Reliability enhancement by integrated liquid cooling in power IGBT modules for hybrid and electric vehicles

Insulated Gate Bipolar Transistor (IGBT) modules in power train system of Hybrid and Electric Vehicles (HEV/EV) are working in harsh environment and high reliability and long lifetime are required. In this work, reliability enhancement by integrated liquid cooling structure in HEV/EV IGBT module is investigated. The thermal resistance of junction to heat sink can be reduced more than 50% by direct liquid cooling as eliminating thermal grease layer, so both active and passive temperature swings decrease significantly which will enhance module reliability and lifetime. The lifetime of modules with conventional and integrated liquid cooling structures are estimated under mission of standard driving cycles. We found that lifetime is prolonged obviously by direct cooling pin–fin base plate, and the compact module also makes the application power system simple and reliable.     

A study on IGBT junction temperature (Tj) online estimation using gate-emitter voltage (Vge) at turn-off

A novel method is presented for online estimation of the junction temperature (Tj) of semiconductor chips in IGBT modules, based on evaluating the gate-emitter voltage (Vge) during the IGBT switch off process. It is shown that the Miller plateau width (in the Vge waveform) depend linearly on the junction temperature of the IGBT chips. Hence, a method can be proposed for estimating the junction temperature even during converter operation – without the need of additional thermal sensors or complex Rth network models. A measurement circuit was implemented at gate level to measure the involved time duration and its functionality was demonstrated for different types of IGBT modules. A model has been proposed to extract Tj from Vge measurements. Finally, an IGBT module with semiconductor chips at two different temperatures has been measured using Vge method and this method was found to provide the average junction temperature of all the semiconductor chips.     

The effect of electro-thermal parameters on IGBT junction temperature with the aging of module

This paper presents the effect of the change of electro-thermal parameters on IGBT junction temperature with module aging. Five IGBT modules are subjected to advance power thermal cycling, and IGBT I–V characterization, switching loss, and transient thermal impedance curve are measured every 1000 power thermal cycles. Then, electro-thermal models of IGBT module under power thermal cycles were built by change electro-thermal parameters, and the influence of various parameters of the electro-thermal model on the junction temperature was researched respectively. Experimental results demonstrate that IGBT collector-emitter voltage, switching loss and thermal resistance increase more quickly with the aging process of module. Simulation results indicate that the variations of electro-thermal parameters have crucial influences on the IGBT junction temperature. After 6000 power thermal cycles, the IGBT steady state junction temperature mean and variation are increased 1.97 K and 0.1656 K over its initial value, respectively. The relative temperature rise is 38.10% and relative temperature variation is 15.08% after 6000 power thermal cycles. The rise in switching loss increases both the steady state junction temperature mean and variation. The change of thermal impedance has great influence on the steady state junction temperature mean, but has little effect on steady state junction temperature variation.     

基于有限元仿真的IGBT混合模块的可靠性分析

集成化与微型化是当今电子信息产业发展的特点,其中电子元件的结温与热应力是影响其可靠性的重要因素。硅基IGBT和SiC基续流二极管组成的混合模块广泛应用于城市轨道交通等领域,其可靠性直接影响轨道交通车辆的运行性能。本文建立IGBT混合模块的仿真模型,随着各层材料厚度、焊料空洞大小和位置的变化,计算分析IGBT混合模块的温度与应变变化规律,对模块封装结构进行优化设计。将高热导率石墨烯应用在IGBT混合模块中,仿真分析应用位置不同对模块可靠性的影响,从而进一步优化混合模块的封装结构。通过仿真计算,优化后的IGBT混合模块可将最高结温降低近3℃,最大热应力下降超过30 MPa。     

Thermo-fluid simulation for the thermal design of the IGBT module in the power conversion system

The junction temperature of the insulated-gate bipolar transistor (IGBT) module, which belongs to power semiconductor devices, directly impacts on the system performance of the power conversion system (PCS), and therefore, the accurate prediction of the airflow rate passing the heat sink block of the IGBT module is very important at the thermal design stage. In this paper, the thermo-fluid simulation was developed with the T–Q characteristic curve to predict the junction temperature of the IGBT module and the airflow rate of the heat sink block. The porous media model was adopted in the heat sink block with fins and the filled air between fins of the heat sink block in the PCS to remove the heavily concentrated mesh problems in the heat sink block. The proposed simulation model was compared to the experimental value for the hot spot temperature on the heat sink block and the differences were within the average 4.0% margin of error in the comparison. This simulation model can be used to evaluate the suitability of the cooling design according to various operating conditions of the fan and IGBT module with benefits of the reduction in the mesh generation and the computation time. Also, this simulation model increases the flexibility of predicting the airflow rates in the PCS due to the change of the airflow passage structure in the PCS or the capacity of the fan.     

Transient temperature measurements and modeling of IGBT's undershort circuit

This paper discusses the estimation of possible device destruction inside power converters in order to predict failures by means of simulation. The study of insulated gate bipolar transistor (IGBT) thermal destruction under short circuits is investigated. An easy experimental method is presented to estimate the temperature decay in the device from the saturation current response at low gate-to-source voltage during the cooling phase. A comparison with other classical experimental methods is given. Three one-dimensional thermal models are also studied: the first is a thermal equivalent circuit represented by series of resistance-capacitance cells; the second treats the discretized heat-diffusion equation; and the third is an analytical model developed by building an internal approximation of the heat-diffusion problem. It is shown that the critical temperature of the device just before destruction is larger than the intrinsic temperature, which is the temperature at which the semiconductor becomes intrinsic. The estimated critical temperature is above 1050 K, so it is much higher than the intrinsic temperature (~550 K). The latter value is underestimated when multidimensional phenomena are not taken into account. The study is completed by results showing the threshold voltage and the saturation current degradation when the IGBT is submitted to a stress (repetitive short circuit)     

Design optimization of an integrated liquid-cooled IGBT powermodule using CFD technique

This paper presents a novel approach to optimize pin array design of an integrated, liquid-cooled, insulated gate bipolar transistor (IGBT) power module. With the aid of a computational fluid dynamics (CFD) code, the fluid field and heat transfer inside the module were analyzed, and several design options on pin arrays were examined. For IGBT die circuitry, the uniformity of temperature distribution among dies is as critical as the magnitude of the die temperature. A noticeable variation in temperature among dies can accelerate the thermal runaway and reduce the reliability of the devices. With geometrically-optimized-pin designs located both upstream and downstream of the channel, a total power dissipation of 1200 W was achieved. The maximum junction temperature was maintained at 100°C and the maximum variation among dies was controlled within 1°C. The results from this study indicated that the device junction temperatures were not only reduced in magnitude but were equalized as well. In addition, the maximum power dissipation of the module was enhanced. Comparison with other direct- (pool boiling) and indirect- (cold plate) liquid cooling techniques was also discussed     

Integrated single and two-phase micro heat sinks under IGBT chips

Experiments have been performed to assess the feasibility of single and two-phase micro heat exchangers applied to the cooling of insulated gate bipolar transistor (IGBT) power components. After a brief recall of the principal characteristics of such heat exchangers, prototypes that have been built and tested are described. Then, the experimental measurements are compared to the predictions of the thermal and hydraulic performance with water and the inert fluorocarbon liquid (FC72) as coolant fluids     

基于IGBT模块饱和压降温度特性的结温探测研究

实验室条件下,IGBT模块的结温探测是瞬态热阻抗测试的关键。首先分别在热稳态和热瞬态下证明了饱和压降温度特性只与芯片有关,然后建立了IGBT模块结温探测模型,利用饱和压降值和集电极电流值来计算结温值,并将用模型计算出的结温与光纤实测的结温相比较,吻合性良好,证明了模型计算法能够准确探测结温。该方法可以用于恒流加热过程中瞬态热阻抗的测量,比起热敏参数法中冷却过程测量瞬态热阻抗相比,更具有实际意义。     

IGBT模块焊料老化状态监测方法及热网络模型优化

焊料老化是绝缘栅双极型晶体管(IGBT)模块内部传热能力退化和结温估计偏离的主要诱因。利用壳温与焊料老化程度间的对应规律构建了两者的量化关系,提出了焊料老化状态监测方法。采用与功率损耗无关的参数对恶化Cauer热网络(CTN)有效传热面积进行表征,提出了焊料裂纹诱导的结温低估补偿机制;考虑温度相关的异质材料导热系数及比热容参量,抑制了温升引起的材料传热特性退化影响。在此基础上,通过对传统CTN模型的优化,克服了传热路径无法自适应配置问题。仿真结果表明,所提方法可有效减小传热退化对模型计算结果的影响,实现对IGBT模块热行为动态变化的精确模拟,且结温估计结果相较传统CTN模型的更为精确。     

高空飞行器供油驱动系统IGBT模块结温特性研究

对高空飞行器供油驱动系统在特定负载状态下的IGBT模块结温特性进行研究。高空飞行器对供油驱动系统的高功率密度要求高及环境散热条件差的状况,使得其关键部件IGBT模块在功率裕量与结温控制方面更为严格。根据负载特性精确计算结温,对于在特定散热条件下系统的可靠运行非常重要。运用非稳态导热的Foster集总参数法,分析IGBT模块点热源特性及其他热源对计算影响,建立一种含校正系数的热网络模型,并在短时脉冲过载及输出低频两种特有状态下,对IGBT模块的结温特性进行分析。通过对高空飞行器飞行过程中IGBT模块结温特性的计算,结合仿真软件Semisel的对比分析,验证了建模和分析本文所提方法的有效性。     

Comparison of the electro-thermal constraints on SiC MOSFET and Si IGBT power modules in photovoltaic DC/AC inverters

This article presents a comparative study between SiC MOSFETs and Si IGBTs regarding changes in their junction temperature in a PV inverter application. The estimation of these variations is made by introducing the current mission profiles extracted from a photovoltaic plant over one year into a calculation tool. The latter is based on a losses model and a thermal model including a coupling between them. The calculation of the losses in SiC MOSFETs in the 3rd quadrant is detailed. The results are the mission profiles of the junction temperature of semiconductors, which allow for determining and comparing the thermal constraints in SiC MOSFET and Si IGBT power modules.     

Static and dynamic finite element modelling of thermal fatigue effects in insulated gate bipolar transistor modules

The aim of this paper is to demonstrate the use of finite element techniques for modelling thermal fatigue effects in solder layers of insulated gate bipolar transistor (IGBT) – modules used in traction applications. The three-dimensional models presented predict how progressive solder fatigue, affects the static and dynamic thermal performance of such devices.Specifically, in this paper, the analysis of an 800 A–1800 V IGBT module is performed. In the first part, the static analysis is realised. The parameters assessed are thermal resistance, maximum junction temperature and heat flux distribution through the different layers comprising the module construction. In the second part of the paper, transient analyses are performed in order to study the dynamic thermal behaviour of the module. The constructed thermal impedance curves allow for calculation of the device temperature variations with time. Stress parameters, such as temperature excursion and maximal temperature at chip and solder interfaces, are determined. Calibration of all simulation models is achieved by comparison with alternative theoretical calculations and manufacturers’ measured values provided in the data sheet book.     

IGBT焊料层中的空洞对器件热可靠性的影响

根据IGBT的基本结构和工作原理,建立了一种新的IGBT三维热模型。该模型考虑了Si材料的温度特性,模拟研究了焊料层空洞对器件热稳定性的影响。研究表明焊料层空洞对IGBT器件的热稳定性有很大的影响。实测结果、超声波显微镜以及红外显微镜的扫描图片证实模拟结果。该研究结果对于改进IGBT器件的可靠性有一定意义,值得器件应用工程师、设计及工艺工程师参考。     

Thermal parameter estimation using recursive identification

A novel method that converts a semiconductor transient thermal impedance curve (TTIC) into an equivalent thermal RC network model is presented. Thermal resistance (R) and thermal capacitance (C) parameters of the model are identified using manufacturer's data and offline recursive least square techniques. Relevant estimation theory concepts and the formulation of an appropriate model for the identification process are given. Model synthesis is illustrated using an isolated base power transistor module. The application of time decoupled theory for high order thermal models is outlined. Simulation of junction temperature responses using model and manufacturer TTICs are compared. Estimated parameter validity is further confirmed by parameter calculation obtained from module physical dimensions     

Thermal lifetime estimation method of IGBT module considering solder fatigue damage feedback loop

The accurate thermal damage assessment and lifetime estimation are essential for ensuring the safety and reliability of semiconductor power devices. This study presents a thermal fatigue feedback loop method for evaluating the lifetime of an Insulated Gate Bipolar Transistor (IGBT) module considering the accumulated effect of solder layer fatigue. First, a three-dimension (3D) finite element method (FEM) model for an IGBT module is established and, combined with the accelerated aging experiments resulting in that the accumulated thermal resistance increment could not be neglected when conducting thermal network modeling and lifetime consumption assessment. Then, the Cauer thermal network is improved for establishing the fatigue feedback loop model, which takes the influence of accumulated solder layer fatigue into account when estimating the power module lifetime. The effectively of this method is validated by experimental results and resisting models. Finally, the lifetime consumption of the IGBT module utilized in a practical wind energy conversion system, is investigated by using the multi-scale feedback loop method. It is found that the Miner model would exaggerate the lifetime of power modules and, the lifetime consumption under low frequency thermal loading is faster than that under a fundamental frequency condition.     

Degradation behavior of 600 V–200 A IGBT modules under power cycling and high temperature environment conditions

One challenge for automotive hybrid traction application is the use of high power IGBT modules that can withstand high ambient temperatures, from 90 °C to 120 °C, for reliability purpose. The paper presents ageing tests of 600 V–200 A IGBT modules subjected to power cycling with 60 °C junction temperature swings at 90 °C ambient temperature. Failure modes are described and obtained results on the module characteristics are detailed. Especially, physical degradations are described not only at the package level, like solder attach delaminations, but also at the chip level, with a shift on electrical characteristics such as threshold voltage. Finally, numerical investigations are performed in order to assess the thermal and thermo-mechanical constraints on silicon dies during power cycling and also to estimate the effect of ambient temperature on the mechanical stresses.     

Junction temperature management of IGBT module in power electronic converters

IGBT power module is the key component of the power electronic converter, but it has the lowest reliability. The junction temperature is the crucial factor which affects power module’s reliability. To some extent, the power handling capability of the converter depends on the thermal stress of the power module. Thermal management is an effective method to improve the reliability of power device, as well as enhance the power capability. For this purpose, this paper introduces the reliability design to the power converter’s traditional compensation controller design for the first time. A new concept of generalized dual-loop controller, which includes temperature control loop and electric power control loop, is proposed. The reliability and stability of the system are both considered, with the help of the hybrid controller, the power converter can operate steadily with higher reliability. The novelty of this paper is to improve the thermal control method of carrier frequency adjustment through experimental implementation during the full life cycle of the converter. The target is to control the temperature variation to be almost a constant value as well as extend the lifetime of the converter. IR sensor is used to measure the chip temperature of the unpackaged IGBT module. The temperature variation and the average temperature are all considered in thermal management, from the reliability improvement point of view. At last, the idea is digital implemented based on a varying load of power inverter system with real-time measurement of the chip’s surface temperature.     

Lifetime estimation of IGBT modules for MMC-HVDC application

Modular multilevel converters (MMCs) usually work in harsh operating environments due to their compact layouts and adverse mission profiles, which accelerate the thermomechanical fatigue process in insulated-gate bipolar transistor modules (IGBTs). Accurate lifetime estimation is desired to conduct reliability prediction and develop maintenance policies. This paper presents an analytical approach to estimating the lifetimes of IGBTs for MMC-HVDC application based on the thermal cycles, which are influenced by the transmission power profile and ambient temperature profile. The structure and operating principle of MMCs are studied to develop an analytical model for computing the IGBT power loss. A thermal equivalent network in the form of a Foster model is adopted to link the power losses and junction temperature. Next, an RC equivalent circuit analytical method for characterizing the fundamental-frequency thermal cycles, developed using electrothermal analogy theory, is proposed. The rainflow counting algorithm is applied to extract the low-frequency thermal cycles from the annual junction temperature data computed at every minute. The Bayerer model is employed to predict the IGBTs lifetime. Finally, the lifetime distribution, mission profiles and comparison of different IGBTs are analyzed via case studies.