ENERGY STORAGE SYSTEM

There is disclosed an energy storage system for an electric aircraft, the energy storage system comprising: at least one battery pack configured to be disposed onboard the aircraft, and a thermal management system. The thermal management system comprises a first circulation loop configured to be disposed onboard the aircraft and configured to contain a first working fluid, the first circulation loop including: a variable speed pump configured to pump the first working fluid around the first circulation loop, a battery heat exchanger configured to provide a thermal interface between the at least one battery pack and the first working fluid, and a controller configured to control operation of the variable speed pump to intermittently pump the first working fluid to distribute heat around the thermal management system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This specification is based upon and claims the benefit of priority from United Kingdom Patent Application No. 2311302.0, filed on 24 Jul. 2023, the entire contents of which are incorporated herein by reference.

BACKGROUND

Technical Field

The present invention relates to an energy storage system for an electric aircraft, and an electric aircraft.

Description of the Related Art

Interest in aircraft with electric and hybrid electric propulsion systems is increasing because of the need to reduce carbon emissions and pollution, and because of developments in the facilitating electrical technologies. Hybrid electric propulsion systems include both internal combustion engines, for example gas turbines or diesel engines, and energy storage, typically in the form of batteries. Purely electric propulsion systems completely dispense with internal combustion engines and use only batteries or, in some instances, fuel cells, as an energy source for their propulsors.

The terms Advanced Air Mobility (AAM) and Urban Air Mobility (UAM) refer to the use of aircraft—typically electric and hybrid electric aircraft—to transport passengers relatively short distances, for example tens or perhaps hundreds of kilometres. Most proposed AAM platforms have Vertical Take-Off and Landing (VTOL) or Short Take-Off and Landing (STOL) capabilities so that the aircraft can take-off and land at locations convenient for passengers, for example at so-called ‘vertiports’ close to or in urban environments. It is expected that the number of passengers carried by AAM platforms will be relatively small—likely fewer than twenty and typically of the order of five to ten.

It is desirable to reduce the weight and cost and improve an efficiency of an electric or hybrid aircraft. Thermal management system (TMS) solutions circulate coolant through battery packs on an electric aircraft to cool the battery packs.

SUMMARY

According to a first aspect, there is provided an energy storage system for an electric aircraft, the energy storage system comprising:at least one battery pack configured to be disposed onboard the aircraft, anda thermal management system, the thermal management system comprising:a first circulation loop configured to be disposed onboard the aircraft and configured to contain a first working fluid, the first circulation loop including:a variable speed pump configured to pump the first working fluid around the first circulation loop,a battery heat exchanger configured to provide a thermal interface between the at least one battery pack and the first working fluid, anda controller configured to control operation of the variable speed pump to intermittently pump the first working fluid to distribute heat around the thermal management system.

The variable speed pump may include any type of pump which can vary the flow rate of fluid.

It may be that the first circulation loop comprises a manifold configured to enable direction of flow of the first working fluid to be reversed within the first circulation loop when the variable speed pump is powered off or stopped, so that the first working fluid flows in the reverse direction when the variable speed pump is subsequently powered on.

Alternatively, the pump may be configured to reverse the direction of flow so that it can be operated to pump fluid in a first direction, and in a second direction opposing the first direction.

It may be that the battery heat exchanger is a plate heat exchanger.

It may be that the variable speed pump is configured to control the flow rate of the first working fluid based on an expected battery thermal load corresponding to operation of the electric aircraft.

For example, when the aircraft is taking off, in an initial climb phase, descending, in a final approach phase, or landing, the expected battery thermal load may be relatively high, such that the variable speed pump may be controlled to increase the flow rate of the first working fluid during these operations. When the aircraft is in cruise, the expected battery thermal load may be relatively low, such that the variable speed pump may be controlled to decrease the flow rate of the first working fluid during this operation. The energy storage system may be configured to maintain an optimal thermal environment of the battery cells. Expected battery thermal load may also be impacted by ambient temperature, on the ground or in the air, such that the variable speed pump may be configured to control the flow rate of the first working fluid based on ambient temperature. For example, in a cold ambient environment (e.g., −40-5 degrees Celsius) the variable speed pump may be configured to control the first working fluid at a relatively low flow rate to warm the cells gradually, and optionally the frequency of the flow reversal may be lower than in a hot environment (e.g., 35-60 degrees Celsius) where the variable speed pump may be configured to control the first working fluid at a higher flow rate to remove excess heat and optionally there may be a high frequency of flow reversal to reduce thermal gradient in the battery.

It may be that the controller is configured to receive signals indicating a battery thermal load, and wherein the controller is configured to control the variable speed pump to vary the flow rate of first working fluid according to a predefined relationship with the battery thermal load.

Signals indicating a battery thermal load may be signals from a temperature sensor indicative of the temperature of the respective battery pack or may be signals indicating expected battery thermal load based on use of the energy storage system, for example in an aircraft, such as a high battery thermal load mode corresponding at least to the aircraft taking off, in an initial climb phase, descending, in a final approach phase, or landing, or a low battery thermal load mode corresponding at least to the aircraft being in cruise or on the ground. In other examples, the battery electrical load may be indicative of an expected battery thermal load, such that signals indicating the battery electrical load may be used as signals indicative of an expected battery thermal load.

It may be that the at least one battery pack comprises a plurality of battery packs, the first circulation loop configured to deliver the first working fluid to a corresponding plurality of parallel lines, wherein a battery heat exchanger is disposed on each of the lines and configured to provide a thermal interface between a respective battery pack and the first working fluid in the line. It may be that the thermal management system comprises a respective temperature sensor for each battery pack, each temperature sensor configured to output a temperature signal indicative of the temperature of the respective battery pack. It may be that a proportional control valve is disposed on each parallel line to independently control mass flow rate of the first working fluid to each battery heat exchanger based on the determined temperature.

The temperature sensor may be disposed on the battery pack to measure the temperature of the battery pack directly, or may be disposed upstream and downstream of the respective battery pack to measure a differential temperature of the first working fluid across the battery pack. The temperature sensor may be in the form of a surface thermistor, to measure the surface temperature of pipework, rather than directly measuring the fluid temperature.

It may be that the energy storage system further comprises a fault detection module configured to detect fluid leaking into any one of the plurality of battery packs, wherein the proportional control valve is configured to cut-off flow to the respective line at which the leak is detected.

In some examples, a leak may be detected based on monitoring a level of working fluid in a header tank over time. In other examples, a leak may be detected with sensors, such as a fluid pressure sensor or flow sensors in each parallel line, or conductivity sensors disposed inside a sealed enclosure of each of the battery packs, which may indicate pooling of moisture or coolant. If the energy storage system is configured to reverse the flow direction of the first working fluid, a proportional control valve May be disposed on either side of each battery pack on each parallel line to control the flow and cut-off through the respective line.

It may be that the at least one battery pack includes a film panel electrical resistive heating pad configured to heat the battery pack when the temperature signal indicates that the temperature of the battery pack is below a predetermined value.

The predetermined value may be based on a charging state of the batteries in the battery pack. If the batteries are charging, the predetermined value may be set to 15 degrees Celsius. If the batteries are discharging, the predetermined value may be set to 10 degrees Celsius.

It may be that the thermal management system further comprises a second circulation loop configured to be disposed offboard the aircraft. It may be that the first circulation loop comprises at least one first connector, and the second circulation loop comprises at least one second connector, the at least one first connector being configured to be coupled to the at least one second connector, so that the first working fluid is permitted to flow30between the first circulation loop and the second circulation loop, wherein the second circulation loop comprises a cooling heat exchanger configured to cool the first working fluid in the second circulation loop.

Alternatively, the second circulation loop may comprise a replacement first working fluid to replace the first working fluid in the first circulation loop. The replacement first working fluid may be at an optimum temperature for the battery packs.

It may be that the at least one first connector and the at least one second connector are dry break connectors.

It may be that the at least one first connector comprises at least two first connectors and wherein the at least one second connector comprises at least two second connectors. It may be that at least one of the first connectors and/or at least one of the second connectors comprise check valves.

It may be that the energy storage system further comprises a third circulation loop configured to be disposed offboard the aircraft and configured to contain a second working fluid, the third circulation loop including a heat-pump configured to pump heat to or from the second working fluid. It may be that the cooling heat exchanger is configured to transfer heat between the first working fluid and the second working fluid.

The second circulation loop may be an open loop which is closed only on connection with the first circulation loop, or it may be a closed loop which allows circulation of fluid through the second circulation loop even when it is not connected to the first circulation loop. This allows flow of fluid through the second circulation loop to maintain thermal stability of the off-board (i.e., on-ground) system.

According to a second aspect, there is provided an electric aircraft with the energy storage system of the first aspect.

It may be that the electric aircraft further comprises a cabin air conditioning system onboard the aircraft, the air conditioning system comprising a compressor, a condenser, an expansion valve, and an evaporator, and configured to condition cabin air, wherein the air conditioning system comprises a refrigerant and the first circulation loop includes a conditioning heat exchanger configured to provide a thermal interface at the evaporator between the first working fluid and the refrigerant.

It may be that the controller is configured to receive signals indicating whether the aircraft is in a high battery thermal load mode or a low battery thermal load mode, the high battery thermal load mode corresponding to operations in which the aircraft is taking off, in an initial climb phase, descending, in a final approach phase, or landing, and the low battery thermal load mode corresponding to operations in which the aircraft is in cruise, and controlling the variable speed pump to have a first speed when it is determined that the aircraft is in a high battery thermal load mode, and controlling the variable speed pump to have a second speed when it is determined that the aircraft is in a low battery thermal load mode, wherein the first speed is higher than the second speed.

According to a third aspect, there is provided a method for controlling the electric aircraft, comprising:determining whether the aircraft is in a high battery thermal load mode corresponding at least to the aircraft taking off, in an initial climb phase, descending, in a final approach phase, or landing, or whether the aircraft is in a low battery thermal load mode corresponding at least to the aircraft being in cruise,operating the variable speed pump at a first speed when it is determined that the aircraft is in a high battery thermal load mode, andoperating the variable speed pump at a second speed when it is determined that the aircraft is in a low battery thermal load mode, wherein the first speed is higher than the second speed.

The method may include, after operating the variable speed pump at a first speed in response to determining that the aircraft is in a high battery thermal load mode:determining that the aircraft is in a low battery thermal load mode,stopping the variable speed pump,manipulating a manifold to enable a reversed flow of the first working fluid around the first circulation loop; andrestarting the variable speed pump at the second speed, so that the direction of flow is reversed to reduce a temperature differential across the battery pack.

DETAILED DESCRIPTION

Referring toFIG.1, the propulsion system of a hybrid electric aircraft is generally indicated at200and incorporates both an engine210, such as a gas turbine engine, and a battery230. Both the engine210and the battery230are used as energy sources to power a motor-driven propeller216, as well as ancillary electrical systems (not shown). The propulsion system200of the hybrid electric aircraft will typically further comprise a generator211, an AC/DC converter212, a high voltage DC (HVDC) distribution bus213, a DC/AC inverter214, a motor215that drives the propeller216, and a DC/DC converter217.

A shaft of the engine210is coupled to and drives the rotation of a shaft of the generator211which thereby produces alternating current. The AC/DC converter212, which faces the generator211, converts the alternating current into direct current which is fed to various electrical systems via the HVDC distribution bus213. These electrical systems include the motor215that drives the propeller216. The motor215will typically be a synchronous motor that interfaces with the HVDC distribution bus213via the DC/AC inverter214.

The battery230, which may be made up of a number of lithium ion battery modules connected in series and/or parallel, is connected to the HVDC distribution bus213via the DC/DC converter217. The DC/DC converter217converts between a voltage of the battery230and a voltage of the HVDC distribution bus213. In this way, the battery230can replace or supplement the power provided by the engine210(by discharging and thereby feeding the HVDC distribution bus213) or can be charged using the power provided by the engine210(by being fed by the HVDC distribution bus213).

A battery will also appear in the propulsion system of a purely electric aircraft, generally indicated as300inFIG.2. The battery330feeds a HVDC distribution bus313, possibly via DC/DC converter (not shown), which delivers power to one or more synchronous motors315via a DC/AC inverter314. The one or more motors315drive the one or more propellers316that propel that aircraft. It is noted that a plurality of batteries may feed into the at least one motor315, such that separate windings of the at least one motor315may be powered by different batteries.

FIG.3shows an electric aircraft101which may be a hybrid aircraft or a purely electric aircraft, comprising a battery pack40. The battery pack40may comprise at least one battery230or330. There may be a plurality of battery packs40, each battery back comprising at least one battery230or330.

FIG.4aandFIG.4b(collectivelyFIG.4) shows a first example energy storage system400which may be used in the electric aircraft101shown inFIG.3. The energy storage system400in this example comprises two battery packs40a-40b. The battery packs40in this example are configured to be disposed onboard the aircraft. Each battery pack40a-40bcomprises a plurality of batteries402. It is noted that the figures are purely schematic and that each of the battery packs40a-40bmay comprise any suitable number of batteries402. It is further noted that the energy storage system400is not limited to comprising two battery packs40a-40band may comprise any suitable number of battery packs40, such as only a single battery pack40or a plurality of battery packs40.

The energy storage system400comprises a thermal management system410. The thermal management system410comprises a first circulation loop420, which is configured to be disposed on the aircraft101, and which is configured to contain a first working fluid. The first working fluid may be selected to provide thermal heat transfer properties, protection against freezing, protecting metals in the system against corrosion, inhibiting foam formation, cavitation and precipitation. The first working fluid may have a high flash point and/or be flame retardant, and it may be non-conductive.

The first circulation loop420comprises a pump422which is configured to pump the first working fluid around the first circulation loop420. In this example, the pump422is a variable speed pump, and can therefore control the flow rate of the first working fluid. The arrows on the figures represent a general direction of fluid flow, with the arrows inFIG.4ashowing circulation of the first working fluid in a generally clockwise direction, while the arrows inFIG.4bshow circulation of the first working fluid in a generally anticlockwise direction (i.e., an opposite or reversed direction of flow toFIG.4a).

The pump may comprise a strainer filter configured to prevent debris from entering the pump. The mesh size for the strainer filter may be 100-500 microns.

The thermal management system410comprises a battery heat exchanger404for each battery pack40a-40b. Therefore, in this example, there are two battery heat exchanger404. In other examples, with more or fewer battery packs, there may be correspondingly more or fewer battery heat exchangers. The battery heat exchangers404in this example are plate heat exchangers. In other examples, the battery heat exchangers may be any suitable type of heat exchanger, such as shell-and-tube, finned-tube, etc. Each battery heat exchanger404is configured to provide a thermal interface between the respective battery pack40a-40band the first working fluid which is circulated through the battery heat exchanger404. In some examples, the batteries402may abut or otherwise be in direct physical contact with a surface of a corresponding battery plate heat exchanger404, or the batteries may be arranged in any suitable configuration about a corresponding battery heat exchanger.

Each battery heat exchanger404comprises one or more openings. In this example, each battery heat exchanger404comprises a first opening424(which acts as an inlet inFIG.4aand an outlet inFIG.4b) and a second opening426(which acts as an outlet inFIG.4aand an inlet inFIG.4b). The one or more openings may permit fluid to flow into or out from the battery heat exchanger404.

The first circulation loop420, in this example, comprises two parallel lines428, each parallel line having a respective battery pack40disposed on it, and being configured to deliver working fluid to each of the battery heat exchangers404in parallel. The lines428connect each of the battery heat exchanger404to a loop so that the first circulation loop420is configured to deliver the first working fluid to the parallel lines428and to the respective battery heat exchangers404, by operating the pump422. In other words, each line428comprises a delivery line and a discharge line, which may change dependent on the direction of fluid flow through the first circulation loop420. As shown inFIGS.4aand4b, each line428is coupled to a respective first opening424and second opening426of the respective battery heat exchanger404. In other examples, the lines428may be arranged in series so that the first working fluid is configured to pass through each of the battery heat exchangers404consecutively. Having the lines in parallel ensures that each of the battery heat exchangers404is exposed to first working fluid at a similar temperature, to achieve even heat exchange across multiple battery packs40. In series, a battery heat exchanger downstream will be likely to receive the first working fluid at a significantly different temperature than an upstream battery heat exchanger, such that heat distribution will not be equal across the battery packs40.

Operation of the pump422is controlled with a controller430. The controller430may control the pump422to intermittently pump the first working fluid through the first circulation loop420to distribute heat around the thermal management system. The pump422may be configured to control the flow rate of the first working fluid based on an expected thermal load of the battery packs40a,40b.The expected battery thermal load may correspond to an operation of the electric aircraft101. For example, when the aircraft (e.g., the electric aircraft101ofFIG.3) is taking off, in an initial climb phase, descending, in a final approach phase, or landing, the expected battery thermal load may be relatively high, such that the variable speed pump630may be controlled to increase the flow rate of the first working fluid during these operations. When the aircraft (e.g., the electric aircraft101) is in cruise, the expected battery thermal load may be relatively low, such that the variable speed pump422may be controlled to decrease the flow rate of the first working fluid during this operation. Expected battery thermal load may also be impacted by ambient temperature, on the ground or in the air. The variable speed pump422may be configured to control the flow rate of the first working fluid based on ambient temperature. For example, in a cold ambient environment (e.g., −40 to 5 degrees Celsius) the variable speed pump422may be configured to control the first working fluid at a relatively low flow rate. The relatively low flow rate at which the variable speed pump422pumps the first working fluid may be in the range of 0-3 L/min (litres per minute). The relatively low flow rate at which the variable speed pump422pumps the first working fluid may be any suitable range. This range may be increased up to 6 L/min, for example, when operation of the pump is intermittent. The batteries330may therefore be warmed gradually. In a hot environment (e.g., 35 to 60 degrees Celsius) the variable speed pump630may be configured to pump the first working fluid at a higher flow rate to remove excess heat from the batteries330. The relatively high flow rate at which the variable speed pump422pumps the first working fluid may be in the range of 3 L/min-20 L/min. The relatively high flow rate at which the variable speed pump422pumps the first working fluid may be any suitable range. A signal indicating the expected battery load may be received by the controller430and the controller430may thereby control the flow rate of fluid by controlling the pump422, for example, according to a predefined relationship with the battery thermal load. The energy storage system400may thereby be configured to maintain an optimal thermal environment of the batteries402. Expected battery thermal load may also be impacted by a charging rate of the batteries402in the battery packs40a,40b.For example, the thermal load of the batteries402at higher charging rates may be high relative to the thermal load of the batteries402at lower charging rates. The variable speed pump422may therefore be configured to control the flow rate of the first working fluid based on a charging rate of the batteries402in the battery packs. The variable speed pump422may be configured to increase the flow rate of the first working fluid as the charging rate of the batteries402in the battery packs40a,40bincreases.

In other examples, the pump422may be configured to control the flow rate of the first working fluid through the first circulation loop420based on an actual thermal load of the battery packs40a,40b.For example, the thermal management system410in this example comprises a temperature sensor432disposed on each of the battery packs40a-40bto measure the temperature of the battery packs directly. In other examples, a temperature sensor may be disposed on at least one of the lines428, such as on the delivery line and/or the discharge line of a respective battery heat exchanger404(i.e., upstream and/or downstream of the respective battery pack). When a temperature sensor is disposed both upstream and downstream of the battery pack, a difference in temperature of the first working fluid across a battery pack40(e.g., a temperature difference between the inlet and the outlet of a battery pack40) may be determined, and the temperature differential is indicative of the battery thermal load. The temperature sensor432may be in the form of a surface thermistor, to measure the surface temperature of pipework, rather than directly measuring the fluid temperature. The temperature sensor432may alternatively be any suitable sensor. The temperature sensor432may alternatively be immersed in the working fluid or be substantially adjacent to a surface of the working fluid. The temperature sensors432may therefore transmit signals indicating an actual battery thermal load to the controller430, and the controller430may be configured to control the pump422based on these signals, for example based on a predefined relationship with the battery thermal load.

It should be noted that althoughFIGS.4aand4bshow only one pump422, there may be more than one pump. The one or more pumps may be in series or in parallel. At least one of the one or more pumps may be a variable speed pump.

In this example, a proportional control valve436is disposed on each of the lines428, for example on the line to the first opening424. In other examples, the proportional control valve436may be disposed on the line to the second opening426. In some examples, there may be a valve on each of the delivery line and the discharge line for each line428. In yet other examples, the valves may be directional shut-off valves or a combination of both. In yet further examples, the proportional control valve436may be disposed inside a battery enclosure. The valves436, in this example, are configured to control a mass flow rate of the first working fluid to a corresponding battery heat exchanger404. The valves436may be configured to control a mass flow rate of the first working fluid to a corresponding battery heat exchanger404based on a temperature of the corresponding battery pack40determined by a corresponding temperature sensor (or sensors)432. Additionally or alternatively, the valves436may be configured to control a mass flow rate of the first working fluid to a corresponding battery heat exchanger404based on a signal indicating a battery thermal load or a signal indicating an expected battery thermal load of the corresponding battery pack. The valves436may be controlled automatically by the controller430or manually. The mass flow rate of the first working fluid in each battery pack40a-40bmay therefore be controlled by corresponding valves436disposed on lines428. Thus, if a battery pack40is hot relative to the other battery packs, the valves436may be controlled to restrict or reduce the flow of the first working fluid in the other battery packs, such that a mass flow rate to the relatively hot battery pack40is increased. An improvement in thermal balancing between battery packs40a-40bmay therefore be achieved, in which each battery pack40a-40bmay be maintained at substantially equivalent temperatures. For example, a temperature difference between battery packs40a-40bmay be limited to 5 degrees Celsius.

The valves436may also be configured to cut off flow to a corresponding battery pack40, for example if a leak is detected. A fault detection module, which may be in the controller430, may be configured to detect a leak. In some examples, a leak may be detected based on monitoring a level of working fluid in a header tank465over time. In other examples, a leak may be detected with sensors, for example, a fluid pressure sensor or flow sensors disposed in each parallel line428and/or battery heat exchanger404. Additionally or alternatively, a leak may be detected using conductivity sensors disposed inside a sealed enclosure of each of the battery packs40a-40b,which may indicate pooling of moisture or coolant.

As shown inFIG.4aandFIG.4b, the first circulation loop420may comprises a plurality of manifolds450(only one is given a reference numeral inFIG.4for clarity) which are configured to enable the direction of flow of the first working fluid, particularly through each of the battery heat exchangers404, to be reversed, without requiring the pump422to reverse its pumping direction. In other examples, there may be any suitable arrangement of lines and manifolds which enable the reversal of flow direction through the battery heat exchangers404. In further examples, the thermal management system410may comprise any system that permits flow to be reversed through the battery heat exchangers404, for example with a reversible pump.FIGS.4aand4bshow the manifolds operating to show opposing flow directions through the battery heat exchangers404.

As mentioned above, the pump422may be configured to operate intermittently. As such, the pump422may be configured to stop or power off periodically to conserve energy and reduce noise generation. For example, the pump422may be configured to operate in a cycle in which the pump is ON (i.e., pumps the first working fluid) for two minutes and then is OFF (i.e., stopped or powered off) for three minutes. The pump422may additionally be controlled to automatically turn ON or remain ON in response to a relatively high-power event or a relatively high expected battery thermal load. The pump422may be configured to operate intermittently when the thermal load of the batteries402is relatively low. The pump422may be configured to operate intermittently when the electrical load of the batteries402is relatively low. The pump422may be configured to stop or power off periodically when the aircraft is in cruise. The pump422may additionally or alternatively be configured to stop or power off periodically during battery cell balancing. The pump422may additionally or alternatively be configured to stop or power off periodically when the rate of charging of the batteries402is relatively low (e.g., when the batteries are gradually charged overnight). The frequency at which the pump422powers off when the thermal load or expected thermal load of the batteries is relatively low may be high relative to the frequency at which the pump422powers off when the thermal load or expected thermal load of the batteries is relatively high.

Means for reversing the direction of flow of the first working fluid may therefore be operated when the pump422is powered off.

Reversing the direction of flow of the first working fluid may reduce a temperature difference between the inlet and the outlet of a battery pack40. Consequently, a substantially homogeneous temperature distribution throughout the batteries402of the battery packs40may be achieved. This, in turn, may improve a life expectancy and reduce a likelihood of performance degradation of the batteries402of the battery packs40.

In some examples, at least one of the battery packs40a-40bmay comprise at least one heating element (not shown). The heating element may be a film panel electrical resistive heating pad. The heating element/elements may be configured to heat the batteries330in the battery pack, or to heat the battery pack40. The heating elements may be configured to heat the battery330in the battery pack40when the at least one temperature sensor432senses that the temperature of the battery330is below a threshold. The optimal battery330temperature range may be 10 degrees Celsius to 40 degrees Celsius when the batteries330are discharging and 15 degrees Celsius to 35 degrees Celsius when the batteries are charging. The heating elements may be configured to heat the battery330in the battery pack, if whilst the batteries330are discharging, the at least one temperature sensor432senses that the temperature of the battery330is below 10 degrees Celsius. Additionally, the heating elements may be configured to heat the battery330in the battery pack, if whilst the batteries330are charging, the at least one temperature sensor432senses that that the temperature of the battery330is below 15 degrees Celsius.

With reference toFIG.5, a second example energy storage system500is shown which comprises similar features to the first example energy storage system400, with like numerals representing similar features. In this example, a second example thermal management system510comprises the first circulation loop420which is connected to four battery packs40a-40dof the energy storage system500, and the thermal management system510further comprises a second circulation loop520and a third circulation loop620. The second circulation loop520and the third circulation loop620are configured to be disposed offboard the aircraft (e.g., offboard the aircraft101shown inFIG.3).

In this example, the first circulation loop420comprises two first connectors460, and the second circulation loop520comprises two corresponding second connectors560. The first connectors460are configured to be coupled to the second connectors560so that first working fluid is permitted to flow between the first circulation loop420and the second circulation loop520. The first connectors460and the second connectors560are dry break connectors, in this example. This may reduce a likelihood of air entrapment in the first circulation loop420and the second circulation loop520. In other examples, there may be any suitable number of first connectors and second connectors. For example, one of each connector may be sufficient to allow transfer of fluid between the first and second circulation loops. Further, the first connectors460and/or the second connectors560may comprise directional check valves. Including directional check valves may help with priming the thermal management system510and further reduce a likelihood of air entrapment and fluid loss in the first circulation loop420and the second circulation loop520.

Therefore, when the aircraft101is on the ground, second connectors560of the second circulation loop520may be coupled to first connectors460of the first circulation loop420. First working fluid can then be permitted to flow into the second circulation loop520. The first circulation loop420may comprise guidance valves570configured to facilitate the flow of first working fluid to the first connectors460rather than around the first circulation loop420.

As such, when the aircraft is on the ground, the first working fluid may be pumped by the pump422around the first circulation loop420and around the second circulation loop520. Although not shown, the second circulation loop520may comprise a further pump. In this example, the second circulation loop comprises a cooling heat exchanger580which is configured to cool the first working fluid in the second circulation loop520. In this example, the cooling heat exchanger580is a liquid-liquid heat exchanger which exchanges heat with a second working fluid contained within the third circulation loop620. In other examples, there may not be a third circulation loop, and the cooling heat exchanger may alternatively be a radiator or any other suitable heat exchanger. Heat is thereby transferred between the first working fluid and the second working fluid, or a surrounding environment, when the first working fluid flows through the cooling heat exchanger580. As such, heat absorbed by the first working fluid in the battery packs40a-40dmay be more effectively transferred away from the first working fluid when the first working fluid is pumped through the cooling heat exchanger580. The second circulation loop520may be configured to contain a replacement first working fluid. The replacement first working fluid may be configured to be within the optimum temperature range (e.g., 15 degrees Celsius-20 degrees Celsius) for cooling the batteries in the battery packs40a-40d.Therefore, when the aircraft101is on the ground and the first circulation loop420and the second circulation loop520are connected, the first working fluid in the first circulation loop420may be replaced by the replacement first working fluid, which may result in faster cooling.

In this example, the second circulation loop520comprises a bypass connection590, which comprises bypass valves592on either end. In other examples, there may be only one bypass valve592on only one end. The bypass valves592are configured to control fluid flow through the bypass connection590. The bypass connection590may comprise a pump (not shown) which enables the first working fluid to be circulated in the second circulation loop520without connection to the first circulation loop, through the bypass connection590which closes the second circulation loop. For example, the replacement first working fluid may be circulated around the second circulation loop520whilst the aircraft101is flying. Circulating the replacement first working fluid around the second circulation loop520may improve a thermal stability of the replacement first working fluid by preventing or reducing a proportion of the replacement first working fluid from being or becoming stationary, and it may enable maintaining the replacement fluid at an optimal temperature, ready for replacing the first working fluid in the first circulation loop420. In other examples, there may be no bypass connection or bypass valves, such that the second circulation loop may be an open loop which is closed only on connection with the first circulation loop.

In this example, the third circulation loop620comprises a pump610configured to pump the second working fluid around the third circulation loop620. In this example, the third circulation loop620comprises a heat pump configured to transfer heat to and/or from the second working fluid. The third circulation loop620may however comprise any system for transferring heat to and/or from the second working fluid. In this example, the third circulation loop620comprises a compressor622, a condenser624, an expansion valve626, and the cooling heat exchanger580. The second working fluid flows through the cooling heat exchanger580separately from the first working fluid. The cooling heat exchanger580is therefore configured to transfer heat between the first working fluid and the second working fluid. The cooling heat exchanger580may be a counter flow heat exchanger or a parallel flow heat exchanger.

Although not shown, the cooling heat exchanger580may comprise an internal bypass. The internal bypass of the cooling heat exchanger580may permit working fluid to flow between the second circulation loop520and the third circulation loop620. For example, the second working fluid may be permitted to flow (via the internal bypass) from the third circulation loop620and into the second circulation loop520. If the second circulation loop520does not contain a replacement first working fluid, then the second working fluid may be pumped by the pump610through the internal bypass into the second circulation loop520, around the second circulation loop520via the bypass connection590, and back into the third circulation loop620via the internal bypass.

FIG.6shows a third example energy storage system800comprising a first circulation loop820which is similar to the first circulation loop420of the first energy storage system400and second example energy storage system500with like reference numerals denoting like features, but differs from the first circulation loop420in the first energy storage systems400and second energy storage system500in that the first circulation loop820of the third energy storage system800comprises further features. In this example, an aircraft (e.g., the electric aircraft101ofFIG.3) comprises a cabin air conditioning system700which is disposed onboard the aircraft101. The air conditioning system700may provide heating or cooling to the cabin of the aircraft. In an example, the air conditioning system comprises a refrigerant circulation loop710comprising a compressor720, a condenser730, an expansion valve740, and a conditioning heat exchanger750disposed on the refrigerant circulation loop710. The refrigerant circulation loop710is configured to contain a refrigerant. In this example, a refrigerant pump760is configured to pump the refrigerant around the refrigerant circulation loop710.

In this example, the first circulation loop820further comprises an air conditioning connecting line880, and the conditioning heat exchanger750is disposed on the air conditioning connecting line880. The air conditioning connecting line880therefore permits first working fluid in the first circulation loop820to be pumped through the conditioning heat exchanger750. The conditioning heat exchanger750may be a liquid-liquid heat exchanger. The conditioning heat exchanger750in this example is configured to hydraulically separate the refrigerant from the first working fluid whilst facilitating heat transfer between the fluids. The conditioning heat exchanger750may be a counter flow heat exchanger or a parallel flow heat exchanger. The conditioning heat exchanger750in this example, acts as an evaporator in the air conditioning system, and thus provides a thermal interface at the evaporator between the first working fluid and the refrigerant. In this example, the refrigerant is warmed in the evaporator by heat transferred via the conditioning heat exchanger750from the first working fluid, while the first working fluid is cooled by the heat transfer. The refrigerant in the condenser730may then release the transferred heat to the cabin.

Although the example of the present disclosure shows a conditioning heat exchanger750configured to separate the first working fluid from the refrigerant, it is noted that the cabin air conditioning system700may be directly integrated into the first circulation loop820. In this aspect, the cabin air conditioning system700and the first circulation loop820may comprise a common fluid system in which the first working fluid may be pumped into the cabin air conditioning system700. This may improve an energy efficiency of the aircraft.

With reference toFIG.7, the present disclosure also relates to a method900of controlling an electric aircraft comprising any example energy management system400,500,800. In block910, the method comprises determining whether the aircraft is in a high battery thermal load or a low battery thermal load mode. The high battery thermal load mode may correspond at least to the aircraft either taking off, being in an initial climb phase, descending, being in a final approach phase, or landing. The low battery thermal load mode may correspond at least to the aircraft being in cruise.

As shown in block920, if it is determined in block910that the aircraft is in a high battery thermal load, then the variable speed pump422may be operated at a first speed. On the hand, as shown in block922, if it is determined in block910that the aircraft is in a low battery thermal load, then the variable speed pump422may be operated at a second speed. The first speed may be higher than the second speed.

The method may proceed to block930following block920, it may be determined that the aircraft is in a low battery thermal load after it has been determined that the aircraft is in a high battery thermal load in block920. This may occur, for example, when the aircraft transitions from the initial climb phase of its flight to cruise.

From blocks922and930, the method900may proceed to block940, in which the variable speed pump422may be controlled to stop, for example, for intermittent operation. Alternatively, from block922, the method may determine that the battery has high load which may trigger the method to proceed to block920instead of block940.

In block950, following block940, the manifold system450may be manipulated to enable a reversed flow of the first working fluid around the first circulation loop420,820. This may be particularly advantageous after the method900has operated in block920. On other examples, the method900may be triggered to proceed to block920after block940if it is determined that the battery has high load. In some examples, block950may be omitted, and the method900may simply stop the variable speed pump in block940for a set rest time, and then proceed to block960to restart the variable speed pump after the set rest time.

Finally, in block960following block950, the variable speed pump422may be restarted at the second speed, and the method900may return to block910.