Comparative research on low speed sensorless control of permanent magnet synchronous motors

This paper carries on the comparative research on the problem of bad performance of convergence and low accuracy of sensor-less control in standstill and low speed region. Although, sensor-less control with high frequency signal injection (HFSI) can be independent of parameters of motors and achieve high performance speed control with vector control scheme, it depends on some complicated digital filters to achieve signal identification and also the high frequency signals injected in motors can arouse boring vibration and acoustic noise. In contrast, an open-loop sensorless control scheme has been proposed in this paper with the advantages of simple structure, without complicated filters, independent of parameters and salient effect and can also achieve self-regulation according to the load conditions. Whereas, the disadvantages of open-loop control are the load capacity of anti-disturbance and speed vibrancies with load variations. For this reason, the selection of control scheme in low speed region needs to be based on the consideration of performance requirement and cost of control system.