Modelling and Disturbance Compensation of a Permanent Magnet Linear Motor with a Discontinuous Track

Abstract

It is very common that industrial applications require linear motion in some part of the process, especially in transportation of products from place to place. Traditional technologies to produce short-distance linear motion are screws, linear belts, and gear motors. In all these cases, the movement of the rotating motor is converted into linear movement with mechanical devices and couplings. Mechanical conversion from rotational into linear motion often includes/requires gears, and there can be backlash and limitations in the speed or position accuracy. Linear motors produce linear motion directly, and they are a viable alternative if high performance in speed and positioning is required and/or the travelling distance is more than a couple of metres.

However, as a direct drive, the linear motor is sensitive to disturbance forces. All disturbance forces have a direct impact on the motion of the motor without damping from the mechanics. Therefore, a key topic in this doctoral dissertation is disturbance compensation, especially in the case of a discontinuous magnet track of the permanent magnet linear motor (PMLM). The disturbances are at highest at the edges of the discontinuous track, and they are difficult to compensate with design of the motor.

An effective way to model PMLMs is essential in the design of the linear motor. In this doctoral dissertation, a method for modelling a PMLM by applying a magnetic circuit model is presented. With the presented method, it is possible to model non-linear phenomena, such as saturation, as well as dynamic operation and effects of motor design, such as end effects, with different kinds of end teeth of the motor.

The initial costs of the PMLM can be reduced with a discontinuous magnet track. This is beneficial especially with applications with long travelling distances. In that case, a significant property of the PMLM is sensorless position control. A method for the position-sensorless control of a non-salient PMLM for the full operation speed range is presented and verified in this doctoral dissertation.