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This paper describes the strategy to design and control an axial-flux (AxF) surface-mounted permanent-magnet machine for achieving a wide flux-weakening (FW) operating region. By using a slotted stator with fractional-slot windings and additional cores enclosing end windings, the AxF machine satisfies the specification of a wide constant-power speed range. The design procedure is presented for increasing FW capability while obtaining low-harmonic back electromotive force and low cogging torque. This technique is applied to design an 8-N. m AxF prototype machine that exhibits about 3 : 1 FW range. To the aim of exploiting full capability of the machine, an FW controller is designed and implemented. This controller utilizes the voltage difference between the current regulator and the output voltage, limited by a voltage source inverter. With this method, the output torque in the FW region is higher than that achieved using the conventional FW method based on the voltage-magnitude feedback. The goodness of both design and control algorithm is proved by experimental tests on a prototype. Index Terms--AC motor drives, axial-flux (AxF) motor, flux-weakening (FW) control, fractional-slot machines.

This paper deals with the design of a permanent-magnet (PM) motor for zero-speed sensorless rotor position detection, by means of injection of a high-frequency signal. Various aspects are investigated: influence of the rotor structure, stator and rotor saturation, reliability of finite-element analysis to predict the motor performance, and influence of rotor iron bridges and of rotor eddy currents induced. The results presented in this paper give the key rules to designing a PM motor suitable for sensorless rotor position detection. Index Terms--High-frequency signal injection, low-speed sensorless control, motor design optimization, permanent-magnet (PM) motor, zero-speed sensorless control.

The fractional-slot permanent-magnet (PM) machines are used in many applications due to their high torque density, low torque ripple, and high efficiency. However, the fractional-slot machines are characterized by high contents of space harmonics in the air-gap MMF distribution. Such harmonics cause flux variation in the air gap, and the main consequence is the induced losses in the rotor. Depending on the combination of slots and poles of the machine, there are different harmonic contents and then rotor losses. By means of a simple model of the rotor losses, this paper investigates the link between the rotor losses and the combination of the slots and the poles of the fractional-slot PM machines. Index Terms--Permanent-magnet (PM) machines, PM motors, rotor losses, variable-speed drives.

The torque produced by a synchronous reluctance machine (including the permanent-magnet-assisted machine) is studied analytically, with the aim of pointing out the effect of the position of the flux barriers on the torque ripple. It is verified that the position of the flux-barrier ends highly influences the torque waveform. With the aim of reducing torque harmonic contents, a new strategy is proposed based on the choice of couples of flux barriers of different shapes. The flux-barrier geometry is chosen so as to obtain a compensation between the torque harmonics produced by each couple. Experimental results on two prototypes confirm the analytical prediction. Index Terms--Low torque ripple, permanent-magnet (PM)-assisted synchronous reluctance machine, synchronous reluctance machine.

The design of electrical machines for extreme operating conditions must include a thermal analysis coupled with the magnetic analysis. However, the traditional coupling of the thermal and the magnetic models can result in an unacceptable increase in computation time, particularly if finite elements (FEs) are used for the machine analysis. This paper proposes a coupled thermal-magnetic analysis of an induction motor (IM) with the primary goal of achieving a rapid and accurate prediction of the IM performance. Only a minimum set of FE magnetic analyses is carried out so as to determine the parameters of the IM equivalent circuit. These parameters are nonlinear and are adjusted on the basis of the operating point. Then, this equivalent circuit is coupled with a lumped-parameter thermal network to predict the temperature in each part of the IM. Since both the equivalent circuit and thermal network solutions are analytic, the analysis converges very rapidly. At the same time, the FE analysis yields a precise estimation of the IM parameters used in the equivalent circuit. Some experimental results are reported, showing the accurate prediction of the proposed methodology. Index Terms--AC motor drives, finite-element (FE) analysis, induction motors (IMs), performance prediction, thermal analysis.

This paper deals with the magnetic analysis and design of fractional-slot permanent-magnet (PM) motors with nonoverlapped coils. The main focus is on the computation of the stator current reaction and of the self and mutual inductances. The goal of this paper is to give an analytical prediction of these quantities. Simple but effective rules are found for a rapid choice of the geometry of fractional-slot PM machines. Finite-element simulations and experimental results confirm the analytical predictions. This paper also aims at suggesting general considerations for the appropriate choice of the combinations of number of poles and slots and the winding type. Index Terms--AC motor drive, fault-tolerant machines, permanent-magnet (PM) machines, PM motor drive.

A rapid and accurate analysis of the induction motor (IM) is the basis of any design process. This paper deals with an analysis procedure of the IM that combines a set of finite-element simulations with an analytical modal. Both three- and single-phase machines are considered. Experimental tests on some IMs confirm the accuracy of the prediction achieved by the proposed analysis. The choice of specific quantities releases the results from the actual motor length and extends them to any motor adopting the same lamination and winding distribution. Index Terms--AC machines, ac motors, electromagnetic forces, finite-element (FE) analysis, FE method, induction motors (IMs), machine windings.

The aim of this paper is to analyze the behavior of a sensorless control system based on a high-frequency signal injection combined with an inset permanent-magnet (PM) motor. The rotor position of a synchronous PM motor with anisotropic rotor can be detected by the control system which superimposes a high-frequency signal to the fundamental stator voltage. The corresponding high-frequency current is modulated by the rotor anisotropy and used to determine the rotor position. These techniques are effective at zero and at low motor speed. Both saturation and cross-coupling have a heavy influence on the correct rotor position detection. In order to highlight the effectiveness of the sensorless technique, the tests are carried out at various operating conditions. Index Terms--High-frequency signal injection, low-speed sensorless control, motor design optimization, permanent-magnet (PM) machine, zero-speed sensorless control.

The torque behavior of a synchronous reluctance motor [including the permanent magnet (PM) assisted configuration] is deeply analyzed. An analytical model is developed, showing the dependence of the torque ripple on the rotor geometry. The results of this model allow to individuate the position of the flux-barrier ends so as to minimize the torque ripple. In addition, the proposed strategy to minimize the ripple is not only based on a suitable choice of the flux-barrier ends, but this choice is combined with the adoption of a rotor formed by two different laminations. This strategy allows an optimal compensation of the torque harmonics so that a smooth torque is achieved. Some motor prototypes have been manufactured and tested in a suitable testing bench. The torque versus position characteristics have been measured at very low speed, to avoid a reduction of the high-order torque harmonics. The experimental results confirm the effectiveness of the proposed strategy. Index Terms--Low torque ripple, permanent magnet (PM) assisted synchronous reluctance machine, synchronous reluctance machine.

The rotor position of a synchronous permanent magnet (PM) motor can be detected by means of the injection of a high-frequency stator voltage superimposed to the fundamental component. Thanks to the rotor anisotropy, the corresponding high-frequency current is modulated and used to determine the rotor position. Two techniques are considered: the first one adopts a pulsating voltage vector in the estimated synchronous reference frame, while the second one adopts a rotating voltage vector. These techniques are effective at zero and at low motor speed. The accuracy of the rotor position detection depends strictly on the rotor saliency, that is, on the geometry of the PM rotor. In fact both saturation and d- and q-axis cross-coupling have a heavy influence on the correct rotor position detection. The aim of this paper is to compare the two sensorless control techniques, together with two rotor geometries, that is, IPM and inset rotor. In order to highlight the effectiveness of the sensorless technique, the tests are carried out at various operating conditions. It is found that the effectiveness of the sensorless rotor position detection strongly depends on the PM rotor geometry. Conversely, the choice of the sensorless control technique affects slightly the rotor position detection. Index Terms--High-frequency signal injection, interior permanent magnet (PM) motor, low-speed sensorless control, motor design optimization, zero-speed sensorless control.

This paper deals with the postfault current control strategies of a five-phase permanent-magnet (PM) motor. The analysis covers both the open circuit of one and two phases and the short circuit at the machine terminal of one phase. The proposed control guarantees safe drive operation after any fault occurrence. For the sake of generality, an analytical model has been used to investigate the properties of each postfault strategy. The results are general, and they apply to PM motor of any power rating. Simulations and experimental results validate the theoretical predictions. Index Terms--AC motor drives, fault-tolerant machines, permanent-magnet (PM) motors, variable-speed drives.

The sensorless control technique based on the superimposition of a high-frequency stator voltage is commonly used to detect the rotor position of a synchronous interior-permanentmagnet (IPM) motor. This technique is effective at zero and low motor speed, where back electromotive force is null or extremely low. Then, the accuracy of the rotor-position detection depends strictly on the rotor saliency, that is, on the geometry of the IPM rotor. This paper aims to determine some IPM rotor-design criteria so as to improve the sensorless rotor-position detection. Since the design has to be effective in different operating conditions, both saturation and cross-coupling effects have to be taken into account. It is found that the effectiveness of the sensorless rotorposition detection can be improved by means of a proper design of the IPM motor geometry even under heavy operating conditions. Index Terms--High-frequency signal injection, interior permanent-magnet (IPM) motor, low-speed sensorless control, motor design optimization, zero-speed sensorless control.

This paper deals with the design of an interior permanent magnet (IPM) motor for power steering. Such an application requires an imperative fault-tolerant capability that is obtained by means of a redundant solution with two motors on the same shaft. A ball-screw system converts the rotating movement into the linear movement of the steering rack. In addition, the IPM motor has to exhibit very low braking torque after a short-circuit fault. Useful relationships between the maximum braking torque and the motor parameters are found and used in the design of the motor. Index Terms--Electric power steering, fault-tolerant system, permanent magnet (PM) motor, steer-by-wire system.

In high speed applications, slotless permanent magnet (PM) motors appear an attractive solution, being almost insensitive to magneto-motive force harmonics and to pulsewidth modulation (PWM) current ripple and exhibiting lower stator iron losses and rotor losses (significant with squarewave current control). This paper illustrates advantages and drawbacks of a high speed drive using a slotless PM motor. The difficulties found during the realization of a 30-krpm 1-kW PM motor prototype are also highlighted. A low-cost commercial sensorless brushless dc motor controller has been used to force squarewave currents without a significant PWM ripple. In order to recognize a possible unexpected rotor arrest, that is not detected by the integrated circuit, an additional control circuit has been designed to detect that anomalous condition and to restart the motor when it occurs. Index Terms--Fault diagnosis, high-speed motor drive, pulsewidth modulation (PWM) losses, sensorless control, slotless permanent magnet (PM) motor drive.

This paper deals with the design criteria for a high-efficiency permanent magnet synchronous motor. The goal is not pursued by a trivial reduction of the electric and magnetic loadings (which decrease motor losses) but optimizing a set of motor design variables, without increasing the overall dimensions, which are typically imposed as design constraints. The effect of the number of slots and of the inner-to-outer diameter ratio on motor losses is investigated. The possibility of designing a stator with a tooth length lower than the total core length, using soft magnetic composites, is studied. Finally, a criterion is proposed to evaluate the convenience of using a nonoverlapping winding. An analytical approach is adopted so as to allows the obtained results to be useful for a wide variety of permanent magnet machines. Index Terms--Electrical machines design, high-efficiency machines, permanent magnet (PM) motor drives.

This paper deals with the design of a 1-kW permanent-magnet (PM) brushless motor operating in the speed range of 20-40 k r/min. The design procedure involves a parametrical investigation of the most adequate motor configuration by means of a coupled thermal and electromagnetic analysis. The design procedure takes advantage of an analytical study based on Maxwell's equations and is refined by finite-element analysis. Both slotted and slotless motor configurations have been taken into account, with different PM materials for an overall comparison of the motor performance. Index Terms--AC motor drives, brushless machines, machine tools, machine windings, motor drives, permanent-magnet (PM) machine, PM motors, synchronous motor drives, variable speed drives.

This paper illustrates potentials and limits of high-speed permanent-magnet (PM) motors. The influence of materials chosen for PM, stator core, and retaining sleeve is highlighted. Slotted and slotless topologies are considered and compared, computing magnetic, electrical, mechanical, and thermal quantities by means of both analytical and finite-element approach. Thermal and PM demagnetization limits as well as rotor losses are evaluated. A criteria of optimization of the motor structure is described, with the diameter ratio and the iron flux density as main design variables. Index Terms--Finite-element (FE) analysis, high-speed motor, motor analysis and design, motor optimization, permanent-magnet (PM) motor.

This paper deals with tubular linear permanent-magnet (TL-PM) motors, including different topologies, i.e., interior and surface-mounted PMs, slotted and slotless motors. After some preliminary analytical considerations, the performance of the TL-PM motor is highlighted, including specific force, maximum acceleration, and cost. Not only are the advantages emphasized, but also the drawbacks, such as detent forces and attractive radial forces due to eccentricity. Different models have been adopted in the various analyses, including two-dimensional and three-dimensional finite-element analysis as needed. In addition, a comparison between predicted and measured performance on a motor prototype are reported. Index Terms--Analysis and design, finite-element (FE) analysis, high-performance machines, permanent-magnet (PM) linear motor, tubular motor.

A procedure for thermal analysis of a run-capacitor single-phase induction motor characterized by two different windings is presented. The procedure allows for the computation of the average winding temperature rise, and the temperature rises of the two different windings separately. The proposed thermal analysis is based on a lumped-parameter network commonly used for the three-phase induction motor. The paper illustrates how this network is adaptable for analysing the run-capacitor single-phase motor temperatures. In order to test the procedure, the predicted results are compared with those obtained from finite-element analysis and experimental data. Both comparisons show an appreciable agreement, confirming the validity of the analysis. Index Terms--Computer-aided design (CAD), electric machine CAD, finite-element (FE) analysis, induction motors, temperature measurement, thermal analysis.

Several techniques may be adopted in designing surface-mounted permanent-magnet motors in order to reduce the cogging torque. This paper describes various classical and innovative techniques, giving a theoretical justification for each of them. To this aim, a simple original model of the cogging torque mechanism and a Fourier analysis are introduced. As a result, it is highlighted that some techniques are not always utilizable, and some of them may even be deprecatory when not used correctly. In addition, effects of cogging torque elimination on back electromotive force are discussed. Index Terms--AC motors, acoustic noise, cogging torque, detent torque, ripple torque, permanent-magnet machines, permanent-magnet motors, servomotors, synchronous motors.

This paper describes two methods--one numerical, the other analytical--for analyzing an axially laminated reluctance (ALAREL) motor. The numerical method, finite-element analysis (FEA), is generally used for estimation of the motor magnetic loading and capability for given stator currents. The accuracy of the FEA prediction is confirmed by a comparison between computed and measured magnetic quantities. The analytical model allows a rapid evaluation of the flux density in different parts of the motor, as well as of the capability for given stator current. It uses a distributed parameter network. The paper compares the results obtained from this network with those obtained from FEA. The methods agree well. Finally, the paper uses the two methods to investigate the effect of the quality of the magnetic material as well as the effect on motor performance of a nonuniform distribution of the laminations in the rotor. It shows that, with grain-oriented steel and nonuniformly distributed laminations, a higher flux linkage can be obtained. Consequently, lower current is required to develop the same motor torque. Index Terms--Finite element analysis, magnetic fields, magnetic flux, modeling, optimization, parameter estimation, reluctance motors, reluctance motor drives, synchronous machines, synchronous motors.

This paper deals with the selection of the motor parameters and the inverter power ratings for a permanent-magnet (PM) synchronous motor drive in order to meet a given flux-weakening torque versus speed characteristic. Appropriate combinations of stator PM flux linkage, d. and q-axis inductances, and inverter current rating at a given voltage are derived, in normalized values, as functions of the specified flux-weakening speed range and torque limits. By means of these sets of data, the drive designer can easily individuate and compare all the suitable synchronous motors (defined by the d- and q-axis inductances and flux linkage) and the related inverter volt-ampere ratings, for the desired flux-weakening performance. Therefore, this paper can be considered a synthesis work rather than an analysis one and can profitably be used for an optimal design of a synchronous motor drive. Index Terms - Flux weakening, motor design, synchronous motor drives.

In this paper an optimization procedure for the optimal design of a transverse-flux induction heating system is presented. Hooke and Jeeves direct search technique is used for the optimization procedure. The finite element method is used for the electromagnetic field calculation and the integral parameter determination. The results obtained by this procedure are compared with those available in literature.

In this paper, the design of a full electrical system for an electrical scooter is presented. The paper explains the design choices that have been made to satisfy the typical main requirements for an electrical vehicle. According to them, an interior permanent-magnet synchronous motor has been incorporated in a drive able to control the motor both in the constant-torque (constant- flux) and in the constant-volt-ampere (flux-weakening) regions. Experimental results carried out on a system prototype are also included in the paper. Index Terms--AC motor drives, electric vehicles, synchronous motor drives.

This paper deals with a tubular slotless linear motor with surface-mounted permanent magnets (PMs). The magnetic field strength and flux density due to the PMs are analytically computed by applying Maxwell's equations. The field problem is solved by introducing a convenient approximation in the PM magnetization, without loss of accuracy in the final solution. The agreement of the analytical results with those obtained by the finite-element method shows the proposed field computation particularly suitable for implemention in motor design software, for a fast analysis of the PM linear motor.

This paper proposes some novel designs of permanent-magnet synchronous motors for extending their flux-weakening capabilities. According to such a proposal, the motors are characterized by a saliency ratio [l.sub.d]/[l.sub.q] greater than one, whereas classical designs exhibit a saliency ratio lower than one. The innovative and classical design solutions are deeply compared in the paper. In order to understand better the basic differences in the motor design, the same base and flux-weakening performance are fixed. The influence of the saliency ratio on inverter voltampere ratings, maximum feasible speed, and current control characteristics is highlighted and discussed. Index Terms--Motor drives, permanent-magnet machines, synchronous machines, variable-speed drives.