Evaluation of Motor Losses and Efficiency in a d-q Axis Current Control Bearingless Motor

This paper presents the motor characteristic, for example, motor efficiency and losses, of a d-q axis current control bearingless motor, which has been proposed by the authors. In the d-q axis current control bearingless motor, both the motor drive and magnetic suspension can be successfully performed by one kind of stator winding. The torque and magnetic suspension characteristics have been found and the superiority of them is recognized. In this paper, the motor characteristic is derived by Finite Element (FE) analysis using a simulation software, and furthermore compared with those of the computed results of the conventional bearingless motors, which two kinds of windings for motor drive and magnetic suspension are wound in a stator core. Three types of the conventional bearingless motor with n-pole motor winding and (n +- 2)-pole suspension winding are taken up in this paper. The stator and rotor iron losses, eddy current loss in the rotor permanent magnets are simulated, respectively. The motor efficiency is also estimated based on the computed output power and motor losses by FE analysis. The efficiency and loss in each part are compared with those of the conventional bearingless motors, respectively, and it is discussed in detail by what the difference of losses between the bearingless motor types is mainly caused.