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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.

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.

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 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.

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).

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.

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.

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.

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 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

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, winding function method in conjunction with the coupled magnetic circuit approach are used to develop the dynamic equations of the five-phase synchronous reluctance machine in the natural frame of reference (a-b-c-d-e). The effect of third harmonic of airgap MMF is included in this development. A five-phase transformation from the (a-b-c-d-e) system to a ([d.sub.1]-[q.sub.1]-[d.sub.3]-[q.sub.3]-n) system is introduced. This transformation removes the angular dependency of the inductances. Using this transformation, equations for a five-phase synchronous reluctance machine including the third harmonic of the airgap MMF were obtained. The resulting equations are compared with the equations in the natural (a-b-c-d-e) system. Simulation traces are used to confirm the validity of the model. Finally, the developed equations are compared to the experimental results and the similarities and discrepancies identified. Index Terms - Concentrated winding, synchronous reluctance motor, third harmonic.

Whenever an electrical machine is meant to be fed by a power converter, the design should be approached as a system optimization, more than a simple machine sizing. A great variety of electrical machines is available to accomplish this goal, and the task of comparing the different options can be very difficult. A general purpose sizing equation, easily adjustable for every topology, that could take into account different waveforms and machine characteristics, would be a very desirable tool. In this paper, a general approach is presented to develop and to discuss such an equation. Sample applications of the sizing and power density equations are utilized to compare the induction machine and the doubly salient permanent magnet (DSPM) machine. Index Terms - Ferrites, magnets, motors, power density, sizing equation.

In this paper, an optimum-efficiency control scheme of synchronous reluctance motors is presented. There exists a variety of combinations of d- and q-axis current which provides a specific motor torque. The objective of the optimum-efficiency controller is to seek a combination of d- and q-axis current components, which provides minimum input power, that is, minimum losses at a certain operating point in steady state. A small amount of perturbation is added to the d-axis current reference for the purpose of searching a minimum input power operating point. Index Terms - Optimum-efficiency operation, synchronous reluctance motor.

It has been previously demonstrated that an induction machine drive with contactorless pole changing can be achieved by reversing current directions of certain stator coil groups. This paper compares the power and torque capability of this drive with conventional four-pole and two-pole induction machine drives. Based on the technique of vector space decomposition, the machine coupled-circuit model is transformed to a reference frame model. As a result of this transformation, the coupled coil group variables can be replaced by equivalent decoupled four-pole and two-pole dq0 variables. This reference frame model facilitates the analysis and control of the machine drive, especially during transients, such as the pole-changing transition. Index Terms - Electronic pole changing, reference frame model, induction motor.

A current-controlled VSI-PWM rectifier and inverter with capacitor dc link is regarded as one of the most important structures for three-phase to three-phase power conversion. This type of converter normally requires twelve switches for a rectifier and inverter composed of self turnoff switch such as a bipolar transistor or an IGBT with an anti-parallel diode. In this paper, a new three-phase to three-phase converter for ac motor drives is proposed. The proposed converter employs only eight switches and has the Capability of delivering sinusoidal input currents with unity power factor and bidirectional power flow. This paper describes the feasibility and the operational limitations of the proposed structure. A mathematical model of the system is derived using the generalized modulation theory and experimental results for steady state and dynamic behavior are presented to verify the developed model. Index Terms - VSI, PWM, current control, reduced switch, rectifier, inverter, ac motor drive, split capacitor dc link.

Pulsewidth modulated (PWM) inverters have recently been found to be a major cause of motor bearing failures in inverter-motor drive systems. Specifically, all inverters generate common mode voltages relative to the earth ground. The voltages provide coupling or bearing currents through motor parasitic capacitances to the rotor iron which flow via the bearings to the grounded stator case. In this paper, a model of bearing currents caused by PWM inverter is proposed. The model is based on transmission line theory which uses an equivalent lumped parameter [Pi]-network to describe the parasitic coupling phenomenon. The model parameters are then identified by matching the calculated model outputs with those of experimental measurement. The validation of the method is demonstrated by the fact that the model can reproduce a variety of experimental results obtained on a test motor. An application of this method also gives a motor grounding current model. As the conducted electromagnetic interference (EMI) in drive systems is related to the grounding currents, the grounding current model can be used for the analysis of conducted EMI in motor-drive systems. Index Terms - Bearing current, bearing damage, bearing failures, induction motor, parasitic capacitive coupling, PWM inverter, shaft voltage, common mode voltage

A new control scheme to extend the speed range of a four-pole induction machine is investigated. A three-phase stator winding is used with each of two coil groups per phase being independent resulting in a six-coupled circuit, six-terminal stator winding. Two inverters supply the machine with the required regulated currents to obtain the effect of either four-pole or two-pole windings. Four-pole operation is proposed from zero speed until the end of its constant power region. Employing contactorless pole changing to obtain two-pole operation extends the constant power region resulting in a doubling of the speed range for approximately the same inverter/machine rating.

An experimental investigation of conducted radio-noise emission from a conventional pulse width modulated (PWM) inverter of medium power feeding an induction motor is described. It is determined that the inverter system generates considerable impulse currents through the power leads feeding the system resulting in serious conducted electromagnetic interference (EMI) problems and significant voltage waveform distortion in the power system. The dominant emission sources in the system are identified. A proposed model of the drive system for the purpose of evaluation of EMI are developed. Several low-cost strategies for improvement in EMC performance of the PWM inverter are then proposed. Experimental results demonstrate that disturbance from the modified system can be dramatically reduced and that the EMC performance of the system has come very close to meeting the IEC CISPR and FCC limits on conducted emissions for digital devices.

A rotor position detection scheme which utilizes the characteristics of the synchronous reluctance motor is proposed. In particular, the dependence of the self and mutual inductances on the rotor position is utilized. The motor currents are controlled by a transistor inverter in the manner of hysteresis current control. The inverter switching creates ripples in the phase currents. The rate change of current in the ripples is then detected and converted to a rotor position signal. The proposed scheme is aimed to provide rotor position information particularly at low rotor speed, even at zero rotor speed. Numerical analysis of the rate change of the phase current of the synchronous reluctance motor is also discussed.

This paper describes a sensorless synchronous machine drive to be used for starting an auxiliary power unit (APU) on commercial transport airplanes. The proposed method utilizes the synchronous generator mounted on the APU, and presently only used as a source of electrical power, as a synchronous motor for starting the APU. The developed sensorless synchronous motor drive starting function involves measurement of machine terminal voltage and current, from which the desired current command is then calculated and implemented by the drive converter. Power into the machine is determined by a power control loop, while the system voltage is limited to a desired value by a field weakening loop in the controller.

A new multiple coupled circuit model is presented for simulation of induction machines with both arbitrary winding layout and/or unbalanced operating conditions. The model is derived by means of winding functions. No symmetry is assumed. The parameters of the model are calculated directly from the geometry and winding layout of the machine. The behavior of an induction machine during starting is simulated using this model. The results are shown to be in good agreement with the solution obtained by a conventional d - q model for symmetric conditions. The new model is then extended to the solution of a wide variety of fault conditions such as broken bars and end rings and open or short circuited motor coils.

A new force commutated three level boost type rectifier is proposed in this paper. The rectifier has the characteristics of drawing nearly sinusoidal current from utility with unity fundamental power factor. High reliability is possible due to its shoot-through free structure. A doubled dc bus voltage compared to a normal two-level rectifier is also possible because of the neutral point clamping. The operating principle, steady state analysis, input current and neutral point voltage control schemes, as well as detailed experimental results are presented in this paper.

A new variable reluctance motor is introduced to help solve the energy circulation problems which exist during commutation in conventional variable reluctance motors (VRM's). The new motor design enables the energy stored in the magnetic field to be retained and utilized within the motor, instead of being returned to the source. The operating principles of the motor and associated converters are presented. The analysis shows that by employing both short pitch and full pitch windings, this new motor can eliminate the two problems without extra conductors in the slots. As a result, the new motor has the following important performance advantages over conventional VRM's: (1) It allows a significant improvement in the turn-off process and therefore allows higher speed capacity; (2) it has higher output with the same or higher efficiency with the same output because of the improvement on the turn-off performance and due to the utilization of the trapped energy; (3) the machine can have a higher output with the same power converter because of the improvement of the energy conversion ratio.

Although design of induction motor drives employing field oriented control has reached a relatively mature state, relatively little effort has been directed toward improving the reliability of these drives. In this paper, a new, improved induction motor control strategy is proposed incorporating a multiphase machine that allows for continuous, disturbance-free operation of the drive even with complete loss of one (or more) legs of the inverter or motor phase. A complete analysis of both an even phase and an odd phase machine utilizing this new control and circuit concept is included.

A unique topological configuration for rotating electromagnetic machines that can produce significantly higher force density than an induction machine is investigated. The stator is constructed using full pitch concentrated windings embedded in conventional slots. Rotor saliency is produced using poles constructed of axially oriented laminations. Operation is such that all of the conductors are actively taking part in torque production all of the time. The means for exciting the stator windings allows for independent control of torque and regulation of the rotor flux. A force density comparison is made based on operation with equal surface current density, conduction losses, and peak air-gap flux density. Construction and testing of a prototype 500-rpm, 28-kW laboratory machine, converter, and controller are described.

This paper proposes a new series compensated induction generator/battery supply topology which provides a constant voltage and frequency at the terminals, allowing minimum current harmonic distortion while at the same time providing a source and sink of real and reactive power. With appropriate control of the reactive power, the speed of the generator is allowed to vary within a relatively wide range. This technique can be further expanded by applying ac capacitors in parallel with the load to lessen the burden of the PWM inverter. Both simulation and experimental results are in agreement with the theory which leads to the conclusion that the system could be feasible for isolated power generation systems (wind, hydro, diesel, or hybrid generation).

A new method for condition monitoring of an electrical machine is proposed. The method uses the power leads to the machine itself as the communication link between the sending station located within the machine and the receiving station located remotely outside the machine. The required communication circuit to realize data transmission in both the cases of the ordinary 60 Hz power line and the special PWM inverter-fed power line is then constructed. The communication circuit uses an asynchronous serial communication protocol and an FSK modulation for realizing frequency multiplexing in the power line. An on-line winding temperature monitoring system for an inverter-fed induction machine is constructed using this power line communication link. Experimental results demonstrate satisfactory operation of the system.

Two squirrel cage induction machines interconnected via a 20 kHz parallel resonant High Frequency (HF) ac link and associated switching Pulse Density Modulated (PDM) converters are investigated, one operating as a generator and the other as a motor. No capacitors are used for the excitation of the generator or motor. Instead, the real power of the generator is controlled so as to maintain the proper link voltage and match the power between the input and output. Current regulated PDM converters operating via Field Oriented Controllers (FOC's) are used to control both machines. A zero voltage switching technique is utilized with the associated PDM converters. Low harmonic distortion waveforms have been obtained both at the input and output due to the high 40 kHz switching frequency. Link voltage build-up and excitation of the generator by an initial charging circuit, power matching between input and output, and peak link voltage regulation techniques are investigated. Both computer simulations and experimental results demonstrate the feasibility of the proposed system.

This paper presents the development and implementation of a direct field orientation controller (DFOC) for induction machines based on determination of the spatial position of the air gap flux from the third harmonic component of the stator phase voltages. The control utilizes spatial saturation harmonic components rotating at synchronous frequency that are generated in the air gap flux when the machine operates in a saturated condition. When the machine is wye connected, the sum of the three phase voltages results in a signal dominated by the third harmonic and a high frequency component due to the rotor slot ripple. It is shown that the third harmonic voltage component can be effectively used to estimate both amplitude and position of the air gap flux. Two methods for estimation of the air gap flux from the third harmonic voltage are discussed in the paper. A complete induction motor direct field orientation control is designed and implemented in the laboratory. Extensive experimental results showing the DFOC drive system performance are presented and discussed.

A new concept for solving the current commutation and energy circulation problems in conventional variable reluctance motors (VRMs) is presented. The concept enables the energy stored in the magnetic field to be retained and utilized within the motor instead of being returned to the source. A new VRM and two companion converters are proposed and described in this paper. The operating principles of the motor and the converters are presented. Simulation results based on a linear model are presented to verify the operating principles. A prototype motor is built and tested to demonstrate the degree of improvement that can be realized with the new motor. The experimental results show that by eliminating these two problems, this new motor has important performance advantages over conventional VRMs.