Efficiency of buried permanent magnet type 5kW and 50kW high-speed bearingless motors with 4-pole motor windings and 2-pole suspension windings

This work focuses on loss prediction for varying operation conditions of the high-speed buried-type interior permanent magnet (IPM) bearingless motors. The investigated motors are 5 kW and 50 kW units configured as twin motor sets, which provide radial suspension and motoring in 5 degrees of freedom levitated rotor systems with the maximum speed of 30000 r/min. The maximum output power of studied rotor systems is 10 kW and 100kW, respectively. Additionally, the power factors of motor and suspension windings as well as inductance maps for various operating conditions are studied. The magnetic field 2-dimentional transient section analysis and time stepping are applied. The selected results are compared with the measured values. In the loss calculation various rotor and stator iron losses, resistive losses, windage losses and additional losses are taken into account. Efficiency maps and power factor estimation are valuable for application of electrical machines. These studies have been performed using various methods for classical motors and generators but are uncommon for bearingless motors working with different loading conditions. The comprehensive efficiency map prediction of the high-speed IPM bearingless motors for different suspension loading is presented for the first time. The variations of motor inductances for different rotor angles and current amplitudes are derived. The differences in results between the machines with the same geometry but different power are discussed.