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.     

Lifetime extrapolation for IGBT modules under realistic operation conditions

In this paper a systematic approach is presented for extrapolating the lifetime due to bond wire lift-off in IGBT modules submitted to cyclic loading. Application profiles of the device are considered, as they are usually encountered in real current converters for railway traction systems. The proposed lifetime prediction scheme is based on the principle of the linear accumulation of the fatigue damage and takes into account the redundancy of the bond wires.     

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.     

一种考虑风电随机性的电力系统电压运行区间计算方法

针对风电场出力的波动性使风电接入地区电网的随机性增强,并网点电压波动的频率和幅度变大,造成的电压稳定问题,以实际风电场的运行数据为基础,通过统计学方法分析风电场输出功率的波动特性,得到风功率波动率在不同时间尺度内的分布参数以及95%置信区间,并分析不同风电水平下的电压波动特性,在此基础上提出使用t location-scale分布函数对电压波动率的概率分布进行拟合,进而得出一种基于风功率波动特性以及仿射区间潮流算法的电压运行区间计算方法,通过该方法计算得到的电压运行区间反映了在风功率波动条件下未来一段时间内电力系统电压的运行区间,对风电接入系统的运行、控制及规划工作具有重要的指导意义。     

Envelop tracking based embedded current measurement for monitoring of IGBT and power converter system

Health monitoring of the power conversion system is very important. Therefore, we developed a new method for measuring IGBT currents and reproducing average load current to monitor IGBTs. This method was successfully tested on an experimental setup which showed that the tiny PCB sensors can be integrated into intelligent power modules. We proposed an inexpensive analogue circuit which is suitable for capturing current information from a tiny PCB Rogowski coil. The sensors and corresponding circuit can be embedded into an Intelligent Power Module. The method was named “Envelop tracking” as it simultaneously measures the currents of the high and low side switches of a power converter and reproduces the upper and lower edges of the load current which can be averaged by further digital processing.     

Double-sided cooling for high power IGBT modules using flip chiptechnology

A new technique for the packaging of IGBT modules has been developed. The components are sandwiched between two direct bond copper (DBC) substrates with aluminum nitride. Wire bonds are replaced with flip chip solder bumps, which allows cooling of components on both sides. Microchannel heat sinks are directly integrated in the package to decrease the thermal resistance of the module. Thus, a very compact module with high thermal performance is obtained. A prototype with two insulated gate bipolar transistors (IGBTs) and four diodes associated in parallel was realized and tested. In this paper, the innovative packaging technique is described, and results of thermal tests are presented     

Substrate-to-base solder joint reliability in high power IGBT modules

Acoustic microscope imaging proved to be an excellent tool to detect and quantify solder fatigue of the substrate to base interface of high power IGBT modules. This technique was used to establish the dependence of the thermal cycling capability on the temperature swing of the module base for a A1N/Cu system. Results from temperature cycling tests were combined with results from power cycling tests to predict the solder joint reliability over a wide range of temperature excursions.     

Degradation mapping in high power IGBT modules using four-point probing

An electrical four-point probing approach is used to estimate local degradation in high power insulated gate bipolar transistor modules subjected to power cycling. By measuring electrical parameters of selected units and components the possibility of mapping the degradation is demonstrated. The development of failures is put in accordance with physical phenomena and materials fatigue. These results are directly usable for reliability purposes with a focus on geometry optimization and enhanced lifetime prediction methods.     

Reliability of AlN substrates and their solder joints in IGBT power modules

The reliability of IGBT modules was investigated with respect to the metallized ceramic (substrate) and the solder layer between the substrate and copper baseplate. Thermal cycles were performed between −55°C and +150°C on substrates based on different technologies and from various manufacturers. An incipient delamination of the metallization could be predicted from the mechanical resonance frequency. The warping of the substrates after cycling due to crack propagation and the adhesion of the metallization were determined. Thermal and active-power cycles were performed on 1200 A / 3.3 kV IGBT power modules to investigate the reliability of the solder joint between substrate and baseplate.     

Effects of current density and chip temperature distribution on lifetime of high power IGBT modules in traction working conditions

This paper deals with ageing parameters of high power IGBT modules in traction applications. Using the results of a great number of power cycling tests on 400A modules, it shows that, in addition to the junction temperature excursion, other parameters like the maximal chip temperature and the current density are involved in thermal fatigue failures. Besides, contact temperature measurements achieved on IGBT chip surface in cycling conditions to localise the maximal thermomechanical stress are presented and correlated with modules failure analysis. The role of the current density in the ageing process is finally shown by determining its influence on the temperature gradient on chip surface.     

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.     

Lifetime modeling and simulation of power modules for hybrid electrical/electrical vehicles

In hybrid electrical vehicles (HEV) and electric vehicles (EV) power semiconductors, packaged in a module, are used. Packaging technologies are suffering several wear out mechanisms, that are typically induced by thermal or power cycling. The type of wear out mechanism is affected by the connection technology but also by the load type. In the design of the inverter the mission profile simulation of the power module is an important step to ensure operation of the power module over the complete vehicle lifetime. Influences of application parameters are presented. Physics of failure based FEM simulation can help to develop appropriate lifetime models which are basis for the mission profile simulation. Available power module technology achieves the lifetime requirement for hybrid electric vehicles/electric vehicles, if the described method is applied in the design phase of the inverter.     

Reliability and lifetime evaluation of different wire bonding technologies for high power IGBT modules

IGBT modules for power transmission, industrial and traction applications are operated under severe working conditions and in harsh environments. Therefore, a consequent design, focused on quality, performance and reliability is essential in order to satisfy the high customer requirements. One of the main failure mechanisms encountered in high power IGBT modules subjected to thermal cycles is wire bond lift-off, which is due to the large thermal expansion coefficient mismatch between the aluminum wires and the silicon chips. The paper describes various bonding technologies using different wire materials directly bonded onto chip metallisation as well as the ABB solution where the wire is bonded on a thin molybdenum strain buffer soldered onto the chip. We assess in the present paper the potential of these technologies to enhance module reliability and lifetime through a power cycling test. Failure analysis results are presented and the failure mechanisms related to each technology are explained in detail.     

Efficient application of power modules in energy converter with microprocessor control

At development of energy converters with application of pulse-duration modulation there are problems related to the concordance of levels and shape of pulses, generated by the microcontroller, with control signals at inputs of power transistors. The method this problem solution is considered in the paper.     

Strategy for designing accelerated aging tests to evaluate IGBT power modules lifetime in real operation mode

Accelerated aging tests are widely used in electronics industry to validate the technological choices of packaging, especially when significant lifetime is required. The thermal coefficient of expansion mismatch between the soldered materials results in crack propagation in the solder joints, which irreversibly increases the thermal resistance of the assembly and progressively leads to the failure of the module. Accelerated testing is very expensive and can last a long time, so that such experiments must be optimized. In addition, thermomechanical behavior of the assembly under realistic operating conditions for long times can be studied in shorter times thanks to finite element simulations. Non-linear finite element simulations have been carried out to make a correlation between accelerated aging tests and real operation. Stress-strain history under representative thermal loading has been determined in both cases. The energy dissipated in solder joints has been calculated and has been used as an estimator of the damage in the solder joint. Finally, thermal fatigue experiments with representative samples have allowed validating the previous results. This study is a step toward the understanding of the correlation between accelerated testing and actual operating conditions.     

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.     

Thermal fatigue effects on the temperature distribution inside IGBT modules for zone engine aeronautical applications

This work examines the thermal fatigue effects on the temperature distribution inside IGBT modules for aeronautical applications. Exactly, they are used in a very different application where temperature cycling due to the working environment is the most limiting fact. In this case, it is concluded that solder delamination does not present any restriction to module lifetime at short term (up to 60% of total delaminated area). In addition, it is proposed only determining the delaminated area behind devices, which is the main responsible of the thermal temperature increase.     

Floorplanning for low power IC design considering temperature variations

Non-uniformity in thermal profiles of integrated circuits (ICs) is an issue that threatens their performance and reliability. This paper investigates the correlation between the total power consumption and the temperature variations across a chip. As a result, floorplanning guidelines are proposed that uses the correlation to efficiently optimize the chip's total power and takes into account the thermal uniformity. It is demonstrated that optimizing a floorplan to minimize either the leakage or the peak temperature can lead to a significant increase in the total power consumption. In this paper, the experimental results show that lowering the temperature variations across a chip not only addresses performance degradation and reliability concerns, but also significantly contributes to chip power reduction. In addition, it is found that although uniformity in the thermal profile can be very effective in lowering the total power consumption, the most uniform temperature distribution does not necessarily correspond to the highest power savings. Consequently, for some applications, a 2% deviation from the minimum total power is traded for up to a 25% increase in thermal uniformity. The presented method is implemented for an Alpha 21264 processor running Spec 2000 benchmarks.     

Temperature measurements and thermal modeling of high power IGBT multichip modules for reliability investigations in traction applications

To study the failure mechanisms induced on high power IGBT multichip modules by thermal cycling stress in traction environment, a good knowledge of the temperature distribution and variations on the chips and in the interfaces between the different layers of the packaging is necessary. This paper presents a methodology for contact temperature measurements on chips surface in power cycling conditions and a fast 3D thermal simulation tool for multilayered hybrid or monolithic circuits. The results of static and dynamic thermal simulation of a 1200A–3300V IGBT module are given and compared with the contact temperature measurements results. The investigation has been done within the RAPSDRA (Reliability of Advanced High Power Semiconductor Device for Traction Applications) European project.     

Comparison of temperature limits for Trench silicon IGBT technologies for medium power applications

This work focuses on determining the switching limits in temperature for Reverse Conducting IGBTs and compares them to “conventional” IGBTs based on Trench technologies, all them belonging to 600 V–50 A application scenario. After, their leakage current under blocking state is tested at several working temperatures, in order to study the leakage current that limits the blocking safe operating area with temperature. Next, overcurrent tests have been performed. This investigation deals with understanding the overcurrent induced failures due to thermal effects using short circuit tests adapted to our needs. As a result, we observe that RC-IGBTs integrating a free-wheeling diode show the highest leakage losses in blocking state, whereas it presents the best ruggedness under short circuit tests.