WO2020219760A1

WO2020219760A1 - Thermal control systems and methods for high altitude long endurance aircraft

Info

Publication number: WO2020219760A1
Application number: PCT/US2020/029635
Authority: WO
Inventors: Peter DELIOUSSINE; James Baker; Brian Jensen; Bart Dean Hibbs
Original assignee: Aerovironment, Inc.
Priority date: 2019-04-25
Filing date: 2020-04-23
Publication date: 2020-10-29

Abstract

Systems, devices, and methods including a battery pack (114) comprising: a case (116); and a battery (120) disposed in the case, where the battery comprises two or more modules (121, 123), where each module (121, 123) comprises two or more sets of battery cells (122, 125), and where each set of the two or more sets of battery cells is separated from an adjacent set of the two or more sets of battery cells by at least one heater (124) and at least one balancer (126).

Description

Thermal Control Systems and Methods for High Altitude Long Endurance Aircraft

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Patent

Application No. 62/838,783, filed April 25, 2019, U.S. Provisional Patent Application No. 62/838,833, filed April 25, 2019, and U.S. Provisional Patent Application No. 62/854,711, filed May 30, 2019, the contents of all of which are hereby incorporated by reference herein for all purposes.

FIELD OF ENDEAVOR

[0002] The invention relates generally to battery packs, and more particularly to thermal control of battery packs.

BACKGROUND

[0003] Unmanned Aerial Vehicles (UAVs) are aircraft with no onboard pilot. UAVs may fly autonomously or remotely. UAVs require an energy source to power the motor in order to sustain flight. Battery powered UAVs may be limited in range and duration by the size and weight of the batteries, since the batteries may constitute a significant portion of the overall payload weight. It is desired to have efficient batteries. This is especially true for solar- powered UAVs where continuous flight needs to be sustained and returning to a ground station to recharge is to be avoided as long as possible. Generally speaking, solar-powered UAVs capture incident solar radiation with an onboard solar array connected to at least one battery. The battery may become substantially charged during the day when the sun is above the horizon, such that the stored energy may be sufficient to sustain flight throughout the night.

SUMMARY

[0004] A system embodiment may include: a battery pack comprising: a case; and a battery disposed in the case, where the battery comprises two or more modules, where each module comprises two or more sets of battery cells, and where each set of the two or more sets of battery cells is separated from an adjacent set of the two or more sets of battery cells by at least one heater and at least one balancer.

[0005] Additional system embodiments may include: an unmanned aerial vehicle (UAV). Additional system embodiments may include: at least one electric motor coupled to the UAV, where the at least one electric motor provides propulsion of the UAV. Additional system embodiments may include: a solar array connected to a top wing surface of the UAV, where the solar array comprises a plurality of solar array cells, where the solar array cells convert captured solar energy into direct current (DC) electrical energy for storage by the battery.

[0006] In additional system embodiments, the battery pack further comprises: an insulating layer disposed in the battery pack, where the insulating layer retains heat produced in the battery pack. In additional system embodiments, the insulating thermal layer surrounds the battery in the battery pack. In additional system embodiments, the insulating electrical layer surrounds each module of the two or more modules of the battery. In additional system embodiments, the insulating layer is a polymer-based insulating material.

[0007] In additional system embodiments, the battery comprises six modules. In additional system embodiments, each set of battery cells is grouped in a set of three battery cells in parallel arranged in a parallel configuration with other groups. Additional sy stem

embodiments may include: a plurality of sensors configured to measure a voltage of each set of battery cells. In additional system embodiments, a proximate balancer of the at least one heater is turned on if the measured voltage of a set of battery cells of the two or more sets of battery cells exceeds a threshold voltage. In one embodiment, the heater and balancer may be a single resistor. In one embodiment, there may be more than one resistor between adjacent groups of battery cells. In one embodiment, the separate heater and balancer may be located within the set of three battery cells. In one embodiment, the combined heater and balancer resistor may be located within the set of three battery cells.

[0008] In additional system embodiments, the battery pack further comprises: a plurality of springs spaced between the insulating layer and the case, where the plurality of springs provide for expansion and contraction of the battery pack while maintaining a constant pressure on the battery. Additional system embodiments may include: at least one power tracker proximate the battery, where the at least one power tracker is configured to receive electrical energy produced by the solar array. In additional system embodiments, the at least one power tracker is configured to regulate voltage provided to the battery.

[0009] Another system embodiment may include: a UAV; a solar array configured to convert solar energy to electrical energy; at least one motor; a battery pack system comprising: a case; an insulating layer; a battery having two or more modules, each module comprised of two or more sets of battery cells, where each set of the two or more sets of battery cells is separated from an adjacent set of battery cells by at least one heater and at least one balancer; a plurality of springs spaced between the insulating layer and the case; where the plurality of springs is configured to provide for expansion and contraction of the case based on the battery size; where the insulating layer retains heat; at least one power tracker in

communication with the solar array, the power tracker configured to receive energy from the solar array; where the battery is capable of receiving the energy from the power tracker to charge the battery; where excess heat generated from the power tracker is utilized and selected to maintain charge of the battery; and where the at least one motor is configured to receive energy from the battery to power the at least one motor.

[0010] A method embodiment may include: measuring a voltage of each set of battery cells of two or more sets of battery cells of a battery by a plurality of sensors; determining if the measured voltage of each set of battery cells of the two or more sets of battery cells exceeds a threshold voltage; activating one or more balancers proximate each set of battery cells of the two or more sets of battery cells that exceeds the threshold voltage; activating one or more heaters proximate the one or more balancers in response to activation of the one or more balancers; and heating the battery by the activated one or more heaters.

[0011] Additional method embodiments may include: activating one or more balancers proximate each set of battery cells of the two or more sets of battery cells during night; activating one or more heaters proximate the one or more balancers in response to activation of the one or more balancers; and heating the battery by the activated one or more heaters.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principals of the invention. Like reference numerals designate corresponding parts throughout the different views. Embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:

[0013] FIG. 1 depicts a system of an unmanned aerial vehicle having an expanding battery pack, according to one embodiment;

[0014] FIG. 2 depicts a cross-section of the expanding battery pack of FIG. 1, according to one embodiment;

[0015] FIG. 3 A depicts a battery of the battery pack of FIG. 2, comprised of a plurality of battery modules, according to one embodiment;

[0016] FIG. 3B depicts an array of battery modules of the battery of FIG. 3 A, comprised of a plurality of battery cells, according to one embodiment; and

[0017] FIG. 4 depicts an arrangement of the battery cells of FIG. 3B, according to one embodiment. DETAILED DESCRIPTION

[0018] The following description is made for the purpose of illustrating the general principles of the embodiments discloses herein and is not meant to limit the concepts disclosed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the description as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.

[0019] The system and method disclosed herein may include a battery pack that expands when charging, where the battery pack is capable of sustaining continuous flight of a solar unmanned aerial vehicle (UAV). In one embodiment, the UAV is a high altitude long endurance aircraft. The battery of the battery pack may drive a motor of the solar UAV. The battery may need enough stored energy to power the motor for continuous flight. As temperatures fall throughout the night, it becomes a challenge to retain heat in the battery. This unwanted heat loss presents a problem for regulating the temperature of the batter}' required for maintaining charge and driving the motor for sustaining continuous flight. It is desired to have a battery system for minimizing wasted heat. It is still further desired to have a batteiy system that leverages wasted heat from other onboard sources for maintaining the requisite battery system temperature. In some embodiments, the system and method disclosed herein may prevent damage to the battery from the cold, allow for rapid charge and discharge, and/or reduce a need to use energy' from the battery to keep the battery warm.

[0020] During the daytime, the aircraft is exposed to solar radiation and a solar array onboard the aircraft collects radiation from the sun to power the battery. The aircraft flies at high altitudes where temperatures can reach as low as -80° Celsius at night. It is desired to minimize heat loss from the battery throughout the night to avoid depleting the battery of charge and/or to prevent failure of the battery'. Furthermore, to keep the solar UAV flying at night when the solar array is no longer exposed to solar radiation, it is imperative to heat the battery pack safely and without wasting heat to maintain a constant temperature despite the lack of exposure to the sun.

[0021] UAV battery packs may include a safety system that balances the battery' cells in a battery pack by running the battery power through a resistor to achieve equal voltage across the cells. In the disclosed embodiments, the balance across the battery cells may be achieved by a heater spaced between the cells. In some embodiments, every three cells in the battery may have a heater, and a balancer, separating adjacent sets of three cells, providing a parallel connection. In other embodiments, every one or more cells in the battery may have a heater, and a balancer, separating adjacent cells, providing a series connection. Having the balance resistor activated may heat the battery. Two tasks may be achieved simultaneously: balancing of the battery cells in the expanding battery pack and heat production therein.

[0022] In some embodiments, the battery pack may include a spring-loaded support structure around the pack to allow the battery pack to expand and contract. The spring-loaded support structure may maintain a constant pressure on the battery as the charge state within the battery pack changes. For example, the temperature inside the battery will increase as the battery charges, and the spnng-loaded support structure maintains a constant pressure on the battery as the battery pack expands due to the expansion of the battery pack. Furthermore, the spring-loaded support structure supports the battery pack and maintains constant pressure on the battery as the battery pack contracts due to decreases in charge state, such as when the UAV flies at night.

[0023] The expanding battery' pack may further include power trackers proximate the battery cells, which take the energy from the solar array and convert the energy to electrical energy for charging the battery pack. Configured as such, the thermally-expanding battery pack may be using both the heaters between the cells and the wasted heat from the electrical energy of the power tracker used to charge the battery to heat the pack at the same time.

[0024] The boost in injected heat coming from the wasted heat of the power tracker, combined with heaters disposed between the cell groupings, allows the battery' pack to sustain a desired operating temperature. In one embodiment, the desired operating temperature is in the range of 10°C to 50°C. The different aspects of the present embodiments affect the ability to maintain continuous flight of the UAV. Furthermore, the battery pack may be insulated to retain the generated heat to survive the cold and sustain flight of the UAV.

[0025] With respect to FIG. 1, embodiments of the systems and methods for an expanding battery pack include an unmanned aerial vehicle (UAV) system 100 UAVs are aircraft with no onboard pilot and may fly autonomously or remotely. In one embodiment, a UAV 108 is a high altitude long endurance aircraft. The UAV 108 may have between one and forty motors, and a wingspan between 100 feet and 400 feet. In one embodiment, the UAV 108 has a wingspan of approximately 260 feet and is propelled by 10 electric motors powered by a solar array covering the surface of the w ing resulting in zero emissions. Flying at an altitude of approximately 65,000 feet above sea level and above the clouds, the UAV 108 is designed for continuous, extended missions of up to months without landing. [0026] The UAV 108 functions optimally at high altitude due at least in part to the lightweight payload of the UAV 108. The UAV 108 is capable of considerable periods of sustained flight without recourse to land. In one embodiment, the UAV 108 may weigh approximately 3,000 lbs. and may include wing panel sections and a center panel, providing for efficient assembly and disassembly of the UAV 108 due to the attachability and detachability of the wing panel sections to each other and/or to the center panel.

[0027] The UAV 108 may include a solar array 110 configured to capture solar energy from the sun when the sun is above the horizon. The solar energy, in turn, is used to power all or part of the UAV’s 108 propulsion. The solar array 110 may be attached on a top wing surface 109 of the UAV 108. In one embodiment, the solar array 110 is attached to the top wing surface 109 with tape around the edges of each sub-module of the solar array 110. In another embodiment, the solar array 110 may be friction fit to the top wing surface 109. Other methods of attachment of the solar array 110 to the UAV 108 are possible and contemplated. A module may include two or more cells electrically connected in parallel. In another embodiment, the module may include two or more cells electrically connected in series. The number of cells may be selected based on a desired capacity. In some embodiments, cells having a desired size may not exist or may not be feasible and so connecting two or more smaller cells in parallel may allow the two or more smaller cells to be treated as if they were one larger cell. In some embodiments, the two or more smaller cells may be three cells connected in parallel. A battery may include one or more modules. Each module may include two or more sub-modules electrically connected in parallel. In another embodiment, the sub- modules may be electrically connected in series. Each sub-module may include one or more cells electrically connected in parallel. Each sub-module may be separated from adjacent sub- modules by at least one heater and at least one balancer.

[0028] As the UAV 108 approaches, recedes, or generally travels below the sun, the solar array 110 captures solar radiation. In one embodiment, as the sun sets, the solar array 110 no longer captures solar radiation; however, the energy captured by the solar array 110 as the UAV 108 headed towards and receded from the sun may be converted to electrical energy to charge or provide power to a battery.

[0029] The UAV 108 further includes at least one electric motor 112 coupled to the UAV 108 for propulsion of the UAV 108. In one embodiment, the UAV 108 has ten electric motors. In one embodiment, the motor 112 is a brushless DC motor in a conventional configuration that includes an outrunner rotor electrically connected with a wye-configuration winding about improved armatures. The motor 112 may be protected by a nacelle. A stator may be positioned inside the rotor.

[0030] In one embodiment, the motor 112 is configured to have windings wound around iron teeth. Additionally, there may be a layer of magnets on the outside of the motor 112 that may remain glued to the motor 112 at extreme temperatures, such as at approximately -80°

Celsius. This is advantageous as the UAV 108 often flies at night and at high altitude with temperatures approaching -80° Celsius.

[0031] In another embodiment, the motor 112 may be an ironless motor to avoid hysteresis losses and eddy current losses, which result in energy being wasted in the form of heat. In another embodiment, the motor 112 may be an iron motor.

[0032] With respect to FIG. 2, the solar array 110 may contain a plurality of solar array cells 111, 113. The cells 111, 113 may be photovoltaic (PV) cells. In one embodiment, the cells 111, 113 convert the captured solar energy into direct current (DC) electrical energy. In one embodiment, the solar array 110 may produce a range of approximately 110-160 volts.

[0033] This conversion of solar energy to electricity may be achieved using semiconducting materials in the PV cells which exhibit the photovoltaic effect, where light (i.e., photons) are converted to electricity (i.e., voltage). In one example, the semiconducting material of the cells 111, 113 is gallium arsenide (GaAs). In another example, the semiconducting material of the cells 111, 113 is silicon. Other semiconducting materials are possible and

contemplated.

[0034] A battery pack system 114 may include a case 116. In one embodiment the case is made of semi-rigid materials, such as plastic or carbon fiber. Other battery pack case 116 materials are possible, such as aluminum, steel, titanium, and reinforced plastics (e.g., fiberglass, Kevlar, and Zylon). The case 116 is designed to have a small footprint and to conserve weight. In one embodiment, the case 116 weighs approximately 21% of the weight of a battery. It is desired to limit the weight of the battery pack system 114 since extra weight requires the UAV to use more power for propulsion. In some embodiments, the case 116 may be opened with a removable plate 115 on the underside of the battery pack system 114 for access to component parts of the battery pack system 114. This provides for easy replacement or maintenance of component parts. In one embodiment, the back of the case 116 may have a thin metal fire shield and/or foam insulation.

[0035] The battery pack system 114 may further include an insulating layer 118. The insulating layer 118 is disposed along the inside of the case 116. In another embodiment, the insulating layer 118 surrounds only a battery 120 of the battery pack 114. In one embodiment, an electrical insulating layer surrounds individual modules of the battery 120 to insulate the battery cells of the individual modules. The insulating layer 118 is configured to retain heat produced by the battery pack system 114. In one embodiment, as the UAV 108 flies at high altitude the ambient temperature may be extremely low. This is especially true as the UAV 108 flies at night, where temperatures may be as low as -80° Celsius. Temperature may affect a battery in many ways, including: efficiency and charge acceptance, power and energy efficiency, safety and reliability, operation of electrochemical systems, and overall cycle life and calendar life. In particular, Lithium ion (Li-ion) batteries are especially sensitive to low temperatures. It is desired to regulate the temperature of the battery pack 114 to remain in a pre-determmed temperature range for optimum performance and life. The insulating layer 118 may provide for retention of heat of the battery back system 114, thereby helping to effectively regulate the temperature of the battery pack 114 in extremely low temperatures. In one example, the insulating layer 118 may be a polymer-based insulating material.

[0036] Additionally, hot gases may be produced within the battery pack system 114 that may be caustic to certain components therein. The thermally insulating layer 118 may be configured for redirecting discharge of any produced hot gases.

[0037] The battery pack system 114 also includes the battery 120 for powering the UAV. In one embodiment, the battery 120 is a lithium ion (Li-ion) battery. Other battery types may include Lithium-metal, Lithium-Sulphur, Lithium-air, and Lithium-Oxygen. It is desired to maximize the life span of the battery 120, such as the“cycle life” and the“calendar life”. Cycle life refers to the aging of the battery 120 based on the overall operating, or usage, time of the battery 120. More specifically, the cycle life is the number of full discharge-charge cycles of the batter 120. The calendar life is the aging of the battery 120 which is just as a function of time. The cycle life may be decreased by a number of factors, including; (1) strain caused by operating a too high or low of a voltage state, (2) high charge rates, (3) charging at very cool temperatures, and (4) high discharge rates. The calendar life of the Li-ion battery 120 may lose capacity with time, and the loss in capacity may be exacerbated by generally operating at very high and low temperatures, and spending too much time at high states of charge during storage. The battery 120 has a long life cycle, enabling the support of extended missions and can be operated in extreme environmental conditions, such as low temperatures.

[0038] The full capacity of the battery 120 may only be needed in the winter, when the nights are the longest. At other times of the year, only a fraction of the battery 120 capacity may be needed. The battery 120 need not be fully charged or fully discharged. By choosing the maximum charge level, and maximum discharge level, the battery cycle life may be optimized.

[0039] The charging and discharging limits may also be adjusted if predicted weather conditions, such as high winds, require more energy during the night. The extra energy may be used to fly above high winds or fly at a higher speed.

[0040] With reference to FIG. 3 A, the battery 120 may be comprised of a plurality of modules 121, 123. In one embodiment, there are six identical modules or“triplets” 121, 123. Other quantities of modules are possible and contemplated. In one embodiment, the modules may be stacked on one another. In one embodiment, the stack may have six modules.

[0041] FIG. 3B is an enhancement of the modules of FIG. 3A. In one embodiment, each module 121 associated with the battery 120 may have battery cells 122, 125 grouped in sets, for example, in sets of three (see also FIG. 4). In one embodiment, the battery cells are fabricated, and, in general, rated for use at atmospheric pressures. In one embodiment, the battery 120 may be comprised of module 121 may be comprised of six stacks 131 of modules 121 with three battery cells per module 121. The group of battery cells 122, 125 may be arranged in a parallel configuration. In another embodiment, the group of battery cells 122, 125 may be arranged in a serial configuration. Each battery cell 122, 125 may be of the same type with equal voltage and capacity as well as the same size. In another example, each battery cell may be of a different type with equal voltage and capacity and may have a different size. In the event of a battery cell 122, 125 failure, a solid state switch may provide for bypassing the malfunctioned battery cell 122, 125 to allow continued current flow.

[0042] It may be prohibitive to do a full battery replacement upon malfunction; therefore, if a battery cell 122, 125 or a set of battery cells 122, 125 of a module 121 fails, that module may be removed and replaced with a new module.

[0043] In one embodiment shown in FIG. 4, a set of battery cells 122, 125 is separated from an adjacent set of battery cells 122, 125 with at least one heater 124 and at least one balancer 126. Each heater 124 is configured to improve the low-temperature charge/discharge performance of the battery 120. The UAV 108 often flies at high altitude and at night where the ambient temperature is very cold. To heat the battery pack system 114, a battery management system may activate balancers 126 with a balance resistor, which in turn, activates the heaters 124. In essence, two tasks may be achieved simultaneously: balancing of the voltage across the battery 120 and heat production within the battery pack system 114. In one embodiment, a single resistor may be the heater 124 and balancer 126. In one embodiment, there may be more than one resistor between adjacent battery cells 122, 125. In one embodiment, the at least one heater 124 and the at least one balancer 126 may be located within the set of battery cells. In one embodiment, the combined heater and balancer resistor may be located within the set of battery cells.

[0044] In one embodiment, a plurality of sensors may measure the voltage of each battery cell 122, 125. If the voltage of a battery cell 122, 125 exceeds a threshold voltage, the sensor may turn on the balancer 126 associated with that battery cell 122, 125 to prevent the voltage from increasing. In one embodiment, the balancers 126 may be used as heaters, such that the balancers may turn on even when balancing is not required, thus generating heat for the battery pack system 114. The UAV 108 may fly at night when the battery 120 does not perform significant self-heating, since the battery 120 is being discharged very slowly;

therefore, the balancers 126 may provide additional heat to the battery pack system 114. In one embodiment, an operator may activate the heaters 124. In another embodiment, the heaters 124 may be activated by the battery management system. In one embodiment, each heater 124 is significantly thinner than each battery cell 122, 125.

[0045] With reference to FIG. 2, a plurality of springs 128 may be spaced between the case 116 and the insulating layer 118. As the battery 120 fluctuates in size due to changes in the charge state, the springs 128 provide for expansion and contraction of the battery pack system 114 while maintaining constant pressure on the battery cells 122, 125, as shown in FIGS. 3B and 4. The expansion and contraction of the battery pack system 114 may allow for the battery' cells 122, 125 to properly operate as the battery cells 122, 125 experience fluctuations in size due to changes in the charge state. The high altitude application of the battery pack system 114 may require the battery cells 122, 125 to be able to operate at near vacuum conditions. In one embodiment, in order to emulate the atmospheric pressure at altitude, mechanical loading may be employed. The requirements of this implementation may be low weight, low volume, and minimal load variation. In one embodiment, the

configuration of the cells varies over 10% of initial thickness with state of charge, total cycles, and temperature. In order to minimize weight, the load path may be limited to the battery cells, Kevlar string, and end plates. In one embodiment, the string may be arranged in such a way that the fixed pressure plate and floating pressure plate are configured as pulleys. This arrangement may provide for the springs 128 to be located underneath the battery cells, where space may already be allocated for thermal runaway venting. In one embodiment, the springs 128 are made of titanium in order to minimize weight and provide sufficient strength and fatigue resistance for a long endurance flight of the UAV. [0046] The battery pack 114 may further include at least one power tracker 130 proximate the batten- 120. In another embodiment, the power tracker 130 may be located outside of the battery pack 114. The power tracker 130 may be in communication with the solar array 110, and the power tracker 130 may be configured to receive electrical energy produced by the solar array 110. More specifically, the cells 111, 113 of the solar array 110 convert sunlight into electrical energy and the power tracker 130 receives the electricity from the solar array 110 from an output 132, such as a bus, of the solar array 110. The solar array 110 may operate at a lower voltage than the bus. In one embodiment, the power tracker 130 is a maximum power point tracker (MPPT) controller configured to boost voltage from the solar array 110 to the output 132 and to adjust a boost ratio to get the maximum power from the solar array 110. Examples of MPPT controllers include Outback® FLEXmax 60/80 MPPT, Xantrex® MPPT Solar Charge Controller, and Blue Sky® Solar Charge Controller.

Generally speaking, the power tracker 130 is configured to maximize the available power going into the battery 120 from the solar array 110. The maximum voltage may be a function of the temperature and illumination of the solar array 110, both of which may vary throughout the day.

[0047] When the battery 120 becomes close to being fully charged the battery 120 may no longer be able to charge rapidly, requiring a slow tapering off of the charge. If the battery 120 is fully charged, the battery 120 may discharge when the battery 120 is left unused and may lose effectiveness. Additionally, over-charging of the battery 120 may cause the generation of heat and gasses, both of which may be harmful for the battery 120. Over-charging of the battery 120 may cause the battery 120 to overheat and in some cases may lead to full or partial failure of the battery 120.

[0048] Once the battery 120 is fully charged, the charging current may need to be reduced as it is desired to taper off the charging process before any damage to the battery 120 occurs, while at all times maintaining the battery 120 temperature within the pre-determined limits of the batter}' 120. In one embodiment, the battery 120 charge rate is maintained within the predetermined limits by adjusting the power tracker 130 voltage boost ratio to operate the solar array 110 conditions that may reduce the energy output of the solar array 110. In another embodiment, the battery 120 charge rate is maintained within the pre-determined limits by absorbing the extra current with the aircraft propulsion system. In another embodiment, the battery 120 temperature is maintained within the pre-determined limits by adjusting the power tracker 130 voltage boost ratio in combination with the aircraft propulsion system. [0049] The power tracker 130 has an output 134 configured for supplying electrical charge to the battery 120. More specifically, the power tracker 130 supplies electncity to the heater 124, as shown in FIG. 4, to heat the battery cells 122, 125. Still further, the power tracker 130 provides electrical energy to activate the balancers 126, as shown in FIG. 4, to maintain equal voltage across the battery 120. In one embodiment, the power tracker 130 is configured to regulate the voltage transmitted to the battery 120. For example, the amount of solar radiation captured, and hence, produced by the solar array 110 may vary throughout the day as the sun’s position changes in the sky. The power tracker 130 may be used to provide a steady voltage to the batteiy 120.

[0050] In another embodiment, the power tracker 130 may taper off the current transmitted to the battery 120 later in the day as the sun is lower on the horizon and the battery 120 may be nearly full. The energy of the battery 120 may be transferred to the UAV motor 112, as shown in FIG. 1, to cause the UAV 108 to ascend to a higher altitude. The UAV 108 may then conserve energy at night by stopping the motor 112 and gliding slowly back down to loiter at lower altitude until sunrise when the UAV solar array 110 may begin to capture solar energy to charge the battery 120.

[0051] In operation, the power tracker 130 may generate excess heat 137 (see FIG. 2) as the power tracker 130 provides energy to the battery 120. The excess heat of the power tracker 130 combined with heaters 124 of the battery 120 allow the battery 120 to sustain a desired operating temperature. In one embodiment, the desired operating temperature is in the range of 10°C to 50°C. Furthermore, the insulating layer 118 may retain the excess heat, thereby preventing the battery 120 from losing charge. In one embodiment, the insulating layer 118 is configured to minimize heat loss from the battery 120 in the battery pack 114 throughout the night to avoid depleting the battery 120 of charge due to excessive use of the heaters 124. More specifically, as the UAV 108 flies at high altitude and/or at night where the ambient temperatures may be as low as -80° Celsius, the insulating layer 118 may provide for retention of heat of the battery pack system 114, thereby preventing heat escape w hich may result in draining the charge of a battery 120. As a result, the UAV 108 may sustain flight throughout the night. In some embodiments, the insulating layer 118 may surround the battery 120 and the power tracker 130 inside the case 116.

[0052] The charged battery 120 is configured to drive the one or more motors 112 of the UAV 108, and the battery pack system 114 ensures that the batteiy 120 will have enough stored energy to power the motor 112 for continuous flight. In one embodiment, the battery 120 has an output 136 configured to transmit electrical energy to the one or more motors 112. In one example, the electrical energy is a DC current. The motor 112 receives the electrical energy from the battery 120 for propulsion of the UAV 108.

[0053] It is contemplated that various combinations and/or sub-combinations of the specific features and aspects of the above embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments may be combined with or substituted for one another in order to form varying modes of the disclosed invention. Further, it is intended that the scope of the present invention is herein disclosed by way of examples and should not be limited by the particular disclosed embodiments described above.

Claims

WHAT IS CLAIMED IS:

1. A system comprising:

a battery pack (114) comprising:

a case (116); and

a battery (120) disposed in the case, wherein the battery comprises two or more modules (121, 123), wherein each module (121, 123) comprises two or more sets of battery cells (122, 125), and wherein each module is configured to provide heat to the two or more sets of battery sells; and wherein the system is configured to use heat produced from other onboard sources as wasted heat and heat produced from each module to maintain a battery system temperature.

2. The system of claim 1, further comprising:

an unmanned aerial vehicle (UAV) (108).

3. The system of claim 2, further comprising:

at least one electric motor (112) coupled to the UAV, wherein the at least one electric motor provides propulsion of the UAV.

4. The system of claim 3, further comprising:

a solar array (110) connected to a top wing surface (109) of the UAV, wherein the solar array comprises a plurality of solar array cells (111, 113), wherein the solar array cells convert captured solar energy into direct current (DC) electrical energy for storage by the battery.

5. The system of claim 1, wherein the battery pack further comprises:

an insulating layer (118) disposed in the battery pack, wherein the insulating layer retains heat produced in the battery pack.

6. The system of claim 5, wherein the insulating layer (118) surrounds the battery in the battery pack.

7. The system of claim 1, wherein an electrical insulating layer (118) surrounds each module of the two or more modules of the battery.

8. The system of claim 5, wherein the insulating layer (118) is configured to minimize heat loss from the battery in the battery pack throughout the night to avoid depleting the battery of charge due to excessive use of the at least one heater.

9. The system of claim 1, wherein the battery comprises six modules.

10. The system of claim 9, wherein each set of battery cells is grouped in a set of three batter cells arranged in a parallel configuration.

11. The system of claim 1, further comprising:

a plurality of sensors configured to measure a voltage of each set of battery cells.

12. The system of claim 11, wherein a proximate balancer of the at least one balancer is turned on if the measured voltage of a set of battery cells of the two or more sets of batter cells exceeds a threshold voltage.

13. The system of claim 12, wherein the system is configured to activate at least one balancer with a balance resistor to activate the at least one heater, thereby

simultaneously balancing the voltage across the battery cells and producing heat within the battery pack.

14. The system of claim 11, wherein the at least one balancer is used as a heater, such that the balancer turns on even when balancing is not required, thereby generating heat for the battery pack.

15. The system of claim 5, wherein the battery pack further comprises:

a plurality of springs (128) spaced between the insulating layer (118) and the case (116), wherein the plurality of springs provide for expansion and contraction of the battery pack while maintaining a constant pressure on the battery.

16. The system of claim 5, further comprising: at least one power tracker (130) proximate the battery, wherein the at least one power tracker is configured to receive electrical energy produced by the solar array (110).

17. The system of claim 16, wherein the at least one power tracker is configured to

regulate voltage provided to the battery.

18. An unmanned aerial vehicle (UAV) system (100) comprising:

a UAV (108);

a solar array (110) configured to convert solar energy to electrical energy;

at least one motor (112);

a battery pack system (114) comprising:

a case (116);

an insulating layer (118);

a battery (120) having two or more modules (121, 123), each module (121, 123) compnsed of two or more sets of battery cells (122, 125), wherein each set of the two or more sets of battery cells (122, 125) is separated from an adjacent set of battery cells (122, 125) by at least one heater (124) and at least one balancer (126);

a plurality of springs (128) spaced between the insulating layer (118) and the case (116);

wherein the plurality of springs (128) is configured to provide for expansion and contraction of the case (116) based on the battery size;

wherein the insulating layer (118) retains heat;

at least one power tracker (130) in communication with the solar array (110), the power tracker (130) configured to receive energy from the solar array (110); wherein the battery (120) is capable of receiving the energy from the power tracker (130) to charge the battery' (120);

wherein excess heat generated from the power tracker (130) is utilized and selected to maintain charge of the battery (120); and

wherein the at least one motor (112) is configured to receive energy from the battery (120) to power the at least one motor (112).

19. A method comprising: measuring a voltage of each set of battery cells (122, 125) of two or more sets of battery cells of a batery (120) by a plurality of sensors;

determining if the measured voltage of each set of batery cells of the two or more sets of batery cells exceeds a threshold voltage;

activating one or more balancers (126) proximate each set of battery cells of the two or more sets of batery cells that exceeds the threshold voltage;

activating one or more heaters (124) proximate the one or more balancers in response to activation of the one or more balancers; and

heating the battery by the activated one or more heaters.

20. The method of claim 19 further comprising:

activating one or more balancers proximate each set of batery cells of the two or more sets of battery cells during night;

activating one or more heaters proximate the one or more balancers in response to activation of the one or more balancers; and

heating the battery by the activated one or more heaters.