Enhanced feedforward control of non-minimum phase systems for tracking predefined trajectory

Abstract

In this thesis, the enhanced feedforward controller is proposed for the accurate tracking of the non-minimum phase(NMP) systems. Moreover, the performance assessment technique for the feedforward controller is also introduced, and the robust feedback controller and the parameter identification method are proposed for the NMP systems. In the many cases of the tracking applications of the NMP systems, the desired trajectory is predefined. Thus, the prior information of the desired trajectory can be utilized in the design of the feedforward controller. The main idea of the proposed controller is that the previewed information of the desired trajectory can be a good material for the phase error compensation, because the phase error, which is caused by the NMP zeros and induces response lag, can be cancelled by injecting the desired trajectory in advance. As the first step, the simple preview based feedforward control(SPBFFC) is proposed. In the proposed SPBFFC, the phase error due to the NMP dynamics is compensated by the time prediction based on the Pade approximation. The proposed SPBFFC has the outstanding performance in the comparison with the existing controller: the extended bandwidth zero phase error tracking controller(EBZPETC). Especially, the SPBFFC has · smaller undershoot and overshoot, and · wider control bandwidth than the EBZPETC. The performance of the SPBFFC is verified though the assessment based on the error vector magnitude(EVM), and the simulation and the experiment with the flexible arm system. As an extended version of the SPBFFC, the optimal preview based feedforward control(OPBFFC) is proposed. For the OPBFFC, the phase error compensator component which can be designed to have zero error at an arbitrary frequency is proposed by utilizing the time shifted information of the desired trajectory. Furthermore, the phase error compensator in the OPBFFC is designed by composing the components. As a result, the control bandwidth of the OP...