Ultra high voltage (UHV, >15 kV) 4H-silicon carbide (SiC) power devices have the potential to significantly improve the system performance, reliability, and cost of energy conversion systems by providing reduced part count, simplified circuit topology, and reduced switching losses. In this paper, we compare the two MOS based UHV 4H-SiC power switching devices; 15 kV 4H-SiC MOSFETs and 15 kV 4H-SiC n-IGBTs. The 15 kV 4H-SiC MOSFET shows a specific on-resistance of 204 m Omega cm(2) at 25 degrees C, which increased to 570 m Omega cm(2) at 150 degrees C. The 15 kV 4H-SiC MOSFET provides low, temperature-independent, switching losses which makes the device more attractive for applications that require higher switching frequencies. The 15 kV 4H-SiC n-IGBT shows a significantly lower forward voltage drop (V-F), along with reasonable switching performance, which make it a very attractive device for high voltage applications with lower switching frequency requirements. An electrothermal analysis showed that the 15 kV 4H-SiC n-IGBT outperforms the 15 kV 4H-SiC MOSFET for applications with switching frequencies of less than 5 kHz. It was also shown that the use of a carrier storage layer (CSL) can significantly improve the conduction performance of the 15 kV 4H-SiC n-IGBTs.

A SiC avalanche breakdown diode (ABD) having a nominal 1-kV breakdown voltage was fabricated to provide improved suppression of voltage transients induced during hard-switched turn-off of solid-state devices. Three SiC ABDs were pulsed 1000 times in an inductive load circuit at peak currents of over 100 A. Superior performance in peak pulse current, clamping voltage, and peak pulse power was seen, compared to the results of two series-connected commercial TVS devices, collectively having a comparable breakdown voltage. The transient thermal response of the SiC ABDs was calculated using a model for energy dissipation in short pulses. SiC ABD design parameters and test data were used to show that the reported performance of these devices was not related to package thermal impedance.

In this work, we report our recently developed 27 kV, 20 A 4H-SiC n-IGBTs. Blocking voltages exceeding 24 kV were achieved by utilizing thick (210 μm and 230 μm), lightly doped N-drift layers with an appropriate edge termination. Prior to the device fabrication, an ambipolar carrier lifetime of greater than 10 μs was measured on both drift regions by the microwave photoconductivity decay (μPCD) technique. The SiC n-IGBTs exhibit an on-state voltage of 11.8 V at a forward current of 20 A and a gate bias of 20 V at 25 °C. The devices have a chip size of 0.81 cm 2 and an active conducting area of 0.28 cm 2 . Double-pulse switching measurements carried out at up to 16 kV and 20 A demonstrate the robust operation of the device under hard-switched conditions; coupled thermal analysis indicates that the devices can operate at a forward current of up to 10 A in a hard-switched environment at a frequency of more than 3 kHz and a bus voltage of 14 kV.

This paper describes the design and implementation of a prototype 30-kW (or 30-kJ/s) pulsed-power supply for capacitor charging. The system operates at 200-kHz maximum switching frequency, which is considerably higher than the conventional practice at this power level, leading to smaller passive components. A high power density of 143 W/in(3) is achieved with the converter operating at a high ambient temperature of 65 degrees C with 90 degrees C cooling oil, by utilizing various technologies on topology, control, devices, passives, and thermal management. The experimental results demonstrate that the converter meets the performance requirements while achieving a high power density.

The presence of multiple thermally resistive layers in power electronics packages diminishes the enhanced convective benefit of high-performance microchannel cold plates. One improvement reported here is the development of stereolithographically defined aluminum nitride (AlN) microchannel integrated coldplates as substrates for power electronics packages. High-resolution fabrication of green ceramic parts using a standard stereolithography machine has been enabled by the development of photosensitive ceramic materials. Complex microchannel integrated AlN substrates with simplified fluid connections have been produced with 2-3 mm channel height and channel width down to 200 mum. This structure bypasses the majority of the traditional thermal stack, bringing the coolant closer to the heat source. The substrates were packaged and tested with 4 mm Silicon Carbide pin diodes as heat sources at pressure drops from < 1 kPa up to 70 kPa (10 psi) and power levels exceeding 80 W (500 W/cm2). Measured total thermal stack resistivity on best performing devices was about 0.1 K-cm2/W at 70 kPa (-10 psi) and 0.14 K-cm2/W at 5 kPa (-0.7 psi). Paths for further performance improvement, broadening of fabrication possibilities, and transition to real-world systems are briefly discussed.

A high-density transformer using nanocrystalline core is developed for a 30 kW, 200 kHz resonant converter. Loss models are established for nanocrystalline cores through experimental characterization. The important parasitic models are also developed considering litz wire effects. Following a minimum size design procedure, several transformers with both nanocrystalline and ferrite cores are designed and prototyped. While all transformers meet the converter performance requirement during testing, using nanocrystalline core can achieve a significantly higher power density even at 200 kHz.

This paper presents a novel protection method for three-level converters. The three-level converter is subject to voltage unbalance, which can result in switch overvoltage and system failure. This abnormal phenomenon can be detected by monitoring the voltage across the flying capacitor (Vcss). Based on simulation analysis, monitoring the Vcss is also an effective way to detect various system faults, including shoot-through. Using the Vcss as the signal for fault detection, the proposed protection scheme can improve the system reliability without any additional components on the power stage and impact on the performance. The protection method can not only protect the system against unbalanced voltage stresses on the switches, but also provide a remedy for the system as faults happen. Furthermore, under/over input voltage lockout can be replaced by the proposed protection scheme. The verification is performed by the experiment with a three-level parallel resonant converter.

The loss density of the nanocrystalline magnetic material is experimentally characterized up to 500 kHz and above 1 Tesla in this paper. B-H hysteresis magnetization curves and loss density of the material under various operating temperatures up to 150 degrees C are measured and presented. The core preparing effect on magnetic loss density is also identified by experiments, which provides information necessary to practical magnetic designs. A new empirical core loss calculation method, flux-waveform-coefficient Steinmetz equation, is proposed and verified for the nanocrystalline material under resonant operations, which are often employed in high-frequency power converter applications. The proposed approach is either more accurate or easier to use than the previous methods.

This paper describes the design and implementation of a prototype 30kW, 200kHz pulsed power supply. A power density greater than 100W/inch3 is achieved with the converter operating at a high ambient temperature of 65 °C, by utilizing various technologies on topology, control, devices, passives, and thermal management, which can help reduce the converter size. The experimental results demonstrate that the converter meets the performance requirements while achieving the high power density.

This study investigates a phase-locked loop (PLL) controlled parallel resonant converter (PRC) for a pulse power capacitor charging application. The dynamic nature of the capacitor charging is such that it causes a shift in the resonant frequency of the PRC. Using the proposed control method, the PRC can be optimized to operate with its maximum power capability and guarantee ZVS operation, even when the input voltage and resonant tank parameters vary. The detailed implementation of the PLL controller, as well as the determination of dead-time and leading time, is presented in this paper. Simulation and experimental results verify the performance of the proposed control method.

This paper presents the relevancy, design, and test results of a 90 kW continuous duty, three-phase, bi-directional, and DC-DC converter for hybrid electric vehicles. Nominal low-side and high-side voltages of 320 V and 600 V, respectively, were used. Continuous boost-mode operation at 90 kW and continuous buck-mode operation at 45 kW were demonstrated using 80 degC (inlet temperature) Castrol 399 oil coolant. The volumetric power density of the three-phase test-bed was 2.7 kW/l in boost-mode at a coolant temperature of 80 degC. Based on two-phase tests, the power density at a coolant temperature of 25 degC is projected to be 4.1 kW/l To increase power level and power density, custom IGBT modules have been built and tested. A design layout for a packaged four-phase converter, using the custom IGBTs, including sensors and control hardware, indicates that a volumetric power density of above 4 kW/l is feasible at an 80 degC coolant temperature

In this paper, a high-density high-voltage distributed power system for pulse power applications is designed and implemented. Different topologies are evaluated for two power stages. According to pulse load condition, system power density is optimized through the tradeoff between power loss and magnetic component size. High power density and high efficiency are verified by the experimental result.

This paper presents double-sided liquid thermal management schemes for MOSFETs using embedded power technology. Physics based RC lumped thermal models were developed for embedded power with double-sided forced liquid convection and a wire bond package with single-sided forced liquid convection. Embedded power with double-sided liquid cooling is expected to produce up to a 40% reduction in thermal resistance compared to a wire bond package with single-sided liquid cooling. A liquid module test bed has been created based on the convection modeled and is used with MOSFET based samples to explore the validity of the modeling results. Temperature measurements from experimental results are comparable to the modeling results for single-side cooled wire bond packaging for a loss between 10 to 100 W and 0.15 to 5 GPM water flow rate. Pulse loss results also mimic transient heat transfer trends depicted in modeling. Experiments for double-sided cooling with embedded power are in progress.

This paper introduces a high power-density, high-efficiency isolated full-bridge boost converter, which is used for the front-end converter of a capacitor charger. The design equations, design considerations and practical trade-offs for the converter power stage are summarized. In addition, by fully taking advantage of the pulsed load profile, a transformer design using a high-saturation flux density material is introduced to maximize the power density. The principle of operation for the converter is analyzed and verified on a 15 kW, 100 kHz front-end converter prototype.

Design issues of high power density transformers for resonant converter systems are discussed. Under the specified operating condition, the transformer is designed to achieve the minimum volume. Finemet/sup /spl reg// nanocrystalline magnetic material is suitable for the pulse applications, due to its superior low loss density and high operating temperature characteristics. 1000 W/in/sup 3/ power density is achieved for the 30 kW pulse operation converter. Based on an energy-based approach, lumped-component transformer equivalent circuit is developed, with leakage inductances and winding capacitances calculated according to certain transformer geometry. The analysis has been verified by the experimental results.

This paper investigates the power MOSFETs high temperature operation from the standpoint of thermal stability. The objective is to identify the electrical and thermal limitations to high temperature and high frequency application of power MOSFETs, and to provide guidelines on how to use them safely and reliably for high temperature operation. Power MOSFETs DC blocking characteristics at high temperatures are studied experimentally and analytically. The loss characteristics including the switching loss, conduction loss, and leakage are tested and analyzed at higher junction temperature. A closed loop thermal system and stability criteria is developed and analyzed. At high switching frequency operation, the switching loss determines the thermal stability. When the junction temperature increases higher, the high leakage current loss can cause thermal instability. From the developed thermal stability system, the maximum witching frequency can be derived for the converter system design. The developed thermal system analysis approach can be extended to other Si devices including IGBT or wideband gap devices such as SiC power MOSFETs.

For paralleling DC/DC converters, this paper investigates the fundamental relationship between the outer-loop current sharing control and the voltage regulation control. By using the concept of output impedance, the inherent function of the current sharing control is clarified and its influences on the voltage regulation of paralleling system are revealed. Although there may exist tradeoffs between dynamic current sharing and voltage regulation, it is possible to have good performances on both aspects, as long as the closed-loop output impedances of individual modules are within a certain tolerance range. After that, a design guideline for the current sharing compensator is proposed. The analyses and designs are verified by the simulation and experimental results.

For high-voltage charging applications, this paper introduces a variable-frequency zero-voltage-switching three-level LCC resonant converter, which is able to utilize the parasitic components of the high-turns-ratio transformer. By applying the three-level structure in the primary side, low-voltage MOSFETs can be used to minimize the conduction loss. Therefore, the switching frequency can be increased to shrink the size of passive components. In addition, a simulation-based process is presented for designing the resonant-tank parameters as a trade-off among the efficiency, power density and component stresses. The principle of operation for the converter is analyzed and verified on a 3 kW, 200 kHz, 10 kV charger prototype.

Future U.S Army electric motor control applications will require power semiconductor devices that operate for thousands of hours at case temperatures of 150°C and higher. For reliable operation of silicon (Si)-based power electronics, the case temperature must be below 120°C. Because of this temperature limitation of Si, new wide bandgap materials, such as silicon carbide (SiC) are being investigated. We report on a SiC gate turn-off thyristor (GTO) and SiC p-i-n diode operating at case temperatures up to 150°C. For high power and high voltage applications the GTO is the switch of choice. In this study, currents up to 2 A where switched by the GTO under pulsed and continuous switching into an inductive load. The turn-on and turn-off gains, the on-state voltage, and the turn-on and turn-off times, as a function of temperature will be discussed.