Alberto Castellazzi

Experimental and Analytical Performance Evaluation of SiC Power Devices in the Matrix Converter

With the commercial availability of SiC power devices, their acceptance is expected to grow in consideration of the excellent low switching loss, high-temperature operation, and high-voltage rating capabilities of these devices. This paper presents the comparative performance evaluation of different SiC power devices in the matrix converter at various temperatures and switching frequencies. To this end, first, gate or base drive circuits for normally-off SiC JFET, SiC MOSFET, and SiC BJT by taking into account the special demands for these devices are presented. Then, four two-phase to one-phase matrix converters are built with different Si and SiC power devices to measure the switching waveforms and power losses for them at different temperatures and switching frequencies. Based on the measured data, four different SiC and Si power devices are compared in terms of switching times, conduction and switching losses, and efficiency at different temperatures and switching frequencies. Furthermore, a theoretical investigation of the power losses of the three-phase matrix converter with normally-off SiC JFET, SiC MOSFET, SiC BJT, and Si IGBT is described. The power losses estimation indicates that a 7-kW matrix converter would potentially have an efficiency of approximately 94% in high switching frequency if equipped with SiC devices.

Electrothermal simulation of multichip-modules with novel transient thermal model and time-dependent boundary conditions

The ability of monitoring the chip temperatures of power semiconductor modules at all times under various realistic working conditions is the basis for investigating the limits of the maximum permissible load. A novel transient thermal model for the fast calculation of temperature fields and hot spot temperature evolution presented recently is extended to include time-dependent boundary conditions for variations of ambient temperature and surface heat flows. For this a Greens function representation of the temperature field is used. Also, general initial temperature conditions are included. The method is exemplified by application to a dc/ac converter module for automotive hybrid drives. The thermal model, which can be represented by a thermal equivalent circuit, then is combined with an electrical PSpice-metal-oxide semiconductor field-effect transistor (MOSFET) model to allow for the fully self-consistent electrothermal circuit simulation of 42-V/14-V dc/dc-converter modules. 670 converter periods with altogether 8000MOSFET switching cycles in the six-chip module can be simulated within 1-h computing time on a Pentium PC. Various simulation results are presented, which demonstrate the feasibility of the simulation method and allow for the optimization of converter losses. Short circuit modes of converter operation are investigated with a high temperature increase also revealing the thermal interaction between different chips.

New Technique for the Measurement of the Static and of the Transient Junction Temperature in IGBT Devices under Operating Conditions

A novel technique is presented, which uses dIce/dt and the transconductance as a thermo-sensitive parameter for the measurement of the static and of the transient average junction temperature in IGBT devices. The paper describes the physics of the signal generation, provides the experimental setup, and discusses the accuracy and the suitability of the technique under operating conditions of the devices.

Single-Phase T-Type Inverter Performance Benchmark Using Si IGBTs, SiC MOSFETs, and GaN HEMTs

In this paper, benchmark of Si IGBT, SiC MOSFET, and Gallium nitride (GaN) HEMT power switches at 600-V class is conducted in single-phase T-type inverter. Gate driver requirements, switching performance, inverter efficiency performance, heat sink volume, output filter volume, and dead-time effect for each technology is evaluated. Gate driver study shows that GaN has the lowest gate driver losses above 100 kHz and below 100 kHz, SiC has lowest gate losses. GaN has the best switching performance among three technologies that allows high efficiency at high-frequency applications. GaN-based inverter operated at 160-kHz switching frequency with 97.3% efficiency at 2.5-kW output power. Performance of three device technologies at different temperature, switching frequency, and load conditions shows that heat sink volume of the converter can be reduced by 2.5 times by switching from Si to GaN solution at 60 °C case temperature, and for SiC and GaN, heat sink volume can be reduced by 2.36 and 4.92 times, respectively, by increasing heat sink temperature to 100 °C. Output filter volume can be reduced by 43% with 24, 26, and 61 W increase in device power loss for GaN-, SiC-, and Si-based converters, respectively. WBG devices allow reduction of harmonic distortion at output current from 3.5% to 1.5% at 100 kHz.

Reliability analysis and modeling of power MOSFETs in the 42-V-PowerNet

This paper analyzes the operation of PowerMOSFETs in the 42-V-PowerNet and shows that very stressful conditions are encountered, which can lead to severe reliability problems. To enable thorough investigations by circuit simulations an accurate physics-based compact model of the devices is proposed: it includes all important electrothermal effects relevant to the description of the observed failure mechanisms. By means of an advanced thermal-modeling approach, multichip assemblies can be accurately described, including mutual heating effects between neighboring devices. Some properly chosen examples demonstrate the validity of the model and its usefulness for reliability investigations

Compact modelling and analysis of power-sharing unbalances in IGBT-modules used in traction applications

IGBT modules are critical components for the reliability of power converters used in traction applications. A thorough analysis of all stressful operating conditions is a complex task, which requires versatile simulation capability. In this paper a comprehensive electro-thermal model of an IGBT-module is developed. Then, circuit simulation is used to investigate the power sharing between parallel chips during transient operation. Unbalances are observed, their causes identified and their influence on device degradation pointed out and discussed.

Transient robustness testing of silicon carbide (SiC) power MOSFETs

This paper presents the development of a unified test set-up and experimental results of the robustness characterisation of new generation of silicon carbide (SiC) power MOSFETs. In particular, unclamped inductive switching (UIS) and short-circuit withstand capability (SC) are investigated, with the aim of assessing the actual limits of operation of the devices and highlighting the underlying physical mechanisms. An electro-thermal device model is used to support the experimental analysis and interpret the observations.

Automated Fast Extraction of Compact Thermal Models for Power Electronic Modules

Virtual prototyping of power electronic modules aims to allow rapid evaluation of potential designs without the need to resort to building and testing physical prototypes. A key requirement for this process is the ability to quickly generate small, compact models describing the thermal performance of a potential design and this study presents a novel approach for this model generation process. The approach starts with a finite-difference mesh of the proposed design and applies a fast sparse matrix solver (GMRES) to determine the steady-state response to a particular power input. In doing this, approximations for the eigenvalues of the system can also be obtained from the same algorithm. It is shown that these two results can then be used to create small compact models describing the dynamic thermal properties within the design. The method is validated against an analytical solution for 1-D heat conduction and against experimental results for a simple power module. This process can be automated and it is shown that compact models can be generated in around 12 s per power input from the finite-difference mesh of the power module containing 14 623 nodes on a standard desktop PC.

SiC power MOSFETs performance, robustness and technology maturity

Relatively recently, SiC power MOSFETs have transitioned from being a research exercise to becoming an industrial reality. The potential benefits that can be drawn from this technology in the electrical energy conversion domain have been amply discussed and partly demonstrated. Before their widespread use in the field, the transistors need to be thoroughly investigated and later validated for robustness and longer term stability and reliability. This paper proposes a review of commercial SiC power MOSFETs state-of-the-art characteristics and discusses trends and needs for further technology improvements, as well as device design and engineering advancements to meet the increasing demands of power electronics.

Failure-relevant abnormal events in power inverters considering measured IGBT module temperature inhomogeneities

In this work, temperature inhomogeneities inside IGBT modules are measured to assess their relevance for the component reliability. Such issue has not been considered in many previous studies, since it is often assumed that the electro-thermal characteristics of IGBTs compensate for such temperature differences. Starting from real temperature measurements, this work discusses such aspect aided by electro-thermal simulations. This method provides useful information for the reliable thermal design of power modules, also considering the actual cooling system.