U.S. patent application number 12/131457 was filed with the patent office on 2009-12-03 for system and method for using a photovoltaic power source with a secondary coolant refrigeration system.
This patent application is currently assigned to Dover Systems, Inc.. Invention is credited to John D. Bittner, John E. Bittner.
Application Number | 20090293523 12/131457 |
Document ID | / |
Family ID | 41378087 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090293523 |
Kind Code |
A1 |
Bittner; John D. ; et
al. |
December 3, 2009 |
SYSTEM AND METHOD FOR USING A PHOTOVOLTAIC POWER SOURCE WITH A
SECONDARY COOLANT REFRIGERATION SYSTEM
Abstract
A secondary coolant refrigeration system powered primarily by a
photovoltaic source and by an alternating current (AC) source as a
backup is disclosed. The secondary coolant refrigeration system has
a pump for pumping secondary coolant fluid through a secondary
coolant fluid loop. The system includes a variable frequency drive
for controlling the speed of the pump. The variable frequency drive
includes drive circuitry configured to provide variable frequency
power to the pump via an output interface. The variable frequency
drive also includes a first interface configured to receive power
from the photovoltaic source and a second interface configured to
receive power from the AC source. The variable frequency drive
further includes a circuit configured to switch between providing
power to the drive circuitry from the first interface and providing
power to the drive circuitry from the second interface. The circuit
is further configured to cause the variable speed drive to be
powered by the photovoltaic source when the power received from the
first interface is adequate and by the AC source when the power
received from the first interface is not adequate.
Inventors: |
Bittner; John D.;
(Bethlehem, GA) ; Bittner; John E.; (Troutville,
VA) |
Correspondence
Address: |
FOLEY & LARDNER LLP
777 EAST WISCONSIN AVENUE
MILWAUKEE
WI
53202-5306
US
|
Assignee: |
Dover Systems, Inc.
|
Family ID: |
41378087 |
Appl. No.: |
12/131457 |
Filed: |
June 2, 2008 |
Current U.S.
Class: |
62/236 ;
700/275 |
Current CPC
Class: |
Y02B 30/745 20130101;
Y02B 30/70 20130101; F25B 25/005 20130101; F25B 21/00 20130101;
F25B 2600/13 20130101 |
Class at
Publication: |
62/236 ;
700/275 |
International
Class: |
F25B 27/00 20060101
F25B027/00; G05B 15/00 20060101 G05B015/00 |
Claims
1. A secondary coolant refrigeration system powered primarily by a
photovoltaic source and by an alternating current (AC) source as a
backup, the secondary coolant refrigeration system having a pump
for pumping secondary coolant fluid through a secondary coolant
fluid loop, the system comprising: a variable frequency drive for
controlling the speed of the pump, the variable frequency drive
comprising: drive circuitry configured to provide variable
frequency power to the pump via an output interface; a first
interface configured to receive power from the photovoltaic source;
a second interface configured to receive power from the AC source;
and a circuit configured to switch between providing power to the
drive circuitry from the first interface and providing power to the
drive circuitry from the second interface, wherein the circuit is
further configured to cause the variable speed drive to be powered
by the photovoltaic source when the power received from the first
interface is adequate and by the AC source when the power received
from the first interface is not adequate.
2. The secondary coolant refrigeration system of claim 1, wherein
the circuit is configured to cause the switch between the first
interface and the second interface to be smooth so that operation
of the pump is not interrupted.
3. The secondary coolant refrigeration system of claim 1, wherein
the switching is automated and does not require human input before
each switch.
4. The secondary coolant refrigeration system of claim 1, wherein
the circuit is configured to determine whether the power received
from the first interface is adequate by comparing the power
received at the first interface to the power received at the second
interface.
5. The secondary coolant refrigeration system of claim 1, wherein
the circuit is configured to determine that the power received from
the first interface is adequate when voltage at the first interface
is equal to or greater than the voltage at the second
interface.
6. The secondary coolant refrigeration system of claim 1, wherein
the circuit is configured to determine that the power received from
the first interface is adequate when voltage at the first interface
is at least 1.35 times higher than the voltage at the second
interface.
7. The secondary coolant refrigeration system of claim 1, wherein
the circuit determines whether the power received from the first
interface is adequate for driving the pump by comparing voltage
from the first interface to a threshold value.
8. The secondary coolant refrigeration system of claim 7, wherein
the variable frequency drive further comprises an input for
receiving a signal from a user interface and wherein the controller
is further configured to adjust the threshold value based on the
received signal.
9. The secondary coolant refrigeration system of claim 1, further
comprising: wherein the pump is one of a plurality of pumps for
pumping secondary coolant fluid; and wherein the variable frequency
drive is one of a plurality of variable frequency drives, each
variable frequency drive configured to drive one of the plurality
of pumps, wherein each variable frequency drive is configured to
receive power from the photovoltaic source or another photovoltaic
source by default.
10. The secondary coolant refrigeration system of claim 1, wherein
the circuit comprises a diode connected to the photovoltaic power
source, the diode configured to have an on-voltage of at least the
normal output voltage from the AC source.
11. The secondary coolant refrigeration system of claim 10, wherein
the circuit further comprises a rectifier configured to receive
power from the second interface and to provide power to a direct
current (DC) bus, the DC bus couples the second interface to
inverter circuitry of the variable frequency drive, and wherein the
output from the cathode of the diode is connected to the DC
bus.
12. The secondary coolant refrigeration system of claim 1, wherein
the circuit comprises a programmable controller.
13. A method for controlling a pump used in a secondary coolant
refrigeration system, the speed of the pump controlled using a
variable frequency drive configured to selectively receive power
from an AC source and a photovoltaic source, the method comprising:
using the variable frequency drive to determine whether power
received from the photovoltaic source is adequate for driving the
pump; configuring the variable frequency drive to use the power
received from the photovoltaic source when the power is adequate
for driving the pump; and using the variable frequency drive to
switch from using the power received from the photovoltaic source
to power received from the AC source when the power received from
the photovoltaic source is inadequate for driving the pump.
14. The method of claim 13, wherein the variable frequency drive is
configured to use power from the photovoltaic source when the
voltage available from the photovoltaic source is equal to or
greater than the voltage available at the AC source.
15. The method of claim 13, wherein the variable frequency drive is
configured to use power from the photovoltaic source when the
voltage available from the from the photovoltaic power source at
least 1.35 times higher than the voltage available at the AC source
when the AC source is a three phase AC source and at least 0.9
times higher than the voltage available at the AC source when the
AC source is a single phase AC source.
16. The method of claim 13, further comprising: comparing a
measurement of voltage of the power received from the photovoltaic
source to a threshold value.
17. The method of claim 16, further comprising: receiving an input
from a user interface; and adjusting the threshold value based on
the received input.
18. The method of claim 13, further comprising: configuring the
variable frequency drive to receive power from the photovoltaic
source by default and the AC source as a backup.
19. The method of claim 13, further comprising: wherein the switch
is smooth and the operation of the pump is not interrupted.
20. The method of claim 13, further comprising: comparing the power
received from the photovoltaic source to the power available from
the AC source.
21. A system for cooling a plurality of refrigeration loads, the
system comprising: a plurality of secondary coolant fluid loops
configured to cool the plurality of refrigeration loads; a
plurality of coolant pumps, each coolant pump associated with at
least one secondary coolant fluid loop; a plurality of variable
frequency drives, each variable frequency drive configured to
control and drive one of the plurality of coolant pumps; and at
least one photovoltaic power source; wherein the plurality of
variable frequency drives are configured to receive power from the
photovoltaic power source and to use the power from the
photovoltaic power source to drive the coolant pumps when the power
from the photovoltaic power source meets a threshold requirement,
and wherein each variable frequency drive is also configured to
receive power from a second power source and to use the power
received from the second power source when the power from the
photovoltaic power source does not meet the threshold
requirement.
22. The system of claim 21, wherein the threshold requirement is a
minimum voltage requirement and wherein the second power source is
one of grid power and a battery backup source.
23. The system of claim 21, wherein a separate photovoltaic power
source is provided for each of the variable frequency drives.
Description
BACKGROUND
[0001] The present disclosure relates generally to the field of
refrigeration systems. More specifically, the disclosure relates to
systems and methods for using a photovoltaic power source with a
secondary coolant refrigeration system.
[0002] It is well known to provide a refrigeration system including
a refrigeration device or temperature controlled storage device
such as a refrigerated case, refrigerator, freezer, etc. for use in
commercial and industrial applications involving the storage and/or
display of objects, products and materials. For example, it is
known to provide a refrigeration system with one or more
refrigerated cases for display and storage of frozen or
refrigerated foods in a supermarket to maintain the foods at a
suitable temperature (e.g. 32 to 35 deg F.). In such applications,
such refrigeration systems often are expected to maintain the
temperature of a space within the refrigerated case where the
objects are contained within a particular range that is suitable
for the particular objects, typically well below the room or
ambient air temperature within the supermarket. Such known
refrigeration systems will typically include a heat exchanger in
the form of a cooling element or loop within the refrigeration
device and provide a flow of a fluid such as a coolant into the
cooling element to refrigerate (i.e. remove heat from) the space
within the refrigeration device. Various known configurations of
refrigeration systems (e.g. direct expansion system and/or
secondary system, etc.) are used to provide a desired temperature
within a space in a refrigeration device such as a refrigerated
case (e.g. by supply of coolant).
[0003] In refrigeration systems having a primary loop that
circulates a direct expansion type refrigerant that interfaces
with, and cools, a liquid coolant in one or more secondary loop(s),
the liquid coolant flows through the secondary loops by way of one
or more pumps, for example multiple variable speed pumps. The speed
of the pump may be adjusted to provide more or less pressure of the
coolant in the coolant loops. The motors for the one or more pumps
for circulating the liquid coolant though the secondary loops are
conventionally powered by an electric alternating current (AC)
source such as a power grid.
SUMMARY
[0004] One embodiment of the disclosure relates to a secondary
coolant refrigeration system powered primarily by a photovoltaic
source and by an alternating current (AC) source as a backup. The
secondary coolant refrigeration system has a pump for pumping
secondary coolant fluid through a secondary coolant fluid loop. The
system includes a variable frequency drive for controlling the
speed of the pump. The variable frequency drive includes drive
circuitry configured to provide variable frequency power to the
pump via an output interface. The variable frequency drive also
includes a first interface configured to receive power from the
photovoltaic source and a second interface configured to receive
power from the AC source. The variable frequency drive further
includes a circuit configured to switch between providing power to
the drive circuitry from the first interface and providing power to
the drive circuitry from the second interface. The circuit is
further configured to cause the variable speed drive to be powered
by the photovoltaic source when the power received from the first
interface is adequate and by the AC source when the power received
from the first interface is not adequate.
[0005] Another embodiment of the disclosure relates to a method for
controlling a pump used in a secondary coolant refrigeration
system. The speed of the pump is controlled using a variable
frequency drive configured to selectively receive power from an AC
source and a photovoltaic source. The method includes using the
variable frequency drive to determine whether power received from
the photovoltaic source is adequate for driving the pump. The
method further includes configuring the variable frequency drive to
use the power received from the photovoltaic source when the power
is adequate for driving the pump. The method yet further includes
using the variable frequency drive to switch from using the power
received from the photovoltaic source to power received from the AC
source when the power received from the photovoltaic source is
inadequate for driving the pump.
[0006] Another embodiment of the disclosure relates to a system for
cooling a plurality of refrigeration loads. The system includes a
plurality of secondary coolant fluid loops configured to cool the
plurality of refrigeration loads. The system further includes a
plurality of coolant pumps, each coolant pump associated with each
secondary coolant fluid loop. The system yet further includes a
plurality of variable frequency drives, each variable frequency
drive configured to controllably drive one of the plurality of
coolant pumps and at least one photovoltaic power source. The
plurality of variable frequency drives are configured to receive
power from the photovoltaic power source and to use the power from
the photovoltaic power source to drive the coolant pumps when the
power from the photovoltaic power source meets a threshold
requirement. Each variable frequency drive is also configured to
receive power from a second power source and to use the power
received from the second power source when the power from the
photovoltaic power source does not meet the threshold
requirement.
[0007] Alternative exemplary embodiments relate to other features
and combinations of features as may be generally recited in the
claims.
BRIEF DESCRIPTION OF THE FIGURES
[0008] The application will become more fully understood from the
following detailed description, taken in conjunction with the
accompanying figures, wherein like reference numerals refer to like
elements, in which:
[0009] FIG. 1 is a block diagram of a refrigeration system
utilizing a secondary coolant system, according to an exemplary
embodiment;
[0010] FIG. 2A is a detailed block diagram of a refrigeration
system and particularly a variable frequency drive, according to an
exemplary embodiment;
[0011] FIG. 2B is a detailed block diagram of a refrigeration
system and particularly a variable frequency drive, according to
another exemplary embodiment; and
[0012] FIG. 3 is a flow chart of a process for controlling a pump
used in a secondary coolant refrigeration system, according to an
exemplary embodiment.
DETAILED DESCRIPTION
[0013] Before turning to the figures, which illustrate the
exemplary embodiments in detail, it should be understood that the
application is not limited to the details or methodology set forth
in the following description or illustrated in the figures. It
should also be understood that the phraseology and terminology
employed herein is for the purpose of description only and should
not be regarded as limiting.
[0014] According to any preferred embodiment, a secondary coolant
refrigeration system, and more particularly a variable frequency
drive for a pump of the system, is configured to be powered
primarily by a photovoltaic power source (e.g., a solar panel). The
variable frequency drive is also configured to receive power from
an AC source (or a secondary DC power source). During operation,
the variable frequency drive is configured to switch from the
photovoltaic power source to the AC source if the power received
from the photovoltaic power source (or available at the DC source)
is inadequate for driving the pump.
[0015] Referring to FIG. 1, a block diagram of a refrigeration
system 100 utilizing a secondary coolant system 101 is shown,
according to an exemplary embodiment. Refrigeration system 100 is
configured to provide a cooling function to one or more
refrigeration loads 104 by controlling coolant flow through one or
more secondary coolant fluid loops 102 (e.g., a hydronic loop, a
heat exchange loop, etc.), shown as four loops, associated with
refrigeration loads 104. Refrigeration loads 104 may include any of
a wide variety of objects to be cooled such as temperature
controlled storage devices (e.g., refrigerated display cases,
walk-in coolers, etc.). Secondary cooling system 101 also includes
one or more pumps 106, one or more variable frequency drives (VFD)
108 associated with pumps 106, and a pump controller 110. Each pump
106 is understood to include a motor that receives the AC electric
power from a VFD 108 and converts the electric power to rotational
motion of a shaft which drives the pump.
[0016] Refrigeration system 100 is also shown to include a primary
refrigerant loop 140 for circulating a refrigerant (e.g., a direct
expansion type refrigerant, etc.) through a compressor 142 and a
condenser 144 and an expansion device 146 to one or more chillers
148 and back to the compressor 142. The chillers 148 are heat
exchangers (e.g., plate type heat exchangers or the like) shown to
be located "downstream" of the secondary coolant pumps 106 and to
provide an interface between the secondary coolant system 101 and
the refrigerant of the primary loop 140 to provide "chilling" or
cooling of the secondary coolant fluid by the refrigerant.
[0017] According to one exemplary embodiment, refrigeration system
100 includes a secondary coolant system 101 with a plurality of
branches or loops 102, as may be used in refrigeration of
refrigeration loads 104 such as temperature controlled storage
devices in facilities such as food retailing outlets (e.g.,
supermarkets, bakeries, etc.). According to other exemplary
embodiments, refrigeration system 100 may be used with another
secondary coolant refrigeration system in any commercial,
industrial, institutional or residential application or may include
one or more loops of a primary coolant refrigeration system. While
FIG. 1 illustrates four refrigeration loads 104 and a loop 102
associated with each refrigeration load 104, according to other
exemplary embodiments, there may be more or fewer than four loads
and/or loops in the system. According to other exemplary
embodiments, one loop may be associated with more than one load.
According to still other exemplary embodiments, more than one loop
may be associated with each load.
[0018] Pump 106 is configured to pump a coolant fluid through loops
102 of secondary coolant system 101 to provide cooling to
refrigeration loads 104. The coolant fluid may be any fluid capable
of absorbing, transporting, and/or emitting heat (e.g., glycol,
water, etc.). While FIG. 1 illustrates three pumps, according to
other exemplary embodiments, more or fewer than three pumps may be
used. According to the exemplary embodiment shown in FIG. 1, pumps
106 are variable speed alternating current (AC) electric motor
pumps. Direct current (DC) pumps may be used according to various
alternative embodiments. According to an exemplary embodiment, the
pump is configured for use in secondary coolant pump applications.
Pump 106 may be a pump of any size suitable for its intended
application, but according to various exemplary embodiments pump
106 has a horsepower range of 1-20 hp and a voltage range of
208-575 volts AC.
[0019] VFD 108 (e.g., adjustable-frequency drive, variable-speed
drive, AC drive, microdrive or inverter drive, etc.) is a device
configured to control the rotational speed of a pump 106 by
controlling the frequency (and thus voltage) of the electrical
power supplied to pump 106. While FIG. 1 illustrates a VFD 108
corresponding to each pump 106, according to other exemplary
embodiments one VFD may be used to control multiple pumps.
According to various exemplary embodiments, the VFD may be a solid
state device, for example using a rectifier bridge (e.g., diode
bridge). According to other exemplary embodiments, the VFD may
include analog circuitry. According to other exemplary embodiments,
the VFD may be another type of adjustable speed drive such a slip
controlled drive or any other adjustable or variable speed
drive.
[0020] Pump controller 110 is generally configured to control the
fluid flow of coolant through system 101 based on pressure readings
from loops 102. Pump controller 110 may control the fluid flow by
controlling the speed of each individual pump 106, controlling the
sequencing of the pumps, and/or conducting other pump controlling
activities. According to various exemplary embodiments, pump
controller 110 may be a digital and/or analog circuit. According to
other exemplary embodiments, pump controller 110 may include a
software controller executed on a processor or other circuit.
[0021] Referring still to FIG. 1, VFDs 108 are shown coupled to an
AC power source 112 and a photovoltaic power source 114. AC power
source 112 may be a power grid (e.g., 1-phase power, 3-phase power,
120-volt AC power, etc.). Photovoltaic power source 114 may be a
solar cell, a solar array, a set of solar arrays, or any other
photovoltaic modules. Photovoltaic power source 114 may be any
photovoltaic power source of the past, present, or future
configured to receive solar energy and to output DC electric
power.
[0022] According to an exemplary embodiment, VFDs 108 are
configured to use DC power from photovoltaic power source 114
unless the received power is inadequate. In this event, VFDs 108
are configured to switch from using the DC power from photovoltaic
power source 114 to using the AC power from AC power source 112.
According to various alternative embodiments, it is important to
note that if power from photovoltaic power source 114 is
inadequate, VFDs 108 may be configured to switch to alternative
power sources other than AC power source 112 (e.g., another DC
power source, a back-up battery, one or more capacitors, etc).
[0023] Referring now to FIG. 2A, a close-up block diagram of a
single VFD 108 connected to power sources 112, 114 and pump motor
106 is shown, according to an exemplary embodiment. VFD 108 is
shown to include an AC interface 204, a DC interface 218, and a
pump interface 212. VFD 108 is further shown to include a source
switch 208, drive circuitry 210, a controller 216, an input/output
(I/O) terminal 224, and a control interface 226. According to an
exemplary embodiment, the components of VFD 108 are located
together and are surrounded by a housing (e.g., a plastic housing,
a metal housing, etc.).
[0024] Source switch 208 is configured to switch between different
power sources such as AC power source 112 and photovoltaic power
source 114. Source switch 208 may be implemented in a number of
different ways. For example, a one or more diodes (or gates created
using other electrical components) may be used between the
photovoltaic power source 114 and the drive circuitry to allow or
deny the flow of current from photovoltaic power source 114 to
drive circuitry 210.
[0025] AC interface 204 and DC interface 218 may be or include any
number of jacks, terminals, receptacles, or other structures
configured to receive cabling from power sources 112, 114. AC
interface 204 and DC interface 218 may also include circuitry
configured to, for example, limit the current received from the
power sources, sense or detect the voltage available from the power
sources, convert the AC to DC, invert the DC to AC, and/or to
conduct other filtering, limiting, sensing, or converting
activities on received power. Any number of protection or safety
mechanisms such as diode 222 and/or switch 220 (e.g., fuse, circuit
breaker, etc.) may also or alternatively be provided between power
sources 112, 114 and VFD 108. AC interface 204 is shown as
connected to AC power source 112 by AC cabling 205. Similarly, pump
interface 212 is shown as connected to pump motor 106 by AC cabling
213.
[0026] Drive circuitry 210 is configured to receive input from
power bus 228, to controllably vary the frequency of the power, and
to provide the power to the output interface 212. Power bus 228 may
be a DC power bus and source switch 208 may include a converter
that converts power received from AC power source 112 to DC (if the
photovoltaic power source 114 is not being utilized). Drive
circuitry 210 may include an inverter circuit with pulse width
modulation voltage control, providing quasi-sinusoidal AC output.
Drive circuitry 210 may include an embedded microprocessor or may
be controlled by controller 216.
[0027] Referring still to FIG. 2A, the decision regarding whether
to switch from DC to AC and vice-versa may occur via controller
216. According to yet other exemplary embodiments, the decision
regarding whether to switch may be accomplished via a logic circuit
that is a part of source switch 208. Controller 216 may be a field
programmable gate array (FPGA), an application specific integrated
circuit (ASIC), a general purpose microcontroller configurable via
computer code stored in memory, and/or any other combination of
circuitry. Controller 216 and/or other control circuitry of VFD 108
may be powered by battery, an auxiliary AC input, AC power source
112 (even if photovoltaic power source 114 is being used to drive
the pump, etc.). Controller 216 may be integrated with source
switch 208 (e.g., circuitry of source switch 208 and/or of
interfaces 204, 218). According to an exemplary embodiment,
controller 216 makes a determination and controls a switch from
photovoltaic power source 114 to AC power source 112 in an
automated fashion (e.g., does not require human input before each
switch).
[0028] Controller 216 may be configured to conduct any number of
activities to determine whether or not to switch from DC to AC.
Controller 216 may be configured to determine whether the power
received from DC interface 218 is adequate by comparing the power
received at DC interface 218 to the power received at AC interface
204. Controller 216, for example, may be configured to determine
that the power received from DC interface 218 is adequate when
voltage at DC interface 218 is equal to or greater than the voltage
at AC interface 204. According to yet other exemplary embodiments,
controller 216 may be configured to determine that the power
received from DC interface 218 is adequate when voltage at DC
interface 218 is measured to be some multiple of voltage measured
at AC interface 204 (e.g., at least 1.35 times higher, etc.).
According to other exemplary embodiments, controller 216 may be
configured to determine whether the power received from the DC
interface 218 is adequate for driving pump 106 by comparing voltage
from the DC interface 218 to a threshold value (e.g., 400 VDC,
etc.) or a setpoint of pump 106 (e.g., as read and/or received from
controller interface 226).
[0029] According to an exemplary embodiment, controller 216 is
configured to seamlessly switch from using DC power to using AC
power, and vice-versa. In other words, controller 216 may be
configured to transition from power source to power source in a
manner that is transparent to end users. Controller 216 may be
configured so that manual input, user input, or any other outside
input (e.g., from pump controller 110 shown in FIG. 1) is not
required for the switching to occur. A smooth transition may be
restored, for example, by receiving power from both the AC power
source 112 and the photovoltaic power source 114 for a brief period
of time (e.g., input from AC source 112 is converted to DC and is
provided in parallel to the DC from the photovoltaic power source
114 to drive circuitry 210). According to other various exemplary
embodiments, the switch from DC to AC is timed so that the delay
between switching the DC off and providing the AC to the drive
circuitry is small (e.g., less than 100 milliseconds). According to
various exemplary embodiments, the DC to AC transition is
accomplished at different rates or via different methods but the
transition is still smooth so as to not effect the operation of the
pump in a significant manner (e.g., not require the pump system to
oscillate in order to re-obtain a lost setpoint).
[0030] VFD 108 is further shown to include I/O terminal 224. I/O
terminal 224 may be or include one or more user controls built-into
VFD 108. For example, I/O terminal 224 may include any number of
buttons, keys, switches, potentiometers, displays, or the like for
receiving tactile input from a user. For example, VFD 108 may be
configured to receive input from a user so that the user may adjust
a threshold value used in the determination of whether the DC power
is sufficient. According to various other exemplary embodiments,
I/O terminal 224 may be used to wire VFD 108 to an external user
input device (e.g., a terminal, a keyboard, etc.). Control signals
may also be provided to VFD 108 (e.g., from pump controller 110)
via control interface 226. Control interface 226 may include one or
more jacks, terminals, receptacles, or other structures for
receiving signals from another controller.
[0031] According to various exemplary embodiments, VFD 108 shown in
FIG. 2A may be configured so that power received from photovoltaic
power source 114 cannot be provided to AC power source 112 (i.e.,
VFD 108 does not include a "grid tied" inverter configured to
provide power from the photovoltaic power source 114 back to the
power grid). In this and other embodiments, VFD 108 may be
configured or adjusted to accept a wide range of voltage levels
from variously sized photovoltaic power sources (e.g., up to and/or
greater than 800 VDC). According to an exemplary embodiment, VFD
108 (and/or the photovoltaic power source 114) may include
components for converting excess power to heat and/or for storing
excess power received from photovoltaic power source 114 for later
use (e.g., in one or more coupled batteries or capacitor banks).
Further, VFD 108 and/or pump 106 may be configured for regenerative
braking so that some kinetic energy of the system is stored and/or
otherwise reused. For example, if a pump is commanded to slow down,
kinetic energy from the pump system may be extracted from the pump
system, converted to electrical power, received by the variable
frequency drive, and stored in a battery system for later use.
[0032] According to an alternative exemplary embodiment, VFD 108
includes a grid tied inverter and is configured to provide power
back to the power grid in the event that the photovoltaic power
source is providing more power than the variable frequency drive
needs to drive the pump.
[0033] Referring now to FIG. 2B, a diagram of VFD 258 connected to
power sources 112, 114 and pump motor 106 is shown. According to
the exemplary embodiment shown in FIG. 2B, VFD 258's switch for
transitioning from DC power received via photovoltaic power source
114 and AC power source 112 is the combination of rectifier bridge
260 and diode 262. Diode 262 is configured to have an "on-voltage"
(i.e., "cut-in voltage") that is about 1.35 times the expected
voltage from AC power source 112. Diode 264 is a redundant diode
used to protect the photovoltaic power source 114 if diode 262
fails. It should be noted that the system will operate with a diode
in the position of diode 262, 264, or both. It should further be
noted that a circuit different than diode 262 (and/or diode 264)
may be provided to VFD 258, the circuit configured to allow current
to flow to DC bus 228 when voltage from photovoltaic power source
114 is sufficiently high. Referring further to the exemplary
embodiment shown in FIG. 2B, when the voltage from photovoltaic
power source 114 is sufficiently high relative to voltage from
rectifier bridge 260, diode 262 allows current to flow from
photovoltaic power source 114 to DC bus 228. In this embodiment,
rectifier bridge 260 is configured to impede the flow of current
from AC power source 112 to DC bus 228 when voltage from
photovoltaic source 114 is greater than that available from
rectifier bridge 260 (e.g., the diodes of rectifier bridge 260 do
not meet their "cut-in voltage" due to the potential available on
DC bus 228 from photovoltaic power source 114 being larger than
that available from DC power source). According to various
exemplary embodiments, the diodes of rectifier bridge 260 are sized
so that they do no break down even if photovoltaic power source 114
is providing its maximum voltage.
[0034] In the exemplary embodiment illustrated in FIG. 2B, no
active switches are used to switch from photovoltaic power source
114 to AC power source 112. Rather, the diodes (e.g., diode 262,
the diodes of rectifier bridge 260) are configured to behave
similar to check valves. Current only flows in one direction, anode
to cathode. The switching between photovoltaic power source 114 and
AC power source 112 is automatically conducted depending on the
voltage of the sources and the properties of the diodes. According
to an exemplary embodiment, the diodes are configured so that the
following results occur: 1) if the voltage of the photovoltaic
source is greater than (1.35*voltage from the AC power source 112),
then current will flow from the photovoltaic source; 2) if the
voltage of the photovoltaic source 114 is less than (1.35*voltage
from the AC power source 112), then current will flow from AC power
source 112; 3) if the voltage of the photovoltaic source 114 is
equal to (1.35*the voltage from the AC power source 112), then
current will flow from both sources. According to an exemplary
embodiment, if single phase AC power source 112 is used, then the
above equations will use 0.9 rather than 1.35. According to an
exemplary embodiment, thresholds of 1.35*AC Voltage and 0.9*AC
Voltage may change in different embodiments depending on the
circuits and diodes used.
[0035] It is important to note that while three phase AC power, a
rectifier bridge suitable for three phase AC power, and a three
phase motor are shown in the drawings, a single phase motor,
inverter, rectifier bridge, and/or AC power source may
alternatively be used.
[0036] Referring now to FIG. 3, a flow chart of a process 300 for
controlling a pump used in a secondary coolant refrigeration system
is shown, according to an exemplary embodiment. Process 300 is
shown to include configuring the VFD to use DC power from the
photovoltaic power source (step 302). Step 302 may include any
number of user input or adjustment steps. For example, step 302 may
include selecting, providing, and connecting the photovoltaic power
source to the VFD. The photovoltaic power source may be selected so
that the output (e.g., output voltage range) is within the range of
acceptable DC input for the VFD. Depending on the output
characteristics of the photovoltaic power source, one or more
thresholds or bias settings of the VFD may be adjusted so that the
VFD does not switch from DC to AC power too frequently. Further,
computer code or other variables stored in memory of the VFD may be
adjusted via one or more user interfaces.
[0037] Process 300 is further shown to include supplying DC power
to the VFD via the photovoltaic power source (step 304). Step 304
may include a number of steps including a step of allowing current
to flow (e.g., via a gate, controlled diode, rectifier bridge,
and/or switch) from the DC source to the drive circuitry of the
VFD. The VFD provides variable frequency power to the pump motor
(step 306) as long as the DC power is sufficient for driving the
pump (e.g., driving the pump though its intended range of
operation, driving the pump at the current setpoint, etc.).
[0038] While the variable frequency power is provided from the VFD
to the pump motor, the VFD may be configured to check, measure,
and/or determine (e.g., continuously, at an interval, etc.) whether
the DC power provided by the photovoltaic power source is
sufficient (step 308). Step 308 may include any number of comparing
steps (e.g., comparing the power available from the DC power source
to the power available from the AC power source, comparing the
power available from the DC power source to a threshold,
determining if a pump setpoint is attainable and/or maintainable
using the DC power source, etc.).
[0039] If the DC power is sufficient, the VFD will continue to
utilize power from the photovoltaic power source (e.g., loop back
to step 304). If DC power is determined to be insufficient, the VFD
is configured to begin a process of switching and/or transitioning
to AC power (step 310).
[0040] The step of transitioning to AC power (step 310) may include
any number of shut-off, current limiting, disconnecting, and/or
other techniques relative to the DC power source and any number of
turn-on, current-allowing, connecting, and/or other techniques
relative to the AC power source. The step of transitioning (step
310) may be gradual, nearly immediate, or otherwise. Further, step
310 may also include any number of setting adjustments in memory of
the VFD and/or via hardware. For example, the bias of a diode may
be reversed, a different software routine may be initiated, a
variable in memory may be set, etc. After (and/or during) the
transition to AC power, the power will be supplied to the VFD via
the AC power source (step 312). While AC power is being utilized by
the VFD, the VFD may regularly or continuously check for whether
the DC power has returned to a sufficient level for driving the
pump (step 316). Program logic and/or circuitry within the VFD may
be configured to immediately affect a switch to DC power if a
threshold is reached. According to other exemplary embodiments, the
switch may be affected only if the threshold has been reached and
maintained for a period of time (e.g., seconds, minutes, etc.).
According to yet other exemplary embodiments, program logic will
examine other characteristics of the DC power or the VFD (e.g.,
volatility, a standard of deviation, an average voltage
measurement, a root mean squared measurement, the number of times
switched to AC power during the day, the setpoint of the pump, a
measurement of the associated refrigerator load, etc.) before
switching back from AC to DC. While DC power is determined to be
insufficient, the AC power source will continue supplying the
driving power to the VFD (e.g., via a loop back to step 312,
etc.).
[0041] It is important to note that the construction and
arrangement of the elements of the refrigeration system are
illustrative only. Although only a few exemplary embodiments of the
present disclosure have been described in detail in this
disclosure, those skilled in the art who review this disclosure
will readily appreciate that many modifications are possible in
these embodiments (such as variations in features such as
components, formulations of coolant compositions, heat sources,
orientation and configuration of the cooling elements, the location
of components and sensors of the cooling system and control system;
variations in sizes, structures, shapes, dimensions and proportions
of the components of the system, use of materials, colors,
combinations of shapes, etc.) without materially departing from the
novel teachings and advantages of the disclosure. For example,
closed or open space refrigeration devices may be used having
either horizontal or vertical access openings; cooling elements may
be provided in any number, size, orientation and arrangement to
suit a particular refrigeration system; and the system may include
a variable speed fan, under the control of the pump control system
or otherwise.
[0042] Thresholds and/or set points of the controller or the switch
may be determined empirically or predetermined based on operating
assumptions relating to the intended use or application of the
pump, variable frequency drive, and/or the refrigeration devices.
According to other alternative embodiments, the refrigeration
system may be any device using a refrigerant or coolant, or a
combination of a refrigerant and a coolant, for transferring heat
from one space to be cooled to another space or source designed to
receive the rejected heat and may include commercial, institutional
or residential refrigeration systems. Further, it is readily
apparent that variations of the refrigeration system and its
components and elements may be provided in a wide variety of types,
shapes, sizes and performance characteristics, or provided in
locations external or partially external to the refrigeration
system. Accordingly, all such modifications are intended to be
within the scope of the disclosure.
[0043] It should further be noted that the variable frequency drive
described herein and the switching activity from a photovoltaic
power source to an AC power source may be applicable in some
applications other than the secondary coolant refrigeration
application.
[0044] Although the figures may show a specific order of method
steps, the order of the steps may differ from what is depicted.
Also two or more steps may be performed concurrently or with
partial concurrence. Such variation will depend on the software and
hardware systems chosen and on designer choice. All such variations
are within the scope of the disclosure. Likewise, software
implementations could be accomplished with standard programming
techniques with rule based logic and other logic to accomplish the
various connection steps, processing steps, comparison steps and
decision steps.
[0045] Embodiments within the scope of the present disclosure
include program products comprising machine-readable media for
carrying or having machine-executable instructions or data
structures stored thereon (e.g., program products/software for
controlling variable frequency drives). Such machine-readable media
can be any available media that can be accessed by a general
purpose or special purpose computer or other machine with a
processor. By way of example, such machine-readable media can
comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk
storage, magnetic disk storage or other magnetic storage devices,
or any other medium which can be used to carry or store desired
program code in the form of machine-executable instructions or data
structures and which can be accessed by a general purpose or
special purpose computer or other machine with a processor. When
information is transferred or provided over a network or another
communications connection (either hardwired, wireless, or a
combination of hardwired or wireless) to a machine, the machine
properly views the connection as a machine-readable medium. Thus,
any such connection is properly termed a machine-readable medium.
Combinations of the above are also included within the scope of
machine-readable media. Machine-executable instructions comprise,
for example, instructions and data which cause a general purpose
computer, special purpose computer, or special purpose processing
machines to perform a certain function or group of functions.
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