DESCRIPTION
Title of Invention: VOLTAGE STABILITY MONITORING DEVICE AND
METHOD
Technical Field
[0001]
The present invention relates to a voltage stability
monitoring device for monitoring power stability of an electric
power system.
Background Art
[0002]
In the related art, in an electric power system, it is
expected that a large amount of a power source (output variation
type power source) in which the output is varied depending on
the weather including a renewable energy (solar power
generation, wind power generation, or the like) is introduced.
In addition, in the recent year, as a result of progressive
liberalization of electric power in many countries, business
investment of the electric power system is suppressed, and an
electric power flow in the existing transmission line is
increased (heavy current flows). When the flow variation
(flow change) is increased in a heavy flow state, there is a
possibility that voltage stability of the electric power system
is degraded. Furthermore, when a failure occurs in the system
3
due to lightning strike or the like, the voltage stability of
the electric power system may deteriorate. A voltage
stability monitoring device which can present voltage
stability improvement countermeasure to a system operator by
accurately monitoring such a deterioration phenomenon of the
voltage stability is required.
[0003]
For example, as a background art of the present technical
filed, a paper that SUZUKI Mamoru, KISHIDA Yukio: "Voltage
Stability Online Monitoring System", Electrical Engineers of
Japan. B, 111(3), 1991 (NPL 1) is included. In this comment
paper, "Online constant period monitoring function" or
"Stability determination function at peak load" are described
(refer to page 248 to page 251).
[0004]
In addition, as the background art of the present
technical filed, JP-A-7-163053 (PTL 1) is included. This
publication describes that "there is provided calculation
means for calculating a monitoring index of voltage stability
in a current state of an electric power system, calculation
means for calculating a phase modifying insertion effect amount
when the phase modifying facility to be controlled as a voltage
stability countermeasure is adjusted, means for automatically
selecting the phase modifying facility that exhibits the
greatest effect among the phase modifying insertion effect
4
amounts which is calculated with respect to the most unstable
point that is the minimum index in a voltage stability
monitoring index, flow calculation means for calculating a
system state after the adjustment of the selected phase
modifying facility is implemented, means for displaying the
system state which is obtained through the flow calculation,
and display means for automatically selecting the system state
after the adjustment of the phase modifying facility that is
the most effective for the most unstable point of the voltage
stability, for the phase modifying inserting effect amount with
respect to the most unstable point, and increasing in the
voltage stability is implemented and for successively
displaying the selected state at a constant interval." (refer
to Abstract).
[0005]
In addition, as the background art of the present
technical filed, JP-A-2011-115024 (PTL 2) is included. This
publication describes that "electric power system information
input means 1 for inputting system information relating to an
electric power system, state estimation means 2 for estimating
state variables of the electric power system based on the system
information, supply and demand increase scenario generation
means 3 for generating a generator output change scenario of
a generator belonging to the electric power system and a load
increase scenario of a load belonging to the electric power
5
system based on the state variables, optimum flow calculation
means 4 for obtaining optimize state variables which are
obtained by optimizing the state variables so as to minimize
a predetermined target function in the generator output change
scenario and the load increase scenario, multi-root analyzing
means 5 for obtaining a lower solution of a P-V curve based
on the optimized state variables, and P calculation means 6
for calculating a voltage stability margin P from the P-V curve
are included." (refer to Abstract).
[0006]
In addition, as the background art of the present
technical filed, JP-A-2005-287128 (PTL 3) is included. This
publication describes that "system state estimation means for
performing a flow calculation using system information to be
input to a electric calculator 4 through information
transmission devices 21, 22, or the like and estimating a node
voltage, the phase angle thereof, and the power demand amount
as a system state value, stability limit calculation means for
estimating a PV curve indicating a relationship between the
electric power demand amount and the system voltage by a
continuous method by using the estimated system state as an
initial value and determining a stability limit of the system
voltage by determining the stability of a solution on the PV
curve by a unique value calculation, stability determination
means for determining the voltage stability using the
6
determined stability limit, and output means for outputting
various data items as the calculation result by each means to
a man-machine interface device 5 are included." (refer to
Abstract).
[0007]
In addition, as the background art of the present
technical filed, JP-A-9-512698 (PTL 4) is included. This
publication describes that "a method for executing an
evaluation of the reliability of voltage stability with respect
to a region of a transmission system including a plurality of
buses and a plurality of invalid storage sources which are
connected to the plurality of buses is provided. The plurality
of buses are grouped into a plurality of voltage control areas
such that each bus in each voltage control area has
substantially the same invalidity limit and the voltage in a
minimum value of the relationship between the corresponding
reactive power and the voltage. A corresponding invalidity
storage container is determined for each of the at least one
voltage control area. The invalid storage container includes
at least one invalidity storage source which is selected based
on a measure of the invalidity accumulation which is depleted
at a predetermined operation point of a transmission system.
An analysis of a single contingency is executed by calculating
the corresponding amount of the invalid storage container in
response to each of multiple single contingencies. The
7
above-described corresponding amount represents a reduction
in the invalidity accumulation in the invalid storage container.
The analyses of a number of contingencies are executed for each
invalid storage container using the single contingency such
that the corresponding amount exceeds a predetermined
threshold." (refer to Abstract).
[0008]
In addition, as the background art of the present
technical filed, JP-A-9-512699 (PTL 5) is included. This
publication describes that "a method for disposing improvement
means for improving the reliability of voltage stability for
a region of an electric transmission system including a
plurality of buses and a plurality of invalid storage sources
which are connected to the plurality of buses is provided. The
plurality of buses are grouped into a plurality of voltage
control areas such that each bus in the voltage control area
has the same corresponding relationship between a reactive
power voltage and a voltage. A first voltage control area for
disposing first improvement means is determined and the first
voltage control area indicates a difference in an internal
invalidity loss exceeding a loss threshold. Furthermore, a
second voltage control area for disposing second improvement
means is determined and the second voltage control area for
disposing the second improvement means indicates a difference
in invalidity accumulation exceeding the invalidity
8
accumulation threshold. The first improvement means and
second improvement means include a switchable shunt capacitor,
a synchronous voltage capacitor, a static var component, or
a combination thereof. Furthermore, third improvement means
including a series capacitor, a parallel line, and a
combination thereof is disposed at an interface between two
adjacent voltage control areas which are determined to indicate
a difference in reactive power loss or reactive power flow
exceeding a predetermined threshold." (refer to Abstract).
Citation List
Patent Literature
[0009]
PTL 1: JP-A-7-163053
PTL 2: JP-A-2011-115024
PTL 3: JP-A-2005-287128
PTL 4: JP-A-9-512698
PTL 5: JP-A-9-512699
Non-Patent Literature
[0010]
NPL 1: SUZUKI Mamoru, KISHIDA Yukio: "Voltage Stability
Online Monitoring System", Electrical Engineers of Japan. B,
111(3), 1991
Summary of Invention
Technical Problem
[0011]
9
Since the output of the renewable energy steeply varies
with time due to the weather, a deterioration area of the
voltage stability also steeply changes with time. However,
in the monitoring techniques of the voltage stability described
in the above-described patent literature and non-patent
literature, it is not assumed of a times-series output change
of the renewable energy. Therefore, the voltage stability may
deteriorate during a constant period, and current or future
voltage stability cannot be accurately monitored. In addition,
as a result of not being accurately monitored, there is a
possibility that an improper voltage stability improvement
countermeasure is performed.
Solution to Problem
[0012]
In order to solve the above problems, in the present
invention, a voltage stability monitoring device for
monitoring voltage stability of a system includes an assumed
change scenario calculation unit for predicting output
variation of a renewable energy connected to the system and
calculating an assumed change time-series power flow state on
the basis of the output variation, a time-series voltage
stability calculation unit for calculating a node voltage
change with respect to demand at each node of the system on
the basis of the power flow state calculated by the assumed
change scenario calculation unit and calculating a voltage
10
stability indicating a relationship curve between the node
voltage and reactive power, and a voltage stability improvement
countermeasure search unit for determining a controlled device
on which an assumed control is to be performed, according to
the voltage stability calculated by the time-series voltage
stability calculation unit.
Advantageous Effects of Invention
[0013]
According to the present invention, since the assumed
change scenario is automatically calculated by referring to
the output variation prediction of the renewable energy and
a suggestion of the voltage stability improvement
countermeasure is dynamically displayed together with the
effect in a case where the voltage stability improvement
measures is required through the voltage stability improvement
countermeasure search calculation and the time-series voltage
stability calculation for the assumed change scenario, it is
possible to accurately monitor current and future voltage
stability of the electric power system to be monitored.
Brief Description of Drawings
[0014]
[Fig. 1] Fig. 1 illustrates an example of an overall
configuration diagram of a voltage stability monitoring
device.
[Fig. 2] Fig. 2 illustrates an example of an overall
11
configuration diagram of a hardware configuration and an
electric power system of the voltage stability monitoring
device.
[Fig. 3] Fig. 3 illustrates an example of a
configuration diagram illustrating a content of program data
of the voltage stability monitoring device.
[Fig. 4] Fig. 4 is a diagram illustrating an example
of renewable energy output variation prediction data.
[Fig. 5] Fig. 5 is a diagram illustrating an example
of renewable energy output margin data.
[Fig. 6] Fig. 6 is a diagram illustrating an example
of assumed change scenario data.
[Fig. 7] Fig. 7 is a diagram illustrating an example
of voltage stability improvement countermeasure threshold
value data.
[Fig. 8] Fig. 8 illustrates an example of a flow chart
of entire processes of the voltage stability monitoring device.
[Fig. 9] Fig. 9 illustrates an example of a flow chart
for illustrating a process of an assumed change scenario
calculation unit.
[Fig. 10] Fig. 10 is illustrates an example of a flow
chart for illustrating a process of a time-series voltage
stability calculation.
[Fig. 11] Fig. 11 illustrates an example of a diagram
illustrating a voltage stability calculation result and a
12
voltage stability margin calculation result using a V-Q curve.
[Fig. 12] Fig. 12 illustrates an example of a diagram
illustrating a time-series voltage stability calculation
result and the voltage stability margin calculation result
using the V-Q curve.
[Fig. 13] Fig. 13 illustrates an example of a flow chart
for illustrating a process of a voltage stability improvement
countermeasure necessity determination.
[Fig. 14] Fig. 14 illustrates an example of a diagram
illustrating a process for calculating a degree of deviation
from before change to after assumed change using the V-Q curve.
[Fig. 15] Fig. 15 illustrates an example of a diagram
illustrating a process for calculating a degree of deviation
from before change of a time series to after assumed change
using the V-Q curve.
[Fig. 16] Fig. 16 illustrates an example of a diagram
illustrating voltage stability improvement countermeasure
necessity determination result data.
[Fig. 17] Fig. 17 illustrates an example of a flow chart
for illustrating a process of a voltage stability improvement
countermeasure search calculation.
[Fig. 18] Fig. 18 illustrates an example of a diagram
indicating a process for calculating a degree of deviation from
before change during executing of an assumed control to after
assumed change in addition to the degree of deviation from
13
before change and after assumed change using the V-Q curve.
[Fig. 19] Fig. 19 illustrates an example of a diagram
illustrating how much the degree of deviation is improved
during implementing the assumed control.
[Fig. 20] Fig. 20 illustrates an example of a diagram
illustrating a location of a recommended controlled device in
an electric power system for a voltage stability improvement
countermeasure search result.
[Fig. 21] Fig. 21 illustrates a diagram illustrating
an example of a screen for displaying a voltage stability
calculation result, a voltage stability margin calculation
result, and a degree of deviation from before change to after
change, as a voltage stability monitoring status.
[Fig. 22] Fig. 22 illustrates a diagram illustrating
an example of a screen for displaying a time-series voltage
stability calculation result, a voltage stability margin
calculation result, and a degree of deviation from before
change to after assumed change, as a voltage stability
monitoring status.
[Fig. 23] Fig. 23 illustrates a diagram illustrating
an example of a screen for displaying a degree of deviation
improvement rate calculation result and a recommended
controlled device calculation result.
Description of Embodiments
[0015]
14
Hereinafter, preferred embodiments for carrying out the
present invention will be described. The followings are
merely examples, and are not intended to intend that the
invention itself is not limited to the following specific
content.
Example 1
[0016]
In the present example, regarding an example of a voltage
stability monitoring device 10 for calculating assumed change
scenario using system data D1, system facility data D2, and
renewable energy output variation data D5, performing a
time-series voltage stability calculation using calculated
assumed change scenario data D7, the assumed change scenario
using system data D1, the system facility data D2, the renewable
energy output variation data D5, the assumed change scenario
data D7, performing a voltage stability improvement
countermeasure necessity determination using threshold data
D3, the assumed change scenario data D7, and time-series
voltage stability calculation result data D8, performing a
voltage stability improvement countermeasure search
calculation using the assumed change scenario using system data
D1, the system facility data D2, the threshold data D3, assumed
control data D4, the renewable energy output variation data
D5, renewable energy output control margin data D6, the assumed
change scenario data D7, the time-series voltage stability
15
calculation result data D8, and voltage stability improvement
countermeasure necessity determination result data D9, and
performing a screen display of a time-series voltage stability
calculation result, a voltage stability margin calculation
result, a degree of deviation from before change to after
assumed change, a degree of deviation improvement rate
calculation result, and a recommended controlled device
calculation result, as a voltage stability monitoring status,
an example of an overall configuration configured of an input
and output indicating a content by a database and data and a
process indicating the content by the calculation unit will
be illustrated in Fig. 1, and an example of a hardware
configuration of an electric power system 100, a monitoring
control device 210, the voltage stability monitoring device
10, a measurement device 43, a power source 110, a load 150,
a bus, an electric transformer, and a transmission line will
be illustrated in Fig. 2.
[0017]
Fig. 1 illustrates an example of an overall configuration
diagram of the voltage stability monitoring device 10 of the
present example, and is a diagram illustrating a configuration
of the voltage stability monitoring device 10 configured of
the assumed change scenario using system data D1, the system
facility data D2, the threshold data D3, the assumed control
data D4, the renewable energy output variation data D5, and
16
the renewable energy output control margin data D6, a voltage
stability monitoring calculation unit 40 which is configured
of an assumed change scenario calculation unit 31, a
time-series voltage stability calculation unit 32, a voltage
stability improvement countermeasure necessity determination
unit 33, and a voltage stability improvement countermeasure
search calculation unit 34, voltage stability monitoring
calculation result data D41 which is configured of the assumed
change scenario data D7, the time-series voltage stability
calculation result data D8, and the voltage stability
improvement countermeasure necessity determination result
data D9, and a display unit 11.
[0018]
The input data of the voltage stability monitoring device
10 is configured of the assumed change scenario using system
data D1, the system facility data D2, the threshold data D3,
the assumed control data D4, the renewable energy output
variation data D5, and the renewable energy output control
margin data D6. In the assumed change scenario calculation
unit 31 of the voltage stability monitoring device 10, the
assumed change scenario data D7 is calculated using the assumed
change scenario using system data D1, the system facility data
D2, and the renewable energy output variation data D5. In
addition, in the time-series voltage stability calculation
unit 32 of the voltage stability monitoring device 10, the
17
time-series voltage stability calculation is performed using
the assumed change scenario data D7, the assumed change
scenario using system data D1, the system facility data D2,
the renewable energy output variation data D5, and the assumed
change scenario data D7 to output the time-series voltage
stability calculation result data D8. In addition, in the
voltage stability improvement countermeasure necessity
determination unit 33 of the voltage stability monitoring
device 10, the voltage stability improvement countermeasure
necessity determination is performed using the threshold data
D3, the assumed change scenario data D7, and the time-series
voltage stability calculation result data D8 to output the
voltage stability improvement countermeasure necessity
determination result data D9. In addition, in the voltage
stability improvement countermeasure search calculation unit
34 of the voltage stability monitoring device 10, the voltage
stability improvement countermeasure search calculation is
performed using the assumed change scenario using system data
D1, the system facility data D2, the threshold data D3, the
assumed control data D4, the renewable energy output variation
data D5, the renewable energy output control margin data D6,
the assumed change scenario data D7, the time-series voltage
stability calculation result data D8, and the voltage stability
improvement countermeasure necessity determination result
data D9, and as a voltage stability monitoring status, a screen
18
display of a time-series voltage stability calculation result,
a voltage stability margin calculation result, a degree of
deviation from before change to after assumed change, a degree
of deviation improvement rate calculation result, and a
recommended controlled device calculation result is
performed.
[0019]
Fig. 2 illustrates an example of a hardware configuration
of the voltage stability monitoring device 10 and an overall
configuration diagram of the electric power system 100 and is
a diagram illustrating an example of the hardware configuration
of the electric power system 100, the monitoring control device
210, the voltage stability monitoring device 10, the
measurement device 43, the power source 110, the load 150, the
bus, the electric transformer, and the transmission line. The
electric power system 100 is configured of any one or more of
a generator 110, an electric transformer 130, the measurement
device 43, and the load 150 which are connected to each other
through a branch (line) 140 and a node (bus) 120, and a
measurement device or a controllable device (a battery, a
rechargeable secondary battery, an EV storage battery, a
flywheel, a phase modifying device (a static condenser (SC),
a shunt reactor (ShR), a static var compensator (SVC), a static
var generator (SVG), a loop power controller (LPC), and the
like)) which is not illustrated in drawings.
19
[0020]
Here, an example of the power source 110 includes a
distributed power source such as a solar power generation and
a wind power generation in addition to a large power source
such as a thermal power generation, a hydraulic generator, or
a nuclear power generator.
[0021]
Here, an example of the measurement device 43 is a device
(VT, PT, or CT) for measuring one or more of a node voltage
V, a branch current I, a power factor , an effective power
P, and a reactive power Q and has a function to transmit a data
measurement location identification ID and data including a
built-in time stamp of the measurement device (telemeter (TM)
or the like). A device for measuring power information (phasor
information of the voltage) with absolute time using GPS,
phasor measurement units (PMU), or other measurement equipment
may be included. It is shown that the measurement device 43
is present in the electric power system 100. However, the
measurement device 43 may be disposed in the bus, the
transmission line, or the like to be connected to the generator
110, the electric transformer 130, the measurement device 43,
and the load 150.
[0022]
Here, measurement data D1 is each of the above data items
measured in the measurement device 43 and is received to a
20
system measurement database 21 through a communication network
300. However, instead of directly receiving the system data
from the measurement device 43, the system data may be received
to the system measurement database 21 through the communication
network 300 after the system data items are aggregated in the
monitoring control device 210 and may be received to the system
measurement database 21 through the communication network 300
from both the measurement device 43 and the monitoring control
device 210. The measurement data D1 may include a unique number
for identifying the data items and a time stamp.
[0023]
A configuration of the voltage stability monitoring
device 10 will be described. The display unit 11, an input
unit 12 such as a keyboard or a mouse, a communication unit
13, a computer or a calculator server (central processing unit
(CPU)) 14, a memory 15, and various types of databases (a
program database 20, the system measurement database 21, a
system facility database 22, a threshold database 23, an
assumed control database 24, a renewable energy output
variation prediction database 25, a renewable energy output
control margin database 26, an assumed change scenario database
27, a time-series voltage stability calculation result
database 28, a voltage stability improvement countermeasure
necessity determination result database 29, and an improvement
countermeasure search result database 30) are connected to a
21
bus line 42. The display unit 11 is configured as a display
device, for example.
[0024]
The display unit 11 may be configured using a printer
device or a sound output device instead of a display device
or with the display device, for example. The input unit 12
can be configured including at least one of a pointing device
such as a keyboard or a mouse, a touch panel, and a sound
instruction device, for example.
The communication unit 13 includes a circuit and a
communication protocol for connecting to the communication
network 300. The CPU 14 reads a predetermined computer program
from the program database 20 and executes the program. The
CPU 14 may be configured as one or a plurality of semiconductor
chips and may be configured as a computer device such as a
calculation server. The memory 15 is configured as a random
access memory (RAM), for example, stores a computer program
read from the program database 20 or stores calculation result
data, image data, or the like required for each process. The
screen data stored in the memory 14 is transmitted to the
display unit 11 and displayed. An example of the screen to
be displayed will be described.
[0025]
Here, a storage content of the program database 20 will
22
be described with reference to Fig. 3. Fig. 3 illustrates an
example of a configuration diagram illustrating a content of
program data of the voltage stability monitoring device. For
example, a state estimation calculation program P60, an assumed
change scenario calculation program P10, a time-series voltage
stability calculation program P20, a voltage stability
improvement countermeasure necessity determination program
P30, a voltage stability improvement countermeasure search
calculation program P40, and a screen display program P50 are
stored in the program database 20.
[0026]
Returning to Fig. 2, the CPU 14 executes the calculation
programs (the state estimation calculation program P60, the
assumed change scenario calculation program P10, the
time-series voltage stability calculation program P20, the
voltage stability improvement countermeasure necessity
determination program P30, the voltage stability improvement
countermeasure search calculation program P40, and the a screen
display program P50) read in the memory 14 from the program
database 20 and performs a calculation of a likeliable system
state, a calculation of the assumed change scenario, a
calculation of the time-series voltage stability (may include
a calculation of a voltage stability margin), a voltage
stability improvement countermeasure necessity determination,
a calculation of the voltage stability improvement
23
countermeasure search, various types of screen displays, an
instruction of image data to be displayed, a search of data
in various types of databases, or the like. The memory 14 is
a memory for temporarily storing calculation temporary data
such as image data for displaying, measurement (monitoring)
data, or monitoring result data and calculation result data.
The necessary image data is generated by the CPU 14 and is
displayed on the display unit 11 (for example, a display screen).
The display unit 11 of the voltage stability monitoring device
10 may be a simple screen only for performing a rewriting each
control program or database.
[0027]
Databases roughly divided into 11 databases are stored
in the voltage stability monitoring device 10. The system
measurement database 21, the system facility database 22, the
threshold database 23, the assumed control database 24, the
renewable energy output variation prediction database 25, the
renewable energy output control margin database 26, the assumed
change scenario database 27, the time-series voltage stability
calculation result database 28, the voltage stability
improvement countermeasure necessity determination result
database 29, and the improvement countermeasure search result
database 30 will be described excluding the program database
20.
[0028]
24
The effective power P, the reactive power Q, the voltage
V, a voltage phase angle , the current I, the power factor
, and the like are included in the system measurement database
21 as system measurement data. Data with a time stamp or PMU
data may be used. For example, a voltage and a voltage phase
angle in a node 120a or 120b to be connected to the electric
power system 100, a line flow (P+jQ) of a branch 140a or 140b
to be connected to the node 120a or 120b to be connected to
the electric power system 100, a line flow (P+jQ) of an electric
transformer 130a or 130b to be connected to the node 120a or
120b to be connected to the electric power system 100, the
voltage V and the voltage phase angle  of a node 121a or 121b
to be connected to the electric transformer 130a or 130b, the
effective power P, the reactive power Q, or the power factor
 of the load 150 or the power source 110 to be connected to
the node 121a or 121b, and the effective power P, the reactive
power Q, the power factor , the voltage V and the voltage phase
angle  of the other node, branch, power source, load,
controlled device, or the like to be connected to the electric
power system 100 for performing a measurement through the
communication network from the measurement device 43, the
monitoring control device 210, or the like. The voltage phase
angle  may be measured using the other measurement device using
the PMU or GPS. The measurement device is the VT, PT, or the
like. The line flow (P+jQ) can be calculated from the current
25
I, the voltage V, and the power factor  which are measured
by the VT or PT. In addition, a result that is a calculation
result of the state estimation calculation program P60 in which
the effective power P, the reactive power Q, the voltage V,
the voltage phase angle , the current I, and the power factor
 of each of the node, the branch, the generator, the load,
and the controlled device of the most preferred system is
estimated and calculated is also saved as the system
measurement data.
[0029]
A system configuration, a line impedance (R+jX), a ground
capacitance (admittance: Y), data necessary for the system
configuration and the state estimation (threshold value of bad
data), generator data, and data necessary for the other flow
calculation, state estimation and voltage stability
calculation are included in the system facility database 22.
The measurement value may be obtained from a monitoring control
device, a central power supply command station, or EMS and may
be directly obtained from the measurement device of the entire
system. When data is input manually, the data is manually input
and stored by the input unit 12. When the input is performed,
the necessary image data is generated by the CPU 14 and is
displayed on the display unit 11. When the input is performed,
it may be set a semi-manual input such that a large amount of
data can be set using a complementary function.
26
[0030]
As illustrated in Fig. 7, a determination threshold value
(voltage stability improvement countermeasure threshold
value) of a rate of deviation (to be described) for determining
voltage stability improvement countermeasure necessity is
stored in the threshold database 23. The voltage stability
improvement countermeasure threshold value is a threshold
value to be used in the voltage stability improvement
countermeasure necessity determination and is used for
selecting as a rough assumed change scenario having the voltage
stability improvement countermeasure threshold value or less.
[0031]
One or more of a connection node, a current output, a
rated output and a capacity, an output control margin, and the
like of a device (a battery, a rechargeable secondary battery,
an EV storage battery, a flywheel, a phase modifying device
(a static condenser (SC), a shunt reactor (ShR), a static var
compensator (SVC), a static C var generator (SVG), a loop power
controller (LPC), and the like)) in which the voltage stability
improvement countermeasure can be performed and controlled and
is saved in the assumed control database 24. These data items
may be used using the 12 of the voltage stability monitoring
device 10 and may be stored from the system measurement data
or the system facility data.
[0032]
27
As illustrated in Fig. 4, an output variation width where
a target renewable energy for generating the assumed change
scenario is predicted after T1 seconds and an output variation
width where the target renewable energy is predicted after T2
seconds are stored in the renewable energy output variation
prediction database 25. The T1 and T2 may be stored using the
input unit 12 of the voltage stability monitoring device 10
and may be received through the communication network 300 from
the monitoring control device 210. The renewable energy
output variation includes an output variation amount or the
like of the solar power generation, the wind power generation,
a mega solar or a wind farm.
[0033]
As illustrated in Fig. 5, an indication that how much
the output of the renewable energy for performing the voltage
stability countermeasure search can be currently (at a time
of measuring) controlled and an indication that how much of
the output of the renewable energy can be controlled among the
output variation widths to be predicted after T1 seconds are
stored in the renewable energy output control margin database
26. The current and the T1 may be stored using the input unit
12 of the voltage stability monitoring device 10 and may be
received through the communication network 300 from the
monitoring control device 210.
[0034]
28
As illustrated in Fig. 6, an indication that how much
of the output of the renewable energy for performing the
calculation of the time-series voltage stability is varied from
the current (at a time point of measuring) and after T1 seconds
and the after T2 seconds is stored in the assumed change
scenario database 27. The assumed change scenario data is to
be calculated by the assumed change scenario calculation
program P10. In Fig. 6, the assumed change is set as the output
variation of the target renewable energy. However, a fault
location and a failure mode may be incorporated as an assumed
change as a fault case assumed in the electric power system
stored using the input unit 12 of the voltage stability
monitoring device 10. As the other elements, a failure
removing timing or the like is included in a list. The
renewable energy output variation includes simultaneous
dropouts of wind farm. As the failure case, it may be only
a rough failure case depending on an operation of the system.
The assumed change scenario data D7 may be set in advance
without using the input unit 12 or may be set the value set
in the monitoring control device 210 through the communication
network 300 and the communication unit 13. By these setting
methods, there is an effect that it is possible to flexibly
set the assumed change scenario data D7.
[0035]
A time-series calculation result of a continuous type
29
flow calculation for evaluating the voltage stability which
is calculated by the time-series voltage stability calculation
program P20 is stored in the time-series voltage stability
calculation result database 28. For example, a V-Q curve
illustrated in Fig. 11 or Fig. 12 is included. The V-Q curve
is calculated for each node. In addition to the V-Q curve,
there is a P-V curve for each node. The continuous type flow
calculation is a method for describing the V-Q curve or the
P-V curve by continuously calculating operations of a
calculation (predictor calculation) for predicting a system
state by changing the load power or the like under a certain
constant condition and obtaining a correspond bus line voltage
by the type flow calculation (corrector calculation). The
detailed continuous type flow calculation will be described.
For example, in a case of the V-Q curve, the time-series voltage
stability calculation may be a change of the node voltage for
a demand of each node and may be a change of the node voltage
for the demand of each node divided by the initial demand of
each node. The change of the node voltage with respect to any
one of demand or a plurality of demands is saved. In addition,
in the time-series voltage stability calculation result
database 28, a reactive power margin Q is stored for each node
from the difference from a bottom to the zero of the reactive
power Q of the V-Q curve to be calculated as illustrated in
Fig. 11 using the V-Q curve of the voltage stability calculation
30
result data D4 which is calculated by the time-series voltage
stability calculation program P20. In the same manner of the
time-series voltage stability calculation, the voltage
stability margin, in also the voltage stability margin, for
example, the V-Q curve to be used when obtaining the reactive
power margin Q from the V-Q curve may be a change of the node
voltage for the demand of each node and the demand of each node
may be a change of the node voltage for a demand divided by
an initial demand of each node. The V-Q curve, the voltage
lower than the reactive power limitation is defined as a
non-stable. In addition, as the evaluation of other than the
Q of the V-Q curve, a method is performed according to a
determining method or an evaluation method described in WECC
"Voltage Stability Criteria, Undervoltage Load Shedding
Strategy, and Reactive Power Reserve Monitoring Methodology",
Final Report, 1998, pp. 33 to 58, and Power System Stability
Operation Technical Committee: "Power system Stability
Operational Technique", the electric cooperative research,
Vol. 47, No. 1, 1991, pp. 24 to 34.
[0036]
A result in which the degree of deviation of each node
of the assumed change scenario as illustrated in Fig. 14 or
Fig. 15 and the rough assumed change scenario in which the
degree of the deviation is less than the threshold value as
illustrated in Fig. 16 are extracted which is calculated by
31
voltage stability improvement countermeasure necessity
determination program P30 using the threshold data D3, the
assumed change scenario data D7, and the time-series voltage
stability calculation result data D8 is stored in the voltage
stability improvement countermeasure necessity determination
result database 29.
[0037]
An improvement result after controlling of the degree
of the deviation of each node of the each assumed change
scenario as illustrated in Fig. 18 and a result in which the
improvement rate of the degree of the deviation of the assumed
control in each scenario as illustrated in Fig. 19 which are
calculated by the voltage stability improvement
countermeasure search calculation program P40 using the
assumed change scenario using system data D1, the system
facility data D2, the threshold data D3, the assumed control
data D4, the renewable energy output variation data D5, the
renewable energy output control margin data D6, the assumed
change scenario data D7, the time-series voltage stability
calculation result data D8, and the voltage stability
improvement countermeasure necessity determination result
data D9 are stored in voltage stability the improvement
countermeasure search result database 30.
[0038]
Next, a calculation process content of the voltage
32
stability monitoring device 10 will be described with reference
to Fig. 8. Fig. 8 illustrates a flow chart of the entire
processes of the voltage stability monitoring device. Firstly,
a simple flow will be described. After the system facility
data D2, the threshold data D3, and the assumed control data
D4 are input and stored, the system measurement data D1, the
renewable energy output variation data D5, and the renewable
energy output control margin data D6 are received, the state
estimation calculation is performed, and the state estimation
calculation result is stored. Next, the assumed change
scenario is calculated using the system measurement data D1,
the system facility data D2, the renewable energy output
variation data D5, and the state estimation result (to be stored
in the system measurement database 21) (to be stored in the
assumed change scenario database 27). Next, after the
time-series voltage stability calculation is performed using
the calculated assumed change scenario data D7, the system
measurement data D1, the system facility data D2, the renewable
energy output variation data D5, and the assumed change
scenario data D7, the voltage stability margin is calculated,
and the voltage stability calculation result and the voltage
stability margin calculation result are stored (the
time-series voltage stability calculation result database 28).
The voltage stability improvement countermeasure necessity
determination is performed using the threshold data D3, the
33
assumed change scenario data D7, and the time-series voltage
stability calculation result data D8, and the voltage stability
improvement countermeasure necessity determination result is
stored (the voltage stability improvement countermeasure
necessity determination result database 29). Next, the
voltage stability improvement countermeasure search
calculation is performed using the system measurement data D1,
the system facility data D2, the threshold data D3, the assumed
control data D4, the renewable energy output variation data
D5, the renewable energy output control margin data D6, the
assumed change scenario data D7, the time-series voltage
stability calculation result data D8, and the voltage stability
improvement countermeasure necessity determination result
data D9, voltage stability improvement countermeasure search
result data D10 is stored (the voltage stability improvement
countermeasure search result database 30). Finally, as the
voltage stability monitoring status, a screen display of the
voltage stability improvement countermeasure search result
data D10 that is the time-series voltage stability calculation
result D8, the degree of deviation from before change and after
assumed change, the degree of deviation improvement rate
calculation result, and the recommended controlled device
calculation result is performed. The various types of
calculation results or data accumulated in the memory during
the calculation may be sequentially displayed on the screen
34
of the monitoring control device 210. Accordingly, an
operator can easily grasp the operational status of the voltage
stability monitoring device 10. In addition, in the voltage
stability monitoring device 10, as the operational status,
monitoring contents (the system data receiving, the present
and absent of the voltage stability monitoring calculation end,
the degree of deviation, the voltage stability calculation
result after T1 seconds and T2 seconds) and the like may be
displayed. Accordingly, an operator can easily grasp the
operational status of the voltage stability monitoring device
10. The screen display of the status from the receiving of
various types of data items to the transmitting of the various
types of calculation results respectively is repeated, until
the change of the monitoring location is executed. Above
process flows will be described for each step.
[0039]
Firstly, in Step S1, in a case where the system facility
data D2, the threshold data D3, and the assumed control data
D4 are not set in advance, the system facility data D2, the
threshold data D3, and the assumed control data D4 are input
using the input unit 12 and the display unit 11. Here, data
may be input from the monitoring control device 210 through
the communication network 300 and the communication unit 13,
and data relating to the system facility data D2, the threshold
data D3, and the assumed control data D4 held in the monitoring
35
control device 210 or the like may be automatically received
at a constant period and may be stored. In addition, in a case
where the system facility data D2, the threshold data D3, and
the assumed control data D4 are set in advance, the correction
may be added, and the data may be used without any change.
[0040]
In Step S2, the system measurement data D1, the renewable
energy output variation data D5, and the renewable energy
output control margin data D6 are received, and the state
estimation calculation is performed, and the state estimation
calculation result is stored in the system measurement database
21. By the state estimation calculation, a result in which
effective power P, the reactive power Q, the voltage V, the
voltage phase angle , the current I, and the power factor 
of each of the node, the branch, the generator, the load, and
the controlled device of the most preferred system is estimated
and calculated is also saved as the system measurement data.
The method of the state estimation calculation is performed
according to the calculation method or the like described in
Lars Holten, Anders Gjelsvlk, Sverre Adam, F.F. Wu, and Wen-Hs
Iung E. Liu, Comparison of Different Methods for State
Estimation, IEEE Transaction on Power Systems, Vol. 3(1988),
pp. 1798 to 1806.
[0041]
In Step S3, the assumed change scenario calculation is
36
performed using the system facility data D2 stored in Step S1,
the system measurement data D1 stored in Step S2, the renewable
energy output variation data D5, and the state estimation
result which is obtained in Step S2, and the result thereof
is stored in the assumed change scenario database 27. Here,
a flow of the assumed change scenario calculation will be
descried with reference to Fig. 9. Fig. 9 illustrates an
example of a flow chart for illustrating a process of the
assumed change scenario calculation unit 31. Fig. 9
illustrates a method for reading the system measurement data
D1, the system facility data D2, and the renewable energy output
variation data D5 through Steps S11 to S18 and repeatedly
calculating the flow for selecting the renewable energy output
variation predictions after selection of the assumed failure
location and the mode and after T1 seconds and T2 seconds and
the saving the selected renewable energy output variation
prediction as the assumed change scenario D7 until the assumed
failure location, the assumed failure mode, and the renewable
energy output variation prediction is selected and ended. The
above process flows will be descried. In Step S11, the system
facility data D2 stored in Step S1, the system measurement data
D1 stored in Step S2, the renewable energy output variation
data D5, and the state estimation result which is obtained in
Step S2 are read in the memory 14. Although not illustrated
in the drawings, an estimation failure list which is formed
37
of the assumed failure location and the assumed failure mode
is held, and is read in the memory 14. In Step S12, one of
the unselected assumed failure locations is selected from the
list of the assumed failure locations read in the memory 14.
In Step S13, one of the unselected assumed failure modes is
selected from the list of the assumed failure modes read in
the memory 14. In Step S14, any one of lower and upper limit
values is selected from the lower and upper limit values of
the variation width of the renewable energy output variation
prediction after T1 seconds read in the memory 14. In Step
S14', any one of lower and upper limit values is selected from
the lower and upper limit values of the variation width of the
renewable energy output variation prediction after T2 seconds
read in the memory 14. In Step S15, a combination of the assumed
failure location and the assumed failure mode, and the
renewable energy output variation prediction selected in Steps
S12 to S14' is saved as one assumed change scenario D7. In
Step S16, in a case where all of the lists of the renewable
energy output variation prediction are not selected, the
process returns to Step S14. In addition, in Step S16, in a
case where all of the lists of the renewable energy output
variation prediction are selected, the process proceeds to Step
S17. In Step S17, in a case where all of the lists of the assumed
failure mode is not selected, the process returns to Step S13.
In addition, in Step S17, in a case where all of the lists of
38
the assumed failure mode is selected, the process proceeds to
Step S18. In Step S18, in a case where all of the lists of
the assumed failure location are not selected, the process
returns to Step S12. In addition, in Step S18, in a case where
all of the lists of the assumed failure location are selected,
the process is ended. Here, regarding the renewable energy
output variation prediction, no output change, an output
reduction (during a certain constant period) and an output
increase (during a certain constant period) can be considered.
However, in this time, in order to assume the severe condition,
an example in which the assumed change scenario is generated
using the lower and upper limit values of the output variation
width is shown. In addition, the renewable energy output
variation prediction may be updated based on data which is
stored by manually inputting for each a constant period, in
the monitoring control device, and the database. Here, as a
combination of the assumed failure location and the assumed
failure mode, and the renewable energy output variation
prediction, a combination of only renewable energy output
variation predictions is present without failure.
Hereinafter, as a case without failure, the content of an
example will be described. Here, an example of the assumed
change scenario data D7 will be described with reference Fig.
7. As illustrated in Fig. 7, as a failure case to be assumed
in the electric power system, a list in which the failure
39
location, and the failure mode, and the renewable energy output
variation prediction are combined is included. As the other
elements, a failure removing timing and the like are included
in a list. The renewable energy output variation prediction
includes the output variation amount of the solar power
generation, the wind power generation, the mega solar, or the
wind farm and simultaneous dropouts of wind farm. As the
failure case, it may be only a rough failure case depending
on an operation of the system. The assumed change scenario
data D7 may be set in advance without using the input unit 12
or may be set the value set in the monitoring control device
210 through the communication network 300 and the communication
unit 13. By these setting methods, there is an effect that
it is possible to flexibly set the assumed change scenario data
D7.
[0042]
Returning to Fig. 8, here, in Step S4, after the voltage
stability calculation is performed using the state estimation
calculation result and the assumed change scenario, the voltage
stability calculation result is stored. The method for
calculating the voltage stability is performed according to
the calculation method descried, for example, PTL 3, Chiang,
H.D, et al., "CPFLOW: A Practical Tool for Tracing Power System
Steady-State Stationary Behavior Due to Load and Generation
Variations", IEEE Trans. on Power Systems, Vol. 10, No. 2, pp.
40
623 to 634, 1995, VVenkataramana Ajjarap, "Computational
Techniques for Voltage Stability Assessment and Control"
Springer, 2006, pp. 49 to 116, or JP-A-6-153397. In addition,
as the calculation method of the assumed change scenario, a
method according to a method disclosed in PTL 1 or a method
described in Power System Stability Operation Technical
Committee: "Power system Stability Operational Technique",
the electric cooperative research, Vol. 47, No. 1, 1991, pp.
24 to 34. In addition, as the evaluation method of the V-Q
curve, a method is performed according to a method disclosed
in Power System Stability Operation Technical Committee:
"Power system Stability Operational Technique", the electric
cooperative research, Vol. 47, No. 1, 1991, pp. 24 to 34 and
a method described in WECC, "Voltage Stability Criteria, Under
voltage Load Shedding Strategy, and Reactive Power Reserve
Monitoring Methodology", Final Report, 1998, pp. 33 to 58. For
example, the reactive power margin Q is used. Here, a flow
of the time-series voltage stability calculation will be
descried with reference to Fig. 10. In Step S21, the system
measurement data D1, the system facility data D2, the renewable
energy output variation data D5, and the assumed change
scenario data D7 are read in the memory 14. In Step S22, one
of load buses is selected. Next, in Step S23, a step width
is determined. Here, relating to first Step S23, as the step
width, the initial value is used. From second Step S23, the
41
step width is determined by considering the number of times
it takes for corrector calculation to converge with the
previous step width. In Step S24, the first step is set as
the setting value or the state estimation value is set as the
predictor, the process proceeds to Step S25. After the second
step, a selected load bus is subjected to a PV instruction,
and a point where the voltage V is reduced is set as the predictor
calculation result using the step width which uses the
effective power as a fixed power. In this time, the effective
power may use the previous value of the convergence calculation
result. Next, in Step S25, the flow calculation is performed
using the point of the predictor which is calculated in Step
S24 as an initial value. In the flow calculation, the
convergence calculation is performed using the Newton Raphson
method. Here, the condition of the convergence determination
in the convergence calculation has a value which is set in
advance. The Newton Raphson method is performed according to
a method descried in WILLIAM. F. TINNEY, et al., "Power Flow
Solution by Newton's Method", IEEE Trans. on Power Systems,
Vol. PAS-86, No. 11, pp. 1449 to 1460 and 1967. In Step S26,
it is determines whether Step S25 is converged within the
defined convergence numbers. The maximum value of the
convergence numbers is previously set. In a case of
convergence, the process proceeds to Step S27, the converged
voltage value is saved. In a case of un-convergence, the
42
process proceeds to Step S28, if the step width is not minimum
value, the step width is reduced, and the process returns to
Step S24. In Step S27, a value which is converged by the flow
calculation is saved. In addition, in Step S28, if the step
width is not minimum value, the process returns to Step S23
and if the step width is the minimum value, the process proceeds
to Step S29, the calculation of the load bus is not performed
(however, an error message is repeated). In Step S29, it is
confirmed whether all of the load buses are selected, and in
a case where all of the load buses are selected, the process
proceeds to Step S30. In a case where all of load buses are
not selected, the process returns to Step S22, the load bus
is selected. In the Step S30, the time-series voltage
stability calculation result D8 is saved. According to flows
in Steps S22 to S30, the V-Q curve is implemented for each
assumed change scenario. By solving the continuous flow
calculation, the continuous flow calculation is implemented
and the V-Q curve is drawn. Here, an example of the time-series
voltage stability calculation result will be described with
reference to Fig. 12. Fig. 12 illustrates an example for
illustrating an image of the time-series voltage stability
calculation unit 31. Fig. 12 can be drawn by subtracting the
reactive power supply portion from the system side from the
reactive power consumption of the voltage Vi of a node i in
a horizontal axis and a node i of the reactive power in a vertical
43
axis. In addition, a time axis is provided in a depth direction,
it is shown that the V-Q curve can be calculated in time-series
according to the assumed change scenario. In Fig. 11, a VQ
curve is present in one time section, and an operation point
is defined as (Vi0, Q0). Furthermore, the reactive power limit
that is a limit of the voltage stability is a location of Qc.
The V-Q curve can be drawn by subtracting the reactive power
supply portion from the system side from the reactive power
consumption of the node i. A function of the voltage
calculation in consideration of output enable constraint data
of effective and reactive power of the generator may be included.
Accordingly, the voltage stability of the electric power system
closer to the reality can be reviewed. The above curves are
calculated for all of the load buses.
[0043]
Returning to Fig. 8, in Step S5, the voltage stability
improvement countermeasure necessity determination is
performed and the voltage stability improvement
countermeasure necessity determination result data is stored.
Here, the flow of the voltage stability improvement
countermeasure necessity determination will be described with
reference to Fig. 13. In Step S31, the threshold data D3, the
assumed change scenario data D7, and the time-series voltage
stability calculation result data D8 are read in the memory
14. In Step S32, the assumed change scenario is selected. In
44
Step S33, the degree of deviation is calculated from the
time-series voltage stability calculation result data D8 and
the threshold data D3 of the assumed change scenario which is
selected in Step S32. Here, the calculation example of the
degree of deviation will be descried with reference to Fig.
14. Fig. 14 illustrates the V-Q curve before assumed change
and after assumed change, respectively. The degree of
deviation is an index indicating that how much the curve after
assumed change is separated from the curve before the assumed
change. When the degree of the deviation is defined as D, the
degree of the deviation can be calculated by Express (1). Here,
Vi represents a voltage of each node and Qc is a bottom value
of the reactive power of the V-Q curve. The calculation of
the degree of deviation may be performed from a difference in
gradient dVi/dQ in the operational point. By using the
gradient, the calculation amount can be reduced. In addition,
an example in which the calculation of the degree of the
deviation is performed in a time series is illustrated in Fig.
15. In a case where the degree of deviation is calculated in
the time series, the calculation of the degree of deviation
can be performed by further adding the degree of deviation at
respective times.
[0044]
45
[0045]
Returning to Fig. 13, in Step S34, it is determined
whether the degree of deviation which is calculated in Step
S33 is within the threshold range which is set in advance. When
the degree of deviation is in the threshold range, the selection
of the assumed change scenario of Step S32 is returned, when
the value is greater than the threshold value, the process
proceeds to Step S35. In Step S35, as the voltage stability
improvement countermeasure necessity determination result
data D9, the degree of deviation and the indication whether
the degree of deviation is within the threshold value are saved.
When the value is greater than the threshold value, the process
proceeds to Step S35, the result that the value is within the
threshold value is held in the memory 14, and when passing
through Step S35, the result is saved. Here, in Fig. 16, a
relationship image of the degree of deviation and the threshold
value of the assumed change scenario is illustrated. In Fig.
16, the assumed change scenario No. 1 becomes a rough assumed
change scenario. The number of the rough assumed scenarios
is not limited to 1, and a case where there is no assumed change
scenario can be included. Returning to Fig. 13, in Step S36,
it is determined whether all of the assumed change scenarios
46
are selected, and when the assumed change scenario which is
not selected is present, the process returns to Step S32. When
all of the assumed change scenarios are selected, the process
is ended, and the process proceeds to Step S6.
[0046]
Returning to Fig. 8, in Step S6, the voltage stability
improvement countermeasure search calculation is performed,
and the voltage stability improvement countermeasure search
calculation result data is stored. Here, a flow of the voltage
stability improvement countermeasure search calculation will
be described with reference to Fig. 17. In Step S41, the system
measurement data D1, the system facility data D2, the threshold
data D3, the assumed control data D4, the renewable energy
output variation data D5, the renewable energy output control
margin data D6, the assumed change scenario data D7, the
time-series voltage stability calculation result data D8, and
the voltage stability improvement countermeasure necessity
determination result data D9 are read in the memory 14. In
Step S42, the assumed change scenario is selected. In Step
S43, the assumed control is selected by the assumed control
data. In Step S44, the time-series voltage stability
calculation is executed, and in Step S45, the degree of
deviation calculation is executed. Here, Fig. 18 indicates
the degree of deviation in a case where the selected assumed
control is executed in a form that is added in Fig. 14 which
47
is calculated at the time of voltage stability improvement
countermeasure necessity determination. The degree of
deviation in the voltage stability improvement countermeasure
search calculation is calculated by the same expression as the
express at the time of voltage stability improvement
countermeasure necessity determination. In addition, Fig. 19
illustrates whether how much the degree of deviation is
improved (the degree of deviation is decreased) using the
calculation before and after assumed control. Here, returning
to Fig. 17, in Step S46, the voltage stability improvement
countermeasure search result data D10 is saved. Next, in Step
S47, it is determined whether all of the assumed controls are
selected. In a case where all of the assumed controls are not
selected, the process returns to Step S43 and in a case where
all of the assumed controls are selected, the process proceeds
to Step S48. In Step S48, it is determines whether all of the
assumed change scenarios are selected. In a case where all
of the assumed change scenarios are not selected, the process
returns to Step S42 and in a case where all of the assumed change
scenarios are selected, the process proceeds to Step S49. In
Step S49, the average values in the respective assumed change
scenario and the assume control are calculated and the
calculated average value is held in the memory 14. In Step
S50, an assumed control group having a low average value of
the degrees of deviation held in the memory is determined as
48
the voltage stability improvement countermeasure. There is
a case where the number of assume control groups is zero or
the number of assume control groups is one. Next, in Step S51,
the voltage stability improvement countermeasure search
result data D10 is saved and ended. The assume control group
which is determined as the voltage stability improvement
countermeasure becomes a recommended voltage stability
improvement countermeasure. By illustrating a geographical
position on the system diagram as illustrated in Fig. 20, an
effect that it is easy to understand where voltage stability
can be improved can be estimated, and the operator can easily
review the countermeasure. In addition, by displaying the
recommended voltage stability improvement countermeasures in
the overlap manner to the plurality of assumed change scenarios
of displaying the other voltage stability improvement
countermeasures in the overlap manner, it is easier to grasp
the tendency that which assumed change scenario is severe and
the improvement rate of which assumed control is low or high.
Accordingly, an effect that the operator can easily review the
voltage stability improvement countermeasures.
[0047]
Returning to Fig. 8, here, in final Step S7, as the voltage
stability monitoring status, a screen display of the voltage
stability improvement countermeasure search result data D10
that is the time-series voltage stability calculation result
49
D8, the degree of deviation from before change and after assumed
change, the degree of deviation improvement rate calculation
result, and the recommended controlled device calculation
result. The various types of calculation results or data
accumulated in the memory during the calculation may be
sequentially displayed on the screen of the monitoring control
device 210. Accordingly, an operator can easily grasp the
operational status of the voltage stability monitoring device
10. In addition, in the voltage stability monitoring device
10, as the operational status, monitoring contents (the system
data receiving, the present and absent of the voltage stability
monitoring calculation end, the degree of deviation, the
voltage stability calculation result after T1 seconds and T2
seconds) and the like may be displayed. Accordingly, an
operator can easily grasp the operational status of the voltage
stability monitoring device 10. The screen display of the
status from the receiving of various types of data items to
the transmitting of the various types of calculation results
respectively, until the change of the monitoring location is
executed. Thereafter, the step may return to a receiving step
of data of Step S2 and by returning to the input process of
the data of Step S1, the input data may be corrected. By
displaying the screen display as an alarm, the effect the
operator's notice can be generated is achieved. On the other
hand, when the alarm is issued too much, there is possibility
50
that the failure occurs in the normal business. Accordingly,
by providing a certain degree of margin, a burden on the
operator can be reduced.
[0048]
Next, in Figs. 21 to 23, display examples of the output
screen are illustrated. Fig. 21 illustrates a diagram
illustrating an example of a screen for displaying a voltage
stability calculation result, a voltage stability margin
calculation result, and a degree of deviation from before
change to after assumed change, as a voltage stability
monitoring status. By arranging the degree of deviation as
a bar graph, an effect that the deterioration in the voltage
stability after assumed change can be understood at once is
achieved. In addition, by displaying the voltage value and
the reactive power margin of each scenario when moving the
designation location, the function that the user can easily
view the data is included. In addition, by displaying the
reactive power margin, the operator can grasp the margin at
once. In addition, several indexes of the voltage stability
can be selected, and the function that can operate respective
results and display on the screen may be included. Accordingly,
severity of voltage stability can be easily evaluated. In
addition, the function that can change the display by selecting
a past history is included. Accordingly, in general, the set
bus is indicated, and it is possible to confirm the V-Q curve
51
of the other set bus. Fig. 22 illustrates a diagram
illustrating an example of a screen for displaying a
time-series voltage stability calculation result, a voltage
stability margin calculation result, and a degree of deviation
from before change to after change, as a voltage stability
monitoring status. By adding a concept of the time axis to
Fig. 21, an effect that a comparative evaluation of each assumed
change scenario when the time is changed is easily performed
is achieved. Fig. 23 illustrates a diagram illustrating an
example of a screen for displaying a degree of deviation
improvement rate calculation result and a recommended
controlled device calculation result. By displaying the
recommended control device on the system diagram in this manner,
an effect that the operator can easily understand the control
location can be achieved. Furthermore, a function that the
different assumed change scenarios are selected with a tab,
the improvement rate of the degree of deviation at this time
is displayed on the screen, the content can be viewed is
included. Accordingly, it is possible to easily recognize one
or more positions of the recommended control device. In
addition, the function that can change the display by selecting
a past history is included.
Reference Signs List
[0049]
10: voltage stability monitoring device
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11: display unit
12: input unit
13: communication unit
14: CPU
15: memory
20: program data (program database)
21: system measurement data (system measurement
database)
22: system facility data (system facility database)
23: threshold data (threshold database)
24: assumed control data (assumed control database)
25: renewable energy output variation prediction data
(renewable energy output variation prediction database)
26: renewable energy output control margin data
(renewable energy output control margin database)
27: assumed change scenario data (assumed change
scenario database)
28: time-series voltage stability calculation result
data (time-series voltage stability calculation result
database)
29: voltage stability improvement countermeasure
necessity determination result data (voltage stability
improvement countermeasure necessity determination result
database)
30: voltage stability improvement countermeasure search
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result data (voltage stability improvement countermeasure
search result database)
31: assumed change scenario calculation unit
32: time-series voltage stability calculation unit
33: voltage stability improvement countermeasure
necessity determination unit
34: voltage stability improvement countermeasure search
calculation unit
40: voltage stability calculation unit
41: voltage stability monitoring calculation result data
(voltage stability monitoring calculation result database)
42: bus line
43: measurement device
51: system measurement data
100: electric power system
110: power source (including renewable energy power
source)
120a, 120b, 121a, 121b: node (bus)
130a, 130b: electric transformer
140a, 140b, 141a, 141b: branch (line)
150: load
210: monitoring control device
300: communication network
310: voltage stability monitoring screen
320: voltage stability calculation result screen of
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time-series, voltage stability margin calculation result
screen, screen of degree of deviation from before change to
after assumed change
330: degree of deviation improvement rate calculation
result screen of each scenario
340: system information screen of recommended controlled
device calculation result
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WE CLAIM:
[Claim 1]
A voltage stability monitoring device for monitoring
voltage stability of a system comprising:
an assumed change scenario calculation unit for
predicting output variation of a renewable energy connected
to the system and calculating an assumed change time-series
power flow state on the basis of the output variation;
a time-series voltage stability calculation unit for
calculating a node voltage change with respect to demand at
each node of the system on the basis of the power flow state
calculated by the assumed change scenario calculation unit and
calculating a voltage stability indicating a relationship
curve between the node voltage and reactive power; and
a voltage stability improvement countermeasure search
unit for determining a controlled device on which an assumed
control is to be performed, according to the voltage stability
calculated by the time-series voltage stability calculation
unit.
[Claim 2]
The voltage stability monitoring device according to
Claim 1, further comprising:
a voltage stability improvement countermeasure
necessity determination unit for determining whether to
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perform the assumed control depending on a predetermined index
to be calculated from the voltage stability.
[Claim 3]
The voltage stability monitoring device according to
Claim 1,
wherein the assumed change scenario calculation unit
calculates the flow state on the basis of an assumed change
including at least one of a failure location of a system device,
a mode or failure releasing timing, and an output variation
of a solar power generation or a wind power generation.
[Claim 4]
The voltage stability monitoring device according to
Claim 1, further comprising:
a display unit for displaying the controlled device which
is determined in the voltage stability improvement
countermeasure search unit.
[Claim 5]
The voltage stability monitoring device according to
Claim 1,
wherein the relationship curve is calculated using a flow
calculation in which a predictor calculation and a corrector
calculation are repeated.
[Claim 6]
The voltage stability monitoring device according to
Claim 1,
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wherein the relationship curve has a time axis in
addition to axes of the voltage and the reactive power.
[Claim 7]
The voltage stability monitoring device according to
Claim 2,
Wherein the voltage stability improvement
countermeasure necessity determination unit calculates a
degree of deviation which is obtained by integrating a
difference between the relationship curves before and after
the assumed change over a predetermined voltage range and
determines whether to perform the assumed control depending
on whether the degree of deviation is in a predetermined
threshold value.
[Claim 8]
The voltage stability monitoring device according to
Claim 7,
wherein the controlled device on which the assumed
control is to be performed when an average value of a plurality
of degrees of deviation becomes lower is determined and the
controlled device is displayed on a screen.
[Claim 9]
The voltage stability monitoring device according to
Claim 7,
wherein an improvement rate of the degree of the
deviation is calculated on the basis of the degree of deviation
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before and after the assumed change and the degree of deviation
after the assumed control is performed.
[Claim 10]
A method of monitoring voltage stability for monitoring
voltage stability of a system, the method comprising:
a step for predicting output variation of a renewable
energy connected to the system and calculating an assumed
change time-series power flow state on the basis of the output
variation;
a step for calculating a node voltage change with respect
to demand at each node of the system on the basis of the power
flow state and calculating a voltage stability indicating a
relationship curve between the node voltage and reactive power;
a step for determining a controlled device on which an
assumed control is to be performed, according to the voltage
stability; and
a step for displaying the determined controlled device
on a screen.