Power allocation in a hybrid electric vehicle

Abstract

Method 300 of power allocation in a hybrid vehicle with a battery, electric machine and supercharger. Obtains indication of battery power 302, determines if an operating state of the vehicle 304 meets

Description

TECHNICAL FIELD The present disclosure relates to power allocation in hybrid electric vehicles. Aspects of the invention relate to a method, a control system, computer readable instructions, a computer readable medium, and a hybrid electric vehicle. BACKGROUND A hybrid electric vehicle (HEV) includes an internal combustion engine and an electric motor (EM) powered by a battery. HEVs may also include an electric supercharger (eSC) that is electrically powered and compresses intake air available to the internal combustion engine. The compressed intake air causes the combustion engine to produce more power for a given engine displacement. The eSC may be powered by the battery. In order to satisfy the power demands of the EM and the eSC, as well as other components of the HEV that consume electric power, the battery may have a power delivery capability that meets or exceeds the maximum power usage of all of the combined electric consumers of the HEV (including the eSC and EM). However, this may be inefficient, for example with regard to the size and cost of the battery. Alternatively, where the peak power demand of combined electric consumers may exceed the power delivery capability of the battery, a fixed portion of the available battery power may be reserved for use by the eSC to ensure that the eSC is usable. However, this may unnecessarily limit use of the EM when the eSC is not used. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a method of power allocation; a control system; computer readable instructions; a computer readable medium; and a hybrid electric vehicle as claimed in the appended claims. According to an aspect of the present invention, there is provided a method of power allocation in a hybrid electric vehicle, in which a battery of the hybrid electric vehicle is arranged to provide power to at least an electric supercharger and an electric machine of the hybrid electric vehicle, the method comprising: obtaining an indication of available battery power; obtaining information describing an operating state of the hybrid electric vehicle; setting, based on the information describing the operating state, a reserved supercharger power, where the reserved supercharger power is a portion of the available power that is reserved for use by the electric supercharger; providing power to the electric supercharger and the electric machine based on the indication of available battery power and the information describing an operating state; wherein the reserved supercharger power is at least maintained while the information describing an operating state is indicative of a predetermined condition. Accordingly, available battery power may be distributed between the electric machine and the electric supercharger in a manner that enhances reliability and efficiency. The predetermined condition may correspond with the operating state of the hybrid electric vehicle meeting a predetermined criterion. Accordingly, available battery power may be distributed between the electric machine and the electric supercharger in a manner that enhances reliability and efficiency. According to an aspect of the present invention there is provided a method of power allocation in a hybrid electric vehicle, a battery of the hybrid electric vehicle arranged to provide power to at least an electric supercharger and an electric machine of the hybrid electric vehicle, the method comprising: obtaining an indication of available power from the battery; obtaining information describing an operating state of the hybrid electric vehicle; determining whetherthe operating state ofthe hybrid electric vehicle meets a criterion; setting, in response to determining that the criterion is met, a reserved supercharger power being a portion of the available power that is reserved for use by the electric supercharger; setting a power limit for power offered to the electric machine based on the indication of available power and the reserved supercharger power; and providing power to the electric supercharger and the electric machine; wherein the power provided to the electric machine is within the power limit; and wherein the reserved supercharger power is not permitted to decrease while the criterion is met. Accordingly, available battery power may be distributed between the electric machine and the electric supercharger in a manner that enhances reliability and efficiency. The indication of available power from the battery (i.e., the indication of available battery power) may be provided by a controller (e.g., a battery controller) ofthe hybrid electric vehicle. The reserved supercharger power may be at least maintained while the criterion is met. The reserved supercharger power may represent a minimum power to be available to (or to be offered to) the electric supercharger while the criterion is met. The reserved supercharger power may be prevented from decreasing while the criterion is met. The reserved supercharger power may be permitted to increase (e.g., up to a maximum operating power of the electric supercharger). The reserved supercharger power may be reset to be a higher power than its current value while the criterion is met, but is not reset to a lower value than its current value while the criterion is met. Thus, the reserved supercharger power may represent a minimum level of power that is to be withheld from being offered to the electric machine. Accordingly, operation, and planned operation, ofthe electric supercharger can be performed reliably. In some embodiments, the method includes determining whether to reserve power for use by the electric supercharger, wherein determining whether to reserve power for use by the electric supercharger includes the determining whetherthe operating state ofthe hybrid electric vehicle meets the criterion. Accordingly, when it is determined that no power is to be reserved for the electric supercharger, the available power may be made available to the electric machine, such that power is not unnecessarily reserved for the electric supercharger. The method may comprise determining an amount of power to reserve as the reserved supercharger power. The amount of power to reserve as the reserved supercharger power may be based on a current amount of power offered to the electric supercharger. The current amount of power offered to the electric supercharger may be based on the available power and an amount of power currently used by the electric machine. Accordingly, the power offered to the electric supercharger may be set such that the power offered to the electric supercharger and the power used by the electric machine do not exceed the available power, such that power can be provided reliably in accordance with the power offered to the electric supercharger. Further, where the electric supercharger begins operating on the basis of an amount of power that is offered to the electric supercharger, by reserving an amount of power based on the power offered (e.g., by setting the reserved supercharger power equal to the power offered to the electric supercharger), the operation of the electric supercharger may be reliably performed. The criterion may be indicative that the electric machine is performing an operation in a set of one or more predetermined operations, and that power is to be reserved for the electric supercharger. The set of one or more predetermined operations may be a set of priority operations, such that the criterion is indicative that the electric machine is performing a priority operation and that power is to be reserved for the electric supercharger. Accordingly, the electric machine and electric supercharger may be appropriately prioritised for power allocation. The priority operation may be an operation that is to be prioritised over starting the electric supercharger. For example, a power requirement of the electric machine in the priority operation may be met before power is made available to start use of the electric supercharger. Starting use of the electric supercharger may include changing the electric supercharger from a state in which it is off (or receiving no power), to a state in which is it on (or receiving power). In some examples, a priority operation may be an operation that causes the electric machine is to be prioritised over the electric supercharger, unless the electric supercharger is currently using power. Accordingly, the electric machine may receive power to perform an operation, while allowing the electric supercharger to continue operating if it is already operating. According to an embodiment, determining that the operating state meets the criterion includes determining that the operating state meets a first criterion, the first criterion indicating an operating state that is compatible with use of the electric supercharger. Accordingly, power may be reserved for the supercharger in dependence on whether use of the electric supercharger is compatible with the current operating state of the hybrid electric vehicle. In an embodiment, the first criterion is based on an engine speed range in which the electric supercharger is usable. In some embodiments, the electric supercharger is not usable outside of the engine speed range. For example, the engine speed range may be between 900 rpm to 2500 rpm. Accordingly, power may be reserved for the supercharger in dependence on whether an engine speed is compatible with use of the electric supercharger. In an embodiment, when it is determined that the operating state does not meet the first criterion, no power is provided to the electric supercharger, no portion of the available power is reserved for use by the electric supercharger, and the power provided to the electric machine is within the indicated available power. Accordingly, no power is reserved for the electric supercharger when use of the electric supercharger is not consistent with the operating state, such that an amount of power up to the available power may be offered to (made available to) the electric machine. According to an embodiment, determining that the operating state meets the criterion includes determining that the operating state meets a second criterion, the second criterion indicating that the electric machine is performing an operation selected from a group comprising at least one of: (i) the electric machine is controlling engine speed to a target speed, and (ii) a transmission of the hybrid electric vehicle is performing, or is to perform, a downshift while an acceleration controller indicates an acceleration demand above a threshold. Accordingly, the reserved supercharger power may be based on whether an operation that can be efficiently performed using the electric machine is occurring or is about to occur. For example, when the electric machine is to perform a torque intervention during a downshift to a lower gear, or when the electric machine is performing idle speed control. The second criterion may be indicative of a priority operation. Accordingly, operations such as a torque intervention or idle speed control may be prioritised over starting the electric supercharger. According to an embodiment, the acceleration controller is an accelerator pedal, and the indication that the acceleration demand is above the threshold corresponds with the accelerator pedal position exceeding a threshold position. According to an embodiment, when it is determined that the operating state does not meet the second criterion, the method comprises: reserving a portion of the available power, by setting a reserved supercharger power, wherein the reserved supercharger power is reserved for use by the electric supercharger, and the reserved supercharger power is set to correspond with a maximum operating power of the electric supercharger. Accordingly, availability of the electric supercharger may be prioritised when the electric machine is not performing a priority operation. According to an embodiment, determining that the operating state meets the criterion includes determining that the operating state meets a third criterion, wherein the third criterion is selected from a group consisting of at least one of: (i) the second criterion is met and the electric supercharger is using power, and (ii) the electric machine is controlling engine speed to the target speed and the engine speed meets a requirement based on the target speed. Accordingly, power may be reserved for the electric supercharger if the electric supercharger is already operating, or if there is sufficient power available after the electric machine has received power to perform a priority operation. Thus, the priority operation of the electric machine may be performed, while also allowing the electric supercharger to complete an operation that is in progress, or to allow the electric supercharger to begin operation if there is sufficient excess power available. The requirement may be that the engine speed is equal to or exceeds the target speed. The requirement may be that the engine speed exceeds the target speed by a set amount. The set amount may be a fixed value, or may be a value based on the target speed. Accordingly, it may be determined that the electric machine has sufficient power to perform the operation that it is currently performing, and additional power is available that may be reserved for use by the electric supercharger. According to an embodiment, when it is determined that the operating state does not meet the third criterion: no portion of the available power is reserved for use by the electric supercharger, the power provided to the electric machine is within the indicated available power, and the method further comprises offering power to the electric supercharger based on the indicated available power and the power used, or predicted to be used, by the electric machine. Accordingly, available power that exceeds power currently used by the electric machine may be offered to the electric machine and electric supercharger, e.g., on a first come, first served basis. This makes the available excess power usable by either the electric machine or the electric supercharger. In an embodiment, the method further comprises (e.g., when the first and second criteria are met, but third criterion is not met) offering a first power to the electric machine and offering a second power to the electric supercharger, wherein a sum of the first power and the second power exceeds (is permitted to exceed) the available power from the battery. The power provided to the electric machine may be limited by the first power and the power provided to the electric supercharger may be limited by the second power. The first power may correspond with the available power. Accordingly, excess available power may be usable by eitherthe electric machine orthe electric supercharger, e.g., on a first come, first served basis. According to an embodiment, the indication of available power from the battery is indicative of a present power supply capability of the battery minus power requirements of electric components to be powered by the battery, other than the electric machine and the electric supercharger. Accordingly, the power requirements of other power consumers in the hybrid electric vehicle may be satisfied, or taken into account, when offering, or reserving, power for the electric supercharger and the electric machine. The electric components may include, for example, a thermal management system, a heating, ventilation, and air conditioning, HVAC, system, an entertainment system, etc. According to an embodiment, a sum of maximum operating power of the electric supercharger and maximum operating power of the electric machine exceeds a maximum supply power of the battery. Accordingly, cost may be reduced by providing a battery that is not required to satisfy the maximum operating power of the electric supercharger and the maximum operating power of the electric machine at the same time. According to another aspect of the invention, a control system for controlling power allocation in a hybrid electric vehicle is provided, the control system comprising one or more processors configured to carry out a method as described herein. An embodiment provides a control system for power allocation in a hybrid electric vehicle, wherein a battery of the hybrid electric vehicle is arranged to provide power to at least an electric supercharger and an electric machine of the hybrid electric vehicle, and wherein the control system comprises one or more processors configured to: obtain an indication of available power from the battery; obtain information describing an operating state of the hybrid electric vehicle; determine whether the operating state of the hybrid electric vehicle meets a criterion; set, in response to determining that the criterion is met, a reserved supercharger power being a portion of the available power that is reserved for use by the electric supercharger; set a power limit for power offered to the electric machine based on the indi cation of available power and the reserved supercharger power; and provide power to the electric supercharger and the electric machine; wherein the power provided to the electric machine is within the power limit; and wherein the reserved supercharger power is not permitted to decrease while the criterion is met. In an embodiment, the control system comprises one or more controllers collectively comprising at least one electronic processor having an electrical input for receiving an input signal; and at least one memory device electrically coupled to the at least one electronic processor and having instructions stored therein; and wherein the at least one electronic processor is configured to access the at least one memory device and execute the instructions thereon so as to carry out a method as described herein. An aspect of the invention provides computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform a method as described herein. A further aspect of the invention provides a computer readable medium comprising computer readable instructions that, when executed by a processor, cause performance of a method as described herein. The computer readable medium may be a non-transitory computer readable medium. Another aspect of the invention provides a hybrid electric vehicle comprising: a control system as described herein, a battery, an electric supercharger, and an electric machine. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in anyway and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 illustrates a hybrid electric vehicle in accordance with an embodiment of the present invention; FIG. 2 illustrates a controller arrangement for a hybrid electric vehicle in accordance with an embodiment of the present invention; FIG. 3 illustrates a method of power allocation in a hybrid electric vehicle according to an embodiment of the present invention; FIG. 4 illustrates a method of power allocation in a hybrid electric vehicle according to an embodiment of the present invention; FIG. 5 shows an example of a device according to an embodiment of the present invention. DETAILED DESCRIPTION FIG. 1 illustrates a hybrid electric vehicle 100 in accordance with an embodiment of the present invention. The hybrid electric vehicle 100 has a combustion engine 102 and an electric machine 104. The electric machine may be an electric motor. The electric machine 104 is coupled with the engine 102, and coupled with the transmission system 106 of the hybrid electric vehicle 100. The engine 102 and the electric machine 104 are each arranged to selectively provide torque to the transmission system 106 in orderto apply torque to the drive wheels 112 of the hybrid electric vehicle 100. An air intake of the engine 102 is provided with an electric supercharger 108. The electric supercharger 108 is arranged to compress air entering the engine 102 to increase the power output of the engine 102. The electric machine 104 and electric supercharger 108 receive electrical power from traction battery 114. The battery 114 may also supply power to other consumers 116 of electrical power. The consumers may include one or more of a thermal management system, a heating, ventilation, and air conditioning, HVAC, system, or an entertainment system, for example. The battery 114 may be a 48V battery, for example. A control system 110 is provided to control operation of the engine 102, the electric machine 104, the electric supercharger 108, and other elements of the hybrid electric vehicle 100. The control system 110 may receive inputs that describe the state of various systems of the hybrid electric vehicle 100, e.g. from sensors provided in the hybrid electric vehicle 100. The inputs may relate to, for example, a battery condition (e.g. state of charge), engine speed, a current gear that the transmission system 106 is in, a gear changed that is planned or in progress, etc. The engine 102 is arranged to selectively provide torque to the electric machine 104 to operate the electric machine 104 as a generator to charge traction battery 114. The electric machine 104 may be linked directly to a crankshaft of the engine 102. In other embodiments (not shown), the electric machine 104 may be connected with the engine 102 via a drive belt, or may be connected to other parts of the drive train. FIG. 2 illustrates a controller arrangement 200 for a hybrid electric vehicle 100 in accordance with an embodiment of the present invention. The controller arrangement 200 comprises one or more controllers 202 that are communicatively coupled to an electric machine 104 and an electric supercharger 108. The controller 202 may form part of the control system 110 of FIG. 1. As in the arrangement of FIG. 1, a battery 114, e.g., a traction battery, is arranged to provide electric power to the electric machine 104 and the electric supercharger 108. The battery 114 may also provide electrical power to one or more other consumers 116. Here, the consumers 116 include consumers of electrical power other than the electric machine 104 and the electric supercharger 108. The consumers 116 may include, for example, a thermal management system, a heating, ventilation, and air conditioning, HVAC, system, an entertainment system, etc. The controller arrangement 200 as illustrated in FIG. 2 comprises one controller 202, although it will be appreciated that this is merely illustrative. The controller 202 comprises a processor 212 and a memory 214. The processor 212 may be any processing means, and may include one or more electronic processing devices. The processor 212 is arranged to execute computer-readable instructions. The memory 214 may be any memory means, and may include one or more memory devices. The memory 214 is communicatively coupled to the processor 212. The memory 214 is configured to store instructions, and the processor 212 is configured to access the memory 214 and execute the instructions stored thereon. The controller 202 comprises an input (e.g. input means, such as an input interface or input communication connection) and an output (e.g. an output means, such as an output interface or output communication connection). The input means may comprise an electrical input of the controller 202. The output means may comprise an electrical output of the controller 202. The input is arranged to receive a first signal 216 indicative of an available battery power, i.e., indicating power available from the battery 114. The first signal 216 may indicate an instantaneous power that is currently available from the battery 114. In some examples, the first signal 216 may indicate the available power after power requirements for the one or more consumers 116 of electrical power have been taken into account. The available power may be determined by subtracting, from the total power output capability of the battery 114, a total power designated to the consumers 116. In some examples, the designated power corresponds with an actual instantaneous power usage of the respective consumers 116. In some examples, the designated power may correspond with power reserved for use by the respective consumers 116. In some examples, the designated power may correspond with a combination of instantaneous power usage by some of the consumers 116 and power reserved for use by others of the consumers 116. The available battery power may be received from a battery management system 222, or a module of a battery management system 222. The battery management system 222 may form part of the control system 110 of FIG. 1. The available battery power may be determined based on one or more of a power rating of the battery 114, a state of charge of the battery 114, power to be supplied to the consumers 116, etc. The input is arranged to receive a second signal 220. The second signal 220 describes an operating state of the hybrid electric vehicle. The second signal 220 may indicate one or more of an engine speed of the hybrid electric vehicle, whether a gear shift is to be performed, whether a gear shift is in progress, whether an acceleration controller, such as an accelerator pedal, is being operated / actuated, a degree of operation / actuation of the acceleration controller (e.g., a height of an accelerator pedal), and acceleration demand (e.g., as indicated by the acceleration controller), etc. The second signal 220 may be received from one or more components or modules 224 of the hybrid electric vehicle, such as an engine management system, etc. The components or modules may form part of the control system 110 of FIG. 1. When the controller 202 determines that the operating state of the hybrid electric vehicle 100 meets a criterion, the controller 202 reserves a portion of the available power by setting a reserved supercharger power for use by the electric supercharger 108. The reserved supercharger power is not permitted to decrease while the criterion is met. Put another way, while the criterion is met, a decrease of the reserved portion (the reserved supercharger power) is prevented. That is, the reserved portion (the reserved supercharger power) is not reduced while the criterion is met. The criterion may be as described in the following embodiments. A power limit for the electric machine 104 is set based on the available power and the reserved portion. For example, the power limit for the electric machine 104 may be equal to the available power minus the reserved portion. The power limit for the electric machine 104 may correspond with an amount of power offered to the electric machine 104, with the electric machine 104 permitted to use any amount of power, up to the corresponding power limit. The power limit may be used for controlling an instantaneous power use by the electric machine 104. The controller 202 is arranged to cause power to be provided to the electric machine 104 and to the electric supercharger 108, with the power provided to the electric machine 104 being within the power limit. For example, the controller 202 may provide a first output signal 226 to electric machine 104 indicating the power limit to the electric machine 104. The controller 202 may also output a second output signal 228 to the electric supercharger 108 indicative of a power available for use by, or a power reserved for use by, the electric supercharger 108. In other examples, one or both of the outputs 226 and 228 may be provided to a controller or control module, such as an element of control system 110, to control power provided to one or both of the electric machine 104 and the electric supercharger 108. Herein, power offered to a component represents power that is available for use by the component. The component may draw an amount of power up to the amount of power offered to the component, but may not exceed the offered amount of power. A component drawing an amount of power, or an indication (e.g., from a controller) that a component is to draw an amount of power may be referred to herein as the component requesting the amount of power. Accordingly, a component may request an amount of power up to the amount of power offered to the component. Herein, an amount of power is reserved for a component corresponds with an amount of the available power that is not offered to other components, such that an amount of power, up to the reserved amount of power, is available for use by the component. An amount of power offered to a component may exceed the amount of power reserved for use by the component. An amount of power used by a component may be less than a power reserved for use by the component, and may be less than an amount of power offered to the component. One or more of the power limit, power offered to the electric machine, power offered to the electric supercharger, or reserved supercharger power may be used by the system (e.g. controller 202) in planning control of the engine, the electric machine 104, or both. For example, a torque limit may be determined based on the power limit orthe power offered to the electric machine. The torque limit may indicate a maximum torque that the electric machine can produce with power within the power limit of the power offered to the electric machine. Similarly, the power offered to, or reserved for, the electric supercharger may be used to determine a maximum duty cycle of the electric supercharger consistent with the offered, or reserved, power. FIG. 3 illustrates a method 300 of power allocation in a hybrid electric vehicle 100 according to an embodiment. The method 300 may be performed by a controller 202, as illustrated in FIG. 2, or a control system 110, as illustrated in FIG. 1. According to the method 300 of FIG. 3, a battery 114 of the hybrid electric vehicle 100 is arranged to provide power to at least an electric supercharger 108 and an electric machine 104 of the hybrid electric vehicle 100. In block 302, an indication of available power from the battery 114 is obtained. In block 304, information describing an operating state of the hybrid electric vehicle 100 is obtained. In block 306, it is determined whether the operating state of the hybrid electric vehicle 100 meets a criterion. In block 308, in response to determining that the criterion is met, a reserved supercharger power is set, being a portion of the available power that is reserved for use by the electric supercharger. In block 310, a power limit for power offered to the electric machine 104 is set based on the indication of available power and the reserved supercharger power. In block 312, power is provided to the electric supercharger 108 and the electric machine 104. The power provided to the electric machine 104 is within the power limit, and the reserved supercharger power is not permitted to decrease while the criterion is met. The criterion may indicate that the electric machine 104 is performing an operation that is in a set of predetermined operations, and also that power is to be reserved for the electric supercharger 108. For example, the set of one or more predetermined operations may be a set of priority operations that indicate that the provision of power to the electric machine 104 should normally be prioritised over the provision of power to the electric supercharger 108, butthat power nevertheless should be reserved for the electric supercharger 108. Accordingly, the reserved supercharger power may represent a minimum power to be available to (or to be offered to) the electric supercharger 108 while the criterion is met. The reserved supercharger power may be at least maintained while the criterion is met. The reserved supercharger power may be permitted to increase (e.g., up to a maximum operating power of the electric supercharger 108). For example, the reserved supercharger power may be reset to be a higher power than its current value while the criterion is met, but is not reset to a lower value than its current value while the criterion is met. Accordingly, the reserved supercharger power may represent a minimum level of power that is to be withheld from being offered to the electric machine 104. In some examples, the method 300 includes determining whether to reserve power for use by the electric supercharger 108, wherein determining whether to reserve power for use by the electric supercharger 108 includes determining whether the operating state of the hybrid electric vehicle 100 meets the criterion. The method 300 may comprise determining an amount of power to reserve as the reserved supercharger power. The amount of power to reserve as the reserved supercharger power may be based on a current amount of power offered to the electric supercharger 108. The current amount of power offered to the electric supercharger 108 may be based on the available power and an amount of power currently used by the electric machine 104. For example, the criterion may identify a situation in which the ability to use the electric supercharger 108 is to be maintained, while also providing power to the electric machine 104. For example, the criterion may identify situations in which it is important to make power available to the electric machine 104, e.g., to prevent the engine 102 from stalling, but where it is also appropriate to allow power usage by the electric supercharger 108, e.g., where the electric supercharger 108 is already in use. In some examples, the priority operation is an operation that is to be prioritised over starting the electric supercharger 108. For example, a power requirement of the electric machine 104 in the priority operation may be met before power is made available to start use of the electric supercharger 108. On the other hand, where the electric supercharger 108 is already operating, power may be reserved for the electric supercharger 108 to allow the electric supercharger 108 to continue operating. Starting use of the electric supercharger may include changing the electric supercharger from a state in which it is off (or receiving no power), to a state in which is it on (or receiving power). Where the electric machine 104 is performing a first priority operation, and the available power exceeds the power used by the electric machine 104, the excess power may be available to start the electric supercharger 108 if the electric supercharger 108 is not already operating. In this case, if the electric supercharger 108 begins operating, power may be reserved for use by the electric supercharger 108, in order to allow the electric supercharger 108 to continue operating, with the amount of power at least maintained while the electric supercharger 108 is operating (e.g. while the criterion is met). That is, the amount of power reserved for use by the electric supercharger 108 may stay the same or increase, but is not permitted to decrease. The first priority operation may be an operation that prioritises operation of the electric machine 104 over operation of the electric supercharger 108, unless the electric supercharger 108 is already operating. The first priority operation may be associated with a gear change, where use of the electric machine 104 provides greater efficiency than use of the electric supercharger 108. For example, the first priority operation may correspond with a downshift (i.e. a change to a lower gear) being performed or being predicted to be performed, while an accelerator pedal position exceeds (e.g. is lower than) a threshold position. Or more generally, where a downshift is expected or predicted, and an acceleration controller indicates an acceleration demand above a threshold. For example, when changing gear in an automatic gearbox there may be a significant increase in actuator speed when synchronising to the new gear. To do this seamlessly, the powertrain torque may be increased to offset an inertia effect of the speed rise. If no torque increase is performed, the energy to accelerate the actuator would be taken from the vehicle and a deceleration of the hybrid electric vehicle 100 would be experienced. In embodiments, the magnitude of the torque increase to offset the inertia is predictable. For example, the speed change is known, from the difference between synchronisation speeds, and the duration of the event may be programmed by the transmission. This allows a rate of change of speed to be determined. The system moment of inertia may be known, and combining this with the rate of change of speed gives an inertia torque, to which calibration adjustments may be applied. Using the electric machine 104, engine 102, or both to apply the appropriate torque may be referred to as a 'torque intervention'. The amount of torque may be communicated to the controller 202 (e.g. to a powertrain control module of the controller) before the gear change begins. The electric machine 104 may be capable of producing the entire torque for the torque intervention, allowing the engine to remain in fuel-cut (i.e. when fuel is not injected into the engine) when decelerating through the gears. However, where sufficient power is not available for use by the electric machine 104, it may be necessary to bring the engine 102 out of fuel-cut to assist the electric machine 104 in performing the torque intervention. According to embodiments, the power needed by the electric machine 104 to perform the intervention may be predicted, e.g. based on predicted intervention magnitude and the maximum speed during the shift. Accordingly, use of the electric machine 104 may be considered to be a priority over starting the electric supercharger 108 during the gear shift. Accordingly, power for the torque intervention may be provided to the electric machine 104, and the engine can remain unused. However, where the electric supercharger 108 is already operating, it may be permitted to continue to operate by at least maintaining an amount of power reserved for use by the electric supercharger 108. It can then be determined whether the remaining power available to the electric machine 104 is sufficient to perform the intervention, or whether the engine 102 should be used. Where the electric machine 104 is performing a second priority operation, and the available power exceeds a power threshold, some or all of the excess power may be reserved for the electric supercharger 108 if the electric supercharger 108 is not already operating. The available power may be set based on at least one of a power currently used by electric machine 104, and a power predicted to be used by the electric machine 104 (e.g. during the second priority operation, or within a time interval). In this case, if the electric supercharger 108 begins operating, the amount of reserved power may be at least maintained, in order to allow the electric supercharger 108 to continue operating. The second priority operation may correspond with the electric machine 104 controlling the engine 102 speed to a target speed. The criterion may include the electric machine 104 performing the second priority operation and a speed of the engine 102 exceeding the target speed by a threshold amount. During idling, for example, the engine speed may be controlled to a minimum value by rapidly changing the engine torque via combustion characteristics, such as ignition angle (i.e., the timing of ignition in the engine cycle), air flow, and fuel mass. This may be referred to as 'idle speed control'. In order to instantaneously increase engine torque, the engine 102 operates with a sub-optimal ignition angle, which may be referred to as ‘torque reserve’, and is inefficient. In a hybrid electric vehicle 100 the electric machine 104 may be used to actuate the rapid torque changes, allowing the engine to run at a more efficient ignition angle and operate more efficiently. Whether or not the electric machine 104 is to be used in this manner may be based on the power available to the electric machine 104, for example, whether the power available to the electric machine 104 is equal to or greater than a power needed to perform this function. Accordingly, making power available to the electric machine 104 may be prioritised over making power available to the electric supercharger 108 when the engine 102 is idling, as it may be more important to avoid stalling the engine than to ensure the electric supercharger 108 is usable by reserving electrical power for the electric supercharger 108. The first and second priority operations may also be referred to as first and second operations, respectively. The first operation may be referred to as a downshift operation, and the second operation may be referred to as an idling operation. The electric supercharger 108 may have a maximum operating power, for example, corresponding with an upper limit of a power range at which the electric supercharger 108 is operable. This may correspond with a power rating of the electric supercharger 108. Power available for use by the electric supercharger 108, or power reserved for use by electric supercharger 108 may be capped at the maximum operating power. That is, where power reserved for the electric supercharger 108 would exceed the maximum operating power, the reserved power is set equal to the maximum operating power. Similarly, the power available for use by the electric supercharger 108 may be set equal to the maximum operating power if it would exceed the maximum operating power. FIG. 4 illustrates a method 400 of power allocation in a hybrid electric vehicle 100 according to an embodiment. The method 400 may be performed by a controller 202, as illustrated in FIG. 2, or control system 110, as illustrated in FIG. 1. One or more of the first, second, and third criteria described below may be included in the criterion in block 306 of FIG. 3. The method 400 begins at block 402. At block 404, it is determined whether the operating state of the hybrid electric vehicle 100 meets a first criterion. The first criterion indicates that the operating state of the hybrid electric vehicle 100 is compatible with the use of the electric supercharger 108. For example, the electric supercharger 108 may be usable only when the engine 102 has a speed within one or more predetermined ranges of engine speed. Alternatively, use of the electric supercharger 108 may be precluded in one or more predetermined ranges of engine speed. Accordingly, the first criterion may be based on an engine speed range in which the electric supercharger 108 is usable. For example, the electric supercharger 108 may be useable in a speed range between 900 rpm to 2500 rpm and unusable at engine speeds outside of that range. If the operating state does not meet the first criterion (i.e. the electric supercharger 108 is not usable), the method 400 proceeds to block 406. At block 406, no power is offered to, or reserved for, the electric supercharger 108, and all of the available power is offered to the electric machine 104. Power offered to a component is indicative of power that is currently available for use by the component. The component may request, and receive, an amount of power up to the offered amount. Power reserved for a component is indicative of an amount of power that is usable only by that component. For example, power offered to other components may be based on an available power minus reserved power. The power requested by, or received by, the component may be less than the power reserved forthat component. In some examples, the amount of power offered to a component may be greater than an amount of power reserved for that component. In that case, the amount of power requested by, or received by, the component may exceed the amount of power reserved for that component. If the operating state meets the first criterion, the method proceeds to block 408. At block 408 it is determined whether the operating state meets a second criterion. The second criterion may be met when the operating state corresponds with the electric machine performing an operation (e.g. a predetermined operation). The predetermined operation may be a priority operation, for example. In some examples the predetermined operation may correspond with the first or second priority operation (first or second operation) described above. In some examples, the second criterion may be considered to set a Boolean value to True if the second criterion is met, and False if the second criterion is not met. The Boolean value may be referred to as a Shift and Idle Boolean. If the second criterion is not met at block 408, the method proceeds to block 410, where a predetermined amount of the available power is reserved for use by the electric supercharger 108. That is, the reserved supercharger power may be set to correspond with (e.g. be equal to) the predetermined amount. The predetermined amount may correspond with a maximum operating power of the electric supercharger. The electric supercharger 108 may also be offered the same amount of the power as the amount of power reserved for the electric supercharger 108 (e.g. the electric supercharger 108 is offered power corresponding with the maximum operating power of the electric supercharger 108). This may correspond with a situation where the use of the electric machine 104 is not to be prioritised, and the full potential power usage of the electric supercharger 108 is reserved for use by the electric supercharger 108, in order to ensure that the electric supercharger 108 is usable. If the second criterion is met at block 408, the method proceeds to block 412, where it is determined whether the operating state meets a third criterion. The third criterion may be indicative of a state that indicates power should be reserved for the electric supercharger 108, notwithstanding a priority operation being performed by the electric machine 104. In some examples, the third criterion may be met when the electric supercharger 108 is operating, or using power, while the second criterion is met. Additionally, or alternatively, the third criterion may be met when the electric machine 104 is controlling engine speed to the target speed (e.g., when the electric machine 104 is assisting with engine idling) and the engine speed meets a requirement based on the target speed. For example, the requirement may be that the engine speed is equal to or exceeds the target speed. Alternatively, the requirement may be that the engine speed exceeds the target speed by a set amount. The set amount may be a fixed value, or may be a value based on the target speed. If the third criterion is not met, the method may proceed to block 416. At block 416, no portion of the available power is reserved for use by the electric supercharger. A first amount of power may be offered to the electric machine 104. The electric machine 104 may request, or may be provided with, an amount of power up to the first amount power. For example, first amount of power may be the available power. A second amount of power may be offered to the electric supercharger 108. The second amount of power may be based on the indicated available power and the power used, or predicted to be used, by the electric machine 104. For example, the second power may equal the available power minus the power used by the electric machine 104 (this may be capped by a maximum operating power of the electric supercharger 108). The power provided to the electric machine 104 may be limited by the first power and the power provided to the electric supercharger 108 may be limited by the second power. As the actual power use of the electric machine 104 may be less than the second power, the sum of the first power and the second power may exceed the available power. However, the actual power used does not exceed the available power, since the sum of the second power and the power actually used by the electric machine 104 does not exceed the amount of available power. Further, the method reaches block 416 when the electric supercharger 108 is not operating. If the supercharger begins operating and receiving power while the second criterion is met, the third criterion is also met and the method would proceed to block 414, as described below. If the third criterion at block 412 is met, the method proceeds to block 414. At block 414 the reserved supercharger power and the power limit for power offered to the electric machine are set. The power limit is set based on the indication of available power and the reserved supercharger power. Power is provided to the electric supercharger 108 and the electric machine, with the power provided to the electric machine being within the power limit. While the first, second and third criteria are met, the reserved supercharger power is not permitted to decrease. In some examples, the reserved supercharger power is set as the amount of power currently used by the electric supercharger 108, for example, when the third criterion is met because the electric supercharger 108 is operating. When the electric machine 104 is controlling to engine speed to a target speed, the reserved supercharger power may be set as the difference between the indicated available power minus the power currently used by the electric machine 104, where the available power is the battery power available after power requirements of consumers 116 other than the electric machine 104 and electric supercharger 108, have been met. Put another way, the reserved supercharger power may be set as the battery power that is not being used by, or reserved for, other components of the hybrid electric vehicle 100, such as the consumers 116 and electric machine 104 (e.g. all currently unused battery power may be reserved for use by the electric supercharger 108). As described previously, the reserved supercharger power may be capped, that is constrained to be less than a predetermined value, e.g. corresponding with a maximum power rating of the electric supercharger 108. The illustration of a particular order to the blocks illustrated in FIG.s 3 and 4, does not necessarily imply that there is a required or preferred order for the blocks. The order and arrangement of the blocks may be varied. Furthermore, it may be possible for some steps in the method to be omitted. Certain methods and systems as described herein may be implemented by one or more processors 212 that process program code (computer readable instructions) that is retrieved from a storage medium, such as non-transitory storage medium. FIG. 5 shows an example of a device 500 comprising a computer-readable storage medium (e.g. memory 214) coupled to at least one processor 212. The computer-readable medium 214 can be any media that can contain, store, or maintain programs and data for use by or in connection with an instruction execution system. The computer-readable medium 214 can comprise any one of many physical media such as, for example, electronic, magnetic, optical, electromagnetic, or semiconductor media. More specific examples of suitable machine-readable media include, but are not limited to, a hard drive, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory, or a 5 portable disc. In FIG. 5, the computer-readable storage medium 214 comprises program code 502 to cause the processor 212 to perform a method 300 corresponding to the embodiment shown in FIG. 3. The program code 502 could alternatively cause the processor 212 to perform the method of FIG. 4, or any of the methods described herein. 10 The device 500 may be included in a controller 202 of FIG. 2, or a control system 110 of a hybrid electric vehicle 100, as illustrated in FIG. 1, for example. It will be appreciated that various changes and modifications can be made to the embodiments of the present invention without departing from the scope of the present application.

Claims

1. A method of power allocation in a hybrid electric vehicle, a battery of the hybrid electric vehicle arranged to provide power to at least an electric supercharger and an electric machine of the hybrid electric vehicle, the method comprising:obtaining an indication of available power from the battery;obtaining information describing an operating state of the hybrid electric vehicle;determining whether the operating state of the hybrid electric vehicle meets a criterion;setting, in response to determining that the criterion is met, a reserved supercharger power being a portion of the available power that is reserved for use by the electric supercharger;setting a power limit for power offered to the electric machine based on the indication of available power and the reserved supercharger power; andproviding power to the electric supercharger and the electric machine;wherein the power provided to the electric machine is within the power limit; andwherein the reserved supercharger power is not permitted to decrease while the criterion is met.

2. The method of claim 1, wherein determining that the operating state meets the criterion includes determining that the operating state meets a first criterion, the first criterion indicating an operating state that is compatible with use of the electric supercharger.

3. The method of claim 2, wherein the first criterion is based on an engine speed range in which the electric supercharger is usable.

4. The method of claim 2 or claim 3, wherein, when it is determined that the operating state does not meet the first criterion, no power is provided to the electric supercharger, no portion of the available power is reserved for use by the electric supercharger, and the power provided to the electric machine is within the indicated available power.

5. The method of any one of claims 1 to 4, wherein determining that the operating state meets the criterion includes determining that the operating state meets a second criterion, the second criterion indicating that the electric machine is performing an operation selected from a group comprising at least one of:the electric machine is controlling engine speed to a target speed, anda transmission of the hybrid electric vehicle is performing, or is to perform, a downshift while an acceleration controller indicates an acceleration demand above a threshold.

6. The method of claim 5, wherein the acceleration controller is an accelerator pedal, and the indication that the acceleration demand is above the threshold corresponds with the accelerator pedal position exceeding a threshold position.

7. The method of claim 5 or 6, wherein when it is determined that the operating state does not meet the second criterion, the method comprises:reserving a portion of the available power, by setting a reserved supercharger power, wherein the reserved supercharger power is reserved for use by the electric supercharger, and the reserved supercharger power is set to correspond with a maximum operating power of the electric supercharger.

8. The method of any one of claims 5 to 7, wherein determining that the operating state meets the criterion includes determining that the operating state meets a third criterion, wherein the third criterion is selected from a group consisting of at least one of:the second criterion is met and the electric supercharger is using power; andthe electric machine is controlling engine speed to the target speed and the engine speed meets a requirement based on the target speed.

9. The method of claim 8, wherein when it is determined that the operating state does not meet the third criterion:no portion of the available power is reserved for use by the electric supercharger;the power provided to the electric machine is within the indicated available power; andthe method further comprises offering power to the electric supercharger based on the indicated available power and the power used, or predicted to be used, by the electric machine.

10. The method of any one of claims 1 to 9, wherein the indication of available power from the battery is indicative of a present power supply capability of the battery minus power requirements of one or more electric components to be powered by the battery, other than the electric machine and the electric supercharger.

11. The method of any one of claims 1 to 10, wherein a sum of maximum operating power of the electric supercharger and maximum operating power of the electric machine exceeds a maximum supply power of the battery.

12. A control system for controlling power allocation in a hybrid electric vehicle, the control system comprising one or more processors configured to carry out the method of any one of claims 1 to 11.

13. Computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method of any one of claims 1 to 11.

14. A computer readable medium comprising computer readable instructions that, when executed by a processor, cause performance of the method of any one of claims 1 to 11.

15. A hybrid electric vehicle comprising:the control system of claim 12;a battery;an electric supercharger; andan electric machine.

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