Philip A. Mawby

An Industry-Based Survey of Reliability in Power Electronic Converters

A questionnaire survey was carried out to determine the industrial requirements and expectations of reliability in power electronic converters. The survey was subjective and conducted with a number of high-profile semiconductor manufacturers, integrators, and users in the aerospace, automation, motor drive, utility power, and other industry sectors. According to the survey, power semiconductor devices ranked the most fragile components. It was concluded that main stresses were from the environment, transients, and heavy loads, which should be considered during power electronic system design and normal operation. This paper has also highlighted that there is a significant need identified by the responders for better reliability-monitoring methods and indicators.

Condition Monitoring for Device Reliability in Power Electronic Converters: A Review

Condition monitoring (CM) has already been proven to be a cost effective means of enhancing reliability and improving customer service in power equipment, such as transformers and rotating electrical machinery. CM for power semiconductor devices in power electronic converters is at a more embryonic stage; however, as progress is made in understanding semiconductor device failure modes, appropriate sensor technologies, and signal processing techniques, this situation will rapidly improve. This technical review is carried out with the aim of describing the current state of the art in CM research for power electronics. Reliability models for power electronics, including dominant failure mechanisms of devices are described first. This is followed by a description of recently proposed CM techniques. The benefits and limitations of these techniques are then discussed. It is intended that this review will provide the basis for future developments in power electronics CM.

A Lifetime Estimation Technique for Voltage Source Inverters

This paper presents a method to estimate the inverter lifetime so that we can predict a failure prior to it actually happening. The key contribution of this study is to link the physics of the power devices to a large scale system simulation within a reasonable framework of time. By configuring this technique to a real system, it can be used as a converter design tool or online lifetime estimation tool. In this paper, the presented method is applied to the grid side inverter to show its validity. A power cycling test is designed to gather the lifetime data of a selected insulated gate bipolar transistor (IGBT) module (SKM50GB123D). Die-attach solder fatigue is found out to be the dominant failure mode of this IGBT module under the designed accelerated tests. Furthermore, the crack initiation is found to be highly stress dependent while the crack propagation is almost independent with stress level. Two different damage accumulation methods are used and the estimation results are compared.

Exploration of Power Device Reliability using Compact Device Models and Fast Electro-Thermal Simulation

This paper presents the application of compact insulated gate bipolar transistor and p-i-n diode models, including features such as local lifetime control and field-stop technology, to the full electrothermal system simulation of a hybrid electric vehicle converter using a lookup table of device losses. The vehicle converter is simulated with an urban driving cycle (the federal urban driving schedule), which is used to generate transient device temperature profiles. A methodology is also described to explore the converter reliability using the temperature profile, with rainflow cycle counting techniques from material fatigue analysis. The effects of ambient temperature, driving style, and converter design on converter reliability are also investigated.

An industry-based survey of reliability in power electronic converters

A questionnaire survey was carried out to determine the industrial requirements and expectations of reliability in power electronic converters. According to the survey, power semiconductor devices ranked the most fragile components. It was concluded that main stresses were from the environment, transients and heavy loads, which should be considered during power electronic system design and normal operation. Further analyses suggest that power device reliability is a key issue and power electronic converter design is correlated with failure costs.

Investigation Into IGBT dV/dt During Turn-Off and Its Temperature Dependence

In many power converter applications, particularly those with high variable loads, such as traction and wind power, condition monitoring of the power semiconductor devices in the converter is considered desirable. Monitoring the device junction temperature in such converters is an essential part of this process. In this paper, a method for measuring the insulated gate bipolar transistor (IGBT) junction temperature using the collector voltage dV/dt at turn-OFF is outlined. A theoretical closed-form expression for the dV/dt at turn-OFF is derived, closely agreeing with experimental measurements. The role of dV/dt in dynamic avalanche in high-voltage IGBTs is also discussed. Finally, the implications of the temperature dependence of the dV/dt are discussed, including implementation of such a temperature measurement technique.

Monitoring Solder Fatigue in a Power Module Using Case-Above-Ambient Temperature Rise

Condition monitoring is needed in power electronic systems as a cost-effective means of improving reliability. Packaging-related solder fatigue has been identified as one of the main root causes of power electronic module failures. This paper presents a method to monitor solder fatigue inside a module by identifying the increase of internal thermal resistance due to that solder fatigue, taking account of the masking effect of the variable operating point. It is assumed that the total loss in the module increases as junction temperature rises, causing an increase in case-above-ambient temperature rise, which can be measured. A dynamic thermal model of the heat sink is utilized to estimate the power loss from temperature measurements, while a device power loss model is developed to estimate the internal thermal resistance by considering the converter electrical loading. Experiment and simulation are used to demonstrate the concept and verify the method.

Condition Monitoring Power Module Solder Fatigue Using Inverter Harmonic Identification

Condition monitoring power semiconductor devices can inform converter maintenance and reduce damage. This paper presents a method to monitor solder fatigue in a voltage source inverter insulated gate bipolar transistor power module by detecting the change of an inverter output harmonic. It is shown that low-order harmonics, caused by nonideal switching, are affected by the device junction temperature, which in turn depends upon module solder condition. To improve the detection accuracy of the phenomenon, the inverter controller is set to cause harmonic resonance at the target harmonic frequency. The would-be resonance is suppressed by an outer control loop where the control action can be used as the condition monitoring signal. Simulation and experiment are presented to validate the method and evaluate its performance in operation.

A Fast Loss and Temperature Simulation Method for Power Converters, Part I: Electrothermal Modeling and Validation

Simulation of power converters has traditionally been carried out using simplified models to shorten simulation time. This will compromise the accuracy of the results. A proposed fast simulation method for simulating converter losses and device temperatures over long mission profiles (load cycles) is described in this paper. It utilizes accurate physics-based models for the device losses, and is validated with experimentally obtained results.

A Fast Loss and Temperature Simulation Method for Power Converters, Part II: 3-D Thermal Model of Power Module

This paper describes the development and implementation of an analytical 3-D thermal model for fast and accurate thermal simulation of power device modules in electrothermal converter simulation. A Fourier-based solution is used to solve the 3-D heat equation. The solution can describe the variation of temperature through the whole inverter power module structure as a function of time. The model can simulate thermal interactions resulting from multiple heat sources. The thermal model is extremely fast to simulate compared to finite-element (FEM) approaches. The new model has been implemented in MATLAB/Simulink in order to cosimulate with the converter model which is in the same form. The model has been validated against the computational fluid dynamics (CFD) software package FLOTHERM and shows good agreement. The required aspects of 3-D heat diffusion are captured successfully by the Fourier-based model.