Reliability Of Power Electronics Research Articles

Air Cooling of Power Electronics Through Vertically Enhanced Manifold Microchannel Systems (VEMMS)

Abstract To improve the reliability and efficiency of power electronics, their thermal management must be further enhanced. Next-generation electronics systems are predicted to dissipate more heat as die size shrinks and power levels increase. Traditional air-cooling approaches usually provide insufficient performance or require heavy and bulky heat sinks to achieve adequate thermal management. To address this problem, a novel air cooled vertically enhanced manifold microchannel system (VEMMS) was developed. While minimizing the footprint required on the printed circuit board, the system offers efficient thermal management in a conformal scheme that accommodates the associated power electronics and their electrical connections. This work describes the manufacturing process of the air-cooled VEMMS heat sink and its experimental characterization and thermo-fluidic performance. Good agreement was obtained between the test results and numerical predictions. Using air at ambient conditions, thermal resistance of 2.6 K/W was achieved with a single-sided cooling architecture with a <1.5 cm2 footprint and <2 cm3 total heat sink volume. A full-bridge electrical power density of ∼84 kWe/L and overall direct current (DC–DC) converter power density of ∼20 kWe/L were achieved at reasonable flow rates and pressure drops using commercially available miniature electric fans.

Overview of Control Algorithm Verification Methods in Power Electronics Systems

The paper presents the existing verification methods for control algorithms in power electronics systems, including the application of model checking techniques. In the industry, the most frequently used verification methods are simulations and experiments; however, they have to be performed manually and do not give a 100% confidence that the system will operate correctly in all situations. Here we show the recent advancements in verification and performance assessment of power electronics systems with the usage of formal methods. Symbolic model checking can be used to achieve a guarantee that the system satisfies user-defined requirements, while statistical model checking combines simulation and statistical methods to gain statistically valid results that predict the behavior with high confidence. Both methods can be applied automatically before physical realization of the power electronics systems, so that any errors, incorrect assumptions or unforeseen situations are detected as early as possible. An additional functionality of verification with the use of formal methods is to check the converter operation in terms of reliability in various system operating conditions. It is possible to verify the distribution and uniformity of occurrence in time of the number of transistor switching, transistor conduction times for various current levels, etc. The information obtained in this way can be used to optimize control algorithms in terms of reliability in power electronics. The article provides an overview of various verification methods with an emphasis on statistical model checking. The basic functionalities of the methods, their construction, and their properties are indicated.

A humidity-induced novel failure mechanism in power semiconductor diodes

Power electronics reliability in a high humidity environment has recently been considered an important aspect of power converters. In this article boost stage power semiconductor modules from two vendors with varying device technologies were exposed to high humidity, high temperature and high voltage reverse bias direct current (H3TRB-HVDC) test conditions. The exposed modules were monitored with in situ leakage current measurement during the test. The in situ monitoring revealed that all samples from one vendor using a glass passivation technique failed while the samples from the second vendor with a polyimide passivation survived. After the test, electrical breakdown and associated thermal hotspots were consistently observed using lock-in thermography on top of the glass passivation covering the high voltage edge termination structure. It was concluded with microstructural and material analysis that the treelike structures that were observed right beneath the surface of the glass passivation were associated with the failure mechanism. The analysis revealed that the formed structures were amorphous and could not be caused by the electrochemical migration of metallic species. The failures were caused by the localised partial dissolution of lead from the glass passivation. The failure mechanism seems to be associated with water treeing.

Advancing Power Electronics Reliability [White Hot

In the last few years I have noticed more and more papers addressing power electronics and reliability. These papers are, as I have noticed, all coming from academia. Now there is even a university re - search center focused on power electronics reliability — the Center Of Reliable Power Electronics (CORPE) at the University of Aalborg in Denmark. I admit that I have been a bit put off by this. As someone who has spent his entire career in industry, my reaction has been "What do these university folks think they know about reliability that industry has not already solved?" The author concludes that he is now glad to see university research on power electronics reliability even though I suspect industry is actually way ahead but unable to publish their results due to business confidentiality needs. Anything that can help move us ahead is welcome. As power electronics becomes more and more central to our lives, reliability, service life, and availability will become increasingly important. While we can never achieve perfect reliability and availability, we can strive to make our semiconductor based power electronics as reliable and long lived as the copper and iron based electronics they will be replacing.

Reliability of Silicon Battery Technology and Power Electronics Based Energy Conversion

Continuous improvements in battery technology has paved the way for adoption in growing number of applications. However, the state-of-the-art graphite anodes remain sensitive to heat dissipation during fast charging or short circuits, and possibly causing inflammation of the battery. This is a limitation for safety critical applications and prevents ultra-high charging rates. In addition, power electronics is required for preventing hazardous and inefficient operating conditions, maximizing, for example, the lifetime of the battery system. Batteries with silicon anodes overcome the limitations of today?s battery technology and enable charging rates of multiple Cs, while operating up to 100 °C and being non-flammable. Nevertheless, this does not reduce requirements for the battery management system (BMS) to control the performance of the battery. The BMS needs to maximize the charging rate, limit mechanical stress of the battery electrodes, which is associated to high charging rates. Thus, obtaining high charging efficiency, while equalizing useful remaining lifetime for all battery stacks. This manuscript is a conceptional review of how silicon anodes could be used in future Lithium-ion (Li-ion) or Li sulfur batteries providing high energy densities, offering the possibility to charge batteries with higher current densities and faster charging times. BMS and the required power electronic converters for integrating battery storage are introduced and their application for the next generation of ultra-fast charging battery system is presented.

Polymer Dielectrics with Simultaneous Ultrahigh Energy Density and Low Loss.

Polymer dielectrics are highly desirable in capacitor applications due to their low cost, high breakdown strength, and unique self-healing capability. However, existing polymer dielectrics suffer from either a low energy density or a high dielectric loss, thereby hindering the development of compact, efficient, and reliable power electronics. Here, a novel type of polymer dielectrics simultaneously exhibiting an extraordinarily high recoverable energy density of 35 Jcm-3 and a low dielectric loss is reported. It is synthesized by grafting zwitterions onto the short side chains of a poly(4-methyl-1-pentene) (PMP)-based copolymer, which increases its dielectric constant from ≈2.2 to ≈5.2 and significantly enhances its breakdown strength from ≈700 MVm-1 to ≈1300 MVm-1 while maintaining its low dielectric loss of <0.002 and high charge-discharge efficiency of >90%. Based on a combination of the phase-field method description of mesoscale structures, Maxwell equations, and theoretical analysis, it is demonstrated that the outstanding combination of high energy density and low dielectric loss of zwitterions-grafted copolymers is attributed to the covalent-bonding restricted ion polarization and the strong charge trapping by the zwitterions. This work represents a new strategy in polymer dielectrics for achieving simultaneous high energy density and low dielectric loss.

Comparison of Fault Tolerant Capability of Three-phase Induction Motor Drives for Automotive Applications

With the increase proliferation of electric vehicles in the world, the demand for more reliable power electronics drive train is also on the rise. While theoretically the use of multiphase (more than three-phase) motors can increase the reliability of electrical drive train for EV, they are generally not commercially ready and available in the market. Hence, three-phase drive train are still the main stream in current EV technology and the fault-tolerant control of these motor drives remain an interesting and important topic. In this presentation, the existing fault tolerant three-phase motor drive topologies and control methods are reviewed. In particular, the post-fault controls of three-phase motor using 4 legs inverters are discussed and the opportunity for voltage utilization improvement with this configuration is demonstrated.

Modular Heat Sinks for Enhanced Thermal Management of Electronics

Abstract Power electronics are vital for the generation, conversion, transmission, and distribution of electrical energy. Improving the efficiency, power density, and reliability of power electronics is an important challenge that can be addressed with electrothermal codesign and optimization. Current thermal management approaches utilize metallic heat sinks (HSs), resulting in parasitic load generation due to different potentials between electronic components on the printed circuit board (PCB). To enable electrical isolation, a thermal interface material (TIM) or gap pad is placed between the PCB and HS, resulting in poor heat transfer. Here, we develop an approach to eliminate TIMs and gap pads through modularization of metallic HSs. The use of smaller modular heat sinks (MHSs) strategically placed on high power dissipation areas of the PCB enables elimination of electrical potential difference, and removal of electrical isolation materials, resulting in better cooling performance due to direct contact between devices and the HS. By studying a gallium nitride (GaN) 2 kW DC–DC power converter as a test platform for electrothermal codesign using the modular approach, and benchmarking performance with a commercial off-the-shelf HS design, we showed identical power dissipation rates with a 54% reduction in HS volume and a 8 °C reduction in maximum GaN device temperature. In addition to thermal performance improvement, the MHS design showed a 73% increase in specific power density with a 22% increase in volumetric power density.

Power Electronics Reliability: State of the Art and Outlook

This article aims to provide an update of the reliability aspects of research on power electronic components and hardware systems. It introduces the latest advances in the understanding of failure mechanisms, testing methods, accumulated damage modeling, and mission-profile-based reliability prediction. Component-level examples (e.g., Si IGBT modules, SiC MOSFETs, GaN devices, capacitors, and magnetic components) are used for illustration purposes in addition to system-level studies. The limitations and associated open questions are discussed to identify future research opportunities in power electronics reliability.

Reliability of Power Electronic Systems for EV/HEV Applications

The electrification of the transportation sector is moving on at a fast pace. All car manufacturers have strong programs to electrify their car fleet to fulfill the demands of society and customers by offering carbon-neutral technologies to bring goods and persons from one location to another. Power electronics technology is, in this evolution, essential and also in a rapid development technology-wise. Some of the introduced technologies are quite mature, and the systems designed must have high reliability as they can be quite complicated from an electrical perspective. Therefore, this article focuses on the reliability of the used power electronic systems applied in electric vehicles (EVs) and hybrid EVs (HEVs). It introduces the reliability requirements and challenges given for the power electronics applied in EV/HEV applications. Then, the advances in power electronic components to address the reliability challenges are introduced as they individually contribute to the overall system reliability. The reliability-oriented design methodology is also discussed, including two examples: an EV onboard charger and the drive train inverter. Finally, an outlook in terms of research opportunities in power electronics reliability related to EV/HEVs is provided. It can be concluded that many topics are already well handled in terms of reliability, but issues related to complete new technology introduction are important to keep the focus on.

Nondestructive Acoustic Testing of Ceramic Capacitors Using One-Class Support Vector Machine With Automated Hyperparameter Selection

The energy transition and electrification across many industries place increasingly more weight on the reliability of power electronics. A significant fraction of breakdowns in electronic devices result from capacitor failures. Multilayer ceramic capacitors, the most common capacitor type, are especially prone to mechanical damage, for instance, during the assembly of a printed circuit board. Such damage may dramatically shorten the life span of the component, eventually resulting in failure of the entire electronic device. Unfortunately, current electrical production line testing methods are often unable to reveal these types of damage. While recent studies have shown that acoustic measurements can provide information about the structural condition of a capacitor, reliable detection of damage from acoustic signals remains difficult. Although supervised machine learning classifiers have been proposed as a solution, they require a large training data set containing manually inspected damaged and intact capacitor samples. In this work, acoustic identification of damaged capacitors is demonstrated without a manually labeled data set. Accurate and robust classification is achieved by using a one-class support vector machine, a machine learning model trained solely on intact capacitors. Furthermore, a new algorithm for optimizing the classification performance of the model is presented. By the proposed approach, acoustic testing can be generalized to various capacitor sizes, making it a potential tool for production line testing.

Impacts of Wide Band Gap Power Electronics on Photovoltaic System Design

The emergence of electrical conversion technologies utilizing silicon carbide and gallium nitride switches and diodes will enable the development of a whole new class of efficient, lightweight, and reliable power electronics based on wide band gap semiconductors for photovoltaic (PV) systems. This article presents the results of a study to model the value proposition of these devices when they are used in dc–ac inverters, medium voltage dc–dc converters, as well as solid state breakers and transformers. The conclusions illustrate the beneficial impact on energy generation, operation and maintenance, plant architecture simplification, and associated reduction in capital cost and levelized cost of electricity that these new solid state devices will enable for the future PV system developer.

Fuzzy logic based open-circuit fault diagnosis in IGBT for CMLI fed PMSM drive

For the objective of enhancing the reliability in power electronics, a fault diagnosis technique has been reported for a three-phase cascaded multilevel inverter (CMLI). This paper presents a fuzzy based fault diagnosis technique based on the average current Parks vector technique for the three-phase CMLI fed permanent-magnet synchronous motor (PMSM) drive. The three-phase normalized currents divided into positive (Eq+) and negative groups (Eq−). Then the average current Park's vector technique is used to measure the fault symptom variables by using the phase current information. The proposed fault diagnosis technique can detect and locate the single or multiple open-circuit faults, and also the intermittent faults in IGBT's at any condition (ex., change in mechanical speed, change in load torque and change in system parameters), which can improve the reliability of the motor drive system. The effectiveness of the proposed method is validated by the simulation and experimental results.

Design and application of electrical power backup and battery charge with a new voltage controller approach for military vehicles

Thanks to the increased reliability and performance of power electronics, their use in military areas is very common. Through the developing technology, military land vehicles can have many equipment rather than just a replenishment and military transport duty. For safety and confidentiality, it is not possible to supply the energy of these equipments with the 28 V lead-acid batteries on the military vehicle during the silent watch (when the vehicle is stationary). In this study, electrical power backup and battery charge circuit has been designed and applied for military land vehicles for this purpose. When providing power to devices and charging the battery in the vehicle, it is important to ensure that the circuit is stable, robust and accordance with military standards. The output voltage of this power circuit is controlled by the use of robust control and nonlinear voltage control methods and this method brings innovation in this field. In this study, voltage surges in power circuit output due to sudden load changes are minimized by the proposed voltage control method. Thus, the conformity of the power circuit to the MIL-STD-1275-E voltage surges standard, which is one of the military standards, is provided by experimental results.

Reliability assessment of the single motor drive of the belt conveyor on Drmno open-pit mine

Reliable operation of controlled electrical drives is one of the standard requirements set as a part of tender conditions and they must be met when designing technological systems in mining industry. Elements of power electronics play a crucial role in controlled electrical drives. In this paper reliability calculations, of one controlled drive with frequency converter and high-power cage induction motor, are shown. This setup is part of the multi-motor conveyor belt station in open-pit coal mine. Available data on reliability of individual components, automation, power electronics and mechanics have been provided by manufacturer or defined by appropriate standards. Possibilities for optimizing the reliability of one single drive have been analyzed depending on frequency converter and drive load.

Liquid-Cooled Aluminum Silicon Carbide Heat Sinks for Reliable Power Electronics Packages

With recent advances in the state-of-the-art of power electronic devices, packaging has become one of the critical factors limiting the performance and durability of power electronics. To this end, this study investigates the feasibility of a novel integrated package assembly, which consists of copper circuit layer on an aluminum nitride (AlN) dielectric layer that is bonded to an aluminum silicon carbide (AlSiC) substrate. The entire assembly possesses a low coefficient of thermal expansion (CTE) mismatch which aids in the thermal cycling reliability of the structure. The new assembly can serve as a replacement for the conventionally used direct bonded copper (DBC)—Cu base plate—Al heat sink assembly. While improvements in thermal cycling stability of more than a factor of 18 has been demonstrated, the use of AlSiC can result in increased thermal resistance when compared to thick copper heat spreaders. To address this issue, we demonstrate that the integration of single-phase liquid cooling in the AlSiC layer can result in improved thermal performance, matching that of copper heat spreading layers. This is aided by the use of heat transfer enhancement features built into the AlSiC layer. It is found that, for a given pumping power and through analytical optimization of geometries, microchannels, pin fins, and jets can be designed to yield a heat transfer coefficients (HTCs) of up to 65,000 W m−2 K−1, which can result in competitive device temperatures as Cu-baseplate designs, but with added reliability.

Failure Analysis of the dc-dc Converter: A Comprehensive Survey of Faults and Solutions for Improving Reliability

In many industrial applications, power interruption is not tolerated, and a highly reliable power electronics system is required. In fact, a failure on the power converter penalizes not only the maintenance cost (to repair or change the converter), but also the operational cost, because the service is interrupted. Thus, this article investigates the failure in dc-dc converters, with the aim to identify the most vulnerable devices and discuss solutions for improving the converter's availability.

Shear Strength and Thermomechanical Reliability of Sintered Ag Joints Containing low CTE Non-metal Additives for Die Attach

Abstract Ag sintering has been paid attention as an alternative to soldering in die attach for decades, especially for high temperature power electronics packages because of its high melting temperature, highly thermal and electrical conductivity of the sintered silver joints, and low process temperature less than 275°C. The coefficient of thermal expansion (CTE) of silver (19.1ppm/°C), however, is much higher than the silicon die (2.6ppm/°C) and the commonly used alumina substrate (7.2ppm/°C). CTE mismatch of the different materials in the various components in a power electronics package lead to the delamination at the interface between interconnection layer and chips or substrate, and/or cracking of the interconnection layer is one of the mostly common causes of failure of power electronics device during thermal cycling or high temperature operation. In recent years we have been developing a series of silver sinter pastes containing low CTE non-metal particles to reduce or adjust CTE of the sintered joints so as to extend the lifetime and reliability of power electronics device in high temperature applications. In the present paper, we will report a new set of silver sinter pastes containing micro scale non-metal particles, a sintering process, microstructural morphologies, thermo-mechanical reliability of the sintered joint and effect of the contents of non-metal particles on shear strength of the sintered silver joints bonding an Ag silicon die on Ni/Au DBC substrates. Shear tests on the sintered joints with and/or without the low CTE non-metal additives have been conducted at room temperature, 200, 250, and 300°C. Thermo-mechanical reliability of the sintered joints was evaluated by thermal cycling, thermal shock, high temperature storage tests (HTS), respectively. X-ray inspection and scanning electronic microscopy (SEM) were used to characterize void, crack and microstructure morphologies of the sintered joints with and/or without the additives.

Cyclic robustness of heavy wire bonds: Al, AlMg, Cu and CucorAl

Development of advanced electronic packages can be drastically affected by implementation of new materials. The ever increasing demands for high performance and reliable power electronics, raise the need for rapid robustness evaluation of interconnects. In this study the lifetime of heavy wire bonded interconnects, fabricated with different wire material types Al, AlMg, Cu and Al coated Cu (CucorAl) bonded onto direct copper bonded ceramic substrates was investigated. The tests were performed using an accelerated mechanical fatigue testing system, which allows to determine the lifetime of the interconnects with regard to wire bond lift-off failure in a short period of time. Thus, the influence of ultrasonic power variation and the impact of aging on the performance of wire bonds with different material combinations was studied. Cu wire bonds showed clearly the best fatigue performance as well as static shear strength followed by AlMg and Al bonds. Increasing the ultrasonic power results in a higher fatigue resistance of CucorAl in comparison to pure Al wires. In certain cases, the results of the fatigue experiments and static shear tests were found to be contradictory. The presented results suggest that accelerated mechanical fatigue testing can be used as an additional fast method for qualification of interconnects and assessment of the influence of wire material, bond parameter and aging.

Junction Temperature Control for More Reliable Power Electronics

The thermal stress of power electronic components is one of the most important causes of their failure. Proper thermal management plays an important role for more reliable and cost-effective energy conversion. As one of the most vulnerable and expensive components, power semiconductor components are the focus of this paper. Possible approaches to control the semiconductor junction temperature are discussed in this paper, along with the implementation in several emerging applications. The modification of the control variables at different levels (modulation, control, and system) to alter the loss generation or distribution is analyzed. Some of the control solutions presented in the literature, which showed experimentally that the thermal stress can be effectively reduced, are reviewed in detail. These results are often mission-profile dependent and the controller needs to be tuned to reach the desired cost-benefit tradeoff. This paper analyzes also the many open questions of this research area. Among them, it is worth highlighting that a verification of the actual lifetime extension is still missing.