A modified theory and a proposed analytical approach clarified asynchronous torque characteristics of linestarting permanent-magnet (PM) motors, taking into consideration the mutual effect among the fields due to armature current, cage-bar current, and PMs. Theoretical and analyzed results revealed that cage torque had an oscillating component with slip frequency due to magnetic saturation. This component cannot be seen in the conventional theory. It was also found that the coupling effect between PM flux and cage-bar flux caused on magnet torque larger oscillation and more significant negative dc component, compared with the case in the conventional theory. The theoretical and analyzed results were validated on the basis of experimental approaches. Results are given for a two-pole prototype motor with P N = 5 kW, n N = 3000 min −1 , V N = 200 V, and Y-connection.

This paper presents two types of prototype motors for line-starting permanent magnet motors; one is a non-salient-pole machine, and the other is a salient-pole machine. Through both the analyses and the experiments, it is proved that the reluctance torque utility boosts up not only the steady-state characteristics but also the line-starting capability. It is also noteworthy that in the steady-state operation the salient-pole machine can realize not only the better efficiency but also the higher power factor. Results are given for a two-pole prototype motor with P N = 5 kW, n N = 3000 min -1 , V N = 200 V, Y-connection.

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Rotor eccentricity in permanent magnet (PM) motors produces a voltage imbalance between parallel circuits that then creates a circulating current. This circulating current causes conduction loss, which is one of the stray losses in motors. The conduction losses of circulating currents need to be reduced in order to make PM more highly efficient. This paper describes the effect of neutral point connections on circulating current caused by static rotor eccentricity in a PM motor, as the circulating current depends on the use of neutral point connections in stator windings. We developed a theoretical expression for a circulating current with a closed circuit and compared its validity with that of measured results. The results of how well the connections of neutral points reduced the circulating current loss are provided.