Analysis of carrier signal injection based sensorless control of PMSM drives under limited inverter switching frequency condition

This paper presents the carrier signal injection based sensorless control of permanent magnet synchronous machine (PMSM) drives with limited inverter switching frequency. Accounting for the influence of stator resistances, the amplitude of carrier current utilised for position tracking can be maximized under an optimized injection frequency, with which signal to noise (S/N) ratio of carrier signal can be significantly boosted and consequently the steady-state performance during sensorless operation can be guaranteed. Further, it is deduced that this optimized injection frequency is mainly related to the ratio of stator resistance to incremental inductance. In addition, the carrier current responses with reduced switching frequency are also examined experimentally. These analyses can provide guidelines to select appropriate carrier injection signal under limited inverter switching frequency conditions. All the theoretical analyses are validated by experiments on a laboratory interior PM (IPM) machine.