| Summary: | 博士 === 國立交通大學 === 電機與控制工程系所 === 93 === The models used are usually imprecise and the parameters of physical systems vary with the operating conditions and time. Designing and implementing a system for a fixed and exact control plant is not usually practical in the natural environments. A inaccurate plant may result from a simplified model and uncertainties in system parameters can always occur in the physical world. Robustness stability is important in analysis and design of practical control systems. Another important phenomena to be considered is undesirable oscillations due to nonlinearities in a feedback closed system and it has been studied by many researchers. It is very instructive for the designer to predict the limit cycle behavior of a perturbed control system with nonlinearities. The describing function technique is mainly employed to predict the existence of constant amplitude oscillations of closed nonlinear systems and has been successfully used in many applications.
The main subject of this dissertation is to propose a novel method based on parameter space method and robust stability criteria to predict limit cycles occurred, analyze the system performances of gain margin and phase margin (GM and PM), and design a desired controller by adjusting the controller coefficients for perturbed control systems to meet specified conditions including GM, PM and sensitivity in frequency domain. A vehicle model is used as an example for simulation. With the help of gain and phase boundary curves resulting from the roots of the characteristic polynomial equation of closed control systems, a methodology is proposed for portraying regions in a selected designed parameter plane so that the performance of the whole system can meet the specified requirements with perturbed parameters varying in given intervals. The same approach is extended to analyze the robust stability for a fuzzy control system. This dissertation also applies the above method on phase-locked loops (PLL) design by frequency domain approach for a perturbed PLL system. The desired system parameters of PLLs in the selected coordinate plane are determined in graphical portrayals. Simulation results have demonstrated and achieved the objectives as desired.
|
|---|
