Guaranteed Stability Robustness Research Articles

仮想的なパラメータ変動を用いたロバスト安定性解析方法―保守性を低減化した解析方法の提案

In this paper, a robust stability analysis problem is considered. μ-Analysis is a useful tool in order to guarantee stability robustness, but obtained results by conventional procedures are sometimes conservative. On the other hand, to guarantee stability robustness of active control systems in space is extremely important. A new robust stability analysis procedure by using virtual parametric variations is proposed in order to carry out tight evaluation of the stability robustness for active control systems. Performance of the proposed procedure is verified by an example of a mechanical vibration control system.

Rate-based flow controllers for communication networks in the presence of uncertain time-varying multiple time-delays

An H ∞ based robust controller is designed for a rate-feedback flow-control problem in single-bottleneck communication networks. The controller guarantees stability robustness to uncertain time-varying multiple time-delays in different channels. It also brings the queue length at the bottleneck node to the desired steady-state value asymptotically and satisfies a weighted fairness condition. Lower bounds for stability margins for uncertainty in the time-delays and for the rate of change of the time-delays are derived. A number of simulations are included to demonstrate the time-domain performance of the controller. Trade offs between robustness and time-domain performance are also discussed.

Operator Performance in Surgical Telemanipulation

The application of telemanipulator systems in minimally invasive surgery (MIS) poses high demands on the quality of force feedback. Forces exerted on the tissue are often small and should be reflected back amplified to the surgeon. The dynamic behavior of a telemanipulator system can be adjusted in three basic ways to guarantee sufficient stability robustness in spite of high force scaling factors: by scaling down the surgeon's input motion, by increasing the compliance at the slave arm, and/or by increasing the motion resistance at the master arm. More “transparent” telemanipulator dynamics can be achieved when the damping provided by the surgeon's hand-arm-system is taken into account (for example, the motion resistance necessary to guarantee stability robustness can be reduced). This paper investigates the effect of the three basic types of telemanipulator dynamics on operator performance in surgical tasks. The impact of improving transparency by making use of operator damping is also studied. Three experiments imitating elementary surgical procedures were conducted: inserting a catheter tip into a vessel, puncturing a membrane, and detecting differences in tissue hardness through palpation. Subjects exerted significantly higher forces when inserting a catheter without force feedback, which shows the benefit of force feedback in surgical telemanipulation. Performance of the subjects was also greatly influenced by the basic type of telemanipulator dynamics. However, differences in outcome between the experiments indicate that the best basic type will generally depend on the surgical task at hand. Improving the transparency of the telemanipulator system by making use of operator damping did not improve performance of the subjects any further. Thus, it appears that providing the appropriate basic type of telemanipulator dynamics for a given task may be even more critical to the performance of the surgeon than an optimized transparency of the telemanipulator dynamics.

Modeling and robust control design for aircraft brake hydraulics

This article describes the modeling of an electrohydraulic pressure servo valve and brake hydraulic system, and the design of an inner-loop controller which can be used with independent anti-skid or auto-brake controllers. The effects of the connecting lines on stability and performance are explicitly taken into account in the control design by using the analytical solutions to 2D viscous compressible model of fluid motion in the pipe. The modal approximation technique is used in the simulations. In order to facilitate control design, singular perturbation analysis is employed to reduce the order of the model in a systematic fashion. Combining partial feedback linearization and linear H/sub /spl infin// control, guaranteed stability robustness against oil parameter variations and component wear is achieved. Both the model reduction and control design are described in some detail. Computational requirements are modest and with careful coding, the inner-loop controller can be incorporated into existing anti-skid controllers.

Thermoacoustic instability: model-based optimal control designs and experimental validation

Active control of thermoacoustic instability has been increasingly sought after in the past two decades to suppress pressure oscillations while maintaining other performance objectives such as low NO/sub x/ emission, high efficiency, and power density. We have developed a feedback model of a premixed laminar combustor which captures several dominant features in the combustion process such as heat release dynamics, multiple acoustic modes, and actuator effects. In this paper, we study the performance of optimal control designs including LQG-LTR and H/sub /spl infin// methods using the model with additional effects of mean heat and mean flow actuator dynamics, and input saturation. We also verify these designs experimentally using a 1 kW bench-top combustor rig and a 0.2-W loudspeaker over a range of flow rates and equivalence ratios. Our results show that the proposed controllers, which are designed using a two-mode finite dimensional model, suppress the thermoacoustic instability significantly faster than those obtained using empirical approaches in similar experimental setups without creating secondary resonances, and guarantee stability robustness.

Multivariable Control of Vapor Compression Systems

This paper presents the results of a study of multi-input multi-output (MIMO) control of vapor compression cycles that have multiple actuators and sensors for regulating multiple outputs, e.g. superheat and evaporating temperature. The conventional single-input single-output (SISO) control was shown to have very limited performance. A low order lumped-parameter model was developed to describe the significant dynamics of vapor compression cycles. Dynamic modes were analyzed based on the low order model to provide physical insight of system dynamic behavior. To synthesize a MIMO control system, the Linear-Quadratic Gaussian (LQG) technique was applied to coordinate compressor speed and expansion valve opening with guaranteed stability robustness in the design. Furthermore, to control a vapor compression cycle over a wide range of operating conditions where system nonlinearities become evident, a gain scheduling scheme was used so that the MIMO controller could adapt to changing operating conditions. Both analytical studies and experimental tests showed that the MIMO control could significantly improve the transient behavior of vapor compression cycles compared to the conventional SISO control scheme. The MIMO control proposed in this paper could be extended to the control of vapor compression cycles in a variety of HVAC and refrigeration applications to improve system performance and energy efficiency.

H∞ robust control design for dynamic ship positioning

Prerequisites to the successful application of the H∞ control design technique to the marine dynamic positioning (DP) control problem are a realistic nominal model, relative bounds on modelling uncertainty, a set of frequency-dependent weighting functions to translate the control design specification into a control solution and a performance index to quantify the robustness. The authors propose procedures and algorithms to achieve these objectives. The H∞ robust control design technique is then used to calculate a robust controller which has superior properties to the conventional DP systems. The trade-off between track keeping and station keeping is undertaken via appropriate weighting functions and a two-degree-of-freedom control structure is employed. The technique proposed shows that effective wave filtering can be obtained with guaranteed stability robustness. The advantage of the proposed control design technique is demonstrated using ship nonlinear simulations.