Active Gate Driver for Improving Current Sharing Performance of Paralleled High-Power SiC MOSFET Modules

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.

The high switching frequency (> 20 kHz) of SiC MOSFET module makes it as an attractive alternative of Si IGBT module for high power density applications. Since SiC MOSFET and Si IGBT have the similar MOS-gated structure, it is normally regarded that the gate driver of SiC MOSFET can directly inherit from that of Si IGBT. However, considering the different device physics properties, some special design considerations need to be taken. In addition, the higher dv/dt and di/dt in SiC MOSFET module leads to more serious EMI issues, which will comprise the switching speed in return. In this work, the high-speed gate drivers for Si IGBT and SiC MOSFET modules with similar ratings are designed and optimized. Based on the experiment of switching characterization, the considerations of gate driver design to migrate from Si IGBT module to SiC MOSFET module are presented. And the EMI issue is the major challenge in the gate driver design for SiC MOSFET module.

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.

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.

Electromagnetic suspension (EMS) Maglev trains attracted to suspend above a track is a green type of track transportation. The suspension control box adopting a closed-loop feedback controller outputs a levitation current that flows into the electromagnets producing a desired magnetic force to levitate the train. Without contact frictions, such a promising type of transportation saves considerable electricity for propulsion. Minimising the volume and weight of Maglev trains attracts great research interests and continuous engineering effort as that is closely correlated with levitation power consumption and, more importantly, the construction cost. This paper mainly discusses volume and weight optimisation of suspension control box that contains a suspension chopper in EMS Maglev trains using the state-of-the-art SiC MOSFET modules. By analysing the mission profile of a typical suspension chopper, SiC MOSFET is found to be perfectly suitable for suspension chopper optimisation because of its low power losses. An optimised heatsink design of suspension chopper is given, whose volume is only 21% of the previous design. By utilising a RC snubber, the new SiC MOSFET suspension chopper prototype is built without showing serious voltage ringing. This provides a promising prospect for further optimisation of suspension control systems.

With the development of power modules for high voltage, high temperature, and high power density, their size is becoming smaller, and the packaging insulation experiences higher electrical, thermal, and mechanical stress. Packaging insulation needs to meet the requirement that internal electric field, temperature, and mechanical stress should be as low as possible. Focusing on the coupling principles and optimization design among electrical, thermal, and mechanical stresses in the power module packaging insulation, a multi-objective optimization design method based on Spice circuit, finite element field numerical calculation, and multi-objective gray wolf optimizer (MOGWO) is proposed. The packaging insulation optimal design of a 1.2 kV SiC MOSFET half-bridge power module is presented. First, the high field conductivity characteristics of the substrate ceramic and encapsulation silicone of the packaging insulation material were tested at different temperatures and external field strengths, which provided the key insulation parameters for the calculation of electric field distribution. Secondly, according to the mutual coupling principles among electric–thermal–mechanical stress, the influence of packaging structure parameters on the electric field, temperature, and mechanical stress distribution of packaging insulation was studied by finite element calculation and combined with Spice circuit analysis. Finally, the MOGWO algorithm was used to optimize the electric field, temperature, and mechanical stress in the packaging insulation. The optimal structural parameters of the power module were used to fabricate the corresponding SiC MOSFET module. The fabricated module is compared with a commercial module by the double-pulse experiment and partial discharge experiment to verify the feasibility of the proposed design method.

Threshold voltage ( V TH) shift due to bias temperature instability (BTI) is a well-known problem in SiC mosfet s that occurs due to oxide traps in the SiC/SiO2 gate interface. The reduced band offsets and increased interface/fixed oxide traps in SiC mosfet s makes this a more critical problem compared to silicon. Before qualification, power devices are subjected to gate bias stress tests after which V TH shift is monitored. However, some recovery occurs between the end of the stress and V TH characterization, thereby potentially underestimating the extent of the problem. In applications where the SiC mosfet module is turned off with a negative bias at high temperature, if the V TH shift is severe enough, there may be electrothermal failure due to current crowding since parallel devices lose synchronization during turn- on . In this paper, a novel method that uses the forward voltage of the body diode during reverse conduction of a small sensing current is introduced as a technique for monitoring V TH shift and recovery due to BTI. This non-invasive method exploits the increased body effect that is peculiar to SiC mosfet s due to the higher body diode forward voltage. With the proposed method, it is possible to non-invasively assess V TH shift dynamically during BTI characterization tests.

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.

In this paper, a high voltage SiC MOSFET module with series-parallel hybrid topology is presented and analyzed. The module consists of two uniform parts in parallel and each of the part includes three sub-parts in series. The sub-part contains three primary parts connected in string where each of these parts has a parallel of two SiC MOSFETs. These SiC MOSFETs are divided into six sub-modules, which are driven by a common driving signal. A 10kV/200A SiC MOSFETs module is fabricated based on this hybrid topology with thirty-six 1200V/40A SiC MOSFET chips. The dynamic switching behavior of the module is tested and analyzed at 5400V/200A with a switching speed of 440ns in turn-on process and 250ns in turn-off process.

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).

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.

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.

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.

The purpose of this paper is to compare and analyze the loss of propulsion inverter using SiC and Si power semiconductors for high efficiency of railway vehicles with renewable energy. Accordingly, loss comparison and analysis were carried out through PSIM Thermal Module and Loss Modeling with a SiC-MOSFET module and Si-IGBT Module. As a result, 2-level 3phase inverter using SiC-MOSFET module had extremely low switching loss compared to propulsion inverter that using Si-IGBT module. If SiCMOSFET module is used in propulsion inverter of traction motor for railway vehicles, it is considered to be advantageous for high efficiency.

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.