Title of Invention

SYSTEMS AND METHOD FOR COORDINATED CONTROL OF A SWITCHED POWER CAPACITOR WITH AN INTEGRATED RESONANCE PROTECTION SYSTEM

Abstract A method for coordinated control of a switched power capacitor with an integrated resonance protection function, comprising the steps of: A. receiving Control parameters and an indication of whether a harmonic resonance condition is present; B. if a harmonic resonance condition is present, then determining if resonance flag is set If a resonance flag is not set, then a. determining if a resonance condition is present; b if a resonance condition is present, then adjusting control parameters and setting a resonance flag; if a resonance flag is set, then a. adjusting control parameters, b. determining if a resonance flag resets condition is present; and c.if a resonance flag reset condition is present, then resetting the resonance flag, and C. performing capacitor switching operations based on said control parameters and returning to step A.
Full Text BACKGROUND OF THE INVENTION
Field of the invention
The present invention relates to systems and methods for coordinated control of a
switched power capacitor with an integrated resonance: protection system. More specifically, die
invention relates to adjusting calculations made by the primary control system in response to a.
determination of a harcr onic resonance condition by the resonance protection system.
Description of the Prior Art
Existing switch d power capacitor control systems may include a primary control system
and a harmonic resonance protection system. The primary control system determines if a
capacitor switching operation is needed by comparing actual control parameters to target control
parameters and determining if a switching operation would make the actual control parameters
closer in value to the target control parameters. Target control parameters are predetermined.
Actual control parameters are calculated by the primfiry control system based on measurements
of voltages and currents obtained with voltage and current transformers respectively. If a
switching operation is required, the primary control system further determines which capacitor
bank is to be switched based on other factors such as, for example, a capacitor's size and whether
a capacitor is connected or disconnected
The resonance protection system monitors the circuit for harmonic; resonance conditions.
Harmonic resonance conditions may be due to capacitor switching operations or system changes
such as, for example, a bad change, a system source impedance change, or a network topology
change. Harmonic resonance may cause significant harmonic distortion in the system voltages
and currents, which may increase the losses m the circuit and cause damage to equipment
operating in the system due to overheating and vibration. When a resonance condition due to
capacitor switching opeaton is detected, the protection system performs additional capacitor
switching operation to d-tune the circuit from the sustained resonance. If a switching operation
is required, the harmen resonance protection system further determines which capacitor is to be
switched based on other factors such as, for example, a capacitor's size and whether a capacitor
is connected or discount cted.
Existing switched power capacitor control systems may contain both an independent
primary control system and an independent resonance protection system. The independence of
these two systems rcsul s in several drawbacks. First, the independent systems must duplicate
certain functions such a;, for example, detennining whether a capacitor is connected and
generating a signal to control a capacitor. Second, the independent systems may, under certain
circumstances, force the capacitor banks into a constant on/off operation deadlock. For example,
the primary control syst sm may determine that a certain capacitor bank needs 10 be switched on.
If switching on this capacitor bank tunes the circuit to a resonance condition, then the resonance
protection system will perform additional capacitor switching operations to de-rune the circuit
from the sustained resonance. It is possible that the resonance protection system may determine
to switch off the same capacitor bank that the primary control system switched on. Once the
capacitor bank is switched off by the resonance protection system, the primary control system
will switch the capacitor bank back on- This operation deadlock can cause excessive wear to the
capacitors and the switching apparatus. Thus, it would be a great improvement in the art to
integrate and coordinate the primary control system and the resonance protection system to avoid
duplication of functions and switching deadlock.
SUMMARY OF THE UNTVENTION
The present invention is directed to systems and methods for coordinated control of a
switched power capacitor with an integrated resonance protection function. The coordination
system receives control parameters calculated by the primary control unit. The coordination
system also receives from the resonance protection system an input indicating whether a
harmonic resonance coidition is present. If a harmonic resonance condition is present, the
coordination system adjusts the control parameters. If no harmonic resonance condition is
present, the control parameters calculated by the primary control system are nor. changed. The
coordination system then performs capacitor bank switching operations based on either the
control parameters originally calculated by the primary control system or the adjusted control
parameters.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present invention will be better understooc. after reading the following detailed
description of the presently preferred embodiments thereof with reference to ihe appended
drawings, in which:
Figure 1 illustrates a switched power capacitor device in accordance with an aspect of the
present invention;
Figure 2 illustrates a block diagram of a control unit of a switched power capacitor device
in accordance with the present invention; and
Figure 3 illustrates a flow chart of an illustrative method for coordinating the control
system of a switched power capacitor in accordance with the present invention.
DETAILED DESCRD7TION OF DLLUSTRATTVE EMBODIMENTS
Systems and methods for coordinated control of a switched power capacitor with an
integrated resonance protection function in accordance with the present invention are described
below with reference to Figures 1-3. Those skilled in the art will readily appreciate that the
description given herein with respect to those figures is for explanatory purposes only and is not
intended in any way to limit the scope of the invention. Throughout the description, like
reference numerals will refer to like elements in the respective figures.
Figure 1 illustrates a switched power capacitor device 120 in accordance with an aspect
of the present invention. As shown, feeder 110 feeds switched power capacitor device 120 that
includes breaker switched capacitor banks 140a and 140b along with control unit 160. Control
unit 160 measures voltage 180 and current 190 to determine switching operations for capacitor
banks 140a and 140b that provide the desired power to load 170.
Figure 2 illustrates a block diagram of the control unit 160 of the switched power
capacitor device 120 in accordance with the present invention. Generally, primary control
system 220 calculates control parameters. Resonance protection system 230 determines if a
harmonic resonance condition is present. Coordination system 240 adjusts the control
parameters if a harmonic resonance condition is present and performs capacitor switching
operations based on the control parameters.
As shown in Figure 2, primary control system 220 transmits control parameters 222 to
coordination system 240. Control parameters 222 comprise any parameter relevant to the control
of a switched power capacitor, such as, for example, power factor and node voltage. Control
parameters 222 consist of both pre-determined target parameters and actual parameters
calculated by primary control system 220. Control parameters 222 may also consist of the
difference between target parameters and actual parameters. Primary control system calculates
actual parameters based on measurements of voltage 180 and current 190 obtained with voltage
and current transformers respectively.
Resonance protection system 230 determines if a harmonic resonance condition is present
and transmits an input 232 to coordination system 240 indicating whether a harmonic resonance
condition had been detected. Exemplary methods for determining if a harmonic resonance
condition is present are described in detail, in U.S. Pat. No. 6,181,113 which is hereby
incorporated by reference in its entirety. If input 232 indicates that a harmonic resonance
condition is present, then coordination system 240 adjusts control parameters 222. Coordination
system 240 adjusts control parameters 222 to de-tune switched power capacitor 120 from a
harmonic resonance condition. Coordination system 240 may adjust control parameters 222 by
any method such as, for example, reducing the target reactive power by the value of the reactive
power provided by one capacitor bank.
Coordination system 240 performs capacitor bank switching operations 244 based on
control parameters 222. Coordination system 240 compares actual control parameters to target
control parameters, and determines if a switching operation is necessary to make the value of the
actual parameters closer to the value of the target parameters. Coordination system 240 further
determines whether a switching operation is needed based on other factors such as, for example,
the operating status 242 of each capacitor bank and the size of each capacitor. Determining the
operating status 242 of each capacitor comprises determining whether the capacitor is connected
or disconnected.
Figure 3 illustrates a flow chart of an illustrative method for controlling a switched power
capacitor in accordance with the present invention. At step 310, coordination system 240 clears
resonance flags. At step 312, coordination system 240 receives control parameters 222 from
primary control system 220. Control parameters 222 comprise any parameter relevant to the
control of a switched power capacitor, such as, for example, power factor and node voltage. At
step 314, coordination system 240 determines if a resonance flag is set.
If a resonance flag is not set, then, at step 316, coordination system 240 determines
whether input 232 indicates that a harmonic resonance condition is present. If a harmonic
resonance condition is present, then, at step 318, coordination system 240 sets a resonance flag
and adjusts control parameters 222. Coordination system 240 may adjust control parameters 222
by any method such as, for example, reducing the target reactive power by the value of the
reactive power provided by one capacitor bank.
If a resonance flag is set, then, at step 320, coordination system 240 adjusts control
parameters 222. The adjustment made at step 320 will be equivalent to the adjustment made at
step 318 to avoid performing multiple switching operations prior to the reset of a resonance flag.
At step 322, coordination system 240 determines if resonance flag reset conditions have been
satisfied. A resonance flag reset condition may be triggered by the expiration of a pre-set time
delay or by a system condition change that exceeds a preset threshold value. A system condition
change may include events such as, for example, a load change, a system source impedance
change, or a network topology change. Such events may de-tune the circuit from a resonance
condition. If a resonance flag reset condition has been satisfied, then, at step 324, coordination
system 240 resets the resonance flag.
At step 326, coordination system 240 determines if a capacitor bank switching operation
244 is needed. To determine if a capacitor switching operation is needed, coordination system
240 compares actual control parameters to target control parameters, and determines if a
switching operation is necessary to make the value of the actual parameters closer to the value of
the target parameters. Coordination system 240 further determines whether a switching
operation is needed based on other factors such as, for example, the operating status 242 of each
capacitor bank and the size of each capacitor. Determining the operating status 242 of each
capacitor comprises determining whether the capacitor is connected or disconnected. If a
capacitor bank switching operation 244 is needed, then, at step 328, coordination system 240
performs capacitor bank switching operations 244. The method then returns to step 312.
While the invention has been described and illustrated with reference to specific
embodiments, those skilled in the art will recognize that modification and variations may be
made without departing from the principles of the invention as described above and set forth in
the following claims. For example, while the invention has been described as adjusting the
control parameters by reducing the target reactive power value by the value provided by one
capacitor bank, the invention may also adjust the control parameters by reducing the target
reactive power value by die value provided by a plurality of capacitor banks. Furthermore, the
resonance protection system may use any method to detect a harmonic resonance condition and
is not limited to the method described in U.S. Pat. No. 6,181,113 which is incorporated by
reference above with reference to Figure 1. Accordingly, reference should be made to the
appended claims as indicating the scope of the invention.
WE CLAIM:
1. A method for coordinated control of a switched power capacitor with an
integrated resonance protection function, comprising the steps of:
A. receiving control parameters and an indication of whether a
harmonic resonance condition is present;
B.. if a harmonic resonance condition is present, then determining if
resonance flag is set;
if a resonance flag is not set, then
a. determining if a resonance condition is present;
b. if a resonance condition is present, then adjusting control
parameters and setting a resonance flag;
if a resonance flag is set, then
a. adjusting control parameters
b. determining if a resonance flag reset condition is present; and
c. if a resonance flag reset condition is present, then resetting the
resonance flag, and
C. performing capacitor switching operations based on said control
parameters and returning to step A.
2. A method as claimed in claim 1, wherein said step of receiving control
parameters comprises receiving target control parameters and actual control
parameters.
3. A method as claimed in claim 1, wherein said step of receiving control
parameters comprises receiving at least one of the power factor and node
voltage.
4. A method as claimed in claim 1, wherein said step of determining if a
resonance flag reset condition is present comprises determining if at least one of
a pre-determined time delay has expired and a system condition change
exceeding a pre-determined threshold value has occurred.
5. A method as claimed in claim 4, wherein said step of determining if a
system condition change exceeding a pre-determined threshold value has
occurred comprises determining if at least one of a load change, a system source
impedance change, and a network topology change exceeding a pre-determined
threshold value has occurred.
6. A method as claimed in claim 1, wherein said step of adjusting the control
parameters comprises reducing the reactive power by the reactive power
provided by one capacitor bank.
7. A method as claimed in claim 1, wherein said step of performing capacitor
switching operations comprises the steps of:
determining if capacitor switching operations are needed; and
if capacitor switching operations are needed, then performing capacitor
switching operations.
8. A method as claimed in claim 7, wherein said step of determining if
capacitor switching operations are needed comprises the steps of:
comparing actual control parameters with target control parameters; and
determining whether a capacitor switching operation would make actual
control parameters closer to target control parameters.
9. A method as claimed in claim 8, comprising at least one determining
whether each capacitor bank is connected or disconnected and determining the
size of each capacitor.
10. A system for coordinated control of a switched power capacitor with an
integrated resonance protection function, comprising a control processor
programmed to perform the following process:
A." receive control parameters and an indication of whether a harmonic
resonance condition is present;
B. if a harmonic resonance condition is present,
determining if a resonance flag is set;
if a resonance flag is not set, then
a. determining if a resonance condition is present;
b. if a resonance condition is present, then adjusting control
parameters and setting a resonance flag;
if a resonance flag is set, then
a. adjusting control parameters
b. determining if a resonance flag reset condition is present; and
c. if a resonance flag reset condition is present, then resetting the
resonance flag, and
C. perform capacitor switching operations based on said control
parameters and return to step A.
11. A system as claimed in claim 10, wherein said control parameters
comprise target control parameters and actual control parameters.
12. A system as claimed in claim 10, wherein said control parameters
comprise at least one of the power factor and node voltage.
13. A.system as claimed in claim 10, wherein said resonance flag reset
condition comprises at least one of the expiration of a pre-determined time delay
and a system condition change exceeding a pre-determined threshold value.
14. A system as claimed in claim 13, wherein said system condition change
comprises at least one of a load change, a system source impedance change,
and a network topology change.
15. A system as claimed in claim 10, wherein adjusting the control parameters
comprises reducing the reactive power by the reactive power provided by one
capacitor bank.
16. A system as claimed in claim 10, wherein performing capacitor switching
operations comprises:
determining if capacitor switching operations are needed; and
if capacitor switching operations are needed, then performing capacitor switching
operations.
17. A system as claimed in claim 16, wherein determining if capacitor
switching operations are needed comprises:
comparing actual control parameters with target control parameters; and
determining whether a capacitor switching operation would make actual control
parameters close to target control parameters.
18. A system as claimed in claim 17, comprising at least one of determining
whether each capacitor bank is connected or disconnected and determining the
size of each capacitor.

A method for coordinated control of a switched power capacitor with an
integrated resonance protection function, comprising the steps of: A. receiving
Control parameters and an indication of whether a harmonic resonance condition
is present; B. if a harmonic resonance condition is present, then determining if
resonance flag is set If a resonance flag is not set, then a. determining if a
resonance condition is present; b if a resonance condition is present, then
adjusting control parameters and setting a resonance flag; if a resonance flag is
set, then a. adjusting control parameters, b. determining if a resonance flag
resets condition is present; and c.if a resonance flag reset condition is present,
then resetting the resonance flag, and C. performing capacitor switching
operations based on said control parameters and returning to step A.

Documents:

904-kolnp-2004-abstract.pdf

904-kolnp-2004-assignment.pdf

904-kolnp-2004-claims.pdf

904-KOLNP-2004-CORRESPONDENCE-(12-12-2011).pdf

904-kolnp-2004-correspondence.pdf

904-kolnp-2004-description (complete).pdf

904-kolnp-2004-drawings.pdf

904-kolnp-2004-examination report.pdf

904-kolnp-2004-form 1.pdf

904-kolnp-2004-form 13.pdf

904-kolnp-2004-form 18.pdf

904-kolnp-2004-form 2.pdf

904-kolnp-2004-form 26.pdf

904-kolnp-2004-form 3.pdf

904-kolnp-2004-form 5.pdf

904-kolnp-2004-granted-abstract.pdf

904-kolnp-2004-granted-assignment.pdf

904-kolnp-2004-granted-claims.pdf

904-kolnp-2004-granted-correspondence.pdf

904-kolnp-2004-granted-description (complete).pdf

904-kolnp-2004-granted-drawings.pdf

904-kolnp-2004-granted-examination report.pdf

904-kolnp-2004-granted-form 1.pdf

904-kolnp-2004-granted-form 13.pdf

904-kolnp-2004-granted-form 18.pdf

904-kolnp-2004-granted-form 2.pdf

904-kolnp-2004-granted-form 26.pdf

904-kolnp-2004-granted-form 3.pdf

904-kolnp-2004-granted-form 5.pdf

904-kolnp-2004-granted-reply to examination report.pdf

904-kolnp-2004-granted-specification.pdf

904-KOLNP-2004-PA-CERTIFIED COPIES-(12-12-2011).pdf

904-kolnp-2004-reply to examination report.pdf

904-kolnp-2004-specification.pdf


Patent Number 239970
Indian Patent Application Number 904/KOLNP/2004
PG Journal Number 16/2010
Publication Date 16-Apr-2010
Grant Date 16-Apr-2010
Date of Filing 28-Jun-2004
Name of Patentee ABB TECHNOLOGY AG
Applicant Address AFFOLTERNSTRASSE 44, CH-8050 ZURICH
Inventors:
# Inventor's Name Inventor's Address
1 GATELLI FABIO VIA MONTIRONE, 40, I-25021 BAGNOLO MELLA
2 EGOLR, WILLIAM M 1702 WALDEN MCADOW DRIVE, AREX, NC 27502
3 HART DAVID G 2726 BLAYDON DRIVE, RALEIGH, NC 27606
4 HU YI 300 FAIRFAX LANE, CARY, NC 27513
5 DI MAIO LUCIANO VIA G. ARGANINI, 10, I-20162 MILANO
PCT International Classification Number H01G
PCT International Application Number PCT/US02/41297
PCT International Filing date 2002-12-20
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/034, 063 2001-12-26 U.S.A.