METHOD FOR ESTIMATING BATTERY CAPACITY IN AN ELECTRIC VEHICLE AND ELECTRIC VEHICLES FOR THIS METHOD

Abstract

Vehicle (100) comprising the following: a traction battery (214), a charger (112) for charging the traction battery (214), and a control device (122) configured to control the charger (112), to postpone charging the traction battery (214) during a battery relaxation period that begins in response to battery current falling below a threshold, and to measure an initial open-circuit voltage of the traction battery (214) after the battery relaxation period has elapsed and before charging the traction battery in order to update a battery capacity value using the initial open-circuit voltage, wherein the control device (122) is configured to retrieve a stored value for the battery relaxation period based on battery temperature, age of the traction battery (214) and state of charge of the traction battery (214); and wherein the control device (122) stops updating the battery capacity value in response to the battery temperature falling below a The battery temperature threshold is reached.

Description

TECHNICAL AREA

[0001] The present invention relates generally to a method for estimating battery capacity in an electric vehicle and electric vehicles for this purpose. STATE OF THE ART

[0002] Vehicles that use electric power as a propulsion source rely on precise battery capacity measurements for numerous purposes, such as battery characteristics, state of charge, remaining range, and the like. Control strategies for charging and discharging traction batteries in battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) are constantly evolving to improve battery life and vehicle performance. The charging and discharging currents applied to the battery result in chemical reactions within the battery. Battery measurements taken before the battery chemistry has stabilized can lead to inaccurate determinations of various battery characteristics.

[0003] US 2014 / 0 077 815 A1 discloses an electric vehicle and a method for determining the battery capacity of the electric vehicle. Further electric vehicles or methods for determining battery capacity are disclosed in US 2011 / 0 285 356 A1, US 2007 / 0 216 361 A1, DE 10 2013 220 015 A1, and US 2013 / 0 110 428 A1. SUMMARY

[0004] Based on this prior art, the invention proposes a vehicle according to claim 1, a method according to claim 8, and a vehicle according to claim 12. Advantageous embodiments of the invention will become apparent from the dependent claims and the following description.

[0005] To improve the precision of battery capacity estimates, battery measurements are taken when the battery is fully relaxed, that is, when the battery chemistry has reached a stable state after a charge or discharge current has ceased. In one embodiment, a control device is configured to determine whether the battery is relaxed based on a stored battery profile and / or a battery relaxation timer. If the battery is not relaxed, charging or drawing power from the traction battery is deferred to improve battery measurement accuracy. The control device can manage a battery charger to stop current to / from the battery to ensure, based on the elapsed time of an associated relaxation period, that the battery is fully relaxed before battery characteristics are acquired.The control device can be configured to immediately begin charging the traction battery if it is determined to be relaxed. The control device can be configured to store a battery profile for use in determining whether the battery is fully relaxed. The control device can be configured to defer charging for a period of time if it determines that the traction battery is not relaxed. If battery capacity data is not available in a memory operationally connected to the control device, the control device can estimate the battery capacity after a relaxation period has elapsed.

[0006] In a representative implementation, the control device estimates the battery capacity using the formula Ce = ∫idt / (SOC1-SOC2), where SOC1 is the state of charge at the beginning of the learning process and SOC2 is the state of charge at the end of the learning process. SOC1 and SOC2 can be separated by at least a minimum relaxation time to ensure the battery is in a relaxed state before the control device estimates the battery capacity. The control device can stop the battery capacity estimation if the battery temperature falls below a predefined temperature threshold.

[0007] Methods can be used to execute any of the control device features described above. For example, the method can include charging a traction battery if the battery is relaxed, as determined by a stored battery profile or the elapse of an associated relaxation time. If the battery is not relaxed, charging is deferred for the relaxation period. The method can set the battery capacity based on the state of charge at the beginning of charging, the charging current, and the state of charge at the end of charging. Charging can begin immediately if the traction battery is found to be relaxed. The method can include storing a battery profile with a minimum battery relaxation time as a function of the battery temperature.The procedure can adjust the battery capacity after a certain period of time if the battery capacity data is not available in a vehicle memory.

[0008] In one example, setting the battery capacity involves using the formula Ce = ∫idt / (SOC). L1 -S0C L2 ), on, where SOC L1 The state of charge at the beginning of charging, and SOC. L2 The state of charge at the end of charging. The SOC L1 and the SOC L2 The battery capacity adjustment process can be separated by at least a minimum relaxation time to ensure the battery is in a relaxed state before the adjustment. The process may include halting the adjustment if the battery temperature falls below a predefined temperature threshold. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic view of a vehicle at a charging station according to an exemplary embodiment. Fig. Figure 2 is a schematic view of a vehicle according to an exemplary embodiment, Fig. Figure 3 is a schematic view of a communication system that a vehicle has according to an exemplary embodiment, Fig. Figure 4 is a view of a vehicle interface according to an exemplary embodiment, and Fig. Figure 5 is a flowchart showing a procedure according to an exemplary embodiment. DETAILED DESCRIPTION

[0009] As required, detailed embodiments are disclosed herein; however, it is understood that the disclosed embodiments are purely exemplary and can be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to illustrate details of certain components. Therefore, the specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching a person skilled in the art how to use the various embodiments of the claimed subject matter in different ways.

[0010] Vehicles can be powered by battery electric vehicles (BEVs) as well as by a combination of energy sources, including battery electric vehicles. For example, hybrid electric vehicles (HEVs) are considered, in which the powertrain is driven by both a traction battery and an internal combustion engine. In these configurations, the traction battery is rechargeable, and a vehicle charger provides energy to replenish the traction battery after it has been discharged.

[0011] With reference to Fig. Figure 1 illustrates a vehicle charging system in accordance with one or more embodiments and is generally designated by reference numeral 110. Wired or inductive charging is used to supply power from a vehicle charger 112 to a vehicle 100 to restore electrical power to the traction battery. In the illustrated embodiment, a charging station 116 is shown, which accommodates the vehicle 100 to be charged by inductive charging. The vehicle 100 docks at the charging station 116, which contains the vehicle charger 112. The vehicle charger 112 can be connected to receive household electrical power, such as that available in a typical home garage. The vehicle 100 may have a charging port 130 to which a charging cable from a charging station 131 can supply electricity to charge the traction battery.

[0012] The vehicle 100 has a secondary coil housed in an induction charging plate 118, which is located on the underside of the vehicle 100. The vehicle's secondary induction charging plate 118 is electrically connected to the vehicle battery. The vehicle 100 also has an AC-DC power converter to rectify and filter the alternating current received by the vehicle charger 112 into direct current for reception by the battery. The vehicle charger 112 is located in the floor beneath the vehicle 100 and has a primary charging coil housed in a corresponding primary induction charging plate 120. The primary induction charging plate 120 is generally positioned horizontally and at a distance from the vehicle's secondary induction charging plate 118. The primary induction charging plate 120 may be height-adjustable to create a suitable gap to facilitate charging the vehicle 100.Electric current is supplied to the primary coil, generating an electromagnetic field around the primary induction charging plate 120. When the vehicle's secondary induction charging plate 118 is near the powered primary induction plate 120, it receives power by being within the generated electromagnetic field. Current is induced in the secondary coil and subsequently transferred to the vehicle battery. The gap between the plates allows for variation in vehicle orientation and also accommodates other approved vehicles with different ground clearances.

[0013] In an alternative embodiment (not shown), the primary induction charging pad of the charging station is designed to be in a generally vertical position, for example, on or near a vertical wall. The vehicle could have a corresponding secondary induction charging pad on a front or rear vertical section, for example, as part of a front or rear bumper. The primary and secondary induction charging pads come close to each other when the vehicle is driven to the charging station and parked in a defined charging position.

[0014] With further reference to Fig. Figure 1 shows the vehicle 100 equipped with a control device 122. Although the vehicle control device 122 is shown as a single control device, it may comprise multiple control devices used to control the various vehicle systems. For example, the vehicle control device 122 may be a vehicle system controller / powertrain control module (VSC / PCM). In this respect, the vehicle charging control section of the VSC / PCM may be software embedded within the VSC / PCM, or it may be a separate hardware device. The vehicle control device 122 generally contains any number of microprocessors, ASICs, ICs, memory (for example, FLASH, ROM, RAM, EPROM, and / or EEPROM), and software code to interact with one another to perform a series of operations.Furthermore, a microprocessor in the vehicle control unit 122 includes a timer to track elapsed time intervals between a time reference and selected events. Predefined intervals are programmed such that the control unit provides specific command signals and monitors certain inputs at selectable time intervals. The vehicle control unit is electrically connected to the vehicle battery and receives signals indicating the battery charge level. The vehicle control unit 22 also communicates via a wired vehicle connection using a common bus protocol (for example, CAN) and can also use wireless communication.

[0015] The vehicle charger 112 can be equipped with a charger control unit 124, which can communicate wirelessly. The charger control unit 124 also has embedded software and is programmable to regulate the power flow supplied by the vehicle charger 112. The software included in the charger control unit 124 also features a timer to track elapsed time between defined events. Under selected conditions or upon receiving defined instructions, the charger control unit 124 can activate, deactivate, or reduce the power flow through the charger 112. The vehicle charger 112 is configured to receive signals indicating charging instructions from the vehicle control unit 124.

[0016] The vehicle control unit 122 is configured to communicate wirelessly with the charger control unit 124. Wireless communication can be achieved through RFID, NFC, Bluetooth, or other wireless methods. In at least one embodiment, the wireless communication is used to perform an association process between the vehicle 100 and the vehicle charger 112 prior to initiating a charging process. The association process may involve the vehicle control unit 122 sending a signal to the charger control unit 124 indicating an authentication request. The control unit 122 then receives a response signal from the charger control unit 124 and uses the response signal to determine whether or not to grant an initial authentication status to the vehicle charger 112.Authentication can be influenced by a number of predefined factors, including the manufacturer, power ratings, security keys, and / or other authentication factors. Based on a corresponding response signal from the charger control unit 124, the vehicle control unit 122 establishes a positive association between the vehicle 100 and the vehicle charger 112. Once an authenticated charger is detected, the vehicle control unit 122 provides an initiation signal to the charger control unit 124 to instruct the charging system to begin a charging procedure. The initial wireless request and subsequent authentication response constitute an association "handshake" between the two devices. The association also ensures further secure communication and control signals between the vehicle 100 and the vehicle control unit 112.If no positive authentication response is received from the vehicle control device 122, a command signal can be provided to prevent charging.

[0017] The vehicle control device 122 can further be configured to generate multiple warning signals. The vehicle 100 is equipped with a user display 126 inside the vehicle interior. The user display 126 serves as a warning mechanism for the operator. The control device 122 can generate several different on-board display messages. For example, a display warning can be generated to indicate that enhanced battery capacity learning is being initiated. The enhanced learning warning can inform the operator that battery charging is being deferred for a battery relaxation period. Other types of warnings, such as a light or an illuminated graphic symbol, can be provided, depending on the specific application and implementation.

[0018] As described above, battery capacity can be used for various monitoring and control functions of the battery monitoring system. Battery capacity determines how much energy is stored in the battery, and this determines the electric-only or electric vehicle (EV) range. Battery capacity can change as the battery ages, especially with intensive use in PHEV / BEV applications. Therefore, it is desirable to provide a method or system that learns or adapts to the battery capacity value over time. However, the precision of the battery measurements used to determine battery capacity can be affected by the timing of these measurements in relation to changes in battery charge / discharge current due to associated changes in battery chemistry.

[0019] The battery capacity can be learned or calculated as follows: Ce=∫idtSOC1−SOC2 where SOC1 is the initial state of charge (SOC) to begin capacity learning (i.e., the SOC immediately before the ampere-hour integration data is collected in the counter), and SOC2 is the final SOC to complete battery capacity learning (i.e., the SOC immediately after the ampere-hour integration data is collected in the counter). Battery capacity learning using Eq. 1 can be applied when the vehicle is driving (for example, in charge depletion mode in PHEVs) and input conditions are met, or when the battery is being charged via the power grid. Representative input conditions might include a difference between SOC1 and SOC2 greater than 40%, a driving time sufficient to obtain a change greater than 40% of the SOC but not exceeding 1 hour, and so on.

[0020] The open-circuit voltage is a precise indicator of the state of charge (SOC) for lithium-ion batteries, which are often used as vehicle traction batteries. SOC1 and SOC2 can therefore be estimated from the battery cell voltage. For best accuracy, open-circuit voltage measurements should be taken when the battery is fully relaxed. However, operator usage patterns and associated battery management systems for PHEVs and BEVs may not facilitate measurements and capacity determinations based on a fully relaxed traction battery. For example, a vehicle operator might drive the vehicle and arrive at charging station 116. The vehicle 100 will then either align with the wireless charging system or be immediately connected to the wired charging system 131.In another use case, the vehicle is charged, and the user immediately begins driving the vehicle after disconnecting it from the charging system, for example, driving away from the wireless charger or disconnecting the vehicle from the wired charging system 131 and immediately driving the vehicle. In these use cases, the traction battery chemistry may not have sufficient time to reach a stable state, meaning the battery is not fully relaxed, and the estimated traction battery capacity may be inaccurate if based on measurements obtained before the battery was fully relaxed.

[0021] Fig. Figure 2 illustrates an example of an electric vehicle, for instance, a plug-in hybrid electric vehicle (PHEV). A plug-in hybrid electric vehicle 202 can have one or more electric motors 204 mechanically connected to a hybrid transmission 206. The hybrid transmission 206 is also mechanically connected to a machine 208, for example, an internal combustion engine. The hybrid transmission 206 can also be mechanically connected to a drive shaft 210, which is mechanically connected to the wheels 212. The electric motors 204 can provide vehicle propulsion when the internal combustion engine 208 is switched off and can provide deceleration capability when the internal combustion engine 208 is switched on. The electric motors 204 also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system.

[0022] The traction battery 214 stores energy that can be used by the electric motors 204. A vehicle battery pack 214 typically provides a high-voltage direct current output. The traction battery 214 can be a battery pack with multiple cells. The traction battery can be a rechargeable battery, for example, a lead-acid, NiCd, nickel-metal hydride, lithium-ion, Li-ion polymer, and, less commonly, a zinc-air and molten salt battery.

[0023] The battery pack 214 is electrically connected to a power electronics module 216. The power electronics module 216 is also electrically connected to the electric motors 204 and provides the capability for bidirectional energy transfer between the battery 214 and the electric motors 204. For example, a battery 214 can provide a DC voltage, while the electric motors 204 may require three-phase AC to operate. The power electronics module 216 can convert the DC voltage into three-phase AC, as required by the electric motors 204, for example, using an inverter module. In a recuperation mode, the power electronics module 216 converts the three-phase AC from the electric motors 204, which act as generators, into the DC voltage required by the battery pack 214.The procedures described here are equally applicable to a purely electric vehicle or to any other device or vehicle that uses a battery pack.

[0024] During vehicle operation or charging from a power source, the battery is in an active state with a charging or discharging current flowing to / from it, creating gradients in the battery chemistry. Measurements of battery characteristics, such as open-circuit voltage, are affected to varying degrees by these gradients. After a period during which no current flows to or from the battery, the 214 battery enters a relaxed state, in which the chemistry has reached a stable condition. As described above, open-circuit voltage measurements used to determine the battery's state of charge are more accurate when obtained after the battery chemistry has reached a stable state for current conditions and battery age, for example, when the battery is fully relaxed.The relaxation time required for the battery chemistry to reach a stable state and for the battery to be fully relaxed can vary based on factors such as the battery's state of charge, temperature, and battery chemistry. One or more battery profiles can be stored in memory and used to determine an associated battery relaxation time or period in response to current battery and environmental conditions.

[0025] In addition to providing energy for propulsion, the battery 214 can supply energy to other electrical vehicle systems. Such a system can include a DC / DC converter module 218, which converts the high-voltage DC output of the battery pack 214 into a low-voltage DC supply compatible with other vehicle loads. Other high-voltage loads, such as compressors and electric heaters, can be directly connected to the high-voltage bus from the traction battery 214. In a vehicle, the low-voltage systems can be electrically connected to a 12 V battery 220. A purely electric vehicle can have a similar architecture, but without the internal combustion engine 208. Power supplied by the traction battery 214 to electrical accessories places the battery 214 in an active, or unrelaxed, state.

[0026] The battery pack 214 can be charged by an external power source 226. The external power source 226 can provide AC or DC power to the vehicle 202 by electrically connecting it via a charging port 224. The charging port 224 can be any port type designed to transfer power from the external power source 226 to the vehicle 202. The charging port 224 can be electrically connected to a power conversion module 222. The power conversion module 222 can condition the power from the external power source 226 to provide the appropriate voltage and current levels to the battery pack 214. In some applications, the functions of the power conversion module 222 can be included in the external power source 226. The vehicle engine, transmission, electric motors, battery, power conversion, and power electronics can be controlled by a powertrain control module (PCM) 228.As described above, current flows to the battery during charging, placing battery 214 in an active state. After a period during which no current flows to or from battery 214, battery 214 enters a relaxed state. Battery capacity learning according to various embodiments of the present disclosure measures the open-circuit voltage when the battery is relaxed in order to determine the state of charge (SOC) more accurately. A stored battery profile can be used to determine a suitable relaxation time corresponding to the current battery and / or environmental conditions, including the battery's state of charge, temperature, and the specific type of battery chemistry.

[0027] In addition to illustrating a plug-in hybrid vehicle, Fig. 2 is representative for a battery electric vehicle (BEV) if the internal combustion engine 208 has been removed. Likewise, Fig. 2 also illustrate a conventional hybrid electric vehicle (HEV) or a power-split hybrid electric vehicle if components 222, 224 and 226 are removed. Fig. Figure 2 also illustrates the high-voltage system, which includes the electric motor(s), the power electronics module 216, the DC / DC converter module 218, the power conversion module 222, and the battery 214. The high-voltage system and the battery include high-voltage components, such as busbars, high-voltage connectors, high-voltage conductors, and disconnect devices. These high-voltage components contribute to the resistance of the battery.

[0028] Fig. Figure 3 shows a battery pack 214 in a simple series configuration of N battery cell modules 302. The battery cell modules 302 can comprise a single battery cell or multiple battery cells connected electrically in parallel. However, the battery pack can be composed of any number of individual battery cells and of battery cell modules connected in series, parallel, or a combination thereof. Each of the cells has an internal battery resistance. A system can have one or more control devices, such as a battery control module (BCM) 308, which monitor and control the performance of the battery pack 214. The BCM 308 can monitor several battery pack level characteristics, such as a pack current measured by a current sensor 306, a pack voltage 310, and a pack temperature 312.The 306 current sensor can be used to determine whether current is flowing to or from the battery, for example, when the battery is in an active state. An active state can be determined if the current does not exceed a corresponding threshold value equal to zero.

[0029] In addition to set-level characteristics, the system can monitor and control battery cell-level characteristics. For example, the terminal voltage, current, and temperature of each cell or a representative subset of cells can be measured. A system can use a sensor module 304 to measure the characteristics of one or more battery cell modules 302. The characteristics can include battery cell voltage, temperature, age, number of charge / discharge cycles, etc. In one example, a sensor module measures battery cell voltage. The battery cell voltage can be the voltage of a single battery or of a group of batteries connected electrically in parallel or in series. The battery cell voltage can be based, at least in part, on electrical connections that link the cells to each other and to other components. The battery 214 can hold up to N cSensor modules 304 are used to measure the characteristics of a representative sample or of all battery cells 302. Each sensor module 304 can transmit the measurements to the BCM 308 for further processing and coordination. The sensor module 304 can transmit signals to the BCM 308 in analog or digital form. The battery 214 can also contain a battery distribution module (BDM) 314, which controls the flow of current into and out of the battery 214.

[0030] Fig. Figure 4 illustrates a representative user interface 400 of the vehicle 100 for reporting the vehicle's status to the operator, including the state of charge (SOC), charge status, battery current, battery relaxation state, and the like. The user interface 400 can also inform the operator about a deferral of supplying power to or from the battery to facilitate improved battery capacity determination according to embodiments of this disclosure. The user interface 400 can be presented by a vehicle control system in the vehicle 100 via a display 401 (for example, a touchscreen or an LCD display). The user interface 400 can include a message 402 informing the operator that improved battery capacity determination is recommended.The operator may be allowed to postpone or cancel the determination via the user interface, depending on the specific application and implementation. In some implementations, the message may only be advisory and not allow the vehicle operator to interrupt the process. As illustrated, message 402 is included in user interface 400 as a message above other content within user interface 400. It should be noted that in other examples, message 402 may be provided in a different format, such as via a full-screen user interface, a light, or illuminated graphics.

[0031] The user interface 400 may further include controls 406, 408, and 410 configured to receive an indication from the user as to whether the user agrees to allow the vehicle time to relax the battery in order to update the battery capacity. For example, the user interface 400 may include a Yes control 406 to receive an indication from the user that the user agrees to the battery capacity update, a No control 408 to receive an indication from the user that the user does not agree to a battery capacity update, and a Ask Me Later control 410 to postpone the battery capacity update to a later date or time.

[0032] The user interface 400 can also be used to notify the user via the display 401 that a battery capacity update is being proposed or has been successfully completed. The user interface 400 can also inform the user that the battery capacity update will be initiated at the next suitable time interval when the battery is in a relaxed state. Furthermore, the user interface 400 can provide the user with input elements to instruct a module in the vehicle to initiate the battery capacity update.

[0033] Fig.Figure 5 illustrates the operation of a system or procedure 500 for updating the traction battery capacity for an electric vehicle or vehicle with an electric auxiliary drive. Battery capacity is a parameter used in the traction battery monitoring system. For example, battery capacity is used to generate an accurate estimate of the state of charge (SOC), which can be provided as a percentage of the battery capacity, for example, based on a voltage measurement. Battery capacity is also used in the vehicle to determine how much energy is stored in the battery and therefore determines the vehicle's range when powered solely by the battery. However, battery capacity can change with operating conditions and age, as described above.A method and system for learning the capacity value over time can therefore be used in an electric vehicle. The battery capacity can be learned using Eq. 1, as shown above.

[0034] In the 501 protocol, the vehicle determines that a battery capacity update is desired. The vehicle can be instructed to initiate the battery capacity update by an external control device via a corresponding message or flag stored in memory. In one example, the vehicle determines that its battery capacity should be updated. Various triggers can indicate to the vehicle that the battery capacity should be updated. In one embodiment, the BECM can determine that a reported value of battery capacity, state of charge (SOC), and / or open-circuit voltage deviates from expected values ​​based on associated diagnostic routines. The vehicle can update the battery capacity based on the elapsed time. This time can vary depending on various factors, such as battery age, number of charge / discharge cycles, etc.For example, the battery control module (BECM) can maintain a timer to record how much time has elapsed since the battery capacity was last updated. The BECM can set a threshold that is lower at the beginning of the battery's lifespan and lower at the end when more variation is expected. Another trigger for battery capacity updates could be the degradation or loss of stored battery capacity, such as when the battery or control module is replaced.

[0035] The improved capacity learning described herein can be performed while the vehicle is in a plug-in or inductive charging process, as opposed to when it is being charged, for example, from regenerative braking or the internal combustion engine. If the vehicle is not in a plug-in or inductive charging process, procedure 500 can proceed to the end described in 520. Otherwise, if a battery capacity update is desired, as described in 501, and the battery is ready to be charged from a wall outlet or by an inductive charging system, the battery capacity update or learning routine, as described in 503, is started. The battery capacity update can be started after the operator has driven the vehicle and then parked it at a charging station near an inductive charging port or connectors in the vehicle.

[0036] The BECM or some other vehicle control unit determines at 505 whether the battery is fully relaxed. As described above, battery relaxation is related to the battery chemistry approaching a steady state or reaching equilibrium after the battery current has dropped to or near zero, such as on the order of milliamperes. The relaxation time can depend on a number of factors, such as the battery current before relaxation (higher current may require a longer relaxation time), the battery temperature, the battery cell voltage, the battery age, the number of charge and / or discharge cycles, and so on. In one example, the battery cell voltage relaxes to a value within 90% of its final steady value within 5 seconds.Based on empirical data and a corresponding threshold, such as 90% or 95% of a final value, it can be determined that the battery is fully relaxed. The empirical data and the corresponding threshold can be stored in a battery profile or lookup table, which is accessed by one or more batteries, the vehicle, or environmental parameters, such as battery temperature and last battery current, to determine an associated battery relaxation time. Different thresholds can be used to determine the degree of battery relaxation, such as 80% of the final voltage value, which corresponds to partial relaxation, and 95% of its final voltage value, which corresponds to full relaxation.If the time elapsed since the battery current became zero or below a minimum threshold is greater than a minimum battery relaxation time (for example, several minutes or up to tens of minutes), the battery is considered to be fully relaxed.

[0037] As described above, open-circuit voltage measurements can be used to derive SOC parameters, which in turn can be used to determine the battery capacity according to Equation 1. The values ​​for SOC1 and SOC2 can be estimated from the battery cell open-circuit voltage, measured or otherwise determined after the battery has been assumed to be fully relaxed at 505. In one embodiment, the BECM or other control device determines that the battery is fully relaxed based on the elapse of a relaxation time triggered in response to the battery current falling below a corresponding threshold. The relaxation time can be determined from a stored battery profile or a lookup table accessed by the battery, the vehicle, and / or environmental parameters, such as battery current, battery temperature, ambient temperature, cell voltage, etc.

[0038] If the battery relaxation period, specified by the battery profile and current operating conditions, has not yet elapsed, meaning the battery is not fully relaxed as determined in 505, the vehicle can inform the operator via a communication, for example on display 400, that charging or another vehicle operation is being postponed to facilitate the improved battery capacity calculation. In various embodiments, the operator can either skip the update or acknowledge the battery capacity update. Embodiments may also include an advisory message that does not allow the operator to cancel or postpone the update via the display or any other user interface. In one embodiment, the message to the operator reads, “Improved capacity learning is in progress. Charging will start in xx seconds.” Similar informational messages may be provided.The Display 400 can, for example, display "Battery diagnostics in progress and will be completed shortly." This message informs the operator that charging or the availability of battery-powered accessories will be delayed.

[0039] The battery current for charging or discharging can be deferred during a battery relaxation period, as shown in Figure 509, to allow the battery chemistry to stabilize and perform the enhanced battery capacity determination. Battery charging, including trickle charging, is deferred during the relaxation period, and the process returns to step 505 to determine if the battery relaxation period has elapsed, indicating that the battery is fully relaxed. Various programmable charging features can allow battery relaxation to be completed without operator notification. For example, battery charging can be programmed to occur during nighttime hours to take advantage of lower electricity prices. In this case, the enhanced battery capacity determination can be initiated at a predetermined time, either before the scheduled battery charging begins or after the scheduled battery charging has finished.

[0040] The improved battery capacity learning can begin when the battery is fully relaxed, as shown in Figure 505. The battery open-circuit voltage can be determined, as shown in Figure 511, to provide a precise value for SOC1 based on a predetermined relationship stored in memory. The battery control module then closes the charging switches and initiates battery charging, as shown in Figure 513, and calculates the current integration expressed in the numerator of Equation 1. To minimize the current integration error, ∫ idt, the maximum available charging power that the charger can provide is used, because shorter charging times result in a smaller cumulative current integration error. Charging energy flows into the battery until the battery reaches the battery charging voltage threshold, at which point charging stops.The battery charging voltage threshold varies depending on the battery type and can be stored in memory associated with one or more vehicle processors.

[0041] After the battery has been charged, the battery control module reads the previously stored SOC1 and ∫ idt values ​​from the corresponding non-volatile memory. The open-circuit voltage is measured again, and a value for SOC2 is obtained from a stored relationship or lookup table for the open-circuit voltage and SOC based on the open-circuit voltage measurement. Using these parameters, the battery capacity is then calculated, for example, using equation 1 at 517. The process then ends at 520.

[0042] There are several scenarios where the battery is disconnected or the charging process is terminated before the battery capacity determination is complete. In such scenarios, the battery capacity learning process is automatically terminated. If battery capacity learning is terminated, the battery control module resets the process and will attempt to update the battery capacity at a later time based on the fulfillment of the input conditions described above. In another example, the battery control module may reject the battery capacity update if the open-circuit voltage-based SOC2 is lower than a predetermined value after the battery has been fully charged. Similarly, the battery control module may reject the battery capacity update if the open-circuit voltage-based SOC1 is higher than a predetermined value before the battery is charged.Since battery capacity can depend on temperature, the process may be terminated if the battery temperature falls below a certain temperature threshold, for example.

[0043] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the claimed subject matter. Instead, the terms used in the description serve to describe, not to limit, the scope, and it is understood that various modifications can be made without deviating from the meaning and scope of the disclosure. Furthermore, the features of different implementations can be combined to form further embodiments within the scope of the claims, even if certain combinations are not explicitly illustrated and described here.

Claims

[1] Vehicle (100) comprising the following: a traction battery (214), a charger (112) for charging the traction battery (214), and a control device (122) configured to control the charger (112), to postpone charging the traction battery (214) during a battery relaxation period that begins in response to battery current falling below a threshold, and to measure an initial open-circuit voltage of the traction battery (214) after the battery relaxation period has elapsed and before charging the traction battery in order to update a battery capacity value using the initial open-circuit voltage, wherein the control device (122) is configured to retrieve a stored value for the battery relaxation period based on battery temperature, age of the traction battery (214) and state of charge of the traction battery (214); and wherein the control device (122) stops updating the battery capacity value in response to the battery temperature falling below a The battery temperature threshold is reached. [2] Vehicle (100) according to claim 1, wherein the control device (122) is configured to retrieve a stored battery profile in order to determine the battery relaxation period. [3] Vehicle (100) according to claim 1, wherein the control device (122) is configured to measure a second open-circuit voltage after the charging of the traction battery (214) has been completed and to update the battery capacity value based on the first and second open-circuit voltage measurements. [4] Vehicle (100) according to claim 1, wherein the control device (122) is configured to update the battery capacity value based on a first battery charge state associated with the first open-circuit voltage. [5] Vehicle (100) according to claim 1, wherein the control device (122) updates the battery capacity value in response to the fact that previously stored battery capacity data is unavailable. [6] Vehicle (100) according to claim 1, wherein the control device (122) is configured to update the battery capacity using a formula Ce = ∫idt / (SOC1-SOC2), where SOC1 is the first state of charge at a beginning of learning, and SOC2 is the second state of charge at an end of learning, Ce is the battery capacity and i is the current. [7] Vehicle (100) according to claim 6, wherein the control device (122) measures a second open-circuit voltage after a second battery relaxation period, which begins in response to the completion of charging the traction battery (214) and determines SOC2 based on the second open-circuit voltage. [8] Procedure comprising the following: Retrieval by a vehicle processor of a first and second Battery relaxation period from a memory associated with the vehicle processor, wherein the first and second battery relaxation periods are stored in a battery profile as a function of battery temperature, age of the traction battery (214) and state of charge of the traction battery (214), Measurement by the vehicle processor of a first and second traction battery open-circuit voltage before and after charging the traction battery (214), wherein the first and second open-circuit voltages are measured after the associated first and second battery relaxation periods have elapsed, and Setting the battery capacity based on collected battery charging current and first and second charge states, each corresponding to the first and second open-circuit voltage; and wherein a control device (122) stops updating the battery capacity value in response to the battery temperature falling below a The battery temperature threshold is reached. [9] Method according to claim 8, further comprising charging the traction battery (214) after the first battery relaxation period has elapsed. [10] Method according to claim 8, wherein the adjustment of the battery capacity occurs in response to the fact that battery capacity data is not available in a vehicle memory. [11] Method according to claim 8, wherein adjusting the battery capacity is adjusting the battery capacity according to Ce = ∫idt / (SOC L1 -SOC L2 ) includes, where SOC L1 a first state of charge, which is associated with the first open-circuit voltage, and SOC L2 a second state of charge, which is associated with the second open-circuit voltage, Ce is the battery capacity and i is the current. [12] Vehicle (100), comprising: a traction battery (214); a charger (112) for charging the traction battery (214), and a control device (122) which is programmed to adjust the battery capacity based on an initial state of charge (SOC). L1 , which is associated with battery open-circuit voltage, which is measured after a first battery relaxation period before battery charging, and a second state of charge (SOC). L2 , which is related to the battery open-circuit voltage, which is measured after a second period of inactivity. The battery relaxation period is measured after charging the battery, and a cumulative battery charging current is updated, wherein the control device (122) determines the battery capacity according to Ce = ∫idt / (SOC L1 -SOC L2 ) updated, where Ce is the battery capacity and i is the current, wherein the control device (122) is further programmed to retrieve the first and second battery relaxation periods from memory based on battery temperature, age of the traction battery (214) and state of charge of the traction battery; and wherein the control device (122) stops updating the battery capacity value in response to the battery temperature falling below a The battery temperature threshold is reached. [13] Vehicle (100) according to claim 12, wherein the control device (122) is further programmed to postpone battery charging after the battery current has fallen below a corresponding threshold for the first relaxation period. [14] Vehicle (100) according to claim 13, further comprising a display screen (400) in communication with the control device (122), wherein the control device (122) is further programmed to generate a message to be displayed on the display screen (400) in response to the deferral. [15] Vehicle (100) according to claim 12, wherein the first and second relaxation periods are based on the age of the battery and begin when the battery current falls below a threshold.

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