Overall vehicle stability for a non-linear multi-varied suspension aimed at disturbance attenuation, energy efficiency and robustness

Nkomo, Lihle Immaculate
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This dissertation presents the design and implementation of a half-car active suspension system with a pre-disturbance detection algorithm that aims at reducing driver experienced vibrations. The first research contribution is slack-based state constrained optimal control which is used to address the limitations of the penalty function methodology. The performance index is designed so that it optimises for the control actuation energy and the driver’s ride comfort. The optimal control results demonstrate displacement attenuation of 97.5 % and acceleration of up to 80 %, which is practically feasible if high performance sensors and actuators are utilised to enable a fast and efficient response of the active suspension system. The second research contribution is derived from extending the slack variable state constrained optimal control to the linearised half-car suspension system by addressing the limitations of input output feedback linearisation as the state transformation often results in hidden state dynamics. The results from the completely linearised controller show a displacement attenuation of up to 81.82 %. The third research contribution is through the application of an adaptive sliding backstepping controller to the con-structed test-rig, that ensures robust control on non-smooth road surfaces consisting of white noise. The results from the adaptive sliding backstepping demonstrate improved attenuated displacement and smoother accelerations of up to 71.3 % and 60 % respectively. Although the adaptive sliding backstepping trade-offs disturbance attenuation performance, it demonstrates adaptive properties when tested on rough road surfaces. To achieve overall vehicle stability, the use of these controllers can be integrated to benefit from the targeted performances such as robustness
A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2020