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Excitation Control PDF

103 Pages·1964·4.759 MB·English
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EXCITATION CONTROL BY G. M. ULANOV TRANSLATED FROM THE RUSSIAN BY L. A. THOMPSON TRANSLATION EDITED BY P. H. WALKER PERGAMON PRESS OXFORD · LONDON · EDINBURGH · NEW YORK PARIS · FRANKFURT 1964 PERGAMON PRESS LTD. Headington Hill Hall, Oxford 4 & 5 Fitzroy Square, London W.l PERGAMON PRESS (SCOTLAND) LTD. 2 & 3 Teviot Place, Edinburgh 1 PERGAMON PRESS INC. 122 East 55th Street, New York 22, N.Y. GAUTHIER-VILLARS ED. 55 Quai des Grands-Augustins, Paris 6 PERGAMON PRESS G.m.b.H. Kaiserstrasse 75, Frankfurt am Main Distributed in the Western Hemisphere by THE MACMILLAN COMPANY · NEW YORK pursuant to a special arrangement with Pergamon Press Limited Copyright © 1964 PERGAMON PRESS LTD. Library of Congress Catalog Card Number 63-11359 PeryjinpOBaHHe no B03MymeHHK> Set in Monotype Times 10 on 12 pt. and printed in Great Britain by W. & G. Baird Ltd., Belfast INTRODUCTION In this book the author deals exclusively with the principle of compensation as applied to automatic control systems in order to permit simultaneous satisfaction of steady state and transient specifications. The original Russian manuscript uses a terminology rather different from that given in English and American textbooks dealing with this subject. For example, the well-established terms of Series Compensation and Feedback Compensation are not used and the author refers to tracing systems rather than position control systems. In the main the author's terminology has been retained except in the cases where some ambiguity of ideas occurred, but it is hoped that in this, the edited versions of the translation, any errors and imperfections have been reduced to a minimum. P. H. W. Vll FOREWORD TO THE ENGLISH EDITION The aim of the present book is to acquaint the reader with the principles of control associated with the use of excitation as a control- ling or regulating effect. Automatic systems incorporating an exci- tation effect, whether they be multi-pulse systems or contain only a single excitation pulse in the control zone, are some of the most important devices in the field of regulation and control. Despite the fact that the importance of constructing such systems has been recog- nized and although these ideas are very fruitful technologically, the theoretical development of these systems is lagging behind that of principles of deviation control. As far as is known to the author, there has been no attempt as yet to present a general account of the theory and applications of automatic control systems based on the excitation effect. Although this book was written with this object in view, it has a more modest aim—namely, the presentation in broad outline of fundamental results of research. The author hopes it will be of use to the English reader and promote the exchange of ideas between research workers. G. M. ULANOV Moscow, 1962. IX CHAPTER I INTRODUCTION 1. GENERAL IDEAS As a result of modern developments in automation and its scien- tific basis—the theory of automatic regulation and control as an engineering science—research workers and engineers are now occu- pied in finding the best possible means of controlling various objects, and developing laws and principles of control. The present brochure deals with one of the comparatively little- developed branches of control connected with the principle of excita- tion (invariance) regulation, and corresponding methods and pro- cedures of measurement, transmission and conversion of information in regulation and control systems. Generally speaking, this branch can be characterized by the use of processes of compensation of excitation. The mathematical principle of these processes has now become the principle of invariance, which was introduced into the theory and practice of automatic control by the work of Soviet scientists: N. I. Luzin, V. S. Kulebakin, A. I. Ishlinskii, B. N. Petrov, A. G. Ivakhnenko, P. I. Kuznetsov and others [1-22]. The term "invariance" is also used to mean compensation of excitation, that is, making a given automatically regulated system fully or partially independent of the excitation processes affecting it. In such automatic control systems, fundamental excitation, which has the most marked effect on processes of regulation, measurement, etc., is often distinguished from secondary excitation. Such typical, external excitations are usually of the loading type and vary the operating conditions of automatic systems (measuring systems, tracing systems, instruments, servomechanisms, etc.) and programme effects controlled by them. These external excitations are normally measured or simply transmitted along various channels to the auto- matically regulated system. The task of measuring or transmitting the excitations usually results in a tendency to eliminate their internal 1 2 EXCITATION CONTROL effect due to the organized effect they have on the automatically regulated system, aimed at achieving better stabilization or repro- ducing a set programme of work for the system. Other methods may be suggested to reduce the effect of external excitations, particularly those due to the internal properties—including non-linear proper- ties—of the systems under consideration. In this case, of course, other secondary external excitations will affect the operating con- ditions of the system, and will not be compensated. The following conditions of invariance are normal for linear, stationary systems of automatic control : A (D) = 0; D s -1 X at where A^D) is the minor of the expression and determines the move- ment of the controlled coordinate x(t) under the influence of an external excitation/(0, usually given in the form: x(t) = ^9/(f); Re A < 0, ft A(D) where X is the root of the equation A(D) = 0. k Some of these conditions may apply when trying to achieve invari- ance x(t) in relation to excitations which may also be excitations from the point of view of other coordinates of the system (this latter case corresponds to conditions of selective invariance—the autono- mous nature of a system). In more complicated systems, including non-linear and non-stationary systems, these conditions are, of course, more complex. Moreover, there is always the question of whether it is physically possible to realize the conditions of invari- ance, and the general problem of solving the mathematical equations involved in complicated systems of automatic control. To a considerable extent, excitation compensation or invariance embraces a large number of ideas, methods, and specialized scientific problems, based on practical experiments involving large amounts of factual material. The fundamental fields of application of the principle of invariance are pulse-operated combined control systems and combined tracing systems, independent automatic control, com- pounding, the construction of systems on an open control cycle, self-adjusting systems, correcting systems of the discrete filter type, simulating and computing devices. The principle of invariance INTRODUCTION 3 proved to be particularly valuable when constructing combined tracing systems having a high dynamic accuracy. These servo- mechanisms, operating in open and closed cycles, with two drive sources, etc., showed high dynamic response qualities, making it possible to achieve the limiting values set for the coordinates, velo- city, acceleration of the servomechanism, etc., which characterize the level of optimization reached. 2. A SHORT HISTORICAL SURVEY The historical development of the principle of excitation regu- lation is very impressive. It is without doubt the oldest regulation principle and dates back to a previous era. Indeed, the first devices for the control of windmills, invented by the Arabs some thousand years ago, already embraced the principles of load control, which lay in the fact that the angular velocity of the windmill was con- trolled according to variations in the sail area as a function of the external load torque. Modern aspects of excitation control and regulation are usually associated with the French scientist Poncelet—and the Russian, Chikolev [23,24], who gave descriptions and technical designs of regu- lators based on the effect of the external load of the control system. The swing towards the devices of Poncelet (1830) and Chikolev (1874) was connected historically with failures (in the mid-19th century) in the application of regulators based on the principle of deviation (Watt governors), which seemed at one time to be inadequate. Then a new type of regulator appeared, different in principle from the Watt type and regulating according to changes in the directly measurable load, and these had an important effect on all control devices. It was subsequently established theoretically that a combi- nation of regulation based on deviation (Watt type) and on the principle of load regulation (Poncelet-Chikolev) can often give the best results. These principles and developments, however, seemed to have been completely forgotten until recent times, when their resurgence and technical justification came about as a result of constant improve- ments to automatic devices, and the consequential increase in the standard of accuracy, speed, etc., of regulation demanded. During this period the theory and even the principle of excitation control 4 EXCITATION CONTROL and regulation caused much discussion and argument. The central point of these discussions was the work of G. V. Shchipanov pub- lished in 1939 [25] on the conditions of full compensation, which was an attempt to develop an "ideal regulator" in which error would be reduced to zero. However, Shchipanov's circuit and a number of his assertions regarding the universality of an "ideal" regulator turned out to be impossible and contained errors, as emerged from a dis- cussion on the subject in 1940 [26-28]. On the other hand, Shchipanov put forward a remarkable idea concerning compensation for external effects as the operating principle of a number of automatic regu- lators, and this proved fruitful. Even this general principle and its importance in the theory and practice of automatic control was decried by its critics, who asserted that the principle of compensation could never be realized in any physical system. After this discussion a long time elapsed during which no funda- mental or significant developments occurred in the theory of auto- matic control systems using excitation compensation. The diffi- culties associated with investigations into this problem meant that it was within the capabilities of only a few scientists working in the fields of mathematics, mechanics and automation, notably N. I. Luzin, V. S. Kulebakin, B. N. Petrov, P. I. Kuznetsov and A. G. Ivakhnenko. They were responsible for the basic research which proved that the idea of excitation compensation could in fact be applied in theory and in practice to a number of physical systems, particularly automatic control systems [1-7]. The work of these Soviet scientists, and also that of some foreign research workers (Moore et al), led to a fundamental change in the situation as regards the question of excitation compensation invari- ance. From then on, the efficiency of this principle became so obvious that its use was no longer in doubt, and there was an end to the flood of papers on its impracticability. Moreover, the use of such compen- sation in practical engineering problems developed rapidly, con- siderably outstripping its theoretical development. For example, whilst discussions in respect of the basic theory were at their height in the Soviet Union, there appeared extremely important and significant designs for systems of combined control of aviation motors, which were much more simple and reliable, and often produced much better results, than the normal method of control based on the principle of deviation. INTRODUCTION 5 Just before the beginning of the Second World War, the Soviet Air Force adopted a system of control of aviation motors whereby any external movement on the part of the pilot represented a new programme of work for the aviation motor and at the same time a transference programme for the controlling system. Many regu- lators of this type (for the pressure feed of aviation motors) were described, constructed and patented, and thus Soviet engineers showed that regulators could be made with a very high degree of accuracy, without abandoning the earlier designs for pressure feed regulators and kinematic control systems of aviation motors, simply by using a simple four-terminal transmitting mechanism. The main result was that combined control made it possible to solve the prob- lem of building fast, manoeuvrable aeroplanes which obey control signals accurately—such famous aircraft as the fighter IL-2 with an AM-38F motor. Ideas of control and regulation based on excitation have under- gone particularly rapid development in the recent past, and a number of specialized branches of regulation control have been formed in various Soviet republics, all working on the problem of excitation control and regulation, together with that of compatible control based on excitation and deviation. Amongst them—and this group doubtless takes pride of place—is the group of Ukrainian scientists (A. I. Ishlinskii, A. G. Ivakhnenko, A. I. Kukhtenko, O. G. Kryzhanovskii et al), which is delving deeply into problems of invariance in automatic control systems. A. G. Ivakhnenko devoted his doctor's dissertation and his book Electro-automation [12] to this problem. He gives a far-reaching theoretical analysis of control processes in combined systems of automatic control, and evolves high-quality tracing systems based on theoretical research. He establishes a number of characteristics peculiar to combined systems, including such important conclusions as proof of an integral control effect in combined systems dependent on the choice of excitation paths. In the autumn of 1958 the Technical Sciences Branch of the Ukrainian Academy of Sciences held a conference covering wide and specialized fields of the theory of invariance and its applications to the theory of automatic control. This conference considered various fields of research on compen- sation of excitation, invariance, and principles of regulation based on excitation. Work done in this direction was summarized, and the 6 EXCITATION CONTROL following scientific and technical problems planned for the next few years : (a) Development of the theory of invariance as applied to regu- lation and control with additional effects based on ancillary and control point setting excitations for linear systems, with constant and variable coefficients, and with lag, and also for self-adjusting systems. (b) Investigation of new ideal methods of measuring excitation effects, and the design of corresponding devices which measure excitation and loads of various characters. (c) Development of methods of analysis and synthesis, and methods of computing these systems. (d) Research into, and classification of, excitations and loads in various industrial systems, and the collection of statistical data on this and a number of other problems. This introduction cannot, of course, pretend to be a complete and exhaustive description of excitation control: it is merely intended to acquaint the reader with the fundamental questions arising in this context, and problems associated with it.

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