U.S. patent application number 14/421914 was filed with the patent office on 2015-07-23 for dc building system with energy storage and control system.
This patent application is currently assigned to Robert Bosch GmbH. The applicant listed for this patent is Robert Bosch GmbH. Invention is credited to John Saussele, Oliver Norbert Steinig.
Application Number | 20150207316 14/421914 |
Document ID | / |
Family ID | 49596338 |
Filed Date | 2015-07-23 |
United States Patent
Application |
20150207316 |
Kind Code |
A1 |
Saussele; John ; et
al. |
July 23, 2015 |
DC BUILDING SYSTEM WITH ENERGY STORAGE AND CONTROL SYSTEM
Abstract
A DC building electrical system includes a DC power consuming
device connected to a DC bus. A source of DC power is connected to
the DC bus and powers the DC power consuming device. An energy
storage device is connected to the DC bus and to a DC emergency
load. The energy storage device powers the DC power consuming
device in conjunction with the source of DC power, and powers the
DC emergency load when source of power other than the energy
storage device is available to the DC power consuming device.
Inventors: |
Saussele; John; (Davidson,
NC) ; Steinig; Oliver Norbert; (Northville,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Robert Bosch GmbH |
Stuttgart |
|
DE |
|
|
Assignee: |
Robert Bosch GmbH
Stuttgart
DE
|
Family ID: |
49596338 |
Appl. No.: |
14/421914 |
Filed: |
August 16, 2013 |
PCT Filed: |
August 16, 2013 |
PCT NO: |
PCT/IB2013/002245 |
371 Date: |
February 16, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61684083 |
Aug 16, 2012 |
|
|
|
61699169 |
Sep 10, 2012 |
|
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Current U.S.
Class: |
700/287 |
Current CPC
Class: |
B60L 53/00 20190201;
H02J 4/00 20130101; H02J 3/383 20130101; G05B 15/02 20130101; H02J
1/002 20200101; H02J 2300/28 20200101; Y02T 90/167 20130101; H02J
3/38 20130101; Y02B 70/30 20130101; Y02E 10/76 20130101; H02J 1/08
20130101; Y02T 10/7072 20130101; Y02T 90/14 20130101; H02J 1/00
20130101; B60L 55/00 20190201; H02J 3/381 20130101; H02J 2310/48
20200101; Y04S 30/12 20130101; Y02B 70/3225 20130101; Y02B 10/70
20130101; H02S 10/20 20141201; H02J 3/14 20130101; G05F 1/10
20130101; H02J 9/065 20130101; Y02E 60/00 20130101; H02J 3/386
20130101; Y04S 20/222 20130101; Y04S 10/126 20130101; H02J 9/061
20130101; H02J 2300/24 20200101; Y02B 10/10 20130101; Y02T 10/70
20130101; H02J 2310/10 20200101; Y02E 10/56 20130101; Y04S 20/248
20130101; H02J 2300/10 20200101 |
International
Class: |
H02J 1/00 20060101
H02J001/00; G05B 15/02 20060101 G05B015/02; H02S 10/20 20060101
H02S010/20 |
Claims
1. A DC building electrical system comprising: a DC bus; a DC power
consuming device connected to the DC bus; a source of DC power
connected to the DC bus and configured to power the DC power
consuming device; a DC emergency load; and an energy storage device
connected to the DC bus and to the DC emergency load, the energy
storage device being configured to: power the DC power consuming
device in conjunction with the source of DC power; and power the DC
emergency load when no source of power other than the energy
storage device is available to the DC power consuming device.
2. The system of claim 1, wherein the source of DC power comprises:
a photovoltaic array producing a DC voltage on the DC bus; and/or a
DC power supply producing DC voltage on the DC bus from AC voltage
received from a utility grid.
3. The system of claim 1, wherein the energy storage device is
configured to power the DC emergency load for a predetermined
period of time when no source of power other than the energy
storage device is available to the DC power consuming device.
4. The system of claim 3, further comprising a renewable energy DC
power source connected to the DC bus and configured provide power
to the DC emergency load in conjunction with the energy storage
device when no source of power other than the energy storage device
is available to the DC power consuming device.
5. The system of claim 1, wherein the DC emergency load is included
in the DC power consuming device and is configured to draw less
power than the DC power consuming device.
6. A DC building electrical system comprising: a DC bus; a DC power
consuming device connected to the DC bus; a source of DC power
connected to the DC bus and configured to power the DC power
consuming device; a motorized vehicle; and an energy storage device
connected to the DC bus and to the motorized vehicle, the energy
storage device being configured to: power the DC power consuming
device in conjunction with the source of DC power; and power the
motorized vehicle.
7. The system of claim 6, wherein the energy storage device is
configured to be an only source of power for the motorized
vehicle.
8. The system of claim 6, wherein the motorized vehicle comprises a
golf cart or a fork lift.
9. A DC building electrical system comprising: a DC bus; a DC power
consuming device connected to the DC bus; a source of DC power
connected to the DC bus and configured to power the DC power
consuming device; an energy storage device connected to the DC bus
and configured to power the DC power consuming device in
conjunction with the source of DC power; and a DC power control
system configured to selectively charge and discharge the energy
storage device based on a current state of charge of the energy
storage device and a predetermined target state of charge of the
energy storage device.
10. The system of claim 9, wherein the DC power control system is
configured to charge the energy storage device during time periods
in which the source of DC power is operable and discharge the
energy storage device during time periods in which the source of DC
power is inoperable, the predetermined target state of charge being
a state of charge that is sufficient to solely power the DC power
consuming device for a predetermined duration of time while the
source of DC power is inoperable.
11. The system of claim 9, further comprising a renewable energy DC
power source connected to the DC bus, wherein the DC power control
system is configured to charge the energy storage device by using
excess power from the renewable energy DC power source.
12. The system of claim 9, further comprising a renewable energy DC
power source connected to the DC bus, wherein the DC power
consuming device is variable, the DC power control system being
configured to respond to the current state of charge of the energy
storage device dropping below the predetermined target state of
charge by adjusting the variable DC power consuming device such
that a level of current drawn by the variable DC power consuming
device is less than a level of current sourced by the renewable
energy DC power source, and such that the energy storage device is
charged to the predetermined target state of charge by the
renewable energy DC power source.
13. The system of claim 9, further comprising a renewable energy DC
power source connected to the DC bus, wherein the DC power
consuming device is variable, the DC power control system being
configured to respond to the current state of charge of the energy
storage device dropping below the predetermined target state of
charge by adjusting a discharge current rate of the energy storage
device by selectively reducing or discontinuing operation of the
variable DC power consuming device dependent upon a building
ambient condition and a corresponding predetermined building
condition.
14. The system of claim 13, wherein the building ambient condition
comprises a level of sunlight.
15. The system of claim 13, wherein the corresponding predetermined
building condition comprises a desired emergency interior lighting
level.
16. The system of claim 9, further comprising a renewable energy DC
power source connected to the DC bus, wherein the DC power
consuming device is variable, the DC power control system being
configured to respond to the source of DC power being inoperable
for a threshold period of time by adjusting the variable DC power
consuming device such that a level of current drawn by the variable
DC power consuming device is thereby reduced.
17. The system of claim 9, wherein the DC power consuming device is
variable, and wherein the DC power control system is configured to
selectively reduce or discontinue operation of the variable DC
power consuming device dependent upon a length of time during which
the source of DC power has been inoperable.
18. The system of claim 9, wherein the DC power consuming device
comprises a motor or a generator, the DC power control system being
configured to charge the energy storage device by discontinuing
power to the motor or generator and operating the motor or
generator in a regenerative mode in which kinetic energy of the
motor or generator is converted to DC power.
19. A microgrid system arrangement comprising: a photovoltaic array
producing a DC voltage on a DC bus; a DC power supply producing DC
voltage on the DC bus from AC voltage received from a utility grid;
a DC power consuming device connected to the DC bus; and a
controller configured to control amounts of DC power provided to
the DC bus by the photovoltaic array and by the DC power
supply.
20. The arrangement of claim 19, further comprising an energy
storage device connected to the DC bus, the controller being
configured to cause the energy storage device to: power the DC
power consuming device in conjunction with the photovoltaic array
and/or the source of DC power; and be an exclusive provider of
power to the DC power consuming device when the photovoltaic array
and the DC power supply are inoperable.
21. The arrangement of claim 20, wherein the controller is
configured to selectively charge and discharge the energy storage
device based on a current state of charge of the energy storage
device and a predetermined target state of charge of the energy
storage device, the predetermined target state of charge being a
state of charge that is sufficient to solely power the DC power
consuming device for a predetermined duration of time while the
photovoltaic array and the DC power supply are inoperable.
22. The arrangement of claim 19, wherein the controller comprises a
first controller, the arrangement comprising a second controller
configured to respond to the photovoltaic array and the DC power
supply being inoperable for a threshold length of time by reducing
a level of power drawn by the DC power consuming device.
Description
CROSS REFERENCES TO RELATED APPLICATIONS/INCORPORATION BY
REFERENCE
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/684,083 filed on Aug. 16, 2012, entitled "DC
MICROGRID BUILDING ENERGY MANAGEMENT PLATFORM" (Attorney Docket No.
13050-40005-US-1), and to U.S. Provisional Patent Application No.
61/699,169 filed on Sep. 10, 2012, entitled "DC MICROGRID BUILDING
ENERGY MANAGEMENT PLATFORM" (Attorney Docket No. 13050-40005-US-2).
The complete subject matters of these patent applications are
hereby incorporated herein by reference, in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to advanced component
technologies which may improve building energy efficiency.
[0004] 2. Description of the Related Art
[0005] Current AC building systems do not use locally-generated
renewable energy in the most cost effective way and require a very
reliable utility grid connection, resulting in excess life-cycle
costs as well as energy security concerns. It is known to utilize
batteries as an energy buffer for a PV array, but such systems do
not eliminate wasteful AC conversions when addressing the most
common building electrical loads, such as lighting and ventilation.
Likewise, it is known to provide a smart building energy management
system, but such systems do not incorporate a DC microgrid to
improve efficiency and energy security. FIG. 1 is a block diagram
of one embodiment of a conventional AC reference system for
comparison with the present invention.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to a DC microgrid without
an inverter. The DC microgrid powers one or more DC powered
devices, which can include lighting and cooling devices. The DC
microgrid offers more efficient use of DC power generated by a
Photovoltaic (PV) array. The DC microgrid is less expensive to
implement than conventional PV systems and offers improved payback.
The DC microgrid enables use of less expensive DC powered devices.
In various embodiments, the DC microgrid can employ the solar
synchronized load and/or maximum power point tracking control
features described in U.S. patent application Ser. No. 13/560,726
and U.S. patent application Ser. No. 13/749,604.
[0007] In other embodiments, the PV array of the DC microgrid can
be sized to provide an advantageous DC bus voltage range for more
efficient Maximum Power Point Tracking (MPPT) control that is lower
and/or narrower than conventional DC bus voltage ranges.
Alternatively or additionally, the PV array can be sized to provide
power within a predetermined range for advantageously balancing
power production by the PV array and a utility grid. For example
the PV array can be sized to provide less than half the power
demand, for example between 25-40% of the power demand.
[0008] The Direct Current (DC) Microgrid Building Energy Management
Platform (DCMG-BEMP) of the invention offers significant benefits
relative to conventional alternating current (AC) building systems
in terms of reduced total cost of ownership (TCO) and increased
energy security. Conventional building-level power distribution
systems suffer from AC-to-DC conversion losses in powering many
common devices, as well as DC-to-AC losses when utilizing locally
produced DC power, such as from renewable energy sources. For
example, these conversions result in up to a 12% greater loss of
energy between photovoltaic (PV) arrays and AC lighting loads, when
compared to the DC microgrid of the present invention. Typical PV
systems also require all power to flow through unreliable and
expensive grid-connected inverter hardware, which prevents the PV
power from being used for mission-critical activities when the grid
power is lost (blackout condition). In addition, current AC
building systems have limited or no ability to manage building peak
power demands, which can lead to demand charges and further grid
instability. The DCMG-BEMP applies a novel approach to using
mature, reliable DC technology and dynamically optimizing power
sources, loads, and energy storage system interaction, minimizing
TCO and reliance on grid-based electricity. Economic modeling using
the BLCC tool shows 15%-25% improvement in Savings to Investment
Ratio (SIR) over 25 years for the DCMG-BEMP compared to equivalent
AC systems. The present invention DCMG-BEMP provides increased
energy efficiency, improved energy security, and a lower total
cost-of-ownership compared to other approaches.
[0009] The invention may provide a DC microgrid configuration in
which DC electrical energy is stored in order to power DC loads
without being converted to AC electrical energy. Such DC energy
storage may be in the form of batteries, capacitors, flywheels,
etc., although only batteries are shown in the drawings.
[0010] One primary advantage of using energy storage in the DC
microgrid configuration is that the energy (e.g., backup power) may
be utilized more efficiently by the DC loads when in the form of DC
from the energy storage elements. One reason for the higher
efficiency is that there are no intermediate conversions from DC
storage to AC and back to DC, as is typically done in
buildings.
[0011] Energy storage elements may be incorporated into the DC
power supply, making it effectively similar to an uninterruptable
power supply (UPS) configuration. Alternatively, energy storage
elements may be connected independently to the DC bus. However, at
least one exemplary embodiment in the drawing includes a battery
incorporated into a DC power supply, which is connected to an AC
grid and is separate from a solar grid (e.g., a renewable DC energy
power source.
[0012] An energy storage device may be directly connected to the DC
bus, or may have intermediate DC/DC converters to optimize voltages
and currents for charging/discharging. An energy storage device may
be charged from the grid through an AC/DC power supply, may be
charged from other DC sources such as solar photovoltaic (PV), or
may be charged by both of these methods.
[0013] A relatively small amount of energy storage capacity in the
DC microgrid may be used to meet the ninety minute emergency
lighting requirement for U.S. buildings, without the need for
dedicated emergency lighting circuits or distributed battery
strategies, as is typical. For example, all the lights may be
dimmed, and/or only a subset of the lights may be turned on, via
software control, in order to meet the emergency lighting
brightness requirement. Using the DC power supply in the
uninterruptable power supply (UPS) mode may enable the DC emergency
lighting to be powered without adding any additional infrastructure
to the building. In the prior art, in contrast, emergency lighting
may require additional infrastructure such as separate AC or DC
lighting circuits and battery systems. The inventive arrangement
may provide advantages such as lower cost, higher reliability, and
flexibility to change which lights are turned on during
emergencies, and which lighting levels are available during
emergencies. These advantages may be realized exclusively via an
inventive software configuration.
[0014] Larger amounts of energy storage may be included in the DC
microgrid to provide varying levels of backup energy. For example,
enough backup energy may be stored to keep a building operating
throughout the night on most nights in an emergency mode in the
event that there is enough excess solar PV energy generated during
the day to put into energy storage systems and subsequently be used
at night in the DC loads when solar energy is not available. The
amount of storage that is required may depend on the amount of
power needed in "emergency mode," (i.e., lower lighting or
ventilation levels may be acceptable in a blackout), and may depend
on the amount of solar energy available in different geographic
regions. These variables may be used to statistically calculate the
"energy security" or probability of powering the building
throughout the night or other desired time period with the excess
solar energy stored from the daytime. Any amount of stored solar PV
energy can reduce the amount of diesel or other fuel needed for
other backup power generation options.
[0015] If the DC microgrid incorporates DC thermal loads (e.g.,
food refrigeration, building HVAC, hot water heating), then the
thermal storage may be combined with the electrical energy storage
to determine the "energy security". For example, frozen food may
stay frozen for some hours even when energy storage is depleted,
which may provide enough protection until solar energy is again
available in the morning. Further, the food may be frozen to a
temperature several degrees below what is required for freezing,
and thus the frozen food itself may effectively store energy.
[0016] In order to extend the availability of energy storage to
keep a building useable in an emergency situation, the electrical
loads in the building may be adjusted to adapt to the availability
of stored energy, solar power, and the duration of the blackout
(e.g., the duration of the loss of utility grid power). For
example, in the first hour of a blackout occurring with full
sunshine and full energy storage reserves, the lighting,
ventilation, or other emergency loads may be kept at full power.
However, as the duration of the blackout continues into the second
hour with less sunshine available, the emergency loads may be
operated at lower power levels in order to conserve stored energy.
For example, lights may be dimmed, ventilation may be operated at
lower speed, etc. Additional such adjustments may be made to the
operation of the loads as the duration of the blackout becomes
longer, and depending on the amount of solar energy available.
Through adaptive adjustment of the emergency loads, the building is
more likely to remain in a usable state through more blackout
scenarios, since short-term blackouts occur more frequently than
long-term blackouts, and since weather conditions (e.g., amount of
sun) may be very different during different blackouts.
[0017] Energy storage which is primarily designed into the DC
microgrid for use as backup may also be used for "demand response"
purposes to help the utility company manage peak power demands. For
example, the utility company may send an electrical signal or
provide an incentive (e.g., time-of-day utility rates or demand
charges) for the DC microgrid to use power from the energy storage
and PV for DC loads rather than from the utility grid for a period
of time, thus reducing the electricity demand on the utility grid
during a peak period ("DC load-leveling").
[0018] Further to the above, the energy storage may be connected to
a DC/AC inverter or bi-directional AC/DC converter which would
allow the energy storage to also be used to offset peak demands
from AC loads in the building or elsewhere on the AC utility grid
("AC load leveling"). The DC microgrid may be configured to provide
a combination of the above--DC load leveling and AC load
leveling.
[0019] Energy storage in the DC microgrid may have the unique
ability to be periodically tested by feeding some or all of the
power for the DC loads from the DC energy storage for test purposes
without affecting building functionality. For example, the lights
may not blink during such testing. In other words, some or all
power may be directed to flow from the DC energy storage to the DC
loads during the test period, temporarily reducing or eliminating
the power needed from the DC power supply, PV, or other energy
source. During this test period, voltages and/or currents may be
measured to validate the rate of discharge and determine the health
of the storage system. Similarly, solar PV or another DC power
source may be used to charge energy storage and determine health of
the energy storage system from the charge rate.
[0020] Building energy storage elements in the DC microgrid also
may be used as an energy supply for commercial electric vehicles
used in and around a building or complex. For example, the
batteries from electric fork-lifts may be used as part of the
building energy storage while they are being charged on or off the
vehicle, and the batteries from electric golf carts may be used as
building energy storage, etc. The above concept may also be used in
a conventional AC connection to the building via a single or
bi-directional AC/DC inverter.
[0021] Industrial fans or other DC motor loads may be used in the
DC microgrid as virtual flywheel storage via use of a
bi-directional variable frequency drive (VFD) on the motor
connected to the DC bus. This concept may also be known as
regenerative braking, or generating power from the slowing down of
a motor. An advantage of this arrangement is that some short-term
storage is realized through the use of existing motor devices,
potentially saving cost through reduction or elimination of
additional storage elements in the system.
[0022] In one embodiment, the invention comprises a DC building
electrical system including a DC power consuming device connected
to a DC bus. A source of DC power is connected to the DC bus and
powers the DC power consuming device. An energy storage device is
connected to the DC bus and to a DC emergency load. The energy
storage device powers the DC power consuming device in conjunction
with the source of DC power, and powers the DC emergency load when
no sources of power, or limited sources of power, (e.g., solar)
other than the energy storage device are available to the DC power
consuming device.
[0023] In another embodiment, the invention comprises a DC building
electrical system including a DC power consuming device connected
to a DC bus. A source of DC power is connected to the DC bus and
powers the DC power consuming device. An energy storage device is
connected to the DC bus and to the motor vehicle. The energy
storage powers the DC power consuming device in conjunction with
the source of DC power, and powers the motor vehicle.
[0024] In another embodiment, the invention comprises a DC building
electrical system including a DC power consuming device connected
to a DC bus. A source of DC power is connected to the DC bus and
powers the DC power consuming device. An energy storage device is
connected to the DC bus and powers the DC power consuming device in
conjunction with the source of DC power. A DC power control system
selectively charges and discharges the energy storage device based
on a current state of charge of the energy storage device and a
predetermined target state of charge of the energy storage
device.
[0025] In another embodiment, the invention comprises a microgrid
system arrangement including a photovoltaic array producing a DC
voltage on a DC bus. A DC power supply produces DC voltage on the
DC bus from AC voltage received from a utility grid. A DC power
consuming device is connected to the DC bus. A controller controls
amounts of DC power provided to the DC bus by the photovoltaic
array and by the DC power supply.
[0026] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the energy
storage device, via a common power network, supplies DC power 1)
powering DC building loads in combination with at least one other
DC power source (e.g., a renewable energy DC power source or an AC
grid); and 2) powering DC emergency loads for a predetermined
period when no other power is available.
[0027] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the energy
storage device is used to power a mobile device used within the
building (e.g., a vehicle such as a fork lift or a golf cart).
[0028] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the DC building
system includes a DC power control system that selectively charges
and discharges the energy storage device during non-emergency
periods based on a state of charge (SOC) of the energy storage
device and a predetermined emergency SOC.
[0029] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the DC building
system includes a DC power control system that charges the energy
storage device using excess power available from a renewable energy
DC power source.
[0030] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the DC building
system includes a DC power control system that when a state of
charge (SOC) of an energy storage device drops below a
predetermined SOC: selectively adjusts a variable DC load so that a
total load on a solar device is less than an available power of the
solar device; and charges the energy storage device to above the
predetermined SOC.
[0031] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the DC building
system includes a DC power control system that when a state of
charge (SOC) of an energy storage device drops below a
predetermined SOC: controls a discharge rate of the of the energy
storage device by selectively reducing or discontinuing operation
of one or more variable DC loads based on a building ambient
condition (e.g., amount of sunlight) and a corresponding
predetermined building condition (emergency interior lighting
level).
[0032] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the DC building
system includes a DC power control system that selectively reduces
or discontinues operation of a variable DC load during emergency
operation based on a duration of the emergency.
[0033] In another embodiment, the invention comprises a DC building
system employing an energy storage device, wherein the DC building
system includes a DC power control system that charges the energy
storage device by discontinuing power to a motor/generator and
operating the motor/generator in a regenerative mode during which
kinetic energy is converted to DC power. The motor/generator may
also directly power the DC loads from regenerative power, and
provide all or part of the energy storage in the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The above mentioned and other features and objects of this
invention, and the manner of attaining them, will become more
apparent and the invention itself will be better understood by
reference to the following description of embodiments of the
invention taken in conjunction with the accompanying drawings,
wherein:
[0035] FIG. 1 is a block diagram of one embodiment of a
conventional AC reference system.
[0036] FIG. 2 is a block diagram of one embodiment of a core DC
microgrid system architecture of the present invention.
[0037] FIG. 3 is a block diagram of one embodiment of an enhanced
DC microgrid system architecture of the present invention.
[0038] FIG. 4 is a block diagram of another embodiment of an
enhanced DC microgrid system architecture of the present
invention.
[0039] FIG. 5 is a block diagram of one embodiment of a DC
microgrid building energy management platform of the present
invention.
[0040] FIG. 6 is a block diagram of one embodiment of a DCMG-BEMP
including a phased installation plan of the present invention.
[0041] FIG. 7 is a block diagram of one embodiment of a DC building
system of the present invention.
[0042] FIG. 8 is a block diagram of one embodiment of a DC power
control system of the present invention.
[0043] FIG. 9 is a block diagram of one embodiment of a DC load
control system of the present invention.
[0044] FIG. 10 is a block diagram of another embodiment of a DC
power control system of the present invention.
[0045] Corresponding reference characters indicate corresponding
parts throughout the several views. Although the exemplification
set out herein illustrates embodiments of the invention, in several
forms, the embodiments disclosed below are not intended to be
exhaustive or to be construed as limiting the scope of the
invention to the precise forms disclosed.
DESCRIPTION OF THE PRESENT INVENTION
[0046] The present invention may: 1) showcase the viability and
optimize the performance of a building-level DC microgrid
subsystem, 2) validate the efficiency improvements of DC-powered
components relative to conventional AC components when powered by
PV, 3) showcase the DC microgrid system's impact on energy security
by providing backup power for mission-critical activities while
minimizing the need for other backup energy sources, and 4)
demonstrate the added value of energy storage in AC and DC
load-leveling scenarios.
[0047] In one embodiment, the invention provides a core DC
microgrid which utilizes PV energy more effectively in common
building loads. Another embodiment includes storage which may
dramatically increase energy security. The DCMG-BEMP of the present
invention addresses the limitations of current building electrical
power distribution systems by implementing a separate DC electrical
distribution microgrid and novel DC-based electrical loads.
Directly utilizing DC power eliminates the multiple conversions
(DC-AC and AC-DC) of typical AC systems. Most renewable energy
production systems (solar, wind, etc.) are tethered to the utility
grid and allow for no direct usage of the power produced. The core
DCMG-BEMP system architecture is designed to optimize the amount of
renewable power used locally within the building. This core system
also eliminates the expensive and unreliable grid-tie inverter. The
DCMG-BEMP is further differentiated from other DC microgrid
applications by an Energy Management Gateway (EMG), which manages
the integrated PV power production, DC loads, and DC sources to
minimize the overall (grid and renewable) energy use and total cost
of ownership (TCO).
[0048] The system architecture simplifies building electrical
wiring by significantly reducing wiring conduit runs, as many of
the DC-based components are either roof- or ceiling-mounted
(including the PV array, lighting, and ceiling-mounted ventilation
fans), and can utilize existing AC wiring for DC power, making the
system well suited to retrofit as well as new construction
applications. The DCMG-BEMP is suitable to many facility types,
since lighting and HVAC are large energy users in most buildings.
As such, the DC loads may be commercial high-bay lighting and a
large industrial ceiling fan that improves HVAC system efficiency.
This broad application base may allow market forces to realize
economies of scale and further improve the cost-effectiveness.
[0049] A DCMG-BEMP of the invention may include three phases, as
shown in FIG. 5, which is a high-level system schematic. A detailed
block diagram is shown in FIG. 6. A core DCMG-BEMP system is first
integrated in Phase I, which includes a PV array, DC power supply,
and a DC-based high-bay induction lighting system. This core system
is relatively small and is sized to match the DC loads, such that
all PV production is immediately used. The result is a simple and
cost-effective solution that does not require a grid-tied inverter.
The core system may incorporate approximately 20 kW of PV depending
on the amount of building loads that can be converted to DC, but
(unlike the latter Phases) the core does not significantly enhance
the facility's energy security.
[0050] Phases II and III build on the core system by adding
additional PV generation and energy storage to dramatically enhance
the facility's energy security and mission assurance during power
outages. The managed energy storage system also performs load
leveling/peak load reduction under normal operation to reduce
utility costs. These phases require substantially more PV power,
and the functionality of the grid-tie inverter is integrated into
the storage system to upload excess PV and stored power to the
grid. A net metering agreement may allow for the uploaded energy to
offset utility-supplied energy. Phase II integrates a battery-based
energy storage system, large-diameter DC-powered ceiling
ventilation fans as an additional DC load, and added PV array
capacity. Ceiling-mounted ventilation fans (e.g., 24 inch diameter)
may be used as DC load, but a DC HVAC system, for example, may also
be used. The fan circulates air so the heated/air-conditioned air
is uniformly distributed, and moving air provides more comfort to
occupants. The result is that the HVAC system can be set to a lower
or higher temperature (depending on the mode), and/or operates less
often, using less energy while maintaining occupant comfort. Each
fan requires 1.5 kW to operate (3 kW total for two fans), which is
substantially less than the HVAC power reduction. Use of large
ventilation fans can reduce air conditioning energy consumption by
36%, reduce heating energy consumption by 20+ %, and elevated air
speed from a large fan can increase productivity by 9% in non-air
conditioned spaces.
[0051] Phase II integrates a battery energy storage system such as
a Green Charge Networks (GCN) GreenStation battery storage system
to provide emergency backup power to critical DC loads. The
GreenStation storage system may also demonstrate AC load-leveling
features by actively using the system's energy storage capacity to
level the building's demand for utility grid power when the system
is not in emergency backup mode. Phase III integrates an additional
PV generation and increased battery capacity as well as an electric
vehicle charging stations (EVCS). The DCMG-BEMP-connected EVCS
further supports mission-critical activities by providing the
ability to charge vehicles even during power outages, such that
personnel mobility can be maintained throughout.
[0052] The Energy Management Gateway (EMG) performs overall system
management and interfaces with existing building network
infrastructure (e.g., LonWorks) if needed. The EMG provides maximum
power point tracking (MPPT) algorithms that keeps the PV System
operating at the highest possible efficiency regardless of weather
and load conditions. The EMG, together with the GCN GreenStation
battery energy storage, also manages the solar-synchronized loads
(SSL) function, including AC and DC load-balancing and
load-shedding to reduce non-critical loads during periods of
reduced PV power (without affecting critical lighting or other
loads). The EMG control software may be optimized and implemented
to manage the DC power sources, lighting and fan systems,
GreenStation energy storage, and EVCS via secure, wired
connections.
[0053] Supplemental grid power is supplied to the DC microgrid via
an AC-to-DC power supply when PV power alone is insufficient, and
when stored power is being conserved. Power flow is controlled by
the EMG to optimize use of grid vs. solar vs. stored power. The
EMG-controlled power supplies respond instantaneously to attenuate
"peak-to-valley" changes during rapidly varying solar energy
production, such as during cloud-shading events. The EMG also
determines and manages times at which it is most effective to
charge the battery system from the PV array and/or utility grid, as
well as times at which it is most effective to export PV and/or
stored power to the building's other AC loads. The result minimizes
grid-based energy and power demands and maximizes renewable energy
usage. The GreenStation's battery energy storage system's
energy-buffering capability also enables the Phase III EVCS
installation to be done without "last-mile" grid upgrades, thus
reducing costs.
[0054] The invention may provide a modular, scaleable, and
optimized DCMG-BEMP system flexibly designed for broad commercial
applications. An efficient DC infrastructure and EMG-managed device
connectivity is an important DCMG-BEMP feature, as it enables
simplified DC microgrid "islanding" for off-grid operation.
Islanding of the DC microgrid allows critical loads to be
unaffected during blackouts by using PV and/or stored energy.
High-priority loads such as lighting are reduced according to the
facility's emergency-mode requirements while lower-priority loads
are allocated energy as it becomes available. As a result, the
reliance on other backup power sources is eliminated or
significantly reduced. This islanding capability is unique to the
inventive system and an ideal fit for providing backup power at
mission-critical facilities and emergency shelters. Conventional
grid-tied inverter-based PV systems cannot provide this backup
functionality, as these systems turn off when grid power is lost. A
programmable emergency power mode may be integrated into the EMG to
manage tradeoffs between building lighting and ventilation levels,
battery storage capacity, and weather effects.
[0055] In one embodiment, the induction lights (Everlast), PV
panels (Bosch), GreenStation (GCN), and DC power supply (Emerson)
are all UL-certified commercial units in serial mass-production.
The equivalent DC version of the Everlast induction light (e.g.
ballast, light, enclosure) may also be UL certified. The EMG may
either be an off-the-shelf solution (e.g. Tridium) or may utilize
mature software platforms (Visual Rules and Inubit) operating on
UL-certified hardware. The large commercial ceiling fans (Delta T
Corp) are mass-produced. The fans are AC-powered, but utilize
variable frequency drives (VFD) that operate internally on DC
power. Either the DC circuits of the existing VFD may be utilized,
or the VFD may be replaced/supplemented with a commercially
available DC-input device. In any case, the complete DC fan unit
may be UL certified and added in Phase II. A commercially available
EV fast-charging station (e.g. Eaton DC Quick Charger) may be
installed in Phase III. The charger may have an AC interface with
the GreenStation. Integrating the EV fast charging station with a
DC connection to the GreenStation may maximize the microgrid's
benefits and capabilities. [0056] Phase I: Install core DC
microgrid including PV and DC lighting. Compare performance vs.
conventional AC system to validate economic advantages. [0057]
Phase II: Expand core system functionality to include large DC
ceiling fan. Add first elements of enhanced system to demonstrate
value of storage in improving energy security. Demonstrate
emergency backup and load-leveling with limited Phase II PV and
storage capacity. [0058] Phase III: Increase capacity of enhanced
system by adding more PV and storage, and install EV charging
station. Demonstrate full value of load-leveling and energy
security features including EV charging during blackout
conditions.
[0059] The present invention may: [0060] Demonstrate the total
cost-of-ownership savings the system provides as a result of
improved energy efficiency, lower upfront cost, lower operating and
maintenance (O&M) costs, and demand charge reductions. The
invention may validate the enhanced facility energy security from
the DCMG-BEMP relative to a conventional AC infrastructure. A
small, conventional 10 kW PV reference system with AC inverter and
AC induction lighting may be constructed next to the DC PV array as
a comparison to the core DC microgrid. Energy use and power demand
of the DC-microgrid and AC-reference systems may be directly
compared to quantify savings, as well as compared to the current
system (using historical data) to quantify the impact of the
lighting upgrade. HVAC energy usage for the baseline system and
that integrating the DC ventilation fans may be analyzed to
quantify the energy-consumption impact. O&M costs for the
demonstration system may be compared with the current
infrastructure to quantify the operating-cost and reliability
impacts. Initial economic analysis indicate the core DC microgrid
power-management functionality may have a net present value that is
less and a Savings to Investment Ratio (SIR) that is higher than a
comparable AC system. [0061] Demonstrate the impact of effective
optimized use and management of renewable solar power to reduce
grid-supplied energy and power demands. Initial estimates based on
simulation results of the proposed core system indicate 8% to 12%
less PV infrastructure (panels, racking, wiring, etc.) in terms of
kilowatts are needed to provide the same PV energy to the DC-based
lighting as compared to the AC reference system. This assumes the
minimum Phase I system on the demonstration facility, in which a
small, 10 kW PV or 20 kW PV system is used in a highly
cost-effective way to supplement the lighting needs. [0062]
Demonstrate the DCMG-BEMP system's unique energy-security
enhancement by providing backup power for mission-critical
activities without requiring outside energy sources (e.g.
liquid/gaseous fuels). Tradeoffs between the PV array size and
battery storage versus energy security may be demonstrated in terms
of the probability of having sufficient power to keep the facility
functional throughout the day and night under various weather
conditions. [0063] Two DC-based microgrid system architectures with
broad application may be demonstrated. The first "core" DC
microgrid system may utilize a relatively small PV array that may
use PV energy far more cost-effectively than conventional AC
systems when paired with DC loads, such as lighting and ventilation
fans. This system has broad application and is especially suited to
buildings operating seven days a week. The second "enhanced" system
is intended for buildings where energy security is of primary
importance. An optional energy storage system and additional PV
array are used to add a scalable amount of energy security,
reducing or completely eliminating the need for on-site fuel
storage for diesel generators. In addition to the backup power
functionality, the battery storage system's ability to provide
utility demand charge reduction and load leveling (while also
reducing the need for infrastructure upgrades) may be demonstrated.
[0064] Additional Benefits: The increased renewable energy usage
may improve air quality and energy use.
[0065] The DCMG-BEMP may effectively reduce overall total cost of
ownership for a building, maximize the use of renewable PV energy
production to minimize grid-supplied energy, improve the
energy-security and backup-power capabilities relative to
conventional AC infrastructure, and demonstrate the added value of
energy storage for building load leveling and peak load
reduction.
TABLE-US-00001 TABLE 1 Quantitative Performance Objectives Summary
Performance Objective Metric Data Requirements Renewable Energy
Renewable Energy Used Meter readings of renewable Usage on
Installation (kWh and energy used by installation; MMBtu) measured
values from data acquisition system Facility Utility Energy Energy
Usage (kWh and Historical utility statements Usage (Electric,
MMBtu) (current system); data acquisition Natural Gas, etc.) system
measurements of facility energy usage Peak Electric Utility Monthly
Peak Power Historical utility statements Load Reduction (kW)
(current system); data acquisition system measurements of facility
peak power Annual Operating Lighting and HVAC data acquisition
system Costs (includes energy Energy Costs ($/year), measurements
of current facility usage and maintenance Maintenance Costs
lighting energy; lighting costs) ($/year) maintenance records
(parts and labor costs) Facility Energy Time without Utility
Time-stamped data acquisition Security/Backup Grid Power during
Grid system measurements of facility Power Availability
Interruptions (hours) energy use during power outages Ensure
Lighting Candle Power of Light at Handheld light intensity meter
Output Fulfills Best Ground Level (target is Practice Standards 50
foot candles) System Scalability and Number of Applicable Detailed
facility inventory data Transferability Facilities in Current
(square footage, building type and Inventory use, ceiling height,
annual electric usage, etc.) System Economics Internal Rate of
Return Utility statements; installation and (IRR) (%), Annual Cost
operational costs; discount rates; Savings ($), Payback usable
lifetimes; etc. Period (years)
[0066] Phase I--Core DCMG-BEMP system with an approximately 20 kW
PV array to power DC-based lighting. The size of the system may be
based on the amount of lighting loads that can be converted to DC.
A small (10 kW) AC-based reference system may be used to collect
baseline data for direct comparison. [0067] Phase II--The Phase I
system plus an additional 35 kW PV, a 32 kWh battery storage
system, and a DC-powered large-diameter ceiling fan. [0068] Phase
III--The Phase II system plus an additional 35 kW PV (for 100 kW
total) PV, an additional 64 kWh of battery storage (for 96 kWh
total), and a fast-charge electric vehicle charging station.
[0069] a) Phase I
[0070] Phase I may include the following: [0071] I-1.Baseline the
energy usage and lighting level of the current AC lighting for
comparison to the Phase I system. Begin long-term data acquisition
of the HVAC system and a complete building electrical energy
profile to use as a baseline in the Phase II load-leveling
demonstration. [0072] I-2.Demonstrate how the core DC microgrid
system operates without a grid-tied PV inverter and more
efficiently transfers energy to DC lighting loads (relative to the
conventional reference PV system utilizing an inverter and AC-based
lights). [0073] I-3.Update the economic analysis comparing the DC
microgrid relative to an equivalent AC system by incorporating the
measured efficiency improvements, installation differences, and
projections of reliability/maintenance differences. [0074] I-4.
Collect summer and winter HVAC temperature settings prior to
installation of DC fan in Phase II.
(1) Task PI-1--Demonstration Site Selection
[0075] The ideal DCMG-BEMP system site is a large, high-ceiling
building (such as a warehouse, gymnasium, commissary, vehicle
maintenance garage, aircraft hangar, etc.) that can accommodate a
PV array and high-bay lighting. The ideal facility would also be
used as an emergency shelter. The ideal building has a large roof,
seven-days-a-week operation, and an electrical consumption pattern
generally aligned with the PV system's energy production. Daily
operation is critical because PV array in the core system is sized
to directly power the lights, eliminating the need for a grid-tie
inverter to feed power back into the grid. The DCMG-BEMP and EMG
are flexible, scalable technologies that optimize energy use in all
climate zones and building sizes, from small structures up to
entire clusters of buildings.
[0076] (2) Task P1-2--Quantify Baseline System Performance
[0077] Energy Usage/Power Demand--A data acquisition system may be
installed to collect electricity usage data for system components
as well as the whole facility to characterize the baseline
utilization profile. These data sets may be analyzed to determine
the baseline system performance, including daily, monthly, average
monthly, and annual energy usage (kWh and MMBtu), electricity
demand (kW), and demand charges ($), as well as the frequency of
utility grid failure events (i.e. blackouts). This information may
also be used to optimize the EMG control software for the
demonstration site's operating characteristics.
[0078] Operating and Maintenance Costs--Historical maintenance and
replacement costs (including parts and labor) may be collected and
analyzed to determine typical, annualized equipment-maintenance
costs. This information may be used within the DCMG-BEMP system's
cost-effectiveness and payback calculations.
[0079] Light Output Test--An evaluation of floor-level lighting may
be done using a handheld light intensity meter. Data points may be
taken along a virtual grid across the gymnasium floor to capture
any potential variations. The test may be performed once to
quantify the induction lighting's output goal (Task PI-3).
[0080] a. Task PI-3--Phase I System Integration Design and
Installation
[0081] To allow for a direct comparison, the Phase I system may be
segmented into two subsystem circuits: (1) the core DC system (min.
20 light fixtures), and (2) a smaller reference AC system (4 light
fixtures) that may serve as a control to determine the DC system's
reduction in lighting power consumption. This AC system may allow
for energy usage comparisons in validating the DCMG-BEMP system's
performance. This reference system requires the addition of a PV
inverter to provide energy to the AC-powered lights.
[0082] The Phase I system includes installation of: (1) a 30 kW
rooftop solar PV array, (2) an Emerson NetSure 4015 System 30 kW,
400 V AC-DC power supply, (3) a Bosch Energy Management Gateway,
(4) a Solectria 10 kW PV inverter, (5) min 24 Everlast EHBUS-RC 250
W induction lights (20 DC-powered and 4 AC-powered), and (6) the
required electrical wiring. A lighting study was completed to
determine the number and power rating of the induction lights. The
current 400 W metal-halide light fixtures may be replaced, with
wiring reused wherever possible. Understanding how existing AC
wiring can be reused for DC circuits is very important for future
retrofit applications. The design may meet current electrical codes
and standards, as well as Fort Bragg's design guidelines. All of
the components used may be UL certified.
[0083] Certain aspects of the hardware design (such as available
space, wiring, etc.) may be designed anticipating Phase II and III
tasks. FIG. 6 provides a system schematic, including the phased
installation plan for the major hardware elements. This phased
installation approach ensures that sufficient capacity is available
for each phase, while evening out monetary expenditures.
[0084] b. Task PI-4--Phase I DCMG-BEMP Operation, Data Collection,
and Analysis
[0085] System Performance Analysis--Once installed and
commissioned, the DCMG-BEMP system may be operated to collect
electricity usage data. Data collection may continue to ensure that
seasonal changes are accurately captured. The EMG may serve as a
data acquisition system, recording the energy and power usage
throughout the demonstration. Since electrical demand charges are
typically defined as the highest average 15-minute peak power in a
given billing cycle, the data acquisition algorithm may be flexible
to capture regular interval data (e.g. 1-second or 5-second data).
The same data parameters used for baseline system analysis may be
collected in this task, including energy usage (kWh and MMBtu) and
demand (kW) data. This data and non-electricity utility statements
(e.g. natural gas) may be analyzed to determine the DCMG-BEMP
system's performance, including daily, monthly, average monthly,
and annual energy usage (kWh.sub.Total, kWh.sub.Grid-Supplied, and
MMBtu), renewable energy usage (kWh), electricity demand
(kW.sub.Total and kW.sub.Grid-Supplied), and demand charges
($).
[0086] 2. Phase II
[0087] Phase II may include the following:
[0088] Add a DC fan as an additional load within the DC microgrid.
The fan can reduce the heating and cooling loads of the current
HVAC system, thus saving energy.
[0089] Additional energy security may be offered by adding a GCN
GreenStation with 32 kWh of battery storage, as well as 35 kW of
PV. Specifically, the amount of backup time available during a
blackout at different emergency lighting levels and various weather
conditions may be increased.
[0090] The load-leveling capabilities may be offered by linking the
GreenStation to the building AC circuits, offering the ability to
compensate for wide, rapid variations in PV power generation and
building loads (from HVAC, etc.) by discharging and charging the
battery storage appropriately.
[0091] The DC fan's speed can be varied to match the amount of PV
power available (on a daily, seasonal, and/or weather-influenced
basis) to further level the building load profile.
[0092] a. Task PII-1--Phase II System Integration Design and
Installation
[0093] The Phase II system builds on the Phase I system by adding:
(1) 35 kW of rooftop solar PV array capacity (65 kW total), (2) a
32 kWh GCN battery storage system, (3) two 24 inch-diameter
ventilation fans, and (4) EMG modifications. The draft SOW includes
the installation upgrade plans for these components. The same
installation subcontractors used in Phase I may be used in both
Phase II and Phase III.
[0094] b. Task PII-2--Phase II DCMG-BEMP Operation, Data
Collection, and Analysis
[0095] 3. Phase III
[0096] Phase III may include the following:
[0097] Additional energy security may be offered by increasing the
GCN GreenStation capacity to a total of 96 kWh of battery storage
and 70 kW of PV. Specifically, the amount of backup time available
during a blackout at different emergency lighting levels,
demonstrated under various weather conditions may be increased.
[0098] Additional load-leveling capabilities may be due to the
increased GreenStation capacity.
[0099] The addition of a fast-charge EVCS to the GreenStation can
effectively be used as part of the load-leveling strategy.
[0100] The EVCS can continue to be used during an emergency
blackout scenario by utilizing PV and stored energy, further
increasing the energy security of the demonstration site.
[0101] A battery storage system and EVCS with DC connectivity
offers the same functionality as the current AC-powered scenario,
while offering improved efficiency during backup and charging
operations.
[0102] a. Task PIII-1--Phase III System Integration Design and
Installation
[0103] The Phase III system builds on Phase II's system by adding:
(1) 35 kW of rooftop solar PV array capacity (100 kW total), (2) an
additional 64 kWh of GCN battery storage (96 kWh total), (3) a
fast-charge EVCS, and (4) EMG modifications. The draft SOW includes
the installation upgrade plans for these components.
[0104] a. Task PIII-2--Phase III DCMG-BEMP Operation, Data
Collection, and Analysis
[0105] System Performance Analysis--The same data parameters used
in baseline system analysis, Phase I, and Phase II may be collected
in this task, including energy usage and demand data. This data and
non-electricity utility statements may be analyzed as detailed
above (in the System Performance Analysis of Task PI-4) to
determine the DCMG-BEMP system's performance under Phase III
operation. [0106] a. Load-Leveling/Peak Power Reduction--Two system
configurations: (1) with a fully functional GreenStation utilizing
the energy storage and the EMG's energy-management algorithms
managing the energy usage of all DC microgrid components (lights,
fans, energy storage, and EVCS), and (2) with the energy storage
disconnected from the building and the EMG's energy-management
algorithms managing the energy usage of all remaining DC microgrid
components (lights, fans, and EVCS). [0107] b. Avoidance of
Technical Risks
[0108] The control algorithms are developed such that, if a code
failure occurs, the system may fail in a way that allows DC devices
to be powered from the grid to ensure building loads are not
interrupted.
[0109] The battery system is not in the critical path of electrical
energy transfer (i.e., from the DC power supply and PV array to the
lighting system), so building functions may continue to operate
normally even as the battery's capacity decreases throughout its
lifetime. The energy storage system may be tested periodically
without affecting building functionality; any faults or reductions
in capacity may be reported accordingly.
[0110] The installation assumes that the existing AC wiring can be
reused for the majority of the DC microgrid wiring. If this is not
possible, separate DC wiring runs may be needed (requiring
additional installation hardware and labor, permitting/inspections,
etc.).
[0111] The ability to island the facility from the utility grid
during a power outage or an emergency is an inherent DCMG-BEMP
feature, as it does not require a grid-tied PV inverter. Islanding
allows the building's DC loads to continue functioning during such
events, enhancing the facility's energy security. Depending upon
building application, the emergency power mode may reduce or
eliminate the need for backup generators (and their associated fuel
usage). The inventive system is scalable and ideally suited to
large, flat-top buildings with high-bay lighting.
[0112] The ceiling fan, especially the large commercial variety
made by companies like Delta T, may be an appropriate DC load to
complement DC lighting (or standalone) in the inventive DC
microgrid. The ceiling fan is a load that inherently synchronizes
very well to the solar PV generation, and can also be varied in
speed to match the desired load conditions (for example, to help
get the system to maximum power point (MPP) of the PV at any exact
moment).
[0113] The DC fan's speed can be varied to match the amount of PV
power available (on a daily, seasonal, and/or weather-influenced
basis) to further level the building load profile. Ceiling fans are
especially well suited to PV power generation because they
generally run at a higher speed in summertime (to help cool
building occupants, allowing a higher air-conditioning thermostat
setting, overall saving HVAC energy cost), and run at a lower speed
in wintertime (just to bring hot air from the ceiling down to the
floor level where the occupants are, allowing the heating system to
run less often, with less heat loss through the ceiling, overall
saving HVAC energy). This can be done in the same rotational
direction winter/summer or reversing directions with season
(typically blowing air down in summer). If the profile of the
summertime/wintertime fan speed and resulting energy use is matched
to the solar PV generation, this can result in a more optimized
size of the PV array for the DC microgrid, since the case where
substantially all the PV energy from the PV array is consumed
locally through DC loads may result in the best economics for the
DC microgrid and shortest payback for the PV elements.
Synchronization of the fan load to other variations in PV
generation (daily variation from morning to night, variations due
to weather such as short-term cloud events, etc.) are also possible
for both DC microgrid configurations and conventional AC systems
where an AC PV inverter is connected to an AC fan. This
synchronization can also be coordinated with the other building
loads, and especially in the DC case can be part of a system-level
PV power point tracking system which would keep the PV operating at
the optimum power point for the current situation. In any case (AC
fan load or DC fan load), consuming locally generated PV energy
locally in the building loads whenever possible results in lower
economic and energy losses which may be associated with consuming
power from the utility grid that is generated remotely, and
associated with sending excess PV power out to the grid, only to
have a need for that same PV energy in the building loads at a
later time.
[0114] FIG. 7 illustrates a DC building system 700 including a
renewable energy DC power source in the form of a solar device 702
whose output is connected to a DC bus 704. In bi-directional
communication with DC bus 704 is a source of DC power in the form
of a DC power supply 706. DC power supply 706 may include an energy
storage device in the form of a battery 708, a DC/DC converter 710,
an AC/DC inverter 712, and a processor in the form of a controller
714. As used herein, the term "DC power supply" may encompass any
device that provides DC electrical energy converted from another
form of energy, such as AC electrical energy, or chemical energy in
the case of a battery.
[0115] Both solar device 702 and DC power supply 706 may provide DC
electrical power to DC bus 704. An AC grid 716 may provide AC power
to DC power supply 706, which AC/DC inverter 712 may convert to DC
power. DC power consuming devices or variable DC loads in the form
of DC lights 718, DC thermal device 720, and DC fan 722 may draw DC
power from DC bus 704. DC fan 722 may include a motor or generator
that is capable of operating in a regenerative mode.
[0116] FIG. 8 illustrates a DC power control system 800 including a
renewable energy DC power source in the form of a solar device
(e.g., a photovoltaic array) 802 whose output is connected to a DC
bus 804. Solar device 802 and DC bus 804 are in communication with
a source of DC power in the form of a DC/DC converter 810 and an
AC/DC inverter 812, and with a processor in the form of a
controller 814. An energy storage device in the form of battery 808
may provide DC power to DC bus 804.
[0117] Solar device 802, battery 808, and an AC power source in the
form of an AC grid 816 may supply DC electrical power to DC bus
804. AC/DC inverter 812 may convert AC power supplied by AC grid
816 to DC power. DC power consuming devices or variable DC loads in
the form of DC lights 818, DC thermal device 820 (e.g., a freezer),
and DC fan 822 may draw DC power from DC bus 804. Accordingly, it
will be appreciated that the DC power consuming devices or variable
DC loads can receive power from one or more of solar device 802,
battery 808, and AC grid 816 via a common power distribution
circuit (not shown). DC fan 822 may include a motor or generator
that is capable of operating in a regenerative mode. Optionally,
one or more energy storage elements 824 may be connected
independently and/or directly to DC bus 804.
[0118] FIG. 9 illustrates a DC load control system 900 which may be
incorporated into DC building system 700 and/or DC power control
system 800. Accordingly, DC load control system 900 will be
described with reference to components of power control system 800.
DC load control system 900 includes a second controller 902
interconnecting DC bus 804 and DC power consuming devices or
variable DC loads in the form of DC building lights 918, DC thermal
device 920, and DC fan 922. Each of these variable DC loads may
draw DC power from DC bus 804. DC building lights 918 may include
emergency lights 924 and other lights (e.g., non-emergency lights)
926. Emergency lights 924 may draw less power than the entirety of
DC building lights 918 and may be a subset of DC building lights
918. Emergency lights 924 and DC fan 922 may function as DC
emergency loads which operate when neither solar device 802 nor the
other sources of DC power 810, 812 are operable. For example,
energy storage device 808 may power each of the DC power consuming
devices 918, 920, 922 in conjunction with solar device 802 and the
other sources of DC power 510, 512 under normal non-emergency
operating conditions. However, under emergency operating conditions
(e.g., when a storm has disabled the AC grid and the solar device),
energy storage device 808 may power the DC emergency loads 922, 924
for a predetermined period of time when no source of power other
than the energy storage device 808 is available to the DC power
consuming devices 918, 920, 922. Second controller 902 may respond
to solar device 802 and the DC power supply 810, 812 being
inoperable for a threshold length of time by reducing a level of
power drawn by at least one of the DC power consuming devices 918,
920, 922.
[0119] DC fan 922 may operate at a slower speed in an emergency
mode than in a non-emergency mode. In another embodiment, emergency
lights are the same as non-emergency lights, but the lights draw
less power and are dimmer in an emergency mode than in a
non-emergency mode. In another embodiment, the emergency lights are
a subset of the non-emergency lights.
[0120] Controller 714 and/or controller 814 may function as a DC
power control system which charges the energy storage device during
time periods in which the source of DC power is operable, and which
discharges the energy storage device during time periods in which
the source of DC power is inoperable. The charging and discharging
may be based on a current state of charge (SOC) of the energy
storage device and a predetermined target SOC of the energy storage
device. For example, charging of the energy storage device may take
place only if and/or whenever the current SOC or voltage level of
the battery is below a desired target SOC or voltage level of the
battery. Discharging of the energy storage device may take place
only if and/or whenever the current SOC or voltage level of the
battery is above a desired target SOC or voltage level of the
battery. The predetermined target SOC may be a state or level of
charge or voltage that is sufficient to solely power at least one
of the DC power consuming devices for a predetermined duration of
time while the source of DC power is inoperable (e.g., during a
lightning storm).
[0121] The DC power control system 800 may charge the energy
storage device 808 by using excess power from the renewable energy
DC power source 802. The DC power control system 814 may respond to
the current SOC of the energy storage device dropping below the
predetermined target SOC by adjusting at least one of the variable
DC power consuming devices 818, 820, 822 such that a level of
current drawn by the variable DC power consuming device 818, 820,
822 is less than a level of current sourced by the renewable energy
DC power source 802, and such that the energy storage device 808 is
charged to the predetermined target SOC by the renewable energy DC
power source 802.
[0122] The DC power control system 800 may respond to the current
SOC of the energy storage device 808 dropping below the
predetermined target SOC by adjusting a discharge current rate of
the energy storage device 802 by selectively reducing or
discontinuing operation of at least one of the variable DC power
consuming devices 818, 820, 822 dependent upon a building ambient
condition and/or a corresponding predetermined building condition.
In one embodiment, the building ambient condition includes a level
of sunlight. In one embodiment, the corresponding predetermined
building condition includes a desired emergency interior lighting
level. In related embodiments, DC power control system 800
selectively reduces operation or discontinues one or more of DC
lights 818 such that a level of light provided by DC lights 818
supplements the level of sunlight to meet the desired emergency
interior lighting level. In this way, DC power control system 800
can control a discharge rate of battery 808 and, more particularly,
can reduce the discharge rate by lowering a number of the DC lights
818 operating to meet the desired emergency interior lighting
level.
[0123] The DC power control system 800 may respond to the source of
DC power 810, 812 being inoperable for a threshold period of time
by adjusting at least one of the variable DC power consuming
devices 818, 820, 822 such that a level of current drawn by the
variable DC power consuming device 818, 820, 822 is thereby
reduced. Moreover, the DC power control system 800 may selectively
reduce or discontinue operation of at least one of the variable DC
power consuming devices 818, 820, 822 dependent upon a length of
time during which the source of DC power 810, 812 has been
inoperable.
[0124] The DC power control system 800 may charge the energy
storage device 808 by discontinuing power to the motor or generator
of the DC fan 822 and by operating the motor or generator in a
regenerative mode in which kinetic energy of the motor or generator
is converted to DC power.
[0125] The DC power control system 800 may control amounts of DC
power provided to the DC bus 804 by the solar device 802 and by a
DC power supply 810, 812 that is fed by the AC grid 816.
Particularly, the DC power control system 814 may control how much
power is provided by the solar device 802 and how much power is
provided by the DC power supply 810, 812 dependent upon how much
power is needed by the DC power consuming devices 818, 820, 822,
the cost of the AC power from the grid 816, how much power is
available from other sources, such as an energy storage device 808,
a motor operating in a regenerative mode, etc.
[0126] FIG. 10 illustrates another embodiment of a DC power control
system 1000 which may be substantially similar to DC power control
system 800, except that system 1000 additionally includes a mobile
device in the form of a motorized vehicle 1028 powered by battery
1008. DC power control system 1000 includes a renewable energy DC
power source in the form of a solar device (e.g., a photovoltaic
array) 1002 whose output is connected to a DC bus 1004. Solar
device 1002 and DC bus 1004 are in communication with a source of
DC power in the form of a DC/DC converter 1010 and an AC/DC
inverter 1012, and with a processor in the form of a controller
1014. An energy storage device in the form of battery 1008 may
provide DC power to DC bus 1004.
[0127] Both solar device 1002 and the DC power supply may provide
DC electrical power to DC bus 1004. An AC grid 1016 may provide AC
power to the DC power supply, which AC/DC inverter 1012 may convert
to DC power. DC power consuming devices or variable DC loads in the
form of DC lights 1018, DC thermal device 1020 (e.g., a freezer),
and DC fan 1022 may draw DC power from DC bus 1004. DC fan 1022 may
include a motor or generator that is capable of operating in a
regenerative mode. Optionally, one or more energy storage elements
(not shown) may be connected independently and/or directly to DC
bus 804.
[0128] Motorized vehicle 1028 may be in the form of a golf cart or
a fork lift, for example. Thus, the energy storage device may power
the DC power consuming devices in conjunction with the solar device
and the other source of DC power, and may also power the motorized
vehicle. Accordingly, battery 1008 may substantially simultaneously
perform both functions of providing emergency power for emergency
loads when the solar device and the other source of DC power are
inoperable, and being the exclusive source of power for a motorized
vehicle.
[0129] It is to be understood that the present invention may
encompass embodiments in which ceiling fans or other motor loads
act in a regenerative braking mode as all or part of the energy
storage to power the lights directly. That is, the regeneration may
not necessarily charge other batteries in the system. In other
words, if there are no batteries in the system, the fans slowing
down could keep supplying power to the DC lights when the grid is
lost. This method may help fill-in power when a cloud passes and
suddenly solar power is lost. This may increase the life of the DC
power supply because the DC power supply does not have as large of
a power surge due to sudden clouds if the fan motors help supply
even a small amount of energy storage.
[0130] While this invention has been described as having an
exemplary design, the present invention may be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles.
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