Series-connected Silicon Carbide Research Articles

A Voltage Equalization Strategy for Series-Connected SiC MOSFET Applications

A novel clamped voltage equalization strategy is presented for series-connected Silicon Carbide (SiC) Metal–Oxide semiconductor Field-Effect transistors (MOSFETs) in this paper. Differences in device parameters and circuit asymmetry result in the uneven voltage distribution of series-connected SiC MOSFETs, which threatens the safe operation of the circuit. Dynamic voltage equalization is difficult to achieve due to the fast switching speed of SiC MOSFETs. This paper analyzes the switching characteristics and dynamic voltage equalization characteristics of SiC MOSFETs. Based on the analysis, an energy recovery strategy based on the clamping auxiliary circuit is proposed. A 2.8 kW (50 KHz) prototype is fabricated and tested to verify the strategy. Measurement results show that the maximum voltage stress is suppressed from 600 V to less than 320 V in the experimental condition.

Variable Turn-OFF Gate Voltage Drive for Voltage Balancing of High-Speed SiC MOSFETs in Series-Connection

Active gate drive with high accurate and self-adaptive closed-loop control is a promising approach to solving the imbalanced voltage problem of series-connected silicon carbide (SiC) <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s. However, due to the inherent time propagation mismatching between Si- and SiC-based devices, behavior adjustment through Si-based ICs during the switching transient takes at least tens of nanoseconds, which limits the minimum allowable turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time of each series unit. In this article, a novel active gate drive with a variable gate voltage regulator (GVR) is proposed. It uses a single P-channel <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> to determine the connection timing of a precharged capacitor in series with the input capacitance in which way the switching transient of each device in the stack is adjustable. It is more advantageous when applied to the low-power SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> applications with relatively smaller external gate resistors. Two sampling and voltage balancing control circuits based on different processors are proposed for the GVR to adapt to different switching frequencies and costs. Its operational principle and design guidelines are specified and its performance on voltage balancing control is experimentally verified. Analytical assessment on switching losses and costs, compared with the previous work, is provided.

Active Voltage Balancing of Series Connected SiC MOSFET Submodules Using Pulsewidth Modulation

Series connection of multiple transistors is an attractive solution to achieve higher voltage capability. However, the voltage imbalance among the series-connected devices is a critical issue caused by mismatches of device characteristics and gate signals. To prevent the failure of devices from the voltage imbalance, voltage balancing control (VBC) is required. In this work, an active VBC for series-connected silicon carbide (SiC) mosfet submodules is proposed with a pulsewidth modulation (PWM) method. A submodule consists of two switches and one shunt capacitor, and the PWM method actively controls the capacitor voltages for balancing. The proposed VBC is simulated in MATLAB/Simulink and experimentally verified with six series-connected SiC mosfet submodules at up to 150 kHz. The voltage balancing is achieved within 3.9% of the targeted balanced voltage.

A High Input Voltage Auxiliary Power Supply Utilizing Automatic Balanced MOSFET Stack

In order to deal with the challenges in establishing a high input voltage high step-down auxiliary power supply (APS) for modular converters, a flyback converter utilizing series-connected silicon carbide (SiC) MOSFETs is proposed in this article. With the aid of a novel snubber circuit structure, the used series-connected SiC MOSFETs can switch with nearly perfect dynamic voltage sharing. Besides, the snubber circuit acts as voltage clamping circuit for the flyback converter, so voltage overshoot caused by transformer leakage inductance can be effectively controlled. Furthermore, the snubber circuit helps to power the control, gate driver, and startup circuits of the APS, leading to a reduction in system complexity and improvement in efficiency. Detailed circuit analysis and design considerations of the APS are presented. Finally, hardware of a 4 kV/120 W APS is established and experimentally verified.

Active Gate Drive With Gate–Drain Discharge Compensation for Voltage Balancing in Series-Connected SiC MOSFETs

Imbalanced voltage sharing during the turn-off transient is a challenge for series-connected silicon carbide (SiC) MOSFET application. This article first discusses the influence of the gate-drain discharge deviation on the voltage imbalance ratio, and its primary causes are also presented and verified by LTspice simulation. Accordingly, a novel active gate drive, which aims to compensate the discharge difference between devices connected in series, is proposed and analyzed. By only using the original output of the driving IC, the proposed gate drive is realized by implementing an auxiliary circuit on the existing commercial gate drive. Therefore, unlike other active gate drives for balancing control, no extra isolations for power/signal are needed, and the number of the devices in series is unlimited. The auxiliary circuit includes three subcircuits as a high-bandwidth current sink for regulating switching performance, a relative low-frequency but reliable sampling and control circuit for closed-loop control, and a trigger combining the former and the latter. The operational principle and the design guideline for each part are presented in detail. Experimental results validate the performance of the proposed gate drive and its voltage balancing control algorithm.

A Compact Series-Connected SiC MOSFETs Module and Its Application in High Voltage Nanosecond Pulse Generator

Nanosecond pulse discharge plasma has many prospects in industrial applications, and high-voltage repetitive nanosecond pulse generators with compact design and light weight have become one of the key issues limiting its development in some applications. This paper presents a high voltage series-connected silicon carbide (SiC) metal-oxide -semiconductor field effect transistor ( MOSFET s) module which can be served as the main switch in a repetitive high-voltage nanosecond pulse generator. This kind of series-connected MOSFET s module with only single external gate driver requiring very few components is very suitable for compact assembly. By analyzing the working principle, three topologies of series-connected MOSFET s module are proposed. The switching behaviors of the three different topologies with four SiC MOSFET s series-connected are compared experimentally. The variation of switching characteristics of series-connection SiC MOSFET s module with different numbers of devices are investigated. The layout is also optimized to shorten pulse front time and improve output pulse quality. Furthermore, a 10 kV SiC MOSFET s module with a turn- on transition time ∼10 ns is developed. The double pulse test result demonstrates excellent switching performances. Finally, a compact and high-voltage pulse generator composed of three 10 kV SiC MOSFET s module is tailored, with a typical rise time ∼40 ns and peak voltage of ∼30 kV.

An Active Voltage Balancing Control Based on Adjusting Driving Signal Time Delay for Series-Connected SiC MOSFETs

Limited by low availability, high price, and poor switching performance of high-voltage power devices, connecting low-voltage devices in series to block much higher voltages is always an option. However, severe voltage unbalance during turn-off transient remains to be solved. Most of the existing methods designed for low-speed silicon (Si) insulated gate bipolar transistor (IGBT) cannot be directly transplanted to the series-connected silicon carbide (SiC) MOSFETs with high switching speed. To maximum the switching performance of SiC MOSFETs, an elegant implementation of adjusting driving signal time delay method is proposed. In addition, a simplified model during drain–source voltage rising transient is discussed to basically reveal features and problems of the series-connected SiC MOSFETs. The factors affecting the appropriate time delay are discussed as well, especially the influence of the load current. The simplified model and the implementation are both verified by experiments. Indeed, the proposed active voltage balancing control works well and has no penalty of sacrificing switching performance of SiC MOSFETs.

Active Gate-Driver With &lt;italic&gt;dv/dt&lt;/italic&gt; Controller for Dynamic Voltage Balancing in Series-Connected SiC MOSFETs

Series connection of individual semiconductors is an effective way to achieve higher voltage switches. However, the inherent unequal dynamic voltage sharing problem needs to be solved, even when well-matched gate drivers and semiconductors are used. A majority of the existing voltage balancing schemes are developed for slow-switching silicon (Si)-based semiconductors, and are also associated with a significant amount of additional losses in the control circuit or on the switches. In this paper, a novel method is proposed for balancing the dynamic voltages among series-connected silicon carbide (SiC) MOSFETs with high dv/dt rates. The method takes advantage of a small capacitor to provide additional current to the gate of the MOSFETs at turn- off , meaning the switching speed (and thus, the device voltage after turn- off ) is controlled. The proposed method generates negligible losses in the control circuit, and also does not significantly increase the switching losses of the semiconductors. Experimental results are provided to prove the effectiveness of the proposed voltage balancing scheme on two SiC MOSFETs inside a module connected in series. In order to do so, an active gate driver is designed embedding the active dv/dt control scheme as well as other essential functionalities needed for operation of SiC MOSFETs.

A Single Gate Driver Based Solid-State Circuit Breaker Using Series Connected SiC MOSFETs

Semiconductor devices based solid-state circuit breakers (SSCBs) are promising in the dc power distribution system as protective equipment for their ultrashort action time. This letter proposes a topology of SSCB using series connected silicon carbide (SiC) metal oxide semiconductor field effect transistors (mosfet s), which only requires a single isolated gate driver. The SSCB has very low cost and high reliability because it only has 13 components including passive components and diodes apart from two SiC mosfet s to achieve both balanced voltage distribution during short-circuit interruption duration and reliable positive gate voltage during on -state. The SSCB prototype is built and experimentally verified to interrupt 75 A short-circuit current under the dc-bus voltage of 1200 V within 1.5 μs.

A Compact Gate Control and Voltage-Balancing Circuit for Series-Connected SiC MOSFETs and Its Application in a DC Breaker

This paper presents a novel compact circuit combining function of gate control and voltage balancing for series-connected silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET). Two series-connected SiC MOSFETs with the proposed circuit only require a single standard gate driver to achieve the gate control and voltage balancing during both steady-state and switching transition. Moreover, the proposed circuit is only composed of ten passive components. Therefore, the proposed circuit provides a low-cost and highly reliable method to increase the blocking voltage of the SiC MOSFET. The operation principles of the proposed circuit are theoretically analyzed. In addition, the high-blocking-voltage device is not only required in switching-mode power supply (SMPS) but also in dc-breaker applications. The proposed circuit is then modified to make it suitable to the dc-breaker applications. The simulation and experimental results validate the effectiveness and superiority of the proposed circuit in both SMPS and dc-breaker applications.