A new sensorless thrust control of linear induction motor

This paper presents the field-oriented thrust control of a linear induction motor without flux or speed sensor. The induction motor is structurally symmetrical but it has the difference of the reluctances between the flux axis and the quadrature axis due to the main flux saturation. This electrical saliency can be utilized to estimate an instantaneous flux angle by high frequency signal injection. In the case of a rotary induction motor, it has been verified that this high frequency signal injection method gives reasonable torque controllability at zero or low stator frequency even under a heavily loaded condition. In this paper, it is shown that the electrical saliency also exists in the linear induction motor and the comparison with the rotary induction motor is described. From this result, the sensorless field-oriented thrust control of a linear induction motor in low operating frequency region is presented and the sensorless control in the overall frequency range is implemented by the combination with an adaptive observer.