Semi-activevibration control system is composed of two integrated controllers; systemcontroller and damper controller. System controller is proposed to estimate thedesired damping force  by using the dynamic responses of the plant, while dampercontroller is used to convert the gains of the system controller into a DCvoltage to supply it to the MR damper. The more advanced the systems controllerwould be the better performance can be achieved since the damping force of theMR damper directly related to the supplied voltage 102.

Inthis thesis, three different advanced controller strategies are used as thesystem controllers to evaluate the ride comfort under different road profilessuch as bump and random road excitations and the seat frame acceleration ( )is used as the error signal.    Firstly, the PID controller isintroduced as the system controller. It is the feedback controller commonlyused in most process industries. It is robust and has simple structure; hence about90% of industrial loops use PID controllers 103. The gains of PID controller canbe described as follows, the proportional gain ( )is responsible to reduce the error responses of the system to disturbances, theintegral gain ( )is used to eliminate the steady-state error, and the derivative gain ( )dampens the dynamic response and improves the system stability 111.

GeneticAlgorithm (GA) is one of theoptimization techniques, which mimics Darwin’s theory about evolutionto offer a robust solution. It is used as optimization tool inorder to find the best parameters of the PID controller. However, these   parametersare relative to a certain system operating condition (uncertain dynamics, timedelays and non-linearity…).

Hence it is necessary to automatically adjust thePID parameters for obtaining satisfactory response. The fuzzy control (FLC) is tuning the PIDparameters on-line according to the error and the change of error. Based on expertknowledge a FLC system transforms a linguistic control strategy into an automaticcontrol strategy 103. FLC has self tuning capabilities in set point trackingperformance.

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