Design and investigation of PA controller for driving nonlinear electro hydraulic actuator with new active suspension system model

Fully active electrohydraulic control of a quarter-car test rig is considered from both a modelling and experimental point of view. This paper develops a nonlinear active hydraulic design for the active suspension system, which improves the inherent trade-off between ride quality and suspension travel. The novelty is in the use of pole assessment controller to drive a nonlinear active suspension with a new insight into the model through consideration of a new term, friction forces. Therefore, this model has taken into account the dynamic inclination angle

Active fault tolerant control of an electro-hydraulic driven elevator based on robust adaptive observers

Faults are minor malfunctions that deteriorate the performance of a system. In a safety critical situation such as the control of an airplane, compounding faults may cascade into a catastrophic event if not properly compensated. Active Fault Tolerant Control (AFTC) addresses the fault accommodation problem - the reliability and robustness of the system in faults - beyond the conventional stability and performance requirements for a normally operating plant. This thesis studies the AFTC of an electro-hydraulic driven elevator, which serves as a primary control surface of an airplane. The proposed AFTC system consists of three components: (1) A Fault Detection and Estimation (FOE) component is designed based on two robust adaptive observers. (1). Adaptive Unknown Input Observer: a disturbance decoupled observer utilizing the geometry property and measurement redundancy of the system; (2). H x /H _ adaptive observer: an optimization based observer to maximize the system's response to faults and minimize that to disturbances. The H x /H _ adaptive observer is constructed with the technique of Unitary System, which is defined as a linear system whose singular values of transfer matrix are equal. (2) A fuzzy Proportional-Integral (PI) controller is designed based on the fuzzy Tagaki-Sugeno (TS) model of a nonlinear system, which consists of different linear models at different operating points. (3) The reconfiguration is carried out based on the fault information available from FDE. To reduce the time needed for the online computation, multiple controllers are designed offline for different faults scenarios. A new controller is constructed online as a fuzzy combination of these controllers to meet the post-fault stability and performance requirements. Simulation results show that, with the proposed AFTC, occurring faults are detected promptly and estimated accurately with the FDE component. The performance of the post-fault elevator is quickly restored after the reconfiguratio

Automotive suspension system modelling and controlling

In both academic and industrial fields, suspension system modelling and associated control design influence vehicle response. Ideal hydraulic force models have been used in active suspension studies for decades, but few studies have investigated hydraulic effects, which are the core of system force generation. Accurate mathematical subsystem modelling is essential in representing physical subsystems and enhancing design estimation control. This thesis details the mathematical modelling of both passive and active suspension and controller design for a quarter-car test rig. When using a conventional passive model, a significant difference between the experimental and simulation results was found for improved modelling of body movements. This led to an investigation in how to resolve this issue, accordingly, the consideration of a new term (friction force) was researched. Establishing a nonlinear friction force became a vital aspect of this work. In addition, emphasis was placed on hydraulic modelling and unknown model parameters that were experimentally identified. This experimental work is unique and helpful for advancing knowledge of any system. A new approach to implementing the friction force was used to identify the system through the transformation of a ¼ car model to one Degree of Freedom (DOF) and two-DOF models. This reduced the model complexity and allowed the parameters to be identified from a series of transfer functions linking vehicle parts and the hydraulic models. Simulation and experimental results were then compared. The hydraulic component model is crucial to the formulation of accurate active control schemes. Full-state feedback controls were realised by Pole-Assignment (PA) and Linear Quadratic (LQ) optimal method. Simulation results suggest that even though the performance of active suspension designed by the PA method is superior to that of passive suspension, it still possesses a design constraint, similar to a passive system, as the design is a compromise between the effects of natural frequency and transmissibility. With a different design concept, the LQ method provided a better solution as it reduced energy consumption by 65% and effectively shifts the dominant natural frequency to a very low-frequency range. Thus, allowing the damping rate to be increased to its critical value with the smallest effect on transmissibility. iv It was estimated for experimental work that the identified model with the LQ controller might be used to predict the dynamic responses of the actual system within a certain range of the design parameters due to the considerable difference between the initial condition of the test rig and the linearised operating design. The servovalve produced issues that did not allow validation of the controller. Both simulation and experimental results, with several conditions, showed consistent agreement, between experimental and simulation output, consequently confirming the feasibility of the newly approved model for passive and active suspension systems that accounted for the actual configuration of the test rig system. These models, that subsequently implemented the nonlinear friction forces that affect the linear supported body bearings, are entirely accurate and useful. The nonlinear friction model captures most of the friction behaviours that have been observed experimentally. Additionally, the models of the nonlinear hydraulic actuators, covered by the dynamic equation for the servovalve, are moderately precise and practical. The suggested Proportional Integral (PI) control successfully guided the road hydraulic actuator and validated the control strategy. The suggested PA and LQ controllers for active systems successfully guided the system to achieve the targets. Ride comfort and handling response are close to that expected for the passive suspension system with road disturbances, whereas there were clear response enhancements for the active system