U.S. patent application number 13/710573 was filed with the patent office on 2014-06-12 for active and passive cooling for an energy storage module.
This patent application is currently assigned to Caterpillar Inc.. The applicant listed for this patent is CATERPILLAR INC.. Invention is credited to Keith Dixler, Wellington Kwok.
Application Number | 20140158340 13/710573 |
Document ID | / |
Family ID | 50879689 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140158340 |
Kind Code |
A1 |
Dixler; Keith ; et
al. |
June 12, 2014 |
ACTIVE AND PASSIVE COOLING FOR AN ENERGY STORAGE MODULE
Abstract
The present disclosure relates to cooling an energy storage
module using passive and active cooling techniques. Passive cooling
is provided by storing heat in a phase change material that is
contact with the energy storage cells of the energy storage module.
Active cooling is provided by circulating coolant through coolant
passages that are in thermal contact with the energy storage cells.
A control system for determining the temperature of the energy
storage module and controlling coolant flow when the temperature
reaches a predetermined threshold is disclosed.
Inventors: |
Dixler; Keith; (Peoria,
IL) ; Kwok; Wellington; (Dunlap, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CATERPILLAR INC. |
Peoria |
IL |
US |
|
|
Assignee: |
Caterpillar Inc.
Peoria
IL
|
Family ID: |
50879689 |
Appl. No.: |
13/710573 |
Filed: |
December 11, 2012 |
Current U.S.
Class: |
165/287 |
Current CPC
Class: |
H01G 9/0003 20130101;
Y02E 60/13 20130101; F28D 20/02 20130101; H01G 11/10 20130101; Y02T
10/70 20130101; H01M 10/6552 20150401; F28D 15/00 20130101; F28F
3/12 20130101; F28D 2021/0043 20130101; Y02E 60/14 20130101; H01M
10/627 20150401; H01M 10/6554 20150401; F28D 20/028 20130101; H01M
10/625 20150401; Y02E 60/10 20130101; H01G 11/18 20130101; H01M
10/643 20150401; H01G 2/08 20130101; F28F 27/00 20130101; H01M
10/659 20150401; H01M 10/635 20150401; H01M 10/613 20150401 |
Class at
Publication: |
165/287 |
International
Class: |
F28F 27/00 20060101
F28F027/00 |
Claims
1. A method for cooling an energy storage module comprising:
determining a first temperature in an energy storage module, the
energy storage module comprising: an array of energy storage cells;
a phase change material in thermal contact with a coolant passage
and said energy storage cells; comparing the first temperature to a
first and second threshold; and changing coolant flow through said
coolant passage based on the comparison.
2. The method of claim 1 wherein the change comprises increasing
coolant flow through said coolant passage when the first
temperature reaches the second threshold.
3. The method of claim 1 wherein the change comprises decreasing
coolant flow when the first temperature reaches the first
threshold.
4. The method of claim 1 wherein the first threshold is modified
based on the net electrical power flowing into or out of said
energy storage module over a predetermined period of time.
5. The method of claim 2 wherein said predetermined period of time
is between one and ten seconds.
6. The method of claim 1 wherein said coolant passage is
incorporated within a block of said phase change material.
7. The method of claim 1 wherein said coolant passage is
incorporated within a cold plate that is in thermal contact with
said phase change material.
8. The method of claim 1 wherein the method further comprises:
determining a second temperature in said energy storage module; and
decreasing coolant flow when the second temperature reaches the
first threshold.
9. The method of claim 8 wherein the first threshold is modified
based on the net electrical power flowing into or out of said
energy storage module over a predetermined period of time.
10. The method of claim 9 wherein said predetermined period of time
is.
11. The method of claim 8 wherein said coolant passage is
incorporated within a block of said phase change material.
12. The method of claim 8 wherein said coolant passage is
incorporated within a cold plate that is in thermal contact with
said phase change material.
13. The method of claim 1 wherein the first temperature is
determined by choosing the maximum of two temperatures.
14. A method for cooling an energy storage module comprising:
determining a first temperature in an energy storage module, the
energy storage module comprising: an array of energy storage cells;
a phase change material in thermal contact with a coolant passage
and said energy storage cells; measuring a coolant temperature;
comparing the first temperature and the coolant temperature; and
taking a corrective action based on the comparison.
15. The method of claim 14 wherein the corrective action comprises
increasing coolant flow through a coolant passage in the energy
storage module if the coolant temperature is less than the first
temperature and when the first temperature reaches a second
threshold.
16. The method of claim 14 wherein the corrective action comprises
decreasing coolant flow through a coolant passage in the energy
storage module if the coolant temperature is less than the first
temperature and when the first temperature reaches a first
threshold.
17. The method of claim 14 wherein the corrective action comprises
derating the performance of the energy storage module if the
coolant temperature is greater than the first temperature.
18. The method of claim 15 wherein the second threshold is modified
based on the net electrical power flowing into or out of said
energy storage module over a predetermined period of time.
19. The method of claim 18 wherein said predetermined period of
time is between one and ten seconds.
20. The method of claim 14 wherein said coolant passage is
incorporated within a block of said phase change material.
21. The method of claim 14 wherein said coolant passage is
incorporated within a cold plate that is in thermal contact with
said phase change material.
22. The method of claim 16 wherein the corrective action further
comprises: measuring a second temperature in said energy storage
module; and decreasing coolant flow when the second temperature
reaches the first threshold.
23. The method of claim 22 wherein the first threshold is modified
based on the net electrical power flowing into or out of said
energy storage module over a predetermined period of time.
24. A system for managing thermal conditions of an energy storage
module comprising: a pump for providing coolant flow; a valve
configured receive signals from a controller and to control said
coolant flow; the controller configured to: receive a first
temperature from a first temperature sensor in an energy storage
module, the energy storage module comprising: an array of energy
storage cells; a phase change material in thermal contact with a
coolant passage and said energy storage cells; compare the first
temperature to a first and second threshold; and send a signal to
said valve to control coolant flow through said coolant passage
based on the comparison.
25. The method of claim 24 wherein said coolant passage is
incorporated within a block of said phase change material.
26. The method of claim 24 wherein said coolant passage is
incorporated within a cold plate that is in thermal contact with
said phase change material.
Description
TECHNICAL FIELD
[0001] The present disclosure relates cooling an energy storage
module, and more particularly, an energy storage module equipped
with coolant passages and a phase change material.
BACKGROUND
[0002] Energy storage modules are increasingly used in mobile and
stationary applications. Uses include hybrid and electric drive
vehicles, as well as stationary power generation. The modules
usually contain battery or ultracapacitor cells as a way of storing
electrical energy for long periods of time, and/or rapidly charging
or discharging as needed. The charge/discharge process quickly
generates a large amount of heat, which should be managed. Also,
the performance and life of the cells depends upon their
temperature. Therefore, the steady state temperature of the cells
should be managed.
[0003] A further requirement of the energy storage module is that
it is capable of operation when exposed to harsh environments.
Shock and vibration are problematic when packaging energy storage
cells into an energy storage module. The cells should be packaged
such that they are not allowed to move rotationally, radially, or
axially. Such movement can break inter-cell connections or wear
through the protective case of the cell. The energy storage module
should protect against shock and vibration while still managing
thermal issues.
[0004] Excess heat or a manufacturing defect can lead to high
levels of heat in a cell which can then cause the destruction of
the cell, known as thermal runaway. Destruction of a cell can cause
heat damage to adjacent cells which can in turn cause destruction
of one or more of the adjacent cells. This is known as cell
propagation. Effective thermal management of the energy storage
module can prevent thermal runaway and cell propagation.
[0005] A known technique for cooling energy storage modules
includes circulating coolant between the energy storage cells.
Coolant passages are typically incorporated into the energy storage
module such heat within the storage cells is transferred to the
circulating coolant. Coolant is circulated by a pump through the
energy storage module and then through a radiator or other type of
heat exchanger. Coolant must be circulated whenever a predetermined
portion of the energy storage module reaches a maximum allowed
temperature.
[0006] A phase change material has been used within energy storage
modules to eliminate the need for coolant circulation. The material
is typically made of graphite that is impregnated with paraffin
wax. Such a material is described in U.S. Pat. No. 6,468,689 to
Al-Hallaj et al of Chicago, Ill. The phase change material is
thermally conductive and is capable of absorbing heat in the form
of latent heat as the paraffin changes state from solid to liquid.
The phase change material acts as a normal heat sink material after
the paraffin has reached the liquid state. The phase change
material works well and can eliminate the need for circulation of
coolant if either the heat generated by the storage cells or the
ambient temperature does not exceed the melting temperature of the
paraffin wax.
SUMMARY OF THE INVENTION
[0007] A method for cooling an energy storage module is disclosed.
The method comprises determining a first temperature in an energy
storage module. The energy storage module comprises an array of
energy storage cells, a phase change material in thermal contact
with a coolant passage and the energy storage cells, comparing the
first temperature to a first and second threshold, and changing
coolant flow through the coolant passage based on the
comparison.
[0008] Further, another aspect of a method for cooling an energy
storage module is disclosed. The method comprises determining a
first temperature in an energy storage module. The energy storage
module comprises an array of energy storage cells, a phase change
material in thermal contact with a coolant passage and the energy
storage cells, measuring a coolant temperature, comparing the first
temperature and the coolant temperature, and taking a corrective
action based on the comparison.
[0009] Further, a system for managing thermal conditions of an
energy storage module is disclosed. The system comprises a pump for
providing coolant flow, a valve configured to receive signals from
a controller and to control the coolant flow. The controller is
configured to receive a first temperature from a first temperature
sensor in an energy storage module. The energy storage module
comprises an array of energy storage cells, a phase change material
in thermal contact with a coolant passage and the energy storage
cells, compare the first temperature to a first and second
threshold, and send a signal to the valve to control coolant flow
through the coolant passage based on the comparison.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows one aspect of the current disclosure
[0011] FIG. 2 shows another aspect of the current disclosure
[0012] FIG. 3 shows a storage cell consistent with the current
disclosure
[0013] FIG. 4 shows another aspect of the current disclosure
[0014] FIG. 5 shows a plot consistent with the current
disclosure
[0015] FIG. 6 shows another plot consistent with the current
disclosure
[0016] FIG. 7 shows another plot consistent with the current
disclosure
[0017] FIG. 8 shows a control system consistent with the current
disclosure
[0018] FIG. 9 shows a flow chart consistent with the current
disclosure
DETAILED DESCRIPTION
[0019] The present disclosure relates to an energy storage module
10 as shown in FIG. 1. The energy storage module 10 secures energy
storage cells 30 in a manner suitable for use in harsh environments
or heavy duty mobile applications.
[0020] The energy storage cells 30 could be battery cells or
capacitors, particularly ultracapacitors.
[0021] Energy storage packages are commonly used in electric drive
vehicles, hybrid vehicles, and stationary power generators. In
electric drive applications, the energy storage package stores
energy from deceleration and provides power for traction motors in
order to propel a vehicle. In hybrid applications, the energy
storage package stores energy from deceleration and augments an
engine in providing power in order to propel a vehicle. In
stationary power generator applications, the energy storage package
can be used to augment the primary engine and generator. Large
amounts of power are charged to and discharged from the energy
storage package in these applications. As the life and performance
of the energy storage cells 30 is dependent on temperature, it is
important to provide cooling for the cells.
[0022] The storage cells 30 themselves are either a battery or a
capacitor. In the case of a battery, voltage of an individual cell
will vary between 1.2 V and 3.4 V depending on battery chemistry.
Many battery cells are connected in series in order to achieve an
energy storage package with enough voltage to supply the higher
voltage required in a vehicle propulsion system or stationary power
application. This system voltage is typically 300-600 V, but can be
as high as 3300 V in high power applications.
[0023] The storage cell 30 may alternatively be a capacitor.
Examples include electrolytic capacitors, supercapacitors, and
ultracapacitors. Due to their high energy density, electric
double-layer capacitors (EDLC) are typically used. EDLCs are
commonly known as ultracapacitors. The individual ultracapacitor
cells are typically several hundred Farads up to several thousand
Farads and have a voltage capacity of 2.5 V. Power capacity varies,
but is approximately 40 W in steady-state and up to 180 W peak.
Like the battery cells, many ultracapacitor cells are connected in
series in order to achieve an energy storage package with enough
voltage to supply the higher voltage required in a vehicle
propulsion system or stationary power application.
[0024] Referring to FIG. 3, the storage cells 30 are generally
cylindrical in shape with a diameter 130. The surface of the
cylinder is composed of a case 90. The terminal end 40 and
non-terminal end 50 of the cylinder is formed by a terminal end cap
70 and a non-terminal end cap 80. Other external features of the
storage cell 30 are the connection terminals 60 and a vent 120. The
connection terminals 60 serve to electrically connect the cell
between the internal cathode and anode and an external electrical
circuit. The connection terminals 60 also provide a means for
mechanically connecting to an external circuit. The connection
terminals 60 may include a threaded hole, threaded post, a
press-fit post, or the like.
[0025] The vent 120 serves to allow gases to escape the cell in the
event of an electrical short of or a thermal failure. Gases
escaping through the vent 120 prevent the case 90 from bursting
during such a failure.
[0026] As stated above, storage cells 30 are typically connected in
series in order to meet the voltage and power required in a vehicle
propulsion system or stationary power application. This requires a
physical package that can accommodate from dozens to hundreds of
storage cells 30. In order to achieve the power density required
from the package, storage cells 30 are typically packaged in a
matrix with their axes aligned physically in parallel. Such an
efficient package helps to achieve a high energy density. The
package should properly locate the cells, protect them from the
environment, and provide adequate thermal management.
[0027] As shown in FIG. 4, storage cells 30 are connected in series
by connecting the anode of one to the cathode of another and so on
until the number of required series storage cells 30 is reached.
Connection between cells is achieved by means of a conductive bus
bar 290. Alternatively a printed circuit board with very thick
conductive traces can be used that includes provisions for
connecting to the storage cells 30. The printed circuit board may
also mount components related to cell monitoring or balancing.
[0028] One way to control the temperature of the storage cells 30
is by surrounding them in a thermally conductive material 310 that
serves as a heat sink. The thermally conductive material 310 would
serve to mechanically locate the storage cells 30 as well as
conducting heat away from the storage cells 30. The thermally
conductive material 310 will conduct the heat throughout the
material. Heat from a storage cell 30 may also be conducted into an
adjacent storage cell 30.
[0029] The thermally conductive material 310 is to be formed into a
block 330. A matrix of generally cylindrical voids 340 is formed
into the block in order to accept the storage cells 30. The spacing
of the rows and columns of the matrix is such that the gap is small
enough to allow for high energy density of the module while large
enough to allow proper heat conduction away from the storage cells
30.
[0030] The cylindrical voids 340 are sized so that the storage
cells 30 can be inserted in a press-fit relationship. A press-fit
ensures that a) there is enough contact to ensure thermal
conduction from the storage cell 30 to the thermally conductive
material 310 and b) that the storage cell 30 is secured from motion
in the radial direction.
[0031] According to the system and method of the current
disclosure, the thermally conductive material 310 is a phase change
material (PCM) 320. The PCM 320 is capable of temporarily storing
heat from the storage cells 30 as latent heat. Such a material is
described in U.S. Pat. No. 6,468,689 to Al-Hallaj et al of Chicago,
Ill.
[0032] The performance of storage cells 30 is dependent on
temperature. In the case of a battery, the charge capacity,
internal resistance, and operating life degrade with increasing
temperature. In the case of an ultracapacitor, the capacitance,
internal resistance, and operating life degrade with increasing
temperature. Such storage cells 30 generate a considerable amount
of heat during charging and discharging and this heat should be
managed in some manner in order to preserve performance.
[0033] FIG. 5 shows the relative performance of a storage cell 30
versus temperature. Storage cell 30 performance is approximately
100% from a lower operating temperature To1 to an upper operating
temperature To2. This represents the normal operating temperature
range of the storage cell 30. As an example, To1 may be around 0
degrees C. while To2 may be around 45 degrees C. Storage cell 30
electrical performance is degraded below To1 and above To2. The
minimum operating temperature Tmin and maximum operating
temperature Tmax are considered the limits of storage cell 30
operation. As an example, Tmin may be around -30 degrees C., while
Tmax may be around 60 degrees C. Typically the performance of the
storage cell 30 is considered to degrade linearly from To1 to Tmin
and from To2 to Tmax.
[0034] Degradation of the electrical performance of the energy
storage cell 30 with temperature is often compensated by limiting
the power that is delivered to it. This is commonly known as
de-rating the capabilities of the device. De-rating is typically
expressed as percentage of the normal electrical performance. A
controller 250 may be configured to sense temperature from one or
more temperature sensors 170. The controller 250 may then limit the
power that is delivered to the energy storage module 10 and
therefore the energy storage cells 30. Power may be limited by
limiting voltage, current or both.
[0035] Ambient temperature can also cause increase the temperature
of the storage cell 30. Ambient heat can be absorbed from outside
the energy storage module 10 into the storage cell 30 and limit the
operating range. For instance, if the energy storage module 10 is
operating in a 40 degree C. environment, there may only be a 5
degree C. margin before the performance of the storage cell 30
needs to be de-rated. Examples of environments that experience high
ambient temperatures include deserts, under-hood applications, and
generator set enclosures.
[0036] It should also be appreciated that since many storage cells
30 are electrically connected in series, the performance of the
entire series network could be limited by the performance of the
weakest cell. It should therefore be appreciated that all storage
cells 30 should be maintained at approximately the same
temperature.
[0037] The PCM 320 provides two primary thermodynamic functions.
The first function is to conduct heat away from the storage cells
30. The PCM 320 is thermally conductive, which may be anisotropic.
The thermal conductivity of the PCM 320 is provided primarily by
the graphite structure. Heat is conducted away from the storage
cells 30 and is dissipated in either the housing 150 or into a heat
sink configured for this purpose. The second function is to store
latent heat. Latent heat capacity is provided by a material,
typically paraffin, that is engineered to change phase in a
predetermined temperature range. The paraffin begins to change from
solid to liquid at temperature Tm1. The paraffin has completely
changed phase to a liquid at temperature Tm2. The material
properties of the graphite structure of the PCM 320 holds the
paraffin in place even after it has changed to a liquid phase.
Storage of latent heat in the PCM 320 will be referred to in this
disclosure as "passive cooling".
[0038] As the storage cells 30 produce heat, the PCM 320 conducts
heat away from the storage cells 30 and the net temperature of the
block 330 of PCM 320 increases. Refer to FIG. 6. The temperature of
the PCM 320 will continue to rise as the storage cells 30 produce
heat until the temperature of the PCM 320 reaches Tm1. At this
point, the temperature of the PCM 320 will stabilize as the
paraffin begins to change phase and heat from the storage cells 30
is stored as latent heat. The temperature of the PCM 320 will
continue to be stable until it reaches Tm2. At this point the
paraffin has completed the transition from solid to liquid and can
no longer store latent heat. The temperature of the PCM 320 will
then continue to rise as before.
[0039] The melting temperature range (Tm1 to Tm2) can be engineered
to generally coincide with the upper operating temperature To2 of
the storage cells 30. For instance, Tm2 can be engineered to
approximately equal To2. During charging and discharging the energy
storage module 10, the PCM 320 will conduct heat away from the
storage cells 30. If the charging and discharging cycle is low
enough in power or short enough in duration or ambient temperature
is low enough, the storage cells 30 will remain below their upper
operating temperature To2. Charging/discharging cycles that are
higher in power or longer in duration or higher ambient temperature
will cause the temperature of the PCM 320 to rise above Tm1 and the
extra heat will be absorbed as latent heat, and the storage cells
30 will still remain below their upper operating temperature To2.
Charging/discharging cycles that are still higher in power or still
longer in duration or still higher ambient temperature will cause
the temperature of the PCM 320 to rise above Tm2. In the latter
condition, the PCM 320 can no longer store latent heat. The
performance of the energy storage module 10 must be de-rated in
order to keep the energy storage cell 30 below To2 unless some
other way to remove heat is provided.
[0040] In addition to the passive cooling provided by the block 330
of PCM 320, an active cooling loop 322 could be incorporated. Refer
to FIGS. 1 and 2. An active cooling loop 322 is to be provided such
that a heat transfer fluid can be circulated through coolant
passages 350 and circulate through the block 330 of PCM 320. The
active cooling loop 322 could be used in combination with a pump
190 and heat exchanger 240 as is known in the art. The active
cooling loop 322 could for instance be formed by a pipe made of
thermally conductive metal such as copper or aluminum. Efforts
should be made to secure the active cooling loop 322 in the
graphite material of the PCM 320 while the graphite material is
compressed. A supporting structure, such as a rack or standoffs
could be incorporated either inside or outside the graphite
material during the manufacturing process. In addition, a
supporting medium 324 within the active cooling loop 322 may be
needed to keep the active cooling loop 322 from being deformed or
crushed during the manufacturing process. The supporting medium 324
would need to be capable of removal after the manufacturing process
in order for the heat transfer fluid to be able to flow through the
active cooling loop 322. Examples of suitable supporting medium 324
could be sand, paraffin wax (melted and removed afterwards), or an
incompressible fluid such as water or oil. The open ends of the
active cooling loop 322 would need to be blocked during
manufacturing in order to retain the supporting medium 324.
[0041] Alternatively, the PCM 320 could be mounted to and thermally
connected to a cold plate 160 as shown in FIG. 2. The cold plate
160 could be made from a thermally conductive metal such as copper
or aluminum. The cold plate 160 would incorporate one or more
coolant passages 350 and may include fittings for connecting hoses
and such.
[0042] The coolant passages 350 incorporated into the energy
storage module 10 may be connected to other components needed
circulate coolant and dissipate heat as shown in FIG. 8. Such
components include a pump 190, a valve 230, and a heat exchanger
240. Other components such as bypass valves, hoses, tanks, and
fittings are not shown. A controller 250 is electrically connected
to a first temperature sensor 170 and possibly a second temperature
sensor 180. The controller 250 is also electrically connected to
and configured to control pump 190 and valves 230.
[0043] One or more temperature sensors may be placed within the
energy storage module 10. For example, it may be useful to have a
first temperature sensor 170 close to a centrally-located storage
cell 30. During charging and discharging, the centrally-located
storage cell 30 may be the hottest part of the energy storage
module 10. It may also be useful to have a second temperature
sensor 180 close to the outside of the energy storage module 10.
During charging and discharging, the second temperature sensor 180
may be the coolest part of the energy storage module. However,
during high ambient temperature conditions, the second temperature
sensor 180 may be the hottest part energy storage module 10. The
controller 250 may use information from the first temperature
sensor 170 when high temperatures are caused by charging and
discharging, and may use the second temperature sensor 180 when
high temperatures are caused by high ambient temperatures.
[0044] The controller 250 is programmed with a first threshold
temperature and a second threshold temperature. The first threshold
temperature corresponds approximately with Tm1 and the second
threshold temperature corresponds approximately with Tm2. As an
example of operation, consider when the heat is being generated in
the energy storage module 10 during a charge/discharge cycle. The
controller 250 may sense when the first temperature sensor has
reached a second threshold temperature. This indicates that the
paraffin has melted and that the PCM 320 is no longer able to store
latent heat. The controller may then start or increase coolant flow
through coolant passages 350 by opening valve(s) 230 and/or
starting pump 190. Coolant will continue to circulate through the
coolant passages 350 until either the first or second temperature
sensor 170, 180 indicate that the PCM 320 has cooled below a first
threshold temperature. At this point the paraffin in the PCM 320
has reached a solid state again and is ready to store latent heat.
The controller 250 will then stop or decrease coolant flow through
coolant passages 350 by either closing valve(s) 230 and/or stopping
pump 190.
[0045] The controller 250 may use information from one temperature
sensor to start or increase coolant flow and another temperature
sensor to stop or decrease coolant flow. For instance, during a
charge/discharge cycle, the controller 250 may use information from
the first temperature sensor 170 to start or increase coolant flow
and information from the second temperature sensor 180 to stop or
decrease coolant flow. This may be useful because the first
temperature sensor 170, near a centrally-located storage cell 30,
will be one of the hottest parts of the energy storage module 10.
The controller 250 is then able to control coolant flow in order to
keep the storage cell 30 below its upper operating temperature To2.
The controller 250 may then use the information from the second
temperature sensor 180 to determine when the outer, and presumably
coolest, part of the energy storage module 10 has cooled below Tm1.
The controller 250 can then be certain that the paraffin in the
entire block 330 of PCM 320 has reached the solid state again. The
controller may choose to de-rate the performance of the energy
storage module 10 if sufficient coolant flow is not available to
keep below its upper operating temperature To2.
[0046] Likewise, during a high ambient temperature condition, the
controller 250 may use information from the second temperature
sensor 180 to start or increase coolant flow and information from
the first temperature sensor 170 to stop or decrease coolant flow.
This may be useful because the second temperature sensor 180, near
an outer storage cell 30, will be one of the hottest parts of the
energy storage module 10. The controller 250 is then able to
control coolant flow in order to keep the outer storage cell 30
below its upper operating temperature To2. The controller 250 may
then use the information from the first temperature sensor 170 to
determine when the central, and presumably coolest, part of the
energy storage module 10 has cooled below Tm1. The controller 250
can then be certain that the paraffin in the entire block 330 of
PCM 320 has reached the solid state again.
[0047] The example shown in FIG. 7 shows heat from a
charge/discharge cycle in a high ambient temperature environment.
In this example, Tm1=42 degrees C., Tm2=48 degrees C., Tw=42
degrees C., and the ambient temperature is 30 degrees C.
[0048] It should be understood that the current disclosure
anticipates the use of as many temperature sensors as needed.
Additional temperature sensors can located throughout the energy
storage module 10, near storage cells 30, on the housing 150, the
cold plate 160, or in the coolant passage 350.
[0049] The first and second threshold temperature can be modified
during operation based on how much power is going into or out of
the energy storage module 10. Power is calculated from multiplying
the current in amperes with the voltage in volts and is expressed
in watts. The power, P, is then used in an expression of Fourier's
Law shown below in Equation 1.
Tj=Tc+P*.theta.jc (1)
[0050] The internal temperature of the storage cells 30 is assumed
to be Tj, while Tc is either the first or second temperature sensor
170, 180 depending on the situation. The term .theta.jc is the
thermal resistance of the material between the two points and will
be considered as a constant. It is seen that for low power, Tj and
Tc will be very close. Therefore, the second threshold can be set
to very near Tm2. But for large power, Tj and Tc will not be close
and the second threshold may be set lower to ensure that there is a
safety margin between the second threshold and the upper operating
temperature To2 of the storage cell 30.
[0051] The controller 250 is configured to sense voltage and
current sensors, calculate power into or out of the energy storage
module 10, and adjust the second threshold based on the power
calculation. A person of ordinary skill in the art will recognize
that the power calculation may be used in several ways without
departing from the scope of the current disclosure. For instance,
instantaneous power may be used to adjust the second threshold.
Additionally, an average power over a period of several seconds may
be used. A rolling average of power may also be used. The rolling
average may be chosen based on the thermal time constant of the
energy storage module 10. The rolling average may be as short as
0.1 seconds or as long as 20 seconds.
[0052] FIG. 9 (flowchart) shows a method consistent with the
current disclosure. The method starts at block 400 then proceeds to
block 410 where Tc is determined. If one temperature sensor is
present, then this value is used as Tc. If more than one
temperature sensors are present, Tc may determined in a number of
ways. For instance, the Tc may be the maximum of all temperature
sensors present or the average of all temperature sensors present.
Alternatively, a first temperature sensor 170 may be used for Tc if
temperature is increasing, while a second temperature sensor 180
may be used for Tc if the temperature is decreasing. For the method
shown in FIG. 9, it is assumed that Tc is the maximum of all
temperature sensors present.
[0053] From block 410, the method proceeds to decision block 420
where Tc is compared to coolant temperature Tw. Coolant temperature
Tw is provided by a sensor somewhere in the coolant passage 350 or
elsewhere in the coolant circulation system. If Tw is greater than
Tc, the method proceeds to decision block 430. If Tc is less than
Tm2, then the method returns to block 400. If Tc is greater than
Tm2, then the method proceeds to action block 500 where the
performance of the energy storage module 10 is de-rated according
to FIG. 5 before returning to block 400.
[0054] Returning to decision block 420, if Tw is less than Tc, the
method proceeds to decision block 440. If Tc is less than Tm2, the
method proceeds to decision block 450. At decision block 450, Tc is
compared to Tm1. If Tc is greater than Tm1, the method returns to
block 400. If Tc is less than Tm1 the the method proceeds to
decision block 470 which checks to see if the coolant flow is zero
or not. This can be determined by the controller 250 by determining
how far valve(s) 230 are displaced or whether pump 190 is running.
If the coolant flow is zero, the method returns to block 400. If
the coolant flow is not zero, the method proceeds to action block
490, which decreases coolant flow before returning to block 400.
Alternatively, the slope of Tc can be used to determine whether
[0055] From block 440, if Tc is greater than Tm2 the method
proceeds to decision block 460 which checks to see if the coolant
flow is at maximum or not. If the coolant flow is at maximum, the
method proceeds to action block 500 where the performance of the
energy storage module 10 is de-rated according to FIG. 5. If the
coolant flow is not at maximum, the method proceeds to action block
480 where flow is increased before returning to block 400.
Alternatively, the slope of Tc can be used to determine whether the
method proceeds to action block 480. Even if Tc is less than Tm2, a
rapidly increasing Tc may indicate that increased coolant flow will
soon be needed. In this way, coolant flow may be increased before
Tc is actually greater than Tm2.
INDUSTRIAL APPLICABILITY
[0056] The energy storage module 10 of the present disclosure is
suitable for use as energy storage for hybrid and electric drive
vehicles, as well as stationary power generation. The phase change
material 320 used to conduct and store heat from the storage cells
30 allows the energy storage module 10 to be used at higher power
levels and at higher ambient temperatures than is allowed by
conventional heat sinks. The PCM 320 can be designed such that heat
from most charge/discharge cycles and ambient temperatures can be
stored and dissipated without need for additional cooling. This
saves the energy needed to run a pump 190 and valves 230.
[0057] However, higher power levels and higher ambient temperatures
can overload the latent heat capacity of the PCM 320. Some
applications using a PCM 320 may then benefit from the use of
additional cooling from an active cooling loop 322 during high heat
loads while still benefiting from the latent heat capacity of the
PCM 320. Use of an active cooling loop 322 along with a PCM 320 may
allow for a smaller capacity heat exchanger 240.
* * * * *