Method and apparatus for determining a virtual sensor measurement for a thermal management system of an electric vehicle

Abstract

There is provided a method of determining a virtual sensor measurement for a reconfigurable thermal management system of an electric vehicle. The method comprises obtaining a plurality of virtual sens

Description

TECHNICAL FIELD The present disclosure relates to a method and apparatus for determining a virtual sensor measurement for a thermal management system of an electric vehicle. In particular, the present disclosure relates to a method and apparatus for determining a virtual sensor measurement for the thermal management system based on at least one sensor measurement value and a virtual sensor model. Aspects of the invention relate to a method, a computer readable medium, computer readable instructions, a control system and a vehicle. BACKGROUND Thermal management of components of electric vehicles may contribute significantly to the overall efficiency of the electric vehicle by controlling the temperature of components of the vehicle to be at, or near, desired operating temperatures. Reconfigurable thermal management systems allow for thermal energy to be transferred between different components of the vehicle, allowing heat energy to be moved from a component requiring cooling to a different component requiring heating. Such transfers may reduce the amount of electrical charge drawn from the battery as compared to cooling / heating each component individually. Control schemes for reconfigurable thermal management systems may make use of a plurality of measurements of system parameters taken from a range of locations within the thermal management system. However, it may be difficult or expensive to provide appropriate sensors to provide all of the parameter measurements used by a control scheme. Furthermore, measurements taken when the thermal management system is operating in a particular configuration may not reflect the measurements that would be taken if the thermal management system was operating in a different configuration. 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 an method of determining an operating mode of a thermal management system of an electric vehicle, a computer program, a control system, and a vehicle as claimed in the appended claims. According to an aspect of the present invention there is provided a method of determining a virtual sensor measurement for a thermal management system of an electric vehicle, the method comprising obtaining a virtual sensor model associated with a configuration of the thermal management system and determining the virtual sensor measurement based on the obtained model and at least one physical sensor measurement. Advantageously, sensor readings for locations within the thermal management system where no actual sensor is located can be predicted based on one or more other sensor measurements taken elsewhere in the thermal management system, allowing virtual sensor measurements to be determined for locations where it is not practical to provide a physical sensor. According to an aspect of the present invention there is provided a method of determining a virtual sensor measurement for a thermal management system of an electric vehicle, wherein the thermal management system is operable in a plurality of configurations, the method comprising obtaining a plurality of virtual sensor models, each virtual sensor model operable to determine a virtual sensor measurement based on at least one sensor measurement value, wherein each virtual sensor model is associated with a configuration of the thermal management system, receiving an indication of a configuration of the thermal management system, receiving a sensor signal indicating a sensor measurement value, selecting a virtual sensor model of the plurality of virtual sensor models based on the indication of the configuration of the thermal management system, determining a virtual sensor measurement value based on the selected virtual sensor model and the received sensor signal, and outputting a signal representative of the virtual sensor measurement value. In embodiments, a virtual sensor measurement comprises a determined value indicating a parameter value associated with a location in the thermal management system, wherein the location is not associated with a physical sensor operable to measure the parameter value. Advantageously, sensor readings for locations within the thermal management system where no actual sensor is located can be predicted based on one or more other sensor measurements taken elsewhere in the thermal management system. In particular, the use of different models for each configuration of the thermal management system allows accurate virtual sensor readings to be determined when the thermal management system is reconfigured between the different operating modes. For example, a virtual sensor may allow an accurate measurement to be determined for a location at which it is not practical or possible to provide an actual sensor. In embodiments, receiving an indication of a configuration of thermal management system comprises receiving an indication of a first configuration while the thermal management system is operating in a second configuration, wherein the first configuration is different from the second configuration. Advantageously, a virtual sensor model can be selected that is for a configuration other than the current configuration in which the thermal management system is operating. That is, the virtual sensor model can be applied for different configurations of the thermal management system to generate a virtual sensor measurement value that could not otherwise be measured, even if a sensor was present, without changing an operating mode of the thermal management system to the target configuration. Optionally, the determined virtual sensor measurement value comprises a predicted measurement value for the first configuration of the thermal management system. Advantageously, a virtual sensor measurement can be predicted for different configurations than the current configuration, allowing the operation of the thermal management system in different configurations to be predicted. In embodiments, the vehicle comprises a plurality of components, the thermal management system operable to transfer thermal energy from a first component of the plurality of components to a second component of the plurality of components, and each configuration of the thermal management system defines a configuration of one or more coolant loops supplying heat transfer fluid to at least one component of the plurality of components of the vehicle. Advantageously, different configurations can allow heat to be transferred between different components of the vehicle, and an appropriate virtual sensor model can be selected for each configuration to allow a virtual sensor measurement to be determined. Optionally, the virtual sensor measurement comprises a virtual temperature value representing a temperature of a portion of the thermal management system. Advantageously, the method may be used to determine a temperature reading for a virtual sensor that can be used as part of a control system for the thermal management system. Optionally, the virtual sensor measurement comprises a virtual mass flow value representing a mass flow through a portion of the thermal management system. Advantageously, the method may be used to determine a mass flow value for a virtual sensor that can be used as part of a control system for the thermal management system. In embodiments, receiving the sensor signal comprises receiving a first sensor signal from a first sensor of the thermal management system and a second sensor signal from a second sensor of the thermal management system, each sensor signal representative of a measured value associated with the respective sensor. Advantageously, using signals from two sensors has been found to provide for an accurate determination of virtual sensor measurement values. 2 Optionally, the virtual sensor model comprises a map of a relationship between the first and second sensor signals, and a corresponding virtual sensor measurement. Advantageously, using signals from two sensors in conjunction with a map of a relationship between the first and second sensor signals has been found to provide for an accurate determination of virtual sensor measurement values and can be easily implemented in real-time on common automotive controllers. According to another aspect of the invention, there is provided computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform a method as disclosed herein. Optionally, the computer readable instructions may be stored on a computer readable medium. According to a further aspect of the invention, there is provided a control system for controlling a thermal management system of a vehicle, wherein the thermal management system is operable in a plurality of configurations, the control system comprising one or more processors collectively configured to obtain a plurality of virtual sensor models, each virtual sensor model operable to determine a virtual sensor measurement based on at least one sensor measurement value, wherein each virtual sensor model is associated with a configuration of the thermal management system, receive an indication of a configuration of the thermal management system, receive a sensor signal indicating a sensor measurement value, select a virtual sensor model of the plurality of virtual sensor models based on the indication of the configuration of the thermal management system, determine a virtual sensor measurement value based on the selected virtual sensor model and the received sensor signal, and output a signal representative of the virtual sensor measurement value. Advantageously, the control system may predict sensor readings for locations within the thermal management system where no actual sensor is located based on one or more other sensor measurements taken elsewhere in the thermal management system. I n particular, the use of different models for each configuration of the thermal management system allows accurate virtual sensor readings to be determined when the thermal management system is reconfigured between the different operating modes. For example, a virtual sensor may allow an accurate measurement to be determined for a location at which it is not practical or possible to provide an actual sensor. According to an embodiment, the control system for controlling a thermal management 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 perform any of the methods as described herein. Optionally, the indication of a configuration of the thermal management system comprises an indication of a first configuration while the thermal management system operates in a second configuration, wherein the first configuration is different from the second configuration. Optionally, the one or more processors are further configured to determine a predicted measurement value for the first configuration of the thermal management system. Optionally, the virtual sensor measurement comprises a virtual temperature value representing a temperature of a portion of the thermal management system, or the virtual sensor measurement comprises a virtual mass flow value representing a mass flow through a portion of the thermal management system. In embodiments, the one or more processors are configured to receive a first sensor signal from a first sensor of the thermal management system, receive a second sensor signal from a second sensor of the thermal management system, wherein each of the first and second sensor signals are representative of a measured value associated with the respective sensor, and wherein the virtual sensor model comprises a map of a relationship between the first and second sensor signals, and a corresponding virtual sensor measurement. 3 According to an aspect of the present invention there is provided a vehicle comprising a thermal management system, and a control system as described herein coupled to the thermal management system. 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 any way 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: Figure 1 shows a system suitable for implementing embodiments of the invention; Figure 2 illustrates a vehicle including the system of Figure 1 and suitable for implementing embodiments of the invention; Figure 3 illustrates a schematic representation of a powertrain thermal management system suitable for implementing embodiments of the invention; Figures 4A to 4F illustrate example configurations of the powertrain thermal management system of Figure 3 in accordance with embodiments of the invention; Figure 5 illustrates a schematic representation of a climate control system suitable for implementing embodiments of the invention; Figure 6 illustrates a method of selecting an operating mode of a vehicle thermal management system according to embodiments of the invention; and Figure 7 illustrates a control system suitable for performing the method of Figure 6, according to embodiments of the invention. DETAILED DESCRIPTION Thermal management of components of an electric vehicle, such as a battery electric vehicle (BEV) or plug-in hybrid electric vehicle (PHEV), and the transfer of excess thermal energy from a first component to a second component where the thermal energy may be usefully employed, may have a significant effect on the efficiency of the electric vehicle. Reconfigurable thermal management systems, having a number of different operating modes with different coolant flow topologies, may facilitate transfer of thermal energy between different components of the electric vehicle. By estimating or predicting an energy cost associated with each configuration or operating mode of the thermal energy management system, an operating mode having a low energy cost can be selected to satisfy thermal energy transfer requirements of components of the vehicle in an energy efficient way. A method of estimating an energy cost associated with an operating mode may rely on knowledge of parameter values, such as temperature or mass flow rate, at certain locations within the thermal energy management system. However, it is not always possible, or economic, to provide appropriate sensors to measure these parameter values at all of the desired locations in the thermal energy management system. Furthermore, when estimating an energy cost associated with an operating mode, or configuration, of the thermal management system, that is different from a current operating mode, a measured parameter value at a particular location in the current operating mode may not be representative of a parameter value measured at that location in the different operating mode being considered, for example due to reconfiguration of the thermal management system. According to embodiments of the invention, a control system may be operable to determine, and output, a virtual sensor measurement value based on one or more real sensor measurement values and using a virtual sensor model corresponding to the operating mode, or configuration, of the thermal management system of an electric vehicle. In the context of the present disclosure, a virtual sensor refers to a location in the thermal management system at which a parameter value can be inferred from one or more parameter values, measured using respective physical sensors present at different locations in the thermal management system. A virtual sensor model may be a predictive model that allows a virtual sensor measurement value, i.e. the inferred parameter value corresponding to the virtual sensor location, to be determined based on the one or more measured parameter values. Each virtual sensor model is associated with a respective configuration of the thermal management system and can be used to determine the virtual sensor measurement value for the thermal management system operating in the respective configuration. With reference to Figure 1, there is illustrated a vehicle thermal management system 100 for an electric vehicle in accordance with an embodiment of the present invention. The vehicle thermal management system 100 includes at least one controller 106 that is communicatively coupled to a powertrain thermal management system (PTM) 102 and a climate control system (CCS) 104 that comprises a heating, ventilation and air conditioning (HVAC) system, to receive state information and / or sensor readings from one or more components of the PTM 102 and HVAC, e.g. coolant or refrigerant temperature and mass flow rate measurements. In embodiments, the controller 106 may be communicatively coupled to one or more components of the electric vehicle, for example via a Control Area Network (CAN) bus or similar network present on the vehicle 200, and operable to obtain thermal energy information from the components. The thermal energy information defines a thermal energy transfer requirement for each of the components of the electric vehicle. The controller 106 is further arranged to provide indications of a selected operating mode to the PTM 102 and CCS 104 to influence the operation of those subsystems. The vehicle thermal management system 100 as illustrated in Figure 1 comprises one controller 106, although it will be appreciated that this is merely illustrative. The controller 106 comprises processing means 108 and memory means 110. The processing means 108 may be one or more electronic processing device 108 which operably executes computer-readable instructions. The memory means 110 may be one or more memory device 110. The memory means 110 is electrically coupled to the processing means 108. The memory means 110 is configured to store instructions, and the processing means 108 is configured to access the memory means 110 and execute the instructions stored thereon. In Figure 2, controller 106, PTM 102, and CCS 104 are provided in electric vehicle 200, such as an automobile. A powertrain of the vehicle 200 comprises at least one electric drive unit 202a / b and a traction battery 204. The electric drive units 202a / b comprise one or more electric traction motors for propelling the vehicle 200. The traction battery 204 is a high voltage (HV) battery and is configured to supply electrical current to the at least one drive unit 202a / b. In the present embodiment, the vehicle 200 comprises a front electric drive unit 202a for driving the front wheels of the vehicle 200; and a rear electric drive unit 202b for driving the rear wheels of the vehicle 200. In use, the front and rear electric drive units 202a, 202b are both powered by the traction battery 204. Each electric drive unit 202a / b may include power electronics, such as an inverter, to convert DC current sourced from the traction battery 204 to AC current to be supplied to the electric traction motors. As illustrated in Figure 1, the PTM 102 is coupled to the CCS 104 of the cabin of the vehicle which is able to control a temperature of the vehicle cabin for occupant comfort. While the traction battery 204, electric drive units 202a / b and HVAC may be the most significant generators and / or users of thermal energy supplied by the PTM 102, it will be recognized that other vehicle components may be coupled to the PTM 102 and may have thermal requirements to be met by the PTM. For example, in embodiments, the vehicle 200 may further include separate power electronics, such as an on-board AC charger, that may be significant generators of thermal energy while requiring cooling to maintain an operating temperature. Similarly, in embodiments, the electrical vehicle 200 may be provided with computer processing hardware that requires active cooling. The components of the vehicle may have associated target operating temperature ranges and operating a component outside of the respective target range may lead to increased power consumption of the component and the vehicle 200 as a whole. For example, when the temperature of the traction battery 204 increases, internal resistive losses within the traction battery 204 may also be expected to increase, while chemical reactions in the traction battery 204 may be inhibited when cold, similarly leading to increased losses in the battery. Such losses, when the powertrain components are not maintained within the desired operating temperature range, will result in reduced range for the vehicle 200. The vehicle thermal management system 100 is operable as a supply or sink of thermal energy to components of the vehicle 200, and in particular PTM 102 is thermally coupled to the traction battery 204 and electric drive units 202a / b and able to extract or supply thermal energy to satisfy thermal energy transfer requirements of these components. In an illustrative example of operation of the vehicle, thermal energy may be supplied via the PTM 102 to the traction battery 204 and electric drive units 202a / b when beginning operation of the vehicle 200 from cold to more quickly bring the components to the desired operating temperature range. During further operation of the vehicle 200, heat may be generated in the traction battery 204 and electric drive units 202a / b, for example due to internal resistance of the cells of the traction battery 204. To maintain the temperature of the powertrain components within the desired temperature range, heat generated in the powertrain components of the vehicle 200 may be extracted by the thermal management system 102. The extracted thermal energy may be transferred between components of the vehicle 200, for example thermal energy extracted from the battery 204 may be supplied to CCS 104 for use in heating the cabin of the vehicle 200, or may be transferred off the vehicle 200, for example via a low temperature radiator to transfer the thermal energy to the outside environment. The vehicle thermal management system 100 may be operable in a large number of different modes of operation to meet the various thermal transfer requirements of the components. Identifying an operating mode having a lowest, or at least reduced, energy cost for operation of the vehicle thermal management system 100 to meet the current thermal energy transfer requirements of the vehicle components may be difficult and may depend on a range of factors. Some of those factors may be external to the vehicle, such as an ambient temperature. Furthermore, selecting an operating mode based only on a current state of the vehicle component may not allow changes in the generation of heat in the vehicle to be taken into account. For example, for an electric vehicle 200 being driven on a clear highway, the power supplied by the battery may be relatively high, leading to significant heat generation within the traction battery 204 due to internal resistance. At the same time, significant airflow may be expected over a low temperature radiator of the vehicle. An operating mode for the vehicle thermal management system 100 may be selected to extract heat generated within the traction battery 204 and reject that heat through the low temperature radiator to the environment, while providing a portion of the heat energy to the CCS 104 for cabin heating. The electric vehicle 200 may then slow, for example due to congestion on the highway or leaving the highway for a local road, resulting in reduced heat generation in the traction battery 102 which may now be insufficient for cabin heating. In order to maintain a comfortable temperature for the cabin occupants, thermal energy may be supplied from another source, such as a heater drawing power from the traction battery 204, which undesirably uses power drawn from the traction battery. A schematic representation of an example PTM 102 is shown in Figure 3. A control valve apparatus 302 is configured to control the circulation of thermal transfer fluid, or coolant, to manage a thermal load of the front electric drive units 202a, the rear electric drive unit 202b, the battery unit 204 and the climate control system, or climate control unit 104 of the vehicle cabin for occupant comfort. The PTM 102 comprises a coolant heater 304; a first heat exchanger 306; and a second heat exchanger 308. The coolant heater 304 is configured to heat the coolant, for example to provide fast warm-up of traction battery 204 when initially operating the vehicle 200. The coolant heater 304 may be a high voltage (HV) heater that draws electrical power directly from traction battery 204. The first heat exchanger 306 may be configured selectively to cool the coolant of the PTM 102. A refrigerant circuit of the CCS 104 is coupled to a refrigerant side of the first heat exchanger 306 to cause the first heat exchanger 306 to operate as a chiller. Thus, the first heat exchanger 306 enables the transfer of heat energy extracted from the coolant to the refrigerant of the CCS 104. In this way, excess thermal energy may be transferred from powertrain components for use in heating the cabin of the vehicle. In some embodiments, the first heat exchanger 306 may be bi-directional and allow the transfer of thermal energy from the refrigerant of the CCS 104 to the coolant of the PTM 102, for example to allow for the supply of heat sourced from the outside environment via an outside heat exchanger of the CCS 104 to heat the coolant. The refrigerant circuit may be coupled to an outside heat exchanger operable to transfer heat between the refrigerant and the outside environment. The supply of refrigerant can be halted to reduced or prevent heat exchange in the first heat exchanger 306. The second heat exchanger 308 is a low temperature heat exchanger (or a low temperature radiator) and is operative to reject heat from the coolant to the outside environment. The control valve apparatus 302 comprises a first pump 310 and a second pump 312. The PTM 102 comprises a first coolant circulation loop 314; and a second coolant circulation loop 316. A liquid coolant, or thermal transfer fluid, is circulated through the first and second coolant circulation loops 314, 316 to perform supply or sinking of thermal energy to the front and rear electric drive units 202a, 202b and the traction battery 204. At least one coolant temperature sensor 318 may be provided for measuring the temperature of the coolant. In the illustrated example, the coolant temperature sensor 318 is provided at an inlet to the second pump 312. The coolant temperature sensor 318 measures the temperature of the coolant supplied to the second pump 312. An electric fan (not shown) may optionally be provided to circulate air over the second heat exchanger 308 to promote cooling of the coolant. Bypass conduits may be provided for one or more components of the first 314 or second 316 coolant loops. A bypass conduit may controllably opened or closed by a valve to control the supply of coolant to the respective component. For example, the first coolant circulation loop 314 is configured to supply coolant to the traction battery 204. The coolant heater 304 and the first heat exchanger 306 are provided in the first coolant circulation loop 314. The coolant heater 304 is provided downstream of the traction battery 204 and, in use, is operative to heat the coolant. The first heat exchanger 306 is disposed upstream of the traction battery 204 and, in use, can be configured to cool the coolant prior to introduction into the traction battery 204. As described herein, the first and second coolant circulation loops 314, 316 may be selectively connected to each other to enable the supply of coolant from the first heat exchanger 304 to the front and rear electric drive units 202a / b. The first coolant circulation loop 314 comprises a battery supply conduit 320, and a battery bypass conduit 322. The battery supply conduit 320 is configured to supply coolant to the traction battery 204. The battery bypass conduit 322 can be selectively opened and closed to control the supply of coolant to perform cooling of the battery unit 204. The second coolant circulation loop 316 is configured to supply coolant to the front and rear electric drive units 202a / b. The second heat exchanger 308 is provided in the second coolant circulation loop 316 downstream of the front and rear electric drive units 202a / b. In some examples, the front 202a and rear 202b electric drive units may each be provided with a respective bypass conduit (not shown) to selectively bypass the respective electric drive unit 202a, 202b, accordingly, transfer of thermal energy to or from the front 202a and rear 202b electric drive units may be permitted when the respective electric drive unit 202 is not bypassed and may be avoided when the respective electric drive unit 202 is bypassed. In use, the second heat exchanger 308 rejects thermal energy from the coolant to the external environment. The second coolant circulation loop 316 comprises a heat exchanger coolant conduit 324 for supplying coolant to the second heat exchanger 308; and a heat exchanger bypass conduit 326 for selectively bypassing the second heat exchanger 308. The control valve apparatus 302 may provide proportional control of the coolant flow rate through the heat exchanger bypass conduit 326, thereby controllably increasing or decreasing the flow through the second heat exchanger 308. Control valve apparatus 302 includes crossflow valves 328 that are arranged to couple or decouple the first coolant circulation loop 314 (battery coolant circulation loop) and second coolant circulation loop 316 (electric drive unit coolant circulation loop). In addition, the crossflow valves 328 determine whether the first heat exchanger 306 is coupled in a coolant circulation loop with the battery 204 or the electric drive units 202. In other words, the crossflow valves 328 determine whether the first heat exchanger 306 is coupled in the first coolant circulation loop 314 or the second coolant circulation loop 316, or both when the first 314 and second 316 coolant circulation loops are coupled. The coupling and decoupling of the first coolant circulation loop 314, second coolant circulation loop 316 and first heat exchanger 306, as well as a state (on or off) of the first heat exchanger 306 defines the configuration of the thermal management system 102. When the first heat exchanger 306 is active, it couples the coolant circuit it is in with the refrigerant circuit. Herein coupling between the first coolant circulation loop 314, second coolant circulation loop 316 and / or refrigerant circuit indicates that the first coolant circulation loop 314, second coolant circulation loop 316 and / or refrigerant circuit are in thermal communication, such that thermal energy may be transferred between them. Similarly, when they are decoupled, they are not in thermal communication, and no thermal energy (or a negligible amount of thermal energy) is transferred between them. Thus, control valve apparatus 302 allows the configuration of the PTM 102 to be controlled to selectively bypass certain components of the thermal management system, such as the second heat exchanger 308, and / or to selectively couple the first and second coolant circulation loops 314, 316 together to allow transfer of thermal energy between the components served by the different coolant circulation loops. This means that there may exist a large number of possible configurations of the PTM 102. For each configuration, one or more components may be controlled to different states, for example first heat exchanger 306 may be on or off depending on whether refrigerant is provided to the first heat exchanger 306, second heat exchanger 308 may be selectively bypassed, etc. As such, there may be multiple operating modes of the PTM 102 for each of the configurations of the PTM, resulting in a large total number of possible operating modes for the PTM 102 from which an operating mode is to be selected by the controller 106 to meet current requirements of the various components of the electric vehicle 200. In embodiments, CCS 104 may include a refrigerant circuit including a compressor, at least one internal evaporator operable to extract heat energy from air in the cabin, at least one internal condenser operable to supply heat energy to the air in the cabin and an outside heat exchanger for exchanging thermal energy with an outside environment. As discussed above, refrigerant of the climate control system 104 may be selectively provided to first heat exchanger 306 to allow heat energy to be transferred between the coolant of the PTM 102 and the refrigerant of the CCS 104. Thus, CCS 104 may be operable in multiple modes. In some embodiments, selection of an operating mode for the CCS 104 may be coordinated with a selected operating mode for PTM 102 to further improve overall efficiency of the vehicle thermal management system 100. The components of the vehicle may include one or more thermal customers. Each thermal customer may have a respective target operating temperature range, or a target operating temperature (for example where the upper and lower limits of the target operating temperature range may be considered to be the same). The thermal management system may be arranged to control temperatures of the thermal customers, e.g., to cause the thermal customers have respective temperatures that are in respective target operating temperature ranges. The traction battery 204; electric drive units 202; and vehicle cabin and / or CCS 104 are examples of thermal customers. FIG. 4A to FIG. 4F show examples of configurations of the system of FIG. 3. Here, the first coolant circulation loop 314 includes the battery 204 and the coolant heater 304, the second coolant circulation loop 316 includes the electric drive units 202a, b and the second heat exchanger 308. The first coolant circulation loop 314 and second coolant circulation loop 316 may be selectively coupled or decoupled by the crossflow valves 328. Further the first heat exchanger 306 may be coupled with either of the first coolant circulation loop 314 or the second coolant circulation loop 316 (or both when the first coolant circulation loop 314 and the second coolant circulation loop 316 are coupled with each other) by the crossflow valves 328. As shown in FIG. 3, the valves 328 in the first and second coolant circulation loops 314, 316 may be arranged in multiple operational positions interconnecting their respective ports 1-4 and 5-8. In FIGS. 4A-4F they have the following arrangements, as will become evident from the description below of the circulation loops resulting when the valves are so arranged: FIGS. 4A and 4B: as shown in FIG. 3, with ports 1 and 3, 2 and 4, 5 and 7 and 6 and 8 being interconnected; FIGS. 4C and 4D: different from FIG 3 and 4A, having ports 5 and 8 interconnected and ports 6 and 7 interconnected; and FIG. 4E and 4F: as for FIGS. 4C and 4D, except ports 1 and 4 are interconnected, as are ports 2 and 3. In FIG. 4A the first coolant circulation loop 314 and second coolant circulation loop 316 are decoupled, and the first heat exchanger 306 is in the first coolant circulation loop 314. The first heat exchanger 306 is not active, such that the first coolant circulation loop 314 is decoupled from the CCS 104 that comprises a refrigerant circuit 408. This leads to three thermal circuits being formed. The first thermal circuit 402a corresponds with the first coolant circulation loop 314 and includes the battery 204 and coolant heater 304. The second thermal circuit 402b corresponds with the second coolant circulation loop 316 and includes the electric drive units 202 and the second heat exchanger 308. The third thermal circuit 402c corresponds with the refrigerant circuit 408 and includes the internal evaporator 404 and the outside heat exchanger 406. FIG. 4B shows the same configuration as FIG. 4A, with the first coolant circulation loop 314 and second coolant circulation loop 316 being decoupled and the first heat exchanger 306 being in the first coolant circulation loop 314. However, in FIG. 4B the first heat exchanger 306 is active, and so the first coolant circulation loop 314 is coupled with the refrigerant circuit 408. This leads to two thermal circuits. A first thermal circuit 402a includes battery 204, coolant heater 304, first heat exchanger 306, internal evaporator 404 and outside heat exchanger 406. The second thermal circuit 402b includes the electric drive units 202 and the second heat exchanger 308. In FIG. 4C the first coolant circulation loop 314 and second coolant circulation loop 316 are coupled. The first heat exchanger 306 is also coupled in the first coolant circulation loop 314 and the second coolant circulation loop 316. The first heat exchanger 306 is not active, such that the first coolant circulation loop 314 and second coolant circulation loop 316 are decoupled from the refrigerant circuit 408. This leads to two thermal circuits being formed. The first thermal circuit 402a corresponds with the combined first coolant circulation loop 314 and second coolant circulation loop 316, and includes the battery 204, coolant heater 304, electric drive units 202, and second heat exchanger 308. The second thermal circuit 402b corresponds with refrigerant circuit 408. FIG. 4D shows the same configuration as FIG. 4C, with the first coolant circulation loop 314 and second coolant circulation loop 316 being coupled. However, in FIG. 4D the first heat exchanger 306 is active, and so the first coolant circulation loop 314 and second coolant circulation loop 316 are coupled with the refrigerant circuit 408. This leads to an arrangement with one thermal circuit 402a that includes all of the illustrated components. In FIG. 4E the first coolant circulation loop 314 and second coolant circulation loop 316 are decoupled, as in FIG. 4A, but now the first heat exchanger 306 is in the second coolant circulation loop 316. The first heat exchanger 306 is not active, such that the second coolant circulation loop 316 is decoupled from the refrigerant circuit 408. This leads to three thermal circuits being formed. These thermal circuits are the same as in FIG. 4A, except that the first heat exchanger 306 is in the second coolant circulation loop 316. As such, the thermal transfer in this arrangement is the same or similar to the arrangement of FIG. 4A. However, these modes of operation are not necessarily equivalent. For example, an energy cost to transition to the mode of FIG. 4A may be less than the energy cost to transition to the mode of FIG. 4E, for example, and so the mode of FIG. 4A may be a better selection than the mode of FIG. 4E in that case. The energy cost of transitioning maybe associated with driving actuators to control the crossflow valves 328, for example. FIG. 4F shows the same configuration as FIG. 4E, with the first coolant circulation loop 314 and second coolant circulation loop 316 being decoupled and the first heat exchanger 306 being in the second coolant circulation loop 316. However, in FIG. 4F the first heat exchanger 306 is active, and so the second coolant circulation loop 316 is coupled with the refrigerant circuit 408. This leads to two thermal circuits. A first thermal circuit 402a includes battery 204 and coolant heater 304. The second thermal circuit 402b includes the electric drive units 202, the second heat exchanger 308, the first heat exchanger 306, the internal evaporator 404, and outside heat exchanger 406. Arrangements, such as those shown in FIG. 3 and FIG. 4A to FIG. 4F, lead to a significant number of possible operating modes for the thermal management system 102. In each of the configurations, components such as the second heat exchanger 308, coolant heater 304 and outside heat exchanger 406 may each be active or inactive. In some examples the number of modes may exceed one hundred. In some examples, the number of modes may exceed two hundred. Where a system is capable of fewer configurations, a smaller number of potential operating modes exist and there are fewer options for heat transfer among the components of a vehicle. In such systems, the selection of an operating mode may be straightforward, e.g„ using a lookup table that indicates a mode based on temperatures of components of the vehicle (e.g. taking into account the temperatures of three or fewer components). However, the reduced options of transferring heat between components may limit the achievable energy efficiency. In some systems that provide a range of configurations of the thermal management system that are comparable to the examples in FIG. 3 and FIG. 4A to FIG. 4F, the full benefit of these configurations may not be achieved where the system allows limited combinations of configurations with operation states of components (such as a heater on / off or radiator used / bypassed). In such systems, only a small subset of the potential modes are selectable. Similarly to the case of where few configurations are available, in such systems, a mode of the thermal system may be selected based on relative temperatures of the components according to a table of selectable modes. In such systems, the number of selectable modes may be fewer than 20 or fewer than 15, for example. Accordingly, these systems provide limited flexibility in controlling heat transfer between components, potentially losing opportunities for energy efficiency. As noted above, in systems having a relatively small number of operating modes (e.g., 20 or fewer), an operating mode may be selected in a relatively straightforward way, e.g. from a table based on temperatures of the components. The table (or other mode selection method) may be defined in advance based on engineer intuition. Expanding such temperature-based approaches by considering heat availability or heat demand in specific components in the selection of particular modes does not address the limitations of a system with few selectable operating modes, and does not take efficiency of the operating modes into consideration when selecting an operating mode. Where the number of operating modes significantly increase, a selection of a mode based on engineer intuition becomes impractical, and reliably selecting an appropriate operating mode becomes increasingly difficult using a simple table-based, or similar, approach. A schematic representation of an example refrigerant circuit 408 of climate control system 104 is shown in Figure 5. The refrigerant circuit of Figure 5 includes an outside heat exchanger 502, chiller 504, in-vehicle evaporator 506, and in-vehicle condenser 508 arranged in a circuit. In-vehicle evaporator 506 may comprise more than one evaporator operable to provide multi-zone climate control within the vehicle. As would be appreciated by the skilled person, other components, such as one or more expansion valves, bypass conduits, etc. may be provided in the refrigerant circuit, but are not shown in Fig. 5 for clarity and brevity. In operation, the compressor 510 operates to raise the pressure of the refrigerant which is then supplied to an input of condenser 508 where heat may be released for use in heating the cabin, if required. An output of condenser 508 is coupled to an input of the outside heat exchanger 502 which may be bi-directional in the sense of being capable of recovering or rejecting heat energy from / to an ambient environment. An output of the outside heat exchanger 502 is coupled to an input of the chiller 504. The chiller 504 is configured to selectively cool a thermal transfer fluid, or coolant, of the PTM 102 to allow heat energy to be transferred from the PTM 102 to the refrigerant of the CCS 104. An output of the chiller 504 is coupled to an input of the in-vehicle evaporator 506 where the refrigerant may absorb heat energy from the cabin (i.e. provide cooling). An output of the in-vehicle evaporator 506 is coupled to the compressor 510 to complete the refrigerant circuit. One or more electric blowers, or fans, may be provided associated with in-vehicle evaporator 506 and / or in-vehicle condenser 508 to provide airflow over the evaporator / condenser and distribute, or extract, thermal energy throughout the cabin. Similarly, airflow may be provided to outside heat exchanger 502 through the use of an electric fan, or by one or more controllable ducts, arranged to direct air from the outside environment over the outside heat exchanger 502. Also provided in the refrigerant circuit are a number of bypass valves to allow components of the refrigerant circuit to be selectively bypassed according to a desired operating configuration of the climate control system 104. A first bypass valve 512 is arranged to selectively bypass refrigerant around the outside heat exchanger 502 in the event that no heat is required to be discharged to or extracted from the outside environment. A second bypass valve 514 is arranged to selectively bypass refrigerant around the chiller 504 in the event that no heat is required to be discharged to or extracted from the PTM 102. A third bypass valve 516 is arranged to selectively bypass refrigerant around in-vehicle evaporator 506 in the event that no cooling of the cabin is required. Bypassing a component effectively removes that component from the refrigerant circuit so that no heat transfer occurs in that component. For example, by selectively bypassing chiller 504 using second bypass valve 514, heat exchange between the CCS 104 and PTM 102 is disabled. Example operating modes, or configurations, of the CCS 104 may include: • Cabin cooling with thermal energy rejected to ambient via the outside heat exchanger 504. In this configuration, second bypass valve 514 is selectively controlled to bypass chiller 504, while first and third bypass valves are selectively controlled to cause the refrigerant to pass through the outside heat exchanger 502 and in-vehicle evaporator 506; • Cabin cooling and assisted powertrain cooling with thermal energy rejected to ambient via the outside heat exchanger 502. In this configuration, first, second and third bypass valves are selectively controlled to cause the refrigerant to pass through the outside heat exchanger 502, chiller 504, and in-vehicle evaporator 506. Thermal energy is transferred from PTM 102 via the chiller 504 providing increased cooling to the powertrain components coupled to the PTM 102; • No cabin thermal demand with assisted powertrain cooling. In this configuration, first and second bypass valves are selectively controlled to cause the refrigerant to pass through the outside heat exchanger 502 and chiller 504. Third bypass valve 516 is selectively controlled to bypass in-vehicle evaporator 506 as there is no heat / cooling demanded by the cabin; • Cabin heating supplied by ambient heat recovery. In this configuration, the second bypass valve 514 is selectively controlled to bypass chiller 504 and the third bypass valve 516 is selectively controlled to bypass in-vehicle evaporator 506, while first valve 512 is selectively controlled to cause the refrigerant to pass through the outside heat exchanger 502. Heat energy is recovered from ambient via the outside heat exchanger 502 and provided to the cabin via condenser 508; • Cabin heating supplied by powertrain heat recovery. In this configuration, the first bypass valve 512 is selectively controlled to bypass the outside heat exchanger 502 and the third bypass valve 516 is selectively controlled to bypass in-vehicle evaporator 506, while second valve 514 is selectively controlled to cause the refrigerant to pass through the chiller 504. Heat energy is transferred from PTM 102 to the refrigerant via chiller 504 and is provided to the cabin via condenser 508; • Cabin heating supplied by ambient heat recovery and powertrain heat recovery. In this configuration, first and second bypass valves are selectively controlled to cause the refrigerant to pass through the outside heat exchanger 502 and chiller 504. Third bypass valve 516 is selectively controlled to bypass in-vehicle evaporator 506. Heat energy recovered from both ambient and the powertrain to provide a thermal energy requirement of the cabin. For the climate control system 408 illustrated in Figure 5, there may be more than one configuration that is able to meet a thermal demand associated with the cabin of the vehicle 200. For example, to supply heat to the cabin, different operating modes may be available to source thermal energy either from the powertrain via PTM 102 and chiller 504, and / or from ambient via outside heat exchanger 502. Furthermore, the relative efficiency of each available operating mode of the climate control system 104 may depend on an operating mode of PTM 102 which is itself reconfigurable to allow thermal energy transfer requirements of powertrain components to be met. Therefore, a whole system approach may be taken to identify a low energy cost operating mode or configuration for the vehicle thermal energy management system 100. Such a whole system approach may rely on determining parameter values at multiple locations within both the PTM 102 and the CCS 104. As discussed above, thermal fluid flows, i.e. the flow of coolant in PTM 102 or refrigerant in CCS 104, are reconfigurable and therefore a measurement taken in a current operating mode, or configuration, may not reflect a parameter value that would be present at that location in a different operating mode, or configuration. One approach to selecting an operating mode for a vehicle thermal management system 100 operable in a large number of operating modes, or configurations, is to determine energy costs associated with different operating modes that are able to meet the thermal demands placed on the system and select an operating mode to be implemented based on a lowest determined cost. This may allow for more reliable selection of an energy efficient operating mode. However, determining an energy cost for a particular configuration of the thermal management system may rely on one or more parameter values relating to operation of the thermal management system in that operating mode, e.g. an energy cost for a particular configuration may be based on determining parameter values at multiple locations within both the PTM 102 and the CCS 104. Furthermore, as discussed above, thermal fluid flows, i.e. the flow of coolant in PTM 102 or refrigerant in CCS 104, are reconfigurable and therefore a measurement taken in a current operating mode, or configuration, may not reflect a parameter value that would be present at that location in a different operating mode, or configuration. According to embodiments, rather than incorporating a large number of sensors into the vehicle thermal management system 100, it may be more efficient to infer virtual sensor measurement values using virtual sensor models for the vehicle thermal management system 100. Furthermore, the use of virtual sensors may allow virtual sensor measurements to be determined for a target configuration that is different from a current operating configuration of the vehicle thermal management system 100, and that would not be possible to measure using a physical sensor without first reconfiguring the vehicle thermal management to the target configuration. The virtual sensor locations may be within the PTM 102 and / or CCS 104, for example to provide virtual temperature measurements of the coolant or refrigerant respectively and / or heat flows in either circuit. As an illustrative example, a temperature of coolant entering the first heat exchanger, or chiller, 306 may be used to determine an energy cost associated with an operating mode. However, this temperature measurement may be dependent on the configuration of the PTM 102. In the configuration discussed above with respect to Figure 4A, the first heat exchanger is coupled to the traction battery 204 and heater 304. Therefore, the temperature of coolant entering the first heat exchanger 306 may be substantially determined by the temperature of the traction battery 204 through which the coolant passes prior to entering the first heat exchanger 306. In contrast, in the configuration illustrated in Figure 4E, the first heat exchanger 306 is decoupled from the first coolant circuit including the traction battery and is instead coupled to the electric drive units 202a / b. Thus, the temperature of coolant entering the first heat exchanger 306 may be independent of the temperature of the traction battery 204, but may instead be substantially determined by the temperature of the electric drive units 202a / b. Measuring the temperature of the coolant entering the first heat exchanger 306 with a physical sensor may provide an accurate and easy way to determine the temperature value for the current configuration of the PTM 102. However, if it is desired to determine a corresponding value for a different configuration of the PTM 102, e.g. to allow an energy cost for that configuration to be determined, a measured value may not accurately reflect the temperature that would be measured in the target configuration for example when considering the configurations illustrated in Figures 4A and 4E. Figure 6 illustrates a method 600 of determining a virtual sensor measurement for a vehicle thermal management system, for example comprising the PTM 102 and CCS 104, of an electric vehicle 200 that can be performed by the controller 106 illustrated in Figure 1. According to the illustrated method 600, a plurality of virtual sensor models may be obtained 602, each virtual sensor model is associated with a configuration of the thermal management system 100 and allows a virtual sensor measurement value to be determined, or predicted, for a virtual sensor location when the thermal management system is operating in the associated configuration. An indication of a particular configuration of the thermal management system is received at block 604. The indicated configuration may be a current configuration of the thermal management system or may be for a different configuration. At least one sensor signal is received 606 from one or more physical sensors present in the thermal management system 100, the physical sensor providing a sensor measurement value corresponding to a measured parameter of the thermal management system at the time the measurement was taken. Based on the indicated configuration of the thermal management system, a virtual sensor model is selected at block 608, and a virtual sensor measurement value is then determined 610 based on the selected virtual sensor mode and the received sensor signal. A signal representative of the virtual sensor measurement value is then output at block 612, for example for use in predicting an energy cost associated with the indicated configuration of the thermal management system. In some embodiments, energy costs associated with a plurality of configurations may be determined based on virtual sensor measurement values, and therefore the method of Figure 6 may be repeated for each configuration of the plurality of configurations to predict virtual sensor measurement values for each configuration. It has to be borne in mind however that, when considering a thermal management system configuration different to a current configuration, a prediction is necessary of what the actual sensor measurements will be in that configuration, when the system operates in that configuration, in order to determine the predicted virtual parameters. That is, there is a two-step process for determining virtual parameters in a system configuration different from a current configuration. The thermal management system may be operable to transfer thermal energy from a first component of a plurality of components to a second component of the plurality of components, where each configuration of the thermal management system defines a configuration of one or more coolant loops supplying heat transfer fluid to at least one component of the vehicle. In embodiments, the virtual sensor measurement value comprises a predicted temperature value at the virtual sensor location, or a predicted mass-flow rate (for example of air, coolant, refrigerant, etc.) at the virtual sensor location. A plurality of physical sensors may be provided in the thermal management system and signals from two or more sensors may be received, each signal representative of a measured value associated with the respective sensor. A virtual sensor measurement value may be determined based on two or more measured values. In embodiments, the virtual sensor model comprises a map of a relationship between the at least two sensor signals and a corresponding virtual sensor measurement. In some embodiments, a one of the at least two sensor signals may comprise a measurement value external to the thermal management system, for example an ambient temperature of the outside environment. The virtual sensor models may be determined by identifying correlations between physical sensor measurements and parameter values at the virtual sensor locations in a data set capturing sensor measurements and operating parameter values for a wide range of operating conditions and for each of the configurations of the vehicle thermal management system. The data set may be generated empirically on a instrumented test system of the vehicle thermal management system, or using a numerical model to simulate the thermal management system. For each virtual sensor model, a regression analysis may be performed on the data set, for example a multi-factor linear regression analysis, to identify a relationship between a virtual sensor measurement value and one or more sensor measurement values provided by physical sensors within the thermal management system. In embodiments, sensitivity analysis may be applied to the data set for a virtual sensor model to determine which of the available physical sensor measurements have the greatest impact on the predicted virtual sensor measurement value. For example, two physical sensor measurements determined to have the greatest correlation with the predicted virtual sensor measurement value may be selected and used to generate a 2D map. The virtual sensor model may then be generated based on the relationship between the identified most impactful sensor measurement values and the predicted virtual sensor measurement value determined according to the regression analysis. In embodiments, the model may be provided as coefficients of an equation defining the determined relationship, as a look-up-table (LUT) of sensor measurements and associated virtual sensor measurement values, as a map, such as a 2D map, of a relationship between physical sensor signals and a corresponding virtual sensor measurement, etc. In some embodiments, multiple 2D maps can be combined in a model, with interpolation between the 2D maps, to provide for more complex relationships to determine a virtual sensor value. Changing from one configuration of the thermal management system to another may introduce discontinuities, or other non-linearities, into relationships between measured parameter values and virtual sensor readings that are to be predicted. According to an embodiment, the full operating range of the vehicle thermal management system may be divided into a plurality of operational zones, each corresponding to a specific configuration of components and functions that are active in the thermal management system. The specific configuration associated with an operational zone may include configurations and active functions of both the PTM 102 and the CCS 104, for example the PTM 102 operating modes illustrated in Figures 4A-4F and the example CCS 104 operating modes discussed above. Each operational zone may be chosen such that relationships between parameter values and virtual sensor measurements when the vehicle thermal management system is operating within that operational zone are substantially linear. Operational zones may be at least partially defined by a range of temperatures in which the system is operating, for example hot or cold ambient conditions. In embodiments, each operating mode of the thermal management system is associated with one of the operational zones. For each defined operational zone, multiple simulations of the vehicle thermal management system may be defined in which input parameters to the model are swept through the full range that will be experienced within that operational zone. The results of the multiple simulations for an operational zone are captures and regression analysis performed to identify the relationships between simulated physical sensor readings within the PTM 102 and CCS 104 and the virtual sensor measurements that are to be modelled. As discussed above, sensitivity analysis can then be applied to identify the most significant, or most impactful, physical sensor measurements for each virtual sensor. In some cases, a virtual sensor measurement associated with a parameter in the PTM 102 may be found to correlate strongly with a physical sensor reading of the CCS 104, and vice versa. For each virtual sensor to be used in a particular operational zone, a model can then be generated, for example in the form of a map or look-up-table, defining the relationship between the most impactful physical sensor readings and the virtual sensor measurement value. A plurality of models, or maps, each associated with a different operational zone are generated for each virtual sensor to allow determination of virtual sensor measurement values in each operating mode of the vehicle thermal management system. In some embodiments, it may not be possible to measure certain input values to be used to determine a virtual sensor using a physical sensor (e.g. due to a location being difficuIt / impossibIe to access with a physical sensor, the required value may not be directly measurable, etc.). Such values may first be generated as intermediate virtual sensor measurement values, as discussed above, and then those intermediate virtual sensor measurement values used in a further virtual sensor model to provide the desired virtual sensor output. In embodiments, the intermediate virtual sensor values may not used other than to determine the desired virtual sensor measurement values. Certain methods and systems as described herein may be implemented by one or more processors that process program code that is retrieved from a non-transitory storage medium. Figure 7 shows an example 700 of a device comprising a computer-readable storage medium 720 coupled to at least one processor 710. The computer-readable media 720 can be any media that can contain, store, or maintain programs and data for use by or in connection with an instruction execution system. Computer-readable media 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 random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory, or a portable disc. In Figure 7, the computer-readable storage medium comprises program code to perform a method corresponding to the embodiment shown in Figure 6, that is: obtaining 602 thermal energy information for a plurality of components of an electric vehicle; obtaining 604 information defining a plurality of operating modes of the thermal management system; determining 606, for each operating mode, an energy cost associated with that operating mode based on the thermal energy information and using a model of the thermal management system; selecting 608 an operating mode having a lowest calculated energy cost; and providing 610 an output indicating the selected operating mode. The device 700 may be included in controller 106 of an electric vehicle 200, as illustrated in FIG. 2, for example. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A method of determining a virtual sensor measurement for a thermal management system of an electric vehicle, wherein the thermal management system is operable in a plurality of configurations, the method comprising:obtaining a plurality of virtual sensor models, each virtual sensor model operable to determine a virtual sensor measurement based on at least one sensor measurement value, wherein each virtual sensor model is associated with a configuration of the thermal management system;receiving an indication of a configuration of the thermal management system;receiving a sensor signal indicating a sensor measurement value;selecting a virtual sensor model of the plurality of virtual sensor models based on the indication of the configuration of the thermal management system;determining a virtual sensor measurement value based on the selected virtual sensor model and the received sensor signal; and outputting a signal representative of the virtual sensor measurement value.

2. The method of claim 1, wherein receiving an indication of a configuration of thermal management system comprises receiving an indication of a first configuration while the thermal management system is operating in a second configuration, wherein the first configuration is different from the second configuration.

3. The method of claim 2, wherein the determined virtual sensor measurement value comprises a predicted measurement value for the first configuration of the thermal management system.

4. The method of any preceding claim, wherein the vehicle comprises a plurality of components, the thermal management system operable to transfer thermal energy from a first component of the plurality of components to a second component of the plurality of components; andwherein each configuration of the thermal management system defines a configuration of one or more coolant loops supplying heat transfer fluid to at least one component of the plurality of components of the vehicle.

5. The method of any preceding claim, wherein the virtual sensor measurement comprises a virtual temperature value representing a temperature of a portion of the thermal management system.

6. The method of any preceding claim, wherein the virtual sensor measurement comprises a virtual mass flow value representing a mass flowthrough a portion of the thermal management system.

7. The method of any preceding claim, wherein receiving the sensor signal comprises receiving a first sensor signal from a first sensor of the thermal management system and a second sensor signal from a second sensor of the thermal management system, each sensor signal representative of a measured value associated with the respective sensor.

8. The method of claim 7, wherein the virtual sensor model comprises a map of a relationship between the first and second sensor signals, and a corresponding virtual sensor measurement.

9. Computer readable instructions which, when executed by one or more processors, cause the one or more processors to perform the method according to any of claims 1 to 8.

10. A control system for determining a virtual sensor measurement for a thermal management system of a vehicle, wherein the thermal management system is operable in a plurality of configurations, the control system comprising one or more processors collectively configured to:obtain a plurality of virtual sensor models, each virtual sensor model operable to determine a virtual sensor measurement based on at least one sensor measurement value, wherein each virtual sensor model is associated with a configuration of the thermal management system;receive an indication of a configuration of the thermal management system;receive a sensor signal indicating a sensor measurement value;select a virtual sensor model of the plurality of virtual sensor models based on the indication of the configuration of the thermal management system;determine a virtual sensor measurement value based on the selected virtual sensor model and the received sensor signal; and output a signal representative of the virtual sensor measurement value.

11. The control system of claim 10, wherein the indication of a configuration of the thermal management system comprises an indication of a first configuration while the thermal management system operates in a second configuration, wherein the first configuration is different from the second configuration.

12. The control system of claim 11, wherein the one or more processors are further configured to determine a predicted measurementvalue for the first configuration of the thermal management system.

13. The control system of any of claims 10 to 12, wherein the virtual sensor measurement comprises a virtual temperature valuerepresenting a temperature of a portion of the thermal management system; orwherein the virtual sensor measurement comprises a virtual mass flow value representing a mass flow through a portion of the thermal management system.

14. The control system of any of claims 10 to 14, wherein the one or more processors are further configured to:receive a first sensor signal from a first sensor of the thermal management system;receive a second sensor signal from a second sensor of the thermal management system, wherein each of the first and second sensor signals are representative of a measured value associated with the respective sensor; andwherein the virtual sensor model comprises a map of a relationship between the first and second sensor signals, and a corresponding virtual sensor measurement.

15. A vehicle comprising:the control system of any of claims 10 to 14; anda thermal management system communicatively coupled to the control system.

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