Modelling a linear PM motor including magnetic saturation

The use of linear permanent-magnet (PM) actuators increases in a wide variety of applications because of the high force density, robustness and accuracy. The paper describes the modelling of a linear PM motor applied in, for example, wafer steppers, including magnetic saturation. This is important because to reach high performance, the feedforward control must predict the force generated by the motor, also when the motor is saturated. The motor is modelled as a reluctance network. The saturating parts of the magnetic circuit are modelled as variable reluctances and magnetomotive forces represent the currents and the magnets. In saturation, a current leading the no-load voltage results in an increase of the generated force. The good correlation between the calculated and the measured force justifies the model.