Adaptive MIMO vibration cancellation in plate structures - design online controller based on PPF control strategy

Author: Chuanyu Sun

Sun, Chuanyu, 2019 Adaptive MIMO vibration cancellation in plate structures - design online controller based on PPF control strategy, Flinders University, College of Science and Engineering

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Flexible structures are widely used in many engineering systems due to their lightweight. This kind of structures is normally vulnerable to vibrations, especially when the system changes. To such systems, the fixed-parameter active vibration controllers cannot provide the best control performance and sometimes even help to excite the system. Therefore, a Real-Time Adaptive Control Scheme (RTACS) is highly demanded to maintain control performance in real-time. The RTACS is required to respond to changes in the system (adjust the parameters of controller online) and provide sufficient vibration attenuations. In this thesis, a top thin plate bonded connected to a vibration base plate by three pairs of sensors/actuators is used as a research vehicle. The top plate can be mathematically modelled as a three-input three-output resonant flexible structure with an infinite number of modes near the natural frequencies of the structure itself. However, only the first three modes are in the concerned frequency range. Therefore, for the controller design purpose, a simplified StateSpace Representation (SSR) model and Second-order Differential Model including these three modes are constructed (the D term is neglected for simplicity). Positive Position Feedback (PPF) is one of the most effective active control algorithms and is widely applied to many MIMO flexible systems due to its advantages. The PPF utilizes a second-order low-pass filter that is insensitive to spillover effect and can control multiple modes through one pair of sensor/actuator. However, designing a PPF requires simultaneous optimization of all controller parameters for different modes and PPF also lead to a relatively large steady-state error for the closed-loop system. According to the above analysis, two new control methodologies based on the technique of PPF are proposed and implemented on the plate system. The first proposed method is Independent Modal Positive Position Feedback (IMPPF) combining the advantages of the Independence Modal Space Control (IMSC) algorithm with the PPF. Thus, the parameters of IMPPF can be designed separately for each vibration mode. The structure of IMPPF is relatively simple as it only uses two controller parameters for each mode (i.e., the control gain and time constant are designed through error elimination method and root locus technology respectively). The computation load of the proposed IMPPF is low, therefore, IMPPF can easily realise online update parameters and be implemented in the proposed RTACS. The second method is the Modified Positive Position Feedback (MPPF), which is developed by adding a first-order filter in parallel to the conventional PPF. The first-order filter has the potential to reduce the damping of the compensator, thereby reducing the steady-state error of the closed-loop system while maintaining the control performance of PPF. The parameters of MPPF can be optimized by utilizing the ∞ norm and Genetic Algorithm. Finally, an RTACS is proposed based on a pre-designed frequency estimator that can select the better controller between IMPPF and MPPF and update controller parameters in real-time. To validate the effectiveness of the proposed methods, numerical simulations are conducted on MATLAB Simulink©. Both IMPPF and MPPF are designed for the built SSR model. The simulation results show that the vibration attenuation effect of IMPPF can reach up to 13 dB, and MPPF can reach up to 20 dB. The simulation result of the RTACS clearly demonstrates its effectiveness in vibration attenuations of the given MIMO flexible plate-structure after the onset of system changes. A real-time physical experiment is conducted upon successful validation of the proposed IMPPF, MPPF and RTACS in simulation. The experiment results show that the control performance of IMPPF and MPPF can reach up to 17dB and 20dB, respectively, that agrees with the results of simulation study. The experiment results also verify the effectiveness of the proposed RTACS to control the first three vibration modes of the given MIMO flexible plate structure, especially after a system change is introduced to the original MIMO flexible plate structure.

Keywords: vibration cancellation, adaptive online control, PPF Control Strategy, MIMO system

Subject: Engineering thesis

Thesis type: Masters
Completed: 2019
School: College of Science and Engineering
Supervisor: Amin Mahmoudi