Due to their fast switching capabilities, silicon carbide (SiC) MOSFETs are increasingly used in high-voltage pulsed-power circuits where fast and flexible high-voltage pulses are required (e.g. for plasma-processing applications), such as in our solid-state Impedance-matched Marx generator. The turn-on time of SiC MOSFETs mainly depends on the gate-driving technique and its implementation. Therefore, many studies focus on SiC MOSFET gate-driving methods. In this article, a gate-boosting driving method that was previously proposed for IGBTs is optimized for SiC MOSFETs and applied to a very fast MOSFET to reduce turn-on time as much as possible. A prototype of the optimized gate-boosting driver was built and tested to assess its performance. The test results validate the effectiveness of the optimized gate-driving method and showed that a MOSFET turn-on time of below 2 ns is achievable at a high operating voltage and moderate current and below 3 ns for a wider range of load-current and operating-voltage conditions. Furthermore, current rise rates of 38.7 kA/ $\mu \text{s}$ at 356-A load current are possible. All these results are considerably faster than ever demonstrated before.

Ultrafast Switching of SiC MOSFETs for High-Voltage Pulsed-Power Circuits

Water treatment is one of the most important issues for all walks of life around the world. Different from the conventional water treatment technology, the advanced power electronic pulse technology has unique features and advantages for the modern water treatment. Unfortunately, there is no literature reported to describe them in a comprehensive and systematic way. To fill this gap, an overview of modern power electronic pulse generators (PPGs) for water treatment is presented. This article, for the first time, classifies the different types of PPGs from the viewpoint of pulse formation. Each of them is discussed, and the advantages and disadvantages are compared and summarized. Aside from that, this article presents the development and trend of the pulse generators suitable for the specified water treatment processes such as electrolysis, sterilization, and discharge degradation. Finally, a list of more than 100 relevant technical papers is also appended for a quick reference.

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Power Electronic Pulse Generators for Water Treatment Application: A Review

The performance of an all solid-state linear transformer driver (LTD) is evaluated based on experimentally verified behavior of a single stage. The single-stage LTD utilizes a low-profile design with robust thyristor switches and high-energy-density mica capacitors to minimize overall system inductance. Subnanosecond jitter is achieved with simultaneous thyristor triggering. The stage is magnetically coupled to a secondary winding through a central nanocrystalline core. A dc current source, decoupled with a large inductance, actively resets the core between pulses. The overall result is a low-impedance ( $ per stage) pulse generator that rivals the performance of traditional Marx systems with the improved reliability, increased lifetime, and fast rep-rate capabilities of solid-state switches. The stage is tested with charging voltages up to 8 kV into various loads and compared with simulations based on an analog behavioral thyristor switch model previously developed at Texas Tech University. The simulation is expanded into a full-scale, multistage LTD simulation and compared with a previously constructed Marx generator.

Performance Analysis of an All Solid-State Linear Transformer Driver

A solid-state repetition linear transformer driver (LTD) for a high-power microwave (HPM) driver is constructed, comprising a total of 50 stage-series structures, with each stage possessing eight parallel bricks. This article describes the primary and secondary circuit differences between a driving source and a modern LTD, as well as analyzing the influence of load impedance on system efficiency in a simplified circuit of the LTD using a Laplace transform. This article also examines the optimum load impedance for a given magnetic core and primary circuit. The current load impedance of one stage is $2~\Omega $ , and the corresponding system efficiency is 95%. A real-time control and triggering system are developed. A trigger transformer with a 100-channel pulse output is designed. The output voltage of the constructed driving source is about 500 kV, the current is 5 kA, the pulsewidth is about 125 ns, and the output power is 2.5 GW. The driving source can work at a repetition rate of 50 Hz. The driving source will drive a low magnetic field relativistic backward-wave oscillator to generate HPMs.

Development of a 500-kV All Solid-State Linear Transformer Driver

Solid-state semiconductor switches are emerging as an attractive choice for the fast switching of compact, repetitive, and pulsed power systems. In particular, the high voltage and fast switching capabilities of SiC MOSFETs are well suited for many applications when appropriately gated. For instance, the turn-on and turn-off characteristics of such devices are strongly dependent on the gate driving circuitry. Traditional commercial gate drivers, typically utilizing push–pull or totem-pole driving topologies, are often not well suited for fast, high current switching with rise times on the order of 10–20 ns, as the driving performance is highly dependent on the combined RLC characteristics of the driving circuitry and the switching device. The proposed gate drive topology utilizes a current-carrying inductor to rapidly charge theMOSFET gate–source capacitance. A high-voltage inductive kick generates the necessary potential to drive the inductor current into the gate through the parasitic gate impedance. As the energy stored in the drive inductor is continuously variable, it can be adjusted such that the gate voltage settles to a lower value, typically 20 V, after the initial kick to prevent excessive gate–source overvoltage. With an inductive drive current of ~23 A, a peak $\text{d}I/\text{d}t$ of 25 kA $\mu \text{s}^{-1}$ was achieved for the tested bare SiC MOSFET die. Additionally, a peak $\text{d}I/\text{d}t$ of 13 kA $\mu \text{s}^{-1}$ was achieved with the TO-247 packaged device.

Fast SiC Switching Limits for Pulsed Power Applications

An innovative gating scheme for wide bandgap semiconductor switches is investigated to fully exploit recent advances of SiC MOSFET properties in hold-off voltage (from single digits to tens of kV) and low on-state resistance (tens of mΩ). Robust gate driving techniques are required to achieve fast risetimes on the order of 10–20 ns. Further, due to the high dI/dt, and subsequent inductive kickback, parasitic inductance may drastically affect the performance of commercially available totem-pole gate drivers. Further, traditionally packaged MOSFETs exhibit additional degradation of switching characteristics due to the introduction of parasitics primarily due to their lead geometry.

Improving Fast SiC MOSFET Switching Using an Inductive Gate Drive Approach

The Marx pulse generator topology has been widely used in pulsed power applications1,2. Another pulse generator topology, the linear transformer driver (LTD), has been developed3 that may serve as a viable alternative to the Marx generator. LTDs utilize inductively added stages to achieve high voltages and currents. Unlike a Marx generator, each stage in an LTD features multiple bricks, all of which are ground referenced and allow current to be distributed amongst an arbitrary number of switches. This allows for LTDs that utilize solid-state switches, potentially resulting in more compact and reliable pulse generators. A solid-state, >10 kA peak current, multiple-stage LTD is developed. The generator's performance will be analyzed for viability as a replacement for driving a high power microwave generator.

Solid state linear transformer driver (LTD) development for HPM sources

The diffusion of transient magnetic fields through the walls of a hollow conductive shell is an important phenomenon of interest throughout a variety of pulsed power applications. Basic solutions do exist for cylindrical geometries in the limiting case that the skin depth is much larger than the wall thickness; however, in many pulsed applications, the transient skin depth is often similar to the conductor thickness. As the underlying thin-wall assumption begins to breakdown, the production of complex eddy current distributions in the conductor walls results in deviation from these simplified analytical solutions of the diffused field. Precise calculation of these current distributions is essential for many applications including inductive shielding and magnetic field diagnostics near conductors. Electromagnetic simulations using the finite-element method provide a more accurate picture of the diffusion process in this regime. A high magnetic field testbed facilitates measurement of the diffused fields in order to verify simulation accuracy. The effect of material conductivity, wall thickness, and conductor geometry on the diffusion process is examined.

Landon Collier

Papers

Performance Analysis of an All Solid-State Linear Transformer Driver

Fast SiC Switching Limits for Pulsed Power Applications

Improving Fast SiC MOSFET Switching Using an Inductive Gate Drive Approach

Solid state linear transformer driver (LTD) development for HPM sources

Magnetic Field Diffusion in Medium-Walled Conductors