Zhenxian Liang

Bio: Zhenxian Liang is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Power module & Power electronics. The author has an hindex of 26, co-authored 69 publications receiving 1744 citations. Previous affiliations of Zhenxian Liang include University of Tennessee & Virginia Tech.

Temperature-Dependent Short-Circuit Capability of Silicon Carbide Power MOSFETs

Abstract: This paper presents a comprehensive short-circuit ruggedness evaluation and numerical investigation of up-to-date commercial silicon carbide (SiC) MOSFETs. The short-circuit capability of three types of commercial 1200-V SiC MOSFETs is tested under various conditions, with case temperatures from 25 to 200 °C and dc bus voltages from 400 to 750 V. It is found that the commercial SiC MOSFETs can withstand short-circuit current for only several microseconds with a dc bus voltage of 750 V and case temperature of 200 °C. The experimental short-circuit behaviors are compared, and analyzed through numerical thermal dynamic simulation. Specifically, an electrothermal model is built to estimate the device internal temperature distribution, considering the temperature-dependent thermal properties of SiC material. Based on the temperature information, a leakage current model is derived to calculate the main leakage current components (i.e., thermal, diffusion, and avalanche generation currents). Numerical results show that the short-circuit failure mechanisms of SiC MOSFETs can be thermal generation current induced thermal runaway or high-temperature-related gate oxide damage.

Technology trends toward a system-in-a-module in power electronics

Abstract: Currently, assemblies of power semiconductor switches and their associated drive circuitry are available in modules. From a few 100 watts downward, one finds silicon monolithic technology as the integration vehicle, while upward into the multi-kilowatt range, mixed mode module construction is used. This incorporates monolithic, hybrid, surface mount and wirebond technology. However, a close examination of the applications in motor drives and power supplies indicates that there has been no dramatic volume reduction of the subsystem. The power semiconductor modules have shrunk the power switching part of the converter, but the bulk of the subsystem volume still comprises the associated control, sensing, electromagnetic power passives and interconnect structures. The paper addresses the improvement of power processing technology through advanced integration of power electronics. The goal of a subsystem in a module necessitates this advanced integration. The central philosophy of this technology development research is to advance the state of the art by providing the concept of integrated power electronics modules (IPEMs). The technology underpinning such an IPEM approach is discussed. The fundamental functions in electronic power processing, the materials, processes and integration approaches and future concepts are explained.

Integrating active, passive and EMI-filter functions in power electronics systems:a case study of some technologies

Abstract: Assemblies of power semiconductor switches and their associated drive circuits are at present available in modules. Upward into the multi-kilowatt range, mixed mode module construction is used. This incorporates monolithic, hybrid, surface mount, and wirebond technology. However, a close examination of the applications in motor drives and power supplies indicates that there has been no dramatic volume reduction of the subsystem. The power semiconductor modules have shrunk the power switching part of the converter, but the bulk of the subsystem volume still comprises the associated control, sensing, electromagnetic power passives (inductors, transformers, capacitors) and interconnects. This paper addresses the improvement of power processing technology through advanced integration of power electronics. The goal of a subsystem in a module necessitates this advanced integration, incorporating active switching stages, electromagnetic interference (EMI) filters, and electromagnetic power passives into modules by integration technology. The central philosophy of the technology development research in the National Science Foundation Engineering Research Center for Power Electronic Systems is to advance the state of the art by providing the concept of integrated power electronics modules (IPEMs) for all these functions. The technology underpinning such an IPEM approach is discussed.

Methodology for switching characterization evaluation of wide band-gap devices in a phase-leg configuration

Abstract: Double pulse tester (DPT) is a widely accepted method to evaluate the switching behavior of power devices. Considering the high switching-speed capability of wide band-gap (WBG) devices, the test results become significantly sensitive to the alignment of voltage and current (V-I) measurement. Also, because of the shoot-through current induced by Cdv/dt, during the switching transient of one device, the switching losses of its complementary device in the phase-leg is non-negligible. This paper summarizes the key issues of DPT, including layout design, measurement considerations, grounding effects and data processing. Among them, the latest probes for switching waveform measurement are compared, the methods of V-I alignment are discussed, and the impact of grounding effects induced by probes on switching waveforms are investigated. Also, for the WBG devices in a phase-leg configuration, a practical method is proposed for switching loss evaluation by calculating the difference between the input energy supplied by a dc capacitor and the output energy stored in a load inductor. Based on a phase-leg power module built with 1200 V SiC MOSFETs, the test results show that regardless of V-I timing alignment, this method can accurately indicate the switching losses of both the upper and lower switches by detecting only one switching current.

Development of Advanced All-SiC Power Modules

Abstract: A thermally integrated packaging structure for an all silicon carbide (SiC) power module was used to realize highly efficient cooling of power semiconductor devices through direct bonding of the power stage and a cold baseplate. The prototype power modules composed of SiC metal-oxide-semiconductor field-effect transistors and Schottky barrier diodes demonstrate significant improvements such as low-power losses and low-thermal resistance. Direct comparisons to their silicon counterparts, which are composed of insulated gate bipolar transistors and PiN diodes, as well as conventional thermal packaging, were experimentally performed. The advantages of this SiC module in efficiency and power density for power electronics systems have also been identified, with clarification of the SiC attributes and packaging advancements.

Review of Silicon Carbide Power Devices and Their Applications

Abstract: Silicon carbide (SiC) power devices have been investigated extensively in the past two decades, and there are many devices commercially available now. Owing to the intrinsic material advantages of SiC over silicon (Si), SiC power devices can operate at higher voltage, higher switching frequency, and higher temperature. This paper reviews the technology progress of SiC power devices and their emerging applications. The design challenges and future trends are summarized at the end of the paper.

Review of Commercial GaN Power Devices and GaN-Based Converter Design Challenges

Abstract: Gallium nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This paper reviews the characteristics and commercial status of both vertical and lateral GaN power devices, providing the background necessary to understand the significance of these recent developments. In addition, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, dynamic $R_{\mathrm {{ds}},\mathrm {{on}}}$ , breakdown mechanisms, thermal design, device availability, and reliability qualification. This review will help prepare the reader to effectively design GaN-based converters, as these devices become increasingly available on a commercial scale.

Optimal design methodology for LLC resonant converter

Abstract: Although LLC resonant converter can achieve wide operation range with high efficiency, lack of design methodology makes it difficult to be implemented. In this paper, based on the theoretical analysis on the operation principles during normal condition and holdup time, the relationship between converter efficiency and operation range with different circuit parameters has be revealed. An optimal design methodology has been developed based on the revealed relationship. A 1MHz, 1kW LLC converter is designed to verify the proposed method.

A Survey of Wireless Power Transfer and a Critical Comparison of Inductive and Capacitive Coupling for Small Gap Applications

Abstract: Inductive power transfer (IPT) and capacitive power transfer (CPT) are the two most pervasive methods of wireless power transfer (WPT). IPT is the most common and is applicable to many power levels and gap distances. Conversely, CPT is only applicable for power transfer applications with inherently small gap distances due to constraints on the developed voltage. Despite limitations on gap distance, CPT has been shown to be viable in kilowatt power level applications. This paper provides a critical comparison of IPT and CPT for small gap applications, wherein the theoretical and empirical limitations of each approach are established. A survey of empirical WPT data across diverse applications in the last decade using IPT and CPT technology graphically compares the two approaches in power level, gap distance, operational frequency, and efficiency, among other aspects. The coupler volumetric power density constrained to small gap sizes is analytically established through theoretical physical limitations of IPT and CPT. Finally, guidelines for selecting IPT or CPT in small gap systems are presented.

PWM Converter Power Density Barriers

Abstract: Power density of power electronic converters in different applications has roughly doubled every 10 years since 1970. Behind this trajectory was the continuous advancement of power semiconductor device technology allowing an increase of converter switching frequencies by a factor of 10 every decade. However, today's cooling concepts, and passive components and wire bond interconnection technologies could be major barriers for a continuation of this trend. For identifying and quantifying such technological barriers this paper investigates the volume of the cooling system and of the main passive components for the basic forms of power electronics energy conversion in dependency of the switching frequency and determines switching frequencies minimizing the total volume. The analysis is for 5 kW rated output power, high performance air cooling, advanced power semiconductors, and single systems in all cases. A power density limit of 28 kW/dm3@300 kHz is calculated for an isolated DC-DC converter considering only transformer, output inductor and heat sink volume. For single-phase AC-DC conversion a general limit of 35 kW/dm3 results from the DC link capacitor required for buffering the power fluctuating with twice the mains frequency. For a three-phase unity power factor PWM rectifier the limit is 45 kW/dm3@810 kHz just taking into account EMI filter and cooling system. For the sparse matrix converter the limiting components are the input EMI filter and the common mode output inductor; the power density limit is 71 kW/dm3@50 kHz when not considering the cooling system. The calculated power density limits highlight the major importance of broadening the scope of research in power electronics from traditional areas like converter topologies, and modulation and control concepts to cooling systems, high frequency electromagnetics, interconnection technology, multi-functional integration, packaging and multi-domain modeling and simulation to ensure further advancement of the field along the power density trajectory.