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

Abstract

An electrified 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 of the EV. The vehicle controller is configured to charge and discharge the battery pack according to power limits defined, when the EV is turned on, by an estimated open circuit voltage (OCV) for each of the battery cells based on voltages measured by the one or more sensors after a last shutdown of the EV and a decay parameter dependent on the voltages and a duration since the last shutdown.

Description

FIELD OF TECHNOLOGY

[0001] The present disclosure generally relates to managing and / or controlling a battery pack for an electrified vehicle. GENERAL STATE OF THE ART

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

[0003] In one non-limiting example, the EV includes a battery management module (BMM) and a control system. Generally, during a discharge event (e.g., driving the EV), the BMM is configured to estimate the SOC and / or power limits of the battery pack, and the control system is configured to control various devices / subsystems within the EV, for example, by determining how much power can be drawn from the battery pack using operating characteristics, inputs from a user, power demands from devices (e.g., motors, HVAC system, etc.), and / or other information. For a charging event, the BMM is configured to provide a charging current / voltage request to the control system, which in turn controls the EV to begin charging the battery pack (e.g.,Controlling an electric vehicle supply equipment (EVSE). SUMMARY

[0004] In one form, the present disclosure is directed to an electrified vehicle (EV) including 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 of the EV. The vehicle controller is configured to charge and discharge the battery pack according to power limits defined, upon power-on of the EV, by an estimated open circuit voltage (OCV) for each of the battery cells based on voltages measured by the one or more sensors after a last shutdown of the EV and a decay parameter dependent on the voltages and a duration since the last shutdown.

[0005] In one form, the present disclosure is directed to a method for controlling an electrified vehicle (EV) having a battery pack including a plurality of battery cells. The method includes, in response to a shutdown request, opening one or more contactors to electrically decouple the battery pack from a charging / discharging system of the EV; and, in response to a startup, closing the one or more contactors to electrically couple the battery pack to the charging / discharging system and charging or discharging the battery pack according to performance limits defined at startup of the EV by an estimated open circuit voltage (OCV) for each of the battery cells based on voltages measured by the one or more sensors after a last shutdown of the EV and a decay parameter dependent on the voltages and a duration since the last shutdown.

[0006] In one form, the present disclosure is directed 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 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 upon power-up of the EV by an estimated open circuit voltage (OCV) for each of the battery cells. The estimated OCV is based on voltages measured by one or more sensors of the EV after a last power-down of the EV and a decay parameter dependent on the voltages and a duration since the last power-down.The decay parameter includes an exponential parameter involving a square root of the duration, and the duration is shorter than an equilibrium time so that active material of each of the battery cells is evenly distributed over one electrode of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exemplary block diagram of an electrified vehicle (EV) according to the present disclosure; Fig. 2 is a block diagram of a battery pack of the EV according to the present disclosure; Fig. 3 is a block diagram of a battery management module of the EV according to the present disclosure; Fig. 4 is a graph illustrating an exemplary relationship between voltage and time after the battery pack is disconnected from a charging / discharging system of the EV, according to the present disclosure; and Fig. 5 is a flowchart of an exemplary battery pack control routine according to the present disclosure. DETAILED DESCRIPTION

[0007] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be greatly exaggerated or reduced to show details of particular components. Therefore, specific structural and functional details disclosed in this specification 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.

[0008] Generally, to manage a battery pack in an electrified vehicle (EV), an EV's vehicle system needs to know a battery pack's state of charge (SOC) to estimate the battery pack's capability / performance limit. For most battery chemistries, SOC is estimated based on a battery pack's open circuit voltage (OCV), which is the battery pack's voltage at rest. As a non-limiting example, for hybrid electric vehicles (HEVs), where battery cell sizes are typically on the order of five (5) amp-hours, the OCV can stabilize within 30 minutes, but may take longer in colder temperatures.Specifically, stabilization occurs when the active material is evenly distributed (by diffusion) throughout the thickness of an electrode, and the time required to achieve stabilization can be referred to as the equilibrium time for the battery cell. Battery charge and discharge reactions occur at the electrode surface. As battery cells become larger, the electrodes tend to become thicker, and thus the equilibrium time increases. Some EV battery cells may require several hours (e.g., over 3 hours) for the OCV to stabilize, which is longer in cold temperatures.

[0009] In various situations, it may be difficult for the EV to remain at rest (i.e., not charging or discharging) for such long equilibrium periods. For example, in one situation, an EV user may stop at a restaurant to eat, which may only take one to two hours. In another example, the user may stop at a charging station, and the amount of time required between turning off the EV and charging the battery pack may be only a few minutes.

[0010] Furthermore, the number of battery cells deployed in the EV's battery pack can also affect the detection of the OCV measured for each battery cell. In particular, some EVs have approximately 96 cells in series, and as the EV moves toward higher electrical power systems (e.g., 800 V to 1200 V), the number of battery cells can double or even triple, increasing the computational requirements of the vehicle system.

[0011] New EV battery warranty protocols may also require the EV to detect a state of certified energy (SOCE) or state of health (SOH), which is the amount of energy a battery pack can deliver for standard drive cycles relative to when the battery pack was new. Accordingly, the resting SOC derived from the OCV must be accurate to obtain a good estimate of capacity decay. In particular, some regulations require an energy estimate within 5% of the actual value, requiring the SOC to be within 2% or less to calculate "reasonably accurate" capacity and therefore energy.

[0012] The present disclosure is generally directed to a vehicle system configured to charge / discharge a battery pack based on an estimated OCV. In particular, the OCV is estimated for each battery cell using voltage measurements and a decay parameter dependent on the voltages since a last shutdown of the battery pack. With the estimated OCV, the vehicle system can, among other actions (e.g., issuing an SOH), estimate a SOC, provide available energy at the beginning of a drive cycle used to predict a vehicle's driving range, and / or provide a power limit estimate. As described in detail herein, the OCV can be estimated within a fraction of the time required for the battery cells to reach equilibrium, and therefore, the accuracy of the SOC and thus the accuracy of the power limit can be improved.In particular, power limits can change rapidly because the OCV is used to ensure a more accurate power limit when the vehicle starts. During the drive / charge cycle, the EV operates the vehicle using power limits estimated using factors other than the OCV.

[0013] With reference to Fig. 1 and Fig. 2, in one form, an EV 100 is provided as a pure battery electric vehicle (BEV) powered by electric motors. In one non-limiting example, the EV 100 includes a powertrain system having one or more electric motors 104 (i.e., electric machines), a battery pack 106 (i.e., a traction battery), and a power electronics module 108. The EV 100 of the present disclosure does not include an internal combustion engine, and thus, the battery pack 106 provides all of the motive power. In other variations, the present disclosure may be applied to other types of EVs, such as a hybrid electric vehicle (plug-in or non-plug-in) having an internal combustion engine, fuel cell electric vehicles (FCEV), and is not limited to pure battery-powered EVs.Additionally, the EV is not limited to four-wheeled automobiles and can be applied to scooters, three-wheeled vehicles, aircraft and / or other vehicles.

[0014] The electric motor 104 provides propulsion to the EV 100 and, in one non-limiting example, is mechanically connected to a transmission 110, which is mechanically connected to a driveshaft 112, which is mechanically connected to wheels 114 of the EV 100. In addition to providing motive power, the electric motor 104 may be configured to operate as a generator to recover energy that may normally be lost as heat in a friction braking system of the EV 100.

[0015] The battery pack 106 provides a high-voltage direct current (HV-DC) output used to power the electric motor 104 via the power electronics module 108, and although one battery pack 106 is shown, the EV 100 may include multiple battery packs. In one form, the power electronics module 108, which includes an inverter, provides bidirectional transfer of power between the battery pack 106 and the electric motor 104. In particular, as is known, the power electronics module 108 converts the DC voltage to a three-phase AC current to operate the electric motor 104, and in a regenerative mode, the power electronics module 108 converts the three-phase AC current from the electric motor 104, acting as a generator, to DC voltage compatible with the battery pack 106.

[0016] The battery pack 106 may be rechargeable by an external power source 120 (e.g., the electrical grid) electrically connected to an electric vehicle power supply (EVSE) 122. The EVSE 122 provides circuitry and controls for managing the transfer of electrical energy between the external power source 120 and the EV 100. The external power source 120 may provide electrical power to the EVSE 122 as DC or AC. The EVSE 122 may include a charging connector 124 for plugging into a charging port 126 of the EV 100.

[0017] The EV 100 may further include a power conversion module 228, which is an on-board charger that includes a DC / DC converter to condition power supplied by the EVSE 122 and provide the appropriate voltage and current levels to the battery pack 106. The power conversion module 228 may interface with the EVSE 122 to coordinate the delivery of power to the battery pack 106.

[0018] In addition to providing electrical energy for propulsion, the battery pack 106 may provide electrical energy for use by other electrical systems within the EV 100, such as high-voltage loads like an electric heating and air conditioning system, and low-voltage loads (LV loads) like an auxiliary battery. In some variations, the battery pack 106 is configured to have bidirectional power transfer capability to provide power to systems external to the EV 100 (i.e., an external system), such as, but not limited to, a residence, a business, and / or an off-grid system.In one non-limiting example, the battery pack 106 is electrically coupled to the external system using the EVSE connector 224 and is operable to provide energy based on a transient load recommended for the external system and an amount of energy available from the battery pack 106.

[0019] In one form, the EV 100 includes a control system 130 to coordinate the operation of the various components. The control system 130 includes electronics, software, or both to perform the necessary control functions to operate the EV 100. The control system 130 may be a combination of a vehicle control system and powertrain control module (VSC / PCM). Although the control system 130 is shown as a single device, the control system 130 may include multiple controllers in the form of multiple hardware devices or multiple software controllers with one or more hardware devices. In this regard, reference to a "controller" herein may refer to one or more controllers.

[0020] In one form, the EV 100 includes a battery management module (BMM) 132 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, using known techniques, controls the operation of the battery pack 106 (e.g., controls the charging / discharging of the battery pack 106). In one non-limiting example, during driving operation, the BMM 132 provides operating characteristics, such as, but not limited to, a power limit and / or SOC, to the control system 130, which determines how much power to draw from the battery pack 106. During a charging event, 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 with the control system 130 and, although illustrated separately from the control system 130, may be integrated into the control system 130. In one form, the BMM 132 and the control system 130 may be referred to as a vehicle controller.

[0021] In one form, the BMM 132 is in communication 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, electrical current, voltage, and / or temperature.

[0022] Among other components, the battery pack 106 includes a plurality of battery arrays 202A and 202B (collectively, “arrays 202”), each array 202 including a plurality of battery cells 204-1 through 204N (collectively, “cells 204”) connected in series ( Fig. 2). The arrays 202 are connected to a positive power bus 206A and a negative power bus 206B (collectively, "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 example provided herein. Additionally, the arrays 202 and / or cells 204 of the battery pack 106 may be configured in various suitable ways. In one non-limiting example, the battery pack 106 may be configured to have the arrays 202 in series, and for each array 202, the cells 204 are provided in parallel.

[0023] The sensors 134 include one or more sensors 134A and 134B for the arrays 202. In one form, the sensors 134 include voltage sensors and current sensors for measuring the voltage and / or electrical current of the array 202 and, in some variations, each battery cell 204. It is readily understood that the sensors 134 may include other sensors, such as, but not limited to, temperature sensors for measuring a temperature of the array 202 and / or the battery pack 106.

[0024] In one form, one or more contactors 210 are provided to prevent or permit electrical current from moving through the power buses 206 to / from the battery pack 106. In particular, the contactors 210 are operable to electrically decouple or couple the battery pack 106 to a charging / discharging system of the EV 100. The charging / discharging system of the EV includes components that either charge the battery pack 106 or act as a load to draw electrical power from the battery pack 106, and thus may include, among other components, the charging port 126, the power electronics module 108, and / or the transmission 110. The contactors 210 may be placed in various suitable positions in the EV 100, such as, but not limited to, between the positive power bus 206A and the power electronics module 108.In one non-limiting example, the contactor 210 may be provided as a relay or electromechanical switch.

[0025] In one form, the BMM 132 is configured to open or close the contactors 210 based on a message / request from the control system 130. In one non-limiting example, the control system 130 is configured to detect when to turn the EV 100 ON or OFF based on a power-up input (e.g., a user pressing a button associated with powering / powering the EV 100 on). If the EV 100 is to be turned ON, the control system 130 provides the BMM 132 with a power-up request to close the contactors 210, thereby electrically coupling the battery pack 106 to the charging / discharging system of the EV 100. If the EV 100 is to be turned OFF, the control system 130 provides a shutdown request to the BMM 132 to open the contactors 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 the connection request when the battery pack 106 is to be charged, which may 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).

[0026] With reference to Fig. 3, the BMM 132 includes, in one form, an actuator 302 for operating the contactors 210 in the 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.

[0027] As a non-limiting example, during driving / discharging of the battery pack 106, the BMM 132 is configured to provide one or more power limits in each direction, along with a minimum and maximum voltage limit, to the control system 130. Among other considerations, the control system 130 considers a driver demand and draws the appropriate amount of power from the battery pack 106 (e.g., providing power to the battery pack 106 if the regenerative braking power exceeds the power from other loads). For HEVs (i.e., plug-in or non-plug-in) and FCEVs, the control system 130 may also manage the SOC to maintain it within the desired range, charging the battery pack from the engine or fuel cell as appropriate.In one form, the BMM 132 is configured to ensure that the voltage limit of the battery pack 106 is not exceeded if the power level is followed.

[0028] In one form, the OCV estimator 308 is configured to estimate the OCV based on voltages measured by the sensors 134 after a previous / last shutdown of the EV 100 and a decay parameter dependent on the voltages and a duration since the last shutdown. More specifically, Equation 1 below is an algorithm employed by the BCE 304 to estimate the OCV for the battery cell 204, where "V" is the voltage of the battery cell 204, "VOCV" is the OCV, and "DP" is the decay parameter. Based on Equation 1, the estimated OCVs represent a difference between the voltages and the decay parameters. V=Vocv+DP

[0029] In one form, the decay parameter has a nonlinear correlation with voltage in that after shutdown, the voltage measurements of each battery cell 204 begin to decrease over time, and the change in voltage is nonlinear. For example, Fig. 4 shows an example graph 400 depicting the electrical characteristics (e.g., voltage and current) of a battery cell 204 over time. At 1260 seconds, the battery pack 106 is decoupled from the charge / discharge system. As illustrated, the voltage begins to decrease non-linearly over time.

[0030] The decay parameter from Equation 1 characterizes the decaying voltage using an exponential parameter involving a square root of the duration and further includes a coefficient and a constant that depend on the voltages. More specifically, the decay parameter can be one of the following: βe−kt, βe−kt or βe−t / k where "β" is a coefficient, "k" is a time constant, and "t" is time. The difference between the various decay parameters is the unit for 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 was (mostly) discharged just before shutdown, the sign of β is negative, indicating that the voltage is lower than the OCV. If the battery pack 106 was (mostly) charged, β is positive.

[0031] In one form, the decay parameter for each battery cell is estimated based on the voltage measurements using known parameter estimation techniques, such as, but not limited to, nonlinear regression models. The decay parameter is determined 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 has elapsed or the estimated decay parameter has not changed by a selected threshold, the BCE 304 determines the OCV based on Equation 1.

[0032] In some variations, the BCE 304 may be configured to employ a refined algorithm to estimate the OCV when the EV 100 is operating under certain conditions. In particular, when the ambient condition is very cold (e.g., lower than -20°C) and / or the SOC is low (e.g., 5%), a single exponential term may not accurately estimate the OSC due to the influence that battery cells 204 may have on each other. Accordingly, the BCE 304 is configured to use Equation 2 shown below to estimate the OCV. In Equation 2, DP1 is a first decay parameter and DP2 is a second decay parameter, where the first decay parameter and the second decay parameter have different coefficients and time constants. In one non-limiting example, the first decay parameter is defined as β1e−k1t provided and is the second waste parameter as β2e−k2t provided. V=Vocv+β1e−k1t+β2e−k2t

[0033] With reference to Fig.5, an exemplary battery pack control routine 500 executed by the BMM 132 and the control system 130 (i.e., a vehicle controller) is provided and supported by the present disclosure. At 502, the BMM 132 determines whether a turn-on request is received, and if received, at 504 the BMM 132 closes the contactors 210 to electrically couple the battery pack 106 to the charge / discharge system of the EV 100. At 506, the controller 132 sets an SOC and initial power limits using OCVs estimated after the last shutdown of the EV 100. At 508, the controller 132 controls the charge / discharge of the battery pack 106 based on operating characteristics of the battery pack 106, including the power limit. Once turned on, the SOC and power limits are updated using known techniques.

[0034] At 510, controller 132 determines whether the shutdown request is received. If not received, controller 132 returns to 508 to control battery pack 106. As is known, values of one or more operating characteristics, such as the power limit and SOC, may be updated using predefined models / algorithms as EV 100 charges / discharges. Accordingly, controller 132 may use updated characteristics to control battery pack 106.

[0035] If the shutdown request is received, at 512, the controller 132 opens the contactors 210 to electrically decouple the battery pack 106 from the charging / discharging system of the EV 100. At 514, the controller estimates the OCV for each of the battery cells using the OCV estimator 308, as described above. From 514, at 502, the controller 132 determines whether the shutdown request is received. If it is not received, the controller 132 estimates the OCV for each battery cell 204. That is, the OCV may be re-estimated if no startup request is received.

[0036] Battery pack control routine 500 may be configured to perform other operations within the scope of the present disclosure and should not be limited to the example described herein. In one non-limiting example, routine 500 may stop estimating the OCV if a predefined period of time based on an estimated equilibrium time for battery pack 106 has elapsed and / or the previous OCVs differ from each other by a selected threshold.

[0037] Instead of waiting for the battery cells 204 to stabilize to obtain the OCV, the BMM 132 of the present disclosure is configured to estimate the OCV for each battery cell with improved accuracy using the OCV estimator 308, thus improving the accuracy of the power limit, SOC, SOH, and other characteristics.

[0038] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. Rather, the terms used in the description are terms of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. In addition, the features of various implementing embodiments may be combined to form further embodiments of the invention.

[0039] As used in this application, the term "module" may refer to, be part of, or include: an application specific integrated circuit (ASIC); a digital, analog, or mixed analog / digital discrete circuit; a digital, analog, or mixed analog / digital integrated circuit; a combinable logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the foregoing, such as in a system-on-chip.

[0040] The term memory or storage device is a subset of the term computer-readable medium. As used in this document, the term computer-readable medium does not include transitory electrical or electromagnetic signals propagating through a medium (such as a carrier wave); therefore, the term computer-readable medium can be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readable medium include non-volatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).

[0041] The devices and methods described in this application may be implemented, in part or in whole, by a special-purpose computer created by configuring a general-purpose computer to perform one or more specific functions embodied in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications that can be translated into computer programs through the routine work of a skilled technician or programmer.

[0042] As used in this document, the phrase at least one of A, B, and C should be interpreted to mean a logical (A OR B OR C) using a non-exclusive logical OR, and should not be interpreted to mean "at least one of A, at least one of B, and at least one of C."

[0043] The description of the disclosure is merely exemplary in nature, and thus variations that do not depart from the essence of the disclosure are intended to be within the scope of the disclosure. Such variations should not be considered a departure from the spirit and scope of the disclosure.

[0044] According to the present invention, an electrified vehicle (EV) is provided, comprising: a battery pack including a plurality of battery cells and operable to provide at least a portion of propulsion power of the EV; one or more sensors; and a vehicle controller configured to charge and discharge the battery pack according to power limits defined, upon power-up of the EV, by an estimated open circuit voltage (OCV) for each of the battery cells based on voltages measured by the one or more sensors after a last shutdown of the EV and a decay parameter dependent on the voltages and a duration since the last shutdown.

[0045] According to one embodiment, the decay parameter includes a coefficient that depends on the voltages.

[0046] According to one embodiment, the decay parameter includes a constant that depends on the voltages.

[0047] According to one embodiment, the decay parameter has a non-linear correlation with the voltages.

[0048] According to one embodiment, the decay parameter includes an exponential parameter involving a square root of the duration.

[0049] According to one embodiment, the vehicle controller is configured to detect the waste parameter using a nonlinear regression model.

[0050] According to one embodiment, the vehicle controller is configured to estimate an initial state of charge of the battery pack based on the estimated OCV, wherein the power limits are defined in part by the initial state of charge.

[0051] According to one embodiment, the duration is shorter than an equilibrium time so that active material of each of the battery cells is evenly distributed over an electrode of the battery cell.

[0052] According to the present invention, a method for controlling an electrified vehicle (EV) having a battery pack including a plurality of battery cells includes: in response to a shutdown request, opening one or more contactors to electrically decouple the battery pack from a charging / discharging system of the EV; in response to a startup, closing the one or more contactors to electrically couple the battery pack to the charging / discharging system; and charging or discharging the battery pack according to power limits defined at startup of the EV by an estimated open circuit voltage (OCV) for each of the battery cells based on voltages measured by one or more sensors after a last shutdown of the EV and a decay parameter dependent on the voltages and a duration since the last shutdown.

[0053] In one aspect of the invention, the decay parameter includes a coefficient that is dependent on the voltages.

[0054] In one aspect of the invention, the decay parameter includes a constant that is dependent on the voltages.

[0055] In one aspect of the invention, the decay parameter has a nonlinear correlation with the voltages.

[0056] In one aspect of the invention, the decay parameter includes an exponential parameter involving a square root of the duration.

[0057] In one aspect of the invention, the method includes detecting the waste parameter using a nonlinear regression model.

[0058] In one aspect of the invention, the vehicle controller is configured to estimate an initial state of charge of the battery pack based on the estimated OCV, wherein the performance limits are defined in part by the initial state of charge.

[0059] In one aspect of the invention, the duration is shorter than an equilibrium time in order for active material of each of the battery cells to be evenly distributed across an electrode of the battery cell.

[0060] According to the present invention, a system is provided for an electrified vehicle (EV) including a battery pack having a plurality of battery cells and operable to provide at least a portion of propulsion power of the EV, comprising: a controller configured to charge and discharge the battery pack according to a state of charge initially defined upon power-up of the EV by an initial state of charge based on an estimated open circuit voltage (OCV) for each of the battery cells, wherein the OCV is based on voltages measured by one or more sensors of the EV after a last shutdown of the EV and a decay parameter dependent on the voltages and a duration since the last shutdown, wherein the duration is less than an equilibrium time,so that the active material of each of the battery cells is evenly distributed over one electrode of the battery cell.

[0061] According to one embodiment, the estimated OCVs represent a difference between the voltages and the decay parameters.

[0062] According to one embodiment, the decay parameter includes a coefficient that depends on the voltages.

[0063] According to one embodiment, the decay parameter has a non-linear correlation with the voltages.

Claims

[1] Electrified vehicle (EV), comprising: a battery pack including a plurality of battery cells and operable to provide at least a portion of propulsion power of the EV; one or more sensors; and a vehicle controller configured to charge and discharge the battery pack according to power limits defined, when the EV is turned on, by an estimated open circuit voltage (OCV) for each of the battery cells based on voltages measured by the one or more sensors after a last shutdown of the EV and a decay parameter dependent on the voltages and a duration since the last shutdown. [2] The EV of claim 1, wherein the decay parameter includes a coefficient dependent on the voltages. [3] The EV of claim 1, wherein the decay parameter includes a constant dependent on the voltages. [4] The EV of claim 1, wherein the decay parameter has a non-linear correlation with the voltages. [5] EV according to claim 1, wherein the decay parameter includes an exponential parameter involving a square root of the duration. [6] The EV of claim 1, wherein the vehicle controller is configured to detect the decay parameter using a nonlinear 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 limits are defined in part by the initial state of charge. [8] The EV of claim 1, wherein the duration is shorter than an equilibrium time for active material of each of the battery cells to be evenly distributed over an electrode of the battery cell. [9] A method for controlling an electrified vehicle (EV) having a battery pack including a plurality of battery cells, comprising: in response to a shutdown request, opening one or more contactors to electrically decouple the battery pack from an EV charging / discharging system; in response to a connection Closing the one or more contactors to electrically couple the battery pack to the charging / discharging system, and Charging or discharging the battery pack according to performance limits defined at EV startup by an estimated open circuit voltage (OCV) for each of the battery cells based on voltages measured by one or more sensors after a last EV shutdown and a decay parameter dependent on the voltages and a duration since the last shutdown. [10] The method of claim 9, wherein the decay parameter includes a coefficient dependent on the voltages. [11] The method of claim 9, wherein the decay parameter includes a constant that is dependent on the voltages. [12] The method of claim 9, wherein the decay parameter has a non-linear correlation with the voltages. [13] The method of claim 9, wherein the decay parameter includes an exponential parameter involving a square root of the duration. [14] The method of claim 9, further comprising detecting the decay parameter using a nonlinear regression model. [15] The method of claim 9, 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 limits are defined in part by the initial state of charge.

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