Szymon Beczkowski

Complete Loss and Thermal Model of Power Semiconductors Including Device Rating Information

Thermal loading of power devices are closely related to the reliability performance of the whole converter system. The electrical loading and device rating are both important factors that determine the loss and thermal behaviors of power semiconductor devices. In the existing loss and thermal models, only the electrical loadings are focused and treated as design variables, while the device rating is normally predefined by experience with limited design flexibility. Consequently, a more complete loss and thermal model is proposed in this paper, which takes into account not only the electrical loading but also the device rating as input variables. The quantified correlation between the power loss, thermal impedance, and silicon area of insulated gate bipolar transistor (IGBT) is mathematically established. By this new modeling approach, all factors that have impacts to the loss and thermal profiles of the power devices can accurately be mapped, enabling more design freedom to optimize the efficiency and thermal loading of the power converter. The proposed model can be further improved by experimental tests, and it is well agreed by both circuit and finite element method (FEM) simulation results.

Improving Power Converter Reliability: Online Monitoring of High-Power IGBT Modules

The real-time junction temperature monitoring of a high-power insulated-gate bipolar transistor (IGBT) module is important to increase the overall reliability of power converters for industrial applications. This article proposes a new method to measure the on-state collector-emitter voltage of a high-power IGBT module during converter operation, which may play a vital role in improving the reliability of the power converters. The measured voltage is used to estimate the module average junction temperature of the high and low-voltage side of a half-bridge IGBT separately in every fundamental cycle of the current by calibrating them at load current. The measurement is very accurate and also measures the voltage at the middle of a pulse-width modulation (PWM) switching. A major objective is that this method is designed to be implemented in real applications. The performance of this technique is measured in a wind power converter at a low fundamental frequency. To illustrate more, the test method as well as the performance of the measurement circuit are also presented. This measurement is also useful to indicate failure mechanisms such as bond wire lift-off and solder layer degradation. The measurements of and rise in the junction temperature after five million cycles of normal operation of the converter are also presented.

A review on real time physical measurement techniques and their attempt to predict wear-out status of IGBT

Insulated Gate Bipolar Transistors (IGBTs) are key component in power converters. Reliability of power converters depend on wear-out process of power modules. A physical parameter such as the on-state collector-emitter voltage (Vce) shows the status of degradation of the IGBT after a certain cycles of operation. However, the Vce mainly shows the wear-out of bond wire lift-off and solder degradation. The Vce is normally used to estimate the junction temperature in the module. The measurement of Vce is sensitive to the converter power level and fluctuations in the surrounding temperature. In spite of difficulties in the measurement, the offline and online Vce measurement topologies are implemented to study the reliability of the power converters. This paper presents a review in wear-out prediction methods of IGBT power modules and freewheeling diodes based on the real time Vce measurement. The measurement quality and some practical issues of those measurement techniques are discussed. Furthermore, the paper proposes the requirements for the measurement and prognostic approach to determine wear-out status of power modules in field applications. The online Vce measurement for a selected topology is also shown in the paper.

Led spectral and power characteristics under hybrid PWM/AM dimming strategy

In order to dim LEDs the pulse width modulation (PWM) or amplitude modulation (AM) dimming scheme is typically used. Previous studies show that these dimming schemes can have opposite effects on diodes peak wavelength shift. An experimental study was conducted to test the behavior of InGaN diodes and phosphor-converted white diodes under hybrid PWM/AM modulation. Feed forward control schemes that provide stable peak wavelength position during dimming and the ability to compensate the thermally induced color shifts and the decrease of the luminous flux are investigated.

Influences of Device and Circuit Mismatches on Paralleling Silicon Carbide MOSFETs

This paper addresses the influences of device and circuit mismatches on paralleling the silicon carbide (SiC) MOSFETs. Comprehensive theoretical analysis and experimental validation from paralleled discrete devices to paralleled dies in multichip power modules are first presented. Then, the influence of circuit mismatch on paralleling SiC MOSFETs is investigated and experimentally evaluated for the first time. It is found that the mismatch of the switching loop stray inductance can also lead to on-state current unbalance with inductive output current, in addition to the on-state resistance of the device. It further reveals that circuit mismatches and a current coupling among the paralleled dies exist in a SiC MOSFET multichip power module, which is critical for the transient current distribution in the power module. Thus, a power module layout with an auxiliary source connection is developed to reduce such a coupling effect. Finally, simulations and experimental tests are carried out to validate the analysis and effectiveness of the developed layout.

An online V ce measurement and temperature estimation method for high power IGBT module in normal PWM operation

An on-state collector-emitter voltage (Vce) measurement and thereby an estimation of average temperature in space for high power IGBT module is presented while power converter is in operation. The proposed measurement circuit is able to measure both high and low side IGBT and anti parallel diode voltages for a half bridge module which are also used to monitor the electrical degradation of the module. The Vce load current is proposed to estimate the variation of average temperature in space at every fundamental cycle of sinusoidal loading current. Initially, the calibration of voltage and junction temperature for load current level is presented and a trend of change in calibration factor for the IGBT is presented. Finally, the variation in temperature for sinusoidal variation of current is presented at initial stage and after an ageing of the IGBT. The measurement technique is simple and easy to implement into a gate driver for field applications.

Short-circuit characterization of 10 kV 10A 4H-SiC MOSFET

The short-circuit capability of a power device is highly relevant for converter design and fault protection. In this paper a 10kV 10A 4H-SiC MOSFET is characterized and its short circuit withstand capability is studied and analyzed at 6 kV DC-link voltage. The test setup for this study is also introduced as its design, especially the inductance in the switching loop, can affect the experimental results. The study aims to present insights specific to the device which are different from that of silicon (Si) based devices. During the short-circuit operation, MOSFET saturation current, ID,sat, increases for a few microseconds before decreasing gently. Degradation of the device can be observed at pulses longer than 5.9μs. The SiC MOSFET failed after-turn off, after a pulse of 8.6μs, due to an increase in the leakage current.

Circuit mismatch influence on performance of paralleling silicon carbide MOSFETs

This paper focuses on circuit mismatch influence on performance of paralleling SiC MOSFETs. Power circuit mismatch and gate driver mismatch influences are analyzed in detail. Simulation and experiment results show the influence of circuit mismatch and verify the analysis. This paper aims to give suggestions on paralleling discrete SiC MOSFETs and designing layout of power modules with paralleled SiC MOSFETs dies.

Test setup for long term reliability investigation of Silicon Carbide MOSFETs

Silicon Carbide MOSFETs are now widely available and have frequently been demonstrated to offer numerous advantages over Silicon based devices. However, reliability issues remain a significant concern in their realisation in commercial power electronic systems. In this paper, a test bench is designed that enables an accelerated power cycling test to be performed on packaged Silicon Carbide MOSFETs (TO-247) under realistic operating conditions. An accelerated power cycling test is then performed, with on-state resistance selected as the observed parameter to detect degradation. On-state resistance is routinely monitored online through the use of an innovative voltage measurement system. The packaged Silicon Carbide MOSFET is shown to exhibit a 25% increase in on-state resistance as the device ages throughout its lifetime, with the test still on-going.

Current measurement method for characterization of fast switching power semiconductors with Silicon Steel Current Transformer

This paper proposes a novel current measurement method with Silicon Steel Current Transformer (SSCT) for the characterization of fast switching power semiconductors. First, the existing current sensors for characterization of fast switching power semiconductors are experimentally evaluated regarding three essential qualities: high bandwidth, suitable physical size, and galvanic isolation. Then, the proposed current measurement method with SSCT is mathematically analyzed, which proves that the proposed method has the capability of measuring fast switching current. Simultaneously, it compensates the mechanical size limitations of the Pearson current monitor. Finally, experimental studied are carried out with both discrete Silicon Carbide (SiC) MOSFET and high current (1000A) Silicon (Si) IGBT power modules. The experimental results validate the effectiveness of the proposed method.