WO2020219993A1

WO2020219993A1 - Battery pack with heater/voltage equalizer and method for high altitude long endurance aircraft

Info

Publication number: WO2020219993A1
Application number: PCT/US2020/029972
Authority: WO
Inventors: Peter DELIOUSSINE; Brian Jensen
Original assignee: Aerovironment, Inc
Priority date: 2019-04-25
Filing date: 2020-04-24
Publication date: 2020-10-29

Abstract

In at least one embodiment, a battery pack for a high altitude long endurance aircraft including a plurality of cells, a thin sheet heater between two of the plurality of cells, a balance circuit connected to the plurality of cells to the thin sheet heater, a battery monitor circuit connected to the balance circuit for balancing charging, and a thermal monitor circuit connected to the thin sheet heater. In at least one implementation, a method is provided for a battery pack for a high altitude long endurance aircraft, which includes determining whether a battery pack needs thermal adjustment, adjusting a temperature of the battery pack using a thin sheet heater interposed between two cells of the battery pack, and balancing charging to at least one battery cell using the thin sheet heater.

Description

Title: BATTERY PACK WITH HEATER/VOLTAGE EQUALIZER AND METHOD FOR HIGH ALTITUDE LONG ENDURANCE AIRCRAFT

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the following applications which are all herein incorporated by reference in their entireties:

U.S. Provisional Application No. 62/838,926, filed 04/25/2019, by Peter Delioussine et al . , entitled BATTERY PACK DESIGN;

U.S. Provisional Application No. 62/897,995, filed 09/09/2019, by Peter Delioussine et al . , entitled BATTERY PACK WITH HEATER/VOLTAGE EQUALIZER FOR HIGH ALTITUDE LONG ENDURANCE AIRCRAFT;

U.S. Provisional Application No. 62/838,783, filed 04/25/2019, by William Sechrist et al . , entitled HIGH ALTITUDE LONG ENDURANCE (HALO) AIRCRAFT; and

U.S. Provisional Application No. 62/854,711, filed 05/30/2019, by Peter Delioussine et al . , entitled THERMAL CONTROL SYSTEMS AND METHODS FOR HIGH ALTITUDE LONG ENDURANCE AIRCRAFT .

BACKGROUND

[0001] In high altitude long endurance battery powered aircraft, batteries are often placed within the aircraft to keep them away from critical components in case the batteries experience thermal runaway, often a catastrophic event for the batteries. Thus, it is advantageous to place the batteries near the exterior skin of the aircraft so that any heat generated from the batteries, and in particular during thermal runaway, can be easily vented through a vent opening to outside of the aircraft .

[0002] Placement of the batteries near the skin of the aircraft, however, make them susceptible to extreme temperatures not just due to nighttime, seasonal, or global temperature extremes, but due the operating altitude of the high altitude long endurance aircraft. Such aircraft can fly at an altitude of 65,000 or more above sea level, where it can experience temperatures approaching -80 degrees Celsius, or less. Further, any vent opening facilitates heat transfer from the battery.

[0003] Furthermore, another difficultly is that different parts of the battery may experience more cooling than other parts, for example batteries near the exterior my be colder than ones near an interior of the battery.

[0004] It is also important in solar powered aircraft to keep weight to a minimum to improve aircraft performance and endurance. Simply placing a heater around the battery in its compartment would take up valuable space and add additional unwanted weight to the aircraft.

[0005] What is needed is an operationally effective solution to keeping the battery operating within the proper temperature range. Further what is needed is a light weight solution to keeping the battery operating within the proper temperature range. Additionally, what is needed is a cost effective solution to keeping the battery operating within the proper temperature range. In addition, what is needed is a solution to keeping that battery operating within the proper temperature range that does take up too much space.

SUMMARY

[0006] In one embodiment, provided is a battery pack for a high altitude long endurance aircraft including a plurality of cells, a thin sheet heater between two of the plurality of cells, a balance circuit connected to the plurality of cells to the thin sheet heater, a battery monitor circuit connected to the balance circuit for balancing charging, and a thermal monitor circuit connected to the thin sheet heater.

[0007] In at least one embodiment, provided is a battery pack for a high altitude long endurance aircraft including a plurality of cells, a thin sheet heater for heating the plurality of cells, the thin sheet heater being interposed between two battery cells, and a balance circuit connected to the thin sheet heater .

[0008] In at least one implementation, a method is provided for a battery pack for a high altitude long endurance aircraft, which includes determining whether a battery pack needs thermal adjustment, adjusting a temperature of the battery pack using a thin sheet heater interposed between two cells of the battery pack, and balancing charging to at least one battery cell using the thin sheet heater.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a simplified schematic diagram showing a battery cell balancing circuit.

[00010] FIG. 2 shows a simplified top view of a portion of a battery pack with battery cells.

[00011] FIG. 3 is a simplified circuit diagram of a thermal monitoring circuit.

[00012] FIG. 4 is a perspective view of a battery pack having battery cells. DESCRIPTION

[00013] In a high altitude long endurance aircraft, there are multiple battery packs each containing multiple battery cells within the aircraft. Multiple cell batteries, and in particular, multiple cell lithium batteries must be voltage balanced. There will be some voltages that creep up and there could be a big voltage spread, from cell to cell, which could either lead to a danger, or just loss of capacity because a battery cell should not be overcharged. If some cells in the battery pack have low capacity, the battery must be cell balanced. This is accomplished by lowering the voltage of the higher voltage cells using an external resistor to bring the voltage of one or more cells down.

[00014] FIG. 1 is a simplified schematic diagram showing a battery cell balancing circuit 100. The balancing circuit 100 is connected across a battery cell or cells 110 and provides a voltage sense signal at 130 to a battery monitor 160. In response, the battery monitor 160 provides a balance signal at 140 drives a MOSFET 150, which enables a balance resistor 120 in the circuit 100. This circuit allows individual addressing of the balancing resistors 120. The circuit 100 can be controlled by a controller 160 which may include a local processor. In one embodiment, a BQ76PL455A battery monitor, available from Texas Instruments, located Dallas, TX, may be used in combination with a control unit. The control unit manages the scheduling, while the battery monitor drives the MOSFETs 150 for enabling the balancing the resistor.

[00015] In some embodiments, the balancing circuit 100 can be used to keep the battery cell voltages within lOmV of each other and is used only when charging. This has a significant affect on cell voltage and ensures balance current is sufficient to keep cells within balance specifications. It also keeps high cells, cells with higher voltage, out of a voltage warning range. [00016] FIG. 2 shows top view of a simplified diagram of a portion of a battery pack 200 with individual battery cells 210a, 210b, 210c, 210d, etc. In this embodiment, the balancing circuit 230a is connected to three battery cells 210a, 210b, 210c, for cost savings while providing sufficient performance as described herein. A balancing circuit 230a could be placed on each cell individually if desired.

[00017] FIG. 2 also shows thin sheet heaters 220a, 220b, and 220c extending between the cells of the battery pack. This allows the temperature of the battery 200 to be monitored and maintained above its minimum acceptable operational temperature, even at high altitude and at night.

[00018] The battery pack heaters 220a, 220b, 220c, are also connected to the balancing circuit 230a, 230b, 230c as the balance resisters 120 (FIG. 1), and utilized for battery cell balancing of the battery pack 200. Thus, the battery heaters 230a 230b, and 230c are connected for both battery cell balancing and for heating the battery pack 200. This saves space and weight in an aircraft.

[00019] Thus, the resistor in the pack is used as a balancing resistor to bring down high cell voltage, and also used as a heater to provide heat directly into/between the battery cells. For thermal management, all of the heaters may be turned on, for example 90 heaters across multiple battery packs within the battery. But, for cell balancing only a heater (or heaters) on for the cell that needs to be brought down in voltage is active.

[00020] Since balancing is typically done to only a few selected cells, with small balancing currents it should not over heat the battery either locally or overall when in the charging mode. The battery typically has a substantial thermal mass, for example there may be 55 pounds of battery cells in a high altitude long endurance solar powered aircraft. Additionally, the heaters/balance resistors provide gentle heat as each heater/balance resistor typically only outputs under a watt of heat. Even when balancing, there are not hot spots created sufficient to endangering the adjacent cells or the battery overall .

[ 00021 ] In conventional applications, the heaters and the balance resistors are located on the boards near the battery, or remotely. In various embodiments of the present invention, the heater/balance resistor may be thin sheet resistor located between selected individual cells of the battery.

[ 00022 ] As shown in FIG. 2, in one application, the cells 210a, 210b, and 210c are wired so there are three cells in parallel or as triplets. Each of one of the triplets has one of the thin sheet heater/balance resistor imbedded either within the triplet, or on an exterior of the triplet so that it is between one triplet and an adjacent triplet. So, one of these heaters/balance resistors is connected to three cells for balancing. As such, in one embodiment, there are 90 heater/balance resistors in an aircraft battery system. Further, in such an embodiment the balance resistor is 24 ohms, one placed every series cell connection (3 cells in parallel and 90 triplets in series) .

[ 00023 ] In one embodiment, the battery monitor may be used to read temperatures using thermistors. The thermistors may be integrated as part of the thin film heaters, or they may be separate, preferably thin film.

[ 00024 ] FIG. 3 is a simplified circuit diagram 300 for monitoring the temperature of an integrated thermistor that is part of the thin film heater 220a, 220b, or 220c. For monitoring, the battery monitor may be used, such as the BQ76PL455A battery monitor discussed above. Auxiliary inputs AUX1 301 and AUX2 302 may be used to read temperatures using thermistors 310 between the AUX1 and AUX2 inputs. The thermistor 310 is connected on one side via series connected resistor R1 to the AUX1 input 301, and on the other side via series connected resistor R2 to the AUX2 input 302. Parallel connected capacitors Cl and C2 are connected to ground, to AUX1 and AUX2, respectively. The Cl capacitor is connected to ground between the resistor R1 and the AUX1 input and the C2 capacitor is connected to ground between the resistor R2 and the AUX2 input. In this embodiment, the thermistor 310 is connected at one side to a voltage potential and at the other side to ground.

[ 00025 ] FIG. 4 is a simplified three dimensional perspective view of a battery pack 400 having battery cells 410 including thin sheet heater/balancer resistors 220a-c, etc. (shown in Fig. 2) .

[ 00026 ] As such, in at least one implementation, a method is provided for a battery pack for a high altitude long endurance aircraft, which includes determining whether a battery pack needs thermal adjustment, adjusting a temperature of the battery pack using a thin sheet heater interposed between two cells of the battery pack, and balancing charging to at least one battery cell using the thin sheet heater.

[ 00027 ] In further implementations, determining whether the battery pack needs thermal adjustment includes detecting the temperature between two cells of the battery. In some implementations, determining whether the battery pack needs thermal adjustment includes sensing the temperature between two cells of the battery using a thin sheet thermistor. In some implementations sensing the temperature between two cells of the battery comprising sensing using a thin sheet comprising the thermistor and the heater located between the two cells.

[ 00028 ] In some implementations, adjusting the temperature of the battery pack includes using the thin sheet heater includes adjusting the temperature when not balancing the charging to the at least one battery cell using the thin sheet heater .

[ 00029 ] In some implementations, adjusting the temperature of the battery pack includes using the thin sheet heater includes adjusting the temperature with the thin sheet heater when the at least one battery cell is not charge balancing .

[00030] In some implementations, adjusting the temperature of the battery pack using the thin sheet heater comprises adjusting the temperature with the thin sheet heater with an other of the at least one battery cell that is not charge balancing. This may done in some implementations while one or more other cells are being charge balanced.

[00031] It is worthy to note that any reference to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in an embodiment, if desired. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[00032] The illustrations and examples provided herein are for explanatory purposes and are not intended to limit the scope of the appended claims. This disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the spirit and scope of the invention and/or claims of the embodiment illustrated.

[00033] Those skilled in the art will make modifications to the invention for particular applications of the invention.

[00034] The discussion included in this patent is intended to serve as a basic description. The reader should be aware that the specific discussion may not explicitly describe all embodiments possible and alternatives are implicit. Also, this discussion may not fully explain the generic nature of the invention and may not explicitly show how each feature or element can actually be representative or equivalent elements. Again, these are implicitly included in this disclosure. Where the invention is described in device-oriented terminology, each element of the device implicitly performs a function. It should also be understood that a variety of changes may be made without departing from the essence of the invention. Such changes are also implicitly included in the description. These changes still fall within the scope of this invention.

[ 00035 ] Further, each of the various elements of the invention and claims may also be achieved in a variety of manners. This disclosure should be understood to encompass each such variation, be it a variation of any apparatus embodiment, a method embodiment, or even merely a variation of any element of these. Particularly, it should be understood that as the disclosure relates to elements of the invention, the words for each element may be expressed by equivalent apparatus terms even if only the function or result is the same. Such equivalent, broader, or even more generic terms should be considered to be encompassed in the description of each element or action. Such terms can be substituted where desired to make explicit the implicitly broad coverage to which this invention is entitled. It should be understood that all actions may be expressed as a means for taking that action or as an element which causes that action. Similarly, each physical element disclosed should be understood to encompass a disclosure of the action which that physical element facilitates. Such changes and alternative terms are to be understood to be explicitly included in the description .

[ 00036 ] Having described this invention in connection with a number of embodiments, modification will now certainly suggest itself to those skilled in the art. The example embodiments herein are not intended to be limiting, various configurations and combinations of features are possible. As such, the invention is not limited to the disclosed embodiments, except as required by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A battery pack for a high altitude long endurance aircraft comprising:

a) a plurality of cells;

b) a thin sheet heater between two of the plurality of cells;

c) a balance circuit connected to the plurality of cells to the thin sheet heater;

d) a battery monitor circuit connected to the balance circuit for balancing charging; and

e) a thermal monitor circuit connected to the thin sheet heater.

2. The battery pack of Claim 1 further comprising a thermal monitor circuit connected to the battery pack.

3. The battery pack of Claim 2, wherein the thermal monitor circuit comprises a thermistor external to the battery pack

4. The battery pack of Claim 2, wherein the thermal detection circuit comprises a thin sheet thermistor.

5. The battery pack of Claim 4, wherein the thin sheet heater further comprises the thin sheet thermistor.

6. The battery pack of Claim 1, wherein the thin sheet heater further comprises thin sheet thermistor.

7. The battery pack of Claim 1 further comprising a thin sheet thermistor located between the two of the plurality of cells having the thin sheet heater.

8. The battery pack of Claim 1 further comprising a thin sheet thermistor located between a different set of cells of the plurality of cells than the two of the plurality of cells with the thin sheet heater therebetween.

9. A battery pack for a high altitude long endurance aircraft comprising:

a) a plurality of cells;

b) a thin sheet heater for heating the plurality of cells, the thin sheet heater being interposed between two battery cells; and

c) a balance circuit connected to the thin sheet heater .

10. The battery pack of Claim 9, further comprising thermal detection circuit connected to the thin sheet heater.

11. The battery pack of Claim 9, further comprising a battery monitor circuit connected to the balance circuit and connected to a thermal sense circuit.

12. The battery pack of Claim 9, wherein the thin sheet heater further comprising a thin sheet thermistor.

13. A method for a battery pack for a high altitude long endurance aircraft, the method comprising:

a) determining whether a battery pack needs thermal adjustment;

b) adjusting a temperature of the battery pack using a thin sheet heater interposed between two cells of the battery pack; and

c) balancing charging to at least one battery cell using the thin sheet heater.

14. The method of Claim 13, wherein determining whether the battery pack needs thermal adjustment comprises detecting the temperature between two cells of the battery.

15. The method of Claim 13, wherein determining whether the battery pack needs thermal adjustment comprises sensing the temperature between two cells of the battery using a thin sheet thermistor.

16. The method of Claim 13, wherein sensing the

temperature between two cells of the battery comprising sensing using a thin sheet comprising the thermistor and the heater located between the two cells.

17. The method of Claim 13, wherein adjusting the temperature of the battery pack using the thin sheet heater comprises adjusting the temperature when not balancing the charging to the at least one battery cell using the thin sheet heater .

18. The method of Claim 13, wherein adjusting the temperature of the battery pack using the thin sheet heater comprises adjusting the temperature with the thin sheet heater when the at least one battery cell is not charge balancing.

19. The method of Claim 13, wherein adjusting the temperature of the battery pack using the thin sheet heater comprises adjusting the temperature with the thin sheet heater with an other of the at least one battery cell that is not charge balancing.