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This paper presents a three-phase voltage-source 36-pulse converter that draws almost sinusoidal currents. The converter results from the combination of a series-connected 12-pulse voltage-source rectifier with a passive voltage-injection circuit and a bidirectional switch, referred to as hybrid injection. The voltage-injection circuit uses a single-phase rectifier bridge and a single-phase transformer. Both the voltage-injection circuit and the bidirectional switch operate at six times the supply frequency and have a low rating. In this paper, the converter operation is explained and analyzed. Subsequently, the converter is evaluated experimentally using a 4-kW 400-Hz prototype, where the [THD.sub.I] of the line currents was measured to be below 1.2%. Index Terms--AC-DC power conversion, aircraft power systems, power quality, rectifiers.

A concern with the isolation transformer in a dual active bridge (DAB) dc–dc converter is the dc bias in magnetization. This article proposes a fluxgate-based current sensor to measure the dc component mixed with a large, high-frequency ac current. Compared with a commercial Hall effect current sensor, the proposed sensor significantly reduces measurement error. This article presents the working principle and design considerations. A prototype is demonstrated for dc bias elimination control in a DAB converter. [ABSTRACT FROM AUTHOR]

A three-phase, multilevel rectifier using active voltage injection with one MOSFET device is presented. The injector consists of a bidirectional switch that modifies the behavior of a 12-pulse rectifier resulting in either 24-pulse or multilevel pulsewidth-modulated (PWM) operation. The resultant input currents are almost sinusoidal, the line current THD being 2.36% for 24-pulse operation and 1.06% for PWM operation. The MOSFET current is 2.9% of the load current. The circuit operation, idealized waveforms and modulation strategy are explained and experimental results are presented. Index Terms--High-power factor rectification, three-phase multipulse rectifier.

A negative input-resistance compensator is designed to stabilize a power electronic brushless dc motor drive with constant power-load characteristics. The strategy is to feed a portion of the changes in the dc-link voltage into the current control loop to modify the system input impedance in the midfrequency range and thereby to damp the input filter. The design process of the compensator and the selection of parameters are described. The impact of the compensator is examined on the motor-controller performance, and finally, the effectiveness of the controller is verified by simulation and experimental testing. Index Terms--Brushless dc motor drive, negative input-impedance instability.

A combination of two, simple, passive injection circuits is used to eliminate virtually all the low-order harmonics from the line currents of a standard 12-pulse rectifier, transforming its performance into that of a 36-pulse system. A line current total harmonic distortion of 1.51% is achieved in a 15-kW, 400-Hz prototype. The basic 12-pulse rectifier comprises two 6-pulse bridges that are series connected on both the ac and dc sides along with a 50 %-rated, delta-star, phase-shifting transformer, while each injection circuit principally consists of a small transformer that operates at six times the supply frequency and carries around 1% of the total power throughput. The injection techniques are also valid for a fully isolated transformer arrangement. Full details of the circuit operation and design are reported. Index Terms--Total harmonic distortion (THD).

A new converter topology for a three-phase multi-pulse rectifier circuit is described. This converter draws almost sinusoidal currents from the ac system with very low harmonic content and typically less than 3% total harmonic distortion. The topology uses only passive components and has a lower component count than other rectifier circuits with similar performance. Two six-pulse rectifier bridges are connected in series, fed by a series connection of transformers, to form a 12-pulse system. An additional low power harmonic injection circuit enhances the performance of the circuit to obtain low harmonic current pollution levels that are comparable with those achieved from a 24-pulse rectifier. The circuit operation is explained and experimental results are presented. Index Terms--Autotransformers, rectifier bridges, sinusoidal currents, three-phase multipulse rectifier circuit.

Fundamental frequency techniques are used to analyze the series-parallel resonant converter under heavy load conditions, both with a continuous, but distorted parallel capacitor voltage waveform, and with a discontinuous capacitor voltage waveform. The analysis is validated with results from an experimental prototype. The application of the technique to the parallel-loaded L-C resonant converter is also considered. Index Terms--Converter, dc-dc converters, parallel capacitor, series-parallel, voltage waveform.

A single-stage, three-phase ac-to-dc converter topology is proposed for high-frequency power supply applications. The principal features of the circuit include continuous current operation of the three ac input inductors, inherent shaping of the input currents, resulting in high power factor, a transformer isolated output, and only two active devices are required, both soft-switched. Resonant conversion techniques are used, and a high power factor is achieved by injecting high-frequency currents into the three-phase rectifier, producing a high frequency modulation of the rectifier input voltages. The current injection principle is explained and the system operation is confirmed by a combination of simulation and experimental results. Index Terms--AC-DC power conversion, harmonic analysis, harmonic distortion, power electronics, resonant power conversion.

Fundamental frequency analysis is used to examine the LCC series-parallel loaded resonant converter with a capacitive output filter when operating as a high-power-factor rectifier. Optimum values are identified for the Q factor and voltage conversion ratio such that zero-voltage switching is just maintained, while minimizing the resonant circuit conduction losses. A simple resonant current control loop is shown to provide an effective mechanism of active control, achieving a high-quality input current waveform over a wide load range. Results are presented from a 1-MHz 160-W prototype. Index Terms - AC/DC converter, high-power-factor rectifier, resonant converter.

This work proposes a methodology for the energy-and cost-efficient 3-D deployment of an unmanned aerial vehicle (UAV)-based aerial access point (AAP), that exchanges a given amount of independent data with a set of ground user equipment (UE). Considering a fly-hover-communicate transmission scheme, the most energy-efficient 3-D hovering points (HPs) of the AAP are determined by decoupling the problem in the horizontal and vertical dimensions. First, we derive analytically the optimal hovering altitude that jointly maximizes the downlink and uplink global energy efficiency (GEE) of the system. Next, we propose the multilevel circle packing (MCP) algorithm to determine the minimal number of HPs and their associated horizontal coordinates, such that the AAP covers all the UEs in the given geographical area. A cost analysis is carried out to observe the variation of both fixed and variable costs; these are then minimized by suitably selecting the AAP's battery parameters, like the depth of discharge (DOD), defined as the portion of battery capacity that is consumed during a discharge cycle, and the velocity of the UAV. Simulation results show that: the UAV energy consumption has a significant impact on the 3-D HPs of the AAP; the time spent during the substitution swap of an out of power AAP has a major influence on the operational cost; the cost of the system can be optimized by suitably selecting the onboard battery and the UAV flight parameters. [ABSTRACT FROM AUTHOR]

A hierarchical control architecture is proposed for the optimal day-ahead commitment of multiple grid support services within a virtual power plant (VPP). The day-ahead optimization considers pricing and cost data to determine the commitment schedule, and a robust Model Predictive Control (MPC) approach is included to minimize the unbalance fees during real-time operations. The multi-level control has been demonstrated experimentally using a hybrid test system, where the VPP is formed of a commercial 240 kW, 180 kWh battery energy storage system (BESS), while the additional assets are modelled in a real-time digital simulator (RTDS). Two case studies are analyzed: the first assumes a purely-electrical VPP, with a single connection to the public network; the second involves a multi-energy approach, with the introduction of a gas-supplied Combined Heat and Power unit (CHP). Both winter and summer price scenarios are tested. The results show the superiority of the multiple-service operation compared to providing a single grid support service. For example, the net revenue is increased by 30% (winter) and 7% (summer) when compared to just frequency regulation, and by +99% (winter) and 30% (summer) when compared to only energy arbitrage. [ABSTRACT FROM AUTHOR]

Accurately predicting the temperature of semiconductor devices is very important in the initial design of the power electronics converter. RC thermal models derived from the well-known methods have some ability to predict the temperature. However, the accuracy is boundary condition specific; hence, these methods cannot be used in the reliability analysis. To make the thermal model more accurate and robust, the factors contributing to discrepancies need to be analyzed carefully. These are power-module-materials’ nonlinear properties, thermal grease layer, and the cooling system (i.e., liquid-cooled cold plate). In this article, the estimation of accurate RC parameters from the FEA thermal model is demonstrated in COMSOL. The electrical model having temperature-dependent power loss model is coupled to a refined thermal model and solved in a circuit simulator, PLECS. The proposed method is applied in two applications: assessing thermal interaction between IGBTs and antiparallel diodes in a half-bridge power module and assessing thermal interaction among the discrete switches in an interleaved bidirectional dc–dc converter. Results show that the impact of material nonlinearity, thermal grease layer, and cooling boundary conditions are significant for accurate prediction of IGBT and diode temperatures. The proposed model is consistent with FEA results and differs by 2%–6.5% compared with the experimental results. [ABSTRACT FROM AUTHOR]

A two-phase buck–boost converter utilizing dual interleaving is presented in this article. The dual interleaving consists of an interphase transformer (IPT) that doubles the ripple frequency together with two conventional buck–boost switching arms, mitigating the inductor ripple current and aiding to increase the power density of the converter. A description of the design and selection of the power devices is presented for a 32-kW, 75-kHz dual interleaved SiC prototype with an IPT, such that a power density of 7.4 kW/kg is achieved. The operation of the circuit is verified experimentally using a prototype with 315–385 V supply range and 350-V output voltage, achieving 97.1% peak efficiency at 32 kW. The experiments reveal that the interleaved coupled currents are equalized without an active balancer. [ABSTRACT FROM AUTHOR]

An investigation is described into the optimization of multi-phase, high power, bi-directional DC-DC interleaved converters suitable for Electric Vehicle (EV) applications. Two dual-interleaved topologies were considered initially for the optimization, the main difference being the magnetic devices: either discrete inductors (DI) or an Interphase Transformer (IPT). The comparison used a comprehensive multi-objective design optimization procedure for an 80 kW case study. High performance inductors comprising a split-core structure and dual-foil windings to reduce losses, and a 180 °C core, enabled the DI to be competitive with IPT in terms of power density and efficiency. The optimized designs are validated experimentally with an 80 kW bi-directional SiC DC-DC converter, achieving a power density of 31.4 kW/L and specific power of 15.7 kW/kg. The study is then extended to 100-kW three and four-phase interleaved topologies. [ABSTRACT FROM AUTHOR]

This paper presents a method for the forecasting of the voltage and the frequency at the point of connection between a battery energy storage system installed at The University of Manchester and the local low-voltage distribution grid. The techniques are to be used in a real-time controller for optimal management of the storage system. The forecasters developed in this study use an artificial neural network (ANN)-based technique and can predict the grid quantities with two different time windows: one second and one minute ahead. The developed ANNs have been implemented in a dSPACE-based real-time controller and all forecasters show very good performance, with correlations coefficients >0.85, and mean absolute percentage errors of <0.2%. [ABSTRACT FROM AUTHOR]

In this paper, the averaged small-signal model of the dual-interleaved buck converter is extended to include the phase interaction effects that arise from the interleaved sampling of the phase currents. Sampler decomposition techniques are used to extend the averaged model, revealing a slow-scale instability that can place significant restrictions on the choice of controller parameters. The model is confirmed by simulations and measurements using a 60-kW dual-interleaved prototype with an interphase transformer; however, the analysis is equally applicable to interleaved converters without magnetic coupling. [ABSTRACT FROM AUTHOR]

A split-core technique is proposed to mitigate the gap losses in high-frequency nanocrystalline cores, which enables significant size reductions in thermally limited designs. Finite element analysis is used to examine the gap loss dependence on core width D revealing a nonlinear relationship of the form loss ∝ $D^{\alpha }$. α is approximately constant for frequencies of 10–200 kHz over the range of core widths typically used in power electronics, but α increases with gap length. Splitting the core into a number of subcores can therefore provide significant reductions in gap loss, especially with larger gap lengths. The results from a 300-A (peak), 200-A (continuous) inductor show that with three subcores and a gap length of 4 mm, the gap losses are reduced by 50%, and the hot-spot temperature is reduced by 24.5 °C. Using the technique it is estimated that the original inductor weight could be reduced by 40% with four split cores, making a significant impact on converter power density. [ABSTRACT FROM AUTHOR]

A comparison of the performance of graphene‐based supercapacitors is difficult, owing to the variety of production methods used to prepare the materials. To the best of our knowledge, there has been no systematic investigation into the effect of the graphene production method on the supercapacitor performance. In this work, we compare graphene produced through several routes. This includes anodic and cathodic electrochemically exfoliated graphene, liquid phase exfoliated graphene, graphene oxide, reduced graphene oxide, and graphene nanoribbons. Graphene oxide exhibited the highest capacitance of approximately 154 F g−1 in 6 M KOH at 0.5 A g−1 attributed to oxygen functional groups giving an additional pseudocapacitance and preventing significant restacking; however, the capacitance retention was poor, owing to the low conductivity. In comparison, the anodic electrochemically exfoliated graphene exhibited a capacitance of approximately 44 F g−1, the highest of the 'pure' graphene materials, which all exhibited superior capacitance retention, owing to their higher conductivity. The cyclability of all of the materials, with the exception of reduced graphene oxide (70 %), was found to be greater than 95 % after 10 000 cycles. These results highlight the importance of matching the graphene production method with a specific application; for example, graphene oxide and anodic electrochemically exfoliated graphene would be best suited for high energy and power applications, respectively. [ABSTRACT FROM AUTHOR]

The emergence of wide-bandgap devices, e.g., silicon carbide (SiC), has the potential to enable very high-density power converter design with high-switching frequency operation capability. A comprehensive design tool with a holistic design approach is critical to maximize the overall system power density, e.g, by identifying the optimal switching frequency. This paper presents a system level design tool that optimizes the power density (volume or mass) of a three-phase, two-level dc–ac converter. The design tool optimizes the selection of the devices, heatsink and passive components (including the design of the line, electromagnetic interference (EMI), and dc-link filters) to maximize the power density. The structure of the optimization algorithm has been organized to reduce the number of potential design combinations by over 99%, and thus, produces fast simulation times. The design tool predicts that when SiC devices are used instead of Si ones, the power density is increased by 159.4%. A 5 kW, 600-V dc-link, three-phase, two-level dc–ac converter was experimentally evaluated in order to confirm the accuracy of the design tool. [ABSTRACT FROM PUBLISHER]

Three pulse-width-modulation (PWM) digital control approaches are evaluated to provide the current sharing between phases in high-power dual-interleaved DC–DC converters. The implementation of a digital peak current, multi-sample averaged current and an enhanced single-sample averaged current control in a TMS320F28377D is described. A summary of stability requirements is provided for designing the controllers and experimental results from a 60 kW, 75 kHz silicon carbide DC–DC converter are used to evaluate the steady-state and dynamic performance of the three control methods. Overall the best performance in terms of tracking and speed of response was achieved by the enhanced single-sample method. The multisampled technique provided the highest tracking accuracy, but at the expense of the slowest dynamic response. The fastest dynamic response was achieved by the digital peak current control, but this method is limited by poor noise immunity and instability for duty ratios in the region of 0.5. [ABSTRACT FROM AUTHOR]

All-GaN-integrated cascode heterojunction field effect transistors were designed and fabricated for power switching applications. A threshold voltage of +2 V was achieved using a fluorine treatment and a metal–insulator–semiconductor gate structure on the enhancement mode part. The cascode device exhibited an output current of 300 mA/mm by matching the current drivability of both enhancement and depletion mode parts. The optimization was achieved by shifting the threshold voltage of the depletion mode section to a more negative value with the addition of a dielectric layer under the gate. The switching performance of the cascode was compared to the equivalent GaN enhancement-mode-only device by measuring the hard switching speed at 200 V under an inductive load in a double pulse tester. For the first time, we demonstrate the switching speed advantage of the cascode over equivalent GaN enhancement-mode-only devices, due to the reduced Miller-effect and the unique switching mechanisms. These observations suggest that practical power switches at high power and high switching frequency will benefit as part of an integrated cascode configuration. [ABSTRACT FROM AUTHOR]

Finite element analysis is used to examine the gap losses that occur in finely laminated nanocrystalline inductor cores under high-frequency operation. The losses are seen to be concentrated in the region of the air gap and the dependence of the losses on key design parameters and operating conditions is explored. The results show that gap losses can be significant in this type of core, creating hot spots around the gap, and the losses are not accurately predicted by established design equations for low-frequency laminated cores. A modified loss equation is proposed. Validation is provided by measurements on a 300-A, 60 kHz inductor. [ABSTRACT FROM AUTHOR]

To provide a basis for controller design in interleaved dc–dc converters, an improved small-signal averaged model is presented. Sampler decomposition techniques are used to represent the interleaved operation of the individual control loops within the converter. The resultant model reveals interaction effects and instability phenomena that are not predicted by a simple noninterleaved model, and which impose significant restrictions on the selection of control parameters. The model is validated by detailed simulations and experimental results from a digitally controlled dual-interleaved boost converter. [ABSTRACT FROM AUTHOR]

This paper analyzes some operational issues of three-phase surface-mounted permanent magnet synchronous generators (PMSGs) connected to a diode rectifier. This simple configuration coupled to a single-switch dc–dc converter is used in small-scale wind energy conversion systems, as well as in energy harvesting systems, to reduce costs. The diode rectifier causes an intrinsic limit for the maximum convertible power, which is related to the load impedance matching, and additional joule losses due to the distorted currents. By using an analytical steady-state model of the rectifier and of the PMSG, this paper discusses how to achieve two particularly meaningful operating conditions characterized respectively by the maximum power transfer and the maximum power per ampere. The theory is validated by simulation and test results on a prototype. [ABSTRACT FROM AUTHOR]

An adaptive energy management control with an integrated variable rate-limit function is described for an energy storage system (ESS). The proposed control protects the primary power source(s) in the system as effectively as possible from sudden load transients within the constraints of the available stored energy. The control can be designed to use the available energy more aggressively during load changes in the low- or high-power regions while offering the lowest possible rate-of-change of the main source power or offers a fixed minimum rate-of-change in power for a given total load and amount of energy. The control design is described in detail and demonstrated experimentally when applied to a supercapacitor ESS within an aircraft test facility. [ABSTRACT FROM PUBLISHER]

A system‐level behavioural modelling technique is described for a switched reluctance motor drive. The model enables simple and efficient analysis or simulation of multiple drive systems such as pumps, actuators and engine starters within a more‐electric network, for example, on‐board an aircraft. The behavioural model is based on a power balance analysis. The transfer functions in the model are parameterised from experimental tests on the drive system, resulting in a simple model that only reproduces the average behaviour of the input–output variables necessary for system‐level analysis. No data from the manufacturer is required to develop the model. The technique is discussed and validated using an engine starter in an aircraft test facility. [ABSTRACT FROM AUTHOR]

A system-level modeling technique for a switched reluctance generator (SRG) is described for aerospace applications. Unlike existing techniques, this model is very simple and only reproduces the average behavior of the input–output variables that are required for system-level analysis of the aircraft power distribution system. The model is parameterized from the measured generator response, avoiding the need for a detailed knowledge of the equipment structure, which may be unavailable. The modeling procedure is described in detail and validated by measurements on an SRG within an aircraft test facility. [ABSTRACT FROM AUTHOR]

The design of a 200-A, all-SiC power-module-based on bipolar junction transistor devices is described, and the impact of the module is assessed on the performance of a 50-kW dc-dc converter for electric vehicle applications, particularly the overall weight and efficiency. Using a hard-switching dual-interleaved topology, which has proven high efficiency and high-power density capability, the operation of a 50-kW, 75-kHz all-SiC converter is compared with that of an insulated-gate bipolar transistor-based silicon converter, switching at 25 kHz, each providing 600-V output. The results show that the total losses are reduced by almost 40%, whilst the overall weight is reduced by 27%, achieving a power density of 10.5 kW/kg. Experimental results of the SiC converter operating at 220-600 V, 52.8 kW are provided, showing an efficiency of 97%. [ABSTRACT FROM AUTHOR]

Two techniques are presented to balance the filter capacitor voltages of a multipulse rectifier with the active injection operating on a variable-frequency supply. The active injector consists of a low-rated bidirectional switch that modifies the behavior of a 12-pulse rectifier at either low or high frequency, resulting in 24-pulse or multilevel pulse width modulation operation, respectively. The operation of the rectifier and the injector, the practical issues that unbalance the capacitor voltages, and the methods to correct this imbalance are explained together with experimental results obtained with a 4-kW prototype. [ABSTRACT FROM AUTHOR]

A negative input-resistance compensator is designed to stabilize a power electronic brushless dc motor drive with constant power-load characteristics. The strategy is to feed a portion of the changes in the dc-link voltage into the current control loop to modify the system input impedance in the midfrequency range and thereby to damp the input filter. The design process of the compensator and the selection of parameters are described. The impact of the compensator is examined on the motor-controller performance, and finally, the effectiveness of the controller is verified by simulation and experimental testing. [ABSTRACT FROM AUTHOR]