U.S. patent application number 10/229041 was filed with the patent office on 2003-03-20 for electrical power control system, and method for setting electric state variables and/or parameters in a current conductor.
Invention is credited to Rehtanz, Christian, Westermann, Dirk.
Application Number | 20030053275 10/229041 |
Document ID | / |
Family ID | 8184113 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030053275 |
Kind Code |
A1 |
Rehtanz, Christian ; et
al. |
March 20, 2003 |
Electrical power control system, and method for setting electric
state variables and/or parameters in a current conductor
Abstract
The invention is directed toward an electrical power control
system (1) in an electrical power system, having: a power control
unit (2) for setting electric state variables and/or parameters in
a current conductor, to be controlled, of the electrical power
system, having: means (3) for -detecting electric characteristic
values (u.sub.1) of the current conductor; a function processor for
applying a control function (F.sub.1(u.sub.1)) from a mathematical
set of control functions to the electric characteristic values, and
for determining controlled variables (y) for achieving the
parameters; and coordination means for determining a control
function (F.sub.1(u.sub.1)) from the set of control functions with
the aid of operating states of the electrical power system. This
system renders it possible to achieve a predictive tuned control of
the electrical power control system which can also stabilize
unusual operating states of the electrical power system.
Inventors: |
Rehtanz, Christian;
(Baden-Dattwil, CH) ; Westermann, Dirk; (Zurich,
CH) |
Correspondence
Address: |
Robert S. Swecker
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
8184113 |
Appl. No.: |
10/229041 |
Filed: |
August 28, 2002 |
Current U.S.
Class: |
361/115 |
Current CPC
Class: |
Y02E 40/20 20130101;
Y02E 40/22 20130101; H02J 3/06 20130101; H02J 3/1842 20130101 |
Class at
Publication: |
361/115 |
International
Class: |
H01H 073/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2001 |
EP |
01810836.5 |
Claims
1. An electrical power control system (1) in an electrical power
system, having: a power control unit (2) for setting electric state
variables and/or variable parameters in a current conductor, to be
controlled, of the electrical power system, having: means (3) for
detecting electric characteristic values (u.sub.1) of the current
conductor; a function processor for applying a control function
(F.sub.1(u.sub.1)) from a mathematical set of control functions to
the electric characteristic values, and for determining controlled
variables (y) for achieving the state variables and/or parameters;
and coordination means for determining a control function
(F.sub.1(u.sub.1)) from the set of control functions with the aid
of operating states of the electrical power system.
2. The electrical power control system (1) as claimed in claim 1,
characterized in that the coordination means has: a coordination
control unit (4), having means (5) for detecting electric
metacharacteristic values (u'.sub.2) of the electrical power system
which characterize the operating state of the electrical power
system; a coordination processor for applying a mapping (G) to the
metacharacteristic values (u'.sub.2) for the purpose of determining
an item of selection information (u.sub.2) for a suitable control
function (F.sub.1(u.sub.1)); means (6) for transmitting an item of
selection information (u.sub.2) at a satisfactory rate via the
suitable control function (F.sub.1(u.sub.1)) to the power control
unit (2); and a metafunction control processor in the power control
unit (2) for determining the suitable control function
(F.sub.1(u.sub.1)) with the aid of the transmitted item of
selection information (u.sub.2).
3. The electrical power control system (1) as claimed in claim 2,
characterized in that the metafunction control processor has means
for applying a metacontrol function (F.sub.2(F.sub.1(u.sub.1),
u.sub.2)) which determines the suitable control function
(F.sub.1(u.sub.1)), and the item of selection information (u.sub.2)
further contains electric metacharacteristic values which are used
when applying the metacontrol function (F.sub.2(F.sub.1(u.sub.1),
u.sub.2)) in order also to determine the controlled variables.
4. The electrical power control system (1) as claimed in one of
claims 2 to 3, characterized by a high-speed link (6) between the
coordination control unit (4) and the power control unit (2).
5. The electrical power control system (1) as claimed in one of
claims 2 to 4, characterized in that the power control unit (2) and
the coordination control unit (4) are combined in one device.
6. The electrical power control system (1) as claimed in one of
claims 1 to 5, characterized in that the coordination processor,
the metacontrol function processor and/or the function processor
are implemented as programs for a data processing system.
7. The electrical power control system (1) as claimed in one of
claims 2 to 6, characterized in that the metacharacteristics are at
least partially identical to the characteristics.
8. The electrical power control system (1) as claimed in one of
claims 2 to 7, characterized in that the metacharacteristics are
measured at least partially in other areas of the electrical power
system than in the current conductor to be controlled.
9. The electrical power control system as claimed in one of claims
1 to 8, characterized in that it further has an analyzing system
(7) for analyzing the characteristics and/or the
metacharacteristics, and for checking and/or, if appropriate,
changing the control functions (F.sub.1(u.sub.1)), the mapping (G)
and/or the function of the metafunction control processor as a
function of a result of the analysis.
10. The electrical power control system (1) as claimed in claim 9,
characterized in that the analyzing system further has means for
analyzing external characteristic values (u.sub.set), which can be,
or are provided by a power management system (8) of the overall
electrical power system.
11. The electrical power control system as claimed in one of claims
2 to 10; characterized in that the set of control functions
(F.sub.1(u.sub.1)) is a countable plurality of control functions
(F.sub.1(u.sub.1)) which is determined by a metacontrol function
(F.sub.2(F.sub.1(u.sub.1), u.sub.2)).
12. The electrical power control system (1) as claimed in one of
claims 2 to 11, characterized in that the set of control functions
constitutes a continuum which is described by a metacontrol
function (F.sub.2(F.sub.1(u.sub.1), u.sub.2)).
13. The electrical power control system (1) as claimed in one of
claims 1 to 12, characterized in that the control functions
(F.sub.1(u.sub.1)) can regulate the controlled variables (y) such
that values of prescribed electric characteristics of the current
conductor to be controlled can be kept within prescribed, stable
ranges of values, a first control function (F.sub.1(u.sub.1)) for
normal operation being able to comply with first stable ranges of
values, and at least one second control function (F.sub.1(u.sub.1))
for a change in the operating state being able to comply with
second stable ranges of values, which also cover the first stable
ranges of values.
14. A method for setting electric state variables and/or parameters
in a current conductor, to be controlled, of an electrical power
system, having the following steps: establishing electric
metacharacteristic values (u'.sub.2); applying a mapping (G) to the
metacharacteristic values (u'.sub.2) in order to generate an item
of selection information (u.sub.2) with regard to a control
function (F.sub.1(u.sub.1)) to be applied; applying the item of
selection information (u.sub.2) to a metacontrol function
(F.sub.2(F.sub.1(u.sub.1), u.sub.2)) which determines a control
function (F.sub.1(u.sub.1)) to be applied from a mathematical set
of control functions; and applying the established control function
(F.sub.1(u.sub.1)) to electric characteristic values (u.sub.1) of
the current conductor which fixes the controlled variables (y) for
controlling the current conductor.
15. The method as claimed in claim 14, characterized in that a
control function (F.sub.1(u.sub.1)) is determined with the aid of
the item of selection information (u.sub.2), which is built into
the control function (F.sub.1(u.sub.1)) as modulating term.
16. The method as claimed in claim 14 or 15, characterized in that
the metacharacteristics (u'.sub.2) are at least partially identical
to the characteristics (u.sub.1).
17. The method as claimed in one of claims 14 to 16, characterized
in that the metacharacteristics (u'.sub.2) are measured at least
partially in other areas of the electrical power system than in the
current conductor to be controlled.
18. The method as claimed in one of claims 14 to 17, characterized
in that the mapping (G) assigns specific ranges of values to
metacharacteristics (u'.sub.2) of specific items of selection
information (u.sub.2) for control functions (F.sub.1(u.sub.1)), and
when the metacharacteristic values (u'.sub.2) belong to a specific
range provides the metacontrol function (F.sub.2(F.sub.1(u.sub.1),
u.sub.2)) with the selection information (u.sub.2) belonging to
this range.
19. The method as claimed in one of claims 14 to 18, characterized
in that the selection information (u.sub.2) further includes
electric metacharacteristic values which are used in the
application of the metacontrol function (F.sub.2(F.sub.1(u.sub.1),
u.sub.2)) in order to determine the controlled variables (y).
20. The method as claimed in one of claims 14 to 19, characterized
in that an analysis is additionally carried out in which the
characteristic values and/or the metacharacteristic values
(u'.sub.2) are used to check and/or, if appropriate, to change the
control functions (F.sub.1(u.sub.1)), the mapping (G) and/or the
metacontrol function (F.sub.2(F.sub.1(u.sub.1), u.sub.2)).
21. The method as claimed in claim 20, characterized in that a
period (.DELTA.T.sub.CC) required for carrying out the method from
establishing electric metacharacteristics (u'.sub.2) to applying
the fixed control function (F.sub.1(u.sub.1)) to electric
characteristics of the current conductor is shorter than a time
interval (.DELTA.T.sub.CR) which is provided for carrying out the
analysis and for changing the control functions (F.sub.1(u.sub.1)),
the mapping (G) and the metacontrol function
(F.sub.2(F.sub.1(u.sub.1), u.sub.2)).
22. The method as claimed in claim 21, characterized in that the
period (.DELTA.T.sub.CC) is at least one hundred times shorter than
the time interval (.DELTA.T.sub.CR).
23. The method as claimed in claim 22, characterized in that the
period (.DELTA.T.sub.CC) is at least one thousand times shorter
than the time interval (.DELTA.T.sub.CR).
24. A controlling system in an electrical power control system (1)
for a current conductor to be controlled in an electrical power
system, having: a mathematical set of control functions
(F.sub.1(u.sub.1)) which are capable of keeping electric state
variables and/or parameters of the controlled current conductor
within prescribed, stable ranges, there being provided for normal
operation a base control function (F.sub.1(u.sub.1)) which can keep
the electric state variables and/or parameters within first
prescribed stable ranges, and the further control functions
(F.sub.1(u.sub.1)) having larger stable ranges with reference to
these electric state variables and/or parameters than the base
control function (F.sub.1(u.sub.1)).
25. The controlling system as claimed in claim 24, characterized in
that a metacontrol function (F.sub.2(F.sub.1(u.sub.1), u.sub.2))
can determine one of the control functions (F.sub.1(u.sub.1)) as
the control function (F.sub.1(u.sub.1)) to be applied, as a
function of electric metacharacteristic values (u'.sub.2) measured
in the electrical power system.
26. The controlling system as claimed in claim 25, characterized in
that it further has a mapping (G) for mapping the
metacharacteristic values (u'.sub.2) onto an item of selection
information (u.sub.2) via the control function (F.sub.1(u.sub.1))
to be applied, and in that the item of selection information
(u.sub.2) can be applied to the metacontrol function
(F.sub.2(F.sub.1(u.sub.1), u.sub.2)), in order to determine the
control function (F.sub.1(u.sub.1)) to be applied.
27. The controlling system as claimed in claim 26, characterized in
that the mapping (G) generates an item of selection information
(u.sub.2) which at the same time has electric metacharacteristic
values, and the metacontrol function (F.sub.2(F.sub.1(u.sub.1),
u.sub.2)) is designed in such a way that these metacharacteristic
values can be or are used for modulating the control function.
28. The controlling system as claimed in one of claims 24 to 27,
characterized in that it further has an analyzing system (7) which
can analyze, and if necessary adapt, the control functions
(F.sub.1(u.sub.1)), the metacontrol function
(F.sub.2(F.sub.1(u.sub.1), u.sub.2)) and/or the mapping (G) with
regard to the stability to be achieved.
29. The electrical power control system as claimed in one of claims
1 to 13, the method as claimed in one of claims 14 to 23, or the
controlling system as claimed in one of claims 24 to 28,
characterized in that it holds for each control function
(F.sub.1(u.sub.1)) from the set of control functions that the
following energy function V(T) exists for instants T.gtoreq.0: 3 V
( T ) V ( 0 ) + 0 T y ( t ) u ( t ) t
.A-inverted.u(.),T.gtoreq.0and the electrical power system is
thereby passive.
30. The electrical power control system as claimed in one of claims
1 to 13, the method as claimed in one of claims 14 to 23, or the
controlling system as claimed in one of claims 24 to 28,
characterized in that it holds for each control function
(F.sub.1(u.sub.1)) from the set of the control functions that the
following condition is fulfilled for the electrical power
system:{dot over (V)}={dot over (V)}.sub.PS+{dot over
(V)}.sub.CO.ltoreq.{dot over (V)}.sub.CO.ltoreq.0
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an electrical power control
system in an electrical power system with modifiable regulation or
control functions and a corresponding method for setting the
electric state variables and/or parameters in a current conductor
which belongs to such an electrical power system.
BACKGROUND OF THE INVENTION
[0002] Electrical power systems serve to provide and/or distribute
electrical power to consumers. They comprise generators such as
hydroelectric, coal-fired or nuclear power stations, storage
batteries and the like (sources), a conductor and cable system, and
consumers, that is to say electric consumers (loads). The wiring
and cable system connects the generators to the consumers in the
manner of a network. All permanently coupled elements participate
in such an electrical power system. Owing to the close links
between the various European power suppliers, it is possible to
speak of a continental electrical power system with reference to
Western Europe.
[0003] In principle, current is carried in the conductor system of,
an electrical power system in accordance with Ohm's law. So-called
power electronics compensators have been developed in order to
achieve a generally uniform capacity utilization despite
non-optimized conductors, and so as to be able to ensure an
economic, environmentally friendly and safe transmission of power.
These units, also denoted as FACTS (flexible alternate current
transmission system) devices, are capable of commutating power from
one conductor to another, for example by means of current
injection, phase-angle control, or power storage. They serve to
ensure the quality and quantity of power.
[0004] It is possible for a power control unit to react robustly
within certain limits to changes in the power supply situation, for
example owing to increased or decreased consumption of a power
consumer, in order to ensure the stability and the other goals,
defined above, for the electrical power system. For this purpose,
the power control unit measures various, electric characteristics
of the current flowing through the current conductor to be
controlled. The values thus determined are used by an algorithm to
determine the measures to be taken by the power control unit. By
means of suitable controlled variables, the power control unit
keeps the state variables/parameters of the conductor to be
controlled within prescribed ranges of values which define a stable
control range in their totality.
[0005] If a power network with a plurality of power control units
is disturbed, for example by a short circuit, it can happen that
two such units that are installed there attempt to compensate this
failure by means of countermeasures, the units possibly operating
against one another such that an instability of the overall
electrical power system can occur which can finally lead to damage
to components. Since the power control units have reaction times in
the millisecond range, while the central system control management
possibly cannot notice the disturbance until after 10 or more
minutes, and could then intervene manually, the prior art devices
are virtually incapable in principle of preventing such
problems.
[0006] In the case of relatively large distances between the power
generators participating in the instability, such instabilities
occur even more quickly, since the impedance between the generators
is decisive for this. Since power control units can also enlarge
the impedance, and thus the apparent distance between generators
increases due to the use of such devices, their use increases the
risk of instabilities in the system.
[0007] Configuring a power control unit is a special design
activity which must be carried out for each individual power
control unit in a specific situation. All other control units of
the electrical power system must be taken into account in designing
a power control unit which is to be integrated.
[0008] If appropriate, all other power control units of the system
must additionally be adapted to the new situation, which has
resulted from the integration of a further power control unit, so
that these can keep the control in a stable range of values.
[0009] The required adaptation is performed with the aid of
computing methods by solving systems of differential equations
which describe the behavior of the electrical power system. Since
such complex systems of equations cannot sensibly be solved in one
step, subsystems are initially calculated and combined as
simplified equations to form metasystems of equations. This mode of
procedure is very laborious and compute-bound, all the more so that
an analysis must be carried out repeatedly for different load
states of the electrical power system.
[0010] Controlled transmission paths are presently becoming
increasingly necessary in order to provide the transmission
logistics required to operate transmission systems competitively.
However, the number of the controlled current conductors is
presently limited, since the link control system of the overall
system is incapable of coping with potential adverse interactions
between the controlled conductors. This problem could possibly be
eliminated by using control units for the overall network, but
these would require a completely new high-speed network control
system. Even then, however, an adverse interaction could not be
reliably excluded.
[0011] There is therefore a need for power control systems which
are capable of operating even in the case of disturbances in stable
ranges, and which require no changes when enlarging or modifying
the overall system. It is therefore the object of the invention to
provide corresponding devices and methods which, owing to their
"neutrality", can be operated without problems in the case of the
most varied changes to the electrical power system.
SUMMARY OF THE INVENTION
[0012] This object is achieved by providing an electrical power
control system in accordance with the independent patent claim 1,
the method in accordance with the independent patent claim 14, and
the controlling system in accordance with the independent patent
claim 24. Further advantageous refinements of the invention follow
from the dependent patent claims, the description and the attached
drawings.
[0013] The invention is based on the principle of allowing, with
regard to novel transmission possibilities and more effective
network utilization, a system enlargement which is as effective as
possible and avoids a complete redesign of the overall system with
reference to control.
[0014] In one aspect, the invention relates to the principle of
predictive tuning, in which the various electrical power control
systems in an electrical power system carry out a coordination with
the electrical power system.
[0015] In a further aspect, the invention relates to an approach
for controlling power conductors in the case of which it is
possible in all operating states to comply with stable ranges of
electric characteristics which are at least not smaller than the
stable range of normal operation.
[0016] In yet another aspect, the invention relates to a control
system for power conductors which can, within a very short time,
react adequately and in a fashion maintaining stability to changes
in operating state.
[0017] In a further aspect, the invention relates to a control
system which can be used both for AC systems and for DC
systems.
[0018] The invention is part of a series of measures which serve
the purpose of the above-defined object, and which are combined
under the term NISC (TM) "nonintrusive system control
architecture".
[0019] The invention is initially directed to an electrical power
control system in an electrical power system, having:
[0020] a power control unit for setting electric state variables
and/or variable parameters in a current conductor, to be
controlled, of the electrical power system, having:
[0021] means for detecting electric characteristic values of the
current conductor;
[0022] a function processor for applying a control function from a
mathematical set of control functions to the electric
characteristic values, and for determining controlled variables for
achieving the state variables and/or parameters; and coordination
means for determining a control function from the set of control
functions with the aid of operating states of the electrical power
system.
[0023] Here, a power control unit is to be understood as a
generically typical device for controlling a current conductor, as
they are known in the prior art, for example FACTS devices,
regulating transformers, simple switches, switched compensation
elements and the like, it being possible, if appropriate, for the
device according to the invention to have additional elements which
enable it to execute the additional functions of the invention.
Most of the elements used to control circuits can be combined with
the invention. It is also possible to use the invention to control
a completely controlled conductor, for example using DC
technology.
[0024] A current conductor to be controlled is a link between two
network nodes, such as a cable or an overhead line, for example for
connecting generators or for the connection to consumers, in an
electrical power system, in which the power control unit is
installed and whose electric state variables/parameters are to be
controlled. Electric state variables or parameters of the current
conductor to be controlled are to be understood as those electric
variables which can serve for describing the current flowing in the
conductor, for example its voltage or current intensity, the phase
angle (if an AC system is involved) and the impedance. In this
case, a state variable is a variable property of the power, while a
parameter is to be understood as a physical property of the
carrier.
[0025] The power control unit can measure various electric
characteristics relevant when complying with the state
variables/parameters, and can derive controlled variables from the
measured values. The electric characteristics are generally tapped
in this case directly at the current conductor to be controlled. It
may be noted that the state variables and/or parameters of the
current conductor and the electric characteristics can be identical
or at least overlapping, since both can be determined on the same
current conductor.
[0026] The controlled variables are, in turn, numerical values
which are relayed to an actuating element which is not part of the
invention and is known from the prior art, and which thereupon
appropriately adapts the state variables and/or parameters of the
current conductor to be controlled.
[0027] The derivation of the controlled variables from the
characteristic values is performed with the aid of a control
function in a function processor which has at least the electric
characteristics as parameters and which calculates them with the
aid of prescribed algorithms such that the controlled variables
emerge as the result. The term control function is to be widely
understood in this case and comprises all possible assignment
methods including the use of value tuple or value pair tables.
[0028] A function processor is to be understood in the sense of the
present invention as any means, be it a data processing program or
a special analog or switching logic unit which is capable of
executing the control function or all the control functions from
the set of control functions.
[0029] According to the invention, the control function to be
applied is determined from a set of control functions by virtue of
the fact that the coordination means undertakes a suitable
detection of the current operating state and uses this state to
determine the control function. The determination is performed in
this case from a set of control functions, the term set requiring
to be understood in the mathematical sense and comprising a
countable number of various control functions, just as it does an
infinite number resulting from the metacontrol function.
[0030] The term determination is likewise to be interpreted widely.
Thus, it can be performed in the modification of a prescribed
control function by special terms dependent on the operating state,
as it can, likewise, by the simple selection of one of several
constant control functions.
[0031] All values and controlled variables used are preferably used
as vectors conditioned by the system, in order to permit simple use
in the functions and/or mappings. Account has been taken of this by
using appropriate underlined variables. However, it goes without
saying that it is also possible to use other types of value
conditioning should these appear to be feasible, and/or represent
the respectively current state of the art.
[0032] What is involved, therefore, is a process which has a total
of three steps and can be executed with the aid of the electrical
power control system according to the invention:
[0033] 1. The operating state of the electrical power system is
determined--somewhere--in the system. Said state is used in
order
[0034] 2. to determine a control function to be applied; and
[0035] 3. the control function is applied to values of
characteristics in order to generate controlled variables.
[0036] Various possibilities are available for implementing the
coordination means, in particular. In a preferred embodiment, the
coordination means has:
[0037] a coordination control unit, having:
[0038] means for detecting electric metacharacteristic values of
the electrical power system which characterize the operating state
of the electrical power system;
[0039] a coordination processor for applying a mapping to the
metacharacteristic values for the purpose of determining an item of
selection information for a suitable control function;
[0040] means for transmitting an item of selection information at a
satisfactory rate via the suitable control function to the power
control unit; and a metafunction control processor in the power
control unit for determining the suitable control function with the
aid of the transmitted item of selection information.
[0041] The electric metacharacteristics should be selected such
that they can give a sufficiently good overview of the respectively
current operating state of the electrical power system. Which
metacharacteristics are suitable also depends on the "intelligence"
of the mapping which uses the metacharacteristic values to generate
an item of selection information which is then used by the
metacontrol function in order to determine the control function to
be applied. The mapping is an important component in this preferred
embodiment of the invention, since here an evaluation of the
characteristics with regard to the putative operating state is
undertaken, and the most suitable "behavior" of the power control
unit is prescribed with the aid of this estimate.
[0042] The item of selection information is a datum or a collection
of data, for example vectorial, in a suitable form in order to be
used by the metacontrol function and to determine the actual
control function to be applied.
[0043] The item of selection information is transmitted by means of
a transmission means from the coordination control unit to the
power control unit, where it is used.
[0044] According to the invention, in this case the transmission is
to be performed at a satisfactory rate. This is to be understood to
mean that the transmission is performed so quickly that the
electrical power control system according to the invention can
react sufficiently quickly in order to maintain the electrical
power system in a stable state even in the case when operating
states are changing.
[0045] The electrical power control system according to the
invention can be characterized in that the metafunction control
processor has means for applying a metacontrol function which
determines the suitable control function, and the item of selection
information further contains electric metacharacteristic values
which are used when applying the metacontrol function in order also
to determine the controlled variables.
[0046] It is possible in this way also to make use of numerical
data such as measured values directly for the purpose. of
determining the control function, specifically to modify it. It is
therefore possible, for example, to make use of the same control
function for different operating states, but respectively to adapt
it, for example by (vectorial or scalar) multiplication by a factor
which is included in the item of selection information and by which
the result of the control function is multiplied, or otherwise used
for calculation.
[0047] One factor in the successful use of the electrical power
control systems according to the invention can be the rate at which
the control function can be determined, the transmission of the
item of selection information to the power control unit being
ascribed an important role. Thus, it is possible to use a
high-speed link between the coordination control unit and the power
control unit, in order to ensure sufficiently fast transmission. It
is likewise possible that the power control unit and the
coordination control unit are combined in one device. It is
possible in this case to dispense with a high-speed link, or the
latter can be optimized within such a device.
[0048] Various possibilities are open for implementing the various
components of the electrical power control system according to the
invention. Thus, the processors can be designed as a plurality of
hardware units or a single one, for example an analog computer. In
an embodiment which is preferred because it is easy to implement
and to integrate with the other components, the coordination
processor, the metacontrol function processor and/or the function
processor can be implemented as programs for a data processing
system.
[0049] Metacharacteristics detected by the coordination means are
intended to give as good an overview as possible of the respective
operating state of the electrical power system. The quality of the
obtainable information depends, however, not only on the derivation
of the operating states and the formulation, associated therewith,
of an item of selection information. In particular, it is preferred
that the metacharacteristics are at least partially identical to
the characteristics. The determination of the operating state can
be simplified and accelerated in this way, since use is made only
of variables which can be derived locally. However, this embodiment
places the highest demands on the evaluation of the
metacharacteristics and therefore on the "intelligence" inherent to
the mapping.
[0050] It is equally possible that the metacharacteristics are
measured at least partially in other areas of the power
distribution system than in the current conductor to be controlled.
It is then desirable to transmit in a way as free from delay as
possible for the purpose of quick identification of changes in the
operating state.
[0051] The design of the regular (normal-state) control function is
based on a thorough network analysis using conventional robust
control unit design methods, for example the H.sub..infin.
(H-infinite) control or the controlled Lyapunov functions (compare
below). Should the control unit thus designed prove to be robust
for all usual operating states, this network analysis need be
carried out only once, and there is then no longer any need for
further characterizations or structural changes.
[0052] However, if the operation is not robust, the efficiency of
the electrical power control system should be checked at regular
intervals, the controlled state variables/parameters requiring to
be adapted correspondingly. For this purpose, the electrical power
control system can preferably have an analyzing system for
analyzing the characteristics and/or the metacharacteristics, and
for checking and/or, if appropriate, changing the control
functions, the mapping and/or the function of the metafunction
control processor as a function of a result of the analysis.
[0053] In order further to improve the analytical capabilities of
the analyzing system, it can also be desirable to provide it with
additional information which renders possible a picture of the
operating state of the electrical power system as a whole. It is
sensible for this purpose to have recourse to existing power
management systems which provide such information. The invention
can therefore be characterized in that the analyzing system further
has means for analyzing external characteristics, which can be, or
are provided by a power management system of the overall electrical
power system. In addition to general information on the electrical
power system, such characteristics can also be desired variables
for the system which all the electrical power control units should
attempt to comply with, and which therefore must likewise be
incorporated in the design of the control functions, the mapping
and the metacontrol function.
[0054] As already mentioned, the term "determination" of a suitable
control function is to be interpreted widely. It covers both
modifications of an existing control function and selection from a
set. Consequently, the term "set" of control functions is also
variable. For example, the set of control functions can be a
countable plurality of control functions which is determined by a
metacontrol function. What is involved in this case is, for
example, a set of control functions which are numbered, the
metacontrol function constituting a simple list assignment which
assigns one of the control functions to specific stipulations from
the selection information.
[0055] The set of control functions can also constitute a continuum
which is described by a metacontrol function. In this case, for
example, the selection information features as a computing term in
the metacontrol function which then, in accordance with its
algorithm, generates a suitable control function from a base
control function, or modulates or modifies the result by its
application.
[0056] An important concept of the present invention is the setting
of stable ranges of values for the electrical power system to be
controlled. These stable ranges are defined initially for regular
operation, but, given changes to the operating state, may not have
new unstable ranges in which instabilities in the overall system
can come about. It is therefore preferred that the control
functions can regulate the controlled variables such that values of
prescribed electric characteristics of the current conductor to be
controlled can be kept within prescribed, stable ranges of values,
a first control function for normal operation being able to comply
with first stable ranges of values, and at least one second control
function for a change in the operating state being able to comply
with second stable ranges of values, which also cover the first
stable ranges of values.
[0057] The changes to the operating state can both be a malfunction
and a change in topology such as an operational extension (or
contraction) of the overall network which belongs to the electrical
power system. Individual control functions can preferably be given
in each case for the various categories of malfunction. In the case
of changes to the system, a range of control functions or an
appropriately modified control function or a combination of the
various possibilities is likewise provided.
[0058] The invention is likewise directed to a method which can be
executed, for example, with the aid of the electrical power control
system according to the invention. All that has been said with
reference to the apparatus also holds for the method presented
below, and vice versa, and so reciprocal reference is adopted and
made.
[0059] The invention is therefore further directed to a method for
setting electric state variables and/or variable parameters in a
current conductor, to be controlled, of an electrical power system,
having the following steps:
[0060] establishing electric metacharacteristic values;
[0061] applying a mapping to the metacharacteristic values in order
to generate an item of selection information with regard to a
control function to be applied;
[0062] applying the item of selection information to a metacontrol
function which determines a control function to be applied from a
mathematical set of control functions; and
[0063] applying the established control function to electric
characteristic values of the current conductor which fixes the
controlled variables for controlling the current conductor.
[0064] It holds here, as well, that the values used are, for
example, conditioned as a matrix or, preferably, as a vector, in
order to facilitate application of the various mappings or
functions.
[0065] A control function can be determined, for example, with the
aid of the item of selection information, which is built into the
control function as modulating terms. This is an application of the
invention in which the set of the control functions constitutes a
continuum whose elements are, as it were, fixed by the terms during
application of the metacontrol function. Of course, other methods
are also conceivable, in which a metacontrol function determines
one of a continuum of control functions.
[0066] As already stated with regard to the electrical power
control system according to the invention, the metacharacteristics
can be at least partially identical to the characteristics, in
order to simplify the measurement and to increase the rate at which
the method is executed.
[0067] Alternatively, or in addition, the metacharacteristics can
be measured at least partially in other areas of the electrical
power system than in the current conductor to be controlled.
[0068] The method can further be designed in a special embodiment
of the invention such that the mapping assigns specific ranges of
values to metacharacteristics of specific items of selection
information for control functions, and when the metacharacteristic
values belong to a specific range provides the metacontrol function
with the selection information belonging to this range. An actual
selection is therefore made in this case from a countable set of
control functions, a continuum of possible metacharacteristic
measured values, for example vectors, being grouped such that in
each case entire ranges of these values lead to the same control
function.
[0069] Again, as already explained, the selection information can
further include electric metacharacteristic values which are used
in the application of the metacontrol function in order to
determine the controlled variables. When substituted as terms into
the metacontrol function, the values therefore cause immediate
modulation of the control function and consequently influence the
controlled variables.
[0070] It is also additionally possible in the method according to
the invention to carry out an analysis in which the characteristic
values and/or the metacharacteristic values are used to check
and/or, if appropriate, to change the control functions, the
mapping and/or the metacontrol function. The possibility of
analyzing and changing the actual core logic in executing the
method is an important option for improving the method behavior,
since it is also possible in this way for unexpected variations in
the operating state of the electrical power system to be
adapted.
[0071] As already indicated, quick execution of the method is
preferred in order to permit a rapid reaction to changes in the
operating state of the electrical power system. Consequently, it is
preferred, in particular, that a period required for carrying out
the method from establishing electric metacharacteristics to
applying the previously fixed control function to electric
characteristics of the current conductor is shorter than a time
interval which is provided for carrying out the analysis and for
changing the control functions, the mapping and the metacontrol
function.
[0072] This period can be at least one hundred times shorter,
preferably at least one thousand times shorter than the time
interval.
[0073] The time interval for carrying out the analysis will usually
be approximately in the range from 5 to 15 minutes but can,
however, also be in the range of hours in the case of complex
analyses, while the method has to be able to react within seconds
or even fractions of seconds in order to avoid instabilities in the
electrical power system. Typical reaction times of control systems
can be in the range of around 50, for example from 30 to 100
milliseconds, but there are also even faster control units.
[0074] Another approach to describing the present invention can
reside in a controlling system which must satisfy specific
requirements.
[0075] In order to be able to ensure correct functioning of an
electrical power system, an electrical power control system must be
capable of keeping the system in a stable range, the so-called
coverage zone, with reference to the characteristics controlled by
it. This purpose is served by the control function, which is
designed such that under specific conditions it can comply with the
stable range. However, as explained in the introductory part,
conventional controllers frequently fail in the event of
disturbances and changes to the topology of the electrical power
system. The solution according to the invention consists in this
view in rendering more than one stable range possible by means of
various control functions, in which case the coverage zones, which
are to be complied with in the event of changes by the other
control functions, may not, in any case, be smaller than the
coverage zone in "normal" operation, since otherwise there would
arise after a change new unstable ranges in which the electrical
power system cannot be operated although the control would permit
these ranges on the controller.
[0076] The invention is therefore likewise directed to a
controlling system in an electrical power control system for a
current conductor to be controlled in an electrical power system,
having:
[0077] a mathematical set of control functions which are capable of
keeping electric state variables and/or variable parameters of the
controlled current conductor within prescribed, stable ranges,
there being provided for normal operation a base control function
which can keep the electric state variables/parameters within first
prescribed stable ranges, and the further control functions having
larger stable ranges with reference to these electric state
variables/parameters than the base control function.
[0078] This controlling system can preferably be characterized in
that a metacontrol function can determine one of the control
functions as the control function to be applied, as a function of
electric metacharacteristic values measured in the electrical power
system.
[0079] Furthermore, it can have a mapping (which corresponds to the
above-defined mapping) for mapping the metacharacteristic values
onto an item of selection information via the control function to
be applied, it being possible to apply the item of selection
information to the metacontrol function, in order to determine the
control function to be applied.
[0080] The mapping can preferably generate an item of selection
information which at the same time has electric metacharacteristic
values, and the metacontrol function is designed in such a way that
these metacharacteristic values can be or are used for modulating
the control function, as was explained above with regard to the
method.
[0081] Furthermore, the controlling system according to the
invention can have an analyzing system which can analyze, and if
necessary adapt, the control functions with regard to the stability
to be achieved.
[0082] An important, preferred aspect of the present invention,
which relates likewise both to the electrical power control system
and to the method and the controlling system, is the analysis and
formulation of control functions which satisfy the requirements
placed on stable operation.
[0083] By developing control functions that are as robust as
possible as early as in the planning phase, it is possible to avoid
frequent downloading of control functions and metacontrol functions
during operation.
[0084] Various approaches, which can also be combined with one
another, are available for achieving such robustness.
[0085] One approach originates from the field of passivity theory.
If a stable power system without a new, controllable device is
assumed, the system is passive when a specific energy function
reproduced below is satisfied.
[0086] It is therefore preferred that it holds for each control
function from the set of control functions that the following
energy function V(T) exists for all instants T.gtoreq.O: 1 V ( T )
V ( O ) + 0 T y ( t ) u ( t ) t .A-inverted.u(.),T.gtoreq.0,
[0087] V(0) being the energy function at the instant 0, y being an
electric output variable, and u being an electric input
variable,
[0088] and the electrical power system is passive.
[0089] If an additional network controller satisfies the same
conditions and is likewise passive, the two systems are likewise
passive and therefore stable in the case of parallel connection or
in a feedback loop. This means that the additional components do
not affect the stability itself if there is no power flow from the
system. This suffices for normal operation with fixed operating
conditions, but this approach is silent on the attenuation response
of the resulting system.
[0090] The other, very similar approach is the controlled Lyapunov
function for a system with the structure 2 x . = f ( x , u ) = f o
( x ) + t = 1 m u t f t ( x )
[0091] If the electrical power system is stable without control
input, it can be shown that there is a positive energy function
V.sub.PS (x), where
{dot over (V)}.sub.PS.ltoreq.0.
[0092] The system with the electrical power control system is
stable if in the event of combination of V.sub.PS with the energy
function of the controllable element V.sub.CO the resulting
function is a Lyapunov function for the new system.
[0093] This holds when the preferred embodiment is applied in
accordance with which it holds for each control function from the
set of the control functions that the following condition is
fulfilled for the electrical power system:
{dot over (V)}={dot over (V)}.sub.PS+{dot over
(V)}.sub.CO.ltoreq.{dot over (V)}.sub.CO.ltoreq.0,
[0094] V being the resulting energy function, V.sub.PS being the
energy function of the system before the addition of a new control
unit, and V.sub.CO being the energy function of the control unit.
By using the above approaches, a redesign of the electrical power
control systems can be avoided, and stable operation with other
control systems can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0095] The aim below is to explain the invention in more concrete
and further-reaching terms, reference being made to the attached
drawings, in which the following is illustrated:
[0096] FIG. 1 shows an electrical power control system according to
a preferred embodiment of the present invention, with a connected
analyzing system;
[0097] FIG. 2 shows, by way of example, stable ranges of an
electrical power system before and after a change to the
system;
[0098] FIG. 3 shows a schematic of the functional relationships
between the various components of the invention;
[0099] FIG. 4 shows the time sequence of the method according to
the invention including an analyzing step;
[0100] FIG. 5 shows the time profile of the method according to the
invention in the case of a changed operating state;
[0101] FIG. 6 shows, by way of example, the response of the
electrical power control system according to the invention in the
case of a three-phase error; and
[0102] FIG. 7 shows, by way of example, the response of the
electrical power control system according to the invention in the
case, of a growth in load.
DETAILED DESCRIPTION OF THE INVENTION
[0103] With reference to novel ways of transmission or
distribution, it is obligatory to provide a system response which
does not impair the rest of the system (except, if appropriate, for
the purpose of providing specific control functions as auxiliary
services). This is achieved by means of a system control
architecture which permits the control of transmission paths
(current conductors or cables), virtually without the rest of the
system being impaired. This system is therefore introduced as
"non-intrusive system control architecture (NISC)".
[0104] It is based on the idea of firstly defining the desired
functions for a controllable transmission system which can be
mapped onto a prescribed control device design in order to
implement these functions. The controller defined in functional
terms in such a way results in controllable components which are
power-electronic or hybrid or conventional components, and which
must be added to the system. These components fulfill only the
desired functions. It is decisive for the invention in this case
that the control design be implemented in a way such that the
remainder of the system is not negatively impaired, and all other
system components remain unaffected.
[0105] Various measures have been implemented in the scope of the
NISC approach, of which one is the electrical power control system
according to the invention with the associated method.
[0106] As a result, the transmitting and receiving ends of a
conductor seem to have a settable generator unit and a load with a
self-adjusting control response, which can then be designated as
non-intrusive with reference to the dynamics of the remainder of
the system. A certain robustness can be achieved by applying the
NISC approach, and this ensures a coordinated control of the
transmitting and receiving ends of a controlled transmission path
even under load peaks and in the event of faults.
[0107] The aim of the NISC architecture is to simplify the design
process such that novel transmission paths can be designed without
having to conduct extensive system studies. The required control
properties should neither negatively influence the overall system,
nor require a redesign of control units already implemented. In
addition, the architecture according to the invention permits a
control reaction to critical events and avoids inadequate, and
therefore incorrect, operation after changes in operating
state.
[0108] The result overall for the NISC architecture is the
following specifications:
[0109] the design of novel control units requires no redesign of
existing network control units;
[0110] various network control units operate in a coordinated
fashion with the same control approach;
[0111] the control units are robust with regard to the requirements
placed on the operation of the electrical power system (that is to
say diurnal and seasonal fluctuations in operating conditions);
[0112] the design of the control units for system control and for
auxiliary services is modular and can be scaled for different
control ranges;
[0113] there is no need for long-distance communication links,
which can therefore be avoided depending on design; and
[0114] no malfunction occurs in overload situations.
[0115] The aim below is to explain the functioning of the invention
by way of example with reference to a concrete embodiment.
[0116] FIG. 1 shows a schematic of the various components of this
exemplary embodiment. The electrical power control system 1 firstly
has a power control unit 2 which receives incoming measured values
u1 of various electric characteristics via an input channel 3. As
made plain by the underscoring, the characteristic values u.sub.2
can be present in this case as a vector, and this simplifies the
calculation. The power control unit now calculates the controlled
variables y by applying the control function to these values:
y=F.sub.1(u.sub.1).
[0117] In this case, however, the determination of the control
function F.sub.1 to be applied is added as a novel component
according to the invention. This can also be performed in the power
control unit 2. The purpose of determining the control function can
be served, for example, by a metacontrol function F.sub.2 into
which an item of selection information u.sub.2 is introduced such
that it follows overall for the calculation of the control function
that:
y=F.sub.2(F.sub.1u.sub.1), u.sub.2)
[0118] u.sub.2 can also be a vector in this case.
[0119] If, for example, a "normal" control function is assumed for
closed-loop control, it is possible to assume a "neutrality" of the
metacontrol function for this closed-loop control, that is to say
that the metacontrol function has no influence in the normal state,
and so it holds that:
F.sub.2(F.sub.1(u.sub.1), u.sub.2).congruent.F.sub.1(u.sub.1).
[0120] The item of selection information is generated in the
coordination unit 4 by applying a mapping G to measured values of
metacharacteristics u'.sub.2. The mapping G can be described in
general as:
G:u'.sub.2.fwdarw.u.sub.2.
[0121] The metacharacteristic values u'.sub.2 are fed via a
measuring channel 5 to the coordination unit 4, where, by applying
G, they are further processed by a suitable processor, for example
an appropriately programmed microcontroller. The coordination
undertaken there is time-variant and depends on the actual network
characteristics and the topology. Consequently, despite functional
parallels, the electrical power control system according to the
invention is not to be regarded as belonging to the class of
adaptive controllers. The principal difference resides in the
mapping G, which defines which type of characteristics are imaged
onto which item of selection information. In particular, by
comparison with centralized real-time network controllers, the
required set of high-speed data transmission is drastically
reduced, since there is no need for an additional broadband or
SCADA system.
[0122] The item of selection information u.sub.2 is transmitted,
for example, to the power control unit via a high-speed channel 6.
This channel 6 must be able, in any case, to operate so quickly
that the electrical power control system 1 can react quickly enough
to changes in the measured values u'.sub.2 in order to avoid
instabilities in the electrical power system. It is likewise
possible to implement the two units 2 and 4 in terms of one device
so that the channel 6 then would constitute only a parameter
transfer in a program, that is to say would be implemented inside a
CPU.
[0123] By implementing the metacontrol function and providing
selection information, the electrical power control system can be
adapted to new situations substantially better than is known in the
prior art. Important for successful determination of a suitable
control function is firstly, the detection of suitable
metacharacteristics, and secondly their mapping onto an item of
selection information. However, in the case of detection of a
suitably large number of metacharacteristics, this criterion is no
longer critical, since it is then assumed that the required
selection information can be generated by skillful mapping.
[0124] In order to obtain permanent control of whether the applied
mapping, the metacontrol function and/or the actual control
functions as well can still fulfill their function in the given
framework of the overall electrical power system, it is possible,
furthermore, to provide an analyzing system 7 which is connected by
connecting channels 11 and 12 to the power control unit 2 and the
coordination unit 4 and receives information which it subjects to
an analysis. The analyzing system 7 investigates the functions or
mappings used for their current ability to maintain the stability
in the electrical power system. No changes are undertaken if this
analysis shows that the currently used functions can maintain the
stability. If the result of the analysis is that instabilities can
occur in the case of specific operating states, the analyzing
system suitably adapts the set of the control functions, the
metacontrol function or the mapping. In addition to the internally
measured characteristics, it is also possible to use for the
analysis data u.sub.set, also including, if appropriate, desired
variables for the electrical power system, of a central power
management system 8 which is connected via a channel 9 to the
electrical power control system 1, specifically to the analyzing
system 7, and which can supply a global overview of the system
status. Use may also be made for this purpose of the SCADA database
10, which likewise contains information on the current state and
time profile of the electrical power system. It is possible in this
case to dispense with a direct link between the SCADA system and
the various control units according to the invention.
[0125] The aim of FIG. 2 is to explain how the term stable ranges
is to be understood. FIG. 2 illustrates two system state variables
X.sub.1 and X.sub.2 as a function of time on the X-axis and Y-axis,
respectively. Here, a range A denotes the range of values of the
two state variables within which the system is stable in the normal
operating state, the so-called coverage zone, and how it can be
complied with by a control function. In the event of a change in
the system, the control function is modified by the metacontrol
function, or exchanged for another control function which has other
stable ranges, denoted by B. It is a characteristic of the present
invention in this case that the new stable range overall is at
least not smaller than the old one, that is to say no regions occur
where originally stable operation was possible before the change,
but unstable states are present after the change. The original
stable range is therefore a subset of the new stable range of
operating points, and the new coverage zone is larger than the old
one.
[0126] It was possible in the prior art for such unstable ranges to
reoccur in the event of changes and they required a redesign of the
power control units affected.
[0127] Typical disturbance events which require a coordination of
control measures for network controllers are, for example:
[0128] short circuits in transmission elements;
[0129] overloading of electrical devices;
[0130] failures of electrical devices;
[0131] quick changes in the power flow, for example ones associated
with disturbances in power stations.
[0132] It is necessary to detect the abnormal situation in the
electrical power system in order to be able to carry out these
coordinated control tasks. One possibility for implementation in
this case is a heuristic analytical event reaction system such as
is illustrated in FIG. 3 as a state diagram. The box 20 in this
case represents the range of an electrical power control system 1
according to the invention, which exerts the actual control, while
the box 21 represents the analyzing system. There is a bubble 22,
which symbolizes the normal operation of the device, inside the
unit 20. If a critical event 25 occurs, a transition is made to the
bubble 23, the change control. After processing of, the critical
state, the change control decides whether to return to the normal
state via route 26 if no topological change has taken place, or
whether, in the event of the presence of a topological change 27,
to trigger an analysis trigger 24 which, via path 28, activates the
analyzing system 21, where a topological analysis and a setup of
the heuristic analytical event controller are undertaken. The
result of this analysis is downloaded in the form of modified (to
the extent necessary) control functions, metacontrol function or
mapping G into the range 20, use being made of the download path
29. The latter corresponds physically to the paths 11 and 12 shown
in FIG. 1.
[0133] The aim below is to explain by way of example the mode of
operation of the supplementary analyzing system according to the
invention. Knowledge of the operation of controllable devices in
critical situations can be formulated in generic rules. For
example, rules of this type are as follows for the case of a fast
power flow controller (PFC) as an example for a power control
unit:
[0134] 1. IF "short circuit on the PFC path" OR "short circuit on a
parallel path" THEN "slow down setpoint control of the PFC".
[0135] This coordinative measure prevents excessive power
oscillations after a short circuit followed by automatic reclosing.
The reason for this is that the power flows fluctuate violently
during the short circuit. Because of the short response time of
such PFCS, these respond immediately and attempt to reset the
setpoints. Consequently, the manipulated variables of the PFC are
strongly increased within a short period and reach the ir maximum
value even before the fault is cleared and the reclosing has
started. After clearing the disturbance and the fault, the
increased values of the variables can lead to oscillations. A
possible countermeasure is to slow down the setpoint control.
Moreover, a PFC can commutate the power flow on parallel paths such
that apparent power flows on the parallel paths can be influenced
by changes in the setpoints for active or reactive power flows on
the controlled path. Thus, it is possible by means of this measure
to avoid device overloading on parallel paths owing to changes in
setpoint.
[0136] 2. IF "device overload on parallel path of the PFC" THEN
"modify the P setpoint of the PFC".
[0137] As a first step for the automatic transformation of these
generic rules into concrete control actions it is necessary to
analyze the network topology automatically. The result is a mapping
of all the parallel paths onto the PFC path. This information is
used in order to create a rule base for the power control unit
according to the invention on the device control level for each
unit according to the invention in an electrical power system. The
rule base is part of the information downloaded from the analyzing
system.
[0138] Specific rule bases which represent coordinating measures
for malfunctions are a function of topology. They can only handle
the "next" event in each case. Once an equilibrium situation has
been reached after a disturbance, the rule bases must be adapted,
if necessary, in accordance with the new situation. The rule bases
must also be appropriately updated for regular changes in the
electrical power system.
[0139] The aim below is to explain in more detail the time sequence
of the analysis and the reaction of the electrical power control
system according to the invention. The analysis carried out in the
optional analyzing system can be, executed in prescribed intervals
in order to adapt the electrical power control system to new
conditions. A typical adaptation cycle (.DELTA.T.sub.CR) comprises
an operating condition analysis with a planning phase and a
downloading phase. The planning phase serves to fix new event
reaction schemes and structural control parameters, and determine
new setpoint conditions for, for example, active or reactive power
flow control or voltage control.
[0140] "Downloading" is the synonym for refreshing the
decentralized information on the status of the electrical power
system in the power control unit and/or the coordination unit. This
permits a coordinated control activity of the electrical power
control systems according to the invention even during
malfunctions.
[0141] FIG. 4 shows the time profile of this adaptation cycle. Time
is depicted on the X-axis, while the various components which are
active are illustrated on the Y-axis. A corresponds in this case to
the analyzing system, B to the coordination means and C to the
power control unit.
[0142] During a time phase .DELTA.T.sub.p, the planning 30 takes
place in A, and the downloading 31 is undertaken in all subranges
A-C. The remainder of the adaptation cycle .DELTA.T.sub.CR is
operated by the electrical power control system in a normal
operating mode, as it is characterized, for example, by the method
according to the invention. In terms of time, a typical adaptation
cycle can be in the range from 5 to 15 minutes, although shorter or
longer periods are also possible, for example, minutes, quarters of
an hour, or days, depending on the purpose of use and
requirements.
[0143] A critical factor in the application of the electrical power
control system according to the invention is the dynamic response
of the electrical power system.
[0144] The coordination must be carried out in accordance with the
changing operating conditions or critical events in the electrical
power system. The invention solves this problem by means of the
approach of predictive tuning. This control mechanism is activated
by trigger signals which characterize a malfunction in the system
and which are converted by the method according to the invention in
accordance with a locally implemented control method within the
electrical power control system according to the invention. As FIG.
5 shows, a cycle of time .DELTA.T.sub.cc is used, which is started,
for example, via a trigger 32 mediated by means of the
characteristic u'.sub.2, and fed to a control reaction unit 33. The
analysis of the cycle time .DELTA.T.sub.CC and of the normal
adaptation cycle .DELTA.T.sub.CR explains in this case, in
addition, that an online coordination of the various electrical
power control systems cannot be achieved in an electrical power
system, since it should be the case that
.DELTA.T.sub.CC<<.DELTA.T.sub.CR
[0145] Consequently, the concept according to the invention is
designated as predictive tuning, since the required analysis is
carried out before an execution cycle .DELTA.T.sub.CC begins.
[0146] Two simulation examples are intended below to explain the
invention with regard to the efficiency of the coordinating
measures. A typical network situation is assumed, in which three
different systems A, B and C are interconnected. C is connected to
B by a PFC in line BC2, A serves as backbone for B, which are
interconnected via lines AB1, AB2 and AB3. A uses a PFC in line AB1
in order to compensate the exchanged power. Within the system B, a
further PFC between the two generators in the range B serves the
purpose of controlling the inner range in order to avoid
disturbances. The PFCs are in this case those in accordance with
the invention.
[0147] Based on this fictional electrical power system, rule bases
and global information for the PFCs used are generated for the
numerical simulations with the aid of the methods described. The
following scenarios are used by a simulation environment in
MATLAB/SIMULINK, in order to show the properties of the predictive
tuning within a system.
[0148] 1. Three-phase short circuit in the connecting line AB2 in
the vicinity of the generator A3 at the instant t=0.1 for 100 ms
with reclosing after 220 ms.
[0149] Line AB2 was identified by a topological analysis as a part
of the parallel path of the two PFCs between A and B and within B.
The modules for the generic rule 1 react directly to the short
circuit and slow down the setpoint tuning of their corresponding
power control units by selecting a suitable control function. The
effect is to be seen from FIG. 6, in which the time profile is
illustrated on the X-axis, and the active power output of the
generator in the range A is illustrated on the Y-axis. As may be
seen, the two PFCs cause only a small rise in the variables during
the short circuit and the following reclosing. The damping is
better with the use of mechanisms according to the invention
(dashed line) than is known from the prior art (continuous
line).
[0150] 2. Power overloading owing to a rapid rise in the load at
the node B3 (part of the range B).
[0151] In the case of a stepwise increase in the power, the load
frequency controllers of the electrical power control systems
operate so as to cover the additional power requirement. The three
adopted PFCs in this case receive the power flow on the controlled
paths. Consequently, they cannot be used to transmit the excess
power. The capacity of the line AB2 which connects, inter alia, the
ranges A and B, is utilized to approximately 94% before the power
rises. In the case of a sudden power rise of 0.24 pu at the instant
t=1 s, the power frequency control contribution of the generator
must be transmitted via line AB2. Without the method according to
the invention (dashed line in FIG. 7, which shows the active power
flow of the line AB2 on the Y-axis), a certain overload results
(the line running at 0.62 pu in FIG. 7 characterizes the thermal
limit). Since the line is detected according to the invention as an
element of a parallel path to the monitored path AB1, the PFC
thereof counteracts the overload by increasing the setpoint for the
active power flow. This results in a power flow commutation, as a
result of which AB2 is relieved. At t=15 s, the power is once again
set to the original value (FIG. 7, continuous line). The control
system resets itself automatically when no further coordinating
control activities are required.
LIST OF REFERENCE SYMBOLS
[0152] 1 Electrical power control system
[0153] 2 Power control unit
[0154] 3 Input channel
[0155] 4 Coordination control unit
[0156] 5 Measuring channel
[0157] 6 High-speed channel
[0158] 7 Analyzing system
[0159] 8 Power management system
[0160] 9 Data channel
[0161] 10 SCADA database
[0162] 11 Connecting channel
[0163] 12 Connecting channel
[0164] 20 Actual control range
[0165] 21 Analyzing system
[0166] 22 Normal operation
[0167] 23 Change control
[0168] 24 Analysis trigger
[0169] 25 Critical event
[0170] 26 Return to the normal state
[0171] 27 Variation of the topology
[0172] 28 Activation path
[0173] 29 Download path
[0174] 30 Planning
[0175] 31 Downloading
[0176] 32 Trigger
[0177] 33 Control reaction
[0178] F.sub.1(u.sub.1) Control function
[0179] F2(F1 (u.sub.1), u.sub.2) Metacontrol function
[0180] G Mapping
[0181] u.sub.1 Characteristic values
[0182] u'.sub.2 Metacharacteristic values
[0183] u.sub.2 Selection information
[0184] u.sub.set External characteristic values
[0185] y Controlled variables
* * * * *