Abstract: As a kind of traction device, interior permanent-magnet synchronous machines (IPMSMs) are widely used in modern electric vehicles. This paper performs a design and comparative study of IPMSMs with different rotor topologies (spoke-type PMs, tangential-type PMs, U-shape PMs, and V-shape PMs). The research results indicate that the IPMSM with V-shape PMs is more satisfying with comprehensive consideration. Furthermore, the IPMSM with V-shape PMs is investigated in detail. The influences of geometrical parameters (magnetic bridge and angle between the two V-shape PMs under each pole, etc.) on the performances of V-shape motor are evaluated based on finite-element method (FEM). For accurate research, the effects of saturation, cross-magnetization, and the change in PM flux linkage on d - and q -axis inductances are considered. The back-electromotive force (EMF), flux leakage coefficient, average torque, torque ripple, cogging torque, power per unit volume, power factor, and flux-weakening ability are investigated, respectively. The experimental results verify the validity and accuracy of the process presented in this paper.

Abstract: Conventional model predictive torque control (MPTC) suffers from weighing factor tuning work and relatively high torque ripple, due to the different units of torque and stator flux and the limited number of voltage vectors. This paper proposes an improved MPTC without the use of weighting factor. The torque and flux magnitude references are converted into an equivalent reference vector of stator flux, hence eliminating the weighting factor of stator flux in conventional MPTC. Furthermore, two voltage vectors are applied during one control period to achieve better steady-state performance. Different from prior method using an active vector and a zero vector, the selected voltage vectors may be two nonzero vectors in the proposed method, which provides more opportunities to reduce both torque and flux ripples. The durations of the selected voltage vectors are determined based on the principle of stator flux error minimization. Both simulation and experimental results are presented to validate the effectiveness of the proposed method.

Abstract: This paper investigates the problem of automatic speed tracking control of an electric vehicle (EV) that is powered by a permanent-magnet synchronous motor (PMSM). A reconfiguration scheme, based on higher order sliding mode (HOSM) observer, is proposed in the event of sensor faults/failures to maintain a good control performance. The corresponding controlled motor output torque drives EVs to track the desired vehicle reference speed for providing uninterrupted vehicle safe operation. The effectiveness of the overall sensor fault-tolerant speed tracking control is highlighted when an EV is subjected to disturbances like aerodynamic load force and road roughness using high-fidelity software package CarSim. Experiments with a 26-W, three-phase PMSM are presented to demonstrate the validity of the proposed fault-detection scheme.

Abstract: An electronic stability control (ESC) algorithm is proposed for a four in-wheel motor independent-drive electric vehicle (4MIDEV) utilizing motor driving and regenerative braking torque distribution control to improve vehicle stability. A stability judgment controller, an upper level controller, and a torque distribution algorithm are designed for the ESC system. The stability judgment controller is designed to generate the desired yaw rate and sideslip angle for vehicle stability, and the control mode, which is normal driving mode or ESC mode, is set according to the driver inputs and measurement signal inputs. The upper level controller consists of a speed tracking controller, a yaw moment controller, and four wheel-slip controllers to calculate the desired value of traction force, the desired value of yaw moment, and the four respective net torque inputs of the four in-wheel motors. The torque distribution algorithm is designed to generate each motor driving torque or regenerative braking torque input for each wheel. An average torque distribution strategy, a tire-dynamic-load-based torque distribution strategy, and a minimum-objective-function-based optimal torque distribution strategy are used separately in the torque distribution algorithm to control the motor driving torque or regenerative braking torque for vehicle stability enhancement. The proposed ESC algorithm was implemented and evaluated in a CarSim vehicle model and a MATLAB/Simulink control model. The three proposed torque distribution strategies can be used to regulate the vehicle to perform the following tasks: “single lane change,” “double lane change,” and “snake lane change.” The simulation studies show that the yaw rate error root mean square [RMS $(\gamma-\gamma_\mathrm{-des})$ ] decreased, on average, by 75 percent using the proposed optimal torque distribution algorithm compared with that without using stability control.

Abstract: In this paper we present the design and control of a novel six degrees-of-freedom aerial vehicle. Based on a static force and torque analysis for generic actuator configurations, we derive an eight-rotor configuration that maximizes the vehicle's agility in any direction. The proposed vehicle design possesses full force and torque authority in all three dimensions. A control strategy that allows for exploiting the vehicle's decoupled translational and rotational dynamics is introduced. A prototype of the proposed vehicle design is built using reversible motor-propeller actuators and capable of flying at any orientation. Preliminary experimental results demonstrate the feasibility of the novel design and the capabilities of the vehicle.

Abstract: This paper presents a comprehensive evaluation of several direct torque control (DTC) strategies for permanent magnet synchronous machines (PMSMs), namely DTC, model predictive DTC, and duty ratio modulated DTC. Moreover, field-oriented control is also included in this study. The aforementioned control strategies are reviewed and their control performances are analyzed and compared. The comparison is carried out through simulation, finite-element analysis, and experimental results of a PMSM fed by a two-level voltage source inverter. With the intent to fully reveal the advantages and disadvantages of each control strategy, critical evaluation has been conducted on the basis of several criteria: Torque ripple, stator flux ripple, switching frequency of inverter, steady-state control performance, dynamic response, machine losses, parameter sensitivity, algorithm complexity, and stator current total harmonic distortion.

Abstract: Finite-state predictive torque control (FS-PTC) is computationally expensive, since it uses all voltage vectors (VVs) available from a power converter for prediction and actuation. The computational burden is rapidly increased with the number of VVs and objectives to be controlled. Moreover, designing a cost function with more than two control objectives is a complex task. This paper proposes a simplified algorithm based on a new direct torque control (DTC) switching table to reduce the number of VVs to be predicted and objectives to be controlled. The new switching table also assists to reduce average switching frequency and its variation range. As a result, the cost function is simplified by not requiring to include the frequency term. Experimental results show that the average execution time and the average switching frequency for the proposed algorithm are greatly reduced without affecting the torque and flux performances achieved in the conventional FS-PTC.

Abstract: This paper analyzes the effects of the rotor position error in the performance of field-oriented-controlled permanent-magnet synchronous machine (PMSM) drives intended for electric vehicle (EV) traction applications. A special focus is given to the torque ripple generated along the characteristic trajectories in the different operating regions of the PMSM. An extended and generalized model of the torque ripple produced by the PMSM as a function of the rotor position error is analytically deduced. An infinite-speed interior-(I)PMSM drive and a finite-speed surface-mounted (SM)-PMSM drive are considered for the simulations carried out in MATLAB-SimPowerSystems. The experimental results have been validated with a TM4 EV drive controlling an 80-kW SM-PMSM. The torque ripple has been evaluated for both motoring and regenerative braking operation modes under maximum torque conditions going from 100 N · m at 1000 r/min up to 55 N · m at 9000 r/min. The obtained simulation and experimental results demonstrate the good accuracy of the proposed model for evaluating the torque ripple produced in PMSMs due to the error from the rotor position sensor.

Abstract: Vernier permanent-magnet (VPM) machines have been obtaining a lot of attention over the past few years due to several advantages, such as their high torque density and simple mechanical structures. Moreover, it is found that the torque ripple of VPM machines is ultralow, even without specific design measures such as a short pitch, skewing slots/poles, magnet shaping technology, etc. This paper presents theoretical analysis and comprehensive simulations on the torque ripple of VPM machines. First, a general instantaneous torque equation of VPM machines is proposed to analyze torque features and the effect of parameters on the torque performance of VPM machines. Subsequently, based on the general torque equation and a finite-element algorithm, it is verified that torque smoothness is the inherent characteristic of VPM machines, and the torque ripple of VPM machines can be below 0.2%. Furthermore, it is demonstrated that the torque density of a VPM machine is 40% larger than that of a regular permanent-magnet machine. All these advantages demonstrate that VPM machines can obtain much better steady and dynamic drive performance. Finally, all the theoretical analyses are verified by experiments on a VPM prototype.

Abstract: This paper proposes an online parameter estimation method based on a discrete-time dynamic model for the interior permanent-magnet synchronous motors (IPMSMs). The proposed estimation technique, which takes advantage of the difference in dynamics of motor parameters, consists of two affine projection algorithms. The first one is designed to accurately estimate the stator inductances, whereas the second one is designed to precisely estimate the stator resistance, rotor flux linkage, and load torque. In this paper, the adaptive decoupling proportional–integral (PI) controllers with the maximum torque per ampere operation, which utilize the previously identified parameters in real time, are chosen to verify the effectiveness of the proposed parameter estimation scheme. The simulation results via MATLAB/Simulink and the experimental results via a prototype IPMSM drive system with a TI TMS320F28335 DSP are presented under various conditions. A comparative study with the conventional decoupling PI control method is carried out to demonstrate the better performances (i.e., faster dynamic response, less steady-state error, more robustness, etc.) of the adaptive decoupling PI control scheme based on the proposed online parameter estimation technique.

Abstract: The actuator power required to resist joint torque caused by the weight of robot links can be a significant problem. Gravity compensation is a well-known technique in robot design to achieve equilibrium throughout the range of motion and as a result to reduce the loads on the actuator. Therefore, it is desirable and commonly implemented in many situations. Various design concepts for gravity compensation are available in the literature. This paper proposes an overview of gravity compensation methods applied in robotics. The examined properties of the gravity compensation are disclosed and illustrated via kinematic schemes. In order to classify the considered balancing schemes three principal groups are distinguished due to the nature of the compensation force: counterweight, spring or active force developed by an auxiliary actuator. Then, each group is reviewed through sub-groups organized via structural features of balancing schemes. The author believes that such an arrangement of gravity compensation me...

Abstract: In this paper, we present a convex optimization problem to generate Center of Mass (CoM) and momentum trajectories of a walking robot, such that the motion robustly satisfies the friction cone constraints on uneven terrain. We adopt the Contact Wrench Cone (CWC) criterion to measure a robot's dynamical stability, which generalizes the venerable Zero Moment Point (ZMP) criterion. Unlike the ZMP criterion, which is ideal for walking on flat ground with unbounded tangential friction forces, the CWC criterion incorporates non-coplanar contacts with friction cone constraints. We measure the robustness of the motion using the margin in the Contact Wrench Cone at each time instance, which quantifies the capability of the robot to instantaneously resist external force/torque disturbance, without causing the foot to tip over or slide. For pre-specified footstep location and time, we formulate a convex optimization problem to search for robot linear and angular momenta that satisfy the CWC criterion. We aim to maximize the CWC margin to improve the robustness of the motion, and minimize the centroidal angular momentum (angular momentum about CoM) to make the motion natural. Instead of directly minimizing the non-convex centroidal angular momentum, we resort to minimizing a convex upper bound. We show that our CWC planner can generate motion similar to the result of the ZMP planner on flat ground with sufficient friction. Moreover, on an uneven terrain course with friction cone constraints, our CWC planner can still find feasible motion, while the outcome of the ZMP planner violates the friction limit.

Abstract: This paper proposes a torque limit-based inertial control scheme of a doubly-fed induction generator (DFIG) that supports the frequency control of a power system. If a frequency deviation occurs, the proposed scheme aims to release a large amount of kinetic energy (KE) stored in the rotating masses of a DFIG to raise the frequency nadir (FN). Upon detecting the event, the scheme instantly increases its output to the torque limit and then reduces the output with the rotor speed so that it converges to the stable operating range. To restore the rotor speed while causing a small second frequency dip (SFD), after the rotor speed converges the power reference is reduced by a small amount and maintained until it meets the reference for maximum power point tracking control. The test results demonstrate that the scheme can improve the FN and maximum rate of change of frequency while causing a small SFD in any wind conditions and in a power system that has a high penetration of wind power, and thus the scheme helps maintain the required level of system reliability. The scheme releases the KE from 2.9 times to 3.7 times the Hydro-Quebec requirement depending on the power reference.

Abstract: Permanent-magnet vernier machine (PMVM) is a relatively new type of PM machines. An analytical subdomain model accounting for tooth-tips and flux modulation poles is developed to accurately predict on-load field distributions in PMVMs. Based on two-dimensional (2-D) polar coordinate and magnetic vector potential, this method solves the Maxwell’s equations in slot, air-gap, flux modulation pole slot (FMPS), and PM regions. Consequently, the electromagnetic performance such as cogging torque, back-electromotive force (EMF), electromagnetic torque, power factor, and magnet loss are calculated. In addition, the model can also be used for the evaluation of demagnetization withstand capability. The finite-element analysis (FEA) and experimental results validate the accuracy of the developed analytical model.

Abstract: A unified power controller for variable-speed fixed-pitch wind energy conversion system (WECS) is designed covering the whole range of wind speed in this paper. The proposed controller is composed of a modified maximum power point tracking (MPPT) controller in low wind speed and a new constant speed and constant power controller in high wind speed. For the former, a combination of modified hill climb searching (HCS) and power signal feedback (PSF) MPPT algorithms is used. The modified HCS method is activated to search for the maximum power point (MPP) first, which is followed by the PSF method once one MPP is found. By using this controller, not only the a priori knowledge of the aerodynamic characteristics of turbine blades is avoided, but also low torque/power ripple is achieved; for the latter, a new auxiliary passive stall control method is proposed. It temporarily increases the output power to force the turbine to operate in deep stall regime, thus to decrease the captured power of the turbine. The proposed controller is implemented on a digital signal processor. The validity of the proposed method is verified by experimental results done on a 10-kW WECS.

Abstract: Electric vehicles (EVs) with four individually controlled drivetrains are over-actuated systems, and therefore, the total wheel torque and yaw moment demands can be realized through an infinite number of feasible wheel torque combinations. Hence, an energy-efficient torque distribution among the four drivetrains is crucial for reducing the drivetrain power losses and extending driving range. In this paper, the optimal torque distribution is formulated as the solution of a parametric optimization problem, depending on the vehicle speed. An analytical solution is provided for the case of equal drivetrains, under the experimentally confirmed hypothesis that the drivetrain power losses are strictly monotonically increasing with the torque demand. The easily implementable and computationally fast wheel torque distribution algorithm is validated by simulations and experiments on an EV demonstrator, along driving cycles and cornering maneuvers. The results show considerable energy savings compared to alternative torque distribution strategies.

Abstract: Motor characterization has a fundamental role in dynamics, torque accuracy, and efficiency of vector controlled Synchronous Reluctance Machine (SynRM) drives. Control performances and robustness in the whole speed/torque range, including the flux-weakening region, and in sensorless operation strongly rely on the knowledge of machine flux versus current characteristics. A convenient flux saturation approximating function is proposed in this paper, together with an efficient parameters self-identification procedure. The adopted strategy is very simple and can be performed at stand-still by injecting a proper voltage stimulus (current control is not involved), and does not require any additional hardware (motor can be either connected or disconnected from mechanical load). Nevertheless, an excellent fitting for the flux curves on both axes is obtained, using reasonable memory and computational resources. These features make the technique very suitable to motor self-identification in industrial drives. Experimental results based on a commercial drive and two SynRMs are reported to demonstrate the effectiveness of the proposal. Extensions of the method to the evaluation of the whole flux map (including cross-saturation effects) or to interior permanent-magnet machines is also investigated and verified.

Abstract: Permanent-magnet motors with rare-earth magnets are among the best candidates for high-performance applications such as automotive applications. However, due to their cost and risks relating to the security of supply, alternative solutions such as ferrite magnets have recently become popular. In this paper, the two major design challenges of using ferrite magnets for a high-torque-density and high-speed application, i.e., their low remanent flux density and low coercivity, are addressed. It is shown that a spoke-type design utilizing a distributed winding may overcome the torque density challenge due to a simultaneous flux concentration and a reluctance torque possibility. Furthermore, the demagnetization challenge can be overcome through the careful optimization of the rotor structure, with the inclusion of nonmagnetic voids on the top and bottom of the magnets. To meet the challenges of a high-speed operation, an extensive rotor structural analysis has been undertaken, during which electromagnetics and manufacturing tolerances are taken into account. Electromagnetic studies are validated through the testing of a prototype, which is custom built for static torque and demagnetization evaluation. The disclosed motor design surpasses the state-of-the-art performance and cost, merging the theories into a multidisciplinary product.

Abstract: This paper presents a simple flux regulation for a direct torque control (DTC) of an induction motor (IM) to improve speed and torque estimations at low- and zero-speed regions. To accomplish this, a constant switching frequency controller (CSFC) is used to replace the three-level hysteresis torque comparator of a DTC IM. The DTC of IM utilizing CSFC (DTC-CSFC) retains the simple structure of a lookup table-based DTC drive. With DTC-CSFC, constant switching frequency is maintained, and at the same, the flux droop problem that normally occurs in DTC with the hysteresis controller (DTC-HC) at low speed is solved; subsequently, the stator flux and torque estimations at low speed are also improved. In the proposed system, the speed feedback for the closed-loop speed control is estimated using an extended Kalman filter, which requires heavy real-time computation. However, due to the simple structure of DTC-CSFC, small sampling time, hence large control bandwidth is possible. The performances of the speed sensorless DTC-HC and DTC-CSFC are compared experimentally under different operating conditions. With the improved stator flux regulation, experimental results of the DTC-CSFC showed a significant improvement in speed and torque estimations at very low and zero-frequency operations.

Abstract: A partitioned stator hybrid excited machine is proposed, in which the permanent magnets and field windings are alternately placed on an inner stator separated from the outer stator having armature windings. This machine inherits the features of brushless machines and benefits from better space utilization. The operating principle and the effects of slot/pole combinations are investigated in detail. Further, based on 2-D finite-element analysis, the electromagnetic performances of the proposed machines, including back-electromotive force, cogging torque, flux regulation range, torque capability, power factor and torque–speed curve, are evaluated. The results reveal that the proposed machines can exhibit wide flux regulation range as well as good torque density. The prototype is manufactured and tested to validate the predictions.

Abstract: This paper presents an improved method of deriving the ideal maximum-torque-per-ampere (MTPA) angle for a permanent-magnet synchronous machine (PMSM). The algorithm accounts for core saturation and cross coupling of the direct- and quadrature-axis magnetic flux. In addition, the impact of various temperatures is also investigated. The algorithm is demonstrated to provide a $d{-}q$ current reference angle that is very close to the real MTPA-angle for the whole operating range. It is found that if the current dependency of the equivalent circuit machine parameters such $L_d$ , $L_q$ , and $\Psi_m$ is updated for each optimization iteration step in an MTPA algorithm rather than being accounted for directly in the optimization, the MTPA angle is predicted up to 7° too low for the investigated machine. However, with the proposed MTPA-angle method here, this discrepancy is eliminated. Moreover, the consequence of utilizing the derived improved algorithm here is that the losses at the peak torque operating point is 6% lower than without the full optimization. This leads to an enhanced take-off ability by increasing the torque at the rated current by up to 3.6%.

Abstract: In this paper, an improved rotor flux estimation method for the Torque model reference adaptive schemes (TMRAS) sensorless induction machine drive is proposed to enhance its performance in low and zero speed conditions. The conventional TMRAS scheme uses an open loop flux estimator and a feedforward term, with basic low pass filters replacing the pure integrators. However, the performance of this estimation technique has drawbacks at very low speeds with incorrect flux estimation significantly affecting this inherently sensorless scheme. The performance of the proposed scheme is verified by both simulated and experimental testing for an indirect vector controlled 7.5-kW induction machine. Results show the effectiveness of the proposed estimator in the low- and zero-speed regions with improved robustness against motor parameter variation compared to the conventional method.

Abstract: This paper develops an appropriate predictive current controller (PCC) for fast torque monitoring and high-performance operation of a permanent-magnet synchronous motor (PMSM) drive involving constant switching frequency. The proposed controller is based on a convenient combination of deadbeat and direct predictive control (DPC) techniques. Its response is compared to that of a typical proportional–integral (PI) current controller in field-oriented control (FOC) strategy. The analysis illustrated improved transient characteristics concerning faster speed changes as well as reduced current and torque ripple while it enables additional control criteria inclusion. The simulated results have been validated by measurements on a test bench.

Abstract: Despite the potential advantages of information storage in antiferromagnetically coupled materials, it remains unclear whether one can control the magnetic moment orientation efficiently because of the cancelled magnetic moment. Here, we report spin-orbit torque induced magnetization switching of ferrimagnetic Co1-xTbx films with perpendicular magnetic anisotropy. Current induced switching is demonstrated in all of the studied film compositions, including those near the magnetization compensation point. The spin-orbit torque induced effective field is further quantified in the domain wall motion regime. A divergent behavior that scales with the inverse of magnetic moment is confirmed close to the compensation point, which is consistent with angular momentum conservation. Moreover, we also quantify the Dzyaloshinskii-Moriya interaction energy in the Ta/Co1-xTbx system and we find that the energy density increases as a function of the Tb concentration. The demonstrated spin-orbit torque switching, in combination with the fast magnetic dynamics and minimal net magnetization of ferrimagnetic alloys, promises spintronic devices that are faster and with higher density than traditional ferromagnetic systems.

Abstract: The Science of Making Torque from Wind 2016 (TORQUE 2016) C.L. Bottasso (TUM), E. Bossanyi (DNV GL), T. Chaviaropoulos (NTUA), P.W. Cheng (Universität Stuttgart), R. De Doncker (RWTH-Aachen), K. Dykes (NREL), D.T. Griffith (Sandia), M.H. Hansen (DTU), S. Ivanell (Uppsala University), J. Jonkman (NREL), G. van Kuik (TUDelft), M. Kühn (ForWind-OL), J. Mann (DTU), J. Meyers (KU Leuven), M. Muskulus (NTNU), A. Natarajan (DTU), J. Peinke (IWES Fraunhofer), F. Porté-Agel (EPFL), P. Schaumann (ForWind-LUH), J. Sørensen (DTU), J.-W. van Wingerden (TUDelft) Wind energy technology is one of the great success stories of the last twenty years. Steadily, wind has been progressively increasing its penetration in the energy mix, and it is today leading the growth of renewables. The progress of wind has been accompanied and made possible by a parallel growth in scientific knowledge. In fact, wind energy has a strong multidisciplinary nature, which spans a very wide range of technical disciplines. Although many of these disciplines are also common to other application areas, wind energy has now emerged as a distinct scientific topic, with its own very specific problems and methods. Today a vibrant scientific community has formed around its core areas, and it is helping propel wind energy knowledge forward. Wind is clearly well positioned to be one of the key players in de-carbonization. However, the continued growth of wind will only be possible through advances in science and technology enabled by a strong and dedicated community, together with continuous public funding and a strong collaboration with industry. A key input to the formation of the wind energy scientific community was given in 2004 by the European Academy of Wind Energy (EAWE), when it first organized in Delft the Science of Making Torque from Wind conference (or TORQUE, for short). Since then, TORQUE has grown to become the main scientific conference series in wind energy worldwide. TORQUE 2016 has been organized by the Technical University of Munich (TUM) following in the steps of the previous editions. We hope you will enjoy this conference, with its rich program and countless opportunities for networking and for the exchange of ideas. The proceedings of TORQUE 2016 contain 309 papers. All submissions were subjected to a two-stage peer review process, which included the review of a three-page abstract followed by the review of the full paper. Accepted papers were grouped in ten technical sessions, each organized by two leading experts in the field who also act as co-editors of these proceedings: E. Bossanyi (DNV GL), T. Chaviaropoulos (NTUA), P.W. Cheng (Universitat Stuttgart), R. De Doncker (RWTH-Aachen), K. Dykes (NREL), D.T. Griffith (Sandia), M.H. Hansen (DTU), S. Ivanell (Uppsala University), J. Jonkman (NREL), G. van Kuik (TUDelft), M. Kuhn (ForWind-OL), J. Mann (DTU), J. Meyers (KU Leuven), M. Muskulus (NTNU), A. Natarajan (DTU), J. Peinke (IWES Fraunhofer), F. Porte- Agel (EPFL), P. Schaumann (ForWind-LUH), J. Sørensen (DTU), J.-W. van Wingerden (TUDelft). In addition, over 150 reviewers helped ensure the quality of the papers. These proceedings and the whole conference would not have been possible without the crucial contribution of all these individuals. We are also very grateful to the two teams at IOP (Sarah Toms and Anete Ashton) and TUM (Pietro Bortolotti, Johannes Schreiber and Wendy Lopens) for their hard work and dedication throughout the whole review process. The partial financial support of TORQUE 2016 from the German Research Foundation (DFG) is gratefully acknowledged. We are looking forward to welcoming you to TORQUE 2016! Garching b. Munchen, September 2016.

Abstract: This paper investigates the surface-mounted permanent-magnet (SPM) and the interior permanent-magnet (IPM) motors for high-speed applications. An SPM motor and an IPM motor are designed with the same power/speed rate and the same key dimensions. Finite-element analysis is used to compare the mechanical, electromagnetic, and antidemagnetization performances of the two motors, and lumped parameter thermal networks are involved to compare their thermal performances. It can be concluded from the comparisons that the IPM motor has comparable electromagnetic performances with the SPM motor in high-speed operations, and its costs and torque per PM weight are superior to those of the SPM motor. However, its rotor structure is not as robust and is prone to irreversible demagnetization.