Sensorless vector control of linear permanent magnet synchronous motor

A practical vector control algorithm for speed control of linear permanent magnet motor without a position sensor is presented. The vector control algorithm is based on decoupled control of d and q-axes currents. The errors in the d and q-axes currents are used as inputs to the two PI controllers to generate the orthogonal d and q-axes components of the reference voltage in rotor flux vector frame of reference. Decoupling of both the d-axis and q-axis currents control loops is achieved by adding the decoupling terms to the command voltages in the rotor flux vector reference frame generated by the PI controllers. These decoupled voltages are further transformed to the stationary frame of reference by using the electrical position of the mover, in order to generate the reference voltage vector by using space vector modulation. A fixed switching frequency is achieved because of space vector modulation which results in a smooth response of both the d and q-axes current control loops. Sensorless estimation of the mover's position is determined from the orthogonal components of the stator flux vector in stationary reference frame and the load angle. The load angle is calculated from the electromagnetic thrust force using a linearized relation between the load angle and the thrust force. The presented control scheme is experimentally validated by its practical application to a prototype linear permanent magnet synchronous motor drive system in the laboratory. Practical results prove the excellent response of both the d-axis and q-axis current control loops. These practical results also imply the effectiveness of proposed sensorless speed estimation algorithm under both the loaded and unloaded operating conditions for the prototype linear permanent magnet synchronous motor.