Comparison of square-wave and sinusoidal signal injection in sensorless polarity detection for PMSMs

This paper compares the non-modulated square-wave voltage injection-based and sinusoidal voltage injection-based polarity detection methods applicable in sensorless PMSM drives. A quadratic PMSM model extension is presented that serves as a basis for the polarity detection techniques. The comparison includes the polarity-dependent current components produced by the injected signals, the design parameters related to the injected signal features and their effect on the probability of correct polarity detection. The performance differences and possible application areas are also discussed.

I. Introduction

The permanent magnet synchronous motors (PMSMs) are used in many different applications ranging from industrial automation to domestic appliances and electric vehicles [1]–[3]. The vector control algorithms of the PMSM drives require rotor position feedback which is obtained by a shaft-mounted optical encoder or a resolver in a conventional drive. The shaft sensor may reduce the overall ruggedness of the drive and increases its cost and size [4]–[6]. To eliminate the electromechanical position sensors, sensorless methods have been introduced, that determine the electrical rotor position usually based on current measurement and an extended machine model. Sensorless methods that are based on the fundamental excitation model are reliable above about 3 % of the nominal speed [6]–[10]. However, to start the PMSM drive without any undesirable vibrations and reverse rotation, the initial rotor position and the polarity of the rotor magnets also have to be detected [11].