Position sensor elimination techniques for synchronous reluctance motor

Abstract

Synchronous reluctance motor drives have recently received renewed attention. This interest is mainly due to modern field oriented control strategies, which have recently been applied to these motors. In particular it has been shown that a properly designed and field oriented synchronous reluctance motor drive can perform as well as an induction motor drive when the field weakening range is not too wide. However, field orientation control of synchronous reluctance motor requires position sensor information as is common for all ac machines. But a discrete position sensor reduces the reliability and ruggedness of the drive and also increases its cost. A new discrete position sensor elimination technique for sinusoidally wound synchronous reluctance motor drive is developed in order to utilize the inherent favorable characteristics of a synchronous reluctance motor. The proposed technique determines the rotor position at zero crossings of the phase currents. The rotor position between two zero crossings is determined by applying extrapolation. Rotor position sensing at standstill is very difficult for commonly used ac drives (induction, brushiess etc.). Thus these motors operate in open loop until the motor induced voltage is large enough to be sensed. Moreover, the sensed voltage is often noisy and very difficult to sense. The synchronous reluctance motor however possess unique features which make position sensing much simpler and reliable even at standstill. An indirect rotor position sensing technique for startup operation is also developed. A sensorless synchronous reluctance motor drive has been built using the proposed indirect rotor position sensing schemes for position estimation in order to demonstrate the feasibility of the schemes. The experimental results showed that the proposed schemes kept excellent track of the rotor position over a wide range of speed operation.