Design and implementation of a fault tolerant vehicle controller - an active steering approach
KTH has developed a novel Research Concept Vehicle (RCV) based on the concept of "autonomous corner modules". An autonomous corner module is basically a wheel with a built-in electric hub motor, and additional actuators to tilt and yaw the wheel. One module is attached at each of the four corners of a 'skateboard' chassis. The addition of a computer to command each corner module, and a battery, results in a vehicle with a completely electric drive train. This topology can provide major advantages with respect to the dynamic behavior of the RCV. On the contrary, major safety issues arise from the individual controllability of the corner modules. This thesis is mainly focused on the design of a fault tolerant controller and its implementation on the RCV. The faults that are being considered include on board system failures i.e. hub-motor or steering actuator failure, all of which can induce unintended yaw rate in the vehicle's response. The proposed controller includes the use of a torque allocation approach combined with an active steering approach which constantly compensate for any divergence in the vehicle's yaw rate response from the reference. This controller utilizes the advantages of both yaw rate control mechanisms enabling the engineers to achieve better vehicle response. Finally, the aforementioned controller showed encouraging results in simulation but due to a mechanical failure in one of the four hub-motors, experimental tests were only conducted using the active steering controller which successfully suppressed the failure's negative effect on the vehicle's response.
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