Delay Compensation in the PMSM Control by using a Smith Predictor

This article presents a structure for speed control in a PMSM drive by compensating the effect of the delay fed into the control loop by the speed sensor (Tachogenerator) by using a Smith Predictor. The inner loop for current and torque control follows the general lines of the FOC (Field Oriented Control) strategy in terms of describing the motor operation equations in d-q model on rotor reference frame (after using the Clark and Park transformations), and obtaining a maximum torque by setting the reference current to zero on d-axis. The control system is a cascade system where the speed control system is the outer loop, and the fixed part is the inner loop for current control together with the PMSM. For the modeling of the fixed part, 2nd and 3rd order continuous and discrete transfer functions are presented, to which the delay block is added. Good results were obtained after the simulations where the transfer function is of the 3rd order, by compensating the delay effect. Considering that the usual delay fed by the speed sensor is lower than the maximum delay compensated by the proposed structure, and the control used is of common PI type with anti-windup, the results of simulations recommend the implementation into a real time embedded system.