Fault-tolerant electrical machine design within a rotorcraft actuation drive system optimisation

This paper presents an approach to weight-optimise an electromechanical actuator (EMA) for helicopter primary flight control systems. Special focus is put on the fault-tolerant electrical machine as a major component in the system. The novelty consists of the detailed machine optimisation in conjunction with the main actuator components: gearbox, screw, converter and filters. An exemplary EMA concept for a primary flight control system for medium weight helicopters is presented and the implications on the fault-tolerance requirements of actuator and electrical machine are elaborated. A deterministic optimisation strategy is presented alongside with models for the main actuator components. A dynamic Reluctance Network (RelNW) and a Thermal Network (ThermNW) are combined to represent the behaviour of the electrical machine. The paper will show the importance of low inertia design and machine operation in magnetic saturation due to high peak-to-rated torque ratio and acceleration requirements.