A QFT Control Design Applied to an Active Suspension without an Explicit Model

Cesar M.C. Vargas and Fabrizio Leonardi


Active Suspension, Frequency Response, QFT


This work studies the controller design of an active suspension based on experimental data of frequency response without using the parametric model. The QFT (Quantitative Feedback Theory) control technique was used based on its convenience for designs without explicit models. As a performance specification, the controller must increase the passengers comfort by reducing the car body absolute acceleration compared to a passive suspension, but without decreasing the safety associated to the transmission of the forces to the ground that are associated with the tires oscillation amplitude. This specification must be maintained in the range of frequencies involving the two resonance frequencies. The experimental data are collected from harmonic excitation tests, where the information is contained in the gain and phase of the response. The controller used was obtained by adding poles and zeros using a Nichols chart, typical in QFT designs. To illustrate the proposed procedure and the controller performance, a physical simulator of a quarter car suspension was used. The experimental data of the closed loop control system suggests that the active suspension with the proposed controller can increase comfort without sacrificing vehicle safety.

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