Sequential Loop Closure Research Articles

A New Decentralized Stabilization Approach with Application to Power System Stabilizer Design

Power system stabilizer design for multi-machine power systems is studied in this paper. The difficulties of applying some existing design methods to stabilizers for day to day commercial operation are first discussed from the practical application point of view. Then, it is shown that whereas the design problem can be conveniently formulated as a large-scale system decentralized stabilization problem, it can also be translated into an equivalent one of feedback controller design for a multi-input multi-output system. The frequency response based sequential loop closure method is suggested for the design and it is applied to a model of 10 machine 54-th order power system. The results from computer analysis and simulation and the nature of the proposed method have showed that, the new design method may have some advantages in avoiding the difficulties discussed

A discrete characteristic locus design for a multichannel structural test system

Structural tests are carried out in the automotive and aerospace industries to assess fatigue and vibration properties of engineering structures. Very often the multivariable nature of these tests is ignored and a sequential loop closure scheme is used with PID controllers in each loop. Earlier work has focused on the application of continuous-time Nyquist Array and Characteristic Locus methods to such tests. This paper extends that work by considering a discrete design approach to the Characteristic Locus method. The design process for a two-input two-output system and subsequent implementation on a beam and vibrator rig is described. With modest computational hardware, excellent results are obtained and shown to be superior to those obtained from the implementation of a discretised continuous-time Characteristic Locus controller.

Multivariable stability and robustness of sequentially designed feedback systems

In sequential loop closure, the importance of evaluating the stability and stability robustness at the intermediate loop closures is well known. However, knowledge concerning how the intermediate loop closures, as well as the final loop closures, contribute to the stability and stability robustness of the overall feedback system holds special significance to the analysis and design of multivariable feedback systems. An analysis of the complete feedback system reveals the multivariable Nyquist contributions from the intermediate loop closures. It is also shown that the results greatly simplify if frequency separation exists between the intermediate loops. The analysis is presented with a two-step loop closure procedure using inner and outer loops that can be generalized to multistep situations. The control of the longitudinal dynamics of an aircraft is addressed to further clarify and demonstrate the results.

Rotorcraft Control System Design for Uncertain Vehicle Dynamics Using Quantitative Feedback Theory

Quantitative Feedback Theory describes a frequency-domain technique for the design of multi-input, multi-output control systems which must meet time or frequency domain performance criteria when specified uncertainty exists in the linear description of the vehicle dynamics. This theory is applied to the design of the longitudinal flight control system for a linear model of the BO-105C rotorcraft. Uncertainty in the vehicle model is due to the variation in the vehicle dynamics over a range of airspeeds from 0-100 kts. For purposes of exposition, the vehicle description contains no rotor or actuator dynamics. The design example indicates the manner in which significant uncertainty exists in the vehicle model. The advantage of using a sequential loop closure technique to reduce the cost of feedback is demonstrated by example.

Autotuning of multiloop proportional-integral controllers using relay feedback

In this paper, a simple method for autotuning multiloop PI controllers for multivariable systems is presented. The procedure is a combination of sequential loop closing and relay tuning often used for tuning single-loop PI/PID controllers. The proposed design offers three major advantages. Firstly, overall closed loop stability is guaranteed; secondly, very little knowledge of the process is required; thirdly, it is an autotuning procedure. Set point and load disturbance responses are improved by introducing set point weighting factors. Some simulation and comparative results are shown for distillation column models commonly used to demonstrate multiloop designs.