Patent ID: 12233697

DETAILED DESCRIPTION

The present disclosure describes the battery system of an electric vehicle. While principles of the current disclosure are described with reference to a battery system of an electric bus, it should be understood that the disclosure is not limited thereto. Rather, the battery systems of the present disclosure may be used in any application (electric vehicle, electric machine, electric tool, electric appliance, etc.). In this disclosure, relative terms, such as “about,” “substantially,” or “approximately” are used to indicate a possible variation of 10% of a stated value. Any implementation described herein as exemplary is not to be construed as preferred or advantageous over other implementations. Rather, the term “exemplary” is used in the sense of example or illustrative.

FIGS.1A and1Billustrate an electric bus10.FIG.1Ashows the top view of the bus10andFIG.1Bshows its bottom view. In the discussion that follows, reference will be made to bothFIGS.1A and1B. Electric bus10may include a body12enclosing a space for passengers. In some embodiments, some (or all) parts of body12may be fabricated using one or more composite materials to reduce the weight of the bus10. In some embodiments, bus10may be a low-floor electric bus. As is known in the art, in a low-floor bus, there are no stairs at the front and/or the back doors of the bus. In such a bus, the floor is positioned close to the road surface to ease entry and exit into the bus. In some embodiments, the floor height of the low-floor bus may be about 12-16 inches (30-40 centimeters) from the road surface. Body12of bus10may have any size, shape, and configuration.

Bus10may include one or more electric motors15that generate power for propulsion, and a battery system14to store the energy needed to power the electric motor(s)15. When the energy stored in the battery system14decreases, it may be recharged by electrically connecting the battery system14to an external energy source. In some embodiments, the bus10may enable recharging of the battery system14by several methods. In some embodiments, a charging interface16may be located on the roof of bus10. The charging interface16may include a charging blade with electrodes and an alignment scoop in the form of a pair of curved rails (that together form a funnel-shaped alignment feature) positioned on either side of the charging blade. The charging interface16may engage with the charging head90of a road-side charging station80to recharge the battery system14. Details of an exemplary charging interface16, and an exemplary method of using the charging interface16, are described in commonly assigned U.S. Patent Application Publication Nos. US 2013/0193918 A1 and US 2014/0070767 A1, which are incorporated by reference in their entirety herein.

Additionally or alternatively, in some embodiments, the battery system14may be charged by connecting an external power supply to a charge port18located on a side surface of the bus10. To charge battery system14through the charge port18, a connector carrying power from an external power supply may be plugged into the charge port18. In some embodiments, the charge port18may be a standardized charge port (e.g., SAE J1772 charge port) that is configured to receive a corresponding standardized connector (e.g., SAE J1772 connector). Details of an exemplary charge port18, and an exemplary method of using the charge port18, are described in commonly assigned U.S. patent application Ser. No. 15/227,163, filed Aug. 3, 2016, which is incorporated by reference in their entirety herein.

In some embodiments, the bus10may be charged using the roof-top charging interface16when travelling on a route, and charged using the charge port18when it is parked in a bus depot (e.g., at night, between trips, etc.). In some embodiments, bus10may also include a wireless charge receiver22configured to use wireless technology (such as, e.g., inductive charging) to recharge the battery system14. The charge receiver22may inductively couple with a corresponding charge transmitter (e.g., positioned on a wall of a charging station or a road surface) to recharge the battery system14using external power. It should be noted that, although the charging interface16, charge port18, and charge receiver22are illustrated as being positioned at specific locations on the bus10, this is only exemplary. In general, these components may be positioned anywhere on the bus10.

Battery system14may include any type of vehicle battery known in the art. In some embodiments, the battery system14may have a modular structure and may be configured as a plurality of battery packs20. AlthoughFIG.1Billustrates the battery packs20as being positioned under the floor of the bus10, this is only exemplary. In some embodiments, some or all of the battery packs20may be positioned elsewhere (roof, inside, etc.) on the bus10. However, since the battery system14may have considerable weight, positioning the battery packs20under the floor may assist in lowering the center of gravity of the bus10and balance its weight distribution, thus increasing drivability and safety.

FIG.2is a schematic illustration of an exemplary battery system14of bus10. Battery system14may include a plurality of battery packs20. Each battery pack20may include a plurality of battery modules30, and each battery module30may include a plurality of battery cells50arranged therein. InFIG.2, the inside structure of one of the battery packs20, and the inside structure of one of the battery modules30of the battery pack20, are shown to aid in the discussion below. The battery cells50may have any chemistry and construction. In some embodiments, the battery cells50may have a lithium-ion chemistry. Lithium-ion chemistry comprises a family of battery chemistries that employ various combinations of anode and cathode materials. In automotive applications, these chemistries may include lithium-nickel-cobalt-aluminum (NCA), lithium-nickel-manganese-cobalt (NMC), lithium-manganese-spinel (LMO), lithium titanate (LTO), and lithium-iron phosphate (LFP). In consumer applications, the battery chemistry may also include lithium-cobalt oxide (LCO). Exemplary battery chemistries are described in commonly assigned U.S. Pat. No. 8,453,773, which is incorporated herein by reference in its entirety.

The plurality of battery packs20of the battery system14may be connected together in series or in parallel. In some embodiments, these battery packs20may also be arranged in strings. For example, battery system14may include multiple strings connected in parallel, with each string including multiple battery packs20connected together in series. Configuring the battery system14as parallel-connected strings allows the bus10to continue operating with one or more strings disconnected if a battery pack20in a string fails or experiences a problem. The plurality of battery modules30in each battery pack20, and the plurality of battery cells50in each battery module30, may also be electrically connected together in series or parallel. In some embodiments, some of the battery modules30in a battery pack20may be connected together in series, and the series-connected modules connected together in parallel. Similarly, in some embodiments, a group of battery cells50in each module30may be connected together in series to form multiple series-connected groups of cells50, and these series-connected groups may be connected together in parallel. That is, some or all battery packs20in the battery system14may include both series-connected and parallel-connected battery modules30, and some or all battery modules30in each battery pack20may include both series-connected and parallel-connected battery cells50. Although not a requirement, in some embodiments, each battery pack20of battery system14may be substantially identical (in terms of number of modules30, number of cells50in each module30, how the modules are connected, etc.) to each other.

In general, the battery packs20of the battery system14may be physically arranged in any manner. In some embodiments, the battery packs20may be arranged in a single layer on a common horizontal plane to decrease the height of the battery system14, so that it may be positioned under the floor of the low-floor bus10. For example, the battery packs20may have a height less than or equal to about 7 inches (18 centimeters), to allow the battery system14to be accommodated under the floor of the low-floor bus10. The low height profile of the battery system14may allow the battery system14to be more aerodynamic, and may increase its surface area relative to the number of battery cells to increase heat dissipation and improve temperature regulation. In general, the battery system14may be configured to store any amount of energy. Increasing the amount of energy stored in the battery system14may increase the distance that the bus10can travel between recharges. In some embodiments, the number of battery packs20, battery modules30, and battery cells50, and the chemistry of the battery cells, etc. may such that the total energy capacity of the battery system14may be between about 200-700 KWh.

In general, battery system14may have any number (e.g., 2, 3, 4, 6, 8, 10, etc.) of battery packs20. In some embodiments, the number of battery packs20in the battery system14may be between about 2-6. Each battery pack20may have a protective housing24that encloses the plurality of battery modules30(and other components of the battery pack20) therein. Although the battery pack20ofFIG.2is illustrated as including six battery modules30arranged in two columns, this is only exemplary. In general, any number (4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, etc.) of battery modules30may be provided in a battery pack20, and each battery module30may include any number of battery cells50(100, 200, 300, 400, 500, 600, 800, etc.) arranged in any manner. In some embodiments, the number of battery modules30in each battery pack20may be between about 10-20, and the number of battery cells50housed each battery module30may be between about 400-700. In some embodiments, the battery modules30housed in the housing24of a battery pack20may be separated from each other with dividers (not shown) that provide electrical and thermal insulation. The dividers may protect the other battery modules30if any battery module30fails (e.g., experiences a high temperature event). The dividers may be made of a material that does not oxidize or otherwise become damaged when exposed to electrical arcs and/or high temperatures.

The housing24of each battery pack20may have a box-like structure, and may be shaped to allow the battery modules30of the battery pack20to be arranged in a single layer on a common horizontal plane to decrease the height of the battery pack20. In some embodiments, the housing24may be watertight (e.g., to approximately 1 meter) and have an International Protection (IP)67rating for dust and water resistance. The housing24may be configured to contain any failures (electric arcs, fires, etc.) within the battery pack20in order to prevent damage to other battery packs or other portions of the bus10if a component inside a battery pack fails. In some embodiments, the housing24may be constructed of corrosion and puncture resistant materials. Housing24may include materials, such as, for example, composite materials, Kevlar, stainless steel, aluminum, high strength plastics, etc.

In addition to battery modules30, housing24may also enclose a pack controller26that monitors the operation of the battery modules30and a cooling system28that assists in cooling the battery modules30of the battery pack20. The pack controller26may monitor the state (humidity, state of charge, current, temperature, etc.) of the battery modules30and the battery cells50in the battery pack20, and control (alone or in cooperation with the other controllers of battery system14) the operations of the battery pack20to ensure that power is safely and efficiently directed into and out of the battery pack20. The cooling system28may include components that circulate cooling air and/or a liquid coolant to the modules30. These components may include known components (such as, for e.g., circulating fans, coolant conduits, heat exchangers, etc.) that assist in circulating air and/or a coolant through the modules30packaged in the housing24to remove heat from the battery pack20.

Battery system14may include a battery management system (BMS60) that cooperates with the pack controller26(and other controllers) to control the operation of the battery system14. The BMS60may include circuit boards, electronic components, sensors, and controllers that monitor the performance of the components (e.g., packs20, modules30, and cells50) of the battery system14based on sensor input (e.g., voltage, current, temperature, humidity, etc.), provide feedback (alarms, alerts, etc.), and control the operation of the battery system14for safe and efficient operation of the bus10. In some embodiments, the BMS60may perform charge balancing between different cells50of a pack20during recharging. BMS60may also thermally and/or electrically isolate sections (cells, modules, packs, etc.) of the battery system14when one or more sensor readings (temperature, etc.) exceed a threshold value. As will be described in more detail later, in some embodiments, BMS60may initiate or control energy discharge from all or selected cells50of one or more modules30in response to predefined trigger events. An exemplary BMS60that may be used in battery system14are described in commonly-assigned U.S. Patent Application Publication No. US 2012/0105001 A1, which is incorporated by reference in its entirety herein.

FIG.3is a schematic illustration of an exemplary battery module30of a battery pack20. The battery module30includes a casing32that encloses the plurality of battery cells50of the module30therein. Similar to housing24of battery pack20, casing32may be configured to contain any failures (electric arcs, fires, etc.) of the cells50of the module30within the casing32in order to prevent the damage from spreading to other modules30of the battery pack20. Casing32may be made of any material suitable for this purpose. In some embodiments, the casing32may be constructed of one or more of materials such as, for example, Kevlar, aluminum, stainless steel, composites, etc. In some embodiments, the casing32may be substantially air-tight to hermetically seal the cells50of the module30therein.

In general, the cells50may have any shape and structure (cylindrical cell, prismatic cell, pouch cell, etc.). Typically, all the cells50of a module30may have the same shape. However, it is also contemplated that different shaped cells may be packed together in the casing32of a module30. In addition to the cells50, the casing32may also include sensors (e.g., temperature sensor, voltage sensor, humidity sensor, etc.) and controllers (e.g., a module controller38) that monitor and control the operation of the cells50. Although not illustrated, casing32also includes electrical circuits (voltage and current sense lines, low voltage lines, high voltage lines, etc.), and related accessories (fuses, switches, etc.), that direct electrical current to and from the cells50during recharging and discharging.

As explained previously, the cells50of module30may be electrically connected together in any manner (parallel, series, or groups of series-connected cells connected together in parallel). These cells50may also be physically arranged in any manner. In some embodiments, cells50of a module30may be packed together tightly to fill the available volume within the casing32. In some embodiments, the cells50may be arranged together to form multiple groups (e.g., bricks) of cells electrically connected together in series. The multiple bricks (each comprising multiple cells50electrically connected together) may then be electrically connected together (e.g., in series or parallel) and packaged together in the casing32. In some embodiments, one or more sensors may be associated with each brick of the module30. Terminals (e.g., positive and negative terminals) electrically connected to the cells50of the module30may be provided on an external surface of the casing32.

The casing32may also include a coolant loop40configured to circulate a coolant through the module30. The coolant loop40may comprise fluid conduits arranged to pass through, or meander (e.g., zigzag) through, the volume enclosed by the casing32. An inlet port34and an outlet port36of the casing32fluidly couples the cooling loop40to a coolant circuit of the battery system14. The coolant enters the cooling loop40through the inlet port34and exits the casing32through the outlet port36. In embodiments, where the module30is air cooled, the casing32may also include inlet and outlet vents configured to direct cooling air into and out of the casing32. In some embodiments, the coolant may cool all the modules30of a battery pack20before exiting the battery pack20. That is, the cooling loops40of the modules30of pack20may be connected in series such that the coolant exiting one module30enters the cooling loop40of another module30. In some embodiments, coolant may be directed into each module30individually (for e.g., from a common coolant gallery of the pack20). It is also contemplated that, in some embodiments, groups of modules30within a pack20may be fluidly connected in series and multiple series-connected modules30may be connected together in parallel.

During operation of the battery system14, the cells50of the module30release heat. This released heat may be transferred to the coolant circulating through the coolant loop40and then removed from the casing32along with the coolant. In general, any known fluid may be used as the coolant. In some embodiments, water (with suitable additives such as antifreeze, etc.) or another suitable liquid may be used as the coolant. The cells50of the module30may be arranged to enhance heat dissipation into the coolant circulating through the module30. For example, in some embodiments, the cells50may abut the surface of the coolant loop40. In some embodiments, the cells50may be placed in contact with metal plates that serve as heat conducting pathways to the cooling loop. It is also contemplated that, in some embodiments, portions of the cells50may be placed in contact with coolant in the cooling loop40.

Module30may also include one or more heaters70positioned within the casing32. In general, any type of heating device (resistance heater, positive temperature coefficient (PTC) heater, etc.) may be used as heater70. In some embodiments, the heater70may be a PTC cartridge heater. Unlike a resistance heater which generates heat at a constant rate, a PTC heater uses ceramic PTC chips which generate heat at a lower rate at higher temperatures. Therefore, a PTC heater is self-regulating and operates at a lower temperature than a resistance heater. Consequently, a PTC heater may be safer for use in battery system14than a resistance heater.

In some embodiments, the heater70(or the multiple heaters) of each module30is powered solely by the cells50of that module30. In some embodiments, the heater70may be connected to voltage sense leads that electrically connect every cell50in the module30to its module controller38. The heater70may be activated by the module controller38and/or by another controller (e.g., pack controller26, BMS60, etc.) of the battery system14. When the heater70is activated, it generates heat using the energy stored in the cells50of that module30. Consequently, the stored energy (or state of charge (SOC)) of the cells50in the module30decrease as a result of activation of the heater70. The heat dissipated by the heater70may be removed from the module30by the circulating coolant (or by conduction). A temperature sensor (or thermistor) of the module30may monitor the heat dissipated by the heater70.

The heater70may be positioned at any location within the casing32. In general, the location of the heater70may be selected such that the maximum energy discharged by the heater70does not damage (or jeopardize the safety of) the battery cells50of the module30. Therefore, in some embodiments, the heater70may be spaced away from (i.e., not directly in contact with) the cells50. The location of the heater70may be also selected such that the dissipated heat can be easily transferred to the body of the battery pack20(thus allowing the heater to dissipate more heat without a resulting increase in temperature). Therefore, in some embodiments, the heater70may be positioned in direct contact with the metal frame of the battery pack20to enhance heat conduction. In some embodiments, the heater70may be positioned close to (as illustrated inFIG.3) the cooling loop40of the module30so that the dissipated heat may be easily transferred to the coolant circulating through the cooling loop40. It is also contemplated that, in some embodiments, the heater70may be positioned within the cooling loop40(i.e., submerged in the coolant of the cooling loop40). In some embodiments, as illustrated inFIG.3, the heater70may be positioned about midway of the cooling loop40in a module30. That is, the heater70may be positioned proximate to (on within) the cooling loop40, and substantially equidistant from the inlet port34and the outlet port36.

Although a single heater70is illustrated inFIG.3, in some embodiments, multiple heaters (similar to heater70) may be positioned within the casing32of each module30. Each of these multiple heaters70will be powered the cells50of that module30so that activating these multiple heaters70will discharge energy from all the cells50at a faster rate as compared to a case when a single heater is used. In some embodiments, a first group of cells50of the module30(e.g., a brick) may power a first heater70, and a second group of cells50of the module30may power a second heater70. In such an embodiment, activating the first heater will selectively discharge energy from the first group of cells, and activating the second heater will selectively discharge energy from the second group of cells. The multiple heaters70may be positioned adjacent to each other or spaced apart from each other in the casing32. In some embodiments, the multiple heaters70may be positioned such that desired regions of the module30can be selectively discharged by activating different heaters.

As explained previously, the heater70may be activated by BMS60alone or in cooperation with the module controller38and/or the pack controller26. In some embodiments, BMS60may simultaneously activate the heaters70embedded in (inserted in, positioned in, included in, etc.) each battery module30of the battery system14to discharge energy from the cells50of every module30, and thereby, reduce the SOC of the entire battery system14. In some embodiments, BMS60may selectively activate the heaters70embedded in selected battery modules30to preferentially discharge energy from (and thereby reduce the SOC of) the selected modules30. For example, if sensors detect that one module30of a battery pack20includes a damaged cell50, the BMS60may selectively activate the heaters70embedded in all the other battery modules30of the battery pack (i.e., except the module30with the damaged battery cell50) to safely decrease the SOC of the battery pack20. In embodiments where multiple heaters70are embedded in a module30, the BMS60may also be configured to selectively activate some heaters70of the module30to preferentially discharge energy from selected cells50(e.g., bricks) of the module30.

BMS60may activate the heaters70embedded in the modules30to discharge energy from (and thus decrease the SOC of) the battery system14of a stranded (or otherwise incapacitated) bus10before service personnel operates on (repairs, removes the batteries from, etc.) the bus10. The battery system14of the bus10stores a relatively large amount of energy (e.g., between about 200-700 KWh). Operating on a bus10with such a large amount of stored energy may involve inherent safety risks to humans. Dissipating the stored energy from the battery system14by activating the heaters70lowers the SOC of the battery system14to level that is low enough for the personnel to safely operate on the bus10. After the SOC of the battery system14has been lowered to a suitable level, the heaters70may be deactivated. Although the discussion above describes embedding a heater70in a module30of a battery pack20, this is only exemplary. In general, any electric load may be embedded in a module30to selectively dissipate energy from the cells of the module30

In general, the heat produced by the heaters70may be dissipated from the battery system14by conduction, convection, or radiation. In general, the heaters70are positioned in the modules30such that the heat produced by them can be safely removed without overheating the cells50of the module30. In some embodiments, the heat produced by the heaters70of a module30may be used to increase the temperature of the battery cells50of the module30. For example, cold battery cells50may be heated using the hot coolant during winter. In some such embodiments, the coolant in the cooling loop40(of a module30) may be heated by the heat dissipated by the heater70of the module30, and the warm coolant may then be used to heat the cells50on its way out of the module30.

In some embodiments, the inlet port34and/or the outlet port36of the cooling loop40may be selectively opened and closed (e.g., using adjustable valves) by the BMS60, based on sensor readings (humidity, temperature, etc.) from within the module30. The BMS60may use these adjustable valves to redirect the coolant flow within the battery system14based on the local conditions within the modules30. In some such embodiments, one or both of these ports34,36may be closed by the BMS60when the temperature within the module30is at or below a threshold value and opened when the temperature is above the threshold value. When the ports34,36of a module30are closed, the warmed coolant in the cooling loop40may heat the cells50of the module30to a higher temperature relatively quickly. Operating the battery system14using warm battery cells50allows it to charge and discharge at higher power levels, thus improving performance.

The implementation of a heater70in every module30of the battery system14(as opposed to providing a coolant heater external to the battery system14) enables the battery cells50of the battery system14to be heated more quickly and efficiently. Further, locating the heater70to be substantially in the middle of the coolant loop40enables the heat dissipated by the heater70to be distributed throughout the coolant loop which will result in improved heating performance in a short amount of time.

The BMS60(and/or other controllers of battery system14) may selectively activate the heaters70of a module30in response to any triggering event. In some embodiments, the triggering event may include input from a human operator or one or more sensors of the bus10. For example, non-limiting examples of a triggering event may include: a signal from a source outside the bus10(e.g., a wireless signal from service personnel, rescue personnel, central location, etc. responding to an incapacitated bus); input from one or more sensors that indicate an incapacitated bus (e.g., a button activated by the driver, airbag sensor, collision sensor, etc.); input from one or more sensors that indicate conditions of the battery system14(e.g., sensors that indicate that the SOC of the battery system14is above a threshold SOC value, sensors that indicate that the temperature of the cells of a module30is above/below a threshold temperature value, sensors that indicate that one or cells50in a module30are damaged, etc.); and a signal from the driver. In some embodiments, the driver of the bus10may trigger the BMS60to activate the heaters70(some or all) by pressing a button on the bus10. In some embodiments, personnel responding to an incapacitated bus may wirelessly trigger the BMS60using a signaling device (smart phone, etc.) to activate the heater70.

In response to the triggering signal, the BMS60may selectively activate one or more of the heaters70embedded in selected modules30(i.e., all or some of the modules30). For example, if sensor readings indicate that one or more battery cells50of a module30may be defective, upon receiving a signal from personnel to decrease the SOC of the battery system14, the BMS60may selectively activate the heaters70embedded in all the modules30, except the module30with the defective battery cells50, to safely decrease the SOC of the battery system14. The heaters70may be deactivated when the SOC of the battery system14is less than or equal to the threshold SOC value (or when the battery temperature is greater than or equal to a threshold temperature value). In general, the rate of energy discharge by the heaters70may be based on the capacity of the heaters70. In some embodiments, the BMS60(or personnel) may select the rate of energy discharge (for e.g., by selecting the number of heaters70to activate in a module30, selecting the voltage or current directed to the heater70, etc.). In some embodiments, the BMS60may also selectively activate the heaters70embedded in a desired region of a module30(e.g., a heater electrically connected to a brick of cells50in a module30) as opposed to other regions, to selectively discharge energy from the these desired regions of the module30.

Exemplary applications of the heaters70of the battery system14will now be described. In some cases, service personnel responding to a disabled bus10(incapacitated, damaged, stranded, etc.) may decide to remove the battery packs20from the bus10, before working on the bus10. If the SOC of the battery system14is too high (e.g., above a threshold value), the service personnel may decide to reduce the SOC of the battery packs20before removing the battery packs20from the disabled bus10.FIG.4Ais a flow chart that illustrates an exemplary method100used by the service personnel to reduce the SOC of the battery system14. The service personnel may send a triggering signal to the BMS60to reduce the SOC of the battery packs20(step110). In general, the triggering signal may be send to the BMS60by any method. In some embodiments, the service personnel may use a diagnostic computer connected to the electrical network of the bus10to access and send the triggering signal to the BMS60.

Upon receipt of the triggering signal, the BMS60activates the heaters70of selected battery modules30to reduce the SOC of the battery system14(step120). That is, the BMS60selectively activates discharge of energy of the modules30of the battery system14. For example, if the BMS60knows (e.g., based on readings from humidity sensors embedded in a battery module30) that a battery cell50of a battery module30is defective (e.g., degassing), upon receipt of the triggering signal (i.e., step110), in step120, the BMS may selectively activate the heaters60embedded in all the battery modules30except the battery module30with the defective cell. Since a heater70embedded in a module30is powered solely by the battery cells50of that module30, activation of the heater70will reduce the energy stored in that module30. The BMS60then checks to determine if the SOC of the battery system14is less than or equal to a threshold SOC value (step130). The threshold SOC value may be a value of SOC that is low enough for human operators to operate on the battery system14. If the SOC≤the threshold SOC value, (i.e., step130=Y), the BMS60deactivates the heaters70(step140). If it is not (i.e., step130=N) the heaters70are kept active until the state of charge decreases below the threshold SOC value. In some embodiments, the energy discharge from the modules30may be continued until the modules30are substantially completely drained.

FIG.4Billustrates an exemplary method200of operating the heaters70to increase the temperature of the battery system14. When sensor inputs indicate that the temperature of the battery system14is below a threshold temperature value (step210), the BMS60selectively activates the heaters70(step220). As explained with reference toFIG.4A, selective activation includes activating only the heaters70embedded in desired (some or all) battery modules30without activating the heaters70embedded in other battery modules30. The heat dissipated from a heater70embedded in a battery module30increases the temperature of the battery cells50of that battery module30. The heaters70may remain active as long as the battery temperature is below the threshold temperature value (step230=Y). When the temperature is greater than or equal to the temperature threshold (step230=N), the heaters70may be deactivated (step240).

While principles of the present disclosure are described herein with reference to the battery system of an electric bus, it should be understood that the disclosure is not limited thereto. Rather, the systems described herein may be employed in the batteries of any application. Also, those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, embodiments, and substitution of equivalents all fall within the scope of the embodiments described herein. Accordingly, the disclosure is not to be considered as limited by the foregoing description. For example, while certain features have been described in connection with various embodiments, it is to be understood that any feature described in conjunction with any embodiment disclosed herein may be used with any other embodiment disclosed herein.