Enea Bianda

Characterization of a 6.5kV IGBT for medium-voltage high-power resonant DC-DC converter

Medium-voltage (MV) high-power converters are usually realized using high-voltage semiconductors (3.3kV, 4.5kV or 6.5kV) operated with low-switching frequencies in the range of several hundred Hz and under hard-switching conditions. However, for medium-voltage high-power DC-DC converters employing transformer for galvanic isolation, it is attractive to increase switching frequency in order to reduce the transformer size. Therefore, it is usually required to consider the use of some sort of soft-switching method. Recently, DC-DC LLC resonant converters are gaining momentum, but are usually considered for low-voltage applications utilizing unipolar devices (MOSFETS). In this paper, switching properties of a medium-voltage bipolar semiconductor (6.5kV IGBT) are analyzed for a high-power LLC resonant converter. Experimental results are presented to illustrate the characteristic operating conditions, highlighting interactions between semiconductors and circuit properties, which both must be simultaneously considered, in order to achieve best utilization of a high-voltage semiconductor operating at higher switching frequencies.

A new concept of a high-current power module allowing paralleling of many SiC devices assembled exploiting conventional packaging technologies

We present a new concept of a high-current SiC power module with the fast switching capability based on a stacked-ceramic-substrate structure. This approach enables to parallel many small area SiC devices in a housing of a Si half-bridge module. The internal design of the module - concept demonstrator was optimized using electromagnetic simulations in order to minimize stray inductance and balanced current sharing. The prototype was assembled exploiting conventional packaging technologies. Performance of the assembled module was tested by a double-pulse measurement test in order to determine switching losses and verify simulated stray inductance.

Full silicon carbide boost chopper module for high frequency and high temperature operation

This paper presents a 1200-V 20-A full silicon carbide boost chopper module designed for high temperature and high frequency operation. The developed module is based on one silicon carbide metal oxide semiconductor field effect transistor chip and two parallel connected silicon carbide schottky diode chips manufactured by Cree, Inc. The static and dynamic characteristics of the module have been experimentally determined and its performance tested in a 2-kW boost converter. The test results show that the developed module performs well and is able to provide a good conversion efficiency even at high switching frequency.

Robust 3.3kV silicon carbide MOSFETs with surge and short circuit capability

An approach to implement electrically robust MOSFETs in a functioning half-bridge will be investigated. For the first time, reverse conducting 3.3kV SiC MOSFETs have been fabricated with dilferent cell pitches from 14μm (p1.0) to 26μm (pl.8) that are able to withstand short circuit pulse of up to 10μs and a 9ms surge current event up to 15x the nominal current. LinPak half-bridge modules have been fabricated showing reduction of the switching loss by more than 90% compared to a silicon IGBT/diode half bridge.

New trends in high voltage MOSFET based on wide band gap materials

Recent advances and new trends in high voltage SiC based MOSFETs are analyzed. The main focus is done on design optimization strategies for reducing the on-state resistance. Gate oxide treatments for improving the interface quality resulting in a lower channel resistance are reviewed as well as solutions for lowering the JFET and bulk resistance components. The 3rd quadrant operation, short-circuit capability and switching performance are analyzed together with design strategies for their improvement. Finally, the limits of high voltage MOSFETs are outlined and future power devices to overcome the MOSFETs limits in ultra-high voltage applications are presented.

On the influence of active area design on the performance of SiC JBS diodes

This paper presents an investigation regarding the influence of the active area design on the static and dynamic performance of SiC JBS diodes. The analysis has been performed on fabricated JBS diodes, rated for 1.7kV applications. For the active area layout, both stripe and hexagonal cell patterns have been used for the implanted p+ regions.

Performance evaluation of custom-made 1.2-kV 100-A silicon carbide half-bridge module in three-phase grid connected PWM rectifier

This paper studies experimentally the benefits of silicon carbide based power semiconductor technology in a low-voltage grid connected three-phase three-wire pulse width modulated rectifier. The power semiconductor module used in the study is a custom-made 1.2-kV 100-A fully silicon carbide based half-bridge type module designed for fast switching speeds and high temperature operation. The experimental tests are carried out with a 40-kVA prototype system built in the frame of a commercial low-voltage motor drive unit. In addition, the impact of the high switching speeds enabled by the silicon carbide based semiconductor devices on conductive electromagnetic emissions are also investigated. The results show that the conversion efficiency can be significantly improved with silicon carbide compared to the state-of-the-art silicon based semiconductor technology. As a drawback, the faster switching speeds increase the conductive electromagnetic emissions to some extent.

A novel method to protect IGBT module from explosion during short-circuit in traction converters

A novel method using gate overdrive is suggested to avoid explosion of IGBT modules in converters. With this method, the gate drive impedance is set to low (~0 Ω), such that the driving capability of the gate drive is not limited by the short-circuit present between the gate and auxiliary emitter terminals of a damaged IGBT. Using the implemented gate driving concept, the fault current can be redirected through good chips in the module and the current concentration in the faulty chip of the IGBT module could be reduced to avoid explosion.

Performance Evaluation of SiC JBS Diodes Rated for 6.5kV Applications

This paper presents an investigation into the performance of SiC JBS diodes rated for 6.5kV applications. For the active area layout, two hexagonal cell designs with different ASchottky/ATotal ratios have been considered. For completeness, the JBS performance is compared to that of SiC PiN diodes, fabricated on the same wafer. A benchmark against state of the art PiN diodes in Si technology is also provided.

Experimental investigation of SiC 6.5kV JBS diodes safe operating area

This paper presents an experimental investigation of the dynamic performance of SiC 6.5kV JBS diodes. Using a hybrid Si SPT IGBT/SiC JBS diodes combination, we have analyzed the turn-off behavior limits of SiC JBS diodes and compared the result against a state-of-the-art Si PiN diode. The experimental results show that the JBS diodes can handle about 40A/chip at 125°C before going into thermal runaway. This maximum turn-off current value increases by about 50% when the diodes are operated at room temperature. The diodes dI/dt behaviour appear to be virtually independent of the DC-link voltage (at RG=18Ω). The comparison between turn-off curves for 6.5kV SiC and Si diodes shows that the use of SiC JBS diodes reduces the reverse recovery losses by more than 98%.