Power Electronic Devices Research Articles

Excellent energy storage properties with ultrahigh Wrec in lead-free relaxor ferroelectrics of ternary Bi0.5Na0.5TiO3-SrTiO3-Bi0.5Li0.5TiO3 via multiple synergistic optimization

Advanced energy storage capacitors play important roles in modern power systems and electronic devices. Next-generation high/pulsed power capacitors will rely heavily on eco-friendly dielectric ceramics with high energy storage density (Wrec), high efficiency (η), wide work temperature range and stable charge-discharge ability, etc. Lead-free Bi0.5Na0.5TiO3 (BNT) based relaxor ferroelectric (RFE) ceramics are considered as one of the most promising candidates for energy storage capacitors. However, the application fields of them are greatly limited by their relatively low Wrec (generally <5 J/cm3). In this paper, excellent energy storage properties characterized by a great breakthrough in Wrec are achieved in a novel BNT system, (1-x)BNT-x(0.7SrTiO3-0.3Bi0.5Li0.5TiO3)+0.5 at.%Nb2O5 (x = 0, 0.1, 0.2, 0.3, 0.4), by synergistically constructing highly dynamic polar nanoregions (PNRs) and nanodomains, ultrafine grains (submicron size) and intrinsic conduction. Of great importance, the x = 0.4 ceramic exhibits an ultrahigh Wrec of 8.63 J/cm3 as well as a high efficiency (ƞ) of 89.6 % under a giant electric field of 520 kV/cm, due to coexistence of ultrahigh polarization difference (ΔP=Pmax −Pr) and high dielectric breakdown electric strength (Eb). Furthermore, excellent temperature stability (20−180 °C), frequency stability (1 − 500 Hz), and cycling stability (1 − 105 times) with the variation of Wrec < ±4 % and η < ±3 % are also found in the x = 0.4 ceramic. These results demonstrate that it is a very promising lead-free dielectric capacitor with enormous energy storage applications.

Comprehensive energy-storage performance enhancement in relaxor anti-ferroelectrics via strengthening local polarization

Lead-free dielectric capacitors with excellent energy-storage performance have gained much attention for their remarkable potential applications in pulsed power electronic systems and devices. However, the large recoverable energy-storage density Wrec is usually accompanied with low efficiency η, hindering their practical applications. Such performance deterioration occurs because the large polarization is generally linked with strong reversal hysteresis, making the synergetic optimization of energy-storage density and efficiency a great challenge. Here we develop a strategy of constructing strengthened local polarization in the lead-free relaxor anti-ferroelectric ceramics 0.9NaNbO3-0.1Bi(Ni2/3Nb1/3)O3 by carefully manipulating the microstructures, the ultrahigh Wrec ∼ 11.2 J/cm3 and large η ∼ 90.5 % have been simultaneously achieved. Moreover, superior charge/discharge performances (power density PD ∼ 548 WM/cm3, discharge speed t0.9 ∼ 27 ns) and outstanding temperature (up to 160 °C) and cycling (up to 106) stabilities are also ensured. The excellent overall properties are mainly attributed to the stabilized antiferroelectric phase, the strong relaxation characteristic, as well as the enhanced local polarization in the polar nano-regions (PNRs) caused by the introduction of Bi(Ni2/3Nb1/3)O3. This work not only provides a lead-free system with remarkable energy-storage performance that demonstrates great potential in the application field of high-power pulse electronic devices, but also proposes a convenient and efficient strategy to design new dielectric materials with excellent energy-storage performance.

Protection scheme for LVDC distribution network based on stepwise blocking of power electronic transformer

AbstractCascaded H‐bridge power electronic transformers (CHB‐PET) can efficiently connect AC/DC distribution networks, realizing power transmission and electric energy conversion. Once a pole‐to‐pole DC fault occurs on the low‐voltage direct current (LVDC) side of CHB‐PET, the fault current has a fast rise and high amplitude, which easily leads to the rapid blocking of power electronic devices and makes it difficult for DC line protection to obtain fault information. A stepwise blocking scheme of PET is proposed for LVDC network protection. When the fault on the LVDC side of PET is detected, cascaded H‐bridge and low‐voltage H‐bridge of dual‐active‐bridge are blocked first, and then high‐voltage H‐bridge of dual‐active‐bridge is blocked after a 5 ms delay. The stepwise blocking can provide fault information for DC line protection. On this basis, wavelet packet transform is employed to extract different frequency components of fault current. The energy of the specific frequency band corresponding to the switching frequency of DAB and the total energy of all frequency bands contained in the fault current is calculated; then their ratio can be utilized to construct the protection scheme. Finally, the PSCAD/EMTDC simulation results verify the feasibility and effectiveness of proposed protection scheme based on stepwise blocking of CHB‐PET.

Nanofluids in microchannel heat sinks for efficient flow cooling of power electronic devices

Nanofluids hold significant potential in the field of heat transfer intensification. The objective of this paper is to investigate the thermal-hydraulic characteristics of Ag, SiO2, and Al2O3 nanofluids in rectangular (MC-R), trapezoidal (MC-T), and omega-shaped (MC-O) microchannel heat sinks (MCHSs) through conjugate numerical simulations under a constant heat flux of 100 W/cm2. Water was used as the base fluid, and nanoparticle volume fraction ranged from 0 to 6 %. The average heat transfer coefficient (HTC), Nusselt number, thermal resistance, pressure drop, and pump power as a function of Reynolds number are studied for different nanofluids and cross-sectional shapes in microchannels. The overall performance is also characterized by thermal performance factor, coefficient of performance (COP), and entropy generation analysis. The simulation results show that adding Al2O3 nanoparticles with a volume fraction of 6 % in MC-R at a Reynolds number of 500 results in a substantial 12.3 % increase in the average HTC and an approximately 8 % reduction in total thermal resistance compared to pure water. For the same nanofluid, MC-O exhibits the highest convective HTC, the highest Nusselt number, and the lowest maximum heat sink temperature. The total entropy generation in the MCHSs decreases obviously with increasing Reynolds number. MC-O has the smallest total entropy generation, meaning it has the optimal flow and heat transfer irreversibility. These findings can not only provide valuable guidance for the rational design of MCHSs but also hold significant implications for the effective cooling of microelectronic components via nanofluid-based thermal management technology.

Effects of Thermal Boundary Resistance on Thermal Management of Gallium-Nitride-Based Semiconductor Devices: A Review.

Wide-bandgap gallium nitride (GaN)-based semiconductors offer significant advantages over traditional Si-based semiconductors in terms of high-power and high-frequency operations. As it has superior properties, such as high operating temperatures, high-frequency operation, high breakdown electric field, and enhanced radiation resistance, GaN is applied in various fields, such as power electronic devices, renewable energy systems, light-emitting diodes, and radio frequency (RF) electronic devices. For example, GaN-based high-electron-mobility transistors (HEMTs) are used widely in various applications, such as 5G cellular networks, satellite communication, and radar systems. When a current flows through the transistor channels during operation, the self-heating effect (SHE) deriving from joule heat generation causes a significant increase in the temperature. Increases in the channel temperature reduce the carrier mobility and cause a shift in the threshold voltage, resulting in significant performance degradation. Moreover, temperature increases cause substantial lifetime reductions. Accordingly, GaN-based HEMTs are operated at a low power, although they have demonstrated high RF output power potential. The SHE is expected to be even more important in future advanced technology designs, such as gate-all-around field-effect transistor (GAAFET) and three-dimensional (3D) IC architectures. Materials with high thermal conductivities, such as silicon carbide (SiC) and diamond, are good candidates as substrates for heat dissipation in GaN-based semiconductors. However, the thermal boundary resistance (TBR) of the GaN/substrate interface is a bottleneck for heat dissipation. This bottleneck should be reduced optimally to enable full employment of the high thermal conductivity of the substrates. Here, we comprehensively review the experimental and simulation studies that report TBRs in GaN-on-SiC and GaN-on-diamond devices. The effects of the growth methods, growth conditions, integration methods, and interlayer structures on the TBR are summarized. This study provides guidelines for decreasing the TBR for thermal management in the design and implementation of GaN-based semiconductor devices.

Reliability issues of GaN HEMT: Current status and challenges

With the development of power electronic devices, there is an increasing demand for energy-saving, emission reduction, and environmental protection. Thus, higher energy conversion efficiency of power electronic devices is required. While traditional Si-based power electronic devices have the disadvantage of low energy utilization efficiency and high thermal losses, GaN-based HEMT has significant advantages, making it a frontier and hotspot in global semiconductor research. However, the failure mechanisms that affect the reliability of GaN HEMTs are not completely comprehended. Many reliability issues affect devices performance, among which electrical reliability and thermal reliability are widely studied concerns. Electrical reliability issues contain inverse piezoelectric effect, hot electron effect, trapping effect, and mental instability. Thermal reliability issues contain self-heating effects, which are caused by the materials unsatisfying thermal conductivity, and improper structure design. This paper is focused on the current research results of the GaN HEMTs electrical reliability and thermal reliability. The first part of this paper gives a review of GaN HEMT reliability issues at their current status, and the second part outlines the challenges of GaN HEMTs in future development. This review will help researchers to better understand factors that affect GaN HEMTs reliability and help with their device design for further research.

Thermal analysis of an α -Ga2O3 MOSFET using micro-Raman spectroscopy

The ultra-wide bandgap (UWBG) energy (∼5.4 eV) of α-phase Ga2O3 offers the potential to achieve higher power switching performance and efficiency than today's power electronic devices. However, a major challenge to the development of the α-Ga2O3 power electronics is overheating, which can degrade the device performance and cause reliability issues. In this study, thermal characterization of an α-Ga2O3 MOSFET was performed using micro-Raman thermometry to understand the device self-heating behavior. The α-Ga2O3 MOSFET exhibits a channel temperature rise that is more than two times higher than that of a GaN high electron mobility transistor (HEMT). This is mainly because of the low thermal conductivity of α-Ga2O3 (11.9 ± 1.0 W/mK at room temperature), which was determined via laser-based pump-probe experiments. A hypothetical device structure was constructed via simulation that transfer-bonds the α-Ga2O3 epitaxial structure over a high thermal conductivity substrate. Modeling results suggest that the device thermal resistance can be reduced to a level comparable to or even better than those of today's GaN HEMTs using this strategy combined with thinning of the α-Ga2O3 buffer layer. The outcomes of this work suggest that device-level thermal management is essential to the successful deployment of UWBG α-Ga2O3 devices.

A Comparative Study of Flow Boiling Heat Transfer and Pressure Drop Characteristics in a Pin-Finned Heat Sink at Horizontal/Vertical Upward Flow Orientations

Abstract With the continuous development of power electronic devices toward miniaturization and compactness, it is necessary to develop more efficient flow boiling heat transfer technologies. In this work, the flow boiling heat transfer and pressure drop characteristics of Novec649 in a pin finned channel under two kinds of flow orientations (horizontal and vertical upward) are experimentally investigated. Heat flux, inlet flow velocity, and inlet subcooling are considered as the variable parameters. The results show that among all boiling operating conditions, the heat transfer performances between two orientations are basically consistent, while the pressure drop of vertical upward pin finned channel is relatively lower, indicating that the comprehensive flow boiling heat transfer performance of vertical oriented channel is better. Subsequently, a series of flow visualization experiments are performed in vertical upward pin finned channel. With the increase of heat flux, four kinds of flow pattern are discovered in the order of dispersed bubble flow, bubble flow, homogeneous flow, and annular flow. In the region of annular flow, although a vapor flow has already formed in the channel, there is still a large amount of liquid phase surrounding the wall and pin fins. Therefore, no obvious heat transfer deterioration was observed in the pin finned channel. Along the flow direction, the diameter of bubbles will increase first, and then present obvious oscillation. As the heat flux increases, both the average bubble detachment diameter and the frequency increase correspondingly. As the fluid velocity increases, the average bubble detachment diameter presents a downward trend, while the average bubble detachment frequency presents an upward trend.

A Novel Method for Diagnosing Power Electronics Devices Using Elastic Wave Emission

This work is an introduction of acoustic emission (AE) signals used in order to detect the malfunction of selected semiconductor elements. The authors proposed the use of internally generated signals (elastic waves) of acoustic emission leading to the detection of the pre-fail state of switching IGBT transistors. The analysis of the AE signals allows the creation of a reference pattern of properly working transistors and at the same time the identification of abnormal signals, which are generated by a defective element. Unlike many papers, this article shows experimental results demonstrating a comparison of undamaged, properly working and defective IGBT transistors which can be used, for example, as a reference for diagnostic tools. Analysis of the signal in the frequency domain obtained from the faulty transistor (overheated or with damaged casing) shows the presence of additional frequencies which can indicate the imminent occurrence of critical damage.

A Novel Approach to Partial Discharge Detection Under Repetitive Unipolar Impulsive Voltage

Partial discharge (PD) detection is an important method to verify the reliability of the insulation structure of high voltage power electronics devices. Although there are many researches on PD detection inside power modules, they mainly focus on traditional electrical detection methods and 50 Hz working conditions, which do not meet the repetitive unipolar impulsive voltage conditions of power modules, and traditional methods cannot solve the electromagnetic interference (EMI) problem under working conditions. This paper proposes a novel approach to PD detection in power modules. This approach designs an optic fiber sensing (OFS) system based on optic theory, and conducts the detailed mathematical theoretical deduction. In addition, A partial discharge inception voltage (PDIV) signal processing method based on PD acoustic signal is proposed. Finally, the proposed approach is applied to a power module. The PD signal and PDIV is successfully captured without EMI interference and new insulation problems.

Novel Gramian-Based Structure-Preserving Model Order Reduction for Power Systems With High Penetration of Power Converters

Renewable energy and high voltage direct current connections increase the number of power electronic devices in the grid, changing how power systems operate and introducing new dynamic behavior. For this reason, it is fundamental to understand what modeling details are needed to represent the system in this new context. This paper proposes a novel model reduction approach using frequency-limited controllability and observability Gramians that preserves the link between the physical structure of the system and the state variables. This method allows understanding and analytically determining how vital each state is to the input-output behavior in different frequency ranges. The primary contribution of this paper is an algorithm that can provide intuitive results to help power system experts understand the simulation tools and minimum modeling details needed to perform different stability studies. Two case studies supported the applicability of the developed method, and a tool for MATLAB/Simulink was developed based on the findings, allowing visualization and immediate identification of the model components that are most relevant for the system dynamics under study. This tool can analyze dynamic behaviors where the cause is poorly understood and provide clarity around modeling detail requirements in converter-rich power systems.

Two Cascade Control Strategy of Generalized Electric Spring

With the gradually increase of the application of new energy in microgrids, Electric Spring (ES), as a new type of distributed compensation power electronic device has been widely studied. The Generalized Electric Spring (G-ES) is an improved topology, and the space limitation problem in the traditional topology is solved. Because of the mode of G-ES use in the power grid, a reasonable solution to the voltage loss of the critical section feeder is needed. In this paper, the voltage balance equation based on the feedforward compensation coefficient is established, and a two cascade control strategy based on the equation is studied. The first stage of the two cascade control strategy is to use communication means to realize the allocation of feedforward compensation coefficients, and the second stage is to use the coefficients to realize feedforward fixed angle control. Simulation analysis shows that the proposed control strategy does not affect the control accuracy of the critical load (CL), and effectively improves the operational range of the G-ES.

Power Electronics Revolutionized: A Comprehensive Analysis of Emerging Wide and Ultrawide Bandgap Devices.

This article provides a comprehensive review of wide and ultrawide bandgap power electronic semiconductor devices, comparing silicon (Si), silicon carbide (SiC), gallium nitride (GaN), and the emerging device diamond technology. Key parameters examined include bandgap, critical electric field, electron mobility, voltage/current ratings, switching frequency, and device packaging. The historical evolution of each material is traced from early research devices to current commercial offerings. Significant focus is given to SiC and GaN as they are now actively competing with Si devices in the market, enabled by their higher bandgaps. The paper details advancements in material growth, device architectures, reliability, and manufacturing that have allowed SiC and GaN adoption in electric vehicles, renewable energy, aerospace, and other applications requiring high power density, efficiency, and frequency operation. Performance enhancements over Si are quantified. However, the challenges associated with the advancements of these devices are also elaborately described: material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference. Alongside the cost reduction through improved manufacturing, material availability, thermal management, gate drive design, electrical insulation, and electromagnetic interference are critical hurdles of this technology. The review analyzes these issues and emerging solutions using advanced packaging, circuit integration, novel cooling techniques, and modeling. Overall, the manuscript provides a timely, rigorous examination of the state of the art in wide bandgap power semiconductors. It balances theoretical potential and practical limitations while assessing commercial readiness and mapping trajectories for further innovation. This article will benefit researchers and professionals advancing power electronic systems.

Additive Manufacturing of Liquid-Cooled Ceramic Heat Sinks: An Experimental and Numerical Study

With recent advances in power electronic packaging technologies, liquid-cooled ceramic heat sinks have been considered as a promising solution for further improving the performance of power electronic devices. In this study, several aluminum oxide heat sinks were fabricated and tested using the digital light processing-based additive manufacturing method, to verify their practical performance. The results showed that the complex cooling structures inside the heat sinks can be completely formed and exhibited high surface quality. The experimental thermal and hydraulic performances of the heat sinks were consistent with the numerically modeled predictions. Furthermore, by exploiting the advantages of additive manufacturing, a direct manifold microchannel (MMC) configuration was designed to reduce the vertical flow of the traditional MMC configuration and achieve an improved cooling efficiency. At a constant volumetric flow rate of 1 L/min, the direct MMC configuration achieved a 19.8% reduction in pressure drop and an 11.8% reduction in thermal resistance, as well as a more uniform temperature distribution.

Obtaining of an Equivalent Circuit of a Redox Flow Battery

This paper focuses on obtaining an equivalent electrical circuit (EEC) type model for a flow battery, with parameter identification from data generated by simulating an electrochemical model of the system. The model with the EEC structure is more versatile to be used, for example, in design and testing of control and energy management strategies in hybrid systems, since it can be simulated in conjunction with other electrical circuit models of power electronics devices. The EEC model is obtained from the data resulting from the simulation of the electrochemical plant before an input signal rich in frequencies, estimating the model parameters by nonlinear least squares fitting, implemented in an algorithm available in the Matlab - Simulink platform.

Research of the system-on-chip-based relay protection technology

The relay protection device is the core equipment that ensures the safe and stable operation of a power grid. With the open access of a large number of distributed generation, DC transmission and electric vehicles, a new deep low-carbon power system dominated by power electronic devices has gradually been formed. It is difficult for the traditional control and protection architecture, methods, and technology to meet the business characteristics and functional requirements of a diversified interaction, agile response, safety, and credibility of the power grid in the future. This paper presents a chip-based relay protection technology based on system-on-chip (SoC), which is described from four aspects, namely, the architectural design of the relay protection SoC, software and hardware cooperative relay protection based on the SoC IP core, experimental verification, and engineering application. The results show that the relay protection SoC proposed in this paper has significantly improved the performance of high-speed data acquisition and interaction through hardware algorithm engine acceleration and software and hardware collaborative computing, which is helpful to realize the local equipment operation and the integration of primary and secondary equipment, shorten the protection action time, and improve the speed, reliability, and stability of relay protection devices.

Influence of processing conditions on the titanium/nickel contact metallization on a silicon wafer for thermal management

Thermal management of both digital and power electronics is becoming challenging with device miniaturization and a need for delivering higher power. Diamond thin films and substrates are attractive for thermal management applications in power electronics because of their high thermal conductivity. However, deposition of diamond by microwave plasma enhanced chemical vapor deposition requires high temperatures, which can degrade metallization used in power electronic devices. In this research, Titanium (Ti)- Nickel (Ni) thin films are deposited by direct current magnetron sputtering on p-type Silicon (Si) (100) substrates using a physical mask for creating dot-patterns for measuring properties of the contact metallization. The influence of processing conditions and post-deposition annealing in Argon and hydrogen at 380 °C for 1 h on the properties of the contact metallization are studied by measuring the current - voltage characteristics and Hall effect. The results indicated ohmic contact resistance for both, the as-deposited films and after post annealing treatments. In addition, the results on contact resistance, resistivity, carrier concentration and hall mobility of wafers extracted from Ti/Ni metal contact to p-type Si (100) are presented and discussed.

Phase field study on electrical treeing under combined AC/DC voltage based on bipolar barrier transfer model

The study of insulation degradation processes is crucial for the reliable operation of power equipment and electronic devices. The phase field method has been widely used in recent years to simulate the degradation process of insulation materials. However, the effect of space charge was ignored. In this paper, a novel phase field method based on the bipolar carrier transfer model is suggested. This model can simulate degradation under different temperatures and DC or combined AC/DC voltage. The cases under AC and combined AC/DC voltage at different temperatures are simulated by COMSOL. Methods to ensure model convergence are proposed. The results show that the field strength distribution under a combined AC/DC field is more uniform, especially for negative polarity. For the same voltage form, temperature and breakdown time show an exponential relationship. The results are consistent with those of previous experimental studies, proving the usability of the model. In addition, the processes of initiation, growth, and breakdown stage of the dielectric degradation process, as well as the stagnation period, are explored theoretically. The stagnation time at low temperatures under combined AC/negative DC voltage is long. The research in this paper is useful for insulation optimization design, condition assessment, and longevity prediction.

A Fatigue Lifetime Prediction Model for Aluminum Bonding Wires

Electrical signal transmission in power electronic devices takes place through high-purity aluminum bonding wires. Cyclic mechanical and thermal stresses during operation lead to fatigue loads, resulting in premature failure of the wires, which cannot be reliably predicted. The following work presents two fatigue lifetime models calibrated and validated based on experimental fatigue results of an aluminum bonding wire and subsequently transferred and applied to other wire types. The lifetime modeling of Wöhler curves for different load ratios shows good but limited applicability for the linear model. The model can only be applied above 10,000 cycles and within the investigated load range of R = 0.1 to R = 0.7. The nonlinear model shows very good agreement between model prediction and experimental results over the entire investigated cycle range. Furthermore, the predicted Smith diagram is not only consistent in the investigated load range but also in the extrapolated load range from R = −1.0 to R = 0.8. A transfer of both model approaches to other wire types by using their tensile strengths can be implemented as well, although the nonlinear model is more suitable since it covers the entire load and cycle range.

1.7-kV vertical GaN p-n diode with triple-zone graded junction termination extension formed by ion-implantation

Edge termination has emerged as an important area in the design and realization of vertical GaN power electronic devices. While the material properties of GaN are promising for high-performance devices, in practice the breakdown voltage can be compromised by inadequate edge termination (ET). While solutions in other materials (e.g. Si, SiC) are well-known, these are challenging to implement in GaN due to inherent difficulties in p-type doping GaN. In this work, we report a etch-free triple-zone graded junction termination extension (JTE) for vertical GaN diodes formed by Nitrogen ion implantation. The triple-zone design offers lower peak fields for effective field control. In addition, the proposed triple-zone JTE is beneficial for increasing the fabrication process window and allowing for more variability in epitaxial wafer growth in terms of p-GaN doping and thickness while maintaining high breakdown voltage. The fabricated GaN p-n diodes with triple-zone JTE obtain a maximum breakdown voltage of 1.73 kV with specific on-resistance Ron of 0.4 mΩcm2. Temperature-dependent reverse characteristics show that the devices have a positive temperature coefficient of the breakdown voltage indicating an avalanche breakdown mechanism. These results suggest that vertical GaN p–n diodes with N-implanted triple-zone JTE are promising for power applications.