Excitation Control

103 Pages·1964·4.759 MB·English

by  G. M. Ulanov, D. W. Fry and W. Higinbotham (Auth.)

EXCITATION
CONTROL
BY
G. M. ULANOV
TRANSLATED FROM THE RUSSIAN
BY
L. A. THOMPSON
TRANSLATION EDITED BY
P. H. WALKER
PERGAMON PRESS
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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.