Semi-Active Axle Suspension for Heavy Trucks
Truck suspension technology has traditionally comprised more or less passive elements that possibly are adjusted slowly compared to the suspension dynamics. In attempts to overcome the inherent comfort-handling trade off, departures from fully passive designs have been made in the past. Fully active suspensions have successfully been implemented in private cars but have gained little ground in the truck industry because of their large energy consumption and high cost. Semi-active suspensions take a middle-ground with lower performance potential but also with considerably lower power requirements and cost of implementation. Effective controller design for a semi-active suspension includes consideration of the passivity constraints imposed on the control force. In this thesis an optimisation algorithm was written in MATLAB in a way that allows for embedded code-generation and was then used for designing a Model Predictive Controller (MPC) with switched passivity constraints. The resulting controller was tested on a 3D truck-trailer model and evaluated, together with other controllers as well as the passive system against both comfort and handling metrics. Non-convexity generally makes an MPC less useful for high sampling rates but with a switched linear approximation of the passivity constraints the resulting controller was shown to still be effective.
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