MOSFET. To address this issue a new current controlled Active Gate Driver mechanism is proposed. The proposed AGD can be realized with cheaper electronic components with sufficient bandwidth to drive a SiC MOSFET. The proposed technique ensures better controllability on the device by directly controlling the injected gate current. The proposed AGD has been experimentally verified in a double pulse test set up with a 1200 V, 35 A SiC MOSFET (ROHM make: SCH2080KE).

This paper presents various issues related to a medium voltage power switch designed with series-connected transistors of the 1700 V/300 A SiC MOSFET power module. The focus of the paper are the voltage imbalance compensation methods: passive snubber circuits and active gate driving. Both methods are simulated in Saber software with the use of detailed models of the transistors and diodes of the module. At first, elements of the DRC snubber were determined and simulated during the double pulse procedure. Then, new active gate driver is proposed and verified via series of simulations. Finally, the test setup was designed with two series connected SiC MOSFETs inside CAS300M17BM2 power modules and experimental tests were performed at 1.5 kV DC to compare two compensation methods.

In this paper, the integrated fast short-circuit protection technique with soft turn-off is proposed for SiC (silicon carbide) MOSFET. Two short-circuit faults, HSF (hard switching fault) and FOF (flashover fault), can be judged by detecting EMI (electromagnetic interference) noises of SiC MOSFET. When there are short-circuit faults for SiC MOSFET, the soft turn-off is initiated to reduce EMI noises and protect SiC MOSFET. The proposed fast short-circuit protection technique is realized on the chip and is verified in a 0.18 μm BCD (Bipolar-CMOS-DMOS) process. Simulation results show that the proposed short-circuit protection has a fast response speed and then SiC MOSFET is turned off slowly when there are HSF and FOF. Therefore, the proposed fast short-circuit protection technique can be well applied for SiC MOSFETs, making SiC MOSFETs safely used in HV (high-voltage) and high current applications.

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

This article shows both theoretical and experimental analyses of a fully integrated CMOS active gate driver (AGD) developed to control the high dv/dt of GaN transistors for both 48 and 400 V applications. To mitigate negative effects in the high-frequency spectrum emission, an original technique is proposed to reduce the dv/dt with lower switching losses compared to classical solutions. The AGD technique is based on a subnanosecond delay feedback loop, which reduces the gate current only during the dv/dt sequence of the switching transients. Hence, the dv/dt and di/dt can be actively controlled separately, and the tradeoff between the dv/dt and EON switching energy is optimized. Since GaN transistors have typical voltage switching times on the order of a few nanoseconds, introducing a feedback loop from the high voltage drain to the gate terminal is quite challenging. In this article, we successfully demonstrate the active gate driving of GaN transistors for both 48 and 400 V applications, with initial open-loop voltage switching times of 3 ns, due to a full CMOS integration. Other methods for dv/dt active control are further discussed. The limits of these methods are explained based on both experimental and simulation results. The AGD showed a clear reduction in the peak dv/dt from -175 to -120 V/ns for the 400 V application.

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.

Wide bandgap (WBG) devices offer the advantages of high frequency, high efficiency, and high power density to power converters due to their excellent performance. However, their low parasitic capacitance and fast switching speed also make them more susceptible to switching oscillations. The switching oscillations can cause voltage and current overshoots, shoot-through, electromagnetic interference, additional power loss, and even device damage, which can seriously affect the performance of power converters and systems. However, a comprehensive and in-depth overview is lacking on this topic. This article reviews the types, the causes and negative effects, the effects of parasitic parameters and suppression methods of these switching oscillations, which is helpful for practical engineering. First, the switching oscillations are divided into different types, and their causes and negative effects are reviewed. Then, the effects of different parasitic parameters on the switching oscillations are overviewed. It is found that due to the different physical structures of silicon carbide metal-oxide-semiconductor field-effect transistors, enhancement-mode gallium nitride high-electron mobility transistors (eGaN HEMTs), and cascode GaN HEMTs, the effects are also different. Finally, the main methods of suppressing the switching oscillations are summarized, and the advantages and disadvantages of these methods are presented. Furthermore, future research works on this topic and the conclusion of this paper are drawn, which will help readers deepen their understanding of the switching oscillations of WBG devices, and inspire readers to better use WBG devices for high-frequency and high-efficient power conversion.

Insulated gate bipolar transistors (IGBTs) are usually connected in series to satisfy the requirements of high-power and high-voltage in power electronics applications. However, due to the parameter deviations of the series-connected IGBTs, it is difficult to ensure an equal voltage sharing between them during both transient and steady-state operations. This paper proposed a novel active gate drive (AGD) which operates basing on the active gate charge control strategy. The proposed active gate drive was able to achieve both minimized switching loss and proper voltage sharing between the series-connected IGBTs. The performance of the proposed active gate drive and active gate control method have been validated by experimental results, and promising results have been obtained.

This paper presents a performance comparison of two wide band gap (WBG) devices, a silicon carbide (SiC) MOSFET and an enhancement mode gallium nitride (eGaN) FET in a resonant inverter operating at 6.78 MHz for wireless power transfer (WPT) applications. While SiC MOSFETs provide high breakdown voltage and good thermal characteristics, eGaN FETs can reduce gate losses due to small gate resistance and input capacitance. In this work, we compare a 1200 V SiC MOSFET in a single-ended class Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> inverter to two 650 V eGaN FETs in a push-pull class Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> inverter. We designed and implemented a 6.78 MHz 2.2 kW single-ended class Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> inverter using a 1200 V customized SiC MOSFET with low-inductance package. In our experiments, the inverter has a 93% efficiency and 2.2 kW output power with input voltage of 440 V. We also implemented a push-pull class Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> inverter using two 650 V eGaN FETs at 6.78 MHz. The push-pull class Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> inverter reduces the input current ripple because of interleaving operation. At 200 V input voltage, the push-pull inverter with two eGaN FETs provides output power of 2 kW with 96% efficiency. In order to reduce a volume and weight of the inverter, we implemented a class Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> inverter with 3D printed inductors.

This paper describes a comprehensive analysis of a three-phase two-level silicon carbide (SiC) MOSFET V2G inverter including the LCL filter design. The efficiency is compared between the SiC MOSFET and Si IGBT. Using a SiC device enables the inverter to operate at high switching frequency and this leads to improved efficiency up to 99.05% at 10 kHz and 97.71% at 100 kHz switching frequency. The output LCL filter is also designed based on a specific switching frequency and the filter value is most significantly reduced at the highest switching frequency. The SiC inverter and LCL filter is simulated using LTSpice and MATLAB Simulink.