Chau-Chung Song

Analysis of Longitudinal Flight Dynamics: A Bifurcation-Theoretic Approach

Bifurcation theory has been used to study the nonlinear dynamics and stability of many modern aircraft, especially in broad angle-of-attack e ight dynamics. However, the main application of bifurcation analysis is based on numerical simulations to predict and explain the nonlinear instability of e ight dynamics by the use of parametric continuation methods. Bifurcation theory is applied to theoretically analyze the nonlinear phenomena of longitudinal e ight dynamics, by the choice of the elevator dee ection and mass of the aircraft as system parameters. Both stationary and Hopf bifurcations may appear at some critical values of elevator command. Discontinuity also may occur at system equilibria as system parameters vary. The bifurcation phenomena occurring in nonlinear aircraft dynamics might result in jump behaviors, pitch oscillations, or system instabilities. Numerical study of a simple third-order model of longitudinal dynamics verie es the theoretical analysis. Qualitative results are obtained to understand the longitudinal e ight dynamics.

Robust stabilization of a centrifugal compressor with spool dynamics

Issues of global stabilization of a centrifugal compressor with spool dynamics are presented. Control schemes are designed for systems with and without system uncertainty. While activating only the close-coupled valve or the throttle as the single control input, backstepping tools are first used to achieve global stability of the working equilibrium for systems without uncertainty. The uncertainties in the spool dynamics and the compressor characteristic are known to be likely to happen in practical applications. Under such circumstances, the compressor torque and the close-coupled valve are then employed to achieve robust global stability of the working equilibrium via the Lyapunov redesign method. Numerical simulations are given to demonstrate the main results.

Bifurcation analysis of power systems with tap changer

A bifurcation analysis of nonlinear dynamics for electric power system with tap changer is presented in this paper. Based on a model of electric power system proposed by Dobson and Chiang (1988) with one extra tap changer added parallel to the local nonlinear power load, the saddle-node bifurcation and Hopf bifurcations are observed by treating the real power, reactive power and tap changer as system parameters. The occurrences of subcritical Hopf bifurcation and saddle-node bifurcation lead to the appearance of dynamic and static voltage collapses, respectively. These phenomena may generate the progressive decrease in voltage magnitude in electric power system.

Design and implementation of dimmable fluorescent lamps with TRIAC phase control

The objective of this paper is to design and implement a phase-control dimming electronic ballast system which consists of a phase controller, a boost converter, a half-bridge inverter and a system controller. The firing angle of the phase controller is sensed as a reference to adjust the output voltage of the converter and switching frequency of the inverter to achieve a dimming feature. The designed system can solve the practical installation problem of the system. Hardware measurements have been presented to verify the proposed method in this paper.

Periodic modeling and analysis of bifurcation dynamics for switching converters

In this paper, the nonlinear dynamics of PWM-type converters is studied. The sampled-data approach is applied to the periodic modeling and stability analysis of switching converters. The period-one and period-two modeling for the converter dynamics is proposed to predict the occurrence of the corresponding bifurcations and used to analyze the stability of converter circuits. The example study of buck converters is presented to demonstrate the feasibility of the methodological approach proposed in this paper. Applying to buck converters, the period-doubling bifurcation is found to exhibit as the input voltage varies, which might produce a series of period-doubling bifurcations and then result in a chaotic motion. Furthermore, the system stability of buck dynamics is studied and evaluated.

Study and implementation of a networking information platform for RFID system

RFID system has been treated as one of the important technologies which are enough to influence the evolutions of the global industry in the near future, especially for the supply chain and logistics management. The RFID technology may provide the requirements of the real-time tracking and high precision in the application of logistic systems. In this paper, a networking information platform integrated with RFID system is studied and proposed by using the internet techniques to increase the management capability and to achieve the network routing function of tag data for the enterprise applications. Since one of the most important factors for RFID applications is to construct the integrated and reliable system platform of networking information, this system platform will play one of key technologies for data routing and networking integration in the infrastructure of RFID systems. The main results of this paper are focused on developing the networking integration technologies to monitor the readers and capture the tag EPC data via Web server and the internet, and implementing the interfacing technologies of Savant middleware between RFID reader and database server to mediate the data flow from the clients to the enterprises. In conclusion, the networking information platform for RFID system is developed and evaluated to demonstrate the practical feasibility of RFID applications in this paper.

Bifurcation Analysis of Boost Converters with PWM IC

The general boost converters designed by the commercial PWM IC are studied in this paper. The commercial TL494 IC is used to implement the PWM-controlled circuit. Applying the sampled-data approach, the mathematical model is constructed to analyze the nonlinear dynamics of the boost converter. The bifurcation theory is applied to study the stability and the nonlinear phenomena of the proposed model, while the system parameters of converters vary. Using the Matlab/Simulink software, the numerical simulation is performed to analyze the system behaviour and time responses merged from bifurcation points. Moreover, the bifurcation phenomena are demonstrated by implementing the experiments of the practical circuit. The understanding of nonlinear dynamics opens up new possibilities of operating regimes that can help to optimize the design of boost converters.

A Feedback Linearization Design for the Control of Vehicle's Lateral Dynamics

In this paper, the feedback linearization scheme is applied to the control of vehicles lateral dynamics. Based on the assumption of constant driving speed, a second-order nonlinear lateral dynamical model is adopted for controller design. It was observed in Liaw and Chung (2006) that the saddle-node bifurcation would appear in vehicle dynamics with respect to the variation of the front wheel steering angle, which might result in spin and/or system instability. Feedback linearization control laws are proposed in this paper to stabilize the vehicles dynamics at bifurcation points. Numerical simulations for an example model demonstrate the effectiveness of the analytical results

Washout-filter based bifurcation control of longitudinal flight dynamics

This paper presents the bifurcation control of longitudinal flight dynamic, via washout filter based design. Based on the mathematical model proposed by Garrard and Jordial (1977). a rich variety of bifurcation phenomena, such as saddle-node bifurcation, Hopf bifurcation, and cycle fold bifurcations are observed in the numerical simulations of longitudinal flight dynamics of F-8 aircraft. The occurrence of saddle-node bifurcation and Hopf bifurcation might result in jump behavior and pitch oscillations of flight dynamics. Bifurcation control laws are proposed to change the property of bifurcation phenomena and hence improve system stability.

Nonlinear control of longitudinal flight dynamics

This paper presents the nonlinear analysis and control of a third-order model for longitudinal flight dynamics. Bifurcation analysis using numerical study for F-8 aircraft reveals that Hopf bifurcations may occur at some critical values of the elevator commands. These results agree with the well-known nonlinear phenomena existed in longitudinal flight dynamics. Furthermore, bifurcation control using both washout filter and direct state feedback are applied to develop the stabilizing laws for system equilibria and periodic solutions emerged from bifurcation points. Numerical simulations are providedto demonstrate these main results.