U.S. patent application number 12/121616 was filed with the patent office on 2009-01-01 for distributed inverter and intelligent gateway.
This patent application is currently assigned to Larankelo, Inc.. Invention is credited to Rajan N. Kapur, Suhas S. Patil, Robert R. Rotzoll.
Application Number | 20090000654 12/121616 |
Document ID | / |
Family ID | 39739524 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090000654 |
Kind Code |
A1 |
Rotzoll; Robert R. ; et
al. |
January 1, 2009 |
DISTRIBUTED INVERTER AND INTELLIGENT GATEWAY
Abstract
A system and method for converting DC from one or more sources
to AC power utilizing a novel partitioning scheme are disclosed.
This partitioning scheme is particularly well suited for
photovoltaic (PV) microinverter applications. The primary goals are
to make installation, operation and maintenance of the system safe
and simple. Secondary goals are to improve reliability and lifetime
of the converter in a cost effective manner. In one embodiment, the
microinverters are placed in one-to-one proximity with the
photovoltaic modules, each proximate microinverter incorporating a
reduced number of functions and components. Remaining common
functions and controls are implemented separately.
Inventors: |
Rotzoll; Robert R.;
(Cascade, CO) ; Kapur; Rajan N.; (Boulder, CO)
; Patil; Suhas S.; (Cupertino, CA) |
Correspondence
Address: |
HOGAN & HARTSON LLP
ONE TABOR CENTER, SUITE 1500, 1200 SEVENTEENTH ST
DENVER
CO
80202
US
|
Assignee: |
Larankelo, Inc.
Colorado Springs
CO
|
Family ID: |
39739524 |
Appl. No.: |
12/121616 |
Filed: |
May 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60938663 |
May 17, 2007 |
|
|
|
Current U.S.
Class: |
136/244 |
Current CPC
Class: |
H02J 3/381 20130101;
Y02B 10/10 20130101; H02J 3/388 20200101; H02J 2300/24 20200101;
H02J 3/385 20130101; H02J 3/386 20130101; H02J 2300/28 20200101;
H02J 2300/26 20200101; Y02E 10/56 20130101; H02J 3/383 20130101;
H02J 3/387 20130101; Y02E 10/76 20130101; H02J 3/38 20130101; H02J
2300/30 20200101; H02M 7/493 20130101; H02M 7/44 20130101 |
Class at
Publication: |
136/244 |
International
Class: |
H01L 31/042 20060101
H01L031/042 |
Claims
1. A system for transforming energy, comprising: a plurality of
photovoltaic modules; a plurality of microinverters electrically
coupled to the photovoltaic modules in a one-to-one relationship;
and a gateway electrically coupled to the plurality of
microinverters, wherein features of the gateway are capable of
being upgraded with at least one of hardware, software, and
firmware.
2. The system of claim 1, wherein the gateway comprises an
interface unit and control unit.
3. The system of claim 1, wherein the interface unit, comprises: a
plurality of sensors to detect dynamic utility grid conditions; a
communication unit to communicate with the plurality of
microinverters and the gateway; and an isolation unit to
substantially prevent communication signals from the microinverters
from appearing on the utility grid.
4. The system of claim 1, wherein the control unit provides a
monitoring functions to monitor the plurality of
microinverters.
5. The system of claim 1, wherein each of the plurality of
microinverters, comprise: an inversion unit to convert DC into AC;
a maximum power point tracking (MPPT) unit to optimize power output
from the plurality photovoltaic modules; a communications unit to
provide communications to the gateway; and a safety unit to provide
safety functions.
6. The system of claim 1, wherein the communications unit permits
communication in at least one of wireless communication, wired
communication, and powerline communication.
7. The system of claim 5, wherein the safety unit is capable of
disabling the microinverter upon detection of the microinverter
being electrically decoupled from either the gateway or the PV
module.
8. The system of claim 5, wherein the safety unit is capable of
disabling the microinverter in response to a communication signal
from the communication unit of the gateway.
9. The system of claim 5, wherein the safety unit is capable of
disabling the microinverter upon detection of predetermined grid
conditions.
10. The system of claim 9, wherein the predetermined grid
conditions include at least one of a low grid voltage, a high grid
voltage, a low grid frequency, a high grid frequency and a
predetermined change in grid impedance.
11. A gateway for use in a system for use in an energy generating
system, comprising: an interface unit for interfacing with a
plurality of microinverters and a utility grid; a control unit
electrically coupled to the interface unit for controlling at least
one of safety functionality, synchronization functionality to
synchronize the plurality of microinverters to the utility grid,
and monitoring functionality to monitor the plurality of
microinverters and the utility grid, wherein the control unit is
capable of being electrically coupled to an external monitor.
12. The gateway of claim 11, wherein the interface unit, comprises:
a plurality of sensors to detect dynamic utility grid conditions; a
communication unit to communicate with the plurality of
microinverters and the control unit; and an isolation unit to
substantially prevent communication signals from the plurality of
microinverters from appearing on the utility grid.
13. The system of claim 12, wherein the communications unit is
capable of communication in at least one of wireless communication,
wired communication, and powerline communication.
14. The system of claim 12, wherein each of the plurality of
microinverters includes a safety unit capable of disabling the
microinverter upon detection of the microinverter being
electrically decoupled from either the gateway or a power
module.
15. The system of claim 12, wherein the power module is a wind
turbine.
16. The system of claim 12, wherein each of the plurality of
microinverters includes a safety unit capable of disabling the
microinverter upon detection of predetermined utility grid
conditions.
17. A photovoltaic system for transforming radiant energy into
alternating current, comprising: a plurality of photovoltaic
modules; a plurality of microinverters coupled to the photovoltaic
modules in a one-to-one relationship, wherein each of the plurality
of microinverters comprise: an inversion unit to convert DC into
AC; a MPPT unit to optimize power from the plurality photovoltaic
modules; a communications unit to provide communications to the
gateway; and a safety unit to provide safety functions; a gateway
coupled to the plurality of microinverters, wherein the gateway
comprises: an interface unit for interfacing with a plurality of
microinverters and a utility grid; and a control unit coupled to
the interface unit for controlling at least one of safety
functionality, synchronization to synchronize the plurality of
microinverters to the utility grid, and monitoring, wherein the
control unit is capable of being coupled to an external
monitor.
18. The system of claim 17, wherein the interface unit comprises a
communications unit permitting communication in at least one of
wireless communication, wired communication, and powerline
communication.
19. The system of claim 17, wherein the safety unit is capable of
disabling the microinverter upon detection of the microinverter
being electrically decoupled from either the gateway or a
photovoltaic module.
20. The system of claim 17, wherein each of the safety unit is
capable of disabling the microinverter upon detection of
predetermined utility grid conditions.
Description
[0001] The present application relates to and claims the benefit of
priority to U.S. Provisional Patent Application No. 60/938,663
filed May 17, 2007, which is hereby incorporated by reference in
its entirety for all purposes as if fully set forth herein. The
present application is further related to co-pending U.S. patent
application Ser. No. LAR004 entitled, "Photovoltaic AC Inverter
Mount and Interconnect" and U.S. patent application Ser. No. LAR003
entitled "Photovoltaic Module-Mounted AC Inverter", both of which
are hereby incorporated by this reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to power conversion including direct
current (DC) to alternating current (AC) and, more particularly, to
photovoltaic module output power conversion to AC.
[0004] 2. Discussion of the Related Art
[0005] In coming years, distributed generation of electricity is
likely to become a larger and larger part of the energy sourced to
utility grids. Distributed sources of electrical energy such as
solar photovoltaic modules, batteries, fuel cells and others
generate direct current (DC) power, which must be converted to
alternating current (AC) power for transmission and usage in
residential and commercial settings.
[0006] Also, as distributed generation increases, the utility grid,
commonly known as the "grid," will be transformed to a still to be
defined smart-grid that will support increased coordination between
multiple generators and multiple loads. "Grid tied" photovoltaic
systems are the most common form of solar electric systems today
and they use a form of coordination called net-metering.
[0007] The larger number of photovoltaic installations are
residential having an average capacity of about 2-3 kW. The bulk of
new generating capacity is being installed in commercial buildings
and utility scale installations. Residential systems commonly
utilize single phase AC, while commercial systems most often use
three phase AC.
[0008] Residential rooftops present a special challenge for the
placement and interconnection of photovoltaic modules, due to the
presence of gables, multiple roof angles, and other such
obstructions. Such rooftops often do not expose a sufficiently
large, commonly directed surface to the sun for photovoltaic
modules to be positioned to harvest maximum power. Currently,
conventional inverter-based interconnections are optimized to
minimize IR (current times resistance) loss. This is referred to as
string design. The inverters perform a function called maximum
power point tracking (MPPT) on strings of PV modules. The MPPT
process evaluates the PV module string output current-voltage curve
on a continuous or sampled basis to determine the correct load
voltage thus maximizing the string output power calculated as the
string output voltage times current. Due to the nature of
residential rooftops, the string design results in MPPT performance
at the levels of the least power producing modules in the
photovoltaic (PV) array. This degrades the AC power harvest from
the entire array.
[0009] The use of microinverters in a one-to-one configuration with
the PV modules removes the string design challenge, thereby
enabling each PV module to produce current at its full capacity and
truly permits MPPT at a per PV module level. The one-to-one
arrangement of microinverters and PV modules is also referred to as
AC PV modules in related art.
[0010] Commercial buildings and larger installations present
slightly different challenges. In commercial buildings, large,
commonly directed surfaces are generally available, but even then,
obstructions, such as HVAC components must be dealt with as the
components may block solar radiation. String design and MPPT also
continue to be of concern. Additionally, since such installations
often consist of thousands of PV modules, monitoring, operation and
maintenance can be time consuming and expensive.
[0011] The use of AC PV modules for commercial installations
simplifies string design, improves AC power harvest and provides
the ability to remotely monitor the entire PV array on a module by
module basis. A multiphase microinverter has the additional
advantage of delivering substantially balanced multiphase AC
power.
[0012] The benefits of microinverters have been documented in
related art dating back almost three decades. Yet, the use of
microinverters continues to be negligible due to their inferior
reliability and efficiency as well as their high cost as compared
to conventional inverters.
[0013] Typically, PV modules are placed in hostile outdoor
environments in order to gain maximum exposure to solar radiation.
Microinverters must be placed in proximity to the PV modules to
realize their full benefits. Conventional inverters are typically
placed in more benign environments, often indoors, e.g., on a
protected wall or in a utility closet.
[0014] When microinverters are placed in proximity to PV modules,
the hostile outdoor environment exacerbates the design challenge
for achieving high reliability, high efficiency and low cost.
Similarly, servicing and replacing microinverters on a rooftop is
potentially more challenging and labor intensive than servicing and
replacing centralized inverters.
[0015] The related art design approach for microinverters has been
to implement them as miniaturized versions of conventional
inverters, incorporating all the functions and components that were
used in conventional inverters. Early versions of related art for
microinverters utilized electrolytic capacitors, having a lifespan
susceptible to degradation at high temperatures. Other versions of
related art microinverters eliminate the electrolytic capacitor,
thereby improving the lifespan.
[0016] FIG. 1 shows a simplified diagram of a related art grid tied
photovoltaic system utilizing a conventional inverter. Referring to
FIG. 1, PV modules 102 are mounted outdoors 110 for direct access
to solar radiation and connected to a conventional inverter 105
using DC wiring 104. Both inverter 105 and DC wiring 104 are
located in a weather protected region 111 such as the interior of a
structure. The inverter 105 output feeds local AC loads 106 through
AC wiring 103. The inverter's output is also tied for
bi-directional flow of energy for net-metering to the utility grid
101 through exterior AC wiring 107.
[0017] FIG. 2 shows a simplified diagram of a related art grid tied
photovoltaic system including microinverters. Referring to FIG. 2,
PV modules 202 are mounted outdoors 210 for direct access to solar
radiation. Microinverters 203 are electrically coupled in
one-to-one proximity to the PV modules 202 (typically under them)
and convert individual PV module DC outputs to AC power which is
then fed to AC wiring 204. The AC wiring 204 feeds local loads 206
and the utility grid 201.
[0018] A problem with the related art microinverters is that they
either collocate all inverter functions including safety and code
compliance within the microinverter or they do not address how
these functions are to be implemented, thereby making the design
for high reliability and long life difficult and expensive. The
collocation may also require redevelopment and replacement of the
microinverter when code compliance requirements change.
SUMMARY OF THE INVENTION
[0019] Accordingly, the invention is directed to a distributed
inverter and intelligent gateway that substantially obviates one or
more of the problems due to limitations and disadvantages of the
related art.
[0020] An advantage of the invention is to provide a system and
method of installation, operation, and maintenance of the a power
conversion system that is simple and safe.
[0021] Another advantage of the invention is to provide a high
degree of reliability and a long lifetime to the microinverter.
[0022] Yet another advantage of the invention is to provide
upgradeability of the system during the lifetime of the system.
[0023] Additional features and advantages of the invention will be
set forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The features of the invention will be realized and
attained by the structure particularly pointed out in the written
description and claims hereof as well as the appended drawings.
[0024] To achieve these and other advantages and in accordance with
the purpose of the invention, an embodiment of the invention is
directed towards a system for transforming energy. The system for
transforming energy includes a plurality of photovoltaic modules.
The plurality of microinverters are electrically coupled to the
photovoltaic modules in a one-to-one relationship. The system also
includes a gateway electrically coupled to the plurality of
microinverters and features of the gateway are capable of being
upgraded with at least one of hardware, software, and firmware.
[0025] In another aspect of the invention, an embodiment of the
invention includes a gateway for use in a system for use in an
energy generating system. The gateway includes an interface unit
for interfacing with a plurality of microinverters and a utility
grid. The gateway also includes a control unit electrically coupled
to the interface unit for controlling at least one of safety
functionality, synchronization functionality to synchronize the
plurality of microinverters to the utility grid, and monitoring
functionality to monitor the plurality of microinverters and the
utility grid. The control unit is capable of being electrically
coupled to an external monitor. In yet another aspect of the
invention, an embodiment of the invention includes a photovoltaic
system for transforming radiant energy into alternating current.
The photovoltaic system includes a plurality of photovoltaic
modules and a plurality of microinverters coupled to the
photovoltaic modules in a one-to-one relationship. Each of the
plurality of microinverters includes an inversion unit, a MPPT
unit, a communications unit, a safety unit, an interface unit and a
control unit. The inversion unit converts DC into AC and the MPPT
unit optimizes power from the plurality photovoltaic modules. The
communications unit provides communications to the gateway. The
safety unit provides safety functions. In addition, a gateway is
coupled to the plurality of microinverters. The gateway includes an
interface unit and a control unit. The interface unit interfaces
with a plurality of microinverters and a utility grid. The control
unit is coupled to the interface unit for controlling at least one
of safety functionality, synchronization to synchronize the
plurality of microinverters to the utility grid and monitoring
where the control unit is capable of being coupled to an external
monitor.
[0026] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawings, which are included to provide a
further understanding of the invention and 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.
[0028] In the drawings:
[0029] FIG. 1 is a diagram of a related art grid tied photovoltaic
system using a conventional centralized inverter;
[0030] FIG. 2 is a diagram of a related art grid tied photovoltaic
system using conventional microinverters;
[0031] FIG. 3 is a diagram of a grid tied photovoltaic system using
distributed converters including microinverters and a gateway
according to an embodiment of the invention;
[0032] FIG. 4 is a block diagram of a distributed converter
utilizing microinverters according to another embodiment of the
invention;
[0033] FIG. 5 is a block diagram of a distributed converter
utilizing string inverters according to another embodiment of the
invention;
[0034] FIG. 6 is a block diagram of a distributed converter
utilizing centralized inverters according to another embodiment of
the invention;
[0035] FIG. 7 is a block diagram of a PV system utilizing
microinverters according to another embodiment of the
invention;
[0036] FIG. 8 is a block diagram of a PV system utilizing multiple
string inverters according to another embodiment of the invention;
and
[0037] FIG. 9 is a block diagram of a PV system utilizing
centralized inverters according to another embodiment of the
invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0038] Embodiments of the invention include a novel approach
whereby only those functions and components that are necessary to
achieve the advantages of microinverters are placed in assemblies
in proximity to the PV modules and other functions including, for
example, system control, are located elsewhere. This separation of
functions and components is termed portioning. The control and
coordination of the system is performed without additional wiring.
Communications may occur via powerline, wired and/or wireless
channels. Disabling the communications channel provides a way for
turning the microinverters off thereby facilitating inverter or PV
module replacement, maintenance or other desired tasks. Moreover,
the partitioning provides for enhanced safety as compared to the
related art. In the related art, in the presence of solar
radiation, the PV module outputs are always enabled and are thus
capable of electrocuting the installer. Accordingly, embodiments of
the invention provide for safer and simpler installation and
maintenance procedures.
[0039] In addition, the partitioning reduces the number and type of
components placed in the PV module proximate assemblies that are
subject to the hostile outdoors environment, such as temperature.
Fewer components and simplified assembly also result in improved
reliability and increased system lifetime. Cost is reduced by
eliminating common system functions from the microinverter. In
embodiments of the invention where these functions are realized
with cheaper or less robust components located in a less hostile
environment, the cost may also be further reduced.
[0040] In some embodiments, the partitioning may include physically
locating programmable functions in an area distinct from the PV
module assemblies, such as, in a gateway. Accordingly, the features
located in the gateway are decoupled or portioned from the PV
module assemblies. The functions and components in the gateway may
be upgraded over the lifetime of the system. Therefore, the
development cycle of the gateway is decoupled from the development
cycle of the microinverter assemblies coupled to the PV module
assemblies, and thus several generations of gateways having
different value added functions can be developed for use with the
same microinverter assemblies. This leads to an upgradeable system
at a significantly reduced cost as compared to the related art.
[0041] Reference will now be made in detail to embodiments of the
invention, examples of which are illustrated in the accompanying
drawings.
[0042] FIG. 3 is a diagram of a grid tied photovoltaic system using
distributed converters including microinverters and a gateway
according to an embodiment of the invention. The grid tied
photovoltaic system includes a plurality of PV modules 302 mounted
outdoors 310 each coupled electrically and mechanically to
microinverter assemblies 303. In this embodiment, the gateway 305
is located in a weather protected environment 311, e.g., indoors,
for accessibility and protection from the elements. However, the
gateway 305 could be located in an outdoor environment or other
location. The gateway 305 receives AC current from the plurality of
microinverters 303 via a first AC wiring 304. The gateway 305 is
connected to the grid 301 and to local loads 306 via a second AC
wiring 307. The loads 306 are thereby always connected to the grid
301. The gateway 305 provides a point of measurement of the AC
performance of the PV system and also the electrical behavior of
the grid 301. The gateway 305 also provides control and monitoring
of the microinverters 303.
[0043] FIG. 4 is a block diagram of a distributed converter
according to another embodiment of the invention. Referring to FIG.
4, a system for transforming energy includes a first photovoltaic
module 401 and a second photovoltaic module 411 coupled to a
distributed inverter 410 with DC wiring 402, 412. The distributed
inverter 410 is functionally partitioned into a gateway 406 and a
first microinverter 404 and a second microinverter 414. The first
PV module 401 connects to the first microinverter 404 via first DC
wiring 402 and the second PV module 411 connects to the second
microinverter 414 via second DC wiring 412. Additional PV modules
can be connected via independent DC wires to associated additional
microinverters.
[0044] The AC output of all microinverters is connected in parallel
via AC wiring 405 to the gateway 406. The gateway 406 includes an
interface unit 407 and a control unit 408. The interface unit 407
is connect to the control unit 408 via interface wiring 409. The
interface unit connects to the utility grid via AC power wiring
420. The control unit connects to an external monitor via data
communications wiring 421 or via a wireless data communications
channel.
[0045] The first and second microinverters 404, 414 include a power
inversion unit, a maximum power point tracking (MPPT) unit, a
communications unit and a safety unit. The power inversion unit
converts DC power from the associated PV module to AC power. The AC
power may be generated in single-phase or multi-phase form. The
MPPT unit detects the output power of the associated PV module and
adjusts the load voltage presented to the PV module in such a way
as to maximize the power available from the PV module. The MPPT
unit and functionality are described by Hussein K. H., Mutta I.,
Hoshino T. and Osakada M., in "Maximum photovoltaic power tracking:
An algorithm for rapidly changing atmospheric conditions", IEE
Proceedings, Generation, Transmission and Distribution, Vol. 142,
No. 1, January 1995, which is hereby incorporated by reference as
if fully set forth herein. The communications unit provides
bi-directional data communications between the microinverter 404,
414 and the gateway 406. Data communications from the gateway 406
to the microinverter 404, 414 includes, for example, power
conversion control, status requests, fail-safe shutdown operation
and other relevant data operations. Data communications from the
microinverter 404, 414 to the gateway 406 includes PV module DC
output voltage and current data, microinverter AC output voltage
and current data, microinverter operational status and other
relevant data.
[0046] The safety unit establishes conditions to enable or disable
current flow from the PV module 401, 411 to the microinverter 404,
414 and from the microinverter 404, 414 to the gateway 406. One
safety function of the safety unit is to establish that the utility
grid voltage available at the AC wiring 405 is within
specifications to allow the inverter to safely drive the grid. If
the appropriate grid voltage specifications are met, then the
safety unit enables both input and output current through the
microinverter 404, 414. This first function is also performed by
the gateway 407 and the function is secondary within the
microinverter 404, 414 as a backup fail-safe system in case of
failure of the primary safety function of gateway 406.
[0047] Another safety function of the safety unit is to test for a
communications signal from the gateway 406 indicating that the grid
is safe to drive with AC output current. If the gateway were
disabled by any means, the communications signal emitted by the
gateway 406 would be disabled. The safety unit detects this
condition and immediately disables all current flow into and out of
the microinverter 404, 414. The communications signal from the
gateway 406 is termed a "heartbeat" and provides a primary
fail-safe mechanism for disabling PV system AC and DC power flow in
the event of a grid failure, fire or other safety hazard.
[0048] Yet another safety function of the safety unit is to support
removal and re-attachment of a the microinverter 404, 414 while the
entire PV system is enabled. This is termed a hot-swap and requires
that the microinverter 404, 414 shut down upon detection of the
removal or reattachment of the microinverter to suppress any arcs
or high voltages that may develop at the microinverter DC wiring
402, 412 or AC wiring 405 terminals. High voltages at the
microinverter terminals are suppressed as a means to insure that
maintenance personnel are not able to contact the exposed terminals
while they are energized. The microinverter 404, 414 shuts down if
either the AC output voltage at AC wiring 405 does not meet
prescribed conditions, such as a disconnect or grid failure, or if
the PV module DC input voltage at DC wiring 402, 412 appears to be
disconnected.
[0049] The gateway 406 acts as master controller in the distributed
inverter 410 by performing functions such as providing the above
described heartbeat to the microinverters, monitoring their output,
monitoring the grid and other related functions. The gateway 407
can turn off the heartbeat when, for example, the gateway detects a
fault or unsafe conditions in the environment, maintenance is to be
performed, an AC power failure occurs and/or other related
operating conditions. Similarly, if the gateway 406 is physically
absent, the heartbeat is thereby also absent, resulting in the
disabling of the microinverters.
[0050] The communication between the gateway 406 and the
microinverters 404, 414 may be performed over the AC wiring 405,
wirelessly, or by other suitable means such as independent wiring.
Both communication over AC wiring and wireless communication have
the advantage that no additional wiring is required beyond that to
support the transfer of AC power in the system. In the case of
communication over the AC wiring 405 a wireline
modulator/demodulator sub-function included within both the gateway
406 and the microinverters 404, 414 to perform the communication
functions utilizing the AC wiring 405.
[0051] In this embodiment, the gateway 406 functions are split into
an interface unit 407 and a control unit 408. The interface unit
407 includes a sensor unit, a communications unit and an isolation
unit. The sensor unit provides a way to dynamically monitor grid
conditions, for example to dynamically measure grid AC voltage,
current, frequency, phase and other related grid signal
characteristics. In addition, the communications unit 408 provides
means to send and receive data from connected microinverters 404,
414. The isolation unit 407 substantially prevents data
communications between the microinverters 404, 414 and the gateway
406 from appearing at the grid wiring 420 or onto the grid.
Similarly, noise and other signals, with the exception of the
desired grid AC power voltage and current, are substantially
prevented from appearing at the AC wiring 405 between the
microinverters 404, 414 and the gateway 406.
[0052] The control unit 408 provides monitoring and control
functions to monitor the microinverters 404, 414. Some of the
control includes controlling at least safety functionality and
synchronization functionality to synchronize the microinverters
404, 414 to the grid and monitoring functionality to monitor the
microinverters 404, 414 and the utility grid. In addition, the
control unit 408 provides grid synchronization, communications
protocols, grid connection performance compliance and system
monitoring. The control unit can be implemented with a computer or
microcontroller.
[0053] In this embodiment, software and firmware run on the control
unit 408 to implement functions such as generating the heartbeat,
monitoring the microinverters, monitoring the grid and monitoring
any AC loads. Using the previously described communications system
the control unit 408 can address each microinverter 404, 414
individually, in subsets, or as an entire ensemble.
[0054] For example in one embodiment, the control unit 408 provides
synchronization signals for matching the frequency and phase of the
microinverter 404, 414 AC output to the grid AC power. The
heartbeat fail-safe is also implemented in the control unit 408.
Other functions may include monitoring the health and productivity
of each microinverter and each PV module.
[0055] The control unit 408 also performs grid related protocols
such as detection of grid failure, anti-islanding detection,
adjustment of parameters utilized in the anti-islanding detection
and related functions. New grid related protocols will be defined
to implement a future smart-grid in which the grid operator may
enable, disable or modify the control system of a grid-connected PV
system. The control unit 408 is constructed with flexible hardware,
software and firmware to adapt to future grid-defined control and
communications protocols, without requiring changes to the
microinverters 404, 414.
[0056] The gateway 406 as a whole can also be upgraded to support
future system requirements by changing the hardware, software or
firmware while utilizing the same microinverters 404, 414. For the
grid connection 420 of the gateway 406, the control unit 408 can
perform load management functions, as directed through the grid
protocol or other external sources. Related art monitoring and
display functions can also be implemented in the control unit
408.
[0057] The wiring 409 carries all data between the interface unit
407 and the control unit 408. External communications to the
gateway 406 from an external monitor occurs via communications
wiring 421, or other communications means such as wireless
communications. This is used to externally monitor and control
operation of the gateway 406 and allows for system remote control
via internet connection or other remote communications means.
[0058] By reducing the functions performed within the microinverter
404, 414 a reduction in the required microinverter complexity is
achieved, thereby leading to simpler implementation of the
microinverter and increased reliability, increased lifetime, and
reduced cost as compared to the related art. In particular, the
elimination from the microinverter of precision grid signal
measurement requirements to support anti-islanding functionality
for grid connection specification compliance as defined, for
example, by IEEE standard IEEE-1547, eliminates considerable
complexity, expense and lifetime limiting components from the
microinverter.
[0059] IEEE standard IEEE-1547, and related standards used
throughout the world, defined a narrow set of circumstances upon
which the grid is driven by the inverter. If a break in the grid
wiring occurs, an inverter could continue driving power into the
un-connected branch of the grid. This region in which the primary
grid generators no longer apply power is termed an island. The
inverter is required by the IEEE-1547 standard to disable its
output power under such conditions so as not to drive the island in
the grid for both safety and technical reasons. This is known as
anti-islanding. The gateway 406 assumes the primary role in
detecting the defined islanding condition and communicates the
associated inverter shut-down command to the microinverters 401,
411 to implement the anti-islanding function. Example grid
conditions for an anti-islanding shutdown are a very high grid
voltage, a low grid voltage, a high grid frequency, a low grid
frequency or a significant variation in grid impedance. The grid is
usually of low impedance, therefore the usual grid impedance
variation is an increase when the island occurs.
[0060] The system of FIG. 4 can also be used to convert power for
primary or secondary power sources other than PV modules 401, 411
such as wind turbines, fuel cells, batteries, and other power
sources.
[0061] FIG. 5 is a block diagram of a PV system according to
another embodiment of the invention. A first PV module string 501
includes a first PV module 502, a second PV module 503 and a third
PV module 504 that are connected in series. A first output DC wire
505 and a second DC output wire 506 from the PV module string 501
are connected to a first string inverter 521. A second PV module
string 511 includes a fourth PV module 512, a fifth PV module 513
and a sixth PV module 514 that are connected in series. A third
output DC wire 515 and a fourth DC output wire 516 from the PV
module string 511 are connected to a second string inverter 522.
The AC outputs of the first string inverter 521 and second string
inverter 522 are connected in parallel via AC wiring 523 to the
gateway 524. The PV module strings 501, 511 may include any number
of PV modules that are series connected. Any number of PV module
strings may be used in conjunction with associated string inverters
in this system.
[0062] PV module strings 501, 511 are not required to include equal
numbers of PV modules 502, 503, 504, 512, 513, 514 as is the case
in related art. This provides the benefit of a simple string design
in which the string DC output voltages are not required to be
matched between strings 501, 511. Moreover, MPPT may be performed
on a per string basis, so one string does not degrade the
performance of another, as is the case with related art where equal
length strings are connected in parallel. This arrangement has the
potential to provide greater AC power harvest than conventional
inverters, but less AC power harvest than microinverters.
[0063] A distributed inverter 520 is functionally portioned into a
gateway 524 and string inverters 521, 522. The functions of the
gateway 524 in this embodiment are the same as the functions of the
gateway 406 as described herein. The gateway 524 includes an
interface unit 525 and a control unit 526, both of which are the
same as described with reference to FIG. 4 herein. Accordingly, the
benefits of partitioning the gateway 524 from the multiple-string
inverters 521, 522 in FIG. 5 are substantially similar to the
benefits of partitioning the gateway 406 from the microinverters
404, 414 in FIG. 4. For example, the benefits include using a
heartbeat for safety and independent upgradeability of the gateway
from that of the string inverters. In this embodiment, the
multiple-string inverters 521, 522 are placed close to the gateway
and away from the hostile outdoors environment. The AC output of
all string inverters 521, 522 are connected to the gateway in
parallel via AC power wiring 523. The gateway 524 is connected to
the grid via wiring 530. External communications to the gateway 524
from an external monitor occurs via communications wiring 531, or
other communications means such as wireless communications. This is
used to externally monitor and control operation of the gateway 524
and allows for system remote control via internet connection or
other remote communications means.
[0064] FIG. 6 is a block diagram of a PV system according to
another embodiment of the invention. A first PV module string 601
includes a first PV module 602, a second PV module 603 and a third
PV module 604 that are connected in series. A first output DC wire
605 and a second DC output wire 606 from the PV module string 601
are connected to the DC combiner 621. A second PV module string 611
includes a fourth PV module 612, a fifth PV module 613 and a sixth
PV module 614 that are connected in series. A third output DC wire
615 and a fourth DC output wire 616 from the PV module string 611
are connected to the DC combiner 621.
[0065] A first DC output 622 and a second DC output 623 from the DC
combiner connects to the DC inputs of an inverter 624. The AC
outputs of the inverter 624 are connected in parallel to other
inverters via AC wiring 625 to the gateway 626. The PV module
strings 601, 611 can include any number of PV modules that are
connected in series. Any number of PV module strings can be used in
conjunction with associated DC combiners. A plurality of inverters
624 may be used with outputs connected in parallel in the
system.
[0066] In this embodiment, the PV module strings 601, 611 must be
of equal length when connected to a common DC combiner 621. This
scheme is consistent with connection of conventional inverters as
known to one of ordinary skill in the art. The AC output of the
inverter 624 is connected to the gateway 626 in parallel via AC
power wiring 625.
[0067] In addition, the inverter 624 is similar to conventional
inverters as known to one of ordinary skill in the art except that
control functions are implemented in a gateway 626 rather than
within the inverters. The functions of the gateway 626 in this
embodiment are substantially similar to its functions in the
embodiment shown in FIG. 4. The gateway 626 includes an interface
unit 627 and a control unit 628, both of which are the same as
discussed with reference to FIG. 4 herein. Accordingly, the
development cycles of the inverters and controllers can be
decoupled with improved system performance and the ability to
upgrade without changing the inverters. The gateway 626 is
connected to the grid via wiring 630. External communications to
the gateway 626 from an external monitor occurs via communications
wiring 631, or other communications means such as wireless
communications. This is used to externally monitor and control
operation of the gateway 626 and allows for system remote control
via internet connection or other remote communications means.
[0068] FIG. 7 is a block diagram showing a PV system according to
another embodiment of the invention. Referring to FIG. 7, a
distributed inverter including a gateway 712 based on the concepts
embodied in FIG. 4. The gateway 712 includes an interface unit 727
and a control unit 728, both of which are the same as discussed
with reference to FIG. 4 herein.
[0069] PV modules 701 are individually coupled to microinverters
702 on a first chain 703, and PV modules 707 are individually
coupled to microinverters 706 on a second chain 708. The outputs of
the microinverters 702 are connected in parallel to each other and,
through AC wire 704, to an AC circuit breaker 705, and on to AC
wiring 711. The outputs of the microinverters 706 are connected in
parallel to each other and, through AC wire 709, to an AC circuit
breaker 710 and on to AC wiring 711.
[0070] The AC wiring 711 is connected to the gateway 712, AC cutoff
713, and to the grid through AC wiring 714. Note that components
and wiring 704, wiring 711, wiring 710, AC cutoff 713 and wiring
714 are conventional AC electrical components and their selection
and installation is consistent with the understanding of one of
ordinary skill in the art.
[0071] FIG. 7 illustrates the scalability of installation using
distributed inverters. The concept of hierarchical or replicated
gateways suggests itself for much larger capacity systems, as does
the concept of additional chains to the same gateway 712. Without
loss of generality, the output of the microinverters can be
single-phase AC, split-phase AC or multi-phase AC.
[0072] FIG. 8 is a block diagram showing a PV system according to
another embodiment of the invention. Referring, to FIG. 8, a
distributed inverter, includes a gateway and a multiple-string
inverter, based on the concepts embodied in FIG. 5. The gateway 816
is the same as the gateway as described in FIG. 5. Accordingly, the
upgradeability, safety features, and enhanced performance benefits
may also be similar. A plurality of PV modules 801 are connected in
a first series string and coupled to first string inverter 803 via
DC wiring 802. A plurality of PV modules 805 are connected in a
second series string and coupled to second string inverter 807 via
DC wiring 806. A plurality of PV modules 809 are connected in a
third series string and coupled to third string inverter 811 via DC
wiring 810.
[0073] The AC output of the first string inverter 803 is coupled
through an AC circuit breaker 804 into AC wiring 814. The AC output
of the second string inverter 807 is coupled through an AC circuit
breaker 808 into AC wiring 814. The AC output of the third string
inverter 811 is coupled through an AC circuit breaker 812 into AC
wiring 814.
[0074] The AC wiring 814 is connected to the gateway 816, AC cutoff
815, and to the grid through AC wiring 818. Optionally, the
inverters 803, 807, 811 and the AC circuit breakers 804, 808, 812
may be placed in a common enclosure 813 to simplify installation
and protect the inverters and circuit breakers from environmental
effects. The system may be expanded by increasing the number of PV
modules in a string, strings, string inverters and AC circuit
breakers.
[0075] FIG. 9 is a block diagram showing a PV system according to
another embodiment of the invention. Referring to FIG. 9, a
distributed converter including a gateway and a multiple inverter,
based on the concepts embodied in FIG. 6. The gateway 917 is the
same as the gateway as described in FIG. 5. Accordingly, the
upgradeability, safety features, and enhanced performance benefits
may also be similar. A plurality of PV modules 901 are connected in
a first series string and coupled to a first DC combiner 903 via DC
wiring 902. A plurality of PV modules 906 are connected in a second
series string and coupled to a first DC combiner 903 via DC wiring
907. A plurality of PV modules 908 are connected in a third series
string and coupled to a second DC combiner 910 via DC wiring 909. A
plurality of PV modules 913 are connected in a fourth series string
and coupled to a second DC combiner 910 via DC wiring 914.
[0076] The DC output of the first DC combiner 903 is connected to
the DC input of a first inverter 904. The AC output of the first
inverter 904 is coupled through an AC circuit breaker 905 into AC
wiring 915. The DC output of the second DC combiner 910 is
connected to the DC input of a second inverter 911. The AC output
of the second inverter 911 is coupled through an AC circuit breaker
912 into AC wiring 915.
[0077] The AC wiring 915 is connected to the gateway 917, AC cutoff
916, and to the grid through AC wiring 918. The AC circuit breakers
905, 912, AC wiring 915, AC cutoff 916 and grid wiring 918.
Optionally, the inverters 904, 911, the DC combiners 903, 910, and
the AC circuit breakers 905, 912 may be placed in a common
enclosure (not shown) to simplify installation and to protect them
from environmental effects.
[0078] 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 spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *