Quarter car active suspension system identification and control

In vehicles to ensure both safety and comfort the suspension system should carry out its duties in strict sense. To provide that firstly one should get a suitable model for the suspension system that has nonlinear structure, then via using this model and with taking into account the performance criterion an appropriate controller can be designed to minimize the road rougness effect onto vehicle. In this thesis the first aim is to derive the model of the quarter car active suspension system by using system identification techniques. In the analysis of real time dynamic system the first and the most important step is to derive the system model. Deriving the mathematical model by using physical laws is so difficult, it is needed a comprehensive knowledge and effort. On the other hand with using system identification there is no need any prior knowledge for deriving system model of a real time dynamic system, only thing to do is that firstly exciting the system with suitable input signals and observe the outputs, then using these inputs and outputs the system model can be derived. Matlab System Identification Toolbox® is used to derive the sytem model, and different types estimated models will be tested on the real system. After these tests, amoung models the more approapriate one will be selected and then for this model the output feedback H_∞ controller will be designed to minimize the infinity norm of the transfer function between performance output and disturbance input. In the standart H_∞ control theory, the designed controller has the same degree as the system. So with using this controller, the degree of the closed loop system is increased twofold. Initially it is seem to be feasible for the lower degree systems, but to achieve the perfomances at issue the filters should be used to weight inputs and outputs of the system, and so this will increase the degree of the system. After adding the same degree controller to the high degree system, the new controlled system can be affected more by even a little error. Further more the usage of the high controllers that obtained with using standart controller methods in the embedded system is not an easy work to accomplish. For these reasons recently the studies over the fixed reduced order H_∞ controller have been increased. However, the fixed-order design problem is defined in a nonconvex cluster, and at peresent there is not any solving algorithm for general solution in nonconvex cluster, so that makes this approach a hard way. The main purpose of this study is to develop full order H_∞ controler with using standart approach and fixed reduced order H_∞ controler with using polynomial approach that will minimize infinity norm of the quarter car suspenson system which model derived by using system identification methods. The nonconvex structure is reduced to a convex shape with Strict Positive Real Lemma.