BACKGROUND
The invention relates generally to solar power conversion systems and,
more particularly, to a system and method for controlling solar power conversion
systems.
With the rising cost and scarcity of conventional energy sources and
concerns about the environment, there is a significant interest in alternative energy
sources such as solar power and wind power. Power converters are used to convert
solar and wind energy to usable power that is transmitted over a power grid or directly
to a load.
For utility scale solar power conversion systems, power converters
typically include central controllers. A central controller may be used to control the
general operations of the power converters in the solar power conversion system as
well as to coordinate combined power firom the power converters by generating
complex commands regarding curtaihnent and power output for example. The central
controller typically monitors grid signals at the point of interconnection to the grid
and generates various commands that are sent to local controllers embedded within
individual power converters. In such embodiments, if the central controller is unable
to transmit commands and control signals, the power converters may cease to operate
in a worst case scenario or, even if operable, will experience increased operational
losses and reduced efficiency.
Additionally, centrally controlled solar power conversion systems may be
more vulnerable to cyber-attacks as the central controller is a single point of contact
for all the power converters such that malicious data from the central controller may
propagate with a higher rate resulting in faster degradation of the solar power
conversion system.
>
Hence, there is a need for an improved system to address the
aforementioned issues.
BRIEF DESCRIPTION
In one embodiment, a solar power conversion system is provided. The
system includes photovoltaic modules for generating direct current (DC) power. The
system also includes power converters for converting the DC power to alternating
current (AC) power. Each of the power converters comprises a local controller and at
least some of the local controllers are individually operable as a central controller for
providing central control signals to the remaining local controllers. Exactly one of the
local controllers from the at least some local controllers is operable as the central
controller at a given point of time.
In another embodiment, a method for controlling a solar power
conversion system comprising a plurality of power converters including respective
local controllers with at least some of the local controllers being individually operable
as a central controller is provided. The method includes operating exactly one of the
local controllers as the central controller. The method also includes using the central
controller for obtaining central control signals. The method further includes
providing the central control signals from the central controller to the remaining local
controllers.
In yet another embodiment, a power conversion system is provided.
The power conversion system includes power converters for converting power from a
power source to power for transmission to a power grid, each of the power converters
includes a local controller and at least some of the local controllers are individually
operable as a cenfral controller for providing central control signals to the remaining
local controllers wherein one of the local controllers from the at least some local
controllers is operable as the central controller at a given point of time.
DRAWINGS
These and other features, aspects, and advantages of the present
invention will become better understood when the following detailed description is
read with reference to the accompanying drawings in which like characters represent
like parts throughout the drawings, wherein:
FIG. 1 is a schematic representation of a solar power conversion
system including one local controller operating as a first in time central controller in
accordance with an embodiment of the invention.
FIG. 2 is a schematic representation of a solar power conversion
system including another local controller operating as a second in time central
controller upon failure of the first in time central controller in accordance with an
embodiment of the invention.
FIG. 3 is a schematic representation of a solar power conversion
system including a device coupled at a point of intercoimection for sensing data in
accordance with an embodiment of the invention.
FIG. 4 is a flow chart representing steps involved in a method for
controlling a solar power conversion system in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION
Unless defined otherwise, technical and scientific terms used herein
have the same meaning as is commonly understood by one of ordinary skill in the art
to which this disclosure belongs. The terms "first", "second", and the like, as used
herein do not denote any importance, but rather are used to distinguish one element
from another. Also, the terms "a" and "an" do not denote a limitation of quantity, but
rather denote the presence of at least one of the referenced items. The term "or" is
meant to be inclusive and mean one, some, or all of the listed items. The use of
"including," "comprising" or "having" and variations thereof herein are meant to
encompass the items listed thereafter and equivalents thereof as well as additional
items. The terms "connected" and "coupled" are not restricted to physical or
mechanical connections or couplings, and can include electrical cormections or
couplings, whether direct or indirect. Furthermore, the terms "circuit," "circuitry,"
"controller," and "processor" may include either a single component or a plurality of
components, which are either active and/or passive and are connected or otherwise
coupled together to provide the described function.
Embodiments of the present invention include a power conversion
system that includes photovoltaic modules for generating direct current (DC) power.
The direct current (DC) power is converted to aUemating current (AC) power by
power converters. Each power converter includes a local controller. At least some of
the local controllers are individually operable as a central controller that provides
central control signals to the remaining local controllers. Although more than one
local controller has the capacity to operate as the central controller, at any given point
in time, exactly one actually operates as the central controller. Various solar power
converter configiirations exist for converting the DC power output from PV arrays
into AC power. One implementation of a solar power converter has two stages
including a DC-DC converter stage and a DC-AC converter stage. The DC-DC
converter controls the flow of DC power from the PV arrays onto a DC bus. The DCAC
converter converts the DC power supplied to the DC bus into AC power that can
be output to the power grid. Another implementation of a solar power converter has a
single stage comprising a DC-AC converter. Embodiments of the present invention
may be used in either type of power converter implementation.
FIG. 1 is a schematic representation of the solar power conversion
system 10 including one local controller operating as a central controller in
accordance with an embodiment of the invention. The solar power conversion system
10 includes photovoltaic modules 12 that generate DC power. The DC power is
transferred to power converters 14 that convert the DC power to AC power and
transmit the AC power to a power grid 16 which may comprise a utility-controlled
type grid and/or one or more loads, for example.
Each of the power converters includes a local controller 20, 24 that
controls at least some of the operations of the respective power converter 14. In one
embodiment, at least some of local controllers 24 are further configured to operate as
the central controller 22. In some embodiments, all of the local controllers are
configured to operate as the central controller 22.
The local controllers 24 that are configured for operating as the central
controllers 22 typically will not all operate in that manner at the same time. In one
embodiment, exactly one local controller 24 operates as the central controller 22 at a
given point of time. In a more specific embodiment, one local controller 24 is
selected randomly to operate as the central controller 22. In another embodiment, the
central controller 22 is selected by using a sequence technique wherein a sequence
number is assigned to each local controller 24 when initiating the control system. For
example, if a local controller 24 with a sequence number 1 operating as the central
controller 22 fails, the local controller 24 with the sequence number 2 will assume the
role of the central controller 22. In other embodiments, information about which local
controllers have worked well or not worked well in the past can be used as part of the
selection process. The local controller 24 assumes control as the central controller 22
by handshaking with each of the local controllers 20, 24 directly or indirectly in the
solar power conversion system 10.
The central controller 22 controls the operations of the remaining local
controllers 20, 24. In one embodiment, the central controller 22 controls at least one
of total output power, reactive power, frequency, and power factor. In addition to
transmitting commands, it is also useful for, the central controller 22 to transmit data
regarding the current state of operations to the local controllers 24 to ensure a smooth
transition of central control to another of the local controllers 24 upon failure of the
central controller 22.
FIG. 2 is a schematic representation of the solar power conversion
system after a failure of the prior central controller 22 and the transition of another
local controller 28 into the role of the central controller 28. If the prior central
controller 22 transmitted the current status of operations to the local controllers 24,
upon failure of the prior central controller 22, the subsequent central controller 28
may use that information to ensure a more smooth transition and continuous operation
of the system. Failure of a prior central controller may be one trigger for a controller
switch. If desired, other triggers may include, for example, automatic shutdowns,
scheduled maintenance, and operator commands, for example. In one embodiment,
the status updates regarding operations further includes the IP address of the central
controller 22. The IP address is used by the other local controllers 20, 24 to
communicate with the central controller 22. Upon transition of operations of the
central controller from one local controller to another, the local controller taking up
the role of central controller also adapts to the IP address of the previous central
controller so that the communication between the local controllers 20, 24 and the
central controller remains unchanged.
FIG. 3 is a schematic representation of the solar power conversion
system 10 including a device 30 coupled at a point of interconnection 32 for sensing
data in accordance with an embodiment of the invention. The device 30 senses data
relating to at least one of current, voltage, and power. The device 30 fiirther provides
the sensed data to the central controller 28, and in some further embodiments to the
local controllers 20, 24, for use by the central controller 28 in generating the control
signals. In one embodiment, the central controller 28, the local controllers 20, 24, and
the device 30 are communicatively coupled to each other via Ethernet or wirelessly.
The device 30 transmits the sensed data to the central controller 28 that generates the
control signals based on the sensed data. The central controller further transmits the
control signals to the local controllers 20, 24 and controls the operations of the power
converters 14 in the solar power conversion system 10. In one embodiment, each of
the local controllers is directly or indirectly coupled to each other. In a specific
embodiment, each of the local controllers is communicatively coupled to each other in
a mesh network.
In another embodiment, the central controller 28 may delegate at least
some of the processing functions of the central controller 28 to the local controllers
20. The commands are generated by the central controller 28 and are transmitted to
the local controllers 20 for execution. For example, if the central controller 28
transmits a command to a local controller 20 to provide five percent reactive power,
the local controller 20 will compute the commands that are necessary to send to the
respective devices coupled to the local controller 20 for regulating the reactive power
generation. Another example of delegation of functions includes following a response
curve transmitted by the central controller 28. The local controller 20 would change
the amount of active power or reactive power generated by the respective power
converter based on the response curve provided by the central controller 28.
FIG. 4 is a flow chart representing steps involved in a method 40 for
controlling the solar power conversion system comprising a plurality of power
converters including respective local controllers with at least some of the local
controllers being individually operable as a central controller in accordance with an
embodiment of the invention. The method 40 includes operating exactly one of the
local controllers as the central controller in step 42. In one embodiment, the local
controller operates as the central controller by handshaking with each of the local
controller directly or indirectly. The method 40 also includes using the central
controller for generating central control signals in step 44. In one embodiment, the
central controller obtains at least one of output voltage, output current and output
power at a point of interconnection in the solar power conversion system for use by
the central controller in generating the central control signals. In another
embodiment, the central controller delegates at least some controls functions to the
remaining local controllers. The method 40 further includes providing central control
signals from the central controller to the remaining local controllers in step 46. In a
specific embodiment, providing the central control signals from the central controller
includes controlling at least one of total output power, reactive power, frequency and
power factor.
In one embodiment, the method 40 includes updating the local
controllers with operating status information from the central controller. In a specific
embodiment, upon failure of the exactly one local controller operating as the central
controller, a new local controller is identified to operate as the central controller. In a
more specific embodiment, the new central controller initiates operations as the
central controller from a last known status of the exactly one failed local controller
operating as the central controller.
8
The various embodiments of the solar power conversion system
described above provide a more efficient and reliable solar power conversion system.
The system described above enables more operational time and efficiency for the
power converter and reduces cyber threats.
It is to be understood that a skilled artisan will recognize the
interchangeability of various features fi-om different embodiments and that the various
features described, as well as other known equivalents for each feature, may be mixed
and matched by one of ordinary skill in this art to construct additional systems and
techniques in accordance with principles of this disclosure. It is, therefore, to be
understood that the appended claims are intended to cover all such modifications and
changes as fall within the true spirit of the invention.
While only certain features of the invention have been illustrated and
described herein, many modifications and changes will occur to those skilled in the
art. It is, therefore, to be understood that the appended claims are intended to cover
all such modifications and changes as fall within the true spirit of the invention.
'i

We Claim:
1. A solar power conversion system comprising:
photovoltaic modules for generating direct current (DC) power; and
power converters for converting the DC power to alternating current (AC)
power,
wherein each of the power converters comprises a local controller and at least
some of the local controllers are individually operable as a central controller for
providing central control signals to the remaining local controllers,
wherein one of the local controllers from the at least some local controllers
operates as the central controller at a given point of time.
2. The system of claim 1, wherein the central controller transmits a
current state of operations to the at least some of the local controllers.
3. The system of claim 1, wherein, upon failure of one of the local
controllers operating as the central controller, a new local controller is identified to
operate as the central controller.
4. The system of claim 3, wherein the new local controller initiates the
operations as the central controller using the current state of operations.
5. The system of claim 1, wherein each of the local controllers is directly
or indirectly coupled to each other.
10
6. The system of claim 1, wherein the local controllers are
communicatively coupled in a mesh network.
7. The system of claim 1, further comprising a device coupled at a point
of interconnection in the solar power conversion system for sensing data relating to at
least one of current, voltage, and power and providing the sensed data to the central
controller for use by the central controller in generating the central control signals.
8. The system of claim 1, wherein the central controller delegates at least
some processing functions to the local controllers.
9. A method for controlling a solar power conversion system comprising
a plurality of power converters including respective local controllers with at least
some of the local controllers being individually operable as a central controller, the
method comprising:
operating exactly one of the local controllers as the central controller;
using the central controller for generating central control signals; and
providing the central control signals from the central controller to the
remaining local controllers.
10. The method of claim 9, ftirther comprising updating the local
controllers with operating status information from the central controller.
11. The method of claim 9, wherein, upon failure of the exactly one local
controller operating as the central controller, a new local controller is identified to
operate as the central controller.
U
12. The method of claim 11, further comprising initiating the operation as
the central controller using the operating status information.
13. The method of claim 9, wherein providing the central control signals
from the central controller comprises controlling at least one of total output power,
reactive power, frequency, and power factor.
14. The method of claim 9, further comprising obtaining at least one of
output voltage, output current, and output power at a point of intercormection in the
solar power conversion system for use by the central controller in generating the
central control signals.
15. The method of claim 9, wherein operating exactly one local controller
as the central controller comprises handshaking with each local controller directly or
indirectly.
16. The method of claim 9, wherein using the central controller for
generating central control functions further comprises delegating at least some
processing functions to the remaining local controllers.
17. A power conversion system comprising:
power converters for converting power from a power source to power for
transmission to a power grid, each of the power converters comprising a local
controller;
wherein at least some of the local controllers are individually operable as a
central controller for providing central control signals to the remaining local
controllers,
1^
wherein one of the local controllers from the at least some local controllers is
operable as the central controller at a given point of time.
18. The system of claim 17, wherein the central controller transmits a
current state of operations to the at least some of the local controllers.
19. The system of claim 17, wherein, upon failure of one of the local
controllers operating as the central controller, a new local controller is identified to
operate as the central controller.
20. The system of claim 19, wherein the new local controller initiates the
operations as the central controller using the current state of operations.