Electrical and Electronic Engineering, Imperial College London
Doi
Abstract
This thesis develops control strategies of a new type of active suspension for high
performance cars, through vehicle modelling, controller design and application, and
simulation validation. The basic disciplines related to automotive suspensions are first
reviewed and are followed by a brief explanation of the new Series Active Variable
Geometry Suspension (SAVGS) concept which has been proposed prior to the work
in this thesis. As part of the control synthesis, recent studies in suspension control
approaches are intensively reviewed to identify the most suitable control approach for
the single-link variant of the SAVGS.
The modelling process of the high-fidelity multi-body quarter- and full- vehicle
models, and the modelling of the linearised models used throughout this project are
given in detail. The design of the controllers uses the linearised models, while the
performance of the closed loop system is investigated by implementing the controllers
to the nonlinear models.
The main body of this thesis elaborates on the process of synthesising H∞ control
schemes for quarter-car to full-car control. Starting by using the quarter-car single-link
variant of the SAVGS, an H∞ -controlled scheme is successfully constructed, which
provides optimal road disturbance and external force rejection to improve comfort
and road holding in the context of high frequency dynamics. This control technique is
then extended to the more complex full-car SAVGS and its control by considering the
pitching and rolling motions in the context of high frequency dynamics as additional
objectives. To improve the level of robustness to single-link rotations and remove the
geometry nonlinearity away from the equilibrium position, an updated approach of
the full-car SAVGS H∞ -controlled scheme is then developed based on a new linear
equivalent hand-derived full-car model. Finally, an overall SAVGS control framework
is developed, which operates by blending together the updated H∞ controller and
an attitude controller, to tackle the comfort and road holding in the high frequency
vehicle dynamics and chassis attitude motions in the low frequency vehicle dynamics
simultaneously. In all cases, cascade inner position controllers developed prior to the work in this
thesis are employed at each corner of the vehicle and combined with the control systems
developed in this thesis, to ensure that none of the physical or design limitations of
the actuator are violated under any circumstances.Open Acces