Unstable Delay Processes Research Articles

Modified Firefly Algorithm based controller design for integrating and unstable delay processes

In this paper, Modified Firefly Algorithm has been used for optimizing the controller parameters of Smith predictor structure. The proposed algorithm modifies the position formula of the standard Firefly Algorithm in order to achieve faster convergence rate. Performance criteria Integral Square Error (ISE) is optimized using this optimization technique. Simulation results show high performance for Modified Firefly Algorithm as compared to conventional Firefly Algorithm in terms of convergence rate. Integrating and unstable delay processes are taken as examples to indicate the performance of the proposed method.

Stability analysis and design of integrating unstable delay processes using the mirror-mapping technique

Robustness analysis and design for the integrating unstable delay systems are discussed in this note. The Nyquist criteria have established the exact stability margin of the novel robust control scheme, which is meaningful in the process control practice. Comparing with the existing results, the control law is designed based on the delay-approximated model (using the all-pole Padé approximation). The unstable system was mirror mapped into a minimum-phase system and then the control law was derived by the closed-loop gain shaping algorithm (CGSA). In addition, a small constant δ was introduced in the algorithm to prevent the integral cancellation limitation, which is inherent in the CGSA. The proposed scheme obtains several advantages: a concise design procedure and easy to implementation due to the simple unit feedback structure. The comparative analysis with respect to recently successful works illustrates a substantial improvement in the performance-robustness tradeoff.

Lead/Lag Compensator Design for Unstable Delay Processes Based on New Gain and Phase Margin Specifications

This paper considers a lead/lag compensator design problem for a class of unstable delay processes based on a new set of gain and phase margin specifications. Due to the nature of the unstable system, both upper and lower gain margins are required to measure the true stability robustness with regard to gain change. In addition to a phase margin, such a combined margin problem leads to a set of nonlinear and coupled equations which have no analytical solution. Thus, an effective graphical method is developed such that the solution is determined from the intersections of the curves constructed by a transformed set of nonlinear equations. The tuning procedure is presented and examples are given for its illustration and comparison.

Stabilization conditions for a class of unstable delay processes of higher order

The presence of zero dynamics is not uncommon in industrial chemical processes. For unstable delay processes that exhibit zero dynamics, the stabilizability by simple controllers has not really been addressed before. The paper studies stabilizing control for such processes, and establishes some stabilizability conditions.

Stabilization of all-pole unstable delay processes by simple controllers

The stabilization of a class of all-pole unstable delay processes of arbitrary order with single unstable pole by means of simple controllers is investigated in details. Complete stabilizability conditions are established and the computational methods for determining stabilizing controller parameters presented. They provide theoretical understanding of such a stabilization problem and can also serve as practical guidelines for actual controller design.

Stabilization of second-order unstable delay processes by simple controllers

The stabilization of second-order unstable delay processes by simple controllers is investigated. The elementary analysis based upon the Nyquist stability criterion is carried out to establish explicit and complete stabilizability results in terms of the upper limit of time-delay size and the computational methods for determining stabilizing controller parameters. The analysis provides both theoretical understanding of such stabilization problem and practical guidelines for actual controller design. The results for other unstable delay processes studied extensively in the literature are also obtained as the special cases of the above second-order one.

A double two-degree-of-freedom control scheme for improved control of unstable delay processes

A double two-degree-of-freedom control scheme is proposed for enhanced control of unstable delay processes. The scheme is motivated by the modified Smith predictor control in [IEE Proc. Control Theory Appl. 16(5) (1999) 359] and devised to improve in the following ways: (i) one more freedom of control is introduced in our scheme to enable manipulation of disturbance transient response, and is tuned based on minimization of the integral squared error criterion; (ii) four controllers in the scheme are well placed to separately tune the denominators and numerators of closed-loop transfer functions from the set-point and disturbance. This allows easy design of each controller and good control performance for both set-point and disturbance responses. Especially, improvement of disturbance response is extremely great, compared with [IEE Proc. Control Theory Appl. 16(5) (1999) 359; Automatica 36 (2000) 1651]. Internal stability of the proposed structure is analyzed, which has not been reported in the literature on modified Smith predictor control before. Examples are provided for illustration.