A New Fuzzy Variable Structure Control of a Type of Nonlinear Multivariable System

In order to improve the robust performance for a type of nonlinear multivariable system, a new fuzzy variable structure control method is introduced in detail, which combined the features of traditional variable structure control method with the advantages of the fuzzy control theory. The present work realized the linearization of the nonlinear multivariable system, and then the new fuzzy variable structure control method is applied to control the linearization system. The robust experiments were carried out on the novel method. The results indicated that the required robust performance could be achieved with high efficiency by utilizing the new method. Introduction The robust control problem of the nonlinear multivariable system is difficult to be solved for long time[1]. In this paper a new fuzzy variable structure control is proposed for a type of nonlinear multivariable system. Firstly, the linearization of the nonlinear multivariable system is realized. It converts the nonlinear multivariable system into the linear one which is easier to be controlled with the linear multivariable control theory[2]. Secondly, a new fuzzy variable structure control approach is proposed for a type of nonlinear multivariable system in order to improve the robustbility of the system. Nonlinear Multivariable System The nonlinear multivariable system to be controlled is showed in Fig.1, which is composed of a motor-pump subsystem and a valve subsystem[3,4]. In the motor-pump subsystem the flow Qp is a nonlinear unit which can be described by the product of the motor speed n and the servo-pump displacement q, i.e. n q Qp ⋅ = . So the whole system is a type of nonlinear system. The Linearization and the Mathematical Modeling The Linearization of the Nonlinear Multivariable System. It is difficult to control the nonlinear multivariable system by the traditional control methods. However , it is found that when the linearization of the system is realized the fuzzy variable structure control method can be used. Fig.2 describes the principle of the new control method. In this figure the combined controller is composed of the motor-pump subsystem, the valve subsystem and the computer control unit. The result is that the whole motor-pump-valve system is converted into a linear system. The flow of the motor-pump subsystem Qp and the flow of the valve subsystem Qv are the flow of the combined controller. Fig.2 can be seen as the simplification of Fig.1. In Fig.2, the nonlinear pump unit is put into the combined controller. Thus the whole system is converted into the linear system. Key Engineering Materials Vols. 315-316 (2006) pp 623-627 online at http://www.scientific.net © (2006) Trans Tech Publications, Switzerland Online available since 2006.07.15 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 130.203.133.33-12/02/08,18:22:27) The Mathematical Modeling of the Linear System. The motor-pump-valve system become a linear system now. According to the force balance equation and the flow continuity equation, the differential equations of the actuator are derived. Control unit Motor-pump actuator Servo valve