Development of control system for electro-mechanical actuator

The issue of environmental sustainability is becoming of primary importance also in aviation field. In this perspective, development of more electric aircraft concept could represent a valid solution, even if new technologies must be developed in future. The work presented in the context of this master’s thesis concerns the development of the control software for an electro-mechanical actuator and its subsequently validation on a test bench. The purpose of this actuator is to replace hydraulic piston actually mounted on braking system of general aviation aircraft. The actuation group is constituted by a linear mechanical actuator driven by Faulhaber’s brushless DC (BLDC) electric motor. The microprocessor unit is C2000 Delfino, while the driver is DRV8305, both from Texas Instruments. The software has been developed using Matlab/Simulink software environment, thanks to an external compiler compatible with C2000 processor. Here, all mathematical computation is done with integer arithmetic, allowing to reduce microprocessor’s workload. This software must be capable of both low-level management of BLDC motor (controlling each driver’s MOSFETs) and high-level management. Because there are no brushes in a BLDC motor, commutation must be reproduced electronically. In order to correctly select which phase must be turned on, the shaft position is sensed thanks to three different Hall digital sensors. An internal function generator allows to generate the reference force signal that feed the controller. Controller includes both an open loop and a closed loop branch. The open loop term allows to both bypass the need for external sensors in case of failure and to guarantee a non-zero phase current when the reference signal has been met, while the closed loop gives a contribution proportional ??to the error between the reference and the actual force signal. The force feedback is provided by an external load cell. Analog-to-Digital Converters are used to measure different physical values, such as force and phase currents. The program has been validated on a test bench specifically designed to make up for temporary lack of real mechanical actuator (still under construction). To safely perform the tests, different safety measures have been implemented. These measures also apply to the real brake architecture and include a limitation on the maximum reference force, a virtual end of stroke and a limitation on the maximum real load. This last limit is performed without the use of external load cell but directly sensing the shaft position. All tests variable, such as function generator settings or controller parameters, can be set by user via serial communication. In the same way, it is possible to log some data useful to characterize the behaviour of the electro-mechanical actuator, allowing further analysis. Results obtained at the end of this work are satisfactory and allow complete control of a single actuation group. Even if this code can be easily duplicated in order to control four different groups (the final configuration of the braking system), it can be suggested to directly write that code using a lower-level language, improving software efficiency.