Pseudo Direct Drives for Safety Critical Applications

Electro-mechanical actuators are currently being developed to replace hydraulic actuation
solutions previously used on existing and new aircraft platforms. The replacement of
hydraulic actuators constitutes an important step towards realising the More/All Electric
Aircraft concept, where all the different power sources used for non-propulsive systems,
are substituted with an electrical power source and distribution network. This new system
architecture is aimed at optimising aircraft performance by reducing weight, decreasing
operational and maintenance costs, improving reliability and efficiency, while reducing
emissions. Conventionally, all the non-propulsive aircraft systems are driven by different
secondary power sources such as pneumatic, hydraulic, and electrical. Advancements in
the field of electrical machines and power electronics are enabling the feasibility of the
More/All Electric Aircraft concept.
The proposed electro-mechanical magnetically geared actuator aims to eliminate the
mechanical gear stages from the actuator drive train by directly connecting a fault tolerant
Pseudo Direct Drive motor to the mechanical drive train. The key advantages in adopting
a magnetically geared motor are reductions of drive train complexity, resulting in reduced
mass and improved reliability, while introducing a compliant transmission acting as a
passive anti-jamming overload protection, which isolates the high kinetic energy
components, i.e. high-speed rotor, from the mechanical drivetrain.
This thesis presents all the stages of the electromagnetic design and manufacture of the
fault-tolerant Pseudo Direct Drive motor for primary flight control actuation. The design
of the magnetically geared electrical machine is centred around achieving a lightweight
fault tolerant machine with a high torque density and reduced output rotor inertia. It is
shown that several PDD topologies exist for which a duplex 3-phase fault tolerantII
configuration can be implemented. It is also shown that adopting a fault-tolerant PDD
results in a considerably lower mass and rotor inertia referred to the mechanical drivetrain
of the actuator, while achieving and exceeding the dynamic requirements of the actuator.
The findings are validated on magnetic gear and fault tolerant PDD demonstrators, which
have been designed and built to meet the requirements of a rudder primary control surface.