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Electric vehicle charging has shifted to higher voltages to achieve higher power for more rapid charging capabilities. This article provides a contactless magnetic plug solution that enables medium-voltage grid connections for electric vehicle charging to achieve 3.5- $\text{kV}_{\rm DC}$ -to-400- $\text{V}_{\rm DC}$ , 150-kW rapid charging capabilities. This novel magnetic plug improves upon existing electric vehicle charging solutions by guaranteeing safe operation and connection through galvanic and physical separation from the medium-voltage side. It achieves this with a gap and barrier in the transformer core. We introduce a unique asymmetry in the core to localize parasitic capacitance, fully separating the medium- and low-voltage regions. This approach eliminates arcing risk and allows rapid charging capabilities to be delivered to the general public. This gapped core constitutes the plug action of our proposed charging system. We present solutions for the unique challenges of this solution through a detailed analysis of the magnetic design. We confirm this analysis in finite-element analysis and experimentation. The solution is verified through a scaled laboratory prototype of 20 kW, 1 $\text{kV}_{\rm DC}$ to 50 $\text{V}_{\rm DC}$ that is representative of the proposed 150-kW design. We demonstrate safe, arc-free, disconnection in included active content, a new solution for high-power electric vehicle rapid charging.

The power losses in high power-density motors due to high rotational speed and/or high pole counts may be reduced adopting metal amorphous nanocomposites (MANCs) featuring low power loss and a relatively high flux density ($\sim$1.3 T). We recently proposed a flux switching permanent magnet (FSPM) motor with a rating of 2.5 kW at 1400 Hz electrical speed that incorporates low loss (

Real-time temperature mapping that solves local overheating problems is important for obtaining an optimized thermal design for high-efficiency power transformers. Internal temperature monitoring of operating power transformers can also be leveraged for asset monitoring applications targeting at fault detection enabling condition-based maintenance. Transformers present a variety of challenging sensing environments such as high levels of electromagnetic interference and limited space for conventional sensors to operate. Immersion of power transformers in insulation oils for thermal management during operation and the presence of relatively large and time-varying electrical and occasional magnetic fields make sensing technologies requiring electrical wires or active power at sensing locations highly undesirable. In this work, we investigate thermal response of a standard telecom fiber instrumented on compact transformer cores by using an optical frequency-domain reflectometry scheme. Correlation between conventional temperature sensing methods and fiber-optic sensing results as well as tradeoffs between spatial resolution and temperature measurement accuracy is discussed and spatially resolved real-time monitoring of temperatures in energized transformers is experimentally demonstrated.

Wireless power transfer (WPT) techniques have been widely explored for various applications including for electric vehicle (EV) and mobile phone charging. Less attention has been paid to the use of WPT for commercial or industrial applications and for power distribution. An isolated wireless power link can enable a touch safe interface without electrically energized contacts eliminating any arc flash or electrocution hazard. This concept can for example enable safe medium voltage distribution inside data centers eliminating low voltage distribution with its large bus bars and cables and bring voltages larger than 1kV directly to the rack. A design methodology is developed for a low loss, high voltage-transfer-ratio wireless power link and a high efficiency medium voltage power converter. The proposed design methodology is evaluated using a 10kW design example and verified by finite element analysis (FEA) and experimental tests. The WPT transformer is developed with a planar magnetics structure. A U-shape ferrite configuration is proposed to improve mutual coupling by providing a low magnetic reluctance coupling path for the magnetic flux. A high efficiency power converter is developed to maintain the output voltage (48V) with a 1kV input over a wide load range. The power transfer efficiency and loss distribution are analyzed.

The use of the advanced manufacturing technique of strain annealing for nanocomposite magnetic ribbons enables control of relative permeabilities and spatially dependent permeability profiles. Tuned permeability profiles enable enhanced control of the magnetic flux throughout magnetic cores, including the concentration or dispersion of the magnetic flux over specific regions. Due to the correlation between local core losses and temperature rises with the local magnetic flux, these profiles can be tuned at the component level for improved losses and reduced steady-state temperatures. We present analytical models for a number of assumed permeability profiles. This work shows significant reductions in the peak temperature rise with overall core losses impacted to a lesser extent. Controlled strain annealing profiles can also adjust the location of hotspots within a component for optimal cooling schemes. As a result, magnetic designs can have improved performance for a range of potential operating conditions.

Metal amorphous nanocomposite (MANC) alloys are an emerging class of soft magnetic materials showing promise for a range of inductive components targeted for higher power density and higher efficiency power conversion applications including inductors, transformers, and rotating electrical machinery. Magnetization reversal mechanisms within these alloys are typically determined by composition optimization as well as controlled annealing treatments to generate a nanocomposite structure composed of nanocrystals embedded in an amorphous precursor. Here we demonstrate the concept of spatially varying the permeability within a given component for optimization of performance by using the strain annealing process. The concept is realized experimentally through the smoothing of the flux profile from the inner to outer core radius achieved by a monotonic variation in tension during the strain annealing process. Great potential exists for an extension of this concept to a wide range of other power magnetic components and more complex spatially varying permeability profiles through advances in strain annealing techniques and controls.

With the increase in size of data centers and cloud computing, its power demand is also rising sharply. Traditionally, this power distribution is achieved at about 400VDC which is inconvenient because it requires very bulky conductor to prevent high copper loss. In this paper, a new power distribution architecture for data centers is reported where direct medium voltage distribution to data-center racks are achieved with SiC based inverter. The safety issues raised due to bringing medium voltage to the racks are addressed with contactless power transfer technology. The rectifier circuit handles a high current at 48V, and synchronous rectification would be suitable to boost the efficiency. In this paper, a GaN based synchronous rectification is studied. This proposed converter circuit is analyzed and simulated in PowerSim 11. A 3kW experimental setup is developed in the lab to verify the analysis and simulation performances of the converter, where the input is 1000V and the output is 48V.

Metal Amorphous Nanocrystalline core materials have shown great promise as the magnetic material for the isolation transformer used in high power, high frequency power converters. However, many current designs require special winding configurations that result in high parasitic capacitance. Similarly, when these designs are used in active bridge circuits where a certain minimum series inductance is required, auxiliary inductors are required. These dramatically reduce the power density and can have impacts on the efficiency. Designs that integrate the series inductance through inherently geometric approaches have resulted in catastrophic increases in losses that are not predicted by typical core magnetizing loss models and have not been viable as a result. This paper demonstrates a method of using a mix of materials to manage and direct the leakage flux through paths that are more efficient. Similarly, this approach enables deliberate tuning and design of the series inductance. This introduces a method to independently design the series inductance with the magnetizing inductance of the transformer. This will prove to enable high efficiency transformer designs with very high power density, empowering wide bandgap semiconductor-based converters to reach their full potential.

Significant research has sought to understand, predict and map passive device performance for high power converters. Magnetic component performance is paramount for proper operation, efficiency and power density requirements. This paper introduces a method to apply the complex, multilevel operational waveforms needed for exact magnetic component performance mapping while using traditional open secondary testing techniques and a simple configuration of WBG devices. This converter easily achieves the high voltages and currents at high bandwidth that are applicable to advanced power converters. The presented testing approach reduces mischaracterization errors by up to 400%. An example characterization case of magnetics for the three port active bridge is shown whereby the transformer design efficiency is measured over the entire converter operational space.

In power electronics applications where various square and other more complex excitation waveforms are prevalent, manufacturers’ data sheets are lacking necessary magnetic characteristic information for detailed and proper magnetic component designs. Therefore, extensive material characterization works on several magnetic materials are independently being performed and organized in an advanced data sheet format for the power electronics community by National Energy Technology Laboratory. These includes core losses and permeability values at many frequencies, duty cycles and induction levels, as well as hysteretic BH loops and anhysteretic BH loop functions. Measurements are performed under a range of excitation conditions relevant for power electronics on full fabricated cores at scale rather than constituent core materials under idealized testing conditions. To date, data sheets of five representative core materials are currently developed and published, which are 3 percent and 6.5 percent silicon-steel, amorphous, nanocomposite, and ferrite magnetic cores. Additional cores are being tested regularly and updates will be provided as new testing results become available.

Usually, the data center racks are supplied power at or below 400V, primarily due to safety. However, because of rapid increase in size of data centers, the power demand is also rising sharply, which results in bulky power cables and inefficient power distribution. In this paper, the idea of inductive coupling is used to increase the distribution voltage level to kVs, while maintaining the required safety aspects of the system. Based on the defined problem, a suitable converter topology is selected, where safety issue are addressed with a gapped-core (or split-core) transformer isolation. The performance of this converter circuit is analyzed, and component ratings are derived. Soft-switching performance of inverter devices are also reported. Due to low voltage and high current at the output, synchronous rectification technique promises significant improvement in efficiency. To verify the performances of the converter circuit, numerical simulation is performed in PowerSIM 11. A 2.5kW lab-prototype is developed, where the input/ output voltage is 1.1kV / 48V, and experimental results are included to justify the suitability of the selected converter.

Integration of solar energy (PV) using isolated high frequency power electronic converters to the utility grid or microgrid is fast becoming an attractive option due to the improvement in power density and elimination of the bulky low frequency transformer. This paper presents and analyzes the integration of solar energy and battery based energy storage system (ESS) to the grid using a two stage topology which includes triple port dual active bridges (DABs) and a conventional 2-level inverter. This paper considers the triple port DABs as the basic building blocks which can be connected in different configurations to meet the voltage and power requirements. Detailed simulation results are provided, investigating various operating and control modes. Experimental result showing the triple port DC-DC converter waveforms are also included. This paper shows that the triple port DAB modules along with the inverter is a viable option for large scale PV-ESS grid integration.

A hybrid active filter with a new voltage synchronization control loop is proposed to improve the harmonic content of nonlinear active front end converters for mobile mining equipment. This hybrid filter topology utilizes the DC bus established by the AFE and provides load harmonics at the PCC. Unlike traditional hybrid active filters, this topology uses no real power or control loops to maintain a DC link as this is provided by the AFE. This paper investigates the hybrid active filters performance in two compensation modes, harmonic current only, and both harmonic current and reactive power injection. Necessary considerations for the medium voltage dc testbed topology, real power flow minimization, and the active filter control during worst case load harmonic currents are also discussed.

Magnetic Core Characterization is returning as a critical area of research. This is due in part to the rise of wide bandgap semiconductors that have enabled new applications, new converter topologies and system designs that are pushing the limits of passive components. Similarly, new core materials are opening design spaces previously unfilled by legacy cores. With all of these new opportunities, it is important to fully understand the magnetic core behavior within a wide operating window. This will enable a better understanding of the materials and better approaches that leads to more globally optimized designs. This paper demonstrates core material characterizations utilizing a new test circuit. It focuses on the excitation profiles of magnetic devices, inductors and transformers, typically utilized in dual and multi-port active bridges. However, the presented characterization methods are applicable to a wide variety of power converter topologies and applications.

Real-time temperature mapping is important to offer an optimized thermal design of efficient power transformers by solving local overheating problems. In addition, internal temperature monitoring of power transformers in operation can be leveraged for asset monitoring applications targeted at fault detection to enable condition based maintenance programs. However transformers present a variety of challenging environments such as high levels of electromagnetic interference and limited space for conventional sensing systems to operate. Immersion of some power transformers within insulation oils for thermal management during operation and the presence of relatively large and time varying electrical and magnetic fields in some cases also make sensing and measurement technologies that require electrical wires or active power at the sensing location highly undesirable. In this work, we investigate the dynamic thermal response of standard single-mode optical fiber instrumented on a compact transformer core by using an optical frequency-domain reflectometry scheme, and the spatially resolved on-line monitoring of transformer core temperature rise has been successfully demonstrated. It is found that spectral shifts of the fiber-optic sensor induced by the temperature rises are strongly related to the locations inside the transformer as would be expected. Correlation between thermal behavior of the transformer core as derived from standard IR-based thermal imaging cameras and fiber-optic sensing results is also discussed. The proposed method can easily be extended to cover situations in which high accuracy and high spatial resolution thermal surveillance are required, and offers the potential for unprecedented optimization of magnetic core designs for power transformer applications as well as a novel approach to power transformer asset monitoring.

The Medium-voltage DC amplifier is a thyristor based power converter with a series DC active filter that provides a highly controllable and responsive platform to establish a high power dc bus. Having bulk power flow through the thyristor converter offers an economical and high power density solution over PWM converters. By designing the system to meet standards requested by the US Navy for the Next Generation Intelligent Power System, this paper will show a platform applicable to many high power DC microgrid fields. In particular, there are promising applications in mobile mining equipment, electric aircraft and ships. This paper proposes a novel control technique to actively mitigate the DC flux that is generated by the load current. This control approach yields significant reductions in the core volume and required transformer turns. The proposed solutions will be evaluated in a 4 kVA 400 VDC laboratory scale test-bed.

A magnetic core testbed is intended to provide a variety of induction curves to fully characterize a magnetic material. Off the shelf solutions are prohibitively expensive and limited in testing range for research purposes. Mainly, high voltages and/ or currents and the ability to create a variety of induction profiles, beyond sinusoidal, is needed for full core characterization. This paper establishes the need for a novel magnetic core testing apparatus to explore high frequency trapezoidal excitation. Then a solution is presented using a novel dual voltage source converter circuit. The authors validate the topology in simulation and present a laboratory prototype. Specifically, the induction profile seen in many dual active bridges is of immediate interest and generated with this approach.

With the rapid availability of new magnetic materials and even more options in post-processing techniques such as field and strain annealing, full property maps of materials and final fabricated components are needed for proper system design. This is especially critical in modern wide bandgap power electronics based converters where medium switching frequencies are used to deliver high power. In these systems, the magnetic design has a significant impact in the overall losses. The magnetics constitute a majority of the losses and magnetic properties have a defining influence on the overall systems, e.g. available power flow and soft switching regions. A new lossless structural harness that allows easy testing of cores and the development of property maps is presented. The harness also enables the testing of mechanical variations such as gapping and clamping pressure on the core.

The solid state transformer (SST) is an emerging technology that can replace conventional passive transformers and actively manage renewable energy resources, energy storage devices, and loads. In this paper, a seamless black start control strategy is proposed for an SST-based smart grid system that has fault ride-through capability when it is islanded from the grid. Also, a method is developed to achieve smooth reconnection to the grid after a fault is cleared. The main component of the proposed control strategy is control of the high-voltage side converter of the SST (HV SST), which is based on a combination of droop control and an LCL filter. A single-loop controller for the capacitor voltage of the LCL filter is proposed, and simple criteria for setting compensator gains are provided. A low-voltage scaled SST system is introduced, and the controllers of the converters within the system are described. The proposed control strategy has been tested in simulation and experimentally on a low-voltage scaled testbed.

To further improve energy management, the US navy is exploring medium-voltage DC as the power supply of choice for next generation integrated power systems (NGIPS). Using the mature technology of multi-pulse thyristor bridge rectifiers, viable topologies are proposed that meet power density expectations. However, due to the non-linear ripple associated with thyristor commutations in such active front-ends (AFEs), a high bandwidth series AC active filter is used to smooth out the current harmonics. Similarly, a high bandwidth hybrid DC active filter is used for DC bus smoothing and improved dynamic performance. This paper will investigate the combined performance and consequential interactions of both active filters.

The medium-voltage dc amplifier is a controllable dc source for the purpose of testing medium-voltage dc system technologies for shipboard applications. In a medium-voltage dc amplifier system, a dc active filter with a series dc coupling transformer is an integral component of the system required for both steady-state and dynamic voltage injection. This paper describes the design aspects and methodology for the series dc coupling transformer in such a system. The design of the transformer is one of the most critical aspects of this system as it has to withstand large continuous dc current offset without saturating. Based on system performance requirements, design criteria for the transformer is defined and two transformer designs based on two Iron-based magnetic materials are evaluated for a 12 kVA, 300 Vdc laboratory-scale amplifier test bed. An optimal design methodology is also proposed in this paper. Various design compromises have been studied and reported. The practical transformer design considerations and feasibility study for a medium-voltage dc amplifier system are given.

To supply the AC high power drive systems, several Active Front-Ends (AFEs) with DC choppers are currently used to ensure reliable operation and an acceptable harmonic current spectrum. Recently, integration of the energy storage system with the mining equipment as an example of large mobile multimotor applications has received industry attention, especially for peak load shaving and energy management of the mines. Currently, the regenerative energy is often burnt into the choppers. The industry is motivated to capture this regenerative energy since it can be as high as 60% of the motoring power, as high as 3MJ in every operation cycle and 24 MW peak power. Hybrid approach for the front-end converter system has shown a technology path to deploy on-board energy storage without sacrificing the efficiency and reliability of the entire system. This paper addresses the dynamic performance analysis of such systems through detailed simulation and laboratory scale experiments.

AC drive systems have gained popularity in multi-motor applications including mining industry because the production rate of mines increases by almost 20% compared to DC drive systems. Typically, to supply the AC drive systems several Active Front Ends (AFE) with DC choppers are used to insure a reliable and acceptable harmonic current spectrum operation. Recently, energy storage system integration with the mining equipment has received industry attention, especially for peak load shaving and smarter energy management of the mine. The energy storage system is intended to capture the regenerative energy and reuse it for the motoring operation of the drive. Currently, the regenerative energy is often burnt into the choppers and is not fed back to the grid‥ The industry is motivated to capture this regenerative power since it can be as high as 60% of the motoring power and as high as 24 MW. Therefore, there is a possibility of large cost reduction and component downsizing. However, present status of development seems not to be very promising mainly because energy storage systems, (such as ultracapacitors) are still considered as an add-on part to existing products. In this paper, we propose power conversion configurations, yet robust and reliable for development of the multi-motor mobile mining equipment that has encouraging incentives for both the manufacturer and the mine operator.

To determine whether task deconstruction is superior to full-task training for the acquisition of transurethral resection skills on a transurethral resection of prostate (TURP) virtual reality trainer previously validated for use in residency training.Eighteen first- and second-year medical students with no previous exposure to TURP in the operating room participated in the study. The subjects were randomized to two treatment arms: full-task TURP training versus task deconstruction training. A 5-minute full-task exercise was done as a pretest and posttest in both groups. Training time was held constant at 45 minutes for both groups. The first group practiced the full-task resection for 45 minutes, while the second group performed four deconstructed tasks for a total of 45 minutes. This comprised of cystoscopy and identification of anatomy, coagulation, cutting, and complete resection exercises. Statistical analysis was performed by the Mann-Whitney test.There was a significant difference in improvement comparing the pretest and posttest performance between the two groups, favoring task deconstruction over full-task training in the amount of tissue resected and grams resected/time on cutting pedal. There was no significant difference noted in number of bleeders coagulated, fluid consumed/gram resected, or bleeders coagulated/time on coagulation pedal. There was no difference in perforation rate between two groups. The mean approval rating of the curricular experience on the simulator was 4.0/5.0 in the task deconstruction group and 3.1/5.0 in the case of the full-task training group.For the acquisition of transurethral resection skills, task deconstruction is superior to full-task training alone, in training novices on the virtual reality TURP trainer. Such a study provides more validity evidence to the unique value of simulation in the urology minimally invasive curriculum.

We assessed the impact of alfuzosin on ureteral stent discomfort.A total of 66 patients scheduled for unilateral retrograde ureteroscopy with stent placement provided consent for the study. Patients were randomized between placebo and the study medication, and investigators and patients were blinded to the randomization scheme. To evaluate pain and urinary symptoms patients were asked to complete the Ureteral Stent Symptom Questionnaire (Stone Management Unit, Southmead Hospital, Westbury-on-Trym, United Kingdom) before ureteroscopy and 3 days after the procedure to minimize the confounding impact of procedural discomfort due to surgery. Patients were also asked to maintain a use log of pain medication each day that the ureteral stent was in place. Procedure outcome and complications were recorded, as were patient study medication use and vital health information before the procedure and at the time of stent removal. Statistical analysis was performed using the Student t, chi-square and Wilcoxon rank sum tests, as appropriate, with p0.05 considered significant.Of 66 patients who provided consent 55 successfully completed the study. In 3 of the 11 failed cases surgery was not done due to spontaneous stone passage, surgery was performed in 3 but no ureteral stent was placed, 4 were excluded from study after obtaining consent due to exclusion criteria and 1 was voluntarily removed from study after obtaining consent but before surgery. Regarding stent type, procedure complications and baseline questionnaire results there were no significant differences between the placebo and alfuzosin arms. When comparing post-procedure questionnaire results, patients in the alfuzosin arm reported less overall pain in the kidney/back/loin area and less pain in the kidney area while passing urine (p = 0.017 and 0.007, respectively). Men in the alfuzosin arm also reported a lesser incidence of excessive urination (p = 0.040). When comparing changes from baseline questionnaire results, the alfuzosin arm experienced a decrease in kidney pain during sleep (p = 0.017), less frequent use of painkillers to control kidney pain (p = 0.020) and a decrease in how much kidney associated pain interfered with life (p = 0.045). There was no significant difference in the amount of narcotics used per day, as reported in patient medication logs.Alfuzosin improves the patient discomfort associated with ureteral stents by decreasing urinary symptoms and kidney pain but it does not affect the amount of narcotics that patients use while the stent is in place.