Dynamical analysis and control designs for plasma torch systems and centrifugal compressor

• Main Authors: Chang, Shih-Tse, 張世澤
• Other Authors: Liaw, Der-Cherng
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/60465752186763844669

博士 === 國立交通大學 === 電控工程研究所 === 100 === Dynamical analysis and controller designs of the nonlinear dynamics in a plasma torch systems and centrifugal compression system are studied in this dissertation. Recently, the study of plasma technology has attracted considerable attention due to the fact that the arc plasma devices have been widely used in industrial applications. A basic plasma device is consisted of plasma torch, power supply and mass flow control system. It is known that both of the power converter and compressor might have the instability with respect to the variation of system parameter. Based on the subsystem in arc plasma device, we focus on the analysis of dynamical behavior in both the nonlinear third-order amplitude equation and centrifugal compressor. Among studies of arc plasma device, Ghorui, Sahasrabudhe, Murthy, Das and Venkatramani claimed that the inherent fluctuation appearing in arc plasma devices might be a chaotic dynamical behavior (e.g. [4]-[6]). Those studies derived the nonlinear third-order amplitude equation to describe the dynamical behavior for the arc plasma device. In this dissertation, we extend the nonlinear third-order amplitude equation to a more general case. Local bifurcation analysis for a class of the nonlinear third-order amplitude equation was employed to solve for the existence conditions of both stationary and Andronov-Hopf bifurcations. Moreover, the scenarios for the possible nonlinear behavior in the nonlinear third-order amplitude equation were also obtained with respect to the variation of system parameters via the numerical simulations, which might provide a guide for finding nonlinear phenomena in the practical application of the plasma torch. In addition, for the analysis of surge instability in a centrifugal compressor, local bifurcation analysis is first studied for finding the existence conditions of nonlinear behavior. Due to the occurrence of bifurcated phenomena, a robust scheme was proposed to eliminate the surge phenomenon appearing in a centrifugal compressor. It is known that the surge instability in compressor might lead to reduce the operating efficiency and even damage the machinery while both of unstable compressor characteristics and compressor load torque are hard to exactly measure in the practical application. Based on the assumption of local sector nonlinearity for system dynamics, a robust control law was proposed to cover the system nonlinearity and uncertainties while guaranteeing the stability of system equilibrium. This is achieved by using the actuation of the driving torque and closed-couple valve. Numerical simulations are given to demonstrate the success of the proposed robust controller design. After that, the output tracking design for preventing the spool dynamics of a centrifugal compressor system was also presented in this dissertation. The proposed controller design not only could provide the stabilization of dynamical behavior but also regulate the system output to the desired trajectory. However, some of the state variables might also be unavailable from the signal feedback. In order to estimate the unavailable state variables, the robust observer-based control design was considered applying to the elimination of surge instability in a centrifugal compressor. Therefore, to achieve robust stabilization and observation, the output tracking control and observer were proposed via the local sector nonlinearity approach and variable structure control, respectively. Numerical simulations were obtained to verify the feasibility of output tracking design via robust observer-based control scheme.