System and method for controlling vehicle battery pack based on open circuit voltage

Abstract

The invention provides a system and method for controlling a vehicle battery pack based on an open circuit voltage. An electrically powered vehicle (EV) includes a battery pack, one or more sensors, and a vehicle controller. The battery pack includes a plurality of battery cells and is operable to provide at least a portion of propulsion power for the EV. The vehicle controller is configured to charge and discharge the battery pack according to a power limit defined by an estimated open circuit voltage (OCV) for each of the battery cells when the EV is activated, the estimated open circuit voltage (OCV) is based on a voltage measured by the one or more sensors after a last deactivation of the EV and an attenuation parameter that is a function of the voltage and a duration since the last deactivation.

Description

Technical Field

[0001] The present disclosure generally relates to managing and / or controlling a battery pack of an electrified vehicle. Background Art

[0002] An electrified vehicle (EV) includes a battery pack, sometimes referred to as a traction battery, for providing power to an electric motor to propel the EV. One or more operating characteristics of the battery pack, such as a power limit and a state of charge (SOC), can be estimated to control charging and discharging operations of the battery pack.

[0003] In a non-limiting example, the EV includes a battery management module (BMM) and a control system. Generally, during a discharging operation (e.g., driving of the EV), the BMM is configured to estimate the SOC and / or the power limit of the battery pack, and the control system is configured to control various devices / subsystems within the EV by determining, for example, how much power can be drawn from the battery pack using the operating characteristics, input from a user, power demands of devices (e.g., a motor, an air conditioning system, etc.), and / or other information. For a charging operation, the BMM is configured to provide a charging current / voltage request to the control system, which in turn controls the EV to start charging the battery pack (e.g., controlling an electric vehicle supply equipment (EVSE)). Summary of the Invention

[0004] In one form, the present disclosure relates to an electrified vehicle (EV) that includes a battery pack, one or more sensors, and a vehicle controller. The battery pack includes a plurality of battery cells and is operable to provide at least a portion of the propulsion power of the EV. The vehicle controller is configured to charge and discharge the battery pack according to a power limit defined by an estimated open-circuit voltage (OCV) for each of the battery cells upon activation of the EV, the estimated open-circuit voltage (OCV) being based on a voltage measured by the one or more sensors after the last deactivation of the EV and an attenuation parameter that is a function of the voltage and a duration since the last deactivation.

[0005] In one form, the present disclosure relates to a method of controlling an electrified vehicle (EV) having a battery pack including a plurality of battery cells. The method includes: in response to a deactivation request, disconnecting one or more contactors to electrolytically decouple the battery pack from the charge-discharge system of the EV; and in response to activation, closing the one or more contactors to electrically couple the battery pack to the charge-discharge system and charging and discharging the battery pack according to a power limit defined by an estimated open-circuit voltage (OCV) for each of the battery cells when the EV is activated, the estimated open-circuit voltage (OCV) being based on a voltage measured by one or more sensors after the last deactivation of the EV and a decay parameter that is a function of the voltage and the duration since the last deactivation.

[0006] In one form, the present disclosure relates to a system for an electrified vehicle (EV) including a battery pack having a plurality of battery cells and operable to provide at least a portion of the propulsion power of the EV. The system includes a controller configured to charge and discharge the battery pack according to a state of charge initially defined by an estimated open-circuit voltage (OCV) for each of the battery cells when the EV is activated. The estimated OCV is based on a voltage measured by one or more sensors of the EV after the last deactivation of the EV and a decay parameter that is a function of the voltage and the duration since the last deactivation. The decay parameter includes an exponential parameter related to the square root of the duration, and the duration is less than an equilibrium time for the active material of each of the battery cells to be uniformly distributed on the electrodes of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is an example block diagram of an electrified vehicle (EV) according to the present disclosure;

[0008] Figure 2 is a block diagram of a battery pack of an EV according to the present disclosure;

[0009] Figure 3 is a block diagram of a battery management module of an EV according to the present disclosure;

[0010] Figure 4 is a graph showing an example relationship between voltage and time after disconnecting a battery pack from a charge-discharge system of an EV according to the present disclosure; and

[0011] Figure 5 is a flowchart of an example battery pack control routine according to the present disclosure. DETAILED DESCRIPTION

[0012] As needed, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely examples of the present invention that can be implemented in various forms and alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show details of particular components. Thus, the specific structural details and functional details disclosed herein are not to be construed as limiting, but rather as a representative basis for teaching those skilled in the art to practice the present invention in various ways.

[0013] Generally, to manage a battery pack in an electrified vehicle (EV), the vehicle system of the EV needs to know the state of charge (SOC) of the battery pack to estimate the power capacity / power limit of the battery pack. For most battery chemistries, the SOC is estimated based on the open-circuit voltage (OCV) of the battery pack, which is the voltage when the battery pack is idle. In a non-limiting example, for a hybrid electric vehicle (HEV), since the size of a battery cell is typically about five (5) ampere-hours, the OCV can stabilize within 30 minutes, but may take longer at lower temperatures. Specifically, stabilization is when the active material is evenly distributed (by diffusion) across the thickness of the electrode, and the time required to reach stabilization can be referred to as the equilibration time of the battery cell. Battery charging and discharging reactions occur at the electrode surface. As the battery cell gets larger, the electrode tends to get thicker, and thus the equilibration time increases. Some battery cells for EVs may take several hours (e.g., more than 3 hours) to stabilize the OCV, and even longer at low temperatures.

[0014] In various situations, it may be difficult for an EV to idle (i.e., not charge or discharge) for such a long equilibration time. For example, in one scenario, the user of the EV may park at a restaurant for a meal, which may only take one to two hours. In another example, the user may park at a charging station, and the amount of time required between turning off the EV and charging the battery pack may only be a few minutes.

[0015] In addition, the number of battery cells employed in the battery pack of an EV may also affect the detection of the OCV measured for each battery cell. Specifically, some EVs have approximately 96 series-connected cells, and as the EV moves towards higher power systems (e.g., 800V to 1200V), the number of battery cells may double or even triple, thereby increasing the computational requirements of the vehicle system.

[0016] The new EV battery warranty agreement may also require the EV to detect the "certified state of energy" (SOCE) or state of health (SOH), which is the amount of energy that the battery pack can deliver within a standard driving cycle relative to the amount of energy delivered when the battery pack was new. Therefore, the SOC at idle derived from the OCV must be accurate in order to obtain a good estimate of the capacity fade. Specifically, some regulations require the energy estimate to be within 5% of the actual value and the SOC to be within 2% or less in order to calculate a "sufficiently accurate" capacity and thus energy.

[0017] The present disclosure generally relates to a vehicle system configured to charge / discharge a battery pack based on an estimated OCV. Specifically, voltage measurements and attenuation parameters are used to estimate the OCV of each battery cell, where the attenuation parameters are a function of the voltage since the last deactivation of the battery pack. Using the estimated OCV, the vehicle system can estimate the SOC, provide available energy at the start of a driving cycle, which is used to predict the vehicle driving range, and / or provide a power limit estimate, as well as other actions (e.g., output SOH). As described in detail herein, the OCV can be estimated within a fraction of the time required for the battery cells to achieve balance, and thus the accuracy of the SOC and thus the power limit can be improved. Specifically, since the power limit can change rapidly, the OCV is used to ensure a more accurate power limit at vehicle start-up. During a drive / charge cycle, the EV operates the vehicle using a power limit estimated using other factors in addition to the OCV.

[0018] Reference Figure 1 and Figure 2 and, in one form, the EV 100 is provided as a full battery electric vehicle (BEV) powered by an electric motor. In a non-limiting example, the EV 100 includes a powertrain having one or more electric motors 104 (i.e., motors), a battery pack 106 (i.e., traction battery), and a power electronics module 108. The EV 100 of the present disclosure does not include an engine, and thus, the battery pack 106 provides all of the propulsion power. In other variations, the present disclosure can be applied to other types of EVs, such as hybrid electric vehicles (plug-in or non-plug-in) with an engine, fuel cell electric vehicles (FCEVs), and is not limited to pure battery electric EVs. Additionally, the EV is not limited to four-wheel vehicles and can be applied to scooters, three-wheel vehicles, aerial vehicles, and / or other vehicles.

[0019] The electric motor 104 provides motive power for the EV 100, and in a non-limiting example, the electric motor is mechanically connected to a transmission 110, the transmission is mechanically connected to a drive shaft 112, and the drive shaft is mechanically connected to the wheels 114 of the EV 100. In addition to providing propulsion power, the electric motor 104 can also be configured to operate as a generator to recover energy that would otherwise be lost as heat in the friction braking system of the EV 100.

[0020] The battery pack 106 provides a high-voltage (HV) direct current (DC) output that is used to power the electric motor 104 via a power electronics module 108. Although one battery pack 106 is shown, the EV 100 can include multiple battery packs. In one form, the power electronics module 108, which includes an inverter, provides bi-directional energy transfer between the battery pack 106 and the electric motor 104. Specifically, as is well known, the power electronics module 108 converts the DC voltage to a three-phase AC current to operate the electric motor 104, and in the regenerative mode, the power electronics module 108 converts the three-phase AC current from the electric motor 104, which is acting as a generator, to a DC voltage compatible with the battery pack 106.

[0021] The battery pack 106 can be recharged by an external power source 120 (e.g., the power grid), which is electrically connected to an electric vehicle supply equipment (EVSE) 122. The EVSE 122 provides the circuitry and controls to manage the electrical energy transfer between the external power source 120 and the EV 100. The external power source 120 can supply DC or AC power to the EVSE 122. The EVSE 122 can have a charging connector 124 for insertion into a charging port 126 of the EV 100.

[0022] The EV 100 can also include a power conversion module 228, which is an on-board charger with a DC / DC converter, to condition the power supplied from the EVSE 122 and provide appropriate voltage and current levels to the battery pack 106. The power conversion module 228 can interface with the EVSE 122 to coordinate the delivery of power to the battery pack 106.

[0023] In addition to providing electrical energy for propulsion, the battery pack 106 can also provide electrical energy for other electrical systems in the EV 100, such as HV loads like electric heaters and air conditioning systems, and low voltage (LV) loads like auxiliary batteries. In some variations, the battery pack 106 is configured to have bidirectional power transfer capabilities to provide power to systems external to the EV 100 (i.e., external systems), such as but not limited to homes, businesses, and / or microgrids. In a non-limiting example, the battery pack 106 is electrically coupled to an external system using an EVSE connector 224 and is operable to provide energy based on the transient load recommended for the external system and the amount of energy available from the battery pack 106.

[0024] In one form, the EV 100 includes a control system 130 to coordinate the operation of various components. The control system 130 includes electronics, software, or both to perform the necessary control functions for operating the EV 100. The control system 130 can be a combination of a vehicle control system and a powertrain control module (VSC / PCM). Although the control system 130 is shown as a single device, the control system 130 can include multiple controllers in the form of multiple hardware devices, or multiple software controllers with one or more hardware devices. In this regard, references to "controller" herein can refer to one or more controllers.

[0025] In one form, the EV 100 includes a battery management module (BMM) 132 that is configured to estimate one or more operating characteristics of the battery pack 106 and provide one or more of the operating characteristics to the control system 130, which uses known techniques to control the operation of the battery pack 106 (e.g., controlling the charge / discharge of the battery pack 106). In a non-limiting example, during driving operation, the BMM 132 provides operating characteristics to the control system 130, such as but not limited to power limits and / or SOC, and the control system determines how much power to draw from the battery pack 106. During charging operation, the BMM 132 notifies the control system 130 of how much power is needed to charge the battery pack 106. The BMM 132 forms part of the vehicle control system together with the control system 130, and although shown separately from the control system 130, can be integrated with the control system 130. In one form, the BMM 132 and the control system 130 can be referred to as a vehicle controller.

[0026] In one form, the BMM 132 communicates with one or more sensors 134 provided with the battery pack 106 to estimate characteristics of the battery pack 106, such as but not limited to current, voltage, and / or temperature.

[0027] In addition to other components, the battery pack 106 includes a plurality of battery arrays 202A and 202B (collectively referred to as "array 202"), where each array 202 includes a plurality of battery cells 204-1 to 204N (collectively referred to as "cells 204")( Figure 2 ). The array 202 is connected to a positive power bus 206A and a negative power bus 206B (collectively referred to as "power buses 206"). Although two arrays 202 are provided, the battery pack 106 may include one or more arrays 202 and should not be limited to the examples provided herein. Additionally, the arrays 202 and / or cells 204 of the battery pack 106 may be configured in various suitable ways. In a non-limiting example, the battery pack 106 may be configured to have series arrays 202, and for each array 202, the cells 204 are provided in parallel.

[0028] The sensor 134 includes one or more sensors 134A and 134B for the array 202. In one form, the sensor 134 includes a voltage sensor and a current sensor for measuring the voltage and / or current of the array 202 and in some variations the voltage and / or current of each battery cell 204. It should be readily understood that the sensor 134 may include other sensors, such as but not limited to a temperature sensor for measuring the temperature of the array 202 and / or the battery pack 106.

[0029] In one form, one or more contactors 210 are provided to inhibit or allow current to travel through the power buses 206 to / from the battery pack 106. Specifically, the contactor 210 is operable to electrically decouple or couple the battery pack 106 from the charge-discharge system of the EV 100. The charge-discharge system of the EV includes components that charge the battery pack 106 or act as a load to draw power from the battery pack 106 and may therefore include a charging port 126, a power electronics module 108, and / or a transmission 110, among other components. The contactor 210 may be placed in various suitable locations in the EV 100, such as but not limited to between the positive power bus 206A and the power electronics module 108. In a non-limiting example, the contactor 210 may be provided as a relay or an electromechanical switch.

[0030] In one form, the BMM 132 is configured to open or close the contactor 210 based on messages / requests from the control system 130. In a non-limiting example, the control system 130 is configured to detect when to turn on or off the EV 100 based on an activation input (e.g., a user presses a button associated with activating / deactivating the EV 100). If the EV 100 is to be turned on, the control system 130 provides an activation request to the BMM 132 to close the contactor 210, thereby electrically coupling the battery pack 106 to the charge-discharge system of the EV 100. If the EV 100 is to be turned off, the control system 130 provides a deactivation request to the BMM 132 to open the contactor 210, thereby electrically coupling the battery pack 106 to the charge-discharge system of the EV 100. Additionally, the control system 130 is configured to cause the BMM 132 to close the contactor 210 by sending an activation request when the battery pack 106 is to be charged, which can be detected by a sensor at the charging port (e.g., a sensor indicating that the EVSE 122 is connected to the charging port 126, a sensor for detecting the opening of a charging port door (not shown), and / or other suitable charging detection methods).

[0031] Reference Figure 3 , in one form, the BMM 132 includes an actuator 302 for operating the contactor 210 in a closed / open position and a battery characteristic estimator (BCE) 304. The BCE 304 is configured to estimate various operating characteristics of the battery pack 106, such as but not limited to the OCV of each battery cell, the SOC of the battery pack 106, the power limit of the battery pack 106, and the temperature of the battery pack 106. As described in detail herein, the BCE 304 includes an OCV estimator 308 to estimate the OCV of each battery cell 204.

[0032] In a non-limiting example, during driving / discharging of the battery pack 106, the BMM 132 is configured to provide the control system 130 with one or more power limits in each direction, as well as a minimum voltage limit and a maximum voltage limit. Among other considerations, the control system 130 also takes into account driver demands and obtains an appropriate amount of power from the battery pack 106 (e.g., if the regenerative braking power exceeds the power from other loads, power is provided to the battery pack 106). For HEVs (i.e., plug-in or non-plug-in) and FCEVs, the control system 130 can also manage the SOC to keep it within a desired range, thereby charging the battery pack from the engine or fuel cell as appropriate. In one form, the BMM 132 is configured to ensure that if the power level is followed, the voltage limits of the battery pack 106 are not exceeded.

[0033] In one form, the OCV estimator 308 is configured to estimate the OCV based on the voltage measured by the sensor 134 after the previous / last deactivation of the EV 100 and a decay parameter, which is a function of the voltage and the duration since the last deactivation. More specifically, the following Equation 1 is the algorithm employed by the BCE 304 to estimate the OCV of the battery cell 204, where "V" is the voltage of the battery cell 204, "VOCV" is the OCV, and "DP" is the parameter. Based on Equation 1, the estimated OCV represents the difference between the voltage and the decay parameter.

[0034] Equation 1.....V = V ocv + DP

[0035] In one form, the decay parameter has a non-linear correlation with the voltage because after deactivation, the voltage measurement of each battery cell 204 begins to decrease over time and the voltage change is not linear. For example, Figure 4 FIG. 400 shows an example graph mapping the electrical characteristics (e.g., voltage and current) of the battery cell 204 over time, and at 1260 seconds, the battery pack 106 is decoupled from the charge-discharge system. As shown, the voltage begins to decay non-linearly over time.

[0036] The decay parameter of Equation 1 uses an exponential parameter involving the square root of the duration to characterize the decaying voltage and also includes a coefficient and a constant as a function of the voltage. More specifically, the decay parameter can be one of the following where "β" is the coefficient, "k" is the time constant, and "t" is the time. The difference between the various decay parameters is the unit of the time constant. Additionally, the sign of "β" depends on the direction of the current just before the battery pack 106 is decoupled. That is, if the battery pack 106 is (primarily) discharging just before deactivation, the sign of β is negative, indicating that the voltage will be lower than the OCV. If the battery pack 106 is (primarily) charged, then β is positive.

[0037] In one form, the decay parameter of each battery cell is estimated based on the voltage measurement using known parameter estimation techniques such as, but not limited to, non-linear regression models. The decay parameter is learned when estimating the OCV because the time constant may change due to the phase change of the anode of the battery cell 204. After a defined period of time or the estimated decay parameter has not changed up to a selected threshold, the BCE 304 determines the OCV based on Equation 1.

[0038] In some variations, BCE 304 can be configured to use a refined algorithm to estimate the OCV when EV 100 operates under certain conditions. Specifically, when the environmental conditions are very cold (e.g., below -20 degrees Celsius) and / or the SOC is low (e.g., 5%), due to the possible influence that battery cells 204 may have on each other, a single exponential term may not accurately estimate the OSC. Therefore, BCE 304 is configured to use Equation 2 shown below to estimate the OCV. In Equation 2, DP1 is the first decay parameter, and DP2 is the second decay parameter, where the first decay parameter and the second decay parameter have different coefficients and time constants. In a non-limiting example, the first decay parameter is provided as And the second decay parameter is provided as

[0039] Equation 2…

[0040] Reference Figure 5 , the present disclosure provides and supports an example battery pack control routine 500 executed by BMM 132 and control system 130 (i.e., the vehicle controller). At 502, BMM 132 determines whether an activation request is received, and if so, BMM 132 closes contactor 210 at 504 to electrically couple battery pack 106 to the charge-discharge system of EV 100. At 506, the controller 132 sets the SOC and the initial power limit using the OCV estimated after the last deactivation of EV 100. At 508, the controller 132 controls the charging / discharging of battery pack 106 based on the operating characteristics of battery pack 106, the operating characteristics including the power limit. Once activated, known techniques are used to update the SOC and the power limit.

[0041] At 510, the controller 132 determines whether a deactivation request is received. If not, the controller 132 returns to 508 to control battery pack 106. As is well known, when EV 100 charges / discharges using a predefined model / algorithm, the values of one or more operating characteristics (such as the power limit and the SOC) can be updated. Therefore, the controller 132 can use the updated characteristics to control battery pack 106.

[0042] If a deactivation request is received, the controller 132 disconnects contactor 210 at 512 to electrolytically decouple battery pack 106 from the charge-discharge system of EV100. At 514, the controller uses the OCV estimator 308 as described above to estimate the OCV of each of the battery cells. The controller 132 determines at 502 whether an activation request is received from 514. If not, the controller 132 estimates the OCV of each battery cell 204. That is, if no activation request is received, the OCV can be estimated again.

[0043] The battery pack control routine 500 can be configured to perform other operations within the scope of the present disclosure and should not be limited to the examples described herein. In a non-limiting example, the routine 500 can stop estimating the OCV if a predefined period of time of the estimated balancing time based on the battery pack 106 has elapsed and / or if the previous OCVs differ from each other by a selected threshold.

[0044] Instead of waiting for the battery cells 204 to stabilize to obtain the OCV, the BMM 132 of the present disclosure is configured to use the OCV estimator 308 to estimate the OCV of each battery cell with improved accuracy, and thus improve the accuracy of the power limit, SOC, SOH, and other characteristics.

[0045] Although the exemplary embodiments have been described above, these embodiments are not intended to describe all possible forms of the invention. Rather, the words used in the specification are descriptive words rather than restrictive words, and it should be understood that various changes can be made without departing from the spirit and scope of the invention. Additionally, the features of the various embodiments can be combined to form additional embodiments of the invention.

[0046] In this application, the term "module" can refer to, be part of, or include the following: an application specific integrated circuit (ASIC); digital, analog, or mixed analog / digital discrete circuits; digital, analog, or mixed analog / digital integrated circuits; combinational logic circuits; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or grouped) that executes code; a memory circuit (shared, dedicated, or grouped) that stores the code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

[0047] The term memory or memory device is a subset of the term computer-readable medium. As used herein, the term computer-readable medium does not cover transitory electrical or electromagnetic signals propagated through a medium (such as on a carrier wave); thus, the term computer-readable medium can be considered tangible and non-transitory. Non-limiting examples of non-transitory tangible computer-readable media are non-volatile memory circuits (such as flash memory circuits, erasable programmable read-only memory circuits, or mask read-only circuits), volatile memory circuits (such as static random access memory circuits or dynamic random access memory circuits), magnetic storage media (such as analog or digital magnetic tape or hard disk drives), and optical storage media (such as CDs, DVDs, or Blu-ray discs).

[0048] The devices and methods described in this application can be implemented partially or fully by a dedicated computer, which is created by configuring a general-purpose computer to execute one or more specific functions embodied in a computer program. Functional blocks, flowchart components, and other elements described above serve as software specifications, which can be translated into a computer program through routine work by a technician or programmer.

[0049] As used herein, the phrase "at least one of A, B, and C" should be interpreted as representing the logic (A or B or C) using non-exclusive logic "or", and should not be interpreted as representing "at least one of A, at least one of B, and at least one of C".

[0050] The description of the present disclosure is merely exemplary in nature, and thus, variations that do not depart from the essence of the present disclosure are intended to be within the scope of the present disclosure. Such variations should not be regarded as departing from the spirit and scope of the present disclosure.

[0051] According to the present invention, there is provided an electrified vehicle (EV) having: a battery pack including a plurality of battery cells and operable to provide at least a part of the propulsion power of the EV; one or more sensors; and a vehicle controller configured to charge and discharge the battery pack according to a power limit defined by an estimated open-circuit voltage (OCV) for each of the battery cells when activating the EV, the estimated open-circuit voltage (OCV) being based on the voltage and decay parameters at the last deactivation of the EV by the one or more sensors, the decay parameters being a function of the voltage and the duration since the last deactivation.

[0052] According to one embodiment, the decay parameter includes a coefficient as a function of the voltage.

[0053] According to one embodiment, the decay parameter includes a constant as a function of the voltage.

[0054] According to one embodiment, the decay parameter has a non-linear correlation with the voltage.

[0055] According to one embodiment, the decay parameter includes an exponential parameter involving the square root of the duration.

[0056] According to one embodiment, the vehicle controller is configured to detect the decay parameter using a non-linear regression model.

[0057] According to one embodiment, the vehicle controller is configured to estimate the initial state of charge of the battery pack based on the estimated OCV, wherein the power limit is partially defined by the initial state of charge.

[0058] According to one embodiment, the duration is less than the equilibrium time for the active material of each of the battery cells to be evenly distributed on the electrodes of the battery cells.

[0059] According to the present invention, a method of controlling an electrified vehicle (EV) having a battery pack including a plurality of battery cells includes: in response to a deactivation request, disconnecting one or more contactors to electrolytically decouple the battery pack from the charge-discharge system of the EV; in response to activation, closing the one or more contactors to electrically couple the battery pack to the charge-discharge system, and charging and discharging the battery pack according to a power limit defined by an estimated open circuit voltage (OCV) for each of the battery cells when the EV is activated, the estimated open circuit voltage (OCV) being based on a voltage measured by one or more sensors after the last deactivation of the EV and an attenuation parameter, the attenuation parameter being a function of the voltage and the duration since the last deactivation.

[0060] In one aspect of the present invention, the attenuation parameter includes a coefficient as a function of the voltage.

[0061] In one aspect of the present invention, the attenuation parameter includes a constant as a function of the voltage.

[0062] In one aspect of the present invention, the attenuation parameter has a non-linear correlation with the voltage.

[0063] In one aspect of the present invention, the attenuation parameter includes an exponential parameter involving the square root of the duration.

[0064] In one aspect of the present invention, the method includes using a non-linear regression model to detect the attenuation parameter.

[0065] In one aspect of the present invention, the vehicle controller is configured to estimate an initial state of charge of the battery pack based on the estimated OCV, wherein the power limit is partially defined by the initial state of charge.

[0066] In one aspect of the present invention, the duration is less than the equilibrium time for the active material of each of the battery cells to be evenly distributed on the electrodes of the battery cells.

[0067] According to the present invention, there is provided a system for an electrified vehicle (EV), the electrified vehicle including a battery pack having a plurality of battery cells and operable to provide at least a portion of the propulsion power of the EV. The system has: a controller configured to charge and discharge the battery pack based on a state of charge, the state of charge being initially defined, when activating the EV, based on an estimated open-circuit voltage (OCV) of each of the battery cells, the OCV being based on a voltage measured by one or more sensors of the EV after the last deactivation of the EV and a decay parameter, the decay parameter being a function of the voltage and a duration since the last deactivation, wherein the duration is less than an equilibrium time for the active material of each of the battery cells to be evenly distributed on the electrodes of the battery cell.

[0068] According to one embodiment, the estimated OCV represents a difference between the voltage and the decay parameter.

[0069] According to one embodiment, the decay parameter includes a coefficient as a function of the voltage.

[0070] According to one embodiment, the decay parameter has a non-linear correlation with the voltage.

Claims

1. An electrified vehicle (EV) comprising: A battery pack including a plurality of battery cells and operable to provide at least a portion of the propulsion power of the EV; One or more sensors; And A vehicle controller configured to charge and discharge the battery pack according to a power limit defined by an estimated open-circuit voltage (OCV) for each of the battery cells upon activation of the EV, the estimated open-circuit voltage (OCV) being based on the voltage measured by the one or more sensors at the last deactivation of the EV and a decay parameter that is a function of the voltage and the duration since the last deactivation.

2. The EV of claim 1, wherein the decay parameter includes a coefficient as a function of the voltage.

3. The EV of claim 1, wherein the decay parameter includes a constant as a function of the voltage.

4. The EV of claim 1, wherein the decay parameter has a non-linear correlation with the voltage.

5. The EV of claim 1, wherein the decay parameter includes an exponential parameter involving the square root of the duration.

6. The EV of claim 1, wherein the vehicle controller is configured to detect the decay parameter using a non-linear regression model.

7. The EV of claim 1, wherein the vehicle controller is configured to estimate an initial state of charge of the battery pack based on the estimated OCV, wherein the power limit is defined in part by the initial state of charge.

8. The EV of claim 1, wherein the duration is less than an equilibrium time for the active material of each of the battery cells to be uniformly distributed on the electrodes of the battery cell.

9. A method of controlling an electrified vehicle (EV) having a battery pack including a plurality of battery cells, the method comprising: In response to a deactivation request, opening one or more contactors to electrically decouple the battery pack from the charge-discharge system of the EV; In response to activation, Closing the one or more contactors to electrically couple the battery pack to the charge-discharge system, and Charging and discharging the battery pack according to a power limit defined by an estimated open-circuit voltage (OCV) for each of the battery cells upon activation of the EV, the estimated open-circuit voltage (OCV) being based on the voltage measured by one or more sensors after the last deactivation of the EV and a decay parameter that is a function of the voltage and the duration since the last deactivation.

10. The method of claim 9, wherein the decay parameter includes a coefficient as a function of the voltage.

11. The method of claim 9, wherein the decay parameter includes a constant as a function of the voltage.

12. The method of claim 9, wherein the decay parameter has a non-linear correlation with the voltage.

13. The method of claim 9, wherein the decay parameter includes an exponential parameter involving the square root of the duration.

14. The method according to claim 9, further comprising using a non-linear regression model to detect the attenuation parameter.

15. The method according to claim 9, wherein the vehicle controller is configured to estimate the initial state of charge of the battery pack based on the estimated OCV, wherein the power limit is defined in part by the initial state of charge.

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