Comparison of high frequency signal injection techniques for rotor position estimation at low speed to standstill of PMSM

Rotor position information is necessary to control PMSM (Permanent Magnet Synchronous Motors). Extracting rotor position information using physical position sensor presents several disadvantages, including increased size, reduced reliability, and additional cost of the whole system. To overcome these drawbacks, there has been considerable interest in sensor less control techniques. Sensor less control of PMSMs can be broadly classified as, fundamental model based methods and machine saliency based methods. Techniques that rely on the fundamental model have the advantages of simplicity and straightforwardness. However these techniques fail to extract rotor position information from low speed to standstill. In the last two decades, a number of high frequency signal injection techniques have been proposed and developed for PMSM rotor position estimation at standstill and low speed without position sensor. These techniques can be classified into continuous signal injection techniques, transient signal injection techniques and high frequency signal embed on to PWM. This paper gives an overview of various approaches to rotor position estimation from low speed to standstill using HFSI techniques. Finally comparison between different rotor position extraction schemes is presented based on hardware complexity, torque ripple, speed range and cost of current measurement system.