Losses in Sensorless Controlled Permanent-Magnet Synchronous Machines

The aim of the research is to investigate how much the losses in a permanent-magnet synchronous machine (PMSM) increase by the test pulses that are injected for sensorless control, i.e., to obtain rotor position information without using a position sensor. The current responses to the voltage test pulses in the machine are used as input of a 2-D transient finite element model (FEM) of the PMSM, to compute the field distribution. The magnet losses are calculated by a 3-D FEM of one magnet and a part of the rotor yoke only. To find the iron losses in the SiFe part of the magnetic circuit, quasi-static and dynamic BH-loops were measured at various amplitudes by using an excitation winding and a measurement winding around the stator yoke of the PMSM. For field waveforms recorded in the 2-D FEM, the corresponding induction is calculated by a static Preisach model. The dynamic field is added based on the theory of loss separation. The test pulses cause minor hysteresis loops. Measurements and simulations show that losses due to the test pulses are usually small and have the same order of magnitude in the permanent magnets and the yoke.