Modelling and Simulation of a Fault-tolerant Electrical Motor for Aerospace Servovalves with Modelica

The paper deals with the design and the simulation of electro-magnetic actuators via object-oriented modelling. The study is carried out in the Modelica-Dymola environment, and focuses on the quadruple-coil direct-drive motor of a modern fly-by-wire servovalve. Starting from basic information about material properties and from a schematic representation of the system geometry, the motor model is created mainly using the components of the Modelica_Magnetic library. The motor performances are then characterised with reference to both the normal operating condition (four active coils) and the worst-case fault-tolerant condition (only two active coils), in terms of current-to-force and current-to-displacement curves. The Modelica model is finally validated by comparing the simulation results with experimental data obtained during previous research activities. The Modelica results are also compared with those provided by a Matlab-Simulink model of the motor, pointing out the advantages of the object-oriented approach for the study of complex electro-magnetic systems. The easy modelling of magnetic circuit networks and the inherent simulation of magnetic material properties allow to achieve accurate results very efficiently, taking into account physical phenomena that are often disregarded during preliminary design phases, such as magnetic saturation or magnetic flux dispersions.