Electric Vehicles make use of permanent magnet synchronous traction motors for their high torque density and efficiency. A comparison between interior permanent magnet (IPM) and surface mounted permanent magnet (SPM) motors is carried out, in terms of performance at given inverter ratings. The results of the analysis, based on a simplified analytical model and confirmed by FE analysis, show that the two motors have similar rated power but that the SPM motor has barely no overload capability, independently of the available inverter current. Moreover the loss behavior of the two motors is rather different in the various operating ranges with the SPM one better at low speed due to short end connections but penalized at high speed by the need of a significant de-excitation current. The analysis is validated through finite-element simulation of two actual motor designs.Index Terms-Electric Vehicle, PM Synchronous motors, PM motor drives, Constant-power speed range, Iron loss, High speed AC drives. . Manuscript

Three different motor drives for electric traction are compared, in terms of output power and efficiency at same stack dimensions and inverter size. Induction motor, surface mounted permanent magnet (SPM) and interior permanent magnet (IPM) synchronous motor drives are investigated, with reference to a common vehicle specification. The induction motor is penalized by the cage loss but it is less expensive and inherently safe in case of inverter unwilled turn-off due to natural de-excitation. The SPM motor has a simple construction and shorter end-connections, but it is penalized by eddy current loss at high speed, has a very limited transient overload power and has a high uncontrolled generator voltage. The IPM motor shows the better performance compromise, but it might be the more complicated to be manufactured. Analytical relationships are first introduced and then validated on three example designs, Finite-Element calculated, accounting for core saturation, harmonic losses, the effects of skewing and operating temperature. The merits and limitations of the three solutions are quantified comprehensively and summarized by calculation of the energy consumption over the standard NEDC driving cycle.

The Magnetic Model Self-Identification of PM Synchronous machines is proposed and experimentally validated. Provided that the shaft is free to turn, the commissioning procedure consists of spinning the machine to positive and negative speed values by way of an appropriate pattern of dq current reference values. The flux linkage versus current curves of the machine are constructed during the test via the standard measurements available on any industrial drive: phase currents, dc-link voltage and shaft position. Respect to the literature, the proposed method does not require a specific test rig nor off-line mathematical manipulation.

The design of ferrite-assisted synchronous reluctance machines is investigated, with particular attention to the pivotal aspect of avoiding irreversible demagnetization. Geometric rules for obtaining a robust design are proposed and described analytically. The safe operating area is quantified in terms of the corresponding maximum electrical loading. Such demagnetization limit is dependent on the operating temperature and the machine size. Furthermore, the comparison between the continuous load and demagnetization conditions shows that small-and mediumsized machines can be stiffer against demagnetization, with respect to larger machines, and have room for transient overload. The analysis is validated by finite elements, and a design example is given, namely, a 12-pole direct-drive machine, rated 910 N · m at 200 r/min.

The paper presents a technique to modify the rotor lamination of a PM-assisted Synchronous Reluctance motor, in order to reduce the magnet volume with no side effect on performance. A closed-form analysis, based on a lumped parameter model points out that the magnets quantity can be minimized with a significant saving of material volume and cost. At a second stage, the risk of de-magnetization is evaluated, since the minimized magnets are thinner than the starting ones and work on lower load lines in their respective B-H planes. A feasible drawing is analytically defined, robust against demagnetization at overload, showing that the saving of magnet quantity depends on the maximum current overload and can be significant. The theoretical formulation is validated with finite-element analysis and experiments on a prototype machine.