Eri Maruyama

Evaluation of increasing rates in eddy-current loss of the motor due to carrier frequency

This paper describes that a theoretical formula for evaluating loss ratio in eddy current of a permanent magnet (PM) motor fed by a PWM inverter is proposed. A formula for evaluating the increasing rates of eddy-current loss in iron core due to carrier frequency corresponding to inverter output parameters (i.e., DC-bus-voltage, modulation index and modulation methods) are derived. Calculated and measured increasing rates of eddy-current loss in iron core were compared. According to the results of this comparison, the difference between the calculated and measured results is within 10 % when the modulation index is less than 0.7. The increasing tendencies of the calculated and measured increasing rates of eddy current loss agree well. The proposed theoretical formula can be applied for improving the efficiency of motor-inverter drive systems.

Circulating current in parallel connected stator windings due to rotor eccentricity in permanent magnet motors

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.

Explicit criteria for reluctance torque utility of permanent magnet motors

This paper presents an explicit criteria for reluctance torque utility of permanent magnet (PM) motors. The criteria can be quantified by PM flux linkage Ψ_p of stator phase windings, and current I, as well as direct- and quadrature-axis inductance L_d and L_q. Through both theoretical formula and experiments, it is proved that the motor with large Ψ_p can utilize little reluctance torque even if the salient-pole ratio L_q/L_d is over 2.0. In such a case, the large salient-pole ratio only leads to an increase in iron loss and hence a decrease in motor efficiency. The invented criteria helps one to understand the property inherent in each motor, and also indicates that in the above case selecting the rotor geometry with less saliency can improve the efficiency. Results are given for two types of 4-pole prototype motors with P_N = 0.6 kW, n_N = 3600 min^-1, Y-connection.