Current controlled active gate driver for 1200V SiC MOSFET

1200 V SiC mosfet is a suitable replacement for Si insulated gate bipolar transistors due to its improved switching behavior. However, high $di/dt$ and $dv/dt$ of SiC mosfet cause very high voltage overshoot and oscillations due to the presence of parasitic inductance in the converter layout and parasitic capacitance of the load. These undesired switching responses increase switching loss and give rise to electromagnetic interference related issues. Therefore, it is important to minimize these adverse effects in order to extract maximum benefits from SiC mosfet . This paper proposes an active gate driving technique for SiC mosfet to improve its overall switching performance in the presence of a moderately higher amount of parasitic inductance in the converter layout. It is achieved by controlling the device $di/dt$ and $dv/dt$ independently in four stages, with appropriate values of gate resistances for both turn- on and turn- off switching transient. The developed active gate driver is tested in a double-pulse test bed and a two-level voltage source inverter driving an induction motor load.

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 breakdown voltage, good thermal properties, and (in case of GaN) a higher field effect mobility compared to Si make the expected performance of GaN and SiC based power devices to be potentially vastly superior to that of the today leading power device technology - Si Insulated Gate Bipolar Power Transistors (Si IGBTs). After many year of development, commercial SiC power diodes and MOSFETs now outperform recent Si IGBTs and are poised to compete in the renewable energy and electrical vehicle markets. The recent generation of the hybrid SiC-Si IGBT modules combine the best features of both competing technologies.. These device hybrid modules handle powers up to 350 kW range at voltages well over 1 kV and have several times higher switching speed than the recent generations of Si IGBTs. SiC power technology is more mature than GaN power technology. However, the GaN enhancement mode High Electron Mobility Transistor (E-HEMT) on Si technology reached power ratings over 10 kW operating at 200 kHz with lower switching losses than Si MOSFETs and SiC MOSFETs. GaN devices already take about 20% of the RF power market with expectations of reaching 40% by 2025. Still, the existing device designs are not fully taking advantages of the superior materials properties of GaN. The lateral-vertical designs for a higher breakdown voltage; quantum well channel designs limiting high electron injection into the buffer layers; a low conducting passivation making the electric field distribution in the gate-to-drain spacing more uniform and therefore increasing the breakdown voltage, improving reliability, and increasing lifetime; perforated channel designs for decreasing the effect of the parasitic resistances and increasing the switching speeds are the innovative design features poised to improve the competitive edge of SiC and GaN technologies. For ultimate performance, the Si substrate in the GaN on Si technology should be replaced by SiC or even diamond, even though in a short run it would be hard for such technologies to be cost competitive. In a more distant feature, even diamond by itself might emerge as superior high power material. In a more near future, AlInN/AlN/GaN on Si technology could become a leading technology for high power applications.

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.

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.

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 switching strategy is proposed for the extended phase shift (EPS) controlled dual active bridge (DAB) converter which using the hybrid switch (HyS) configured by paralleling SiC MOSFET and Si IGBT, considering the special soft switching characteristic of DAB. For most of the existing literature, the common switching strategy of HyS is to switch on the SiC MOSFET before Si IGBT and switch off the SiC MOSFET after Si IGBT. However, if only using this switching strategy, the SiC MOSFET may be damaged by long-time operating at the over rated current condition. The proposed switching strategy for the HyS is that the SiC MOSFET is only conducted for a short while during the process of switching Si IGBT on or off. The proposed switching strategy can shorten the conduction time of SiC MOSFET, decrease the losses of HyS and extend the safe operation area of HyS. Simulation results on a 30 kW HyS DAB converter verify the availability of the proposed switching strategy.

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.

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.

Flyback converters with synchronous rectifiers are an important topic in power electronics, given their widespread use in various applications and the focus on efficiency improvement. However, flyback converters suffer from a high overvoltage across the synchronous rectifier on their secondary side. This overshoot voltage is a result of resonance between the flyback transformer stray inductance and the output capacitance of the rectifier. This paper presents an in-depth experimental study on the optimization of dead time and Active Gate Driving in flyback converters employing synchronous rectifiers, i.e. Silicon Carbide Power MOSFETs in place of the secondary rectifier driven synchronously with the primary switch. The focus is the influence of symmetrical dead time variation between the primary and secondary switches on switching losses and overshoot voltage. In addition, the influence of a three voltage level active gate driver on the overshoot voltage and switching losses is examined, finding no significant influence. The findings from this study contribute to the existing body of knowledge by providing a nuanced understanding of dead time optimization in flyback converters with synchronous rectifiers, as well as the utilization of Active Gate Drivers in such systems. The results have implications for the design and operation of these converters, potentially leading to more efficient and reliable systems.

6.5 kV silicon IGBTs are used in multi-megawatt medium voltage power converters for rail traction applications, AC drives and grid-connected power converters. The 6.5 kV, 30 A SiC MOSFETs, recently launched by Wolfspeed, have the potential to replace Si IGBTs. Static and dynamic characteristics of the 6.5 kV SiC MOSFETs have been reported earlier. During the extreme transient conditions, the SiC MOSFETs can be subjected to high voltage overshoot and high short circuit current. In this work, ruggedness of these MOSFETs is established by short-circuit tests and single shot avalanche tests at room temperature. The 6.5 kV SiC MOSFET is observed to withstand 7.75 J of short-circuit energy at 20 V gate voltage with a stress withstanding time of 6 μs. The single shot avalanche test result shows an avalanche energy of 5.0 J. The increase in junction temperature of the SiC MOSFET at the avalanche failure is estimated from the experimental results.

SiC MOSFET being fast switching, high voltage blocking, high junction temperature withstanding, and low loss device, has the edge over Si IGBT. Therefore, SiC MOSFET's applications are in high power density matrix converter, battery charger in electric vehicles, and many other. The matrix converter utilises four-quadrant switches, which allow both positive and negative current and block both positive and negative voltage. Since SiC MOSFETs being much better than Si IGBTs, the four-quadrant switches are realised using them. The conducting and blocking devices for the four-quadrant switch vary with the change in quadrant of operation, and the switching involves the turn ON and turn OFF of two devices. Therefore, the characteristics and power loss are bound to vary with the quadrant of operation. Very limited work is available on SiC based four-quadrant switches in the literature. Hence, a thorough investigation of the four-quadrant switch as a single entity along with power loss analysis is done in this paper. Further, this paper presents approximate conduction and switching power loss analysis of the four-quadrant switch. The research is performed by developing approximate mathematical equations for power loss and then testing the SiC MOSFET based four-quadrant switch in all four quadrants.

For a trade-off between turn-off and on-state of power switches in medium and high power applications, it is crucial to consider the switching speed restrictions due to turn-off peak voltage. By varying the p-emitter efficiency and the front side plasma level of an IGBT, an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{\text{off}}-V_{\text{ce},\text{sat}}$</tex> trade-off curve for a fixed turn-off peak voltage can be obtained. It is shown that a turn-off behavior similar to that of a SiC MOSFET can be achieved with an IGBT with low carrier confinement, but with the drawback of a higher on-state voltage drop. At low current operations, the losses dissipated by the SiC MOSET are lower, not only in the on-state, but also during turn-off. The charge carrier plasma in the IGBT reduces both <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{d}v/\mathrm{d}t$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{d}i/\mathrm{d}t$</tex> for lower current densities. Switching curves at the rim of the RBSOA and beyond show that there is no dynamic avalanche in the SiC MOSFET. However, a quasi-static clamping mode can be observed for both types of devices.

SiC MOSFET has gradually obtain more attention in the field of power converter, due to its good performance of high blocking voltage and fast switching speed. However, fast switching transient process makes it more sensitive to parasitic parameters than the silicon counterparts, leading to the more electrical stress. In serious cases, device failure or damage may directly occur. In addition, switching oscillation interacting between the circuit stray inductance and parasitic capacitance will result in more switching losses and undesirable electromagnetic interference noise. In the paper, simple and effective simulating models taken account of all key parameter are established for the analysis of the oscillation frequency and voltage overshoot in turn-off process of SiC MOSFET. Simulation and experiments both show that turn-off oscillation frequency is determined by SiC MOSFET output parasitic capacitance and power loop parasitic inductance. Moreover, turn-off maximum peak voltage will shift regularly with various switching speed.

The work presented in this paper investigates the switching behavior of the power semiconductors at a hybrid Si/SiC ANPC circuit, where the Si IGBTs switch at line frequency while the SiC MOSFETs switch at PWM frequency. In particular, this work quantifies the impact of the forward recovery voltage (FRV) originated in the bipolar devices, i.e., IGBTs and freewheeling diodes, during the transition from non- to full-conduction. Such transition being originated by the on/off commutation of the SiC devices. The obtained experimental results also show the impact of various operational and environmental factors on the FRV magnitude and evolution. The evaluation done indicates that FRV effects must be taken into account both in terms of power loss dissipation and voltage overshoots when using hybrid Si/SiC ANPC topology.