Scott Leslie

U.S. Department of Energy, Washington, Washington, D.C., United States

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Publications (20)1.76 Total impact

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    ABSTRACT: This paper summarizes the different steps that have been undertaken to design medium voltage power converters using the state-of-the-art 15 kV SiC N-IGBTs. The 11 kV switching characterization results, 11 kV high dv/dt gate driver validation, and the heat-run test results of the SiC IGBT at 10 kV, 550 W/cm2 (active area) have been recently reported as individual topics. In this paper, it is attempted to link all these individual topics and present them as a complete subject from the double pulse tests to the converter design, for evaluating these novel high voltage power semiconductor devices. In addition, the demonstration results of two-level H-Bridge and three-level NPC converters, both at 10 kV dc input, are being presented for the first-time. Lastly, the performance of two-chip IGBT modules for increased current capability and demonstration of three-level poles, built using these modules, at 10 kV dc input with sine-PWM and square-PWM modulation for rectifier and dc-dc stages of a three-phase solid state transformer are presented.
    No preview · Article · May 2015
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    ABSTRACT: The ultrahigh voltage (> 12 kV) SiC IGBTs are promising power semiconductor devices for medium voltage power conversion due to feasibility of simple two-level topologies, reduced component count and extremely high efficiency. However, the current devices generate high dv/dt during switching transitions because of the deep punch-through design. This paper investigates the behavior of dv/dt during the two-slope (different slopes before and after punch-through) turn-on and turn-off voltage transitions of these devices, by varying the device current, temperature and field-stop buffer layer design. It is shown that the dv/dt can be minimized by increasing the gate resistance, by taking the turn-on transition as reference. However, it is found that the increase in gate resistance has very weak impact on dv/dt above the punch-through voltage, and also resulting in significantly increased switching energy loss. It is shown that this problem can be addressed by using a two-stage active gate driver, where the gate current is appropriately controlled to limit the dv/dt over punch-through voltage and to minimize the switching energy loss under the punch-through voltage. Experimental results on 15 kV SiC N-IGBTs with field-stop buffer layer thickness of 2 μm and 5 μm are presented up to 11 kV with a detailed discussion of the results.
    No preview · Article · Nov 2014
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    ABSTRACT: This paper presents extensive experimental switching characteristics of a state-of-the-art 15 kV SiC N-IGBT (0.32 cm2 active area) up to 10 kV, 10 A and 175°C. The influence of the thermal resistance of the module package, cooling mechanism, and the increased energy loss with temperature are investigated for determining the switching frequency limits of the IGBT. Detailed FEM analysis is conducted for extracting the thermal resistance of each layer in the 15 kV module from the IGBT junction to the base plate, and then down to the ambient. Using this thermal information and the experimental switching data, the inductive switching frequency limits are analytically evaluated for liquid and air cooling cases with 660 W/cm2 and 550 W/cm2 power dissipation densities respectively, considering 150°C as maximum junction temperature. The air cooling power dissipation density of the 15 kV IGBT is experimentally validated using a dc-dc boost converter at 10 kV, 6.4 kW output and 550 W/cm2 under steady state operating conditions. The gate resistances used for the entire experiments are RG(ON) = 20 Ω and RG(OFF) = 10 Ω.
    No preview · Conference Paper · May 2014
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    ABSTRACT: The 4H-SiC n-IGBT is a promising power semiconductor device for medium voltage power conversion. Currently, Cree has successfully built 15 kV n-IGBTs. These IGBTs are pivotal for the smart grid power conversion systems and medium voltage drives. The need for complex multi-level topologies or series connected devices can be eliminated, while achieving reduced power loss, by using the SiC IGBT. In this paper, characteristics of the 15 kV n-IGBT have been reported for the first time. The turn-on and turn-off transitions of the 15 kV, 20 A IGBT have been experimentally evaluated up to 11 kV. This is highest switching characterization voltage ever reported on a single power semiconductor device. The paper includes static characteristics up to 25 A (forward) and 12 kV (blocking). The dependency of the power loss with voltage, current and temperature are provided. In addition, the basic converter design considerations using this ultrahigh voltage IGBT for high power conversion applications are presented. Also, a comparative evaluation is reported with an IGBT with thicker field-stop buffer layer as a means to show flexibility in choosing the IGBT design parameters based on the power converter frequency and power rating specification. Finally, power loss comparison of the IGBTs and MOSFET is provided to consummate the results for a complete reference.
    No preview · Conference Paper · Sep 2013
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    ABSTRACT: In this paper a new method for implementation of a 3-phase medium voltage rectifier is presented for Active Front End grid interface applications. A current source based PWM buck rectifier with Silicon Carbide (SiC) devices, different from the traditional GTO based current source rectifier, is used to grid tie with 3-phase, 4.16 kV grid. The power level considered is 100 kVA. Simplicity of construction, very high efficiency, better input line current control and small volume are the main advantages of this system. Due to low switching losses compared with traditional GTOs, PWM operation of the rectifier at higher switching frequencies is possible. A detailed simulation shows the validity of the proposed method. Efficiency comparison of the PWM Buck rectifier with 10 kV/10 A SiC MOSFET and 15 kV/20 A SiC IGBT as the active devices is also presented. Low voltage hardware prototype based high frequency switching validation is also carried out.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: The 15kV /20A, 4H-SiC n-IGBT is the state-of-the-art high voltage power semiconductor device. The transformerless intelligent power substation (TIPS) [1] for 13.8kV grid interfacing is built using this device. It is proposed to use a three-phase, three-level, diode clamped topology as the front end converter (FEC) in TIPS. A modular-leg structure has been employed for FEC. In modular-leg structure, each phase-leg will have its own DC-link capacitors and a low inductance bus-bar. However, modular-leg structure adds complexity in DC bus over-load protection, which is studied in this paper. Experimental results of modular-leg converter at 3kV DC link voltage and scale down prototype of AC switch for DC bus fault protection are presented.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: The complementary inverter topology with N-channel and P-channel switching devices is a known method of eliminating dv/dt stress on the gate drivers. In the Silicon (Si) based applications, this advantage did not gain wide attention due to inherent inefficiency of the P-type devices, and the matured technology to handle the dv/dt stress levels produced by these devices with highest blocking voltage rating of 6.5 kV. On the other hand, the ultrahigh voltage (> 12 kV) SiC devices generate high dv/dt due to their high speed switching. This requires meticulous design of the gate drivers for reliable operation of high power converters. As an easy alternative, the option of using a complementary inverter has been explored in this paper. Both N-channel and P-channel IGBTs with blocking capability of 15 kV have been investigated for the complementary structure. The N-IGBT is found to be more efficient than the P-IGBT, based on the experimental switching characterization results at 6 kV and 5 A. The results of the 3 kV half-bridge complementary inverter prototype are also presented. The option of trade-off of P-IGBT field-stop buffer layer parameters (thickness, doping concentration and lifetime) for better switching characteristics can provide the use of complementary topologies a promising alternative for high power conversion.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: Transformer less Intelligent Power Substation (TIPS) is a solid state replacement for the conventional bulky distribution transformers used for 13.8kV and 480V grid interconnectivity. A 100kVA 3L NPC converter is being built using 12kV SiC n-IGBT for the high voltage grid interface. In this paper, detailed thermal behavior of this converter is studied for optimum thermal design. The thermal profile at the die level at different power factor of operation is studied. This study helps the optimum component placement in the converter. Also it shows that the operating modes of the converter play a key role in optimum thermal design.
    No preview · Conference Paper · Sep 2012
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    ABSTRACT: This paper presents a hybrid switch that parallels a power MOSFET and an IGBT as the main switch of a zero-voltage switching inverter. The combination features the MOSFET conducting in the low current region and the IGBT conducting in the high current region, and the soft switching avoids the reverse recovery problem during the device turn-on. A custom hybrid switch module has been developed for a variable-timing controlled coupled-magnetic type ZVS inverter with a nominal input voltage of 325 V and the continuous output power of 30-kW for a traction motor drive. Experimental results of the hybrid-switch based inverter with the total loss projected by temperature indicate that the inverter achieves 99% efficiency at the nominal condition and demonstrate ultrahigh efficiency operation over a wide load range. At 375-V input, the maximum measured efficiency through temperature projection and loss separation analysis is 99.3%.
    No preview · Conference Paper · Sep 2012
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    ABSTRACT: Silicon Carbide (SiC) devices and modules have been developed with high blocking voltages for Medium Voltage power electronics applications. Silicon devices do not exhibit higher blocking voltage capability due to its relatively low band gap energy compared to SiC counterparts. For the first time, 12kV SiC IGBTs have been fabricated. These devices exhibit excellent switching and static characteristics. A Three-level Neutral Point Clamped Voltage Source Converter (3L-NPC VSC) has been simulated with newly developed SiC IGBTs. This 3L-NPC Converter is used as a 7.2kV grid interface for the solid state transformer and STATCOM operation. Also a comparative study is carried out with 3L-NPC VSC simulated with 10kV SiC MOSFET and 6.5kV Silicon IGBT device data.
    No preview · Conference Paper · Sep 2012
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    ABSTRACT: The performance of Junction Barrier Schottky (JBS) diodes developed for medium voltage hard-switched Naval power conversion is reported. Nominally 60 A, 4.5kV rated JBS freewheeling diodes were paired with similarly rated Si IGBTs and evaluated for temperature dependent static and dynamic characteristics as well as HTRB and surge capability. The SiC JBS/Si IGBT pair was also directly compared to Si PiN diode/Si IGBT with similar ratings. Compared to Si, the SiC freewheeling diode produced over twenty times lower reverse recovery charge leading to approximately a factor-of-four-reduction in turn-on loss. Alternatively, for equivalent total switching loss, the SiC JBS/Si IGBT hybrid configuration allows for at least a 50% increase in specific switched power density. Reliability testing showed the devices to be robust with zero failures.
    No preview · Article · May 2012 · Materials Science Forum
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    ABSTRACT: The majority carrier domain of power semiconductor devices has been extended to 10 kV with the advent of SiC MOSFETs and Schottky diodes. Twenty-four MOSFETs and twelve JBS diodes have been assembled in a 10 kV half H-bridge power module to increase the current handling capability to 120 A per switch without compromising the die-level characteristics. For the first time, a custom designed system (13.8 kV to 465/√3 V solid state power substation) has been successfully demonstrated with these state of the art SiC modules up to 855 kVA operation and 97% efficiency. Soft-switching at 20 kHz, the SiC enabled SSPS represents a 70% reduction in weight and 50% reduction in size when compared to a 60 Hz conventional, analog transformer.
    No preview · Article · May 2012 · Materials Science Forum
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    ABSTRACT: The majority carrier domain of power semiconductor devices has been extended to 10 kV with the advent of SiC MOSFETs and Schottky diodes. The devices exhibit excellent static and dynamic properties with encouraging preliminary reliability. Twenty-four MOSFETs and twelve Schottky diodes have been assembled in a 10 kV half H-bridge power module to increase the current handling capability to 120 A per switch without compromising the die-level characteristics. For the first time, a custom designed system (13.8 kV to 465/√3 V solid state power substation) has been successfully demonstrated with these state of the art SiC modules up to 855 kVA operation and 97% efficiency. Soft-switching at 20 kHz, the SiC enabled SSPS represents a 70% reduction in weight and 50% reduction in size when compared to a 60 Hz conventional, analog transformer.
    Preview · Conference Paper · Oct 2011
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    ABSTRACT: In this paper, the extension of SiC power technology to higher voltage 10 kV/10 A SiC DMOSFETs and SiC JBS diodes is discussed. A new 10 kV/120 A SiC power module using these 10 kV SiC devices is also described which enables a compact 13.8 kV to 465/√3 solid state power substation (SSPS) rated at 1 MVA.
    No preview · Article · Apr 2011
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    ABSTRACT: In this paper we report the electrical and thermal performance characteristics of 1200 V, 100 A, 200 degrees C (T(j)), SiC MOSFET power modules configured in a dual-switch topology. Each switch-diode pair was populated by 2 x 56 mm(2) SiC MOSFETs and 2 x 32 mm(2) SiC junction barrier Schottky (JBS) diodes providing the 100 A rating at 200 degrees C. Static and dynamic characterization, over rated temperature and power ranges, highlights the performance potential of this technology for highly efficient drive and power conversion applications. Electrical performance comparisons were also made between SiC power modules and equivalently rated and packaged IGBT modules. Even at a modest Tj=125 degrees C, conduction and dynamic loss evaluation for 20kHz, Id=100A operation demonstrated a significant efficiency advantage (38-43%) over the IGBT components. Initial reliability data also illustrates the potential for SiC technology to provide robust performance in harsh environments.
    Preview · Article · Apr 2010 · Materials Science Forum
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    ABSTRACT: This paper presents a 55kW three-phase soft-switching inverter for hybrid electric vehicle drives at high temperature conditions. Highly integrated soft-switching modules have been employed to achieve switching loss as well as conduction loss reduction. Detailed experimental evaluations of inverter efficiency have been conducted through both inductive load and motor-dynamometer load at coolant temperatures ranging from 25°C to 90°C. Efficiency measurement using power meter showed that the peak efficiency is around 99%, and it drops slightly at lower speed and higher temperature conditions. To ensure measurement fidelity, a double chamber differential calorimeter system was designed and calibrated for the inverter testing. Through long-hour testing, the measured efficiencies consistently showed 99% and higher. The soft-switching inverter has been operated reliably and demonstrated high efficiency at different temperature and test conditions.
    Full-text · Conference Paper · Mar 2010
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    ABSTRACT: A custom multi-chip power module packaging was designed to exploit the electrical and thermal performance potential of silicon carbide MOSFETs and JBS diodes. The dual thermo-mechanical package design was based on an aggressive 200 o C ambient environmental requirement and 1200 V blocking and 100 A conduction ratings. A novel baseplate-free module design minimizes thermal impedance and the associated device junction temperature rise. In addition, the design incorporates a free-floating substrate configuration to minimize thermal expansion coefficient induced stresses between the substrate and case. Details of the module design and materials selection process will be discussed in addition to highlighting deficiencies in current packaging materials technologies when attempting to achieve high thermal cycle life reliability over an extended temperature range.
    Full-text · Article · Jan 2010
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    ABSTRACT: Recent dramatic advances in the development of large area silicon carbide (SiC) MOSFETs along with their companion JBS diode technology make it possible to design and fabricate high power SiC switch modules. An effort underway by the Air Force Research Laboratory has lead to the development of a 1.2 kV/100 A SiC dual switch power module capable of operating at a junction temperature of 200degC. Two additional efforts are set on achieving the megawatt goal. An effort by the Army Research Laboratory is focused on 1.2 kV modules to be used for traction and power conversion applications. The highest power 1200 V all-SiC dual switch power modules produced is capable of 880 amps. A DARPA effort to develop a solid state power substation has produced a 10 kV/50 A SiC dual switch power module. Higher current modules in both voltage ratings have been designed. These SiC MOSFET modules represent the next level of integration for SiC power devices. This is a critical technical milestone in the progression toward highly reliable, high efficiency, power systems. This technology is relevant in the current energy-conscious environment and will translate to significant energy savings for hybrid and electric vehicles, solar power and alternative energy system inverters, and industrial motor drives.
    Full-text · Conference Paper · Oct 2009
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    ABSTRACT: The DARPA WBGS-HPE program is developing 100 A, 10 kV SiC power modules to demonstrate the viability of a 2.75 MVA Solid State Power Substation that uses 10 kV, 20 kHz switching-capable devices. Thermal network component models for these modules are developed and are validated with temperature measurements obtained through various methods for a range of power dissipation levels. The models include the direct-bond-copper materials required to obtain 15 kV baseplate isolation and are parameterized in terms of the structural and material properties of the package to provide flexibility for different configurations. This enables the use of electro-thermal simulations to optimize SiC module parameters for specific system requirements.
    No preview · Conference Paper · Jul 2008
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    ABSTRACT: Discrete 4H-SiC PiN diode chips have been developed for extremely high power handling applications. These diodes have a forward voltage of less than 3.2 V at 180 A (100 A/cm) and are capable of blocking 4.5 kV with a reverse leakage current of less than one muA. At 1.5 cm times 1.5 cm, these discrete 4H-SiC PiN diode chips have over two times the area of the previous largest discrete 4H-SiC power device. Furthermore, considerable progress has been made in achieving V<sub>F</sub> stability, as no measurable increase in V<sub>F</sub> was observed on a packaged diode following a 120 hour DC stress at 90 A. When switched from 180 A forward current at a dI/dt of 300 A/mus, the diodes showed a peak reverse current of 50 A and a reverse recovery time of 320 ns. These diodes demonstrate the outstanding capabilities of 4H-SiC power devices given state-of-the-art 4H-SiC substrates, epitaxy, device design, and processing
    No preview · Conference Paper · Jul 2006