The present subject matter relates generally to electrical generation and,
more particularly, to a system and method for limiting overvoltage events during
islanding of one or more sources of electrical generation.
BACKGROUND OF THE INVENTION
In some instances, sources of electrical generation may be located in
remote areas far from the loads they serve. This is particularly true for renewable
energy sources such as wind turbine generators, solar/photovoltaic generation,
hydroelectric generators, and the like. Typically, these sources of generation are
connected to the electrical grid through an electrical system such as long transmission
lines. These transmission lines are connected to the grid using one or more breakers.
Sudden tripping of the transmission line breaker at the grid side while the source of
generation is under heavy load may result in an overvoltage on the transmission line
that can lead to damage to the source of generation or equipment associated with the
source of generation such as converters and inverters.
Accordingly, an improved system and/or method that provides for
sufficient voltage limitation to prevent damaging the sources of generation and
equipment associated with the sources of generation would be welcomed in the
technology.
BRIEF DESCRIPTION OF THE INVENTION
Aspects and advantages of embodiments of the invention will be set forth
in part in the following description, or may be obvious from the description, or may
be learned through practice of the invention.
In one aspect, the present subject matter discloses a method for
overvoltage protection of an electrical system. The method may generally include
detecting an overvoltage condition on an electrical system; and switching on, in
response to the detected overvoltage condition, an impedance connected to the
electrical system, wherein the impedance clamps voltage on the electrical system.
In another aspect, the present subject matter discloses a method for
overvoltage protection for a grid-islanding event of an electrical system. The method
may generally includedetecting a grid islanding event on a poly-phase electrical
system, wherein the grid islanding event is caused by disconnecting of one or more
sources of electrical generation from an electrical grid; switching on, in response to
the detected grid islanding event, an impedance connected between each phase of the
poly-phase electrical system, wherein a overvoltage caused by the grid islanding event
is limited by the impedance clamping voltage on the poly-phase electrical system; and
switching off the impedance connected between each phase of the poly-phase
electrical system when the overvoltage event drops below a threshold voltage value.
In another aspect, the present subject matter discloses a system for
overvoltage protection of an electrical system. The system may be comprised of one
or more impedance elements; one or more switches in series with the one or more
impedance elements; and a controller, wherein the controller is configured to: receive
an indication of a detection of an overvoltage condition on an electrical system; and
cause the one or more switches to connect the one or more impedance elements to the
electrical system in response to receiving the indication of the detected overvoltage
condition, wherein the overvoltage condition is limited by the one or more impedance
elements clamping voltage on the electrical system.
These and other features, aspects and advantages of the present invention
will become better understood with reference to the following description and
appended claims. The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
A full and enabling disclosure of the present invention, including the best
mode thereof, directed to one of ordinary skill in the art, is set forth in the
specification, which makes reference to the appended figures, in which:
FIG. 1 is a schematic diagram of an exemplary power generation system that
includes at least one power generation unit;
FIG. 2A is a simplified single-line diagram of an electrical power system
network;
FIG. 2B illustrates the electrical power system network of FIG. 2A, where the
grid-side breaker has opened;
FIG. 3A illustrates a simplified form of a three-line diagram of an embodiment
of an electrical network further comprising an embodiment of a system for
overvoltage protection;
FIG. 3B illustrates a simplified form of a three-line diagram of an embodiment
of an electrical network further comprising an embodiment of a system for
overvoltage protection, wherein the one or more switches are comprised of three
SCRs;
FIGS. 3C and 3D illustrate alternate embodiments of simplified forms of
three-line diagrams of embodiments of an electrical network further comprising
embodiments of systems for overvoltage protection;
FIG. 4 illustrates a schematic diagram of one embodiment of a controller;
FIG. 5 illustrates one embodiment of a method for overvoltage protection of
an electrical system; and
FIG. 6 illustrates an embodiment of a method for overvoltage protection for a
grid-islanding event of an electrical system.
DETAILED DESCRIPTION OF THE INVENTION
Reference now will be made in detail to embodiments of the invention,
one or more examples of which are illustrated in the drawings. Each example is
provided by way of explanation of the invention, not limitation of the invention. In
fact, it will be apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing from the scope or
spirit of the invention. For instance, features illustrated or described as part of one
embodiment can be used with another embodiment to yield a still hrther
embodiment. Thus, it is intended that the present invention covers such modifications
and variations as come within the scope of the appended claims and their equivalents.
Before the present methods and systems are disclosed and described, it is
to be understood that the methods, systems and computer program products are not
limited to specific synthetic methods, specific components, or to particular
compositions. It is also to be understood that the terminology used herein is for
describing particular embodiments only and is not intended to be limiting.
As used in the specification and the appended claims, the singular forms
"a,', "an', and "the" include plural referents unless the context clearly dictates
otherwise. Ranges may be expressed herein as from "about" one particular value,
and/or to "about" another particular value. When such a range is expressed, another
embodiment includes from the one particular value and/or to the other particular
value. Similarly, when values are expressed as approximations, by use of the
antecedent "about," it will be understood that the particular value forms another
embodiment. It will be hrther understood that the endpoints of each of the ranges are
significant both in relation to the other endpoint, and independently of the other
endpoint.
[0013] "Optional" or "optionally" means that the subsequently described event or
circumstance may or may not occur, and that the description includes instances where
said event or circumstance occurs and instances where it does not.
Throughout the description and claims of this specification, the word
"comprise" and variations of the word, such as "comprising" and "comprises," means
"including but not limited to," and is not intended to exclude, for example, other
additives, components, integers or steps. "Exemplary" means "an example of' and is
not intended to convey an indication of a preferred or ideal embodiment. "Such as" is
not used in a restrictive sense, but for explanatory purposes.
Disclosed are components that can be used to perform the disclosed
methods and systems. These and other components are disclosed herein, and it is
understood that when combinations, subsets, interactions, groups, etc. of these
components are disclosed that while specific reference of each various individual and
collective combinations and permutation of these may not be explicitly disclosed,
each is specifically contemplated and described herein, for all methods and systems.
This applies to all aspects of this application including, but not limited to, steps in
disclosed methods. Thus, if there are a variety of additional steps that can be
performed it is understood that each of these additional steps can be performed with
any specific embodiment or combination of embodiments of the disclosed methods.
The present methods and systems may be understood more readily by
reference to the following detailed description of preferred embodiments and the
Examples included therein and to the Figures and their previous and following
description.
In general, the present subject matter is directed to a system and methods
for limiting voltage on an electrical system. In particular, aspects of the invention are
directed at limiting voltage on an electrical system caused by the islanding of one or
more sources of electrical generation. Islanding occurs when one or more sources of
electrical generation such as a wind park comprised of one or more wind turbine
generators abruptly and unexpectedly is disconnected with the electrical grid. For
example, islanding can occur when a breaker on the grid side of an electrical system
such as a transmission line opens thereby disconnecting the one or more sources of
electrical generation from the grid. This can result in high voltages on the electrical
system. If the one or more sources of electrical generation utilize an AC-DC
converter and/or a DC to AC inverter, then high voltages can occur on the DC link
that connects the converter and inverter (if used) and can damage converter and/or
inverter components. This can be more readily seen with reference to FIG. 1.
FIG. 1 is a schematic diagram of an exemplary power generation system
100 that includes at least one power generation unit 102. Power generation unit 102
includes a wind turbine, a solar panel or array, a he1 cell, a geothermal generator, a
hydropower generator, and/or any other device that generates electrical power. More
specifically, in the exemplary embodiment, power generation unit 102 can be a device
that generates direct current (DC) electrical power from at least one renewable energy
source. Alternatively, power generation unit 102 is a gas turbine, a steam turbine,
and/or any other device that generates DC or alternating current (AC) power from a
renewable or non-renewable energy source.
In the exemplary embodiment, power generation unit 102 is coupled to a
power converter system 104, or a power converter 104. DC power generated by
power generation unit 102 is transmitted to power converter system 104, and power
converter system 104 converts the DC power to AC power. The AC power is
transmitted to an electrical transmission and distribution network 106, or "grid."
Power converter system 104, in the exemplary embodiment, adjusts an amplitude of
the voltage and/or current of the converted AC power to an amplitude suitable for
electrical transmission and distribution network 106, and provides AC power at a
frequency and a phase that are substantially equal to the frequency and phase of
electrical transmission and distribution network 106. Moreover, in the exemplary
embodiment, power converter system 104 provides three phase AC power to electrical
transmission and distribution network 106. Alternatively, power converter system
104 provides single phase AC power or any other number of phases of AC power to
electrical transmission and distribution network 106.
In the exemplary embodiment, power converter system 104 includes a DC
to DC, or "boost," converter 108 and an inverter 110 coupled together by a DC bus
112. Alternatively, power converter system 104 may include an AC to DC converter
108 for use in converting AC power received from power generation unit 102 to DC
power, and/or any other converter 108 that enables power converter system 104 to
function as described herein. In one embodiment, power converter system 104 does
not include converter 108, and inverter 1 10 is coupled to power generation unit 102
by DC bus 112 and/or by any other device or conductor. In the exemplary
embodiment, inverter 110 is a DC to AC inverter 110 that converts DC power
received from converter 108 into AC power for transmission to electrical transmission
and distribution network 106. Moreover, in the exemplary embodiment, DC bus 1 12
includes at least one capacitor 114. Alternatively, DC bus 112 includes a plurality of
capacitors 114 and/or any other electrical power storage devices that enable power
converter system 104 to function as described herein. As current is transmitted
through power converter system 104, a voltage is generated across DC bus 112 and
energy is stored within capacitors 1 14.
Power converter system 104 includes a control system 116 coupled to
converter 108 and/or to inverter 110. In the exemplary embodiment control system
116 includes and/or is implemented by at least one processor. As used herein, the
processor includes any suitable programmable circuit such as, without limitation, one
or more systems and microcontrollers, microprocessors, reduced instruction set
circuits (RISC), application specific integrated circuits (ASIC), programmable logic
circuits (PLC), field programmable gate arrays (FPGA), andlor any other circuit
capable of executing the functions described herein. The above examples are
exemplary only, and thus are not intended to limit in any way the definition and/or
meaning of the term "processor."
In the exemplary embodiment, control system 1 16 controls and/or operates
converter 108 to adjust or maximize the power received from power generation unit
102. Moreover, in the exemplary embodiment, control system 116 controls and/or
operates inverter 110 to regulate the voltage across DC bus 112 and/or to adjust the
voltage, current, phase, frequency, and/or any other characteristic of the power output
fi-om inverter 1 10 to substantially match the characteristics of electrical transmission
and distribution network 106.
During an islanding event, power generation unit 102 becomes
disconnected from the grid 106. This can result in an overvoltage on the electrical
system that connects the generation unit 102 with the grid 106. An overvoltage can
be a short-term or longer duration increase in the measured voltage of the electrical
system over its nominal rating. For example, the overvoltage may be 1%, 5% lo%,
50% or greater, and any values therebetween, of the measured voltage over the
nominal voltage. This overvoltage on the AC side of the inverter 108 causes energy
to be pumped into capacitors 114, thereby increasing the voltage on the DC link 112.
The higher voltage on the DC link 112 can damage one or more electronic switches
such as a gate turn-off (GTO) thyristor, gate-commutated thyristor (GCT), insulated
gate bipolar transistor (IGBT), MOSFET, combinations thereof, and the like located
within the inverter 1 10 and/or converter 108.
FIG. 2A is a simplified single-line diagram of an electrical power system
network 200. In this exemplary arrangement, the electrical generation unit 102 is
connected to the grid 106 through a transformer 202 that steps up or steps down the
AC power created by the generation unit 102 alone or in cooperation with a convertor
1 10 and/or inverter 108. AC power is routed through a generator-side breaker 204, a
transmission line 206, a grid side breaker 208 and to the grid 106. Components of the
network 200 can be comprised of AC single phase, AC poly-phase or DC electrical
apparatus, as needed. For example, the transmission line 206 may be a three-phase
(AC) transmission line. As shown, both the generator-side breaker 204 and the gridside
breaker 208 are closed.
FIG. 2B illustrates the electrical power system network 200 of FIG. 2A,
where the grid-side breaker 208 has opened. This can be the result of a fault on the
grid 106, a fault on the transmission line 206, a malfunction of the grid-side breaker
208, an accidental opening of the breaker 208, and the like. The transmission line 206
may also be opened by an open circuit fault such as that caused by cutting or breaking
the transmission line 206. Such an open circuit condition, whatever the cause, can
create an overvoltage on the affected phases of the transmission line 206 if the
electrical generation unit 102 is under load and producing power at the time of the
open circuit event. In some instances, the controller may not recognize the open
circuit or islanding event, or may react too slowly to the event, and damage may occur
to components that comprise the electrical system. In particular, electronic switches
used in a convertor 1 10 andlor inverter 108 may be damaged during the overvoltage.
FIG. 3A illustrates a simplified form of a three-line diagram of an
embodiment of an electrical network 200 further comprising an embodiment of a
system for overvoltage protection. In this embodiment, the overvoltage system
comprises one or more impedance elements 302 connected between the phases 304 of
the electrical system 206. Though the electrical system 206 illustrates three phases, it
is to be appreciated that embodiments of the present invention can be configured to
adapt to any single-phase or poly-phase electrical system. The shown embodiment
further comprises one or more switches 306 in series with the one or more impedance
elements 302. In one aspect, the switches 306 can be one or more electronic or
mechanical switches or combinations thereof. For example, the switches can be
mechanical switches that are controlled by motors, springs, and the like. In another
aspect, the switches 306 can be electronic switches such as silicon controller rectifiers
(SCRs) that are controlled by a gate, as are known in the art. Other electronic
switches that may be suitable include integrated gate-commutated thyristors (IGCTs),
insulated gate bipolar transistors (IGBTs), and the like. FIG. 3B illustrates a
simplified form of a three-line diagram of an embodiment of an electrical network
200 further comprising an embodiment of a system for overvoltage protection,
wherein the one or more switches 306 are comprised of three SCRs 308.
Returning to FIG. 3A, the impedance elements 302 can be comprised of
resistance elements, inductive elements, or combinations thereof. Generally, the
impedance elements 302 can be connected between each phase 304 of a poly-phase
electrical system 206. The impedance elements 302 can be sized based at least in part
on a voltage of the electrical system 206, impedance of the electrical system 310 to
the point where the impedance elements 302 are connected to the electrical system
206, current supplied by any sources of electrical generation 102 connected to the
electrical system 206, and a desired clamping level of the overvoltage condition.
Though not shown in FIG. 3A (or FIGS. 3B, 3C and 3D), switches 306 can be
controlled (i.e., placed in a conducting or non-conducting state) by commands from a
controller. In one aspect, the controller can be configured to receive an indication of a
detection of an overvoltage condition on an electrical system 206; and cause the one
or more switches 306 to connect the one or more impedance elements 302 to the
electrical system 206 in response to receiving the indication of the detected
overvoltage condition, wherein the overvoltage condition is limited by the one or
more impedance elements 302 clamping voltage on the electrical system. In this way,
the impedance elements 302 act as a voltage divider for the phases of the electrical
system 206 (in conjunction with the line impedance 310), and thus the desired
clamping level can be set by sizing the impedance elements 302 to the desired level.
In one aspect, the overvoltage condition on the electrical system 206 can be caused by
islanding of one or more sources of electrical generation 102 from an electrical grid
106. In various aspects, the one or more sources of electrical generation 102 can
comprise one or more wind turbine generators, one or more sources of
solar/photovoltaic generation, one or more hydroelectric generators, one or more gas
turbine generators, one or more steam turbine generators, combinations thereof, and
the like. Figures 3A and 3B generally illustrate the impedance elements 302
connected in a wye configuration. This configuration has the advantages of lower
voltage stress on the SCR 308 or switch 306 because L-N voltage is lower than L-L
voltage.
FIGS. 3C and 3D illustrate alternate embodiments of simplified forms of
three-line diagrams of embodiments of an electrical network 200 further comprising
embodiments of systems for overvoltage protection. The configuration illustrated in
FIGS. 3C and 3D allow a single impedance element 302 to be connected between the
phases 304 of the electrical system 206. This can be compared to FIGS. 3A and 3B
where two impedance elements 302 are connected in series between two phases when
the switches 306 are in a conducting state. In FIG. 3D, the overvoltage system
comprises two SCRs 308 per impedance element. FIGS. 3C and 3D illustrate the
impedance elements 302 connected in a delta configuration. This configuration has
the advantages of redundancy, such that any one of the SCRs 308 or switches 306 can
fail, and the remaining two of the three switches will still provide a short circuit
across all three phases (if the component values are designedselected to take
advantage of this redundancy). Similarly, if any one of the impedance elements 302
or the wiring in any phase fails open, the remaining phases can still provide a short
circuit to limit the voltage across all the phases. To do this, the value of impedance
element 302 is lower to limit the total voltage to a desired level. Also the current
rating of the switches 306 must be higher to allow them to cany the total current in
two switches, which would have been divided between three switches when all three
are working properly.
Advantages of embodiments of this invention in general include being less
expensive than adding dynamic braking to every wind turbine in the wind farm. It
allows for a single control to decide when to operate it, which avoids any problems of
individual turbines acting independently. In other words, avoids any possibility of the
sources of electrical generation 102 fighting each other, some turning on and off at
different times. This also offers the advantage of higher reliability and higher
availability because it requires fewer components than adding dynamic braking to
every sources of electrical generation 102 such as every wind turbine in a wind farm.
Referring now to FIG. 4, as noted above, some embodiments of systems
for overvoltage protection can include a control system or controller 36. In general,
the controller 36 may comprise a computer or other suitable processing unit. Thus, in
several embodiments, the controller 36 may include suitable computer-readable
instructions that, when implemented, configire the controller 36 to perform various
different functions, such as receiving, transmitting andor executing control signals.
As such, the controller 36 may generally be configured to control the various
operating modes (e.g., conducting or non-conducting states) of the one or more
switches 306 andor components of embodiments of the overvoltage protection
system. For example, the controller 36 may be configured to implement methods of
operating embodiments of the overvoltage protection system.
FIG. 4 illustrates a block diagram of one embodiment of suitable
components that may be included within an embodiment of a controller 36, or any
other controller that receives signals indicating overvoltage andor islanding
conditions in accordance with aspects of the present subject matter. In various
aspects, such signals can be received from one or more sensors 58, 60, or may be
received from other computing devices (not shown) such as a supervisory control and
data acquisition (SCADA) system, a turbine protection system, and the like. As
shown, the controller 36 may include one or more processor(s) 62 and associated
memory device(s) 64 configured to perform a variety of computer-implemented
functions (e.g., performing the methods, steps, calculations and the like disclosed
herein). As used herein, the term "processor" refers not only to integrated circuits
referred to in the art as being included in a computer, but also refers to a controller, a
microcontroller, a microcomputer, a programmable logic controller (PLC), an
application specific integrated circuit, and other programmable circuits. Additionally,
the memory device(s) 64 may generally comprise memory element(s) including, but
not limited to, computer readable medium (e.g., random access memory (RAM)),
computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a
compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital
versatile disc (DVD) andor other suitable memory elements. Such memory device(s)
64 may generally be configured to store suitable computer-readable instructions that,
when implemented by the processor(s) 62, configure the controller 36 to perform
various functions including, but not limited to, directly or indirectly transmitting
suitable control signals to one or more switches 306, monitoring overvoltage andor
islanding conditions of the electrical system 206, and various other suitable computerimplemented
functions.
Additionally, the controller 36 may also include a communications module
66 to facilitate communications between the controller 36 and the various components
of the electrical system 206 andor the one or more sources of electrical generation
102. For instance, the communications module 66 may serve as an interface to permit
the controller 36 to transmit control signals to the one or more switches 306 to change
to a conducting or non-conducting state. Moreover, the communications module 66
may include a sensor interface 68 (e.g., one or more analog-to-digital converters) to
permit signals transmitted fiom the sensors (e.g., 58, 60) to be converted into signals
that can be understood and processed by the processors 62. Alternatively, the
controller 36 may be provided with suitable computer readable instructions that, when
implemented by its processor(s) 62, configure the controller 36 to calculate and/or
estimate whether a detected overvoltage condition of the electrical system 206 is the
result of islanding of the one or more sources of electrical generation based on
information stored within its memory 64 and/or based on other inputs received by the
controller 3 6.
Referring now to FIG. 5, there is illustrated one embodiment of a method
for overvoltage protection of an electrical system. This embodiment may be
implemented by the controller 36 or other computing device. As shown, the method
generally includes step 502, detecting an overvoltage on an electrical system.
Generally, this is accomplished by the controller 36 receiving one or more signals that
indicate the presence of an overvoltage condition. In one aspect, the controller 36 can
determine that the overvoltage is caused by an islanding of one or more sources of
electrical generation 102. In one aspect, detecting the overvoltage condition on the
electrical system comprises detecting when a voltage on the electrical system meets or
exceeds a voltage threshold value. For example, the voltage threshold value can be
adjustable and can be set at I%, 5%, lo%, 15% or any other value over the nominal
voltage of the electrical system. In one aspect, a delay in overvoltage protection may
be implemented in order to avoid acting on signals that may be mere noise rather than
an actual overvoltage condition. Alternatively, at step 502, a grid islanding event may
be detected (not shown in FIG. 5). This event may be detected by overvoltage or by
other signals not associated with overvoltage such as, for example, reverse power
flow, sharp swings in phase angle, and the like. Embodiments of the present
invention include current methods and systems to detect grid islanding as well as
those that may be later developed. At step 504, an impedance connected to the
electrical system is switched on in response to the detected overvoltage, wherein the
impedance clamps voltage on the electrical system. In one aspect, switching on, in
response to the detected overvoltage condition, an impedance connected to the
electrical system, wherein the impedance clamps voltage on the electrical system
comprises switching on the impedance using one or more electronic or mechanical
switches or combinations thereof. In one non-limiting example, the electronic
switches can comprise one or more silicon controlled rectifiers (SCRs). In one aspect,
switching on, in response to the detected overvoltage condition, an impedance
connected to the electrical system, wherein the impedance clamps voltage on the
electrical system comprises switching on an impedance connected between each
phase of a poly-phase electrical system. In one aspect, the impedance connected
between each phase of a poly-phase electrical system is sized based at least in part on
a voltage of the electrical system, a grid impedance of the electrical system, current
supplied by any sources of electrical generation connected to the electrical system,
and a desired clamping level of the overvoltage condition. In one aspect, switching
on, in response to the detected overvoltage condition, an impedance connected to the
electrical system, wherein the impedance clamps voltage on the electrical system
comprises switching on an impedance comprised at least in part of one or more
inductors.
FIG. 6 illustrates an embodiment of a method for overvoltage protection
for a grid-islanding event of an electrical system. This embodiment may also be
implemented by the controller 36 or other computing device. At step 602, a grid
islanding event is detected on an electrical system, wherein the grid islanding
comprises disconnecting one or more sources of electrical generation from an
electrical grid. As noted above, detecting a grid islanding event can be performed by
systems and methods now known in the art or those later developed. At step 604, an
impedance connected to the electrical system is switched on in response to the
detected grid islanding event. In one aspect, the impedance is connected between
each phase of a poly-phase electrical system, wherein an overvoltage event caused by
the grid islanding is limited by the impedance clamping voltage on the poly-phase
electrical system. At step 606, the impedance connected to the electrical system is
switched off when the overvoltage event drops below a threshold voltage value.
As described above and as will be appreciated by one skilled in the art,
embodiments of the present invention may be configured as a system, method, or a
computer program product. Accordingly, embodiments of the present invention may
14
be comprised of various means including entirely of hardware, entirely of software, or
any combination of software and hardwate. Furthermore, embodiments of the present
invention may take the form of a computer program product on a computer-readable
storage medium having computer-readable program instructions (e.g., computer
software) embodied in the storage medium. Any suitable non-transitory computerreadable
storage medium may be utilized including hard disks, CD-ROMs, optical
storage devices, or magnetic storage devices.
Embodiments of the present invention have been described above with
reference to block diagrams and flowchart illustrations of methods, apparatuses (i.e.,
systems) and computer program products. It will be understood that each block of the
block diagrams and flowchart illustrations, and combinations of blocks in the block
diagrams and flowchart illustrations, respectively, can be implemented by various
means including computer program instructions. These computer program
instructions may be loaded onto a general purpose computer, special purpose
computer, or other programmable data processing apparatus, such as the processor(s)
62 discussed above with reference to FIG. 4, to produce a machine, such that the
instructions which execute on the computer or other programmable data processing
apparatus create a means for implementing the functions specified in the flowchart
block or blocks.
These computer program instructions may also be stored in a nontransitory
computer-readable memory that can direct a computer or other
programmable data processing apparatus (e.g., processor(s) 62 of FIG. 4) to function
in a particular manner, such that the instructions stored in the computer-readable
memory produce an article of manufacture including computer-readable instructions
for implementing the function specified in the flowchart block or blocks. The
computer program instructions may also be loaded onto a computer or other
programmable data processing apparatus to cause a series of operational steps to be
performed on the computer or other programmable apparatus to produce a computerimplemented
process such that the instructions that execute on the computer or other
programmable apparatus provide steps for implementing the functions specified in the
flowchart block or blocks.
Accordingly, blocks of the block diagrams and flowchart illustrations
support combinations of means for performing the specified functions, combinations
of steps for performing the specified functions and program instruction means for
performing the specified functions. It will also be understood that each block of the
block diagrams and flowchart illustrations, and combinations of blocks in the block
diagrams and flowchart illustrations, can be implemented by special purpose
hardware-based computer systems that perform the specified functions or steps, or
combinations of special purpose hardware and computer instructions.
Unless otherwise expressly stated, it is in no way intended that any method
set forth herein be construed as requiring that its steps be performed in a specific
order. Accordingly, where a method claim does not actually recite an order to be
followed by its steps or it is not otherwise specifically stated in the claims or
descriptions that the steps are to be limited to a specific order, it is no way intended
that an order be inferred, in any respect. This holds for any possible non-express
basis for interpretation, including: matters of logic with respect to arrangement of
steps or operational flow; plain meaning derived from grammatical organization or
punctuation; the number or type of embodiments described in the specification.
Throughout this application, various publications may be referenced. The
disclosures of these publications in their entireties are hereby incorporated by
reference into this application in order to more fully describe the state of the art to
which the methods and systems pertain.
Many modifications and other embodiments of the inventions set forth
herein will come to mind to one skilled in the art to which these embodiments of the
invention pertain having the benefit of the teachings presented in the foregoing
descriptions and the associated drawings. Therefore, it is to be understood that the
embodiments of the invention are not to be limited to the specific embodiments
disclosed and that modifications and other embodiments are intended to be included
within the scope of the appended claims. Moreover, although the foregoing
descriptions and the associated drawings describe exemplary embodiments in the
context of certain exemplary combinations of elements and/or functions, it should be
appreciated that different combinations of elements and/or functions may be provided
by alternative embodiments without departing from the scope of the appended claims.
In this regard, for example, different combinations of elements andlor functions than
those explicitly described above are also contemplated as may be set forth in some of
the appended claims. Although specific terms are employed herein, they are used in a
generic and descriptive sense only and not for purposes of limitation.
1112 I DC bus
Parts List
1 114 I capacitor
Reference
Number
3 6
5 8,60
62
64
66
68
100
102
1 04
106
108
110
Description
controller
one or more sensors
one or more processor(s)
associated memory device(s)
communications module
sensor interface
exemplary power generation system
Power generation unit
power converter system
electrical distribution network
a DC to DC, or "boost," converter
inverter
116
200
202
204
206
208
3 02
3 04
306
308
3 10
control system
electrical power system network
transformer
generator-side breaker
transmission line
a grid side breaker
one or more impedance elements
phases of the electrical system
one or more switches
silicon controller rectifiers (SCRs)
impedance of the electrical system

We Claim:
1. A method of overvoltage protection comprising:
detecting an overvoltage condition on an electrical system; and
switching on, in response to the detected overvoltage condition, an impedance
connected to the electrical system, wherein said impedance clamps voltage on the
electrical system.
2. The method of claim 1, wherein detecting the overvoltage condition on the
electrical system comprises detecting an overvoltage event caused by islanding of one
or more sources of electrical generation from an electrical grid.
3. The method of claim 2, wherein the one or more sources of electrical
generation comprise one or more wind turbine generators.
4. The method of claim 1, wherein detecting the overvoltage condition on the
electrical system comprises detecting when a voltage on the electrical system meets or
exceeds a voltage threshold value.
5. The method of claim 1, wherein switching on, in response to the detected
overvoltage condition, an impedance connected to the electrical system, wherein said
impedance clamps voltage on the electrical system comprises switching on the
impedance using one or more electronic or mechanical switches or combinations
thereof.
6. The method of claim 5, wherein switching on, in response to the detected
overvoltage condition, an impedance connected to the electrical system, wherein said
impedance clamps voltage on the electrical system comprises switching on the
impedance using one or more silicon controlled rectifiers (SCRs).
7. The method of claim 1, wherein switching on, in response to the detected
overvoltage condition, an impedance connected to the electrical system, wherein said
impedance clamps voltage on the electrical system comprises switching on an
impedance connected between each phase of a poly-phase electrical system.
8. The method of claim 7, wherein the impedance connected between each phase
of a poly-phase electrical system is sized based at least in part on a voltage of the
electrical system, a grid impedance of the electrical system, current supplied by any
sources of electrical generation connected to the electrical system, and a desired
clamping level of the overvoltage condition.
9. The method of claim 1, wherein switching on, in response to the detected
overvoltage condition, an impedance connected to the electrical system, wherein said
impedance clamps voltage on the electrical system comprises switching on an
impedance comprised at least in part of one or more inductors.
10. A method of overvoltage protection for a grid-islanding event comprising:
detecting a grid islanding event on a poly-phase electrical system, wherein
said grid islanding event comprises disconnecting one or more sources of electrical
generation from an electrical grid; and
switching on, in response to the detected grid islanding event, an impedance
connected between each phase of the poly-phase electrical system, wherein an
overvoltage on the poly-phase electrical system caused by the grid islanding event is
limited by said impedance clamping voltage on the poly-phase electrical system.
11. The method of claim 10, further comprising switching off said impedance
connected between each phase of the poly-phase electrical system when the
overvoltage drops below a threshold voltage value.
12. The method of claim 10, wherein switching on, in response to the detected
grid islanding event, the impedance connected between each phase of the poly-phase
electrical system, wherein the overvoltage on the poly-phase electrical system caused
by the grid islanding event is limited by said impedance clamping voltage on the polyphase
electrical system comprises switching on the impedance using one or more
electronic or mechanical switches or combinations thereof.
13. The method of claim 12, wherein switching on, in response to the detected
grid islanding event, the impedance connected between each phase of the poly-phase
electrical system, wherein the overvoltage on the poly-phase electrical system caused
by the grid islanding event is limited by said impedance clamping voltage on the polyphase
electrical system comprises switching on the impedance using one or more
silicon controlled rectifiers (SCRs).
14. The method of claim 10, wherein the impedance connected between each
phase of a poly-phase electrical system is sized based at least in part on a voltage of
the poly-phase electrical system, a grid impedance of the poly-phase electrical system,
current supplied by the one or more sources of electrical generation connected to the
poly-phase electrical system, and a desired clamping level of the overvoltage
condition.
15. The method of claim 10, wherein switching on, in response to the detected
grid islanding event, the impedance connected between each phase of the poly-phase
electrical system, wherein the overvoltage on the poly-phase electrical system caused
by the grid islanding event is limited by said impedance clamping voltage on the polyphase
electrical system comprises switching on an impedance comprised at least in
part of one or more inductors.
16. A system for overvoltage protection of an electrical system, comprising:
one or more impedance elements;
one or more switches in series with the one or more impedance elements; and
a controller, wherein said controller is configured to:
receive an indication of a detection of an overvoltage condition on an
electrical system; and
cause the one or more switches to connect the one or more impedance
elements to the electrical system in response to receiving the indication of the
detected overvoltage condition, wherein said overvoltage condition is limited
by said one or more impedance elements clamping voltage on the electrical
system.
17 The system of claim 16, wherein the overvoltage condition on the electrical
system is caused by islanding of one or more sources of electrical generation from an
electrical grid.
18. The system of claim 17, wherein the one or more sources of electrical
generation comprise one or more wind turbine generators.
19. The system of claim 16, wherein the one or more impedance elements
comprise one or more inductors and the one or more switches comprise one or more
electronic or mechanical switches or combinations thereof and causing the one or
more switches to connect the one or more impedance elements to the electrical system
comprises switching on an impedance element connected between each phase of a
poly-phase electrical system.
20. The system of claim 19, wherein the impedance element connected between
each phase of a poly-phase electrical system is sized based at least in part on a voltage
of the electrical system, a grid impedance of the electrical system, current supplied by
any sources of electrical generation connected to the electrical system, and a desired
clamping level of the overvoltage condition.
Dated this 1 1 th day of April, 2013.
MANISHA SIWGH NAIR
Agent for the Applicant [INPA-7401
LEX ORBIS
Iittellectual Property Practice
70917 10, Tolstoy House,
15- 17, Talstoy Mnrg,
New Delhi- 11 000 1