In the previous works, the author developed a method of optimal design for expansion of existing water distribution networks. The novel feature of this method is that it clarifies the trade-off relationship between enhancement of the supply stability (or reliability) and reduction of the construction cost. This paper generalizes the formulation so that it copes with the existence of a variety of hydraulic elements and introduces a combination of the penalty functions and the Newton method instead of the previous solution based on the generalized reduced gradient method so that the computational time is reduced and ill-conditioned problems are made solvable.
This paper presents a robust stability condition for feedback systems in practice with uncertain nonlinearity. First, the boundedness of the “gain” for a nonlinear subsystem is discussed by means of some block diagram transformation. Secondly, a main theorem for L2-stability is derived using the small gain theorem and the input-output approach, after some considerations on the stability of the linearized nominal closed-loop system. This theorem is equivalent to the Popov criterion, but exhibits the stability margin explicitly. The relation between Aizerman's conjecture and this robust stability condition is also discussed. Then, a condition for the validity of Aizerman's conjecture is presented. Finally, typical examples including a counterexample to the conjecture are given to illustrate the results.
This paper is concerned with the design of adaptive control system to settle the property of foundry green sand to optimum one in a mulling process. The mulling process of foundry green sand can be modelled as a single-input, single-output (SISO) system, where the manipulated variable is the water quantity to be injected and controlled variable is the moldability index. Dynamical behavior of mulling process changes over a wide region between batches according to the variation of sand-binder ratio, environmental conditions and so on. An adaptive controller (implicit MRACS) is applied to this mulling process and is compared with the conventional PID and LOI control approaches. The adaptive controller is shown to provide good control quality under the tested conditions.
This paper is concerned with a test for robust stability. In order to overcome the conservativeness of usual stability test based on the small gain theorem, a new graphical test is introduced for robust stability of scalar systems, which takes account of both gain and phase information. The method is then extended to a class of multivariable systems.
The so-called vector control method is currently used for induction motor drives.This method aims at high speed control of induction motor drives to take place of the d. c. motor in high speed industrial applications. It has not been established, however, whether this method can stabilize the induction motor system in the large, nor is there any discussion about its robustness to the present. This paper proposes a nonlinear feedback control of induction motor drives, where the induction motor is regarded as a bilinear system. The stability of the induction motor system in the large is guaranteed, and this stability is robust against substantial motor constant variation from the nominal value. Simulation results also show that the control method proposed in this paper is superior to the vector control method.