Remaining useful lifetime prediction and extension of Si power devices have been studied extensively. Silicon carbide (SiC) power devices have been developed and commercialized. Specifically, SiC mosfet s have been utilized for the next generation high-voltage, high-power converters with smaller size and higher efficiency, covering various mainstream applications, including photovoltaic systems, electric vehicles, solid-state transformers, and more electric ships and airplanes. However, the SiC-based devices have different failure modes and mechanisms compared with Si counterparts. Therefore, a comprehensive review is critical to develop accurate lifetime prediction and extension strategies for SiC power converter systems. The SiC power device component-level failure modes and mechanisms are first investigated. Different accelerated lifetime tests and component-level lifetime models are then compared. Power converter system-level offline lifetime modeling techniques and software tools are further summarized. Besides, the SiC power converter condition monitoring strategies and health indicators are surveyed. The online measurement challenges are also studied. Furthermore, the system-level lifetime extension strategies are reviewed. By integrating device physics, statistical modeling, reliability engineering, and mechanical engineering with power electronics, this article is intended to provide a comprehensive overview, address existing challenges, and unfold new research opportunities regarding the SiC power converter real-time lifetime prediction and extension.

Overview of Real-Time Lifetime Prediction and Extension for SiC Power Converters

Parallel connection of silicon carbide (SiC) MOSFETs is a cost-effective solution for high-capacity power converters. However, transient imbalance current, during turn- on and - off processes, challenges the safety and stability of parallel SiC MOSFETs. In this paper, considering the impact factors of device parameters, circuit parasitics, and junction temperatures, in-depth mathematical models are created to reveal the electrothermal mechanisms of the imbalance current. Moreover, with the incorporation of a differential mode choke (DMC), an effective approach is proposed to suppress the imbalance current among parallel SiC MOSFETs. Physics concepts, operation principles, and design guidelines of the DMC-based suppression method are fully presented. Besides, to reduce the equivalent leakage inductance and equivalent parallel capacitance of the DMC, winding patterns of the DMC are comparatively studied and optimized to suppress turn- off over-voltage and switching ringing. Concerning the influence of winding patterns, load currents, gate resistances, and junction temperatures, experimental results are comprehensively demonstrated to confirm the validity of theoretical models and the function of the proposed DMC-based suppression method. It is turned out the low-cost DMC is easy to design and utilize without complex feedback circuits or control schemes, which is a cost-effective component to guarantee consistent and synchronous on–off trajectories of parallel SiC MOSFETs.

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Imbalance Current Analysis and Its Suppression Methodology for Parallel SiC MOSFETs with Aid of a Differential Mode Choke

This paper presents the power loss model analysis and efficiency of three-level neutral-point-clamped (3L-NPC) inverter that is widely employed in solar photovoltaic energy conversion system. A silicon carbide (SiC) 3L-NPC inverter is developed in this paper by employing wide bandgap semiconductor power devices, such as SiC MOSFET and SiC diode (SiC D). These devices are used due to their superior characteristics over silicon (Si) semiconductor devices for the reduction of inverter power losses, and as a result, an improving efficiency at the high switching frequency. Accurate and detailed power loss calculation formula and power loss distribution over switching devices of the SiC 3L-NPC inverter are derived according to the modulation technique and inverter operation. The switching energy loss of SiC MOSFET is then measured and determined experimentally via inductive clamp double pulse test (DPT) at the real working condition of the circuit. Afterward, this experimental data is used in the thermal description file of the device’s library of PLECS simulation software to determine the total power loss of SiC 3L-NPC inverter. The developed simulation model replicates the real operating conditions of the 3L-NPC inverter. This method gives results close to the practical test. Finally, the power loss of SiC 3L-NPC inverter is measured and compared with the theoretical results. Furthermore, SiC MOSFET and SiC D are employed to achieve high system efficiency at the high switching frequency. The results verify the features of SiC 3L-NPC inverter, the corresponding modulation technique used and their effects on reducing and improving power loss in solar SiC photovoltaic inverters.

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Power Loss Model and Efficiency Analysis of Three-Phase Inverter Based on SiC MOSFETs for PV Applications

The multichip power module is an irreplaceable component for high-capacity industrial converters. Dynamic current imbalance among parallel chips challenges the electrothermal stability and limits the maximum current rating of the power module. In this paper, general mechanism models are proposed to reveal the layout-dominated dynamic current imbalance in the multichip power module. The influence of the layout on the current sharing is comparatively evaluated by power modules with and without Kelvin connections. Focusing on the dynamic current imbalance, based on a commercial multichip power module, finite-element analysis and equivalent electric circuit are utilized to illustrate the impact of Kelvin connection. General mathematical and graphical models are created to address the current sharing of parallel chips affected by networked parasitic impedances. Based on the fabricated power module prototypes, extensive experiments and detailed analyses are presented concerning the current sharing, transient time, and switching loss. It is demonstrated that the Kelvin connection can elevate switching speed and reduce switching loss of parallel chips, while its functionality to eliminate dynamic current imbalance depends on the parasitic impedances. Some general design guidelines of the multichip power module are presented for current sharing. To achieve satisfactory current sharing, advanced packaging layout by using the optimized chip arrangement and wire interconnection is further needed for the multichip power module.

Layout-Dominated Dynamic Current Imbalance in Multichip Power Module: Mechanism Modeling and Comparative Evaluation

Carrying on SiC devices, the air-cooled inverter of the electric vehicle (EV) can eliminate the traditional complicated liquid-cooling system in order to obtain a light and compact performance of the powertrain, which is considered as the trend of next-generation EV. However, the air-cooled SiC inverter lacks strategic design methodology and heterogeneous integration routine for critical components. In this article, a stepwise design methodology is proposed for the air-cooled SiC inverter in the power module, dc-link capacitor, and heat sink levels. In the power module level, an electrical–thermal–mechanical multiphysics model is proposed. The multidimension stress distribution principles in a six-in-one SiC power module are demonstrated. An improved power module is presented and confirmed by using the observed multiphysics design principles. In the dc-link capacitor level, ripple modeling of the inverter and capacitor are created. Considering the tradeoffs among ripple voltage, ripple current, and cost, optimal strategies to determine the material and minimize the capacitance of the dc-link capacitor are proposed. In the heat sink level, thermal resistance of air-cooled heat sink is modeled. Structure and material properties of the heat sink are optimally designed by using a comprehensive electro-thermal analysis. Based on the optimal design results, the prototypes of the customized SiC power module and heterogeneously integrated air-cooled inverter are fabricated. Experimental results are presented to demonstrate the feasibility of the designed and manufactured air-cooled SiC inverter.

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Stepwise Design Methodology and Heterogeneous Integration Routine of Air-Cooled SiC Inverter for Electric Vehicle

The superior electro-thermal properties of silicon carbide (SiC) power devices permit higher temperature of operation and enable higher power density compared with silicon devices. Nevertheless, the reliability of SiC power modules has been identified as a major area of uncertainty in applications which require high reliability. Traditional power module packaging methods developed for silicon chips have been adopted for SiC and the different thermomechanical properties cause different fatigue stresses on the solder layer of the chip. In this paper, a 2-D finite element model has been developed to evaluate the stress performance and lifetime of the solder layer for Si devices, which has been validated using accelerated power cycling tests on Si IGBTs. The proposed model was extrapolated for SiC devices of the same voltage and current rating using the same solder material and the results show that under the same cyclic power loss profile the induced stress and strain energy in the die attach layer is much higher and concentrates on the die/solder interfacial area for SiC chips. Using the validated stress-based model, the lifetime can be quantified when SiC chips are used. This ability to extrapolate the available power cycling and lifetime data of silicon chips to SiC chips would be a key element for developing reliable packaging methods for SiC devices.

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Failure and Reliability Analysis of a SiC Power Module Based on Stress Comparison to a Si Device

High efficiency, high power density, and high reliability are always the technical trends of converters for renewable energy applications. Silicon carbide (SiC) devices can break through the technical limitations of silicon (Si) devices. Thus, SiC devices are considered as the foundations of next-generation high-performance converters. Aimed at the photovoltaic (PV) power system, this study surveys state-of-the-art of PV inverters. The future requirements of PV inverters on efficiency, power density, reliability, and cost are proposed. The possible benefits and available demonstrations of SiC-based PV inverters are presented. Then, some technical challenges of SiC PV inverters, including switching ringing, cross-talk, short-circuit withstand, gate driver, package, high-capacity module, and thermal interface material, are comprehensively illustrated through experimental results. Available researches on these challenges are overviewed, and some research trends on SiC-based PV inverter are presented. This paper is helpful for the research and development of next-generation SiC-based inverters for renewable energy integration.

Changes and challenges of photovoltaic inverter with silicon carbide device

In renewable energy and grid applications, solder-attached power modules are subject to fatigue stress cycles of low amplitudes, but the devices will be in service for decades. This article aims to understand the slow aging process by focusing on the initial defects and their growth under the stress cycles of concern. A finite-element analysis (FEA) is performed to obtain the thermomechanical stress distribution around the defects, which is combined with the solder material’s property to give a lifetime model. Effort is made to validate the model by power cycling plus microscale computed tomography (CT) scanning. It is found that a void in the solder layer may first transform into a crack on the material boundary, which then grows progressively more rapidly until device failure. A numerical example is shown for evaluating the lifetime of an IGBT power module in a “soft-open-point” (SOP) converter designed for an 11-kV power network.

Long-Term Reliability Evaluation of Power Modules With Low Amplitude Thermomechanical Stresses and Initial Defects

This paper reports a distributed thermal monitoring scheme for power electronic modules (PEMs) in wind turbine converters. The sensing system is based on utilizing electrically non-conductive and electromagnetic interference immune fiber Bragg Grating (FBG) sensing technology embedded in the PEM baseplate. The design and implementation features of the proposed scheme are presented first. The scheme is then applied in a commercial PEM operating within an inverter bridge, equipped also with a conventional distributed thermal monitoring system using a multiple point thermo-couple (TC) sensor suite. A range of tests are performed to evaluate the performance of the FBG distributed thermal monitoring system and correlate it to TC measurements under steady-state and transient operating conditions representative of PEM operation in an actual wind turbine application. It is shown that the proposed FBG monitoring system can offer practical operational improvements in establishment of distributed thermal sensing schemes for wind turbine PEM.

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Distributed Thermal Monitoring of Wind Turbine Power Electronic Modules Using FBG Sensing Technology

Power semiconductor chips are paralleled in modules to increase current rating. Under thermo-mechanical stresses in service, the die-attach solder layers will gradually develop into different levels of degradation. Early fault detection requires to monitor the occurrence of such an uneven degradation pattern. Internal temperature differences only slightly affect the current sharing between chips, and some temperature sensitive electric parameters are considerably weakened at module terminals. This article presents an external heat-flux-based condition monitoring method, implemented in a two-stage neural network. The first stage consists of a set of subnetworks to represent the mapping between the electrical operating point of the module and its external temperature distribution, for a range of solder degradation patterns and severities. The respective levels of matching are then extracted and applied to the second stage to diagnose the health condition of the power module. This condition monitoring method, validated by experiment, can sensitively detect individual solder degradation in multichip power modules or multimodule power electronic systems.

Borong Hu

Papers

Failure and Reliability Analysis of a SiC Power Module Based on Stress Comparison to a Si Device

Changes and challenges of photovoltaic inverter with silicon carbide device

Long-Term Reliability Evaluation of Power Modules With Low Amplitude Thermomechanical Stresses and Initial Defects

Distributed Thermal Monitoring of Wind Turbine Power Electronic Modules Using FBG Sensing Technology

Heat-Flux-Based Condition Monitoring of Multichip Power Modules Using a Two-Stage Neural Network