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Geared devices are commonly used to match the operating speed and torque of the power source with the second mover. Such geared devices are usually mechanical gears. As counterparts of the conventional mechanical gears, magnetic gears (MGs) are becoming promising devices, mainly due to the merits of physical isolation between moving parts, no gear lubrication, no mechanical fatigue, inherent overload protection and reduced maintenance, etc. Recently, several new topologies have been proposed to achieve better performances. In this paper, a general review of MGs is presented, including a discussion of the most common and upcoming topologies and a description of the working principle. A comparison of different topologies is carried out in terms of gear ratio and torque density. The main computational techniques generally adopted for coaxial MGs are listed and described. Some key aspects concerning the design, the existed challenges, and potential applications are also discussed. This paper aims to provide a comprehensive overview of the MG for readers working in this field. [ABSTRACT FROM AUTHOR]

The number of applicable carrier-based pulsewidth modulation (PWM) patterns increases with the growth of output levels in scalable multilevel topologies, such as active-neutral-point-clamped (ANPC) converters. Therefore, it is hard to optimize PWM for such topology, especially with large output levels. In this paper, a simplified and modular carrier-based PWM design approach for multilevel ANPC converters is proposed. Inspired by the decomposition theory, the topology decomposition is introduced in this paper to decompose an N-level ANPC converter into low-level subtopologies. Then, the complete set of applicable PWM patterns is derived based on ANPC operation principles, which makes it possible to optimize the performance based on the various requirements in applications. Meanwhile, the carrier-based PWM is implemented through the utilization of subtopologies with low-level modulation schemes, such that the design process of carrier-based PWM is greatly simplified and modularly realized. Both the complete PWM patterns and PWM design examples with experimental results of several ANPC converters are provided to show the feasibility and modularity of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a single-phase ac–dc–ac converter composed of a transformer and two three-leg converters connected in series. The proposed converter allows to supply the load with a voltage with constant amplitude and frequency, and to operate with the grid current with low harmonic distortion and high power factor. In addition, the converter can be used to mitigate fundamental overvoltage and voltage harmonics at the grid. The system model, regions of operation, a power flow analysis, and a method to regulate the dc-link voltages using the voltage vector redundancies are given. In the first version of this paper, two pulsewidth modulation (PWM) techniques (including space vector PWM) and a control system were provided. The proposed topology is compared with two conventional systems in terms of operation range, harmonic distortions, and semiconductor losses. Simulation and experimental results are provided to validate the feasibility of the system. [ABSTRACT FROM AUTHOR]

This paper presents a dual active bridge (DAB) converter with reactive power control capability (Q-capability) for a battery energy storage system (BESS) or an electric vehicle (EV) to deliver vehicle-to-home (V2H) and vehicle-to-grid (V2G) services. The DAB topology is preferable for EV charging systems due to its galvanic isolation and bidirectional power flow capabilities. However, this topology increases reactive current peak and loses zero voltage switching (ZVS) operation at light loads if it is not controlled with improved modulation strategies and proper Q control. This paper proposes a mixed modulation method and a reactive power optimization (RPO) algorithm based on power system load flow concepts. Due to the complexities associated with the analytical solution using time domain analysis, this paper develops detailed universal expressions of a DAB converter using the harmonic analysis method. Analytical identification of ZVS boundaries and DSP implementation of the RPO algorithm become easier with these universal expressions. Multiple modes analysis for different operational states is no longer required. Simulation results have been shown for different modulation strategies of the DAB converters. The theoretical analysis of modulation strategies, RPO algorithm and ZVS operation are validated by experimental results on a DAB prototype. Results show that the proposed control strategy reduces the reactive power and provide ZVS operation over a wide ranges of voltages. [ABSTRACT FROM AUTHOR]

This paper concerns the force density optimization for medium-stroke reluctance actuators applied in antivibration applications. The force density in a conventional E-core reluctance actuator is limited for medium strokes by the nonlinear force–displacement characteristic. In this paper, different tooth topologies are analyzed to maximize the force density along the stroke using the finite-element analysis. Teeth parameters are tuned in each topology to analyze the influences on the force density over a stroke of $\pm$12.5 mm. An analytic thermal model is used to estimate the surface temperature and is verified with finite-element simulations. The optimal topology is validated by experiments on a prototype. [ABSTRACT FROM AUTHOR]

Multilevel inverters (MLIs) are playing a pivotal role in the power sector with potential applications, such as interfacing renewable energy sources with the grid and several industrial drive applications. MLIs with a smaller number of switching devices are more promising due to their compact size, reduced cost, and higher efficiency compared with their traditional counterparts. This paper, therefore, presents a new three-phase seven-level inverter. This topology is a combination of two cascade-connected two-level voltage-source inverters (VSIs) and H-bridge cells with flying capacitors (FCs). This paper presents the operating principle and the balancing technique for the dc-link capacitors and FCs. The generation of various output voltage levels and the limitation of the sinusoidal pulsewidth modulation control for FC voltage balancing is also presented. The number of components in the proposed circuit configuration and their voltage ratings are considerably lower compared with the recently proposed topologies. The behavior of the proposed circuit configuration is first assessed with simulation studies and is then tested with a laboratory prototype. The simulation and experimental results validate the effectiveness of the proposed topology and the voltage balancing technique. [ABSTRACT FROM AUTHOR]

This paper deals with a multilevel ac–ac double conversion system that uses the intercell transformer (ICT) for applications which include generating systems and the interfacing of renewable energy sources with the utility grids. Each phase of the proposed configuration is formed through the ICT interleaving operation of two multilevel 5-level E-type legs to achieve the 3-phase 5-level back-to-back E-type converter (3Φ5L BTB E-type converter). The analytical procedure to select the inductance and capacitance values of both the input and output filters is described in the paper. Furthermore, the design and implementation of the input/output ICTs and inductors is discussed. The simulation and the experimental results on the 20-kVA interleaved 3Φ5L BTB E-type converter prototype are presented to validate the proposed analysis. [ABSTRACT FROM AUTHOR]

There has been increasing interest in solid-state transformers (SSTs) as a future replacement for conventional distribution transformers as it is able to provide ancillary services in addition to step-up/step-down of voltages. In SSTs, a common topology used in the ac–dc stage is the cascaded H-bridge (CHB) multilevel converter. This paper proposes a novel dual-model predictive control method for the CHB multilevel converter with faster dynamic response, improved harmonic performance, and voltage balancing of the CHB cells. The primary model enables conventional control over source current and output voltages, whereas the secondary model is able to generate the reference source current through power modeling, which eliminates the need for a proportion-integral (PI) controller, thus resulting in faster dynamic response. A Luenberger-based observer is also implemented to estimate the dc load current in each CHB cell. The second-order harmonic notch filter and the CHB cell dc voltage balancing cost function aim at improving the performance of the source current and CHB cell dc voltages, respectively. The proposed control techniques are then validated under steady-state and transient conditions through simulation and experiment with a laboratory prototype. [ABSTRACT FROM AUTHOR]

The use of electronic equipment and other dc-compatible appliances in homes and offices is increasing at a very fast rate, as well as the distributed generation of energy. These two statements will most likely trigger, in a near future, the adoption of district-scale dc grids, connecting dc microgeneration plants and consumers, in an effort to cut the number of conversion steps required to deliver power to dc appliances. DC–DC converters will be fundamental in these systems, allowing the establishment of several voltage levels. The reliability of these converters plays a critical role, ensuring service continuity of the loads connected to them. With the increment of reliability in mind, this paper proposes a simple yet effective open-circuit fault diagnostic method suitable for interleaved dc–dc boost converters, but equally functional for other dc–dc converter topologies. The improvements introduced in this paper greatly simplify the diagnostic action, while making the correct diagnostic of faults independent of the switching duty cycle. Moreover, an alternative reconfiguration scheme is proposed to mitigate the adverse impacts of such faults. To prove the effectiveness of these strategies, a three-phase interleaved boost converter prototype was used in the experiments. [ABSTRACT FROM AUTHOR]

In this paper, an investigation into an alternative topology for reluctance synchronous machine rotor flux barriers is presented. The investigated topology employs a high number of flux barrier variables with an alternative asymmetric rotor structure. The focus in this paper is on maximizing average torque and minimizing torque ripple, using finite element-based design optimization, in order to study the possibility of achieving acceptably low torque ripple. A subsequent investigation into the effect of rotor skew on the proposed optimized design to reduce torque ripple even further is also conducted, as well as the manufacturing and testing of the proposed flux barrier prototype. [ABSTRACT FROM PUBLISHER]

The emulation of virtual resistance finds various applications in the power processing industry. This paper proposes a novel notion of adaptive sliding mode based loss free resistor (ASLFR). This is achieved by allowing the input power of the power-out power-in (POPI) system to vary, in order to accommodate the load demands. In this paper, the concept is illustrated for power-factor correction (PFC) applications. The ASLFR is used to achieve the dual purpose of harmonics-free rectification along with excellent system response under load and line transients. The scheme serves itself as an efficient single-stage PFC solution. A generic mathematical formulation of the scheme is presented, which can be used for different converters. Then on, a boost topology, operating in continuous conduction mode, is chosen to demonstrate theoretical developments and to showcase the effectiveness of the scheme. The robustness of the proposed controller to any line or load variation is established. A fast voltage recovery with almost no undershoot/overshoot is achieved at transients by using the proposed controller. Additionally, a qualitative analysis is provided to demonstrate the expediency of the proposed ASLFR. The theoretical claims are well supported by simulation as well as experimental results. [ABSTRACT FROM AUTHOR]

A novel partitioned-primary hybrid-excited flux-switching linear machine with dual-PM excitation (DP-PPHEFSLM) is proposed and investigated in this paper. Unlike conventional single-primary hybrid-excited topologies, this proposed topology separates armature windings and field windings into two different parts of the partitioned-primary, with each part also having sandwiched or buried PMs. Due to greatly increased armature and field slot areas, it thus solves the problem of a crowded primary, which is typically encountered with conventional structures. Besides, the thrust density is further increased by skillfully positioning PMs on both primary parts. In this paper, first, the topology, operation principles, and viable primary/secondary pole-number combinations of the proposed machine are elaborately addressed. Based on 2D finite-element method (FEM), the proposed machines are globally optimized using genetic algorithms and their electromagnetic performances further investigated. Moreover, the proposed machine is compared with conventional topologies in terms of electromagnetic performances, which shows that the proposed machine exhibits multiple merits such as higher thrust density, improved space utilization, and more flexible flux control capability. Finally, a 6/7 DP-PPHEFSLM prototype machine is manufactured and tested to validate the 2D FEM-predicted results. [ABSTRACT FROM AUTHOR]

This paper proposes a novel open-winding brushless doubly-fed reluctance generator (OW-BDFRG) with dual two-level converters in order to reduce the converter rating and switching frequency for large-scale wind turbine applications. The new converter topology is equivalent to a three-level converter directly connected to the control winding of typical BDFRG. The OW-BDFRG system with this topology structure requires lower converter rating and switching frequency, and has a more flexible control mode, better operation performance, and fault redundancy capability. For the OW-BDFRG, this paper also proposes a new control scheme combining direct power control (DPC) with sliding mode variable structure (SMVS) control to implement the power tracking. The voltage-vector switching table of DPC is redesigned according to the error signals of active and reactive powers of the power winding, as well as the sector location of control winding flux. The active and reactive powers of the OW-BDFRG can be directly decoupled and independently controlled by properly selecting the switching voltage vectors. The novelty of this paper lies in an OW-BDFRG topology driven by dual two-level converters to improve the system characteristics, and the use of SMVS control to improve the DPC accuracy and robustness to parameter variations. Finally, the effectiveness of the proposed system is verified through simulation and experimental studies. [ABSTRACT FROM AUTHOR]

This paper presents an improved dc-link voltage balancing algorithm for a three-level neutral-point-clamped inverter by considering phase current direction. Detailed studies on the effects of change in load current direction on the dc-link capacitor voltages are presented. A maximum value of power factor is numerically derived, above which it affects the capacitor voltage balancing capability. Compared with the previously presented research work, the inputs to the space-vector pulsewidth-modulation block are the three phase currents and the difference between the two capacitor voltages. Depending on the states of the two dc-link capacitor voltages and phase current direction, redundant voltage vector sequences are selected. The selected vectors keep the capacitor voltage deviations within 5% of the total dc-link voltage. Two zero switching vectors (i.e., PPP and NNN) are also removed from all subsectors of the earlier proposed strategy, which one used to produce higher common-mode voltages. Detailed simulation and experimental results are presented in this paper for a 6.0-kW surface permanent-magnet synchronous machine. Both the simulation and experimental results show the required performance of the proposed system. [ABSTRACT FROM AUTHOR]

A mobile charging system (MCS) for electric vehicles (EVs) is presented in this paper. The proposed MCS has a 2-MWh energy storage capacity for charging five EVs simultaneously with 75-kW individual charging rates. The MCS would be rechargeable from the available power substations (three phase, 480 V) with 375-kW charging rate. The appropriate modular power interface is designed and implemented between the MCS, batteries of the EVs, and the power substations. Experimental validation is presented in this paper to demonstrate the system performance and effectiveness under rapid charging requirements. [ABSTRACT FROM AUTHOR]

This paper proposes a new carrier-based modulation strategy for symmetrical cascaded multilevel converters denominated phase disposition with sorting (PDS). It deals with the issue of irregular distribution of PWM signals and power for each converter cell that occurs when using the conventional phase disposition (PD) modulation. Although some alternatives have been proposed in the literature for overcoming these problems, most of them do not consider operation of the converter under fault conditions on the power cells. Therefore, one of the contributions of the proposed PDS modulation strategy is the ability to evenly distribute the pulse signals for the converter semiconductor switches, resulting in the same power being processed by all cells, maintaining the good quality of the synthesized output voltages, even with faults in one or more power cells. In addition, it allows implementation in commercial digital signal processors, not requiring additional hardware. The good performance of the proposed modulation strategy is validated through experimental results for a three-phase symmetrical cascaded multilevel converter with three cells per phase, considering normal and faulty conditions on the power cells. [ABSTRACT FROM AUTHOR]

Unipolar-pulsewidth modulation (UP-PWM) inverter takes advantages of high power efficiency and small output chokes which is widely used in the industry. However, UP-PWM inverters cannot be used in parallel operation due to a current unbalance problem. This paper studies the current unbalance problem of paralleled UP-PWM inverters with common dc bus and ac bus. First, the problem of unbalanced inductor current is defined and analyzed. Second, a technique to eliminate unbalanced currents is proposed. The proposed current balancing technique only requires one more current sensor in an inverter module rather than changing converter topology or modulation method, which makes it possible to apply UP-PWM inverters in parallel-operation while keeping the advantages of unipolar switching. The proposed current balancing method is verified by both simulation and hardware experiment. Experimental verification is performed on two 1 kW, 400 V input, and 120 V/60 Hz output prototypes, which shows a good agreement to the analytical study. [ABSTRACT FROM AUTHOR]

High efficiency and low cost power converters for interfacing energy storage have become critical in renewable energy systems. In this paper, a fractional charging converter (FCC) is proposed to reduce power rating as well as cost of the dc–dc converter for hydrogen production by alkaline electrolyzer cells. The FCC configuration only processes the partial power resulting from the voltage difference between the source and the energy storage element.  Moreover, the converter employed in such configuration can be either isolated or non-isolated, which simplifies topology selection. An analysis and comparison of two dc–dc topologies using a high-frequency transformer based on component stress factor (CSF) is performed to determine the optimal solution for the evaluated application. Based on the results of the CSF analysis, and due to its capability of handling wide input voltage, the isolated full-bridge boost converter is designed, built, and tested. Experimental results prove the feasibility of the fractional charging configuration with a reduction of 80% of the power rating compared to the traditional interconnection, which implies a reduction in cost, weight, and an increase in efficiency. The converter's maximum voltage gain achieved is 25 and the highest measured system efficiency is 98.2%. [ABSTRACT FROM AUTHOR]

In this paper, a dual-fed (DF) common dc-link topology open-end winding permanent magnet synchronous motor for aircraft high-speed starter–generator application is considered. While on one hand the common dc bus configuration significantly simplifies and reduces the costs of the topology, on the other hand it allows the zero-sequence current (ZSC) to flow freely in the system. High-speed machines are characterized by low phase inductance, which implies low zero-sequence impedance. A small time constant of the zero-sequence circuit produces a high-frequency, high-intensity ZSC ripple with the risk of harming the switching devices. This paper presents a novel hybrid space vector pulsewidth modulation that allows to instantaneously eliminate the zero-sequence voltage (ZSV) produced by the two voltage source converters (VSCs) by square wave modulating one of the two VSCs. The non-sinusoidal machine back electromotive force (EMF) has been considered and the effect of the converters’ dead time on the ZSV has been analyzed. The square-wave-modulated VSC uses insulated-gate bipolar transistor (IGBT) devices, whereas the other uses Silicon Carbide (SiC) technology. The proposed topology is tested through both simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper presents a three-port three-phase current-fed dc–dc converter with high-frequency isolation and bidirectional power flow. Port I is fed by a battery bank, port II employs a set of photovoltaic modules, and port III is connected to a dc link. The topology uses three single-phase H-bridge cells in the primary side and a three-phase H-bridge converter in the secondary one. High-frequency isolation is ensured by three single-phase transformers connected in an open delta-wye configuration. The theoretical analysis is performed considering the fundamental component of the voltage across the transformers. Maximum power point tracking, the battery current, and the power flow between the primary and secondary sides are controlled by the use of variable duty cycle technique in the primary side and the use of phase-shift technique between the primary and secondary bridges. In order to validate the study, experimental results of the proposed system considering the dc rated voltages as 48 V/96 V/380 V for Ports I/II/III, respectively, and rated power of 3.5 kW are carried out. [ABSTRACT FROM AUTHOR]

One of the recent trends in power electronics field is to achieve high efficiency and compact size by using wide bandgap power devices such as silicon carbide (SiC) or gallium nitride switches. This paper compares the efficiency, the motor terminal voltage quality (dv/dt), and the common mode current of the SiC-based variable frequency drives (VFDs) according to the inverter topologies with and without the output filters. For this purpose, both the 2-level (2L) and 3-level (3L) topologies with SiC devices are built and tested. Here, the well-known 2L half-bridge inverter is compared with the well-known 3L T-type neutral point clamped inverter. A dv/dt filter and a sine wave filter have been discussed to satisfy the National Electrical Manufacturers Association standards as well. The experiments have been carried out with a 380-V/60-Hz, 3.7-kW induction motor and the custom designed power stages. Additionally, the experiments with both a 3-m and a 50-m cable length between the VFD and the induction motor are performed and reported. [ABSTRACT FROM AUTHOR]

Multilevel converters are a proven solution for medium-voltage and high-power applications, including renewable energy conversion. Developing 6.6-kV converters is a key goal for the wind turbines industry. Considering the voltage rating of commercially available semiconductors, five-level converters are necessary to reach 6.6 kV. The five-level active neutral-point-clamped converter (5L-ANPC) is one of the most advantageous topologies among five-level multilevel converters. This paper presents a new 5L-ANPC topology that overcomes the features of the previously employed 5L-ANPC topology. Along this paper, the properties and working principle of this new 5L-ANPC are explained. Finally, the validity of the new converter is validated via simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes two high-performance switched flux hybrid magnet memory machines (SF-HMMMs) based on the design concepts of E-core and C-core SF permanent magnet (PM) machine topologies. Since two kinds of PMs (i.e., NdFeB and low coercive force magnets) are employed, the proposed machines can offer the merits of high torque capability, excellent flux adjustability, and high efficiency across a wide speed range. In this paper, the PM arrangement and dimensions, stator/rotor pole number combination, as well as the major design parameters are optimized first. Then, the electromagnetic characteristics of the proposed machines are investigated and compared with their conventional 12-stator pole SF-HMMM. It is found that compared with their conventional 12-stator pole counterpart, the proposed machines offer improved torque density and flux adjustability, even with the reduced PM usage. Finally, two machine prototypes are manufactured and tested to validate the analyses. [ABSTRACT FROM PUBLISHER]

This paper presents design of an isolated high-step-down dc–dc converter based on a class-DE power stage, operating at a 10-MHz switching frequency using enhancement-mode gallium nitride transistors. The converter operating principles are discussed, and the power stage design rated for 20 W is presented for a step down from 200–300 V input to 0–28 V output. Commercially available magnetic materials were explored and the high-frequency resonant inductor and transformer designs using a low-loss Fair-Rite type 67 material are presented. Finite-element simulations have been performed to estimate the parameters of magnetics at 10-MHz. Experimental results are presented at 12 W, 254 V input to 22 V output and 5 W, 254 V input to 14 V output on a laboratory prototype operating at 10-MHz. At 20 W, the experimental prototype achieved an efficiency of 85.2%. [ABSTRACT FROM AUTHOR]

Electrostatic motor can work as a supplement to the electromagnetic motor due to its simple structure, low cost, light weight, and high efficiency. This paper presents a dielectric-gas-based single-phase electrostatic motor with simplified construction. The motor design is focused on increasing the capacitance, subsequently the torque, to make the electrostatic motors competitive with the electromagnetic ones. Three-dimensional (3-D) finite element analysis (FEA) simulation and optimization process of the electrostatic motor is performed. A 50 W electrostatic motor with the torque of 0.25 N·m, which is the same order in magnitude with the fluid-filled electrostatic machine and induction machine at the similar power level, is designed. Losses including the friction loss, windage loss, and dielectric loss are predicted. Thermal fields are analyzed using FEA and the electrostatic motor presented can work stably at high ambient temperature. 3-D printing is used to build a prototype machine to eliminate the process of mould manufacture and achieve a weight reduction. Predicted capacitance of machine is compared with measured result and good agreement is achieved. [ABSTRACT FROM AUTHOR]

Low-voltage dc distribution systems have gained significant attention over the last years, since they provide simpler and more efficient integration of distributed generators and storage devices, establishing a pathway to net zero energy buildings. In low-power units, transformerless utility interface is preferred to reduce footprint and losses. However, the lack of galvanic isolation introduces a common-mode (CM) path between the dc distribution bus and the utility service grounding, leading to the presence of high CM voltages at the dc bus feeders. The attenuation of the CM voltage reduces the touch voltage amplitude and leakage current, contributing to a safer environment. In this paper, a feed-forward active compensation of the CM voltage is proposed. It relies on utility voltage parameters, estimated by a phase locked loop, to generate a counter CM voltage; hence, it does not require previous knowledge of the system CM path model or the addition of voltage sensors. Experimental results show that this technique can attenuate the CM voltage to non-dangerous magnitudes without interfering with the microgrid differential mode behavior. [ABSTRACT FROM AUTHOR]

This paper analyzes a cost-effective modification of the power topology commonly found in small wind turbine systems based on a passive rectifier and a boost converter. The boost-converter inductor and the input filter capacitor often placed at the rectifier output can be replaced by the generator-phase inductance. Different controller structures have been proposed for this low-cost inverter, but they have been focused on the converter itself rather than the overall turbine control. Moreover, only steady-state behavior has been demonstrated. This paper proposes a control structure only requiring retuning of the boost-current controller found in systems equipped with boost inductance, with other control loops remaining unchanged. The inductorless converter dynamic performance is studied and compared with the conventional topology in terms of current- and torque-control capability. The system efficiency, including the losses’ distribution in the generator, is analyzed. Simulation and experimental results are presented to demonstrate the technical viability of this proposal. [ABSTRACT FROM AUTHOR]

Multioutput converters with single input source are currently studied as an alternative to conventional dc–dc topologies in order to improve power density in low-power multiload applications. This paper reviews three different ways in which a boost topology can be customized to supply multiple outputs. The first way uses a charge-sharing approach using individual switches to distribute inductor energy to different capacitors. The second method of creating a multiport converter (MPC) combines two converters with similar front end to generate two outputs using only one controlled switch. Using this method, a boost converter can be combined with single–ended primary–inductor converter (SEPIC), Cuk, and current source converter topologies. The third method uses time multiplexing of switches to produce two regulated ports and is referred to as switched-boost action. This method uses relatively less number of switches and allows regulation and control of all the outputs. Practical utility of switched-boost action based MPC is reported in this paper. This switched-boost MPC is applied to a renewable power converter system to interface a solar panel, a battery, and home loads to produce a 12-V and a 48-V bus. The 12-V bus is interfaced to battery and capable of optimally charging the battery in constant current–constant voltage (CC-CV) mode. The converter is demonstrated to operate with solar panel as it supplies a 12-V battery and a 48-V load bus. When the solar power is not available, the converter automatically goes into a mode in which the 12-V battery supplies the loads on the 48-V bus. [ABSTRACT FROM AUTHOR]

A programmable electronic load (PEL) solution is usually needed for comprehensive testing of power supplies. In this paper, a novel PEL based on a hybrid five-level voltage source inverter (VSI) is introduced to emulate a variety of static load behaviors, such as R, L, C loads, high-frequency harmonic loads, and unbalanced loads. Dynamic load behavior, for example, modulation loads, can also be achieved in this paper. A dedicated control structure is proposed for the emulation of different load behaviors and the detailed compensator design is presented to evaluate the system dynamic performance. The proposed PEL system has isolated active dc links to support multilevel converter topology, and it can either dump the energy to a passive load or recycle the energy back to the utility grid through another VSI. Simulation and experimental results are provided to validate the effectiveness of proposed control methods in terms of successfully achieving a variety of load profile functions. [ABSTRACT FROM AUTHOR]

A breaker-less shipboard medium-voltage dc (MVDC) system is gaining more attention recently due to its advantage in dealing with a dc fault by using switched-mode power modules and disconnectors. The specific power module investigated in this paper is the power conversion module (PCM) that transforms power from a MVDC to a low-voltage dc (LVDC) bus. The PCM plays an important role in a system-level fault management. The recently emerging isolated modular multilevel dc/dc converter and the widely used dual active bridge converter are promising solutions for PCM applications. The control algorithms including fault protection strategy for both topologies have been developed and presented in this paper. The MVDC side fault and LVDC side fault of each topology has been analyzed and evaluated. The simulation and experimental results are provided to demonstrate the fault protection features of two topologies in a breaker-less dc system. [ABSTRACT FROM AUTHOR]

This paper proposes a medium-frequency (MF) solid-state transformer (SST) based grid interface for high-power multipulse rectifiers. In the proposed approach, the low-frequency ac (grid) voltage is transformed to MF voltage via front-end converters. The three single-phase MF outputs from these converters are fed to the primary side of a three-phase, five-limb multiwinding isolation transformer (or alternately three one-phase transformers). The secondary side windings from the transformer are configured in a certain “zig-zag” arrangement, which are connected to the inputs of three-phase diode rectifier modules as in a typical multipulse system. The proposed topology can better than double the power density by reducing volume (or weight) of the required front-end isolation transformer while maintaining the same input current quality as a conventional low-frequency transformer based approach. Usage of an open-loop square wave pulse width modulation for the front-end converters makes this approach simple to implement. This paper explains the proposed concept taking an adjustable speed drive application's perspective using modeling, simulation, and experimental results from a scaled down laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a single-stage three-phase-to-single-phase current-fed high step-up ac–dc matrix converter. The proposed converter inserts a boost-type matrix converter, which is formed by three boost inductors and six bidirectional switches, between a three-phase ac source and a Cockcroft–Walton voltage multiplier (CWVM). By using this topology associated with power factor correction technique, the proposed converter not only achieves almost unity power factor and sinusoidal input currents with low distortion but also obtains high voltage gain at the output end. Moreover, the matrix converter generates an adjustable-frequency and adjustable-amplitude current, which injects into the CWVM to regulate the dc output voltage and smooth its ripple. With this flexible injection current, the performance of the proposed converter is superior to the conventional CWVM, which is usually energized by a single-phase ac source. The operation principle, control strategy, and design considerations of the proposed converter are detailed in this paper. Finally, simulation and experimental results demonstrate the claims and validity of the proposed converter. [ABSTRACT FROM PUBLISHER]

The double rotor, toothed, toroidal-winding permanent-magnet (PM) machine is not a well known concept and has received very limited attention in literature. In this study, the concept is proposed for use as a direct-drive wind generator. Due to the varying design requirements of wind generators over the different power ranges, the PM generator is optimized over the entire installed wind power range. For each power level, the optimum design is compared with optimum nonoverlap-winding and conventional overlap-winding PM machine designs. This also gives a much broader indication on the scaling of different wind generator technologies. Although the electromagnetic design, by means of finite-element analysis, of the generator is the main focus of the paper, some of the implementation issues are also discussed. An existing 15-kW double rotor PM wind generator is modified to include a toroidal-winding, which is used as a case study. Both simulated results and practical measurements in the laboratory for the 15-kW case study toroidal-winding PM generator are presented in this paper. [ABSTRACT FROM PUBLISHER]

Multilevel power electronic topologies are being proposed in the recent technical literature for use in power generating units, especially when the reduction in the power filter overall dimensions and the lowering of current and voltage waveform ripple and total harmonic distortion are considered of primary importance. This is the case of high-speed gen-set units, where recent design techniques on high rotational speed permanent-magnet synchronous generators (PMSGs) have significantly reduced the inductance even for industrial voltage rated applications. This paper deals with a five-level unidirectional T-rectifier (5L T-RECT); the proposed topology is theoretically investigated, and simulation results and losses analysis are achieved with reference to an insulated-gate bipolar transistor (IGBT) phase-leg module which has been manufactured on purpose and tested. [ABSTRACT FROM AUTHOR]

This paper proposes a Y-D multifunction balance transformer (YD-MFBT)-based power quality control system (MBT-PQCS) to deal with the power quality problems in the single-phase power system. The MBT-PQCS mainly consists of a YD-MFBT and a three-phase full-bridge converter (FBC). It fully explores the inherent negative sequence current (NSC) suppressing the ability of YD-MFBT, which makes the power flow transformed by FBC less than that of the conventional transformer-based compensating system. In addition, since the YD-MFBT exits three-phase output ports in relatively low-voltage level, FBC can directly connect with the main transformer via the output ports, without using the auxiliary step-down transformer. Therefore, the initial investment cost, installing difficulties and covering space of the whole compensating system, can be reduced significantly. In this paper, the current transforming relationship and the compensating principle of MBT-PQCS are presented, and the detection and control methods are given as well. Both the simulation and the experiment are used to verify the effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

Large power consumers often have on-site generation. If the utility tie opens, it is essential to isolate the on-site generators to prevent generator equipment damage before the utility attempts to reclose in a possible out-of-synchronism condition. Typically, islanding detection schemes are used to detect this condition and disconnect on-site generation quickly, thereby allowing successful utility reclose. This paper introduces a reliable islanding detection solution that was proposed, implemented, and tested at a refinery in Texas. The facility houses two on-site generators and is interconnected to the utility via a looped system. A topology-based islanding detection scheme was originally installed at this facility but was later decommissioned because of difficulties in adapting to evolving topology changes. Following an undesirable event in the utility system that could have resulted in damage to the refinery on-site generator equipment, the refinery decided to implement an islanding detection scheme that is independent of system topology changes and only relies on local-area measurements. However, the dependability of a traditional local measurement-based scheme is vulnerable to the dynamic generation–load mismatch, making it possibly unreliable. This paper describes a solution using a redundant high-speed multiprinciple islanding detection scheme that incorporates a unique voting supervision logic to achieve security. [ABSTRACT FROM AUTHOR]

In this paper, winding topologies for one- and two-pole-pair rotors are analyzed and compared for a slotless bearingless disk drive with toroidal windings. The basis of the studies is a six-phase motor with a diametrically magnetized one-pole-pair rotor. Due to the absence of mechanical bearings and the significantly large air-gap capability, the motor is suitable for applications with high purity and special chemical demands. Its slotless design results in low losses even at high rotational speeds. To improve the operational behavior of the rotor in different applications, the influence of higher pole pair numbers on the passive bearing stiffness is examined. A possible winding configuration for these rotors is proposed and evaluated for their bearing and motor performance. Based on the results, a further prototype was built and is presented in this paper. [ABSTRACT FROM AUTHOR]

This paper deals with the torque production capabilities of fractional-slot permanent-magnet synchronous machines (FSPMSMs) under open-circuit faulty conditions. The developed approach considers a class of FSPMSMs where an armature is inserted in double-layer slots and is arranged by connecting in parallel the coils or suitable combinations of coils of each phase. In light of this, the machine operates at a low-voltage level. Accordingly, its integration within 42-V-technology-based automotive systems becomes much more realistic. Moreover, the adopted approach leads to a significant improvement in the fault tolerance capability under an open-circuit faulty operation. Indeed, a failure affecting a coil would discard one branch among the parallel branches of the corresponding phase, rather than affecting the total phase in FSPMSMs with series-connected coils in the armature. The approach is initiated by an identification allied to a characterization of the slot/pole combinations enabling the parallel connection of the FSPMSM phase coils or group of coils. Then, this paper considers the selected three-phase and five-phase FSPMSMs. Following an assessment of their healthy operation, the torque values developed by both machines are predicted using a 2-D finite-element analysis under different open-circuit faulty scenarios. Then, a simple control strategy based on the readjustment of the reference sinusoidal current initial phases is proposed to recover the torque production capability of both machines under a branch open-circuit fault. [ABSTRACT FROM PUBLISHER]

This paper concerns the superposition of 2-D semianalytical models to model 3-D shielding configurations. The 2-D semianalytical models are used to describe the effect of magnetic shielding on the stray field of a single-sided coreless linear permanent-magnet motor. The modeling results are compared to 3-D finite-element analysis and to measurements. It is found that an accurate description of the tendencies and the order of magnitude is given. Furthermore, the comparison of the superposition of 2-D semianalytical models with the measurements shows that saturation and neglecting the 3-D effects cause the deviation between model and measurement. [ABSTRACT FROM PUBLISHER]

This paper presents a new compact three-phase cascaded multilevel inverter (CMLI) topology with reduced device count and high-frequency magnetic link. The proposed topology overcomes the predominant limitation of separate dc power supplies, which CMLI always require. The high-frequency magnetic link also provides a galvanic isolation between the input and output sides of the inverter, which is essential for various grid-connected applications. The proposed topology utilizes an asymmetric inverter configuration that consists of cascaded H-bridge cells and a conventional three-phase two-level inverter. A toroidal core is employed for the high-frequency magnetic link to ensure compact size and high-power density. Compared with counterpart CMLI topologies available in literature, the proposed inverter has the advantage of utilizing the least number of power electronic components without compromising the overall performance, particularly when a high number of output voltage levels is required. The feasibility of the proposed inverter is confirmed through extensive simulation and experimentally validated studies. [ABSTRACT FROM AUTHOR]

Multilevel converters with floating capacitors (FCs) are widely applied in recent years in a wide range of industrial applications from high-voltage direct current systems to high power drives. However, some FC topologies lack complete FC voltage balancing capability due to the inherent topology limitation or the insufficient switching state for capacitor balancing. This will result in large ripples on capacitors at low frequency (such as fundamental frequency), limiting their performance and application, particularly, when the fundamental frequency is very low in low-speed drive operations. Typical examples of those multilevel converters are modular multilevel converters (MMC), nested neutral-point-clamped (NNPC) converter, etc. In order to improve the FC balancing for this kind of multilevel converters, this paper proposes a carrier-based pulse-width modulation (PWM) method, named stair edge PWM method. This method can obtain sufficient redundant switching states for FC voltage balancing by producing multiple levels in one PWM period. The FC voltage balancing is thus achieved at switching frequency, which can greatly reduce the capacitor voltage ripple and therefore enable the use of much smaller FCs. Meanwhile, the voltage stress on each device and low $dv/dt$ feature are still the same as the normal multilevel operation, reserving two of the most salient features of multilevel converters. The proposed method also features much simpler and easier implementation compared with space-vector-based approaches, particularly when high-level converters are considered. An application example using a four-level NNPC converter is provided in this paper. The effectiveness and performance of the proposed method are verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

Finite state model predictive control (MPC) has been recently applied to several converter topologies, as it can provide many advantages over other MPC techniques. The advantages of MPC include fast dynamics, multitarget control capability, and relatively easy implementation on digital control platforms. However, its inherent variable switching frequency and lower steady-state waveform quality with respect to standard control, which includes an appropriate modulation technique, represent a limitation to its applicability. Modulated model predictive control (M2 PC) combines all the advantages of MPC with the fixed switching frequency characteristic of pulse-width modulation algorithms. The work presented in this paper focuses on the indirect matrix converter (IMC), where the tight coupling between rectifier stage and inverter stage has to be taken into account in the M2PC design. This paper proposes an M2PC solution, suitable for IMC, with a switching pattern that emulates the desired waveform quality features of space vector modulation for matrix converters. The switching sequences of the rectifier stage and inverter stage are rearranged in order to always achieve zero-current switching on the rectifier stage, thus simplifying the current commutation strategy. [ABSTRACT FROM AUTHOR]

This paper presents the electromagnetic analysis of two permanent magnet transverse-flux outer rotor machines with and without magnetic shunts. The research started with designing and analyzing a permanent magnet transverse-flux machine with an inner rotor, previously patented by J. Giearas in 2010. However, the results obtained from the prototype test differed significantly from the estimated results. Applying three-dimensional (3-D) finite element method (FEM), the main problem of the machine was detected. The problem was in high flux leakage that weakened magnetic flux density in the stator poles. Such observation led to designing two machines with outer rotor, with and without magnetic shunts. The role of the magnetic shunts is to minimize flux leakage in the stator in order to improve the performance of the machine. Electromechanical parameters of both outer rotor machines, with and without magnetic shunts, are compared in the paper. Three-D FEM results are supported by laboratory analysis of the machines’ prototypes. Experimental measurements proved that the machine with magnetic shunts demonstrated better performance as compared with the machine without magnetic shunts. Presence of the magnetic shunts in the machine resulted in reducing of flux leakage and cogging torque. [ABSTRACT FROM AUTHOR]

In this paper, it is described how the circulating current flows between inverters that have isolated dc link such as cascaded H-bridge (CHB) topology when they are operating in parallel. In this case, zero sequence circulating current, which normally flows through shared dc link, cannot flow between inverters in parallel. However, circulating current is provoked by asynchronous switching instant of devices, difference of dc-link voltages of parallel inverters, and unbalanced impedance. The circulating current should be suppressed by a sharing inductor that is inserted between inverters. Generally, all of the inverters should synthesize the same output voltage reference for load current control to minimize the size of this sharing reactor. However, this conventional method cannot guarantee diminishing circulating current in the transient state and even in the steady state. In this paper, in order to reduce sharing reactance, after deriving circulating current model from general case of n-parallel operation, circulating current control method is devised based on the model. This proposed algorithm is applied to active front end five-level-CHB inverter system for medium voltage drive. Simulation and experimental results are provided to verify the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a new isolated three-port bidirectional dc–dc converter for simultaneous power management of multiple energy sources. The proposed converter has the advantage of using the least number of switches and soft switching for the main switch, which is realized by using an inductor–capacitor–inductor ( $LCL$) -resonant circuit. The converter is capable of interfacing sources of different voltage–current characteristics with a load and/or a dc microgrid. The proposed converter is constructed for simultaneous power management of a photovoltaic (PV) panel, a rechargeable battery, and a load. Simulation and experimental results show that the proposed converter is capable of maximum power point tracking control for the PV panel, when there is solar radiation, and controlling the charge and discharge of the battery, when there is surplus energy and power deficiency with respect to the load, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents the performance analysis and comparison of two types of bidirectional dc–dc converters—cascaded buck–boost capacitor in the middle and cascaded buck–boost inductor in the middle for use in plug-in electric and hybrid electric vehicles. The comparison of the two converters is based on device requirements, rating of switches and components, control strategy, and performance. Each of the converter topologies has some advantages over the other in certain aspects. Efficiency analysis has been carried out for specific scenarios in vehicle applications. The simulation and experimental results are provided for both converter types. [ABSTRACT FROM PUBLISHER]

The incremental efficiency improvements achieved with induction motors have been mostly accomplished by adding material to the designs of the prior efficiency level. In order to achieve levels beyond NEMA Premium (or beyond IE3), it has been recognized that a different technology must be employed. The working groups for International Electrotechnical Committee efficiency levels have stated that inverter-fed permanent-magnet motors are the likely technology to reach IE4 levels. Other motor technologies (such as synchronous reluctance) which also require inverters for operation have also been proposed for higher motor efficiency. This paper will discuss a technology which can be utilized without requiring an inverter and that can achieve beyond-IE4 levels of efficiency while using less active material in the motor. This discussion is based on testing of technology demonstration prototypes in the range of 30–250 hp. Capabilities as well as limitations of this technology will be discussed. [ABSTRACT FROM AUTHOR]

The benefits of variable-frequency drives (VFDs) have not been fully realized in many applications because they compete in the power density of legacy equipment, such as electromechanical motor controllers. This is particularly the case in Navy shipboard systems where sensitive equipment is in close proximity to VFDs. This paper compares the power densities, efficiency, and costs of both voltage-source- and current-source-based VFDs. A meaningful comparison is made based on actual hardware implementations that meet stringent power quality and electromagnetic compatibility requirements. The hardware results of a current-source-rectifier (CSR)-fed voltage-source inverter (VSI), or a CSR–VSI-based VFD, are provided in order to support the findings of this paper. Special consideration is given to operation at light loads. [ABSTRACT FROM AUTHOR]

Efficient power conversion technologies are strategic to the advancement of fuel cell vehicles (FCVs). This paper presents an overview of power conditioning system (PCS) architectures for an FCV propulsion system. Two new power conversion topologies to obtain variable ac from the fuel cell system are proposed. The switching of the power devices are based on the proposed hybrid modulation technique that minimizes the switching losses in the inverter. The proposed converters do not use the dc-link filter capacitors. Elimination of the dc-link capacitor not only reduces the size and volume but also helps in retaining the sine wave modulated information at the input of a three-phase inverter. Bidirectional converter topologies are proposed for interfacing low-voltage battery and fuel cell dc bus. Experimental results are presented for the proposed topologies. [ABSTRACT FROM AUTHOR]

This paper presents an asymmetrical cascaded multilevel inverter based on a five-level transistor-clamped H-bridge power cell. A two-cell configuration with a dc link voltage ratio of 4 : 1 is presented. The modulation method is based on the fundamental frequency switching. An analysis of the inverter output voltage and harmonics is presented. Injection of the third harmonic voltage as to maximize the output voltage and the issue of the inverse power flow or regeneration in the low-voltage cell are presented. The prototype of the proposed inverter was built, and its functionality was verified through experimental results. [ABSTRACT FROM AUTHOR]