This paper analyzes and compares the performances of permanent-magnet-assisted synchronous reluctance machines (PMa-SynRMs) and interior permanent magnet synchronous machine (IPMSM) on their constant power speed range (CPSR) capability for electric vehicle (EV) applications. The recent trend of less rare-earth magnet makes the IPMSM unfavorable despite its excellent CPSR. As an alternative, the PMa-SynRM possesses a higher saliency with lower PM quantity. The two different rotor designs would affect the CPSR and these need to be investigated and compared. As a key performance index for EV traction motors, the CPSR calculated by analytical methods often suffers low accuracy due to omission of saturation. Finite-element analysis (FEA) can be used to obtain the CPSR but significant computation time is required. This would be disadvantageous for accurate performance prediction in design stage. To resolve these problems, six 10 kW, 30 Nm/L designs are studied and compared, covering IPMSMs and PMa-SynRMs. An approach associating analytical methods with FEA is developed for accurate and rapid calculation of CPSR for these machines. A discussion on PMa-SynRM rotor designs and suggestion for their PM quantity are provided considering performance, cost, and demagnetization. Two prototypes were tested, one being IPMSM and the other PMa-SynRM to validate the analysis.

This paper evaluates the electromagnetic and thermal performance of several traction motors for electric vehicles (EVs). Two different driving cycles are employed for the evaluation of the motors, one for urban and the other for highway driving. The electromagnetic performance to be assessed includes maximum motor torque output for vehicle acceleration and the flux weakening capability for wide operating range under current and voltage limits. Thermal analysis is performed to evaluate the health status of the magnets and windings for the prescribed driving cycles. Two types of traction motors are investigated: two interior permanent magnet motors and one permanent magnet-assisted synchronous reluctance motor. The analysis results demonstrate the benefits and disadvantages of these motors for EV traction and provide suggestions for traction motor design. Finally, experiments are conducted to validate the analysis.

The paper aims to provide a guideline for rotor design of permanent magnet (PM) assisted synchronous reluctance machine (PMa-SynRM). Unlike interior PM machines, the PMa-SynRM is essentially an SynRM with dominant reluctance torque. The PMa-SynRM is often designed by directly embedding magnets into an SynRM rotor to improve the performance. However, how the PMs can be arranged in the rotor to enhance motor performance has not been fully discussed. This paper investigates the influence of several key factors concerning the PM arrangements, including number of PM layers, inserted positions, and PM sizes. The torque, flux linkages, power factor, and motor performance are comprehensively evaluated. Based on the analysis, a brief guideline is suggested for PMa-SynRM rotor design. Finite element analysis is used for evaluation and experiments are conducted to validate the analysis.

This paper proposes a flux-intensifying permanent magnet-assisted synchronous reluctance motor (FI-PMa-SynRM) using surface-inset permanent magnet (PM) instead of embedded PM in the rotor. The proposed FI-PMa-SynRM employs a small amount of PM that is inset on the rotor surface facing d-axis instead of facing q-axis as in common PMa-SynRMs. It also differs from conventional flux-intensifying interior PM motor, where the PM is embedded inside the rotor. The proposed motor enables making use of the arrangements of two types of flux barriers (FBs): the cutoff FB and the magnet FB, collectively referred to the outer FBs, to enhance the torque output and reduce the torque ripple. The first objective in this paper is to explain the principles of the proposed FI-PMa-SynRM, and the second is to analyze the proposed technique for enhancement of the torque output with small PM volume while keeping the lowest possible torque ripple. The finite-element analysis is employed to validate the proposed motor and analyses, and the results demonstrate their advantages and effectiveness.

This paper utilizes conductors with insulation of high thermal conductivity combining suitable cooling methods to enhance the performance of traction motors for electric vehicles. The performance of a 10-kW interior permanent magnet (IPM) motor without forced cooling is considered as a benchmark. Then, the conductors with two conventional insulation materials and two with high thermal conductivity are applied to the IPM motor windings. Two cooling methods: finned housing (no forced cooling) and water cooling are considered here. It is found that using conductors with high thermal conductivity insulation without forced cooling can only cool the windings by several degrees; however, the temperature can be considerably reduced by combining water cooling with an appropriate flow rate. The torque and power output of the IPM motor can also be significantly improved. This indicates that forced cooling can further enhance the effectiveness of conductors with insulation of high thermal conductivity. Two induction motors using conductors with two different insulations materials (0.1 W/mK and 3 W/mK) are tested. The experimental results validate the analysis.

This paper investigates the demagnetization problem of permanent magnets for permanent magnet-assisted synchronous reluctance motors (PMa-SynRM) and applies ``demagnetization ratio'' as an index to evaluate demagnetization of permanent magnet (PM). The PMa-SynRM is often designed with multilayer flux barriers to improve saliency and reluctance torque in the rotor. Weaker or less PM (than that for interior PM motors) is embedded into the rotor which could be demagnetized in high-performance operation. PM demagnetization involves temperature, current magnitude, current phase angle, designed PM operating point, or combined effect of the above factors. This work investigates the demagnetization risk for PMs in all the layers of PMa-SynRM rotor considering these factors. In particular, the current phase angle for flux weakening operation is often omitted in demagnetization analysis. First, the motor performance to satisfy the operation condition over a wide speed range is analyzed and the proportion of motor torque components, i.e., reluctance torque and electromagnetic torque, considering temperature is investigated. Then, the flux density distributions on PMs at each position/layer are studied and the PM operating points are obtained based on the variation of excitation current, current phase angle, and temperature in order to evaluate the demagnetization risk. The analysis suggests that the high current phase angle combining the effect of high temperature is the major cause of irreversible demagnetization. Finally, a method incorporating the index ``demagnetization ratio'' is proposed to redesign the PMa-SynRM to avoid demagnetization. Experiments are conducted to validate the simulation.