Modelling and control of a permanent magnet linear synchronous motor featuring unbalance and saturation including cross-saturation

Abstract

Due to their structure linear motors feature more or less unbalance. In case of highly magnetic utilisation the electrical parameters depend on the degree of saturation and consequently depend on the currents in the machine. For highly dynamic control accurate modelling of the motor is inevitable. The control of a motor with variable parameters can either be robust based on a simple model but with inferior dynamics or highly dynamic and accurate based on a detailed model. Despite the motor's unbalance it is modeled in a two axes domain, but with parameters that depend significantly on the motor currents and the mover's position. This allows the acquisition of the motor parameters by measurement for a variety of currents and positions even with an unavailable neutral point. On the other hand the motor parameters can be deduced from a finite element calculation. Both methods will be discussed in the paper. Mechanical quantities such as thrust or torque are normally controlled by controlling the electrical quantities, either stator currents or stator flux. While the stator currents are easily measurable the flux is not directly acquired. Here both the current or the flux is controlled by a deadbeat controller and the choice of the sampling time is discussed with respect to the variable machine model and its digital system representation.