Unposition sensor for permanent magnet linear motor

The invention discloses an unposition sensor for a permanent magnet linear motor. Before a motor starts, a designated trigger signal is inputted into an inverter, a corresponding line inductance value is solved, the calculation is realized by combining the existing inductive parameters of the motor for preliminarily obtaining an initial position of a linear servo motor and then high-frequency voltage is immediately introduced to judge the direction of a magnetic pole of the rotor; after the motor starts, the position of the rotor is detected at the low-speed phase in real time by a method of combining the injection of the high-frequency voltage with the repetition of a controller; position information of the rotor is acquired at the middle-high speed phases in real time by a method of combining a sliding-mode observer based on an extended counter electromotive force model with a saturation function algorithm. According to the unposition sensor disclosed by the invention, an initial position detection method, a rotating high-frequency injection method, repeated control and the sliding-mode observer are combined together, so that the position information of the linear servo motor can be accurately and effectively detected, the defects caused by the existence of a mechanical sensor are overcome and the reliability of the system is improved.