A multi-physics design methodology applied to a high-force-density short-duty linear actuator

This paper presents an iterative coupled electromagnetic and thermal design methodology applied to a short-duty high-force-density permanent magnet tubular linear actuator. A difficulty with such coupled methodologies is balancing the accuracy of the modelling methods with the computation time. This problem is often addressed by employing a relatively detailed electromagnetic model and a coarse low computational cost thermal model. The thermal model typically requires calibration or is evolved from previous validated designs. In this paper, a two-dimensional electromagnetic finite element model is coupled with a thermal equivalent circuit model which is automatically constructed and parameterised using geometric and material data. A numerical method of estimating the equivalent thermal properties of the winding amalgam is used along with published empirically derived convection and radiation heat transfer correlations. The relatively high number of network nodes and more accurate thermal material properties minimise the need for thermal model calibration and allows for improved temperature prediction, including winding hot-spots, whilst maintaining a low computational cost for steady-state and transient analyses. Thereby allowing the actuator to be designed to operate with a peak temperature close to the thermal limit of the electrical insulation system which is difficult to achieve with more traditional lumped parameter models containing few nodes. The effectiveness of the design methodology is demonstrated by the design and experimental test of a prototype actuator.