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A new dead-time compensation method for vector-controlled ac motor drives is proposed. The method only compensates the fundamental and sixth harmonic component of the inverter-output distortions in synchronous reference frame. The fundamental component is compensated by feedforwardly adding a predetermined compensation signal to the voltage reference of ac motor drive. To compensate the harmonic distortions, the harmonic compensator with all-pass-based adaptive bandpass filter is proposed and builds up the feedback loop with current controllers in order to minimize the distortions due to dead-time effects. The method is software intensive and independent of the polarity of the phase currents and nonlinear-switching characteristics varied with operating conditions of the inverter. It is simulated and implemented on a 750-W laboratory ac motor drive, where its effectiveness is verified. Index Terms--AC drives, dead-time compensation, induction motor.

The focus of this paper is the use of structured neural networks for sensorless control of ac machines using carrier-signal injection. Structured neural networks allow effective compensation of saturation-induced saliencies as well as other secondary saliencies. In comparison with classical compensation methods, such as lookup tables, this technique has advantages such as a physics-based structure, general scalability, reduced size and complexity, and correspondingly reduced commissioning time. When compared with traditional neural networks, structured neural networks are simpler, physically insightful, less computationally intensive, and easier to train. All make the proposed method an improved implementation for sensorless drives. Index Terms--Rotor position estimation, sensorless control, structured neural networks.

This paper presents a comparative analysis involving several fault-tolerant operating strategies, applied to three-phase induction-motor drives, that intend to compensate for inverter faults. The results presented show the advantages and the inconveniences of several fault-tolerant drive structures, under different control techniques, such as the field-oriented control and the direct torque control. Experimental results concerning the performance of the three-phase induction motor, based on the analysis of some key parameters, like induction-motor efficiency, motor power factor, and harmonic distortion of both motor line currents and phase voltages, will be presented. Index Terms--AC motor drives, fault tolerance, induction-motor drives, reliability.

AC machines supplied in parallel by a common voltage source inverter are sometimes used in industrial drives and railway traction applications. This reduction of power and control electronics leads to a reduction of cost, weight, and dimensions that is very useful for on-board systems. But this common supply imposes common voltages to all machines and the possibilities of independent behavior are reduced. In this paper, a graphical modeling is suggested to model such parallel drives for a railway application. A weighted control is then systematically deduced from this modeling and different possibilities of control are highlighted. Experimental results are provided to compare two of the deduced controls. Index Terms--AC motor drives, control systems, railways, traction motor drives, variable-speed drives.

Direct torque control (DTC) is an induction motor control technique that has been successful because it explicitly considers the inverter stage and uses few machine parameters, while being more robust to parameter uncertainty than field-oriented control (FOC). This paper presents a formal derivation of DTC based on singular perturbation and nonlinear control tools. The derivation elaborates an explicit relationship between DTC performance and machine characteristics; low-leakage machines are expected to perform better under DTC. It is shown that DTC is a special case of a sliding-mode controller based on the multiple time-scale properties of the induction machine. The known troublesome machine operating regimes are predicted and justified. Explicit conditions to guarantee stability are presented. DTC is shown to be a suboptimal controller because it uses more control effort than is required for flux regulation. Finally, compensation strategies that extend DTC are discussed. The derivation does not require space vector concepts thus, it is established that the traditional link between DTC and space vectors is not fundamental. Index Terms--AC motors, direct torque control (DTC), induction motor drives, singularly perturbed systems, vector control.

This paper analyzes the sensorless control of ac machines based on the zero-sequence voltage generated by the injection of a carrier-signal voltage. The analysis focuses on rotor position estimation (tracking of rotor-position-dependent saliencies), but the methods discussed apply equally to flux position estimation (tracking of flux-dependent saliencies). Analyses of relevant aspects like selection of the carrier-signal frequency, measurement of the zero-sequence carrier-signal voltage, and decoupling of saturation-induced saliencies are included. Index Terms--Rotor position estimation, saliency-based sensorless control, zero-sequence voltage.

A stable sensorless controller for DTC of induction motor fed by three-level inverter using the Radial Basis Function Network (RBFN) is presented in this paper. The torque ripple can be drastically reduced and low speed performance can be obtained in the DTC system for high performance induction motor drives. However, speed control performance is still influenced by the lumped uncertainties of the system such as parameter variations, external load disturbances, and unmodeled dynamics which make it difficult to obtain an exact mathematical model. In this paper, the lumped uncertainties are estimated on-line by the RBFN. Simulations as well as experimental results are shown to illustrate the performance of the proposed system. Index Terms--AC motor drives, Direct Torque Control (DTC), neural network applications, observers.

This paper presents a detailed analysis of the asynchronous torque components (average cage, magnet braking torque and pulsating) for a single-phase capacitor-start, capacitor-run permanent magnet motor. The computed envelope of pulsating torque superimposed over the average electromagnetic torque leads to an accurate prediction of starting torque. The developed approach is realized by means of a combination of symmetrical components and d-q axes theory and it can be extended for any m-phase AC motor--induction, synchronous reluctance or synchronous permanent magnet. The resultant average electromagnetic torque is determined by superimposing the asynchronous torques and magnet braking torque effects. Index Terms--AC motors, capacitor motors, permanent magnet motors, starting, torque simulation.

In this work, performance analyses of slip energy recovery drives during and at recovery after instantaneous power-supply failure in one or more supply phases have been carried out. Transient slip energy recovery drive currents and voltages under such fault conditions have been obtained theoretically using mathematical models which take into account the three-phase, single-phase, and disconnected power-supply conditions. A detailed set of theoretical and experimental results is given to clarify the expected behavior of the drive under instantaneous power-supply failure of a few cycles duration and at recovery. Insertion of an external bypass resistor into the dc link by the use of a static switch has been discussed to suppress the induced overvoltages and, hence, overcurrents in the rotor windings and converters, after recovery of the supply. Index Terms--AC motor drives, power-supply failure, slip energy recovery.

A sensorless hybrid direct torque control (DTC) drive for high-volume low-cost industrial, domestic, and automotive applications has been developed using the inexpensive TMS329F243 digital signal processor controller. Under transient operating conditions, the drive is controlled using the classic bang-bang DTC. In the steady state, using linear torque and flux controllers, the control system generates a reference voltage vector for the inverter feeding the induction motor. The vector is then realized using the well-known space-vector pulsewidth modulation (SVPWM) technique. As a result, the irregular switching pattern typical for the classic DTC strategy is replaced with a quasi-optimal one, typical for the SVPWM. Description of the drive, including a novel motor state observer, is followed by selected experimental results confirming its excellent operating characteristics. Index Terms--Direct torque control (DTC), observers, sensorless ac drives, space-vector pulsewidth modulation (SVPWM).

This paper systematically explores the static nonlinear mapping property of feedforward neural networks for various waveform processing and delayless filtering that are applicable to power electronics and ac drives area. Neural-network-based processing of waves gives considerable simplification of hardware and/or software that are traditionally used for such applications. Two general cases have been investigated: The voltage or current waveforms which have constant frequency but variable magnitudes, and the other case is variable-frequency variable-magnitude voltage or current waves. The former case is mainly important for power electronics that operate on a utility system and general-purpose constant-frequency converter power supplies, and the latter is important for the adjustable-speed ac drives area. In both cases, the performance of neural-network-based waveform processing and delayless filtering with offline training was found to be excellent. The results of this study are also applicable to other areas of electrical engineering. Index Terms--AC drives, delayless filtering, neural network, power electronics, waveform processing.

This paper discusses the approach to analytical calculation of the cogging torque in permanent-magnet (PM) brushless motors. Magnetic field energy in the air gap has been used to obtain the cogging torque equations. Two equations have been derived: with the PM circumferential width taken into account, and a simplified equation, i.e., without the effect of the finite width of the PM. The effect of eccentricity has also been included. Calculation results have been compared with laboratory test results Index Terms--AC motors, brushless motors, cogging torque, magnetic flux density, permanent-magnet (PM) machines, PM motors, stator slots, torque ripple.

This paper presents a review of recently used direct torque and flux control (DTC) techniques for voltage inverter-fed induction and permanent-magnet synchronous motors. A variety of techniques, different in concept, are described as follows: switching-table-based hysteresis DTC, direct self control, constant-switching-frequency DTC with space-vector modulation (DTC-SVM). Also, trends in the DTC-SVM techniques based on neuro-fuzzy logic controllers are presented. Some oscillograms that illustrate properties of the presented techniques are shown. Index Terms--AC motors, direct torque control (DTC), voltage-source inverters.

This paper analyzes saliency-based sensorless control methods for ac machines. The paper focuses on three different methods, which utilize the following signals: negative-sequence carrier-signal current, zero-sequence carrier-signal voltage, and pulesewidth-modulation-switching zero-sequence voltage. Applicability of these methods for both rotor position estimation (tracking of rotor-position-dependent saliencies) and flux position estimation (tracking of flux-dependent saliencies) is studied for each method, as well as aspects of their implementation. Index Terms--Flux angle estimation, rotor position estimation, saliency-based sensorless control.

We have adapted an analytical computer model, RMxprt, to predict the operating parameters of both single-phase and three-phase induction motors as a function of motor lamination material property curves. The model uses newly defined parameters, integrated average core loss (IACL) and integrated average permeability (IAP), rather than the material characteristic commonly used today, 1.5-T permeability, which is not effective in predicting motor efficiency. IACL and IAP have been shown to be excellent predictive parameters of the efficiency of motors, and these parameters are considered the best for specifying motor laminations. IACL is closely correlated with the 1.5-T core loss and IAP is closely correlated with the 1.0-T permeability and, for semiprocessed materials, the 1.5-T core loss. Therefore, the 1.5-T core loss alone can be used to specify semiprocessed cold-rolled motor lamination materials for motors. For all cases studied, directionally averaged IACL and IAP are almost the same as the L&T Epstein pack properties. Therefore, the L&T Epstein pack properties, obtained by conventional Epstein testing, can be used in lieu of the directionally averaged properties. Index Terms--AC motors, current, eddy-current losses, electromagnetic analysis, ferromagnetic materials, finite-element analysis, induction motors, iron alloys, magnetic permeability, magnetic variables measurement, modeling.

This paper shows how to integrate fault compensation strategies into two different types of configurations of induction motor drive systems. The proposed strategies provide compensation for open-circuit and short-circuit failures occurring in the converter power devices. The fault compensation is achieved by reconfiguring the power converter topology with the help of isolating and connecting devices. These devices are used to redefine the post-fault converter topology. This allows for continuous free operation of the drive after isolation of the faulty power switches in the converter. Experimental results demonstrate the validity of the proposed systems. Index Terms--AC motor drive, fault tolerant, pulsewidth-modulation (PWM) inverter.

This paper presents an overview analysis and a discussion of field experience with different drive configurations used in shovel applications. The analysis includes different drive topologies, shovel duty cycles for a typical truck pass loading, and energy regeneration capabilities. Special attention is given to the interaction between the high power shovel drives and the grid: harmonics injection, reactive power requirements, and voltage regulation. This paper presents operational experiences obtained in copper mine industries. The main characteristics of the newest shovels with active front end (AFE) at the line side are also included. Finally, a critical evaluation of the different topologies is presented, showing that the shovel drive operation strongly affects the behavior of the power distribution system and that the introduction of the AFE technology produces an important performance improvement. Index Terms--AC drives, active front end (AFE), dc drives, mining, shovels.

The universal or ac commutator motor, widely used in hand tools and domestic appliances generally uses a two-pole stator with a concentrated winding and an armature with interlocked coils elements. The copper volume and the axial length of the end windings of such conventional structures are then usually very important. In this paper, the authors present a new universal motor structure based on an efficient use of the isotropic magnetic properties of the soft magnetic composites and on the concentrated winding technique. The stator core presents a claw-pole structure and the armature has a concentrated winding with several coils wound around the same tooth. With this new ac commutator motor structure, a reduction of the total volume by a ratio equal to 200% is obtained when compared to a classical universal motor structure with nearly identical performance. Index Terms--Brush ac machines, commutator ac motors, machine windings, powdered magnetic materials, universal motors.

This paper describes an efficient calculating procedure for the steady-state operation of a single-phase line-start capacitor-run permanent-magnet motor. This class of motor is beginning to be applied in hermetic refrigerator compressors as a high-efficiency alternative to either a plain induction motor or a full inverter-fed drive. The calculation relies on a combination of reference-frame transformations including symmetrical components to cope with imbalance, and dq axes to cope with saliency. Computed results are compared with test data. The agreement is generally good, especially in describing the general properties of the motor. However, it is shown that certain important effects are beyond the limit of simple circuit analysis and require a more complex numerical analysis method. Index Terms--AC motors, capacitor motors, permanent-magnet (PM) motors, steady-state performance.

In this paper, a 12-V 1-kW permanent-magnet ac motor drive is tested extensively at a wide frequency range, and the frequency spectra are partitioned for identification of noise sources and their propagation paths. Switching characterization of the power MOSFET and its body diode reverse-recovery characterization are evaluated for circuit modeling. The parasitic components and common mode path are identified and measured with the time-domain reflectometry (TDR) method. The inverter circuit model is then constructed with major parasitic inductance and capacitance in device modules, passive components, leads, and interconnects. To verify the validity of the inverter model, a comparative study is performed with computer simulations and hardware experiments. The fundamental mechanisms by which the electromagnetic interference (EMI) noises are excited and propagated are analyzed, and the significant roles of parasitic elements coupling with device switching dynamics in EMI generation are examined. The results indicate that the identification of parasitic inductance through TDR measurement helps verify the voltage spike during turn-off, or vice versa. The conducted EMI noise caused by parasitic components of bus capacitor, dc bus, and devices is proven to be identifiable with the characterization and simulation techniques used in this paper. Index Terms--Electromagnetic interference (EMI) simulation, parasitic models.

The use of an extended Kalman filter (EKF) as a nonlinear speed and position observer for permanent-magnet synchronous motor drives is a mature research topic. Notwithstanding, the shift from research prototype to a market-ready product still calls for a solution to some implementation pitfalls. The major and still unsolved topic is the choice of the EKF covariance matrices. This paper replaces the usual trial-and-error method with a straightforward matrices choice. These matrices, possibly combined with a novel self-tuning procedure, should put the EKF drive much closer to an off-the-shelf product. The proposed method is based on the complete normalization of the EKF algorithm representation. Successful experimental results are included in the paper. Index Terms--AC motor drives, extended kalman filter (EKF) tuning, permanent-magnet synchronous motor (PMSM) drives, sensorless drives.

In recent years, much has been written about motors on variable-speed drives, high-speed rigid shaft motors, impact of API Standard 541, motor diagnostics, etc. Most of these papers and articles assume that the reader has significant knowledge of motor theory and operation. However, this assumption is overly optimistic, considering that only a few colleges teach motor theory today, and that application experience at motor user locations has been reduced in recent years. Index Terms--AC induction motor, bearing currents, bearing life, motor sizing, motor torque, rotor bars, shaft currents.

Modern frequency power converters generate a wide spectrum of harmonic components. Large converters systems can also generate noncharacteristic harmonics and interharmonics. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present and the periodicity intervals are fixed, while periodicity intervals in the presence of interharmonics are variable and very long. A novel approach to harmonic and interharmonic analysis, based on the 'subspace' methods, is proposed. Min-norm harmonic retrieval method is an example of high-resolution eigenstructure-based methods. The Prony method as applied for signal analysis was also tested for this purpose. Both high-resolution methods do not show the disadvantages of the traditional tools and allow exact estimation of the interharmonics frequencies. To investigate the methods several experiments were performed using simulated signals, current waveforms at the output of a simulated frequency converter, and current waveforms at the output of an industrial frequency converter. For comparison, similar experiments were repeated using the fast Fourier transform (FFT). The comparison proved the superiority of the new methods. However, their computation is much more complex than FFT Index Terms--AC motor drives, discrete Fourier transform, power system harmonics, Prony method, spectral analysis, subspace methods.

The voltage output is inevitably delayed in a full-digital implementation of a current regulator due to an arithmetic calculation and the pulsewidth modulation. In the case of the synchronous frame current regulator, the time delay is accompanied by a frame rotation. In some applications where the ratio of the sampling frequency to the output frequency is insufficient, such as a high-power drive or a super-high-speed drive, the effect of the frame rotation during the delay time causes a phase and magnitude error in the voltage output. The error degrades the dynamic performance and can cause instability in the current regulator at high speed. It is also intuitively known that advancing the phase of the voltage output can mitigate this instability. In this paper, the errors in the voltage output and the instability problems have been studied analytically and a compensation method for the error is proposed. Using a computer simulation and complex root locus analysis, a comparative study with conventional methods has been carried out and the utility of the proposed method has been verified experimentally. Index Terms--Digital delay, pulsewidth-modulation (PWM) ac drives, synchronous reference frame current regulator.

Passive filters are conventionally used to suppress overvoltage in the motor terminal, either by reducing the voltage rising rate at the inverter output, or by decreasing the motor terminal impedance. We propose an overvoltage suppression scheme that renders the use of passive filters unnecessary. This approach differs from general filter methods, in that it is independent of dv/dt and does not try to reduce dv/dr. Our scheme utilizes the middle voltage level [V.sub.DC]/2 at each pulsewidth modulation voltage transition, where [V.sub.DC] represents the dc-link voltage. The duration of the middle voltage level is controlled in such a way that reflected voltages are cancelled out at the motor terminal. Optimal cancellation is achieved when the duration of [V.sub.DC]/2 is equal to twice the transport delay of the cable. Further, if reflection coefficients at the motor terminal and the inverter output are equal to [+ or -] 1, no overvoltage takes place. The proposed scheme requires the use of six auxiliary insulated gate bipolar transistor switches. Simulation as well as experimental results are presented here. Index Terms--Overvoltage suppression, pulsewidth modulation drive, transmission line, transport delay.

This paper presents an improved method of estimating flux angle, rotor position, and velocity by tracking the position of spatial saliencies in an ac machine. Specifically, a machine model is presented which accurately models the behavior of ac machines with multiple spatial harmonic saliencies. The effects of multiple spatial harmonic saliencies on the estimation of flux angle, position, and velocity is analyzed, and methods are presented utilizing multiple spatial harmonic saliencies to provide wide bandwidth, high accuracy estimates of flux angle, rotor position, and velocity. Index Terms - Flux estimation, position estimation, saliency, self sensing, sensorless control.

As a potential source of turn insulation failure, the steep-fronted voltage at the motor terminal generated by pulsewidth modulation drive switching or cable ringing is not uniformly distributed among the coils of the windings and among the turns of the coils. This paper presents a detailed electromagnetic analysis of the parameters of a transient model of coil and coil group which includes iron loss, skin, and proximity effects. The finite-difference method is applied to solve the model for the interturn and intercoil voltage distributions. The simulation is compared to a simplified lattice diagram analysis and to test results. A turn insulation surge-withstanding capability study is then presented with a flexible insulation test system that models the repetitive steep-fronted voltage stress and temperature stress. Index Terms - AC motors, insulation life, machine windings, pulsewidth modulation inverters, surges, voltage distribution.

A new approach to medium-voltage variable-frequency static ac drives offers improvements in power quality. Harmonic current injection into the power lines is below the most severe requirements of IEEE Standard 519-1992. The power factor of this new type of drive exceeds 94% at full load and is above 90% at 10% load. Motor voltage and current waveforms are improved so that torque pulsations are reduced. Peak voltage stress on motor insulation does not exceed peak input line voltage, and no zero sequence voltage is imposed. Drive efficiency exceeds 96%. This paper describes the new approach and some of the results achieved. Index Terms - Harmonic cancellation, medium-voltage drive, motor-friendly drive, multilevel PWM, power-quality drive, series converters.

This paper describes how the A - [Psi] formulation may be applied to determine the losses in the stator duct spacers of large a.c. motors. The model is described in terms of its geometry and boundary conditions. The novel aspects of the application of the formulation to this problem are explained. These include the modelling of fixed currents sources (the stator windings), the location of the necessary cut surfaces and the determination of their magnetic scalar potential differences, and the implementation of periodic boundary conditions for vector variables. Results are presented showing how the duct spacer losses vary with load, and with the relative permeability of the spacer material. The effects of modelling iron non-linearity, of both the spacer and the steel laminations, are also illustrated.

Permanent magnet ac (PMAC) motor drives are finding expanded use in high-performance applications where torque smoothness is essential. This paper reviews a wide range of motor- and controller-based design techniques that have been described in the literature for minimizing the generation of cogging and ripple torques in both sinusoidal and trapezoidal PMAC motor drives. Sinusoidal PMAC drives generally show the greatest potential for pulsating torque minimization using well-known motor design techniques such as skewing and fractional slot pitch windings. In contrast, trapezoidal PMAC drives pose more difficult tradeoffs in both the motor and controller design which may require compromises in drive simplicity and cost to improve torque smoothness. Controller-based techniques for minimizing pulsating torque typically involve the use of active cancellation algorithms which depend on either accurate tuning or adaptive control schemes for effectiveness. In the end, successful suppression of pulsating torque ultimately relies on an orchestrated systems approach to all aspects of the PMAC machine and controller design which often requires a carefully selected combination of minimization techniques.

A main research topic in PWM-VSI inverter-driven electrical machines is to reduce the generated acoustic noise which often is dominated by a multiple of the switching frequency in the inverter. This paper proposes a modulation scheme for reducing the acoustic noise effect from an AC-machine which can be implemented digitally for low and high performance systems. The scheme is based on a Stator-Flux Asynchronous Vector Modulation (SFAVM) imposed by a digital band limited PWM white noise generator for varying the switching frequency randomly. The white noise generator can be used for 8-, 16- and 32-bit microcontrollers. The modulation strategy is tested in a 1 kVA high performance 16-bit microprocessor controlled ac-drive system. Voltage-spectra on the line-to-line voltage and the acoustic noise spectra are presented and show that the new modulation strategy can decrease the noise effect. The stator-flux-polygon and the line current are measured and demonstrate the random modulation strategy. Finally, the total sound pressure level from the ac-machine is investigated with fixed switching frequencies and with different randomly modulated frequency spans. It is concluded that a properly chosen fixed switching frequency has the lowest total sound pressure level. However, the random modulation strategy distributes the noise frequencies and the noise is more comfortable and less annoying.

The need for higher levels of motor efficiency is increasing significantly. Numerous opportunities are available to reach these levels, many of which are being influenced by changes in government regulations, rebate programs, and industry standards. The purpose of this paper is to update users on the opportunities available to achieve higher performance levels and to summarize those activities that are driving these higher levels. The impact of adjustable-frequency drives will be included. A summary forecasting the future required levels and the method of demonstrating compliances is provided. The relationship and tradeoffs between efficiency and power factor will also be addressed.

In this paper, a new current control scheme based on programmed PWM switching patterns is presented for ac motor drives. In this scheme, reference and feedback current correspondence is maintained with simultaneous optimization of a performance objective. The proposed scheme overcomes the disadvantages of the existing current regulators employing the direct control approach and exhibits several advantages in terms of reduced switching frequency, minimum current/torque ripple, higher efficiency, and improved performance in the ac motor drive. Analytical and experimental investigations on a current-regulated induction motor drive confirm the predicted advantages of the scheme.

This paper studies the effect of neglecting stator transients in doubly fed induction generators. The simulated cases involve two extreme operation points: one at subsynchronous speed and one at supersynchronous speed. A short-circuit fault is applied at the generator terminals. The evolution of different variables is examined using two different models: one of them accounts for the stator transients and the other one neglects them. Index Terms--AC generators, doubly fed induction generators, induction generators, power system transient stability, wind power generation.

The anisotropy of the lamination material, which is usually negligible in the fundamental wave behavior of inverter fed machines, influences the transient control signals and may act as a disturbance during operation. The anisotropy is determined by torque measurements of lamination sheets as well as by the evaluation of the transient electrical behavior of inverter fed induction machines and can produce errors up to 40%. Index Terms--Crystalline anisotropy, inverter-fed ac machines, lamination material, shaft sensorless control.

This paper reviews the results of tests performed on the stator windings of a 13.8 kV, 15000 hp variable speed slipring induction motor in order to assess its insulation condition and quantify the impulse strength of the motor winding. A surge voltage distribution test showed severe nonlinearity of turn voltage where up to 120% of the applied voltage was achieved across the first coil with 0.1-[[micro]second] risetime. The effect of a surge capacitor was also demonstrated when a substantial reduction of the first coil voltage could be obtained at low risetime of 0.1 [[micro]second]. Measurements of breakdown voltage (BDV) of coils at different locations gave indirect evidence that turn insulation degradation was most likely surge related. Finally, the paper contains a proposal of an alternative testing criteria to quantify impulse strength of turn insulation of large ac machines.

A computationally efficient speed and position estimation algorithm, generally applicable to ac motor drives, is designed and analyzed. Applications include: a) sensorless permanent-magnet and reluctance synchronous motor drives using the fundamental excitation as information source; b) sensorless drives using saliency and signal injection; and c) sensored drives using resolvers. Particular attention is given case a). Low parameter sensitivity in the entire speed range (except at low speeds for the reluctance motor)--implying a small position estimation error--and good dynamic properties at nominal speeds are verified. Index Terms--Phase-locked loop, position estimation, resolver, sensorless control, speed estimation.

A commutation method for the permanent-magnet ac motor is presented, which combines a Hall-effect encoder with a quadratic extrapolation scheme, and reduced-order state estimation in order to satisfy the design constraints prescribed by certain military and traction applications. Index Terms--Hall-effect devices, permanent-magnet machines, state observer, torque controller.