System for estimating battery power capacity

Abstract

The present disclosure provides a system for estimating battery power capacity. One or more controllers charge and discharge the traction battery after startup of the vehicle according to a power limit that is based on a polarization voltage describing an internal state of the traction battery and that is a function of: a polarization voltage present at a last deactivation of the vehicle; and a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery.

Description

Technical Field

[0001] The present disclosure relates to a vehicle system for estimating a power capacity of a vehicle battery and operating the vehicle according to the power capacity. Background Art

[0002] Electric vehicles (EVs) rely on one or more traction batteries to supply electrical energy to the motor for propulsion. The driving operation of the vehicle may depend on the power capacity of the traction battery. The power capacity may be affected by various factors such as battery temperature, voltage, state of charge (SOC), etc. Summary of the invention

[0003] An electrical power system for a vehicle includes one or more controllers that charge and discharge a traction battery after startup of the vehicle according to power limits that are based on a polarization voltage describing an internal state of the traction battery and are a function of the polarization voltage that existed at a last shutdown of the vehicle and a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery.

[0004] A method includes, after starting of a vehicle, charging and discharging a traction battery of the vehicle according to power limits that are based on a polarization voltage describing an internal state of the traction battery and are a function of the polarization voltage present at a last stop of the vehicle and a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery.

[0005] A vehicle includes a traction battery and one or more controllers that charge and discharge the traction battery according to a power limit after startup of the vehicle. The power limit is derived from a polarization voltage based on a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 An example block topology of an electrified vehicle is shown, showing the drive train and energy storage components;

[0007] Figure 2 A block diagram showing an arrangement for a traction battery controller of a battery electric vehicle (BEV) to monitor a traction battery of the BEV;

[0008] Figure 3 a schematic diagram showing a conventional equivalent circuit model (ECM) of a traction battery; and

[0009] Figure 4A timing diagram of a process for estimating the power capacity of a vehicle battery is shown. DETAILED DESCRIPTION

[0010] Embodiments are described herein. However, it should be understood that the disclosed embodiments are merely examples and that other embodiments may take various and alternative forms. The drawings are not necessarily drawn to scale. Some features may be enlarged or minimized to show details of particular components. Therefore, the specific structural details and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art.

[0011] The various features shown and described with reference to any one of the accompanying drawings may be combined with features shown in one or more other drawings to produce embodiments not explicitly shown or described. The combinations of features shown provide representative embodiments for typical applications. However, for specific applications or implementations, various combinations and modifications of features consistent with the teachings of the present disclosure may be desired.

[0012] The present disclosure proposes, among other things, a system and method for estimating the power capacity of a vehicle's traction battery at vehicle start-up and operating the vehicle based on the power capacity.

[0013] Figure 1 A plug-in hybrid electric vehicle (PHEV) is shown. The plug-in hybrid electric vehicle 112 may include one or more motors (electric motors) 114 mechanically coupled to a hybrid transmission 116. The motor 114 may be capable of operating as a motor or a generator. In addition, the hybrid transmission 116 is mechanically coupled to an engine 118. The hybrid transmission 116 is also mechanically coupled to a drive shaft 120, which is mechanically coupled to wheels 122. The motor 114 can provide propulsion and deceleration capabilities when the engine 118 is turned on or off. The motor 114 can also act as a generator and can provide fuel economy benefits by recovering energy lost as heat in the friction braking system. The motor 114 can also reduce vehicle emissions by allowing the engine 118 to operate at a more efficient speed and allowing the hybrid electric vehicle 112 to be operated in an electric mode when the engine 118 is turned off under certain conditions.

[0014] The traction battery or battery pack 124 stores energy that can be used by the motor 114. The vehicle battery pack 124 can provide a high voltage DC output. The traction battery 124 can be electrically coupled to one or more battery electric control modules (BECM) 125. The BECM 125 can be provided with one or more processors and software applications configured to monitor and control various operations of the traction battery 124. The traction battery 124 can also be electrically coupled to one or more power electronics modules 126. The power electronics module 126 can also be referred to as a power inverter. One or more contactors 127 can isolate the traction battery 124 and the BECM 125 from other components when open, and connect the traction battery 124 and the BECM 125 to other components when closed. The power electronics module 126 can also be electrically coupled to the motor 114 and provide the ability to transfer energy bidirectionally between the traction battery 124 and the motor 114. For example, the traction battery 124 can provide a DC voltage, and the motor 114 can operate using a three-phase AC current. The power electronics module 126 may convert the DC voltage into a three-phase AC current for use by the motor 114. In regenerative mode, the power electronics module 126 may convert the three-phase AC current from the motor 114 acting as a generator into a DC voltage compatible with the traction battery 124. The description herein is equally applicable to pure electric vehicles. For pure electric vehicles, the hybrid transmission 116 may be a gearbox connected to the motor 114 and the engine 118 may not be present.

[0015] In addition to providing energy for propulsion, the traction battery 124 can also provide energy for other vehicle electrical systems. The vehicle includes a DC / DC converter module 128 that converts the high voltage DC output of the traction battery 124 to a low voltage DC supply that is compatible with other low voltage vehicle loads. The output of the DC / DC converter module 128 can be electrically coupled to an auxiliary battery 130 (e.g., a 12V battery).

[0016] The vehicle 112 may be a battery electric vehicle (BEV) or a plug-in hybrid electric vehicle (PHEV), wherein the traction battery 124 may be recharged by an external power source 136. The external power source 136 may be a connection to an electrical outlet. The external power source 136 may be a distribution network or grid provided by an electric utility company. The external power source 136 may be electrically coupled to an electric vehicle supply equipment (EVSE) 138. The EVSE 138 may provide circuits and controls to regulate and manage energy transfer between the power source 136 and the vehicle 112. The external power source 136 may provide DC or AC power to the EVSE 138. The EVSE 138 may have a charging connector 140 for plugging into a charging port 134 of the vehicle 112. The charging port 134 may be any type of port configured to transfer power from the EVSE 138 to the vehicle 112. The charging port 134 may be electrically coupled to a charger or an onboard power conversion module 132. The power conversion module 132 may condition the power supplied from the EVSE 138 to provide the appropriate voltage and current levels to the traction battery 124. The power conversion module 132 may interact with the EVSE 138 to coordinate the delivery of power to the vehicle 112. The EVSE connector 140 may have pins that mate with corresponding recesses of the charging port 134. Alternatively, the various components described as being electrically coupled may transfer power using wireless inductive coupling. Although reference is made to Figure 1 The vehicle 112 is shown as a BEV or a PHEV, but the present disclosure is not limited thereto. The vehicle 112 may also be a hybrid electric vehicle (HEV) or a fuel cell electric vehicle (FCEV) under substantially the same concept.

[0017] One or more electrical loads 146 may be coupled to the high voltage bus. The electrical loads 146 may have associated controllers that operate and control the electrical loads 146 as appropriate. Examples of electrical loads 146 may be heating modules, air conditioning modules, and the like.

[0018] 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 150 may be present to coordinate the operation of the various components. It should be noted that the system controller 150 is used as a general term and may include one or more controller devices configured to perform various operations in the present disclosure. For example, the system controller 150 may be programmed to enable powertrain control functions to operate the powertrain of the vehicle 112. The system controller 150 may also be programmed to enable telecommunication functions with various entities (e.g., servers) via a wireless network (e.g., a cellular network).

[0019] The system controller 150 and / or the BECM 125 may be programmed, individually or in combination, to perform various operations related to the traction battery 124. The traction battery 124 may be a rechargeable battery made of one or more rechargeable cells (e.g., lithium-ion cells). For example, the BECM 125 may be a traction battery controller operable to manage the charging and discharging of the traction battery 124 and to monitor the operating characteristics of the traction battery 124. The BECM 125 may be operable to implement an algorithm for measuring (e.g., detecting or estimating) the operating characteristics of the traction battery 124. The BECM 125 may control the operation and performance of the traction battery 124 based on the operating characteristics. The operation and performance of other systems and components of the vehicle 112 may be controlled based on the operating characteristics of the traction battery 124.

[0020] The operating characteristics of the traction battery 124 include the charge capacity and the state of charge (SOC) of the traction battery 124. The charge capacity of the traction battery 124 indicates the maximum amount of electrical energy that can be stored in the traction battery. The SOC of the traction battery 124 indicates the current amount of charge stored in the traction battery. The SOC of the traction battery 124 may be expressed as a percentage of the maximum amount of charge that can be stored in the traction battery 124.

[0021] Another operational characteristic of the traction battery 124 is the power capacity of the traction battery. The power capacity of the traction battery 124 is a measure of the maximum amount of power that the traction battery can provide (i.e., discharge) or receive (i.e., charge) in a specified time period. To this end, the power capacity of the traction battery 124 corresponds to charge and discharge power limits that define the amount of power that can be supplied or received by the traction battery 124 at a given time. These limits can be provided to other vehicle controls, such as by the system controller 150, so that the information can be used by systems that can draw power from or provide power to the traction battery 124. The vehicle controls need to know how much power the traction battery 124 can provide (discharge) or receive (charge) in order to meet the driver's driving needs and HVAC (heating, ventilation, and air conditioning) needs and optimize energy usage. To this end, knowing the power capacity of the traction battery 124 allows the management of electrical loads and electrical sources so that the requested power is within the allowed voltage limits and current limits that the traction battery can handle.

[0022] refer to Figure 2 , continue to refer to Figure 1 , a block diagram of an arrangement for the BECM 125 to monitor the traction battery 124 is shown. In this example, the BECM 125 may be integrally formed with the traction battery 124, but the disclosure is not limited thereto. The traction battery 124 includes a plurality of battery cells 202. The battery cells 202 may be physically connected together (e.g., as shown in FIG. 1 ). Figure 2 Serial connection as shown in ).

[0023] The BECM 125 may be operable to monitor pack level characteristics of the traction battery 124, such as a battery current 204, a pack voltage 206, and a battery temperature 208. The battery current 204 is the current output from (i.e., discharging) or input to (i.e., charging) the traction battery 124. The pack voltage 206 is the terminal voltage of the traction battery 124.

[0024] The BECM 125 may also be operable to measure and monitor battery cell level characteristics of the battery cells 202 of the traction battery 124. For example, the terminal voltage, current, and temperature of one or more of the battery cells 202 may be measured. The BECM 125 may measure the battery cell level characteristics using one or more battery sensors 210. The battery sensor 210 may measure the characteristics of one or more battery cells 202. The BECM 125 may utilize Nc battery sensors 210 to measure the characteristics of all battery cells 202. Each battery sensor 210 may communicate the measurement results to the BECM 125 for further processing and coordination. In one embodiment, the functionality of the battery sensor 210 may be incorporated into the interior of the BECM 125.

[0025] The traction battery 124 may have one or more temperature sensors (such as thermistors) in communication with the BECM 125 to provide data indicative of the temperature of the battery cells 202 of the traction battery 124 for the BECM to monitor the temperature of the traction battery and / or the battery cells. The vehicle 112 may also include one or more temperature sensors 208 to provide data indicative of the ambient temperature for the BECM 125 to monitor the ambient temperature.

[0026] The BECM 125 may control the operation and performance of the traction battery 124 based on the monitored traction battery level characteristics and battery cell level characteristics. For example, the BECM 125 may use the monitored characteristics to measure (e.g., detect or estimate) operating characteristics of the traction battery 124 (e.g., power capacity of the traction battery, SOC of the traction battery, etc.), such as for use in controlling the traction battery and / or the vehicle 112.

[0027] As known to those skilled in the art, the BECM 125 may estimate parameter values ​​of the ECM (e.g., resistance and capacitance of circuit elements of the ECM) and state values ​​of the ECM (e.g., voltage and current across circuit elements of the ECM) by recursive estimation based on such measurements. For example, the BECM 125 may estimate the values ​​of model parameters and model states using some adaptive estimation method, such as an extended Kalman filter (EKF).

[0028] In order for the values ​​of the operating characteristics of the traction battery 124 measured by the BECM 125 to accurately agree with the actual values ​​of the operating characteristics of the traction battery, the ECM must accurately model the traction battery. In order for the ECM to accurately model the traction battery 124, (i) the ECM must have a sufficient set of parameters (e.g., resistances and capacitances of circuit elements of the ECM), and (ii) the estimated values ​​of the model parameters and model states must be at least substantially similar to the values ​​of the parameters and states of the ECM that accurately model the traction battery (i.e., the estimated parameter and state values ​​must be at least substantially similar to the actual parameter and state values).

[0029] As explained, an accurate model of the traction battery 124 enables the BECM 125 to properly control the traction battery, which directly affects vehicle performance and range for a given full charge. ECMs are widely used in electrified vehicle traction battery control systems in order to meet real-time control system requirements for computational speed and RAM / ROM usage. Specifically, n-RC ECMs where n=1 or 2 are widely used (an n-RC ECM is a type of ECM having "n" RC circuit elements, each RC circuit element including resistor ("R") parameters and capacitor ("C") parameters; where n=1, a 1-RC ECM includes one such RC circuit element; and where n=2, a 2-RC ECM includes two such RC circuit elements). As indicated, the parameters of the ECM are learned using an online learning method such as a Kalman filter or an extended Kalman filter (EKF) .

[0030] According to the present disclosure, the BECM 125 adopts an equivalent circuit model of the traction battery 124 that efficiently represents the complex battery dynamics of the traction battery. The number of parameters of the proposed ECM is less than the number of parameters of a multi-RC pair ECM having three or more RC circuit elements, and the parameters of the proposed ECM can be learned using an EKF or similar method at reasonable BECM capabilities (such as CPU utilization ratio and RAM / ROM availability).

[0031] Reference now Figure 3 , continue to refer to Figure 1 and Figure 2 , shows a schematic diagram of an ECM 300 for a traction battery 124. According to the ECM 300, the traction battery 124 is modeled as a circuit having in series: a voltage source (OCV / (SOC)) 302, a resistor R0 304, a first RC pair 306 having a first resistor R1 308 and a first capacitor C1 310 connected in parallel, and one or more such additional RC pairs 312. To this end, the conventional ECM 300 is an n-RC ECM, where n≥2.

[0032] Voltage source 302 represents the open circuit voltage (OCV) of traction battery 124. The OCV of traction battery 124 depends on the state of charge (SOC) and temperature of traction battery 124. Resistor R0 304 represents the internal resistance of traction battery 124. The RC pair represents the diffusion process of traction battery 124. To this end, the diffusion process of traction battery 124 in conventional ECM 300 can be represented by RC pairs R1 and C1, ..., R n and C n to describe.

[0033] Voltage V0 314 is the voltage drop across resistor R0 304 due to battery current I 316 flowing across resistor R0 304. Voltage V1 318 is the voltage drop across first RC pair 306 due to battery current IR1 flowing across resistor R1 308. Voltage drops are across each additional RC pair 312. Voltage V t 320 is the voltage across the terminals of the traction battery 124 (ie, the terminal voltage).

[0034] The parameters of the ECM 300 may include resistors (ie, resistor R0, resistor R1, and resistor R n ) and capacitors (i.e., capacitor C1 and capacitor C n ). The parameters will have values ​​whereby the calculated output of the ECM 300 in response to a hypothetical given input represents the actual output of the traction battery 124 in response to the actual given input. The values ​​of the parameters may be learned online or locally by the BECM 125, such as with an EKF.

[0035] refer to Figure 4 , shows an example timing diagram of a process 400 for estimating the power capacity of a traction battery of one embodiment of the present disclosure. Figures 1 to 3 , the timeline of the process 400 can be generally divided into a first key-on period 402 when the vehicle 112 is in operation, a key-off period 404 when the vehicle 112 is parked, and a second key-on period 406 when the vehicle 112 is restarted for operation. The process 400 can be used to determine the power capacity immediately or shortly after detecting a key-on signal that initiates the second key-on period 406.

[0036] During the first key-on period 402, the vehicle 112 is in an operating state in which the traction battery 124 supplies power to the motor 114 for propulsion. As discussed above, an extended Kalman filter (EKF) learning process 408 may be performed by the BECM and / or the system controller 150 during all or a portion of the first key-on period 402. In this example, a 4RC equivalent circuit model (ECM) (not shown) may be used to represent the battery cell model. The SOC of the traction battery 124 may be dynamically calculated as

[0037]

[0038] Where Δt represents the time elapsed from time k, I k represents the battery current at time k, and Q represents the total capacity of the traction battery 124. Because a 4RC ECM is used in this example, the voltage across each of the four RC pairs can be calculated using the following equations:

[0039]

[0040] where τ1, τ2, τ3, and τ4 represent the time constants associated with each corresponding RC pair.

[0041] Therefore, the output voltage of the EKF learning process 408 can be calculated as follows:

[0042] V t，k =OCV(SOC) k -R 0,k I k -V 1，k -V 2,k -V 3,k -V 4，k

[0043] In addition, the state vector (x) of EKF 408 can be expressed as

[0044]

[0045] The EKF 408 matrix can be expressed as

[0046]

[0047] where the time constant τ can be calculated as τ 1，k Function:

[0048] τ2=γ*τ 1,k 2

[0049] τ3=α*γ*τ 1,k 2

[0050] τ4=α 2 *γ*τ 1,k 2

[0051] As can be seen from the above equation, the time constant τ of the successor RC pair is longer than the time constant τ of the predecessor RC pair. As an example, the time constant τ1 of the first RC pair can be 7 seconds. In this case, the time constant τ2 of the second RC pair can be calculated to be equal to about 49 seconds, the time constant τ3 of the third RC pair can be calculated to be equal to about 196 seconds, and the time constant τ4 of the fourth RC pair can be calculated to be equal to about 784 seconds.

[0052] The voltage EKF estimated by the EKF process 408 may be compared to the actual measured voltage, and corrections may be made to the states and parameters based on the comparison results.

[0053] When the vehicle 112 is parked and turned off at t0, the process 400 enters a key-off period 404 and the main contactor 127 opens, thereby isolating the traction battery 124 from the rest of the vehicle 112. The key-off period 404 begins at t0, which is used as a reference point, and ends at t0+Δt 关断 Therefore, the key-off period 404 lasts for Δt 关断 duration of the key-off period 404. In the present disclosure, the cell balancing process 410 may be performed during the key-off period 404. By operating in the first key-on period 402 (and other previous battery cycles), the cells 202 of the traction battery 124 may be at slightly different SOCs and have capacity changes compared to each other. The cell balancing process 410 may redistribute charge between the cells 202 so that the SOC of each cell 202 is the same across all cells 202 of the traction battery 124. Although the cell balancing process 410 may be applied to the entire key-on period 402 and the key-off period 404, in the present disclosure, the cell balancing process 410 is only applied to a portion of the key-off period. More specifically, the cell balancing process 410 is performed at t after t0. cb_接通 starts at t0+Δt 关断 Before cb_关断 Therefore, the key-off period 404 can be further divided into a pre-balancing period 412 , a cell balancing period 414 , and a post-balancing period 416 .

[0054] During the pre-balancing period 412 , the SOC of the traction battery 124 may be calculated as follows:

[0055] SOC(t)=SOC(0)=SOC(t 关断 )

[0056] Where SOC(t 关断 ) represents the state of charge of the traction battery 124 at the time of key-off. The voltage of each of the battery cells 202 can be calculated as

[0057]

[0058] During the pre-balancing period, the total SOC of the traction battery 124 is unchanged, and the cell temperature is assumed to remain substantially the same as at key-off time t0. Therefore, the cell temperature may be used in an open-loop manner to determine the mapped parameter data without using voltage feedback.

[0059] During the balancing period 414, the battery SOC may be calculated as follows:

[0060] SOC(t)=SOC(0)-(t cb_关断 -t cb_接通 )*I cb / Q

[0061] Among them I cb represents the current between the cells caused by the cell balancing process 410, and Q represents the capacity of the battery cell 202. Because for the passive cell balancing circuit, the cell balancing current I cb Relatively small, so the cell balancing current I can be ignored cb Effect on battery voltage and cell voltage. Therefore, the main factor of the battery cell voltage is still the time elapsed during the cell balancing process 410, which is calculated as follows:

[0062]

[0063] Because cell balancing is performed internally between cells 202 within traction battery 124, the overall SOC of traction battery 124 remains the same. Similarly, cell temperature may be used in an open loop manner to determine mapped parameter data without using voltage feedback.

[0064] The cell balancing process 410 is performed before receiving the next key-on signal. cb_关断 During the post-balancing period 416, since no current flows, the SOC of the battery 124 remains unchanged:

[0065] SOC(t 关断 )=SOC(t cb_关断 )

[0066] However, the voltage of each cell may decay based on the corresponding time constant as follows:

[0067]

[0068] The parameters calculated during the key-off period 404 can be used to determine the power capacity immediately or shortly after receiving the next key-on signal. 关断 The key-on signal is received and the BECM 125 , along with other components of the vehicle 112 , are powered up to determine the power capacity of the traction battery 124 .

[0069] The BECM 125 activates the vehicle sensors 210 , 208 , 204 to measure battery parameters such as battery temperature T, voltage V, and current I. An open circuit voltage (OCV) of the traction battery 124 may be estimated based on the battery temperature T and the SOC dynamically determined during the key-off period 404 .

[0070] Using the proposed 4RC ECM, the BECM 125 can derive the discharged battery current limit as

[0071]

[0072] Where V t are the battery terminal voltages V1(0), V2(0), ..., V n (0) is the voltage across each corresponding pair at time t=0 or the instant of updating the power estimate. τ2, τ3, ..., τ4 are functions of τ1, and R2, R3, ..., R n is a function of R1.

[0073] During a discharge condition (assuming the discharge current is positive), the BECM 125 determines the discharge current limit by:

[0074]

[0075] Where V t最小 is the traction battery minimum voltage limit. The traction battery minimum voltage limit V can be determined in various ways. For example, the minimum voltage limit V 最小 This may be the highest of: 1) the minimum voltage at which each component (e.g., electric drive, DC / DC converter, heater, etc.) may operate, or 2) the lowest voltage at which the battery pack may safely operate (and maintain life, etc.). As an example, the lowest voltage at which the battery pack may safely operate may be the minimum cell voltage multiplied by the number of cells in series, or the average / average voltage of cells 202 multiplied by the number of cells. In some examples, the battery may operate at a lower voltage at low temperatures than at room temperature. These system limits (e.g., traction battery minimum voltage limit V 最小 ) can be defined during the development of the vehicle.

[0076] Given the above, the voltage at maximum discharge current will be

[0077]

[0078] Typically, a battery system may be associated with various limits. As a few non-limiting examples, the limits may include a minimum battery voltage V 最小 , maximum current i 最大 and minimum cell voltage V 电芯_最小 The power capacity should be calculated under the condition that all these limits are met. For example, if the battery 124 is voltage-limited (e.g., V 最小_ If the battery 124 is current limited, the power capacity may be the pack voltage multiplied by the current required to achieve the pack voltage. Alternatively, if the battery 124 is current limited, the power capacity may be the maximum current multiplied by the voltage that the battery will encounter at the maximum current. Alternatively, if the battery 124 is cell voltage limited, the power capacity may be the current required to achieve the minimum cell voltage multiplied by the voltage per cell at the corresponding current.

[0079] Therefore, the discharge power capacity at a later time t seconds will be

[0080]

[0081] The examples of the present disclosure do not use the current value i without further examination. 最大 , but i 最大 With the discharge limit current i dis_极限 Compare to determine i 最大 Is it less than or equal to i dis_极限 The reason for this is that the discharge limit current i dis_极限 Can provide less than i 最大 of the border.

[0082] Having determined the discharge power capacity, the system controller 150 and / or the BECM 125 may use the power capacity to operate the discharge of the traction battery 124. For example, in response to detecting that the power demand for propulsion from the electric machine 114 is greater than the power capacity of the traction battery 124, the system controller 150 and / or the BECM 125 may use the power capacity to limit the power output from the traction battery 124.

[0083] It should be noted that although the process 400 described above relates to determining the power capacity of the entire traction battery 124, the present disclosure is not limited thereto. The process 400 may also be applied to determine the power capacity of each individual battery cell 202. The equations used to calculate the voltage, current, SOC, etc. of the traction battery 124 may be used to calculate the same parameters of the individual battery cells 202 under substantially the same principles.

[0084] The algorithm, method or process disclosed herein can be delivered to or implemented by a computer, a controller or a processing device, which may include any dedicated electronic control unit or a programmable electronic control unit. Similarly, the algorithm, method or process can be stored in various forms as data and instructions that can be executed by a computer or a controller, including but not limited to information permanently stored on a non-writable storage medium such as a read-only memory device and information that can be changed and stored on a writable storage medium such as an optical disk, a random access memory device or other magnetic and optical media. The algorithm, method or process can also be implemented by a software executable object. Alternatively, a suitable hardware component (such as an application-specific integrated circuit, a field programmable gate array, a state machine or other hardware component or device) or a combination of firmware, hardware and software components can be used to embody the algorithm, method or process in whole or in part.

[0085] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms covered by the claims. The words used in the specification are descriptive rather than limiting, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. The words "a processor" and "multiple processors" are interchangeable herein, as are the words "a controller" and "multiple controllers".

[0086] As previously mentioned, the features of the various embodiments may be combined to form additional embodiments of the invention that may not be explicitly described or shown. Although 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, it will be appreciated by those of ordinary skill in the art that one or more features or characteristics may be compromised to achieve desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, strength, durability, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, and the like. For this reason, embodiments described as being less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of this disclosure and may be desirable for specific applications.

[0087] According to the present invention, there is provided an electrical power system for a vehicle having one or more controllers that charge and discharge a traction battery after start-up of the vehicle according to power limits that are based on a polarization voltage describing an internal state of the traction battery and are a function of the polarization voltage that existed at a last stop of the vehicle and a decay value having a time constant based on the state of charge of the traction battery and a temperature associated with the traction battery.

[0088] According to an embodiment, the decay value is an exponential decay value.

[0089] According to an embodiment, the polarization voltage is also a function of the duration between a last deactivation of the vehicle and a activation of the vehicle.

[0090] According to an embodiment, the polarization voltage is also a function of the start time and the stop time of the cell balancing during the duration.

[0091] According to an embodiment, the temperature is the temperature of the traction battery at the last time the vehicle was stopped.

[0092] According to an embodiment, the temperature is an average of a temperature of the traction battery at a last deactivation of the vehicle and a temperature at a start-up of the vehicle.

[0093] According to an embodiment, the state of charge is the state of charge of the traction battery at a last stop of the vehicle.

[0094] According to the invention, a method comprises, after starting of the vehicle, charging and discharging a traction battery of the vehicle according to power limits based on a polarization voltage describing an internal state of the traction battery and being a function of the polarization voltage present at the last stop of the vehicle and a decay value having a time constant based on the state of charge of the traction battery and a temperature associated with the traction battery.

[0095] In one aspect of the invention, the decay value is an exponential decay value.

[0096] In one aspect of the invention, said polarization voltage is also a function of the duration between a last deactivation of said vehicle and a activation of said vehicle.

[0097] In one aspect of the invention, the polarization voltage is also a function of the start time and the stop time of cell balancing during the duration.

[0098] In one aspect of the invention, said temperature is the temperature of said traction battery at a last stop of said vehicle.

[0099] In one aspect of the invention, the temperature is an average of the temperature of the traction battery at the last deactivation of the vehicle and the temperature at the start of the vehicle.

[0100] In one aspect of the invention, the state of charge is the state of charge of the traction battery at the last time the vehicle was deactivated.

[0101] According to the present invention, a vehicle is provided having: a traction battery; and one or more controllers programmed to charge and discharge the traction battery according to a power limit after starting of the vehicle, wherein the power limit is derived from a polarization voltage based on a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery.

[0102] According to an embodiment, the decay value is an exponential decay value.

[0103] According to an embodiment, the polarization voltage is also derived from the duration between a last deactivation of the vehicle and a activation of the vehicle.

[0104] According to an embodiment, the polarization voltage is also derived from a start time and a stop time of the cell balancing during the duration.

Claims

1. An electric power system for a vehicle, comprising: One or more controllers programmed to charge and discharge a traction battery after startup of the vehicle according to power limits that are based on a polarization voltage describing an internal state of the traction battery and are a function of the polarization voltage that existed at a last deactivation of the vehicle and a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery. The power system of claim 1 , wherein the decay value is an exponential decay value.

3. The power system of claim 1, wherein the polarization voltage is also a function of a duration between the last deactivation of the vehicle and the activation of the vehicle.

4. The power system of claim 3, wherein the polarization voltage is also a function of a start time and a stop time of cell balancing during the duration.

5. The power system of claim 1 wherein said temperature is a temperature of said traction battery at said last deactivation of said vehicle.

6. The power system of claim 1, wherein the temperature is an average of a temperature of the traction battery at the last deactivation of the vehicle and a temperature at the startup of the vehicle.

7. The power system of claim 1 wherein said state of charge is a state of charge of said traction battery at said last stop of said vehicle.

8. A method comprising: After starting of the vehicle, a traction battery of the vehicle is charged and discharged according to power limits that are based on a polarization voltage describing an internal state of the traction battery and are a function of the polarization voltage present at a last stop of the vehicle and a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery. The method of claim 8 , wherein the decay value is an exponential decay value.

10. The method of claim 8, wherein the polarization voltage is also a function of a duration between the last deactivation of the vehicle and the activation of the vehicle.

11. The method of claim 10, wherein the polarization voltage is also a function of a start time and a stop time of cell balancing during the duration.

12. The method of claim 8, wherein said temperature is a temperature of said traction battery at said last deactivation of said vehicle.

13. The method of claim 8, wherein the temperature is an average of a temperature of the traction battery at the last deactivation of the vehicle and a temperature at the activation of the vehicle.

14. The method of claim 8, wherein the state of charge is the state of charge of the traction battery at the last time the vehicle was deactivated.

15. A vehicle comprising: Traction batteries; as well as one or more controllers programmed to charge and discharge the traction battery according to a power limit after starting of the vehicle, wherein the power limit is derived from a polarization voltage based on a decay value having a time constant based on a state of charge of the traction battery and a temperature associated with the traction battery.

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