Electric Power Devices Research Articles

(Invited) GaN Power Electronics and Associated Fundamental Limits

How does it impact the design principles of power electronics in ultra-wide bandgap semiconductors? What fundamentally different roles does a p-region play in a power electric device in comparison to a semi-insulating region, for example, in the popular GaN HEMT based power transistors? What are the practical fundamental limits for the unipolar devices such as Schottky Barrier Didoes without the help of p-type? What are the unique advantages a polar semiconductor family like GaN can offer? What is polarization doping and how is polarization-doping fundamentally different from impurity doping? I will reflect on our efforts in seeking answers to these questions in the past 20 years in GaN power electronic devices as well as realizing state-of-the-art devices; some example publications can be found in references 1-12.Our work has been in part supported by ARPAe SWITCHES, AFOSR FA9550-17-1-0048, and NSF DMREF 1534303, making use of shared facilities at CNF (NSF ECCS-1542081), CCMR (NSF MRSEC DMR-1719875) and equipment supported by DMR-1338010.

Multilevel Simulation Methodology for FMECA Study Applied to a Complex Cyber-Physical System

Complex systems are composed of numerous interconnected subsystems, each designed to perform specific functions. The different subsystems use many technological items that work together, as for the case of cyber-physical systems. Typically, a cyber-physical system is composed of different mechanical actuators driven by electrical power devices and monitored by sensors. Several approaches are available for designing and validating complex systems, and among them, behavioral-level modeling is becoming one of the most popular. When such cyber-physical systems are employed in mission- or safety-critical applications, it is mandatory to understand the impacts of faults on them and how failures in subsystems can propagate through the overall system. In this paper, we propose a methodology for supporting the failure mode, effects, and criticality analysis (FMECA) aimed at identifying the critical faults and assessing their effects on the overall system. The end goal is to analyze how a fault affecting a single subsystem possibly propagates through the whole cyber-physical system, considering also the embedded software and the mechanical elements. In particular, our approach allows the analysis of the propagation through the whole system (working at high level) of a fault injected at low level. This paper provides a solution to automate the FMECA process (until now mainly performed manually) for complex cyber-physical systems. It improves the failure classification effectiveness: considering our test case, it reduced the number of critical faults from 10 to 6. The remaining four faults are mitigated by the cyber-physical system architecture. The proposed approach has been tested on a real cyber-physical system in charge of driving a three-phase motor for industrial compressors, showing its feasibility and effectiveness.

Enhancing Student Engagement with a Small-Scale Car That Is Motion-Controlled through Chemical Kinetics and Basic Electronics

A five day activity that involves the construction and characterization of a small car whose motion is controlled by the vitamin C clock reaction is presented. The purpose of the activity is to engage first-year Science, Technology, Engineering, and Mathematics (STEM) students not majoring in the chemical sciences. Throughout the activity students learn and put into practice basic concepts of electronics and chemical kinetics, while testing four different types of electric power devices: galvanic cells, thermoelectrical cells, fuel cells, and solar panels. They also learn to analyze the vitamin C clock reaction with a simple kinetic model to calculate the time elapsed for a color transition from transparent to dark. A target-distance competition takes place on the last day of the activity.

A Battery Health Monitoring Method Using Machine Learning: A Data-Driven Approach

Batteries are combinations of electrochemical cells that generate electricity to power electrical devices. Batteries are continuously converting chemical energy to electrical energy, and require appropriate maintenance to provide maximum efficiency. Management systems having specialized monitoring features; such as charge controlling mechanisms and temperature regulation are used to prevent health, safety, and property hazards that complement the use of batteries. These systems utilize measures of merit to regulate battery performances. Figures such as the state-of-health (SOH) and state-of-charge (SOC) are used to estimate the performance and state of the battery. In this paper, we propose an intelligent method to investigate the aforementioned parameters using a data-driven approach. We use a machine learning algorithm that extracts significant features from the discharge curves to estimate these parameters. Extensive simulations have been carried out to evaluate the performance of the proposed method under different currents and temperatures.

Controlling the crystallization of Nd-doped Bi4Ti3O12 thin-films for lead-free energy storage capacitors

Environmentally benign non-lead-based dielectric thin film capacitors with high electrostatic energy density, long-term stability, and fast charge/discharge capability are strongly demanded in advanced electrical and pulsed power devices. Here, we propose that insufficient crystallization is an effective method to achieve high energy storage performance. A high efficiency of 84.3%, together with a good energy density of 41.6J/cm3 and an excellent fatigue endurance, is obtained in a lead-free Nd-doped Bi4Ti3O12 film of low crystallization. An increase in the annealing temperature increases the crystallinity and grain size, which improves the ferroelectric polarization of a thin film. A narrow hysteresis loop with large maximum polarization and small remnant polarization is obtained in the insufficiently crystallized film, which is annealed in the intermediate temperature. This film also shows a lower leakage current compared with the fully crystallized counterpart due to the less defective microstructure. This work provides a straightforward and executable method to design ferroelectric materials for the applications of energy storage capacitors.

Coupling time constants and ac loss characteristics of spiral copper-plated striated coated-conductor cables (SCSC cables)

We conducted electromagnetic field analyses of spiral copper-plated striated coated-conductor cable (SCSC cable), where the striated (multifilament) and copper-plated coated conductors were twisted spirally around a round core in order to decouple the filaments. We used a numerical model which was formulated with current vector potential and in which thin-strip approximation was applied to the superconductor layer of the coated conductors. The nonlinear conductivity obtained from measured electric field–current density characteristics was used to represent the superconducting properties. To confirm the effect of the spiral twist in the SCSC cables, we determined their coupling time constants from the frequency dependences of their calculated magnetisation losses, under an ac transverse magnetic field with a small amplitude. Moreover, we calculated the ac losses in the SCSC cables under simultaneous application of ac transverse magnetic fields and ac transport currents, which represent practical operating conditions for electrical power devices and magnets.

Superconducting state stability in second generation high-temperature superconducting wires with varying copper stabilizer thickness under AC overcurrent conditions

Superconducting state stability in high-temperature superconducting (HTS) wires is of great importance for the reliable operation of superconducting electric power equipment. To this end, a study was made of the steady state operation and transients under AC current overloading in second generation (2G) HTS tape wires with a copper stabilizing layer of varying thickness. The existence of a threshold stabilizer thickness has been found, such that determines the HTS tape I-V curve and transients when an overcritical current flows. If the current exceeds the critical value, primary instability takes place in a wire with no stabilizer layer as well as with a layer of any thickness. In a wire with the stabilizer thickness less than the threshold level, an irreversible superconducting-to-normal transition occurs. However, if the copper layer thickness exceeds the threshold thickness, the HTS wire stable overloaded state recovers after some transients that have an irregular oscillation shape. The recovery of the stable thermal state under overcurrent conditions in HTS wires with an over-threshold stabilizer thickness is applicable in a variety of superconducting electric power devices, such as transformers and current limiters with a high capability to withstand faults. The measurements also show that the loss of superconductivity under AC overcritical current is followed by the phase angle changing between voltage and current. This phenomenon could be used for fast response normal zone detection in current-carrying conductors of superconducting equipment.

Supercapacitors and their military applicability

There are several types of the electrical power devices that are hardly known outside professional circles. One of them is the supercapacitor, which is very interesting attributable to its capabilities. Given its parameters, it can be considered unique, thus, its use in some special equipment is indispensable. With the spread of electricity, there will be more and more military equipment in which currently there is no alternative to its use. It is therefore well worth learning a bit more about it.

Design of Efficient Power Supply for the Proper Operation of Bio-Mimetic Soft Lens

Soft Robotics is one of the emerging and top-notched researched fields in Robotics which collaborate and Interact with Human Machine Interface (HMI). Several power electronics and electrical devices are used for the proper operation of these robots, among them high voltage power supply plays a vital role. Several approaches are used for the design of the high voltage power supply but still there is a deficiency in the design of the power supply which fulfill our desires level (highly efficient and less complex). This paper presents the efficient power supply for the control of bio-mimetic lens. The proposed power supply is designed by the use of boost converter, single phase inverter and the cock-croft Walton Voltage Multiplier. The work employs the use of power electronics for the achievement of the efficient high voltage power supply and boost the level of voltage up to 5 kV. Numerical simulations are performed for the comprehensive testing of the proposed model. Simulink is used for designing of the high voltage supply for simulation work. More-over the results are verified with the designing of laboratory setup. The experimental results are close to the simulation results with an error less than 3%. This proof the validity of proposed high voltage power supply.

Обеспечение достоверности методической поддержки управления объектов электроэнергетических систем

Enhancing the validity of methodical recommendations is one of the main problems that have to be solved in developing intelligent systems for managing maintenance and repair of electric power system equipment and devices. A risk of making an erroneous decision exists mainly due to availability of gross errors and abnormal values in statistical data on operation. The difficulty of solving this problem becomes still more obvious obvious if this risk is taken together with the fact that non-random samples of statistical data on operation differ from the theoretical representative samples of random quantities from the general totality of data, the need to consider a multidimensional nature of statistical data on operation, and lack of methods for analyzing scanty samples of multidimensional data. A method that allows abnormal realizations to be revealed based on the fiducial approach and statistical hypothesis testing theory is developed. By applying express methods for calculating the fiducial interval critical values for the selected significance level, this problem can be solved without using special tables and a computer.

Enabling the Smart and Flexible Management of Energy Prosumers via the Energy Router With Parallel Operation Mode

With the increasing penetration of renewable distributed generations (DGs), large numbers of “energy prosumers” are emerging rapidly. There will be severe impacts on the utility grid if these renewable DGs are not managed properly. Smart electrical power devices which enable high flexibility in energy management, alleviation in harmonic pollutions and friendly interactions with the utility grid are needed urgently. To meet all these requirements, a novel energy router which enables a unique parallel operation mode to the energy prosumer is presented. Facilitated with a bi-directional DC/AC converter, a switch array module and a fuzzy logic based hierarchical control strategy, the presented energy router enables plug-and-play connections and reliable energy management for the energy prosumer. The switch array and the parallel mode enable the loads to be flexibly scheduled to reduce energy cost and improve system performance. MATLAB/Simulink model of the energy prosumer is set up and a fuzzy logic based hierarchical control strategy is implemented for transient power balance control in various operation modes. Simulation results have demonstrated high flexibility, stability and feasibility of the proposed energy router in energy management of the prosumer, which will contribute to the better utilization of the ever-growing renewable energies.

Визуализация смерчеобразных структур с целью совершенствования систем охлаждения электротехнических устройств

Визуализация смерчеобразных структур с целью совершенствования систем охлаждения электротехнических устройств

Adaptive cascaded Delayed Signal Cancellation PLL for three-phase grid under unbalanced and distorted condition

Grid synchronization is an important part in monitoring, accessing, and automatically controlling the grid-connected generators and other power electronic converters. The phase of fundamental frequency needs to be tracked in real-time to control energy delivery. However during normal operation the waveforms’ frequency, magnitude, and symmetry are varying due to load change, distortions generated by certain electrical power devices and the occurrence of faults. In this paper, an efficient and fast synchronization scheme based on Delayed Signal Cancellation (DSC) for harmonics rejection purposes has been proposed for extracting the fundamental signal. Also, a detailed αβ-frame Cascade DSC (αβCDSC) analysis is presented and an αβCDSC-PLL scheme with fast dynamic response under transients is proposed. Based on the proposed PLL, an adaptive control loop is also developed to improve disturbance resistance during faults. Both simulation and real-time hardware-in-the-loop (HIL) experiments are used to verify the unbalance resistance, distortion rejection as well as performance improvement of the two proposed αβCDSC-PLL schemes.

Control shunt active filter based on dq frame using current model prediction

The nonlinear loads present more in the power systems in the practice today by developing of electronic technology and using the small distributed power sources (solar power, wind power etc.), this causes the increasing the high frequency switch devices etc. in the power network. Nonlinear loads cause non-sinusoidal currents and voltages with harmonic components, increasing the reactive power, overload of power lines and electrical devices, low power factor and affecting badly to the networks. Shunt active filters (SAF) with current controlled voltage source inverters (CCVSI) are used effectively to reduce the harmonics and to balance the phases sinusoidal source currents by generating the currents to compensate the harmonic currents caused by the nonlinear loads. In this paper we suppose a control strategy to generate the compensation currents of SAF by using the current model predictive engineering. This method is better than the control strategy using PI controller in term of transient time. The desired compensation currents can track exactly the reference compensation currents on the dq frame. The simulation results implemented on the nonlinear load, a full bridge rectifier and 3 phase unbalance load, show that the transient period decrease from 0.1s to 0.02s in comparing with PI controller. The experimental results proof that the THD of source currents decrease from 24.8% to 5.4% when using the proposed method.

Distributed jet array impingement boiling on particle sintered porous surfaces

Due to the excellent heat transfer performance and adaptability in dealing with local hot spots, jet array impingement boiling is promising for the high heat flux cooling in a variety of power electrical and electronic devices, such as high-performance CPU, IGBT, and laser diode. A distributed jet array with effusion ports adjacent to jet holes can extract spent flow immediately to avoid the negative crossflow effect in a normal jet array. Consequently, the heat transfer coefficient (HTC) and critical heat flux (CHF) can be both improved greatly. In order to further improve the heat transfer performance of distributed jet array impingement boiling, enhanced boiling surfaces could be used. Particle sintered porous surfaces have been widely investigated in pool boiling and achieved significant enhancement effect owing to the increased nucleation sites and wetting areas. Although several studies on the sintered porous structure have been done for jet impingement boiling, none is for distributed jet array. In this paper, a pumped two-phase loop was built up and three kinds of porous surfaces were experimentally investigated to enhance the distributed jet array impingement boiling of dielectric coolant, HFE7000. The porous structures were sintered with the copper particles of 50, 100 and 200 μm in diameter on a target surface of 11 mm ×20 mm and had a fixed thickness to particle size ratio of 2.0. A distributed jet array with 10 jet holes and 12 effusion holes was used. The diameters of the jet and effusion holes were 1 mm and 2 mm, respectively, while the distances between jet holes or effusion holes were 5 mm. The volume flow rate through the test section was 0.4 L/min, and the liquid inlet temperature and phase change saturation temperature were controlled at 35 and 60  C, respectively. An experimental apparatus was also established up to compare the wickability of the three porous surfaces. The 100 and 200 μm particles sintered surfaces were proved to have the better wickability. The experimental results turn out that the single-phase heat transfer is significantly improved due to the increased heat transfer area and flow turbulence within the porous structures, and the enhancement ratio increases with the increasing of flow rate. The porous surfaces sintered with 100 and 200 μm particles have close heat transfer performances, which are much better than that sintered with 50 μm particles. As for boiling heat transfer regime, the porous structures can provide more nucleation sites but at the same time will increase the flow resistance of effusion vapor. As a trade-off, the best performance is achieved by 100 μm particle, with its largest heat transfer coefficient upon DNB (departure from nucleate boiling) increased by 61% compared with that of the smooth surface. The wickability of porous layer however has no obvious effect on CHF due to the dominant role of distributed jet impingement on liquid feeding as well as the low surface tension of HFE7000. The maximum enhancement of CHF by 17% is acquired using the 100 μm particle sintered porous surface. Nevertheless, the heat flux range between DNB and CHF is greatly extended for the porous surfaces, which is beneficial to practical applications. A number of spots are found to be randomly distributed on the original smooth particle surfaces after many times of boiling experiments, but seem to have little influence on heat transfer performance. The long-term durability of the enhancement surface however needs further investigation.

Large energy storage density performance of epitaxial BCT/BZT heterostructures via interface engineering

We grew lead-free BaZr0.2Ti0.8O3 (BZT)/Ba0.7Ca0.3TiO3 (BCT) epitaxial heterostructures and studied their structural, dielectric, ferroelectric and energy density characteristics. The BZT/BCT epitaxial heterostructures were grown on SrRuO3 (SRO) buffered SrTiO3 (STO) single crystal substrate by optimized pulsed laser deposition (PLD) technique. These high-quality nanostructures exhibit high dielectric permittivity (∼1300), slim electric field-dependent polarization (P-E) curve with high saturation polarization (∼100 µC/cm2) and low remnant polarization (∼20 µC/cm2) through interface engineering to develop new lead-free ferroelectric system for energy storage devices. We observe an ultrahigh discharge and charge energy densities of 42.10 and 97.13 J/cm3, respectively, with high efficiency, which might be highly promising for both high power and energy storage electrical devices.

The Plug-and-Play Electricity Era: Interoperability to Integrate Anything, Anywhere, Anytime

The inforrmation age continues to transform the mechanics of integrating electric power devices and systems, from coordinated operations based purely on the physics of electric power engineering to an increasing blend of power with information and communication technology. Integrating electric system components is not just about attaching wires. It requires the connection of computer-based automation systems to associated sensing and communication equipment. The architectural impacts are significant. Well-considered and commonly held concepts, principles, and organizational structures continue to emerge to address the complexity of the integrated operational challenges that drive our society to expect more flexibility in configuring the electric power system, while simultaneously achieving greater efficiency, reliability, and resilience. Architectural concepts, such as modularity and composability, contribute to the creation of structures that enable the connection of power system equipment characterized by clearly defined interfaces consisting of physical and cyberlinks. The result of successful electric power system component connection is interoperation: the discipline that drives integration to be simple and reliable.

Epitaxial growth of β-Ga2O3 thin films on Ga2O3 and Al2O3 substrates by using pulsed laser deposition

In this work, we have successfully grown high quality epitaxial [Formula: see text]-Ga2O3 thin films on [Formula: see text]-Ga2O3 (100) and Al2O3(0001) substrates using pulsed laser deposition (PLD). By optimizing temperature and oxygen pressure, the best conditions were found to be 650–700∘C and 0.5[Formula: see text]Pa. To further improve the quality of hetero-epitaxial [Formula: see text]-Ga2O3, the sapphire substrates were pretreated for atomic terraced surface by chemical cleaning and high temperature annealing. From the optical transmittance measurements, the films grown at 600–750∘C exhibit a clear absorption edge at deep ultraviolet region around 250–275[Formula: see text]nm wavelength. High resolution transmission electron microscope (HRTEM) images and X-ray diffraction (XRD) patterns demonstrate that [Formula: see text]-Ga2O3(-201)//Al2O3(0001) epitaxial texture dominated the epitaxial oxide films on sapphire substrate, which opens up the possibilities of high power electric devices.

(Invited) Ag Sinter Joining Technology for Different Metal Interface (Au, Ag, Ni, Cu, Al) in Wide Band Gap Power Modules

Ag sinter joining as a promising alternative die attach material have received more and more attention for next generation wide band gap (WBG) power modules. Here we report a robust joint by Ag sinter joining technology for different metal interface (Au, Ag, Ni, Cu, Al) in WBG power modules. Micron-scale Ag flakes were used as the Ag fillers. Sinter Ag joint for different metal interface was implemented by a sintering process under temperatures of 250 °C in air without pressure. The die shear strength of all the joint structures was larger than 25 MPa and the sinter Ag on the Ag metallized substrate shows the maximum value about 40 MPa. The die shear strength was larger than the value of traditional Sn–Pb solders (19~24MPa). Bonding mechanism for Ag sinter joining for different metal interface also was analyzed by SEM, EDS, and TEM observation. This study will add to the understanding of Ag sinter joining and expand its application in various power electric device interconnects.

Efficient Design for a High-Energy and High-Power Capability Hybrid Electric Power Device with Enhanced Electrochemical Interfaces.

Fabrication of novel electrode architectures with tailored electrochemical interfaces (EI) is an effective strategy for enhancing charge and mass transport processes within electrochemical devices. Here, we design and fabricate a well-hybrid electrode based on the coupling of polyaniline (PANI) nanowires and Pt-based electrocatalysts to manufacture a hybrid electric power device (HEPD) combining the advantages of supercapacitors and fuel cells. Because of the boosted charge transfer between PANI nanowires and Pt-based materials via enhanced EIs, the HEPD assembled with hybrid electrodes shows remarkable performance with a peak power density of 222 mW cm-2, a specific power of 3810 W kg-1, and a specific energy of 2100 Wh kg-1, normalized to the mass of membrane electrode assemblies. The in situ Raman spectra and extended electrochemical studies demonstrate the intrinsic mechanism of charge transfer processes within hybrid electrodes, shedding light on the alternative progress of electrochemical energy conversion systems and storage devices.