Patent Publication Number: US-2020303788-A1

Title: Thermal regulation of batteries

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/821,287, filed Mar. 20, 2019, the contents of which are herein incorporated by reference in their entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under contract number NNC14CA32C awarded by the National Aeronautics and Space Administration. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to thermal management and more particularly to thermal management for aircraft batteries. 
     2. Description of Related Art 
     Aircraft batteries need thermal management to avoid damage due to overheating and overcooling. During cruise, the batteries on an aircraft may experience cold soak in which they run the risk of a substantial loss of capacity and a reduction in vehicle range. This is especially true for batteries that are idle, and therefore are not generating any heat on their own, which occurs during charge and discharge. 
     Depending on the storage location for the batteries, some areas may be climate-controlled and some may not be. Idle batteries that are not located in climate-controlled compartments may experience cold soak due to protracted exposure to subfreezing conditions common at cruising altitude. Even when batteries are located in a climate-controlled compartment, they may experience cold soak if a loss of fuselage pressure results in ambient air entering the compartment. Furthermore, cold soak may occur on cold days on the ground (e.g. overnight parking in cold climates). 
     The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved thermal management for batteries. This disclosure provides a solution for this need. 
     SUMMARY OF THE INVENTION 
     A battery thermal management system for an air vehicle includes a liquid heat exchange circuit, an air heat exchange circuit in selective fluid communication with ram air, a liquid-air heat exchanger positioned on the liquid heat exchange circuit and the air heat exchange circuit to exchange heat therebetween. The system includes at least one battery in thermal communication with the liquid heat exchange circuit. The at least one battery is configured to at least one of charge or discharge to heat the at least one battery above a pre-determined minimum battery temperature. 
     In certain embodiments, the system includes a battery temperature sensor operatively connected to the at least one battery. The system can include a state-of-charge sensor operatively connected to the at least one battery. The system can include at least one of a motor or a generator operatively connected to the at least one battery to receive electric power therefrom or provide power thereto. The system can include a battery resistance heater electrically coupled to the at least one battery. The system can include an auxiliary load circuit electrically coupled to the at least one battery. The system can include a battery heat exchanger positioned on the liquid heat exchange circuit in thermal communication with the at least one battery and the liquid heat exchange circuit. 
     In some embodiments, the system includes a bypass valve positioned in the liquid heat exchange circuit upstream from the liquid-air heat exchanger. The system can include a bypass line branching from the liquid heat exchange circuit upstream from the liquid-air heat exchanger and reconnecting to the liquid heat exchange circuit downstream from the liquid-air heat exchanger. The system can include a bypass line valve positioned on the bypass line. 
     In accordance with another aspect, a method for controlling a thermal management system for an air vehicle includes determining if at least one battery is within a thermal range of operation for heating. The method includes at least one of charging or discharging the at least one battery to heat the at least one battery if the at least one battery is within the thermal range of operation for heating. 
     Determining if the at least one battery is within the thermal range of operation for heating can include sensing a temperature of at least one battery with a temperature sensor. At least one of charging or discharging the at least one battery can include at least one of charging or discharging the at least one battery if the temperature is below a pre-determined threshold. Determining if the at least one battery is within the thermal range of operation for heating can include referencing a pre-determined operating schedule that corresponds with a phase of flight. 
     The method can include closing a bypass valve positioned in a liquid heat exchange circuit upstream from a liquid-air heat exchanger if the at least one battery is within the thermal range of operation for heating. The method can include opening a bypass line valve in a bypass line branching from a liquid heat exchange circuit upstream from a liquid-air heat exchanger and reconnecting to the liquid heat exchange circuit downstream from the liquid-air heat exchanger if the at least one battery is within the thermal range of operation for heating. At least one of charging or discharging can include charging the at least one battery when a state-of-charge of the at least one battery is below a pre-determined state-of-charge threshold. Charging the at least one battery can include charging the at least one battery with energy generated with an engine. At least one of charging or discharging can include discharging the at least one battery when a state-of-charge of the at least one battery is above a pre-determined state-of-charge threshold. Discharging can include discharging energy generated from the at least one battery to an electric load such as a motor operatively coupled to a to an engine and/or to a battery resistance heater. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG. 1  is a schematic representation of an embodiment of a battery thermal management system constructed in accordance with the present disclosure, showing the battery operatively connected to a generator; 
         FIG. 2  is a schematic representation of another embodiment of a battery thermal management system constructed in accordance with the present disclosure, showing the battery operatively connected to a motor; and 
         FIG. 3  is a plot representing air temperature versus altitude, showing a maximum and minimum battery temperature. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a schematic view of an exemplary embodiment of the battery thermal management system in accordance with the disclosure is shown in  FIG. 1  and is designated generally by reference character  100 . Other embodiments of the battery thermal management system in accordance with the disclosure, or aspects thereof, are provided in  FIG. 2  as will be described. The systems and methods described herein can be used to keep batteries warm in order to promote quick charging, avoid capacity loss and the concomitant reduction of vehicle range, or avoid other degradation during cold soak. The systems and methods described herein utilize existing hardware on aircraft, or a minimal addition of hardware, for an efficient and cost-effective approach. 
     As shown in  FIG. 1 , a battery thermal management system  100  for an air vehicle includes a controller  102 , a liquid heat exchange circuit  116 , an air heat exchange circuit  114 , and a liquid-air heat exchanger  112 . Signals to and from the controller  102  can be routed to and from dedicated ports on the controller  102 , or the sensors and actuators (described below) can be networked together with each device having its own address. In some embodiments, the components may communicate with the controller via a standard communication protocol involving the transfer of digital information. The system  100  includes a battery heat exchanger  106  positioned on the liquid heat exchange circuit  116  in thermal communication with a bank of batteries  104 . The bank of batteries  104  are in thermal communication with the liquid heat exchange circuit  116  by way of battery heat exchanger  106 . The battery heat exchanger  106  is positioned on the liquid heat exchange circuit  116  in thermal communication with the at least one battery and the liquid heat exchange circuit  116 . The batteries  104  are configured to charge and/or discharge to heat themselves above a pre-determined minimum battery temperature. 
     Batteries  104 , for example, without limitation, can be depleted batteries, reserve batteries, or batteries of a hybrid electric aircraft propulsion system where the batteries and electric motors assist with takeoff and climb, but are inoperative during cruise. The batteries  104  could be positioned in a variety of locations throughout the aircraft, for example, in the wings (e.g. in wing roots). In some embodiments, batteries  104  can furnish energy to a hybrid-electric or all-electric propulsion system for propulsion power or for transient operation (e.g. to avoid stall) or for other applications. In some embodiments, batteries  104  can be stored in a compartment, rack or housing of some kind. The system  100  assists in avoiding drastic battery storage capacity loss that occurs at low temperature, thereby maintaining vehicle range (or diminishing range loss). In addition, some battery types cannot be recharged quickly at low temperatures, so by keeping batteries above a given temperature, embodiments of the present invention can reduce the time required to recharge batteries. 
     With continued reference to  FIG. 1 , the system  100  includes a battery temperature sensor  107  operatively connected to the batteries  104 . The temperature sensor  107  is operatively connected to the batteries  104  and controller  102 . Those skilled in the art will readily appreciate that, due to the complexities involved in obtaining a battery temperature, the temperature sensor  107  may be operatively connected to the heat transfer fluid exiting the battery heat exchanger  106  in liquid heat exchange circuit  116  as a proxy for battery temperature. Those skilled in the art will readily appreciate that referring to “battery temperature,” “battery heat load” or other singular reference to battery, could mean the temperature/heat load of an individual battery  104  or group of batteries  104 . Controller  102  is configured to receive information about battery temperature from temperature sensor  107  and relay a command, if needed, to one or more of motor  111 , pump  109 , or valves  110  and  120  (described below). Those skilled in the art will readily appreciate that referring to “battery temperature,” “battery heat load” or other singular reference to battery, could mean the temperature/heat load of an individual battery  104  or group of batteries  104 . In some embodiments, it is also contemplated that controller could send a command to temperature sensor  107 . The system  100  includes a state-of-charge sensor  121  operatively connected to the batteries  104 . State-of-charge sensor  121  is operatively connected to controller  102  for sending and/or receiving data or commands thereto. The system  100  includes a generator device  124  (e.g. a motor/generator device) operatively connected to the batteries  104  to provide power to batteries. In some embodiments, the generator may be configured to function as a motor as well, in which the motor/generator device is operatively connected to the batteries  104  to provide electric power thereto to recharge the batteries in generator mode, but can also serve as a motor by receiving electric power input from the batteries  104 . Generator device  124  is operatively connected to an engine  126 , e.g. a reciprocating combustion engine, a turbomachine, or the like. A power electronics interface  122  is disposed between the generator  124  and the batteries  104 . The circuit between batteries  104  and the power electronics interface  122  can include a relay switch  119 . Power electronics interface  122  can include one or more rectifiers, inverters, or the like. 
     As shown in  FIG. 1 , generator device  124  and engine  126  offer a charging source for batteries  104 . For example, if system  100  was on a hybrid electric aircraft, batteries  104  could be charged by the generator  124  of the combustion engine  126 . In some embodiments, this charging occurs during cruise where batteries are typically idle (and potentially cold) and where batteries  104  can take advantage of the excess power that aircraft engines typically have (as they are no longer accelerating, due to lower density of air at elevated altitude, and due to fuel weight loss that results in less propulsive thrust required from aircraft engines). In some embodiments, charging batteries  104  during cruise allows landing approach with batteries at an elevated state-of-charge beyond which is required for aborted landings (go-around) and reserve missions. In other words, in these embodiments, the state-of-charge threshold includes sufficient power to supplement these go-around and/or reserve missions. Also, warm batteries can charge more quickly, so pre-heating batteries  104  during cruise may lead to a quicker turn-around time on the ground. In some scenarios, charging the battery to recover some of the energy may offer advantages over powering resistance heaters to warm the battery (described below). 
     The system  100  includes a battery resistance heater  108  electrically coupled to the batteries  104 . The resistance heater  108  is located in close proximity to batteries  104  along a heat conduction path and includes a battery heat resistance relay switch  119 . As an alternative, resistance heater  108  can warm a heat transfer fluid that is circulated through the batteries  104  (or their corresponding compartment). The system  100  includes an auxiliary load circuit  117  electrically coupled with the batteries  104 . Auxiliary load circuit  117  and resistance heater  108  offer two options for battery discharge. Auxiliary load circuit  117  also includes a relay switch  119 . In circumstances where charging is not available, it is contemplated that discharging the batteries  104  is also an option. Charge and discharge of the batteries  104  tends to generate waste heat due to the internal resistances of the batteries  104  that serves to keep the batteries  104  warm. Batteries  104  may be charged and discharged continuously or intermittently for thermal regulation. Any suitable electric load served by the battery (propulsion motor, lighting, avionics, entertainment system, etc.) will generate heat. The electricity can be routed to resistance heaters  108  which warm the batteries. In some embodiments, batteries  104  may also discharge to a motor such as generator  124  configured as a motor/generator to offer additional power to the corresponding propulsion system for propulsion power, or for transient operation, or for other applications. 
     With continued reference to  FIG. 1 , a coolant pump  109  is upstream from the battery heat exchanger  106 . The coolant is a heat transfer fluid flowing through liquid heat exchange circuit  116  used for thermal regulation of the batteries  104  which includes both heating and cooling. The heat transfer fluid can be any of a number of fluids, including but not limited to water and other aqueous fluids, as well as polar and non-polar organic fluids. In some embodiments, the heat transfer fluid can be in liquid form, but can also be in gaseous form as well as including gas or liquid form such as in a vapor compression heat transfer loop. Examples of heat transfer fluids include but are not limited to glycols such as ethylene glycol or propylene glycol, alcohols such as methanol or ethanol, water and aqueous solutions such as heat transfer brines, and other organic fluids such as propane, butane, and substituted hydrocarbons (e.g., fluoro-substituted) and other organic compounds such as 2,2,3,3-tetrafluoropropene or 1,1,1,2-tetrafluoroethane. A motor  111  is operatively connected to the coolant pump  109  to drive coolant pump  109 . The controller  102  is in operative communication with pump  109  and motor  111 . Pump  109  circulate heat transfer fluid to heat the batteries  104  downstream. Pump  109  and its corresponding liquid heat exchange circuit  116  are used to provide cooling to batteries  104 . However, where the temperature sensor  107 , the state-of-charge sensor  121 , and/or pre-determined reference table indicate to controller  102  that heating is required, controller  102  relays a shut-off command, if needed, to one or more of motor  111 , pump  109 , or valves  110  and  120  (described below). The pre-determined reference table may be located in electronic storage of controller  102 , or located in the electronic storage of another device that transmits a signal to controller  102 . Flight-critical components of a propulsion system  100 , such as a coolant circulation pump  109 , may be present in duplicate on an aircraft for redundancy. In view of this, there can be two pumps  109  that can operate on their own or in conjunction with one another. Moreover, it is contemplated that more than two pumps  109  can be used in system  100 . Those skilled in the art will readily appreciate that pump  109  can be a centrifugal pump, a reciprocating pump, a screw pump, a diaphragm pump, or any other suitable mechanical pump. 
     The system  100  includes a bypass valve  120  positioned in the liquid heat exchange circuit  116  upstream from the liquid-air heat exchanger  112 . The system  100  includes a bypass line  118  branching from the liquid heat exchange circuit  116  upstream from the liquid-air heat exchanger  112  and reconnecting to the liquid heat exchange circuit  116  downstream from the liquid-air heat exchanger  112 . The system  100  includes a bypass line valve  110  positioned on the bypass line  118 . Bypass line valve  110  and bypass valve  120  include respective motors  105  in operative communication with controller  102  to receive open/close commands therefrom. In some embodiments, valves  110  and  120  can be combined into a three-way valve that directs flow either to liquid-air-heat exchanger  112  or to bypass line  118 . Bypass line  118  assists in diverting around the liquid-air heat exchanger  112  to avoid cooling the fluid during cold soak conditions. Depending on the data from the pre-determined operating schedule, the state-of-charge of the batteries, and whether the temperature is below a second pre-determined threshold, which can be the same or different from the pre-determined minimum battery temperature threshold described above, controller  102  operates to command valve  110  open and valve  120  closed (e.g. by way of their respective motors  105 ). Motors  105  receive a command from controller and, in turn, operate to open or close their respective valves  110  or  120 . The reverse command can be executed once the temperature rises back up above the second pre-determined threshold. Valves  120  and/or  110  can be a gate valve, a globe valve, a needle valve, or any other proportional valve. 
     With continued reference to  FIG. 1 , the liquid-air heat exchanger  112  is positioned on the liquid heat exchange circuit  116  and the air heat exchange circuit  114  to exchange heat therebetween. The air heat exchange circuit  114  is in fluid communication with a ram air door  115  for providing cooling air (ram air) during non-idle conditions. Ram air is air outside of the fuselage of an aircraft. While the heat sink for air heat exchange circuit  114  is described herein as ram air, those skilled in the art will readily appreciate that heat exchange circuit  114  can be operatively connected to other ducts to receive fan duct bypass air, cabin outflow air, conditioned air from an environmental control system, or the like. Air heat exchange circuit  114  can also include a fan or the like for idle conditions. In the systems and embodiments of the present invention, the flow of cooling air can be curtailed or eliminated during cold soak conditions by closing the ram air door  115  either partially or fully. Ram air door  115  can similarly be operatively connected to controller  102  and can receive a close or open command therefrom depending on the data from the pre-determined operating schedule, the temperature measured at the temperature sensor  107  and/or the state-of-charge of the batteries measured with the state-of-charge sensor  121 . Since it is common for several heat exchangers to share a common ram air duct, the air heat exchange circuit  114  may be optionally outfitted with an air splitter (not shown) to branch the flow of ram air to individual heat exchangers. In this case, a flow control valve such as a butterfly valve can be located upstream of liquid-air heat exchanger  112  to restrict flow. 
     As shown in  FIG. 3 , system  100 , for example, can be used even on a hot day. On a hot day, as the altitude increases, the temperature of the atmospheric air still decreases to temperatures that can be below the batteries&#39; preferred minimum temperature of operation. Line  302  represents the air temperature, line  304  represents the minimum battery temperature and line  306  represents the maximum battery temperature. Those skilled in the art will readily appreciate that the temperatures shown herein may vary depending on battery chemistry, weather, time of day, or the like. Where, for example, the minimum battery temperature is approximately 5 degrees Celsius, heating to prevent cold soak at those high altitudes may be needed. The pre-determined threshold for the temperature, described above, can be set based on the minimum battery temperature for a given battery chemistry. 
     As shown in  FIG. 2 , another embodiment of a battery thermal management system  100  for an air vehicle is shown. The system  100  of  FIG. 2  is the same as the system  100  of  FIG. 1 , except that, instead of a generator  124  and an engine  126 , system  100  of  FIG. 2  only includes a motor  224  that is configured to be driven by batteries. In other words, the power generation function (e.g. charging) provided by engine  126  and generator portion of motor/generator  124  is not present in system  100  of  FIG. 2 . Discharging, similar to that described above relative to  FIG. 1 , may still be formed by system  100  of  FIG. 2 . Charging of system  100  of  FIG. 2  can also occur if a power source is provided. 
     A method for controlling a thermal management system, e.g. system  100 , for an air vehicle includes determining if batteries, e.g. batteries  104 , are within a thermal range of operation for heating. The method includes charging and/or discharging the batteries to heat the batteries if the batteries are within the thermal range of operation for heating. Determining whether to charge or discharge the batteries is determined by measuring a state-of-charge of the batteries with a state-of-charge sensor, e.g. state-of-charge sensor  121 . 
     In some embodiments, determining if the batteries are within the thermal range of operation for heating includes sensing a temperature of the batteries with a temperature sensor, e.g. temperature sensor  107 . If the temperature is below a pre-determined threshold, the method includes charging and/or discharging the batteries to generate heat. The controller compares the battery temperature, T_bat, with a threshold temperature (e.g. 5° C.). For example, if T_bat &lt;5° C., heating can be initiated by charging and/or discharging. 
     If the state-of-charge of the batteries is below a pre-determined state-of-charge threshold (e.g. with the capacity to recharge), and the batteries can actually be charged (such as pure electric propulsion plugged into charging, hybrid electric propulsion during cruise with turbofan/prop), the method includes charging the batteries. The method includes comparing the battery state-of-charge with a maximum condition (e.g. &lt;99.9%) which, if less than the maximum condition results in the controller actuating battery charging. Otherwise the controller actuates battery discharging (e.g. resistance heaters). The method may include a prediction of the state of charge of batteries in lieu of a measurement. 
     If the state-of-charge of the batteries is above a pre-determined state-of-charge threshold, e.g. without the capacity to charge, or generally cannot be charged (e.g. electric aircraft in flight or unplugged on ground), the method includes discharging the batteries. The method can include comparing the battery state-of-charge with a minimum condition (e.g. some energy may be required in reserve) with the controller. If the temperature is sufficiently low, and if the battery has sufficient state-of-charge, then the method includes actuating a load to be drawn/discharged from the batteries to a motor such as one that assists a propulsor (if batteries are part of hybrid/electric propulsion) and/or to a battery resistance heater. (e.g. resistance heaters to warm the battery). For a battery that is already cold-soaked, it may be necessary to heat the battery before it can be charged or discharged. 
     In some embodiments, determining if the batteries are within the thermal range of operation for heating includes referencing a pre-determined operating schedule that corresponds with a phase of flight. For example, certain durations at cruise (where the batteries may be idle) may be linked to charging and/or discharging the batteries in order to keep them above a given minimum battery temperature. 
     When allowed by the state-of-charge, temperature of the batteries, and/or pre-determined operating schedule, charging the batteries includes charging the batteries with energy generated with an enginer. The rate of charging can be adjusted to provide the desired heat generation as well as charge state. For example, a trickle charge will warm the batteries, store some charge, and allow faster charging on the ground. Charging on the ground, in some embodiments, may be preferred in order to utilize renewable energy sources. Battery temperature is a function of several variables including battery mass, battery heat capacity, initial battery temperature, heat sink temperature, and thermal loads due to charging, discharging, and environmental conditions. The expected temperature of a battery can be calculated according to standard methods by those who are skilled in the art in order to determine the best rate at which to charge or discharge a battery in order to maintain a desired minimum temperature. 
     In accordance with some embodiments, the method includes charging batteries on the ground on a cold day for pre-heating purposes. This generates heat that warms the batteries and thereby increases their capacity and thus vehicle range. If ground power is available to charge, then the electricity can also feed a battery resistance heater, e.g. battery resistance heater  108 , to further warm the batteries to a target temperature. In one embodiment, the electricity is provided to an electrical bus that charges the batteries as well as supplies power to the resistance heaters. 
     Where charging the batteries is not available, e.g. in the embodiment of  FIG. 2  or where the state-of-charge of the battery does not permit, the method includes discharging the batteries to at least one of a motor, e.g. motor/generator  124  or motor  224 , a battery resistance heater, e.g. battery resistance heater  108 , and/or an auxiliary load circuit, e.g. auxiliary load circuit  117 . The method includes closing a bypass valve, e.g. bypass valve  120 , positioned in a liquid heat exchange circuit, e.g. liquid heat exchange circuit  116 , upstream from a liquid-air heat exchanger, e.g. liquid-air heat exchanger  112 , if the batteries are within the thermal range of operation for heating. The method includes opening a bypass line valve, e.g. bypass line valve  110 , in a bypass line, e.g. bypass line  118 , branching from a liquid heat exchange circuit upstream from the liquid-air heat exchanger and reconnecting to the liquid heat exchange circuit downstream from the liquid-air heat exchanger if the batteries are within the thermal range of operation for heating. The method further includes restricting the flow of a heat sink, e.g. closing ram air door  115  or a closing a valve that regulates ram air flow, when the batteries are within the thermal range of operation for heating. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for thermal battery control with superior properties including reduced battery storage capacity loss, decreased recharging time, maintained vehicle range, and/or diminished vehicle range loss. The systems and methods of the present invention can apply to automotive batteries, aircraft batteries, terrestrial batteries, or the like. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.