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This paper analyzes the power-cycling capability of insulated-gate bipolar transistor (IGBT) modules in a conventional matrix converter used as a motor drive. The analysis is made under various conditions for this topology, including low-speed-operation capability, high-speed thermal- and power-cycling capabilities, etc. It was found that the power-cycling mean time to failure of IGBT in a matrix converter is low when the input and output frequencies are close to each other or when the output frequency of the converter is low. As a result, the chip size of the conventional matrix converter may be larger than the other candidates. In the end of this paper, some guidance for designing a matrix converter for long-term reliabilities is also discussed. Index Terms--Conventional matrix converter, mean time to failure (MTTF), power cycle, thermal cycle.

We present an analytical method for the calculation of electromagnetic torque in surface permanent-magnet (PM) motors. Our method uses conformal mapping to calculate the electromagnetic torque by integrating the Maxwell stress tensor inside the air gap. It uses the radial and tangential components of the flux density in the slotted air-gap produced by the currents flowing in the three-phase armature winding. We demonstrate our analytical solution on a 7-kW four-pole surface PM motor and compare the results with finite-element solutions. We present the results for various angular spans of permanent magnets and various sizes of the slot opening to confirm the validity of the analytical approach. Index Terms--Air-gap permeance, electromagnetic torque, magnetic fields, permanent-magnet motors.

This paper presents a systematic evaluation approach of three-phase pulsewidth-modulated (PWM) ac-ac converter topologies for high-density applications. All major components and subsystems in a converter are considered and the interdependence of all the constraints and design parameters is systematically studied. The key design parameters, including switching frequency, modulation scheme, and passive values, are selected by considering their impacts on loss, harmonics, electromagnetic interference (EMI), control dynamics and stability, and protection. The component selection criteria as well as the physical design procedures are developed from the high-density standpoint. The concept of using the same inductor for harmonic suppression and EMI filtering is introduced in the design. With the proposed methodology, four converter topologies, a back-to-back voltage source converter (BTB-VSC), a nonregenerative three-level boost (Vienna-type) rectifier plus voltage source inverter (NTR-VSI), a back-to-back current source converter (BTB-CSC), and a 12-switch matrix converter, are analyzed and compared for high specific power using SiC devices. The evaluation results show that with the conditions specified in this paper, BTB-VSC and NTR-VSI have considerably lower loss, resulting in higher specific power than BTB-CSC and the matrix converter. The proposed methodology can be applied to other topologies with different comparison metrics and can be a useful tool for high-density topology selection. Index Terms--High density, SiC devices, switching frequency, three-phase ac-ac converter.

This paper investigates the impact of input voltage unbalance and sags on stresses in the dc-bus choke inductor and dc-bus electrolytic capacitors of adjustable-speed drives (ASDs). These stresses are primarily attributable to the rectifier's transition into single-phase operation, giving rise to low-order harmonic voltages (120 Hz, 240 Hz, etc.) that are applied to the dc-link filter components. These harmonics elevate the ac-flux densities in the dc choke core material significantly above values experienced during normal balanced-excitation conditions, causing additional core losses and potential magnetic saturation of the core. It is shown that the effects of voltage unbalances and sags on the de-link capacitor lifetime will be the same when either line inductors or a de-link choke inductor are used if the dc choke-inductance value is twice the value of the line inductance. Simulations and experimental tests are used to verify the accuracy of predictions provided by closed-form analysis and simulation for a 5-hp or 3730-W ASD system. Index Terms--Adjustable-speed drives (ASDs), tic-link capacitor stress, de-link inductor stress, input voltage sag and unbalance, power quality.

The paper presents a current-source inverter topology tailored for large mniti-megawatt wind turbines. The proposed topology can inherently benefit from the distance between the generator and the mains because the consequent length and possible layout of the power cables may enable the realization of a significant portion of the dc-link inductance. In order to improve the efficiency and to allow the possible utilization of rugged inexpensive thyristors, pulsewidth modulation (PWM) modulation is not used. Unity fundamental power factor at the mains is guaranteed at any load condition while the fifth and seventh harmonics of the mains line currents can be reduced by proper system design at a desired turbine speed, considered most suitable for its operation. Further harmonic reduction is achievable through an active filter controlled via a newly proposed PWM methodology that does not belong either to a carrier-based or to a classical space vector modulation approach. Such a controller relies on a real-time minimization of a proper functional and is capable of implementing true-feedback current regulation. Experimental results from a 10 kW prototype are presented and validate the developed analytical computations. Index Terms--Current-source topology, harmonics reduction, power factor control (PFC), wind turbines.

We present a two-dimensional complex steady-state finite-element method for calculating the lift and thrust or breaking forces created when a magnetic rotor is translationally moved and rotated over a conducting sheet. The method replaces the magnetic rotor with an equivalent current sheet by equating the current sheet's and magnet rotor's magnetic vector potentials. We validate the steady-state method by comparing the forces with transient finite-element models. The utility of this steady-state model is that it enables a study of the effects of parameter changes for such a machine to be undertaken rapidly. Index Terms--Eddy currents, electromagnetic analysis, finite-element methods, Halbach rotor, maglev.

When a magnetic rotor is both rotated and translationally moved above a conductive, nonmagnetic, guideway eddy currents are induced that can simultaneously create lift, thrust, and lateral forces. In order to model these forces, a 3-D finite-element model with a magnetic charge boundary has been created. The modeling of the rotational motion of magnets by using a fictitious complex magnetic charge boundary enables fast and accurate steady-state techniques to be used. The conductive regions have been modeled using the magnetic vector potential and nonconducting with the magnetic scalar potential. The steady-state model has been validated by comparing it with a Magsoft Flux 3D transient model (without translational velocity) and with experimental results. The 3-D model is also compared with a previously presented 2-D steady-state complex current sheet model. Index Terms--Eddy currents, finite-element method, maglev, magnetic charge.

We present an analytical method for the calculation of cogging torque in surface permanent-magnet (PM) motors. The cogging torque is calculated by integrating the Maxwell stress tensor inside the air gap. The principle of complex relative air-gap permeance derived from conformal transformation of the slot geometry is used to take into account the effect of slotting and to calculate the radial and tangential components of the air-gap flux density required for integration of the tangential component of the Maxwell stress tensor. We implemented the proposed analytical solution on a 7-kW four-pole surface PM motor and compared the results with finite-element solutions. We present an example of finding the optimal magnet angular span to yield minimum cogging torque as an example of the effectiveness of the method. Index Terms--Air-gap permeance, cogging torque, magnetic fields, permanent-magnet motors.

This paper analyzes the effects of injecting additional signals in induction machines for the purpose of speed control. A new saturation model able to correctly model the interaction between the added signal and saturation of the motor core due to the main torque-producing flux is presented. The introduction of a variable saturation factor is used to model the variation of the saturation level due to the additional signal. A third harmonic rotor circuit is also introduced to take account of the third harmonic component of the air-gap flux, due to saturation. An additional balanced voltage set is added to the normal supply to analyze the effects of such signals on a saturated induction motor. Simulation results of such a model both at no load and full load are presented together with experimental measurements. Index Terms--Air-gap flux harmonics, flux position estimation, q-d model, saturation modulation, sensorless control.

The mechanical rotation of a radially positioned permanent-magnet Halbach array above a conducting, nonmagnetic track induces eddy currents in the track that can inductively create suspension and propulsion forces simultaneously. The parameters that affect the performance of this electrodynamic wheel are studied using a 2-D steady-state finite-element method. Tradeoffs between the lift and thrust force performance are investigated and methods to improve the thrust efficiency are proposed. Index Terms--Eddy currents, electromagnetic analysis, finite-element methods, Halbach array, maglev.

This paper presents a current-source inverter topology that is suitable for multi-megawatt wind turbines. The proposed scheme utilizes two series-connected three-phase inverters that employ fully controllable switches and a proper interconnection transformer with the mains. In order to improve the efficiency and to allow the use of high-power devices, the inverters are switched at the mains frequency. The axial-flux permanent-magnet (PM) generator is directly coupled to the turbine (gearless solution), and its design reduces the dependence of the output voltage on the load current. The overall control technique allows to independently impose two desired quantities that can be selected out of the set of three composed of: 1) the total average voltage at the dc side of the inverters, which is directly related to the turbine speed; 2) the fundamental power factor at the mains interconnection point, which can be chosen unitary, leading, or lagging; and 3) the amplitude of one desired component of the spectrum of the mains line currents. The two chosen quantities univocally determine the third one. At specific operating points of the turbine, a significant reduction of the fifth and seventh harmonics can already be achieved without additional filters and/or active harmonic compensation. Nevertheless, the introduction of an active harmonic compensator is necessary to provide the required harmonic reduction (also up to higher orders) more independently and on a wider range of operating conditions. The almost independent regulation of the dc-link current allows further control of the average generator torque. Experimental results that are obtained from a 10-kW prototype with an axial-flux PM generator are presented. Index Terms--Axial-flux permanent-magnet (PM) generator, current-source topology, harmonics reduction, power-factor control, reactive power (VAr) compensation, wind turbines.

This paper proposes a new definition of instantaneous reactive power in the complex synchronous rotating frame and control scheme under unbalanced networks. The mathematical model of instantaneous active and reactive power has been derived for a pulsewidth-modulated (pwm) ac/dc converter under generalized unbalanced operating conditions. Based on this model, an unbalanced compensating control algorithm is proposed. Simulation and experimental results confirm the mathematical model as well as the control performance. The ripple component of instantaneous reactive power is found to be exactly the same as that of active power. The proposed definition of instantaneous reactive power in the synchronous rotating frame is shown to be consistent with the classical definition in both time and phasor domain. The proposed definition makes it possible to effectively design the controller for pwm converters under unbalance conditions. Index Terms--AC-DC power conversion, current control, power quality, reactive power control.

We present an analytical method for calculation of no-load magnetic field distribution in the slotted air gap of a surface permanent-magnet (PM) motor with radial or parallel magnetization. The method introduces the notion of complex relative air-gap permeance, calculated from the conformal transformation of the slot geometry, to take into account the effect of slotting. As a result, an accurate solution of both radial and tangential components of the flux density can be obtained--one that shows excellent agreement with the results of finite-element simulations. As an example of the effectiveness of the model, we present calculations of the back electromotive force and the cogging torque waveforms in a surface PM motor. Index Terms--Air-gap permeance, magnetic fields, permanent-magnet motors.

In this paper, pulsating torque components of permanent magnet machines and pulsating torque minimization techniques are discussed for axial flux surface-magnet disc-type PM machines. The pulsating torque analysis describing general instantaneous electromagnetic torque equation and torque ripple factor is briefly provided in order to analyze torque ripple component. Detailed finite-element analyses focusing on the minimization of cogging and torque ripple components using several techniques are also given. A detailed comparison of the two techniques is also illustrated in this paper. Index Terms--AC motors, permanent magnet machines, permanent magnet motors, traction motors.

This paper proposes a control method to null the magnet flux in an interior permanent-magnet (IPM) motor following short-circuit-type faults in either the inverter drive or motor stator windings. Phase-based control is employed to implement the flux-nulling-control method so that it is possible to take advantage of a zero-sequence current in order to minimize the current in the shorted phase. It is shown that phase-based control results in a smaller induced current than when employing a synchronous-frame dqO current regulator. The induced torque is also less than that when employing a purposely commanded symmetrical short circuit in response to a short-circuit-type fault. In the paper, the complete magnet-flux-nulling-control algorithm is derived with reference to the proposed phase-current-control method. The impact of controlling the zero-sequence current on the resulting phase currents is presented. Both simulation and experimental results are presented, verifying the operation of the proposed methods. Index Terms--Current regulation, inverter shutdown, magnet flux, short-circuit fault, variable-speed drive.

Filter networks for long cable drives have been studied in the last decade to solve the overvoltage problem at the motor terminals. However, little research has been dedicated to analyze their influence on the voltage distribution in the motor stator winding and on the circulation of the common-mode currents. In this paper, the project of dv/dt filters through simulation and analysis from previous work is extended, including the motor voltage distribution and common-mode current analysis. Simulation and experimental results are presented, demonstrating the usefulness of the filter networks on the motor overvoltage mitigation. Three filter topologies will be discussed and compared here: RLC filter at the motor terminals, RLC filter at the inverter output and reactor filter, which is extensively used in the industry. Simulation and experimental results demonstrate that the RLC filter at the inverter output is the most interesting solution among the main types of passive filter networks. Index Terms--Electrical drive systems design and applications, industrial drives, overvoltage and dv/dt filter design.

Cascaded multilevel inverters can be implemented through the series connection of single-phase modular power bridges. This paper presents details on how these bridges should be implemented and operated to synchronize their pulse-width-modulation (PWM) carriers, fundamental references and sampling instances to implement a network-controlled cascaded inverter with distributed PWM computation and overall optimal system performance. The paper begins by detailing the development and control of an integrated power bridge, designed with its own digital signal processor and associated control circuitry. Details describing the networked control algorithm and signal protocol needed for synchronizing the multiple power bridges through a dynamically fast data communication network, are then presented to achieve optimum harmonic cancellation and reduced common-mode voltage. The practicality and performance of the presented modular implementation concepts have been confirmed through the close match between simulation and experimental results obtained using a modular cascaded five-level inverter prototype. Index Terms--Common-mode voltages, distributed computation, harmonic analysis, integrated power bridges, multilevel inverters, synchronization.

This paper compares the many fault tolerant three-phase ac motor drive topologies that have been proposed to provide output capacity for the inverter faults of switch short or open-circuits, phase-leg short-circuits, and single-phase open-circuits. Also included is a review of the respective control methods for fault tolerant inverters including two-phase and unipolar control methods. The output voltage and current space in terms of dq components is identified for each topology and fault. These quantities are then used to normalize the power capacity of each system during a fault to a standard inverter during normal operation. A silicon overrating cost factor is adopted as a metric to compare the relative switching device costs of the topologies compared to a standard three-phase inverter. Index Terms--Inverter faults, phase-leg short-circuits, silicon overrating cost factor (SOCF), single-phase open-circuits, three-phase inverter, three-phase ac motor drive topologies.

This paper proposes operating a three-level neutral-point-clamped (NPC) inverter using a two-level pulsewidth-modulation method. This allows for the clamping diodes to be rated at a fraction of the main switches due to their low average current requirement. The use of a bootstrap charge pump as a low-cost method to obtain the isolated gate drive power supplies is extended for use with the NPC topology. Using this control method and circuits, an inverter based on high-volume, low-cost, low-voltage power MOSFETs is experimentally demonstrated as a possible economic alternative to an insulated-gate-bipolar-transistor-based drive for 120-Vrms-supplied systems. Index Terms--Adjustable-speed drives, bootstrap, charge pump, inverters, multilevel systems, pulsewidth modulation.

A novel machine family--the dual-rotor, radial-flux, toroidafiy wound, permanent-magnet (RFTPM) machine--has been proven in a previous paper to be able to improve the machine efficiency and boost the torque density. This paper will present the key design equations and design procedure of the RFTPM machines, analyze parameter effects on machine performance, and give design guidelines to achieve specific design objectives. In addition, finite-element analysis is employed to prove the effectiveness of the design equations and find the machine overload capability. Experimental measurements of a prototype, which match the design specifications well, verify the effectiveness of the design equations. Index Terms--Parameter effect analysis, permanent-magnet (PM) machine design, radial-flux, toroidally wound, permanent-magnet (RFTPM) machine.

Electrolytic capacitors are used in nearly all adjustable-speed drives, and they are one of the components most prone to failure. The main failure mechanisms include loss of electrolyte through outgassing and chemical changes to the electrolyte and oxide layer. All the degradation mechanisms are exacerbated by ripple current heating. Since the equivalent series resistance of electrolytic capacitors is a very strong function of frequency it must be properly modeled to accurately calculate the power loss. In this paper, a method to reduce the ripple current in a constant Volts/Hertz pulse-amplitude-modulation (PAM)/pulsewidth-modulation (PWM) converter driving an induction motor is investigated. The dc-bus voltage amplitude is reduced in proportion to speed by a buck or current stiff rectifier and the PWM modulation index is maintained at a high level to achieve a reduced ripple current below base speed. By comparison with a diode-bridge-fed PWM voltage stiff inverter, it is shown that the PAM/PWM mode of operation can lead to a significant reduction in capacitor power loss leading to increased capacitor lifetime or decreased capacitor size. The capacitor heating is analyzed using numerical and analytical techniques. Experimental results are provided to verify the analytical results. Index Terms--Adjustable-speed drive (ASD), buck rectifier, current ripple, current stiff rectifiers (CSRs), electrolytic capacitor modeling, equivalent series resistance (ESR), industrial drives, pulse amplitude modulation (PAM), pulsewidth modulation (PWM), voltage stiff inverter (VSI).

The design of a linear synchronous motor for an electromagnetic air launch system that uses high-temperature superconducting (HTS) material is discussed. A comparison between a permanent magnet motor and a linear induction motor designed for the same application indicate that bulk-superconducting magnets are superior at temperatures below 40K.

In this paper the magnetic characteristics of surface-mounted permanent-magnet machines are analyzed and modeled. The air-gap and zigzag leakage fluxes are analytically expressed in terms of the magnetic material properties and the motor dimensions. Both factors are essential quantities for the accurate prediction of the flux distribution within the machine and of the machine torque. Therefore, they are desired for the purpose of machine design and optimization. In order to evaluate the validity of the proposed models, the finite-element method (FEM) analysis is used. The results show that the errors between the FEM results and analytical predictions are less than 7% for the nonsaturated tooth flux and less than 17% for the saturated case. Finally, the models are applied to a novel permanent-magnet machine design. Index Terms--Air-gap leakage flux, permanent-magnet (PM) machine, PM machine design, zigzag leakage flux.

This paper presents a new hysteresis current regulation technique with reduced common mode switching for three-phase multilevel inverters. The proposed technique uses three independent multilevel hysteresis current regulators to generate three sets of complementary gating signals through the comparison of the measured current errors with implemented hysteresis limits. These gating signals are then distributed to each complementary switch pair of the multilevel inverter structure to switch with reduced common mode voltage. Additionally, by intelligently compensating for transition delays during dead-times, common mode voltage can essentially be eliminated completely. Two versions of the common mode regulation technique are derived by using either the line currents or differences between the line currents, known as delta currents, as the control variables. A detailed investigation is presented to determine that the delta currents are the optimal control variables. The performance of the proposed strategy is confirmed through both simulation and experimental investigations. Index Terms--Common mode voltages, current regulation, hysteresis, multilevel inverters.

In this paper a description and operating principles of a consequent-pole permanent-magnet machine are presented. In addition, a sizing analysis, finite-element analysis, and experimental results for a prototype machine are addressed. Due to its particular configuration, this machine allows for a wide range of control of the air-gap flux with minimum field ampere-turn requirements and without brushes or slip rings. Two components of the field flux are produced. One, which is almost constant, is produced by the permanent magnet located on the rotor surface. The other, which is variable, is produced by a field winding positioned circumferentially in the center of the stator. These two flux components converge in the air gap. The excitation level of the machine is manipulated by controlling the dc field current. Three-dimensional finite-element analysis and experimental results demonstrate that it is possible to vary the flux over a wide range to keep the terminal voltage constant as the speed increases. A 3-kW 1000-3000-r/min eight-pole and 32-Vac generator using this configuration is tested to verify the flux control capability of this structure. Index Terms--Electric machine design, flux weakening, permanent-magnet (PM) machine.

A novel machine family--dual-rotor, radial-flux, toroidally wound, permanent-magnet (RFTPM) machines--is proposed in order to substantially improve machine torque density and efficiency. After the principles of operation, configurations, and features are discussed, the machine design and optimization guidelines are given. A prototype has been designed, built, and tested. The measured torque density of the prototype, which well matches the design value, is almost three times of that of the induction machine with the same power of 3 hp and speed. Meanwhile the efficiency is still kept high and the material cost is kept low by using ferrite magnets. Three novel approaches are proposed to reduce the cogging torque in the RFTPM machines, whose validity is verified by finite-element analysis results and experimental measurements. Index Terms--Cogging torque, electrical machine optimization, permanent-magnet (PM) machine design, radial-flux, toroidally wound, permanent-magnet (RFTPM) machines, toroidal windings.

Previous work has shown that space vector modulation and carrier modulation for two-level inverters achieve the same phase leg switching sequences when appropriate zero sequence offsets are added to the reference waveforms for carrier modulation. This paper presents a similar equivalence between the phase disposition (PD) carrier and space vector modulation strategies applied to diode clamped, cascaded N-level or hybrid multilevel inverters. By analysis of the time integral trajectory of the converter voltage, the paper shows that the optimal harmonic profile for a space vector modulator occurs when the two middle space vectors are centered in each switching cycle. The required zero sequence offset to achieve this centring for an equivalent carrier based modulator is then determined. The results can be applied to any multilevel converter topology without differentiation. Discontinuous behavior is also examined, with the space vector and carrier based modulation methods shown to similarly produce identical performance. Both simulation and experimental results are presented. Index Terms--Multilevel inverter, pulse width modulation, space vector modulation, zero sequence offset.

This paper presents modulation strategies for cascaded multilevel inverters that substantially eliminate common-mode voltage on the output phases. The paper begins by developing generic multilevel inverter reference waveforms that use only 'allowed' space vectors to achieve reduced common-mode voltage. A graphical technique is then proposed that allows various carrier disposition modulation strategies for a diode-clamped inverter to be converted to equivalent modulation of a cascaded inverter for any fundamental reference waveform. This graphical technique is confirmed for both Alternative Phase Opposition Disposition and Phase Disposition equivalent modulation of a cascaded inverter, and is then used to create reduced common-mode modulation strategies for cascaded inverters from their equivalent counterparts for diode-clamped inverters under hath continuous and discontinuous switching conditions. The strategies have been confirmed by both simulation and experimental results obtained using a cascaded five-level inverter. Index Terms--Common-mode voltages, harmonic analysis, multilevel inverters, pulsewidth modulation (PWM).

This paper presents a novel method for measuring the magnetizing inductance of an induction machine. The approach uses a static dc excitation technique which can be employed whenever the neutral of the machine is accessible. The proposed method measures only the magnetizing inductance and not the self inductance which normally includes the effect of the stator leakage inductance. Because this test uses a dc excitation, the iron losses in the motor are considerably reduced as well and minimally influence the measurement when compared to the traditional 60-Hz no-load test. By using the proposed method for measuring only the magnetizing inductance, the stator leakage inductance can be later individually determined by performing a separate no-load test. Test results using the method are compared with theoretical values and confirm its feasibility. Index Terms--DC test, inductance measurement, induction machines, leakage inductance, locked-rotor test, magnetizing inductance, no-load test.

Most multilevel inverter hysteresis current regulators use either multiple hysteresis bands, or a time-based switching logic that forces the current error back to zero by recursively stepping through successive voltage levels. Of these two alternatives, the time-based approach has the merit of only requiring simple analog circuitry and digital logic to implement the voltage level selection process for inverters of any number of voltage levels. However, the approach can be less stable and has a poorer dynamic response than a multiple hysteresis band system. This paper presents a double-band regulator that uses the slope of the current error to help determine the appropriate steady state voltage level to keep this error within the inner hysteresis band, while still allowing switching to the extreme inverter states during transient conditions to reduce the current error as rapidly as possible. The regulator achieves better stability and dynamic performance than previously reported schemes. The paper also presents an adaptation of the system to control a hybrid seven-level inverter. Theory, simulation, and experimental results are presented. Index Terms--Current control, digital logic synthesis, hybrid inverters, hysteresis, multilevel inverters.

A novel low-cost single-phase induction machine drive containing only two controlled solid-state switches is presented. The drive is intended for heating, ventilation, and air conditioning or a similar type of application requiring variable-speed operation with a fan-type load characteristic. An experimental drive based on the proposed setup has been built to verify its practical viability and to analyze its properties. The paper presents the results obtained from an investigation into this new topology and discusses the properties and characteristics of the drive for the entire speed range from 0 to 60 Hz. Index Terms--AC motor drives, converters, induction motor drives, single-phase machines.

This study introduces a field oriented controlled (FOC) induction machine based flywheel energy storage (FES) system fed from a 20 kHz high frequency (HF) ac link and pulse density modulated (PDM) Converter. The feasibilty of FES system is investigated both in software and hardware and is demonstrated succesfully in both cases. The investigated system offers a good potential as a temporary energy storage system for various applications from automobile industry to aerospace applications.

Three-phase pulsewidth-modulated (PWM) boost-buck rectifiers with power-regenerating capability are investigated. The converters under consideration are capable of: 1) both voltage step-up and step-down; 2) bidirectional power processing; and 3) almost unity-power-factor operation with nearly sinusoidal ac current. Expected advantages are: 1) applicability to lower voltage applications, e.g., direct retrofit to replace diode or thyristor rectifiers; 2) switching loss reduction in the inverter load; 3) low-order harmonic control in the inverter load output voltage; 4) blanking time effect mitigation in the inverter load; and 5) a modest level of voltage sag/swell compensation. In this paper, firstly, a step-by-step, power stage derivation process is described. Then, taking the Cuk-Cuk realization as an example, its operating principle and modulation scheme are described. A steady-state model and dynamic model for controller design are also described. Representative results of circuit simulations and hardware experiments are presented. Through these procedures, the feasibility of the presented three-phase PWM boost-buck rectifier with power-regenerating capability is demonstrated. Index Terms--Boost-buck converter, power regeneration, pulsewidth-modulated rectifier.

The use of six-phase induction motor for industrial drives presents several advantages over the conventional three-phase drive such as improved reliability, magnetic flux harmonic reduction, torque pulsations minimization, and reduction on the power ratings for the static converter. For these reasons, six-phase induction motors are beginning to be a widely acceptable alternative in high power applications. A typical construction of such drives includes an induction machine with a dual three-phase connection, where two three-phase groups are spatially shifted 30 electrical degrees, a six-leg inverter, and a control circuit. By controlling the machine's phase currents, harmonic elimination and torque-ripple reduction techniques could be implemented. This paper describes a technique of injecting third harmonic zero sequence current components in the phase currents, which greatly improves the machine torque density. Analytical, finite-element, and experimental results are presented to show the system operation and to demonstrate the improvement on the torque density. Index Terms--Induction machine analysis and design, industrial drives, six-phase drives.

High-frequency simulation models for power cables and motors are key tools to aid a better understanding of the overvoltage problem in pulsewidth modulation drives with long feeders. In this paper, frequency responses of the cable characteristic and the motor input impedances are obtained experimentally and suitable models are developed to match the experimental results. Several lumped segments incorporating a lossy representation of the line are used to model the cable. The cable and induction motor models may be implemented using a computational tool such as MATLAB, thereby providing a convenient method to analyze the overvoltage phenomena. Simulation and experimental results are presented for a typical 3-bp induction motor, showing the suitability of the developed simulation models. The most promising dv/dt filter networks are also investigated through simulation analysis, and a design approach based on a tradeoff between filter losses and motor peak voltage is proposed. Experimental results of an RC filter placed at the motor terminals demonstrate the validity of the simulation models. Index Terms--Adjustable-speed drives, converter machine interactions.

This paper presents a novel variable-frequency motor drive system for a three-phase induction machine. In this drive system, the machine is excited by unidirectional stator currents shaped and sequenced such that a rotating air-gap flux is induced so that the machine can operate. Due to the unidirectional nature of the currents, an 'inverter' that incorporates only three active, insulated-gate-bipolar-transistor-type switches, and three freewheeling diodes can synthesize them. The drive system requires an asymmetric induction machine that can easily be obtained by externally rewiring a motor with a dual-wound stator. The inverter is supplied by a single-phase input via a voltage-doubler diode rectifier; hence, it can be operated with residential service. In this paper, theoretical control methods are presented and both simulation and experimental results are provided proving the validity of the proposed drive system. Index Terms--Induction machine, inverter, motor drive, three-switch, unipolar.

This paper presents an active solution to a common-mode voltage created by typical three-phase inverters. It is shown that the addition of a fourth leg to the bridge of a three-phase inverter eliminates the common-mode voltage to ground created by the modulation of the inverter. An appropriate four phase LC filter is inserted between the inverter and the load in order to create sinusoidal output line-to-line voltage. A simple modification of the modulation strategy is implemented for the four-phase inverter to achieve a three-phase wye-output neutral-to-ground voltage which is equal to zero at all times for an ideal inverter. The modulation strategy thereby completely eliminates the common-mode potential produced by traditional modulation techniques with traditional three-phase inverter topologies. Index Terms- Common mode voltage, electromagnetic interference, four-phase inverter, modulation, pulsewidth modulation, resonant dc link

This paper deals with an active gate drive (AGD) technology for high-power insulated gate bipolar transistors (IGBT's). It is based on an optimal combination of several requirements necessary for good switching performance under hard-switching conditions. The scheme specifically combines together the slow drive requirements for low noise and switching stress and the fast drive requirement for high-speed switching and low switching energy loss. The gate drive can also effectively dampen oscillations during low-current turn-on transient in the IGBT. This paper looks at the conflicting requirements of the conventional gate drive circuit design and demonstrates using experimental results that the proposed three-stage AGD technique can be an effective solution. Index Terms: Active gate drive, gate drive circuit, gate resistor, insulated gate bipolar transistor switching transient

A new on-line dead-time compensation technique for low-cost open-loop pulsewidth modulation voltage-source inverter (PWM-VSI) drives is presented. Because of the growing numbers of open-loop drives operating in the low-speed region, the synthesis of accurate output voltages has become an important issue where low-cost implementation plays an important role. The so-called average dead-time compensation techniques rely on two basic parameters to compensate for this effect: the magnitude of the volt seconds lost during each PWM cycle and the direction of the current. In a low-cost implementation, it is impractical to attempt an on-line measurement of the volt-seconds error introduced in each cycle - instead an off-line measurement is favored. On the other hand, the detection of the current direction must be done on line. This becomes increasingly difficult at lower frequencies and around the zero crossings, leading to erroneous compensation and voltage distortion. This paper presents a simple and cost-effective solution to this problem by using an instantaneous back calculation of the phase angle of the current. Given the closed-loop characteristic of the back calculation, the zero crossing of the current is accurately obtained, thus allowing for a better dead-time compensation. Experimental results validating the proposed method are presented. Index Terms: AC drives, blanking time, current measurement, induction motors, volt-second compensation, volts per hertz.

Based on the concept of the converter fed machine (CFM), an optimal machine design can be considered as the best match of the machine topology, the power electronic converter and the performance specification. To compare power production potential of axial flux machines with various topologies, different waveforms of back emf and current, general purpose sizing and power density equations for such machines are needed. In this paper, a general approach is presented to develop and to interpret these equations. Sample applications of the sizing and power density equations are utilized to compare the axial flux toroidal permanent magnet (AFTPM) machine and the axial flux two-stator permanent magnet (AF2SPM) machine.

This paper describes a new direct field orientation (DFO) scheme based on a modified flux observer using measured stator voltages and currents. The proposed approach addresses the problem of torque control of speed sensorless drives at low-zero speed, where rapid speed changes do not occur and signal frequency can approach zero. The scheme can maintain field orientation and stable torque control with simultaneous resistance and speed tuning taking place. Simulations and locked rotor experiments with torque measurements are used for verification. Index Terms - Direct field orientation, low-zero speed, speed sensorless, torque control, zero frequency.

In this paper, a generalized discontinuous pulsewidth modulation (GDPWM) method with superior high modulation operating range performance characteristics is developed. An algorithm which employs the conventional space-vector PWM method in the low modulation range, and the GDPWM method in the high modulation range, is established. As a result, the current waveform quality, switching losses, voltage linearity range, and the overmodulation region performance of a PWM voltage-source inverter (PWM-VSI) drive are on-line optimized, as opposed to conventional modulators with fixed characteristics. Due to its compactness, simplicity, and superior performance, the algorithm is suitable for most high-performance PWM-VSI drive applications. This paper provides detailed performance analysis of the method and compares it to the other methods. The experimental results verify the superiority of this algorithm to the conventional PWM methods. Index Terms - Discontinuous modulation, harmonics, inverter, pulsewidth modulation, switching losses.

Bearing currents and shaft voltages of an induction motor are measured under hard- and soft-switching inverter excitation. The objective is to investigate whether the soft-switching technologies can provide solutions for reducing the bearing currents and shaft voltages. Two of the prevailing soft-switching inverters, the resonant de-link inverter and the quasi-resonant de-link inverter, are tested. The results are compared with those obtained using the conventional hard-switching inverter. To ensure objective comparisons between the soft- and hard-switching inverters, all inverters were configured identically and drove the same induction motor under the same operating conditions when the test data were collected. An insightful explanation of the experimental results is also provided to help understand the mechanisms of bearing currents and shaft voltages produced in the inverter drives. Consistency between the bearing current theory and the experimental results has been demonstrated. Conclusions are then drawn regarding the effectiveness of the soft-switching technologies as a solution to the bearing current and shaft voltage problems. Index Terms - Bearing currents, common-mode currents, common-mode voltages, hard switching, induction machine, induction motor, power converter, pulsewidth modulation inverter, quasi-resonant de-link converter, resonant de-link converter, shaft voltages, soft switching.

The passively clamped quasi-resonant dc-link (PCQRL) inverter basic topology and other quasi-resonant inverters have been shown to be only partially compatible with pulsewidth modulation (PWM), due to a minimum dwell time created by the clamping mode in the inverter operation. This paper addresses this kind of modulation nonlinearity, employing the space-vector approach as a modeling tool. Closed-form expressions are obtained, defining the inverter linear modulation range in terms of the dwell time and other inverter and load parameters and characteristics. An alternative implementation of the resonant snubber that eliminates the low-order harmonics in the output voltages is presented. Experimental and simulation results are presented to support the theoretical analysis. Index Terms - Quasi-resonant inverters, soft-switching inverters, space-vector pulsewidth modulation.

A novel open-loop speed control method for induction motors that provides high output torque and nearly zero steady-state speed error at any frequency is presented. The control scheme is based on the popular constant volts per hertz (V/f) method using low-cost open-loop current sensors. Only stator current measurements are needed to compensate for both stator resistance drop and slip frequency. The scheme proposed fully compensates for the current-resistance (IR) voltage drop by vectorially modifying the stator voltage and keeping the magnitude of the stator flux constant, regardless of changes in frequency or load. A novel slip frequency compensation, based on a nonlinear torque-speed estimate, is also introduced. This method reduces the steady-state speed error to almost zero. It is also shown that a linear torque-speed approximation is a special case of the nonlinear estimate and that it leads to large speed errors for loads greater than rated. It is shown that, by using the proposed method, the speed can be accurately controlled down to, at least, 1.2 Hz with load torques of more than 150% of rated value. Since the only machine parameter required, the stator resistance, is automatically measured at startup time, using the same pulsewidth modulated voltage-source inverter without additional hardware, the proposed drive also exhibits self-commissioning capability. Index Terms - Constant volts per hertz, induction machine, low speed, slip compensation.

In this paper, the overmodulation region voltage-gain characteristics and waveform quality of carrier-based pulsewidth-modulated (PWM) methods are investigated. Through detailed analytical study, voltage-gain characteristics are extracted independent of carrier frequency. The influence of blanking time and minimum pulsewidth (MPW) control on the inverter gain characteristics are studied and shown to be significant. A comparative evaluation of the modulator characteristics reveals the advantageous high-modulation-range characteristics of discontinuous PWM methods and, in particular, the superior overmodulation performance of a discontinuous PWM method. The modulation methods under consideration are tested on a PWM voltage-source inverter (VSI)fed induction motor drive in the laboratory, and the theoretical results are verified by experiments. Also, a gain linearization technique is presented and experimentally verified. The results of this study are useful in design, performance prediction, and development of high-performance overmodulation strategies for PWM-VSI drives. Index Terms - Current harmonics, inverter, overmodulation, voltage gain.