Circuit and method for detecting battery cell discharge

Abstract

Battery management system that includes: at least one controller programmed to output a cell self-discharge diagnostic indicator in response to a magnitude of a difference between an average cell state of charge at a beginning of a battery rest period and at least one of a plurality of cell states of charge estimated at predetermined intervals during the battery rest period being greater than a predetermined value.

Description

TECHNICAL FIELD

[0001] This application generally relates to the detection of battery cell self-discharge for vehicles. BACKGROUND

[0002] A hybrid electric or fully electric vehicle contains a traction battery composed of multiple battery cells connected in series and / or parallel. The traction battery provides power for the vehicle's propulsion and auxiliary devices. During operation, the traction battery can be charged or discharged based on operating conditions. Under normal circumstances, a traction battery can retain a charge while the battery is at rest. A traction battery that cannot effectively retain a charge while the battery is at rest can cause operator dissatisfaction if the traction battery becomes completely discharged in a short period of time.

[0003] A system and a device for monitoring a traction battery is known from US 6 424 157 B1. SUMMARY

[0004] A battery management system includes at least one controller programmed to output a cell self-discharge diagnostic indicator in response to a magnitude of a difference between an average cell state of charge at the beginning of a battery rest period and at least one of a plurality of cell states of charge estimated at predetermined intervals during the battery rest period being greater than a predetermined value. The at least one controller may be further programmed to output the cell self-discharge diagnostic indicator in response to a magnitude of a difference between an average rate of change in the cell state of charge during the predetermined intervals and a rate of change in the cell state of charge between the predetermined intervals being less than a predetermined threshold for each of the predetermined intervals.The at least one controller may be further programmed to output the cell self-discharge diagnostic indicator in response to a magnitude of a difference between a cell state of charge estimated at predetermined intervals and a cell state of charge at the beginning of the battery rest period being greater than a predetermined difference.

[0005] The at least one controller may be further programmed to operate a traction battery during a period of battery use according to a cell self-discharge rate based on the cell state of charge at the predetermined intervals and a cell state of charge at the beginning of the battery rest period. The at least one controller may be further programmed to operate the traction battery according to a battery power limit that is a predetermined minimum value when the cell self-discharge rate is greater than a predetermined threshold. The at least one controller may be further programmed to operate the traction battery according to a battery power limit that is a predetermined percentage of a base battery power limit when the cell self-discharge rate is greater than a predetermined threshold.The at least one controller may be further programmed to operate the traction battery according to a battery power limit of zero when the cell self-discharge rate is greater than a predetermined threshold and the cell state of charge is outside a predetermined range at the predetermined intervals.

[0006] The average cell state of charge at the beginning of the battery rest period may be an average of all cell states of charge at the beginning of the battery rest period. The battery rest period may be a period in which a battery current value is less than a predetermined current.

[0007] A vehicle includes a traction battery including a plurality of cells and at least one controller programmed to operate the traction battery according to a cell self-discharge rate based on a cell state of charge at a beginning of a battery rest period and the cell state of charge at predetermined intervals during the battery rest period. The at least one controller may be further programmed to output a cell self-discharge diagnostic indicator in response to a magnitude of a difference between an average cell state of charge at a beginning of the battery rest period and a cell state of charge estimated at predetermined intervals during the battery rest period being greater than a predetermined value.The at least one controller may be further programmed to output a cell self-discharge diagnostic indicator in response to a magnitude of a difference between an average change in cell state of charge between the predetermined intervals and a change in cell state of charge between the predetermined intervals that is less than a predetermined threshold for each of the predetermined intervals. The cell self-discharge rate may be further based on a battery capacity and a lapsed time since the start of the battery rest period. The at least one controller may be further programmed to operate the traction battery according to a battery power limit that is a predetermined minimum value when the cell self-discharge rate is greater than a predetermined threshold.The at least one controller may be further programmed to operate the traction battery according to a battery power limit that is a predetermined percentage of a base battery power limit when the cell self-discharge rate is greater than a predetermined threshold.

[0008] A method of operating a traction battery includes issuing, by a controller, a cell discharge diagnostic in response to a cell state of charge estimated at predetermined intervals during a battery rest period and being outside a predetermined range around an average cell state of charge calculated at a beginning of the battery rest period. The method further includes operating, by the controller, the traction battery according to the cell discharge diagnostic and a cell self-discharge rate. The cell self-discharge rate may be based on a difference between the cell state of charge at the beginning of the battery rest period and the cell state of charge at the predetermined intervals. Operating the traction battery may include limiting battery power to a predetermined minimum value if the cell self-discharge rate is greater than a predetermined threshold.Operating the traction battery may include limiting the battery power to a predetermined percentage of a base battery power limit when the cell self-discharge rate is greater than a predetermined threshold. Outputting the cell discharge diagnostic may further be based on a rate of change of the cell state of charge between the predetermined intervals that is within a predetermined range of an average rate of change of the cell state of charge during the predetermined intervals. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a diagram of a hybrid vehicle illustrating typical powertrain and energy storage components. Fig. Figure 2 is a graphical representation of a possible battery pack arrangement comprising multiple cells and monitored and controlled by a battery energy control module. Fig. Figure 3 is a graph illustrating a possible relationship of open circuit voltage (Voc) versus battery state of charge (SOC) for a typical battery cell. Fig. Figure 4 is a flowchart illustrating a possible set of operations for identifying a cell discharge diagnostic. DETAILED DESCRIPTION

[0009] Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely examples, and that other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show the details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.As will be understood by those of ordinary skill in the art, the various features illustrated and described with respect to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described. The combinations of the illustrated features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desired for particular applications or implementations.

[0010] Fig. 1 illustrates a typical plug-in hybrid electric vehicle (PHEV). A typical plug-in hybrid electric vehicle 12 may include one or more electric machines 14 mechanically connected to a hybrid transmission 16. The electric machines 14 may operate as a motor or as a generator. Furthermore, the hybrid transmission 16 is mechanically connected to an engine 18. The hybrid transmission 16 is also mechanically connected to a driveshaft 20, which is mechanically connected to the wheels 22. The electric machines 14 may provide propulsion and deceleration capability when the engine 18 is on or off. The electric machines 14 also act as generators and may provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system.The electric machines 14 may also reduce vehicle emissions by enabling the engine 18 to operate at more efficient speeds and by enabling the hybrid electric vehicle 12 to operate in an electric mode with the engine 18 off under certain conditions.

[0011] A traction battery or battery pack 24 stores energy that can be used by the electric work machines 14. A vehicle battery pack 24 typically provides a high-voltage direct current output. The traction battery 24 is electrically connected to one or more power electronics modules 26. One or more contactors 42 can isolate the traction battery 24 from the other components when opened and connect the traction battery 24 to the other components when closed. The power electronics module 26 is also electrically connected to the electric work machines 14 and provides the capability to transfer energy bidirectionally between the traction battery 24 and the electric work machines 14. A typical traction battery 24 can, for example,provide a DC voltage, while the electric machines 14 may operate using three-phase AC power. The power electronics module 26 may convert the DC voltage to three-phase AC power for use by the electric machines 14. In a regenerative mode, the power electronics module 26 may convert the three-phase AC power from the electric machines 14, which act as generators, to the DC voltage compatible with the traction battery 24. The description herein is equally applicable to a fully electric vehicle. For a fully electric vehicle, the hybrid transmission 16 may be a manual transmission connected to an electric machine 14, wherein the prime mover 18 may not be present.

[0012] In addition to providing power for propulsion, the traction battery 24 may provide power to other vehicle electrical systems. A typical system may include a DC / DC converter module 28 that converts the high-voltage DC output of the traction battery 24 into a low-voltage DC supply compatible with the other vehicle loads. Other high-voltage loads 46, such as compressors and electric heaters, may be directly connected to the high voltage without the use of a DC / DC converter module 28. The low-voltage systems may be electrically connected to an auxiliary battery 30 (e.g., a 12V battery).

[0013] The vehicle 12 may be an electric vehicle or a plug-in hybrid vehicle in which the traction battery 24 may be recharged by an external power source 36. The external power source 36 may be a connection to an electrical outlet that receives power from a utility company. The external power source 36 may be electrically connected to an electric vehicle supply equipment (EVSE) 38. The EVSE 38 may provide circuitry and controls to regulate and manage the transfer of energy between the power source 36 and the vehicle 12. The external power source 36 may provide DC or AC electrical power to the EVSE 38. The EVSE 38 may include a charging connector 40 for plugging into a charging port 34 of the vehicle 12. The charging port 34 may be any type of port configured to transfer power from the EVSE 38 to the vehicle 12.The charging port 34 may be electrically connected to a charger or an on-board power conversion module 32. The power conversion module 32 may condition the power supplied by the EVSE 38 to provide the proper voltage and current levels to the traction battery 24. The power conversion module 32 may be connected to the EVSE 38 to coordinate the delivery of power to the vehicle 12. The EVSE connector 40 may have terminal pins that mate with the corresponding recesses of the charging port 34. Alternatively, various components described as being electrically connected may transfer power using wireless inductive coupling.

[0014] One or more wheel brakes 44 may be provided to decelerate the vehicle 12 and prevent movement of the vehicle 12. The wheel brakes 44 may be hydraulically actuated, electrically actuated, or any combination thereof. The wheel brakes 44 may be part of a braking system 50. The braking system 50 may include other components to operate the wheel brakes 44. For simplicity, the figure depicts a single connection between the braking system 50 and one of the wheel brakes 44. A connection between the braking system 50 and the other wheel brakes 44 is implied. The braking system 50 may include a controller to monitor and coordinate the braking system 50. The braking system 50 may monitor the braking components and control the wheel brakes 44 for deceleration of the vehicle. The braking system 50 may respond to driver commands and may also operate autonomously to implement features such asThe controller of the braking system 50 may implement a method for applying a requested braking force when requested by another controller or subfunction.

[0015] One or more electrical loads 46 may be connected to the high-voltage bus. The electrical loads 46 may have an associated controller that operates and controls the electrical loads 46, if appropriate. Examples of electrical loads may be a heating module or an air conditioning module.

[0016] The various components discussed may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., a Controller Area Network (CAN)) or via discrete conductors. A system controller 48 may be present to coordinate the operation of the various components.

[0017] A traction battery 24 can be constructed from various chemical formulations. Typical battery chemistries can be lead-acid, nickel-metal hydride (NIMH), or lithium-ion. Fig. 2 shows a typical traction battery group 24 in a series configuration of N battery cells 72. However, other battery groups 24 may consist of any number of individual battery cells connected in series or parallel, or any combination thereof. A battery management system may include one or more controllers, such as a Battery Energy Control Module (BECM) 76, that monitor and control the performance of the traction battery 24. The BECM 76 may include sensors and circuitry to monitor several battery group-level properties, such as group current 78, group voltage 80, and group temperature 82. The BECM 76 may include non-volatile memory so that the data may be retained when the BECM is in a power-off state. The retained data may be available on the next key cycle.

[0018] In addition to the group-level properties, there may be properties at the level of the battery cells 72 that are measured and monitored. For example, the terminal voltage, current, and temperature of each cell 72 may be measured. The battery management system may use a sensor module 74 to measure the properties of the battery cell 72. Depending on the capabilities, the sensor module 74 may include sensors and circuitry to measure the properties of one or more of the battery cells 72. The battery management system may support up to N cSensor modules or battery monitor integrated circuits (BMIC) 74 can be used to measure the characteristics of all battery cells 72. Each sensor module 74 can transmit the measurements to the BECM 76 for further processing and coordination. The sensor module 74 can transmit the signals to the BECM 76 in analog or digital form. In some embodiments, the functionality of the sensor module 74 can be incorporated internally into the BECM 76. That is, the hardware of the sensor module 74 can be integrated as part of the circuitry in the BECM 76, and the BECM 76 can handle the processing of the raw signals.

[0019] The BECM 76 may include circuitry for connection to one or more contactors 42. The positive and negative terminals of the traction battery 24 may be protected by the contactors 42.

[0020] The battery pack state of charge (SOC) provides an indication of how much charge remains in the battery cells 72 or the battery pack 24. The battery pack SOC may be output similarly to a fuel gauge to inform the driver how much charge remains in the battery pack 24. The battery pack SOC may also be used to control the operation of an electric or hybrid electric vehicle 12. Calculating the battery pack SOC may be performed by various methods. One possible method for calculating the battery SOC is performing an integration of the battery pack current over time. This is well known in the art as ampere-hour integration.

[0021] The battery SOC can also be derived from a model-based estimation. The model-based estimation can use cell voltage measurements, group current measurements, and cell and group temperature measurements to estimate the SOC value. The apparatus and methods described herein are not dependent on the specific method used to calculate the SOC.

[0022] The BECM 76 can have power available at all times. The BECM 76 can include a wake-up timer so that a wake-up can be scheduled at any time. The wake-up timer can wake the BECM 76 so that predetermined functions can be performed. The BECM 76 can include non-volatile memory so that data can be saved when the BECM 76 is turned off or loses power. The non-volatile memory can include electrically erasable programmable read-only memory (EEPROM) or non-volatile random access memory (NVRAM). The non-volatile memory can include a microcontroller's FLASH memory.

[0023] During operation of the traction battery 24, the SOC of the battery cells 72 may differ from one another. The BECM 76 or the sensor modules 24 may include a cell balancing device that allows the SOC of the cells to be balanced to a specific level. The specific level may be an average SOC of the group. The average SOC of the group may be the average of all SOC values ​​of the cells. The cell balancing device may include a switch and a resistor across each of the battery cells 72. When the switch is closed, current may flow through the resistor to remove charge from the battery cell 72. When the traction battery 24 is operating normally, the SOC values ​​of the individual cells may be within a predetermined tolerance band around the average SOC. That is, the states of charge of the individual cells may have a range of values ​​defined by SOC avg± K1, where K1 is a specified tolerance (e.g. 5%).

[0024] The SOC of a battery cell 72 can drift from the balanced value for many reasons. If the cell SOC falls below the tolerance band around the group average SOC, the condition may be referred to as a cell self-discharge condition. A cell self-discharge condition may be caused by internal conditions of the cell. Conditions external to the battery cell, such as short circuits, may also cause a cell self-discharge condition of the battery cell 72. The external conditions may be in the sensor circuitry 74 or within the wiring of the battery group 24. A diagnostic condition may be detected when the battery cell SOC is less than the tolerance band around the group average SOC.

[0025] The battery management system may attempt to detect any cell self-discharge conditions that may be present in the battery pack 24. Each battery cell 72 may have an associated flag in the non-volatile memory to indicate a cell self-discharge condition for the battery cell 72. This flag may be referred to as a cell self-discharge flag. In response to the cell self-discharge flag, the BCEM 76 may initiate a diagnostic response. The diagnostic response may include alerting the operator and operating the traction battery 24 in a modified manner.

[0026] Each battery cell 72 may also store an associated cell self-discharge rate in the non-volatile memory. Assuming a fixed interval between measurements, the cell self-discharge rate may be stored in units of current (e.g., milliamperes (mA)). The described logic is applicable regardless of the units selected for the cell self-discharge rate. The cell self-discharge rate may be zero for a normally operating battery cell. A normally operating battery cell may also have a relatively small non-zero cell self-discharge rate (e.g., 0.01 mA). The cell self-discharge rate may vary within a predetermined range for a normally operating traction battery. A battery cell with a cell self-discharge rate above a predetermined threshold may indicate a diagnostic condition associated with that battery cell.If the cell self-discharge rate is above the specified threshold, the cell self-discharge flag can be set for this battery cell.

[0027] After a driving cycle, the SOC of each battery cell (SOC ko ( X )) are stored in the non-volatile memory at the time of key-off. When key-off, the BECM 76 may operate during a period before shutting down or entering a low-performance mode. Before shutting down, an average battery group voltage (SOC avg ) can be calculated as the average of the cells' SOC values. That is, the average battery group voltage can be calculated as the sum of all individual cell SOC values ​​divided by the number of cells.

[0028] The BECM 76 can be configured to wake up at predetermined time intervals (e.g., every 30 minutes) to perform specified functions. Upon waking up, the BECM 76 can measure the open-circuit voltage for each of the battery cells. The SOC of each cell can be calculated based on the open-circuit voltage measurement. For a lithium-ion battery cell, it is well known that after a period of battery inactivity, the open-circuit voltage can be determined by measuring the battery cell's terminal voltage. When no current flows through the battery, the open-circuit voltage is equivalent to the terminal voltage. When a current flows through the battery, the open-circuit voltage and the terminal voltage differ due to the internal resistances and capacitances within the battery.

[0029] For a typical lithium-ion battery cell, there is a relationship between the SOC and the open circuit voltage (Voc) such that V oc = f(SOC) holds. Fig. 3 shows an exemplary curve 124 showing the open circuit voltage V oc as a function of SOC. The relationship between SOC and V oc can be determined from an analysis of the battery properties or from testing the battery cells. The function can be such that the SOC is f -1 (V oc ) can be calculated. The function or the inverse function can be implemented as a lookup table or an equivalent equation. The exact shape of the curve 124 can vary based on the exact formulation of the lithium-ion battery. The voltage V occhanges as a result of charging and discharging the battery. It is noted that the curve may vary depending on the battery chemistry. For example, the voltage associated with a 100% SOC may vary for different battery chemistries. The OCV / SOC characteristic may depend on the battery temperature and can be represented as a series of curves for different temperatures.

[0030] As in Fig. As can be seen in Figure 3, as the SOC increases, the open circuit voltage generally increases as well. As the battery is charged, the SOC increases and the open circuit voltage rises. The rate of voltage increase can depend on the state of charge. The slope at different points on the curve (e.g., 120 and 122) can be different. The open circuit voltage based on the SOC can be referred to as the SOC ocv be referred to.

[0031] The cell SOC at wake-up time can be compared with the average cell SOC value recorded at key off or shutdown. The battery cells can be considered functioning properly if the following expression is satisfied for all battery cells. SOCavg−K1≤SOCocv(x)≤SOCavg+K1 for all x.

[0032] A diagnostic condition can be stored if the following expression is satisfied for any of the battery cells. |SOCocv(x)−SOCavg|>K1)

[0033] A cell SOC above the average SOC range may indicate a balancing problem. A cell SOC below the average SOC range may indicate a cell discharge problem. The cell self-discharge rate for each battery cell can be calculated as: Cell self-discharge rate(x)=(SOCko(x)−SOCocv(x))*Q / TRest where Q is the capacity of the battery in ampere hours and T Ruhe is the elapsed time since the key was turned off and the time the open-circuit voltage was measured. It is stated that the cell self-discharge rate decreases as the SOC change decreases. The cell self-discharge rate can be calculated so that a decrease in SOC over the battery rest period yields a positive value. Other sign conventions are possible, and the various thresholds can be adjusted accordingly.

[0034] Additional conditions can be considered for storing the values ​​and setting the cell self-discharge flags. For example, the system can determine that the sensor modules 74 are functioning properly before setting the cell self-discharge flags. Furthermore, the cell voltages can be checked to ensure that the measurements are within a valid operating range. Cell voltages that may be out of range due to short-circuit or open-circuit conditions, for example, cannot be considered. Furthermore, the cell state of charge values ​​can be checked to ensure that the values ​​are within a valid state of charge range.

[0035] In the case where charge is discharged from a battery cell, the SOC value may be lower during each wake-up cycle of the controller 76. Assuming a constant cell self-discharge rate and a constant wake-up interval, the SOC may decrease by a similar amount between each wake-up cycle. The controller 76 may calculate the decrease in SOC between each of the wake-up cycles. An average decrease in SOC may be calculated as an average of a predetermined number of decreases in SOC. For example, an average decrease in SOC may be calculated as the sum of the last N decreases in SOC divided by N.

[0036] The change in SOC for the x-th cell from the previous wake-up cycle can be defined as ΔSOC(x,k)=SOCocv(x,k)−SOCocv(x,k−1) where k indicates the current wake-up cycle and k - 1 indicates the immediately preceding wake-up cycle. It is stated that the SOC ocv (x, 0) of the SOC avg from the last key-off event. The average change in SOC can be defined as: ΔSOCavg(x)=(ΔSOC(x,1)+ΔSOC(x,2)+…+ΔSOC(x,N)) / N be expressed.

[0037] Before setting the cell self-discharge flag, the battery management system can check to determine whether the SOC change is within a specified range around the average between wake-up cycles. The following expression can be satisfied to confirm the setting of the cell self-discharge flag: [ΔSOCavg(ex)−K5]<ΔSOC(x,k)<[ΔSOCavg(x)+K5] where K5 is a specified tolerance (e.g. 2%). The condition can alternatively be defined as |ΔSOC(x,k)−ΔSOCavg(x)| <K5 The expression can be evaluated for each of the wake-up cycles (k). The setting of the cell self-discharge flag can be conditioned on the change in cell SOC between each of the wake-up cycles being within a predetermined tolerance of the average change in cell SOC. This condition can indicate that the decrease in SOC is caused by an actual cell discharge problem and not by noisy voltage measurements. If a nearly consistent rate of change in cell SOC is detected, the cell self-discharge flag can be set and stored for the battery cell.

[0038] For each wake-up cycle, a cell self-discharge rate can be calculated and stored, as described. The cell self-discharge rate can be used to select a diagnostic response if the associated cell self-discharge flag is set. The magnitude of the cell self-discharge rate can be compared to one or more predefined thresholds to determine a course of action.

[0039] The cell self-discharge rate may be compared to a first threshold, K4. The K4 threshold may indicate a level for driver notification and greater control response. For example, battery power limits may be reduced to a predefined minimum power level (e.g., 1.5 kW) when a cell self-discharge rate is above the K4 threshold. More restrictive control actions may be taken in conjunction with other conditions. For example, the traction battery may be shut down when a cell self-discharge rate is above the K4 threshold and other conditions are present, such as when the cell SOC is outside a predefined range or the cell voltage is outside predefined voltage limits.

[0040] Driver notification may include storing a diagnostic trouble code (DTC) in non-volatile memory. The DTC may trigger the display of an indicator to the operator. For example, a message indicating that battery service is due soon may be displayed to the operator. The DTC may be available for display to service personnel via a diagnostic tool.

[0041] The cell self-discharge rate can be compared to a second threshold, K3. The K3 threshold can specify a level for driver notification and a moderate control response. For example, the battery power limits can be set to 75% of the base battery power limits if the cell self-discharge rate is above the K3 threshold.

[0042] The cell self-discharge rate can be compared to a third threshold, K2. The K2 threshold can specify a level for driver notification without any control action. If the cell self-discharge rate is greater than the K2 threshold, a diagnostic trouble code (DTC) can be set and stored in non-volatile memory without any further control action. The K2 threshold can indicate impending problems with the battery cell.

[0043] The thresholds may be selected to balance the availability of traction battery functionality with the desire to report battery problems to the operator. Generally, the thresholds may be configured such that K2 < K3 < K4. The specific values ​​selected for the thresholds may depend on the battery chemistry and configuration. Additionally, the system may determine the number of cells reporting a cell self-discharge flag. The diagnostic response may be further determined based on the number of cells reporting a cell self-discharge flag. For example, if the number of cells reporting a cell self-discharge condition reaches a predetermined threshold, major control responses may be triggered.

[0044] Fig.4 illustrates a flowchart for one possible implementation of the described system. The operations represented by the flowchart may be implemented in a controller 76. Operation typically begins while the vehicle is in an operating mode, such as driving or charging. The current logic may begin 200 when a shutdown is requested. In operation 202, the controller 76 may calculate the average SOC value and store it in non-volatile memory. In operation 204, the controller 76 may store the SOC value for each cell in non-volatile memory. The system may then shut down 206. During shutdown, the controller 76 may be in a low-power mode. Before shutdown, operations may be performed to initiate a wake-up after a predetermined period of time (e.g., 30 minutes) has elapsed.

[0045] After the predetermined period of time has passed, the controller 76 may wake up 208. In operation 210, instructions may be executed to calculate the SOC for each of the battery cells. In operation 212, instructions may be executed to calculate the cell self-discharge rate for each cell. In operation 214, instructions may be executed to calculate the rate of change of the SOC for each of the cells. In operation 216, instructions may be executed to determine the presence of a diagnostic condition, as previously described. If a diagnostic condition is present, instructions in operation 218 may be executed to determine the diagnostic response. As previously described, the diagnostic response may depend on the magnitude of the cell self-discharge rate.After the diagnostic response, operation 220 may be executed to store the calculated values ​​in non-volatile memory.

[0046] If no diagnostic condition exists, the instructions in operation 220 can be executed to save the calculated values ​​to non-volatile memory. In operation 222, the controller can be shut down again until the next wake-up cycle.

[0047] The processes, methods, or algorithms described herein may be deliverable to / implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or a dedicated electronic control unit. Similarly, the processes, methods, or algorithms may be stored as data and instructions executable by a controller or computer in many forms, including, but not limited to, information permanently stored in non-writable storage media, such as read-only memory devices, and information modifiably stored in writable storage media, such as floppy disks, magnetic tapes, compact discs, RAM devices, and other magnetic and optical media.The processes, methods, or algorithms may also be implemented in an executable software object. Alternatively, the processes, methods, or algorithms may be implemented in whole or in part using suitable hardware components, such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), state machines, controllers, or other hardware components. or devices, or a combination of hardware, software and firmware components.

[0048] While exemplary embodiments have been described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. As previously described, the features of the various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated.While various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art will recognize that one or more features or characteristics may be compromised to achieve the desired overall system characteristics, depending on the specific application and implementation. These features may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, etc.The embodiments that have been described as less desirable than other embodiments or prior art implementations with respect to one or more features are not, as such, outside the scope of the disclosure and may be desirable for particular applications.

Claims

[1] Battery management system comprising: at least one controller programmed to output a cell self-discharge diagnostic indicator in response to a magnitude of a difference between an average cell state of charge at a beginning of a battery rest period and at least one of a plurality of cell states of charge estimated at predetermined intervals during the battery rest period being greater than a predetermined value. [2] The battery management system of claim 1, wherein the at least one controller is further programmed to output the cell self-discharge diagnostic indicator in response to a magnitude of a difference between an average rate of change in the cell state of charge during the predetermined intervals and a rate of change in the cell state of charge between the predetermined intervals being less than a predetermined threshold for each of the predetermined intervals. [3] The battery management system of claim 1 or 2, wherein the at least one controller is further programmed to output the cell self-discharge diagnostic indicator in response to a magnitude of a difference between a cell state of charge estimated at predetermined intervals and a cell state of charge at the beginning of the battery rest period being greater than a predetermined difference. [4] The battery management system of any preceding claim, wherein the at least one controller is further programmed to operate a traction battery (24) during a period of battery use according to a cell self-discharge rate based on the cell state of charge at the predetermined intervals and a cell state of charge at the beginning of the battery rest period. [5] The battery management system of claim 4, wherein the at least one controller is further programmed to operate the traction battery (24) according to a battery power limit that is a predetermined minimum value when the cell self-discharge rate is greater than a predetermined threshold. [6] The battery management system of claim 4 or 5, wherein the at least one controller is further programmed to operate the traction battery (24) according to a battery power limit that is a predetermined percentage of a base battery power limit when the cell self-discharge rate is greater than a predetermined threshold. [7] The battery management system of any one of claims 4 to 6, wherein the at least one controller is further programmed to operate the traction battery (24) according to a battery power limit of zero when the cell self-discharge rate is greater than a predetermined threshold and the cell state of charge is outside a predetermined range at the predetermined intervals. [8] A battery management system according to any one of the preceding claims, wherein the average cell state of charge at the beginning of the battery rest period is an average of all cell states of charge at the beginning of the battery rest period. [9] A battery management system according to any one of the preceding claims, wherein the battery rest period is a period in which a magnitude of a battery current is less than a predetermined current. [10] A method for operating a traction battery (24), comprising: Outputting, by a controller, a cell discharge diagnosis in response to a cell state of charge estimated at predetermined intervals during a battery rest period and being outside a predetermined range around an average cell state of charge calculated at a beginning of the battery rest period; and operating, by the controller, the traction battery (24) according to the cell discharge diagnosis and a cell self-discharge rate. [11] The method of claim 10, wherein the cell self-discharge rate is based on a difference between the cell state of charge at the beginning of the battery rest period and the cell state of charge at the predetermined intervals. [12] The method of any one of claims 10 or 11, wherein operating the traction battery (24) includes limiting the battery power to a predetermined minimum value when the cell self-discharge rate is greater than a predetermined threshold. [13] The method of any one of claims 10 to 12, wherein operating the traction battery (24) includes limiting the battery power to a predetermined percentage of a base battery power limit when the cell self-discharge rate is greater than a predetermined threshold. [14] The method of any one of claims 10 to 13, wherein outputting the cell discharge diagnosis is further based on a rate of change of the cell state of charge between the predetermined intervals that is within a predetermined range of an average rate of change of the cell state of charge during the predetermined intervals.

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