HYBRID VEHICLE AND CORRESPONDING CONTROL SYSTEM

Abstract

A vehicle includes an electric motor, a battery, and a control unit. The battery is configured to supply power to the electric motor to propel the vehicle. The control unit is programmed to reduce the battery discharge power in response to a voltage drop below a first threshold during discharge and a voltage change rate above a second threshold during discharge. The reduction in discharge power is based on a proportion of the difference between the first threshold and the voltage, and a proportion of the difference between the rate and the second threshold.

Description

AREA OF TECHNOLOGY

[0001] The present disclosure relates to hybrid and electric vehicles and batteries for hybrid and electric vehicles. GENERAL STATE OF THE ART

[0002] Hybrid and electric vehicles can be powered by an electric machine that draws power from a battery. SUMMARY

[0003] A vehicle includes a battery and a control unit. The battery is configured to supply power to an electric motor to propel the vehicle. The control unit is programmed to reduce the discharge power to less than the commanded value, based on a fraction of the difference between the rate and the threshold rate, if the rate of change of the battery voltage during discharge exceeds a threshold rate. The control unit is further programmed to maintain the discharge at the commanded value if the rate of change during discharge remains below the threshold rate.

[0004] A vehicle includes an electric motor, a battery, and a control unit. The battery is configured to supply power to the electric motor to propel the vehicle. The control unit is programmed to reduce the battery discharge power in response to a voltage drop below a first threshold during discharge and a voltage change rate above a second threshold during discharge. The reduction in discharge power is based on a proportion of the difference between the first threshold and the voltage, and a proportion of the difference between the rate and the second threshold.

[0005] A vehicle includes a battery and a control unit. The battery is configured to supply power to an electric motor to propel the vehicle. The control unit is programmed to reduce the discharge power from the battery to a specified value during discharge, based on a fraction of the difference between the voltage threshold and the battery voltage, in response to the battery voltage dropping below a specified voltage threshold during discharge. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic illustration of a representative powertrain of an electric vehicle, which includes a battery; Fig. 2A-2D are a series of diagrams comparing the battery performance according to different models in relation to test data; Fig. Figure 3 is a schematic illustration of an equivalent circuit model that is representative of the battery; Fig. Figure 4 is a flowchart illustrating a procedure for estimating the battery's performance; Fig. Figure 5 is a flowchart illustrating a procedure for controlling the power output of the battery; and Fig. Figure 6 is a diagram illustrating the power output of the battery when based on the values ​​in relation to the Fig. 5 and Fig. The procedure described in section 6 is controlled. DETAILED DESCRIPTION

[0006] This document describes embodiments of the present disclosure. It is understood, however, that the disclosed embodiments are merely examples and that other embodiments may take different and alternative forms. The figures are not necessarily to scale; some features may have been enlarged or reduced to show details of specific components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching the person skilled in the art how to use the embodiments in various ways. The person skilled in the art will understand that various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not expressly illustrated or described.The illustrated combinations of features provide representative embodiments for typical applications. However, different combinations and modifications of the features, consistent with the teachings of this disclosure, might be desired for specific applications or implementations.

[0007] With reference to Fig. Figure 1 illustrates a schematic representation of an electric vehicle 10 according to an embodiment of the present disclosure. Fig. Figure 1 illustrates representative relationships between the components. The physical placement and orientation of the components within the vehicle may vary. The electric vehicle 10 includes a powertrain 12. The powertrain 12 includes an electric machine, such as an electric motor / generator (M / G) 14, which drives a transmission (or gearbox) 16. In particular, the M / G 14 may be rotatably connected to an input shaft 18 of the transmission 16. The transmission 16 may be placed in PRNDSL (park, reverse, neutral, drive, sport, low) by means of a gear selector lever (not shown). The transmission 16 may have a fixed gear ratio that provides a single gear ratio between the input shaft 18 and an output shaft 20 of the transmission 16.A torque converter (not shown) or a starting clutch (not shown) can be arranged between the M / G 14 and the transmission 16. Alternatively, the transmission 16 can be a multi-stage automatic transmission. An associated traction battery 22 is configured to supply electrical power to or receive electrical power from the M / G 14.

[0008] The M / G 14 is a drive source for the electric vehicle 10, configured to power the electric vehicle 10. The M / G 14 can be implemented by any of a variety of electric machines. For example, the M / G 14 can be a permanent magnet synchronous motor. Power electronics 24 conditions the direct current power (DC power) supplied by the battery 22 to meet the requirements of the M / G 14, as described below. For example, the power electronics 24 can supply three-phase alternating current (three-phase AC) to the M / G 14.

[0009] If the transmission 16 is a multi-stage automatic transmission, it may include gear sets (not shown) that are selectively engaged at different gear ratios by selectively engaging friction elements such as clutches and brakes (not shown) to produce the desired multiple separate or staged drive ratios. The friction elements are controlled by a shift schedule that engages and disengages certain elements of the gear sets to control the ratio between the transmission output shaft 20 and the transmission input shaft 18. The transmission 16 is automatically shifted from one ratio to another based on various vehicle and environmental operating conditions by an associated control unit, such as a powertrain control unit (PCU). Power and torque from the M / G 14 can be delivered to and received by the transmission 16.The gearbox 16 then provides the output shaft 20 with drivetrain output power and torque.

[0010] It is understood that the hydraulically controlled transmission 16, which may be coupled with a torque converter (not shown), is only one example of a transmission or gearbox arrangement; any multi-ratio transmission that accepts input torque(s) from a power source (e.g., M / G 14) and then provides torque to an output shaft (e.g., output shaft 20) at different ratios is acceptable for use with embodiments of the present disclosure. For example, the transmission 16 may be implemented by an automated mechanical (or manual) transmission (AMT) incorporating one or more servomotors to move / rotate shift forks along a shift rod to select a desired gear ratio.As the average professional generally understands, an AMT can be used, for example, in applications with higher torque requirements.

[0011] As in the representative embodiment in Fig. As shown in Figure 1, the output shaft 20 is connected to a differential 26. The differential 26 drives a pair of drive wheels 28 via respective axles 30 connected to the differential 26. The differential 26 transmits approximately the same torque to each wheel 28 while allowing slight differences in rotational speed, such as when the vehicle is cornering. Different types of differentials or similar devices can be used to distribute torque from the drivetrain to one or more wheels. In some applications, the torque distribution can vary, for example, depending on the specific operating mode or operating condition.

[0012] The powertrain 12 also includes an associated control 32, such as a powertrain control unit (PCU). Although illustrated as a single control, the control 32 can be part of a larger control system and be controlled by various other control units throughout the vehicle 10, such as a vehicle system controller (VSC). Accordingly, it is understood that the powertrain control unit 32 and one or more other control units together can be referred to as a "controller" that controls various actuators in response to signals from various sensors to control functions such as operating the M / G 14 to provide wheel torque or charge the battery 22, selecting or scheduling gear changes, etc.The controller 32 can include a microprocessor or a central processing unit (CPU) that communicates with various types of computer-readable storage devices or media. Computer-readable storage devices or media can include volatile and non-volatile memory, such as read-only memory (ROM), random-access memory (RAM), and keep-alive memory (KAM). A KAM is a persistent or non-volatile memory that can be used to store various operating variables while the CPU is powered off.Computer-readable storage devices or media may be implemented using any of a number of known storage devices, such as PROMs (programmable read-only memory), EPROMs (electrical PROM), EEPROMs (electrically erasable PROM), flash memory, or any other electrical, magnetic, optical, or combination storage devices capable of storing data, some of which represent executable instructions used by the controller in controlling the internal combustion engine or vehicle.

[0013] The controller 32 communicates with various vehicle sensors and actuators via an input / output interface (I / O interface) (which includes input and output channels), which can be implemented as a single integrated interface providing various raw data or signal conditioning, processing and / or conversion, short-circuit protection, and the like. Alternatively, one or more dedicated hardware or firmware chips can be used to condition and process specific signals before they are fed to the CPU. As in the representative embodiment in Fig. As generally illustrated, the control unit can send 32 signals to the M / G 14, the battery 22, the transmission 16, the power electronics 24, and any other component of the powertrain 12 that may be included, but in Fig. 1 not shown (i.e., a starting clutch that may be located between the M / G 14 and the transmission 16), communicate with and / or receive signals from these. Although not explicitly illustrated, the person skilled in the art will recognize various functions or components within each of the subsystems identified above that can be controlled by the controller 32. Representative examples of parameters, systems, and / or components that can be actuated directly or indirectly using control logic and / or algorithms executed by the controller 32 include components of a front-end accessory drive (FEAD), such as an alternator, an air conditioning compressor, battery charging or discharging, regenerative braking, operation of the M / G 14, clutch pressures for the transmission 16 or any other clutch that is part of the drivetrain 12, and the like.Sensors that communicate inputs via the I / O interface can be used to indicate, for example, wheel speeds (WS1, WS2), vehicle speed (VSS), coolant temperature (ECT), accelerator pedal position (PPS), ignition switch position (IGN), ambient air temperature (e.g., ambient air temperature sensor 33), gear, transmission ratio or mode, transmission oil temperature (TOT), transmission input and output speed, deceleration or shift mode (MDE), or battery temperature, voltage, current, or state of charge (SOC).

[0014] The control logic or the functions performed by the controller 32 may be represented in one or more figures by flowcharts or similar diagrams. These figures provide representative control strategies and / or control logic that may be implemented using one or more processing strategies, such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. Accordingly, various illustrated steps or functions may be performed in the illustrated sequence or in parallel, or in some cases, omitted. Although not always explicitly illustrated, the average person will recognize that one or more of the illustrated steps or functions may be performed repeatedly, depending on the specific processing strategy employed.Likewise, the processing sequence is not strictly necessary to achieve the features and benefits described herein, but is provided for the sake of simplicity in illustration and description. The control logic can be implemented primarily in software, executed by a microprocessor-based vehicle and / or powertrain control unit, such as the control unit 32. Of course, depending on the specific application, the control logic can be implemented in software, hardware, or a combination of both in one or more control units. When implemented as software, the control logic can be provided in one or more computer-readable storage devices or media containing data that represent code or instructions executed by a computer to control the vehicle or its subsystems.Computer-readable storage devices or media may include one or more of a number of known physical devices that utilize electrical, magnetic and / or optical storage to hold executable instructions and associated calibration information, operating variables and the like.

[0015] An accelerator pedal 34 is used by the vehicle's driver to provide the powertrain 12 (or more precisely, the M / G 14) with a requested torque, power, or drive command to propel the vehicle. Generally, pressing and releasing the accelerator pedal 34 generates an accelerator pedal position signal, which can be interpreted by the control unit 32 as a request for increased or decreased power. A brake pedal 36 is also used by the vehicle's driver to provide a requested braking torque to decelerate the vehicle. Generally, pressing and releasing the brake pedal 36 generates a brake pedal position signal, which can be interpreted by the control unit 32 as a request to reduce the vehicle's speed.Based on inputs from the accelerator pedal 34 and the brake pedal 36, the control unit 32 commands the torque and / or power to the M / G 14 and the friction brakes 38. The control unit 32 also controls the timing of gear changes within the transmission 16.

[0016] The M / G 14 can function as a motor and provide drive power for the drivetrain 12. To power the vehicle using the M / G 14, the traction battery 22 transfers stored electrical energy via wiring 40 to the power electronics 24, which may include, for example, an inverter and a rectifier circuit. The inverter circuit of the power electronics 24 can convert DC voltage from the battery 22 into AC voltage for use by the M / G 14. The rectifier circuit of the power electronics 24 can convert AC voltage from the M / G 14 into DC voltage, which is stored using the battery 22. The controller 32 instructs the power electronics 24 to convert voltage from the battery 22 into an AC voltage supplied to the M / G 14 to provide positive or negative torque at the input shaft 18.

[0017] The M / G 14 can also act as a generator, converting kinetic energy from the drivetrain 12 into electrical energy, which is stored in the battery 22. In particular, the M / G 14 can function as a generator during periods of regenerative braking, during which torque and rotational energy (or kinetic energy) from the rotating wheels 28 are transferred back through the transmission 16 and converted into electrical energy for storage in the battery 22.

[0018] It is understood that the vehicle configuration described herein is merely exemplary and is not intended to be limiting. Other configurations of electric or hybrid electric vehicles should be construed as disclosed herein. Other configurations of electric or hybrid vehicles may include, but are not limited to, series hybrid vehicles, parallel hybrid vehicles, series-parallel hybrid vehicles, plug-in hybrid electric vehicles (PHEVs), fuel cell hybrid vehicles, battery-operated electric vehicles (BEVs), or any other vehicle configuration known to the average person skilled in the art.

[0019] In hybrid configurations that include an internal combustion engine, such as a gasoline, diesel, or natural gas-powered combustion engine, or a fuel cell, the controller 32 can be configured to control various parameters of such an internal combustion engine. Representative examples of parameters, systems, and / or components for internal combustion that can be actuated directly or indirectly using control logic and / or algorithms executed by the controller 32 include fuel injection timing, rate, and duration; throttle position; spark plug ignition timing (in spark-ignition engines); intake and exhaust valve timing and duration, etc.Sensors that communicate inputs through the I / O interface of such an internal combustion engine to the control unit 32 can be used to indicate turbocharger boost pressure, crankshaft position (PIP), internal combustion engine speed (rpm), manifold absolute pressure (MAP), throttle position (TP), presence of exhaust oxygen (EGO) or other exhaust components, intake airflow (MAF), etc.

[0020] It goes without saying that the in Fig. The schematic representation shown in Figure 1 is for illustrative purposes only and is not intended to be limiting. Other configurations are considered without deviating from the scope of the disclosure. For example, the vehicle powertrain 12 may be configured to supply power and torque to one or both of the front wheels instead of the rear wheels 28 shown.

[0021] The estimated performance of a battery in a hybrid or electric vehicle (e.g., battery 22) may be difficult to predict using an equivalent circuit model (ECM) if there is a sudden drop in battery cell voltage, especially under conditions of low state of charge (SOC), low battery temperatures, and high current demand.

[0022] In an electrified vehicle (e.g., a hybrid or electric vehicle), it is the responsibility of the battery control system to inform the vehicle how much power (or current) can be drawn from the high-voltage battery. Different vehicles may have different architectures and terminology; in this case, the Battery Energy Control Module (BECM) is used. The BECM may be included as part of the controller 32, as shown in Fig. 1 shown, or can be a separate controller that can communicate with controller 32.

[0023] A BECM can broadcast one or more power limits for charging the battery and one or more power limits for discharging the battery. The power limits are defined as the maximum amount of power the battery can provide (e.g., discharge power to operate the M / G 14) or accept (e.g., power to charge battery 22) for a specified duration at the current battery state of charge and temperature. When the power limit is observed, the battery voltage and current remain within desired limits. Several factors can be used to determine the permissible power limit, one of which is the battery's capacity. Other factors may include maximizing drivability, battery condition, and diagnostic fault responses.

[0024] Battery control systems can measure battery voltage, current, and temperature and must derive battery properties from such measurements. Batteries are nonlinear systems, and the best physics-based electrochemical models are complex and memory-intensive, and therefore typically not installed in the control unit or computer memory within a vehicle. Furthermore, sensors, as well as the physical properties of a battery, can have uncertainties. For example, a battery's capacity can change by 30% or more over its lifetime. A battery's performance changes not only with its lifetime, state of charge, and temperature, but also depending on how the battery is used. For example, a battery may provide more power for a short period than for a long period.

[0025] A BECM can estimate performance using equivalent circuit models and reduced-order electrochemical models. A type of Kalman filter, such as an extended Kalman filter (EKF), can be used to learn the parameters of such models, especially equivalent circuit models. Extended Kalman filters can be used because of the nonlinear nature of such models.

[0026] In certain situations, particularly at higher currents, lower states of charge, and lower temperatures, sudden voltage drops can occur, usually due to the loss of active material at the cell surface. This loss is caused by active material being removed and / or converted faster than more active material can diffuse to the surface. This behavior is not repeatable from case to case, preventing the development of a consistent battery model. More importantly, during voltage dip events, the second-order voltage difference reverses direction, a behavior that cannot be captured by the resistor-capacitor (RC) pairs of an ECM. This is evident in the Fig. Figure 2A-2D illustrates how a 4RC model (a battery model with four RC pairs) adequately represents the battery voltage during current flow until the voltage drops below a threshold and / or the voltage drop rate accelerates when the current load remains constant. However, the 4RC model does not accurately represent the cell performance at lower states of charge (SOC) during a voltage dip (e.g., Fig. 2D). Consequently, the performance estimated based solely on the ECM may overestimate the performance of a battery in cases of rapid voltage drops.

[0027] As in the Fig. As shown in diagrams 2A-2D, the ECM error increases as the SOC decreases below a specific threshold, such as 20%. Below the SOC threshold, the error becomes larger as the SOC continues to decrease, affecting the accuracy of the estimated battery performance within that SOC range. While the problem is described in the Fig. While the 2A-2D model is illustrated using an ECM, it is also applicable to other types of models, such as physics-based models. The 4RC model is used with the open-circuit voltage (OCV), a 1RC model (a battery model with one RC pair), and measurement data obtained through testing (e.g., test data) at various states of charge (SOCs) in the Fig. 2A-2D compared at a low battery temperature (e.g. -10 °C).

[0028] Typically, the estimated performance of a battery falls within the range of (1-αL, 1+αH) of the battery's true performance, where αL and αH denote the confidence level of the estimate, which can be determined through offline comparison using test data during the product development process. Therefore, the range of (1-αL, 1+αH) widens as the confidence level of the estimated performance decreases in response to increases in error.

[0029] If the ECM uses the state of charge (SOC) to help determine ECM parameters, errors in the SOC can lead to inaccuracies in predicted performance. For example, if the ECM uses the SOC to determine parameters V0 or OCV, a situation can arise where the estimated SOC is higher than the actual SOC, leading to an overestimation of the battery's performance. The extent of this overestimation depends on the slope of the OCV / SOC curve. For most chemical compositions, this slope is steepest at very low states of charge.

[0030] The basic discharge power limit due to the capacity or the battery can be calculated using equation (1): Discharge power limit or discharge power threshold = ϒ * estimated power capability where Υ is a safety factor. Υ can be set to 0.95 if the discharge power limit requirement is within 90% to 100% of the battery's true capacity during vehicle operation.

[0031] Solely using the safety factor Υ has limitations. For example, the battery model constraint (e.g., ECM) might be able to predict performance in the event of a sudden battery voltage drop, as described above, which could lead to an overestimation of the battery's performance. As another example, during vehicle operation, the BECM's estimated performance should always be less than or equal to the battery's true performance. If the performance is overestimated, the battery's voltage or current limits could be violated, potentially compromising battery integrity or causing the vehicle to shut down. This implies a constraint that must be followed: Υ(1+α_H) < 1. In real-world operation, the confidence level of the estimated performance varies across different state-of-charge (SOC) ranges.The confidence level is higher in medium to high SOC ranges, resulting in smaller values ​​for αL and αH. As described above, the confidence level is lower in lower SOC ranges, resulting in larger values ​​for αL and αH. This variability can make it easier to violate the constraint Υ(1+αH) < 1 in lower SOC ranges when using a constant value for Υ.

[0032] Regarding Fig. Figure 3 illustrates a schematic representation of an ECM that is representative of a battery (e.g., battery 22). Specifically, the ECM can be a 4RC model. The model includes various resistors, capacitors, and voltage nodes to simulate the battery's response to different operating conditions. In the model, R0 represents the battery's internal resistance, which yields the instantaneous voltage drop when a current (I) flows through the circuit. The voltage drop across R0 is labeled V0. This resistance captures the immediate effects of internal losses due to ion movement and electrical contact resistance within the battery.

[0033] The remaining components within the ECM account for the slower, time-dependent behaviors of the battery. Each resistor (R1) is paired with a capacitor (e.g., τ1 / R1, (γτ1)τ1 / R1, αγτ1). 2 / R1 or α 2γτ1 2 / R1), forming RC networks that represent the diffusion and relaxation processes of the battery. Here, τ1 denotes the time constant of the battery response, which influences how quickly the battery reacts to current changes. Additionally, α is assigned to the Warburg impedance, which indicates the influence of diffusion processes within the battery electrodes. The parameter γ is a scaling factor that sets the time constant and reflects variations in the battery's dynamic behavior under different conditions, such as changes in state of charge (SOC) or temperature. The voltage drops across each RC network are specified as V1, V2, V3, and V4, which together contribute to the overall dynamic response of the battery.

[0034] V batteryThis represents the terminal voltage, which is the net output voltage after accounting for all internal resistances and dynamic processes. This ECM effectively captures both the instantaneous voltage drop due to R0 and the more gradual changes due to the electrochemical dynamics within the battery, thus providing a useful tool for simulating and predicting battery performance under various operating conditions.

[0035] Regarding Fig. Figure 4 illustrates a flowchart of a procedure 100 for estimating the power output limit or capacity of the battery (e.g., battery 22). The procedure 100 can be stored as control logic and / or as an algorithm within the controller 32. The controller 32 can implement the procedure 100 by controlling the various components of the vehicle 10.

[0036] Method 100 uses voltage feedback control to address overestimation of discharge capability, enabling accurate estimation of battery voltage drops during discharge. The estimated capability can be based on the ECM (Electro-Circular-Mechanism) and is adjusted using proportional and / or differential (PD) feedback control of the battery terminal voltage. A type of Kalman filter, such as an extended Kalman filter (EKF), can be used to learn the ECM parameters. If the battery voltage drops below a temperature-dependent voltage threshold, proportional control is used to adjust the estimated capability accordingly.If the battery voltage drop rate (defined as the derivative of the battery voltage difference) exceeds a temperature-dependent voltage drop rate limit, differential control is used to reduce the estimated power output. If both the battery voltage and the voltage drop rate exceed their limits, proportional and differential (PD) control is applied to adjust the estimated power output.

[0037] Procedure 100 begins at block 102, where the estimated power capability based on the battery (EKF / ECM(t)), the battery terminal voltage (Battery_V(t)), and the battery temperature (T(t)) are input into the controller. The terminal voltage (Battery_V(t)) and the battery temperature (T(t)) can be measured via sensors, while the estimated power capability is based on the ECM set via the EKF. It should be noted that although the ECM shown here includes four RC pairs, the ECM used in Procedure 100 can include any number of RC pairs or be a different type of model, such as reduced-order models and / or electrochemical models.

[0038] Procedure 100 then proceeds to Block 104, where a voltage limit or threshold (Voltage_Limit (T)(t)), a voltage drop speed limit or threshold (Voltage_Drop_Speed_Limit (T)(t)), and a voltage drop rate ((Battery_V(t)-Battery(t-dt)) / dt) are calculated. The voltage drop rate (Voltage_Drop_Speed ​​= (Battery_V(t)-Battery(t-dt)) / dt) corresponds to the rate at which the battery voltage changes, which can be derived by measuring the battery terminal voltage. The voltage limit or threshold (Voltage_Limit (T)(t)) and the voltage drop speed limit or threshold (Voltage_Drop_Speed_Limit (T)(t)) are each dependent on the battery temperature.The voltage limit or threshold (Voltage_Limit (T)(t)) and the voltage drop speed limit or threshold (Voltage_Drop_Speed_Limit (T)(t)) each have a linear relationship to the battery temperature. The voltage limit or threshold (Voltage_Limit (T)(t)) and the voltage drop speed limit or threshold (Voltage_Drop_Speed_Limit (T)(t)) can either increase or decrease with increasing or decreasing battery temperature.

[0039] Procedure 100 then proceeds to Block 106, which determines whether the battery voltage (e.g., the measured battery terminal voltage or as determined by the ECM) is less than the voltage limit or voltage threshold (Voltage_Limit (T)(t)). The output of Block 106 determines the parameter r_P, which is set at either Block 108 or Block 110. If the battery voltage (e.g., the measured battery terminal voltage) is not less than the voltage limit or voltage threshold (Voltage_Limit (T)(t)), r_P is set to zero at Block 108. If the battery voltage (e.g., the measured battery terminal voltage or as determined by the ECM) is less than the voltage limit or voltage threshold (Voltage_Limit (T)(t)), r_P at block 110 is set to a value proportional to the difference between the battery voltage (e.g.,the measured terminal voltage of the battery) and the voltage limit or voltage threshold (Voltage_Limit (T)(t)). In particular, r_P can be represented by equation (2):. r_P=Pp∗(Voltage_Limit(T)(t))−Battery voltage) where Pp is a proportional calibrated value. It should be noted that r_P is always less than or equal to one and greater than or equal to zero. It is important to note that any value between zero and one, including fractions, can represent a percentage for r_P. For example, 1 can represent 100%, 0.50 can represent 50%, 0.25 can represent 25%, 0.125 can represent 12.5%, 0 can represent 0%, and so on.

[0040] Depending on the result at block 106, the value r_P is then entered into block 112 either by block 108 or block 110. The value r_P represents the proportional control parameter of procedure 100.

[0041] Procedure 100 also transitions from block 104 to block 114, determining whether a filtered value of the rate of change of a battery current (di / dt) is less than a current rate limit (di_lim) and whether an absolute and filtered value of the rate at which the battery voltage changes (Voltage_Drop_Speed) is greater than the voltage rate limit or voltage rate threshold (Voltage_Drop_Speed_Limit (T)(t)). The battery current (di / dt) and the rate at which the battery voltage changes (Voltage_Drop_Speed) can be filtered by a Savitzky-Golay filter or another filter to eliminate or reduce noise.

[0042] The output of block 114 determines the parameter r_D, which is set at either block 116 or block 118. If the filtered value of the battery current rate of change (di / dt) is not less than the current rate limit (di_lim), and if the absolute and filtered value of the battery voltage rate of change (Voltage_Drop_Speed) is not greater than the voltage rate limit or voltage rate threshold (Voltage_Drop_Speed_Limit (T)(t)), then r_D is set to zero at block 116.If the filtered value of the rate of change of a battery current (di / dt) is less than the current rate limit (di_lim), and if the absolute and filtered value of the rate at which the battery voltage changes (Voltage_Drop_Speed) is greater than the voltage rate limit or voltage rate threshold (Voltage_Drop_Speed_Limit (T)(t)), then r_D at block 118 is set to a value proportional to the difference between the rate at which the battery voltage changes (Voltage_Drop_Speed) and the voltage rate limit or voltage rate threshold (Voltage_Drop_Speed_Limit (T)(t)). In particular, r_D can be represented by equation (3). r_D=Pd∗(Voltage_Drop_Speed−Voltage_Drop_Speed_Limit(T)(t)) where Pd is a proportional calibrated value. It should be noted that r_D is always less than or equal to one and greater than or equal to zero. It is important to note that any value between zero and one, including fractions, can represent a percentage for r_D. For example, 1 can represent 100%, 0.50 can represent 50%, 0.25 can represent 25%, 0.125 can represent 12.5%, 0 can represent 0%, and so on.

[0043] Depending on the result at block 114, the value r_D is then entered into block 112 either by block 116 or block 118. The value r_D represents the derivative or differential control parameter of procedure 100.

[0044] Block 118 calculates a setting parameter (r_Vdrop) for the estimated power capability based on EKF / ECM(t). This setting parameter (r_Vdrop) can be a percentage of the estimated power capability based on EKF / ECM(t). The setting parameter (r_Vdrop) can be represented by equation (4): r_Vdrop=1−r_P−r_D

[0045] The sum of r_P and r_D (i.e., r_P + r_D) is always less than or equal to one and greater than or equal to zero. Therefore, r_Vdrop is also always less than or equal to one and greater than or equal to zero. It's important to note that any value between zero and one, including fractions, can represent a percentage for r_P + r_D. For example, 1 can represent 100%, 0.50 can represent 50%, 0.25 can represent 25%, 0.125 can represent 12.5%, 0 can represent 0%, and so on.

[0046] The procedure then proceeds to block 120, where the estimated power capability based on EKF / ECM(t) is set by multiplying the estimated power capability based on EKF / ECM(t) by the setting parameter (r_Vdrop), as can be represented by equation (5): Set power capability=(Estimated Power Capability Based EKF / ECM(t))∗r_Vdrop where the set performance reflects the battery's performance once it has been set by r_Vdrop.

[0047] Since r_Vdrop is always less than or equal to one and greater than or equal to zero, it either has no effect on the estimated power capability (EKF / ECM(t)) or reduces it to a percentage of its original value. Values ​​of zero for both r_P and r_D do not change the estimated power capability (EKF / ECM(t)). Non-zero values ​​of both r_P and r_D result in a setting (e.g., a reduction) of the battery's performance (Estimated Power Capability Based EKF / ECM(t)) of both r_P and r_D to a percentage of an original battery performance value, where the percentage is complementary to the sum of r_P and r_D.A value of zero for r_P and a non-zero value for r_D result in a setting (e.g., a reduction) of the battery's estimated power capability (EKF / ECM(t)) from r_D alone to a percentage of an original battery power capability value, where the percentage is only complementary to r_D. A value of zero for r_D and a non-zero value for r_P result in a setting (e.g., a reduction) of the battery's estimated power capability (EKF / ECM(t)) from r_P alone to a percentage of an original battery power capability value, where the percentage is only complementary to r_P.

[0048] It goes without saying that the flowchart in Fig. 4 serves only for illustration and that procedure 100 is not based on the flowchart in Fig. 4 is to be interpreted in a limited way. Some of the steps of procedure 100 can be rearranged, while others can be omitted entirely.

[0049] Regarding Fig. Figure 5 illustrates a flowchart that demonstrates a procedure 200 for controlling the power output of the battery (e.g., battery 22) by implementing procedure 100. The procedure 200 can be stored as control logic and / or as an algorithm within the controller 32. The controller 32 can implement the procedure 200 by controlling the various components of the vehicle 10. The procedure 200 represents a use case scenario in which the battery 22 is operated at or near its power output limits (see, e.g., equation (1)). In such a scenario, a decrease in the battery's power capability (Estimated Power Capability Based EKF / ECM(t)) via r_P (i.e., proportional control parameter) and / or r_D (i.e.,Derivative control parameters) also lead to a decrease in the battery's power output due to the battery's estimated power capability (EKF / ECM(t)) decreasing to less than a commanded battery power output.

[0050] Procedure 200 begins at block 202, where a command to deliver power to the M / G 14 from battery 22 is generated. Next, procedure 200 proceeds to block 204, where it determines whether the voltage of battery 22 is less than a first threshold (e.g., Voltage_Limit (T)(t)) and / or whether the rate of change of the voltage of battery 22 exceeds a second threshold (e.g., Voltage_Drop_Speed_Limit (T)(t)). If the voltage of battery 22 is not less than the first threshold and the rate of change of the voltage of battery 22 does not exceed the second threshold, procedure 200 proceeds to block 206, where the power delivered by battery 22 to the M / G 14 is maintained at the commanded value (e.g., the value commanded at block 202).It should be noted that at block 206, the power delivered from battery 22 to the M / G 14 can have a value up to the Estimated Power Capability Based EKF / ECM(t), where the Estimated Power Capability Based EKF / ECM(t) has not been reduced by a percentage corresponding to the setting parameter (r_Vdrop). However, the power output at block 206 can be limited by multiplying the Estimated Power Capability Based EKF / ECM(t) at block 206 by the safety factor Υ according to equation (1).

[0051] Back at block 204, if the voltage of battery 22 is less than the first threshold and / or the rate of change of the voltage of battery 22 exceeds the second threshold, procedure 200 passes to block 208, in which the power delivered by battery 22 to the M / G 14 is reduced to less than the ordered value (e.g. less than the value ordered at block 202).

[0052] In Block 208, when both the voltage of battery 22 is less than the first threshold and the rate of change of battery 22's voltage exceeds the second threshold, the power delivered by battery 22 to M / G 14 is reduced to less than the ordered value based on both the proportion of the difference between the first threshold and the voltage of battery 22 and the proportion of the difference between the rate of change of battery 22's voltage and the second threshold according to procedure 100, since battery 22 is operating at or near the power output limits of battery 22.For example, in block 208, the power delivered by battery 22 to M / G 14 is reduced in the same way as the Estimated Power Capability Based EKF / ECM(t), which is reduced by a percentage equal to the setting parameter (r_Vdrop), where the setting parameter (r_Vdrop) is set by both the parameter r_P and the parameter r_D, since both the parameter r_P and the parameter r_D have non-zero values.

[0053] In Block 208, if the voltage of Battery 22 is less than the first threshold but the rate of change of Battery 22's voltage does not exceed the second threshold, the power delivered by Battery 22 to the M / G 14 is reduced to less than the commanded value solely based on the ratio of the difference between the first threshold and the voltage of Battery 22 according to Procedure 100, since Battery 22 is operating at or near its power output limits. For example, in Block 208, the power delivered by Battery 22 to the M / G 14 is reduced in the same way as the Estimated Power Capability Based EKF / ECM(t), by a percentage equal to the setting parameter (r_Vdrop), where the setting parameter (r_Vdrop) is set only by the parameter r_P, since the parameter r_P has a non-zero value, while the parameter r_D has a value equal to zero.

[0054] In Block 208, if the voltage of battery 22 is not less than the first threshold but the rate of change of battery 22 exceeds the second threshold, the power delivered by battery 22 to the M / G 14 is reduced to less than the ordered value only on the basis of the proportion of the difference between the rate of change of battery 22 and the second threshold according to procedure 100, since battery 22 is operated at or near the power output limits of the battery.For example, in block 208, the power delivered by battery 22 to M / G 14 is reduced in the same way as the Estimated Power Capability Based EKF / ECM(t), which is reduced by a percentage equal to the setting parameter (r_Vdrop), where the setting parameter (r_Vdrop) is only set by the parameter r_D, since the parameter r_D has a non-zero value, while the parameter r_P has a value equal to zero.

[0055] Procedure 200 returns to block 204 from both block 206 and block 208. This allows procedure 200 to switch between blocks 206 and 208 if the voltage of battery 22 exceeds the first threshold (e.g., changes from greater than to less than the first threshold or vice versa) and / or the rate of change of the voltage of battery 22 exceeds the second threshold (e.g., changes from greater than to less than the second threshold or vice versa) while power is being delivered from battery 22 to the M / G 14.

[0056] It should be noted that the power output at block 208 can be further limited by multiplying the Estimated Power Capability Based EKF / ECM(t), as reduced, at block 208 by the safety factor Υ according to equation (1). It is understood that the flowchart in Fig. 5 serves only for illustration and that procedure 200 is not based on the flowchart in Fig. 5 is to be interpreted restrictively. Some of the steps of procedure 200 can be rearranged, while others can be omitted entirely.

[0057] Regarding Fig. Figure 6 illustrates diagram 300 of the power output of battery 22 when controlled based on procedure 100 and procedure 200. Line 302 illustrates the Estimated Power Capability Based EKF / ECM(t), which may be reduced by the safety factor Υ according to equation (1). Line 304 illustrates a commanded power output from battery 22 to the M / G 14. Line 306 illustrates the actual power delivered from battery 22 to the M / G 14. Between time points T1 and T2, the Estimated Power Capability Based EKF / ECM(t) 302 relative to the commanded power output 304 was reduced by procedure 100 in response to the battery 22 voltage being less than a first threshold (e.g., Voltage_Limit (T)(t)) and / or the rate of change of the battery 22 voltage exceeding the second threshold (e.g., Voltage_Drop_Speed_Limit (T)(t)). This is also described in Fig. Figure 2D illustrates this, where the reduction of the Estimated Power Capability Based EKF / ECM(t) 302 occurs simultaneously with the voltage of battery 22 being less than a first threshold and the rate of change of the voltage of battery 22 exceeding the second threshold. The actual power 306 delivered by battery 22 to M / G 14 is reduced to less than the commanded power output 304 from battery 22 to M / G 14 between times T1 and T3, since the commanded power output 304 is greater than the reduced Estimated Power Capability Based EKF / ECM(t) 302. This illustrates a use case where delivered power is reduced due to a decrease in the Estimated Power Capability Based EKF / ECM(t) 302.

[0058] An alternative method uses the confidence level of the estimated performance across varying state-of-charge (SOC) ranges, temperature conditions, and battery lifetime to calculate the battery's discharge and charge power limits based on the estimated performance. This alternative method can be used for both long-term and short-term performance. During a discharge scenario of battery 22, the discharge power limits of battery 22 can be based on the estimated performance of battery 22 according to equations (6) and (7): Discharge power limits = ϒ_total * estimated discharge power capability ϒ_total=ϒ∗ϒ_conf_dis∗ϒ_life where Υ is a safety factor or coefficient that ensures that the discharge power limits fall within the range of X% of the battery's capacity, Υ_conf_dis is an adjustable parameter designed to compensate for increased uncertainty at lower SOC and lower temperature ranges for the estimated discharge capacity, and Υ_life is a parameter that varies with the battery's life cycle.

[0059] Υ can be a constant value, such as 0.95. Υ_conf_dis is a function of the SOC and temperature of battery 22, denoted as Υ_conf_dis = f(SOC, T), and can be represented as a calibrated two-dimensional table (e.g., Table 1) under battery discharge conditions. It should be noted that Υ_conf_dis decreases under battery 22 discharge conditions as the temperature and SOC of battery 22 decrease. Table 1 T°C\SOC(%) 0 % 5 % 10 % 20 % 30 % 40 % 50 % 95 % 100 % -40 °C 0,6 0,8 0,84 0,88 0,9 0,9 0,9 0,9 0,9 -30 °C 0,7 0,85 0,91 0,93 0,95 0,95 0,95 0,95 0,95 -20 °C 0,8 0,9 0,94 0,98 0,98 0,98 0,98 0,98 0,98 -10 °C 0,82 0,92 0,96 1 1 1 1 1 1 0 °C 0,85 0,94 0,98 1 1 1 1 1 1 10 °C 0,85 0,96 1 1 1 1 1 1 1 25 °C 0,85 0,96 1 1 1 1 1 1 1 45 °C 0,85 0,96 1 1 1 1 1 1 1 60 °C 0,85 0,96 1 1 1 1 1 1 1

[0060] At the start of a new life cycle, the initial value of Υ_life can be set to one. As the battery's lifespan progresses, Υ_life can decrease from one, but always remains greater than zero. During a discharge scenario of battery 22, the discharge power limits of the battery can be based on the battery's performance according to equations (8) and (9): Charging power limits = ϒ_total * estimated charging power capability ϒ_total=ϒ∗ϒ_conf_charge∗ϒ_life

[0061] `Υ_conf_charge` is an adjustable parameter designed to compensate for increased uncertainty in the estimated charging capability at higher SOC and lower temperature ranges. It is a function of the battery's SOC and temperature, denoted as `Υ_conf_charge = f(SOC, T)`, and can be represented as a calibrated two-dimensional table (e.g., Table 2) under battery charging conditions. Note that `Υ_conf_charge` decreases under battery 22 charging conditions as the battery 22's temperature decreases and its SOC increases. Table 2 T°C\SOC(%) 0 % 5 % 10 % 20 % 30 % 40 % 50 % 95 % 100 % -40 °C 0,6 0,8 0,84 0,88 0,9 0,9 0,9 0,9 0,85 -30 °C 0,7 0,85 0,91 0,93 0,95 0,95 0,95 0,95 0,9 -20 °C 0,8 0,9 0,94 0,98 0,98 0,98 0,98 0,98 0,92 -10 °C 0,82 0,92 0,96 1 1 1 1 1 0,96 0 °C 0,85 0,94 0,98 1 1 1 1 1 0,96 10 °C 0,85 0,96 1 1 1 1 1 1 0,96 25 °C 0,85 0,96 1 1 1 1 1 1 0,96 45 °C 0,85 0,96 1 1 1 1 1 1 0,96 60 °C 0,85 0,96 1 1 1 1 1 1 0,96

[0062] The alternative procedure, which includes equations (6)-(9), Table 1 and Table 2, can be stored as control logic and / or as an algorithm in the controller 32. The controller 32 can implement the alternative procedure by controlling the various components of the vehicle 10.

[0063] It is understood that the designations first, second, third, fourth, etc., for any component, state, or condition described herein may be arranged differently in the claims so that they have a chronological order with respect to the claims. Furthermore, it is understood that any component, state, or condition described herein that does not have a numerical designation may be given a designation first, second, third, fourth, etc., in the claims if one or more of the specific component, state, or condition are claimed.

[0064] The terms used in the description are descriptive and not limiting, and it is understood that various modifications may be made without altering the nature and scope of the disclosure. As previously described, the features of different embodiments may be combined to form further embodiments that may not be expressly described or illustrated. Although various embodiments may have been described in such a way that they offer advantages or are preferred over other embodiments or implementations prior art with respect to one or more desired properties, the person skilled in the art understands that compromises may be made with respect to one or more features or properties in order to achieve desired overall system attributes, which depend on the specific application and implementation.Accordingly, embodiments that are described as less desirable than other embodiments or implementations according to the prior art with regard to one or more properties are not outside the scope of the disclosure and may be desirable for specific applications.

[0065] According to the present invention, a vehicle is provided comprising: a battery configured to supply power to an electric machine for propelling the vehicle; and a controller programmed to, during a discharge of power from the battery at a commanded value and in response to a rate of change of a voltage of the battery during discharge increasing to more than a threshold rate, reduce the discharge power to less than the commanded value based on a fraction of a difference between the rate and the threshold rate, and, during a discharge of power from the battery at the commanded value and in response to the rate during discharge remaining less than the threshold rate, maintain the discharge of the battery at the commanded value.

[0066] According to one embodiment, reducing the discharge power to less than the ordered value corresponds to reducing the discharge power to a percentage of the ordered value, wherein the percentage is complementary to the proportion of the difference between the rate and the threshold rate.

[0067] According to one embodiment, the controller is further programmed to reduce the discharge power from the commanded value to less than the commanded value based on a proportion of the difference between the voltage threshold and the voltage, in response to the discharge of power from the battery at the commanded value and to the fact that the battery voltage drops to less than a voltage threshold during discharge.

[0068] According to one embodiment, the control system is further programmed to maintain the discharge of the battery at the commanded value in response to the discharge of power from the battery at the commanded value and to the fact that the voltage of the battery remains greater than the voltage threshold during discharge.

[0069] According to one embodiment, reducing the discharge power to less than the ordered value corresponds to reducing the discharge power to a percentage of the ordered value, wherein the percentage is complementary to the proportion of the difference between the voltage threshold and the voltage.

[0070] According to one embodiment, the voltage is based on an equivalent circuit model.

[0071] According to one embodiment, the threshold rate depends on the temperature of the battery.

[0072] According to the present invention, a vehicle is provided comprising: an electric machine; a battery configured to supply power to the electric machine to propel the vehicle; and a controller programmed to reduce the battery discharge power in response to (i) the battery voltage decreasing to less than a first threshold during battery discharge and (ii) the rate of change of voltage increasing to more than a second threshold during discharge, based on (a) a proportion of the difference between the first threshold and the voltage and (b) a proportion of the difference between the rate and the second threshold.

[0073] According to one embodiment, the controller is programmed to reduce the battery discharge power only on the basis of the proportion of the difference between the rate and the second threshold in response to (i) the battery voltage remaining above the first threshold and (ii) the rate of change of the voltage increasing above the second threshold.

[0074] According to one embodiment, the controller is programmed to reduce the battery discharge power only on the basis of the proportion of the difference between the first threshold and the voltage, in response to (i) the battery voltage decreasing to less than the first threshold and (ii) the rate of change of the voltage remaining below the second threshold.

[0075] According to one embodiment, the controller is programmed to maintain a current battery discharge power in response to (i) the battery voltage remaining above the first threshold and (ii) the rate of change of the battery voltage remaining below the second threshold.

[0076] According to one embodiment, reducing the discharge power corresponds to reducing the discharge power to a percentage of a current value, wherein the percentage is complementary to a sum of (i) the proportion of the difference between the first threshold and the voltage and (ii) the proportion of the difference between the rate and the second threshold.

[0077] According to one embodiment, the voltage is based on an equivalent circuit model.

[0078] According to the present invention, a vehicle is provided comprising: a battery configured to supply power to an electric machine for propelling the vehicle; and a controller programmed to reduce the discharge power from the battery to a commanded value during discharge, in response to a decrease in the battery voltage below a voltage threshold during discharge, based on a fraction of the difference between the voltage threshold and the voltage.

[0079] According to one embodiment, the controller is further programmed to maintain the discharge of the battery at the commanded value during the discharge of power from the battery at the commanded value and in response to the fact that the voltage of the battery remains greater than the voltage threshold during discharge.

[0080] According to one embodiment, reducing the discharge power to less than the ordered value corresponds to reducing the discharge power to a percentage of the ordered value, wherein the percentage is complementary to the proportion of the difference between the voltage threshold and the voltage.

[0081] According to one embodiment, the control is further programmed to reduce the discharge power to less than the commanded value based on a proportion of the difference between the rate and the threshold rate in response to the discharge of power from the battery at the commanded value and to the fact that the rate of change of the battery voltage during discharge increases to more than a threshold rate.

[0082] According to one embodiment, the control system is further programmed to maintain battery discharge at the commanded value in response to the discharge of power from the battery at the commanded value and to the fact that the rate during discharge remains greater than the threshold rate.

[0083] According to one embodiment, reducing the discharge power to less than the ordered value corresponds to reducing the discharge power to a percentage of the ordered value, wherein the percentage is complementary to the proportion of the difference between the rate and the threshold rate.

[0084] According to one embodiment, the voltage threshold depends on the temperature of the battery.

Claims

Vehicle comprising: a battery configured to supply power to an electric machine for propelling the vehicle; and a controller programmed to, during a discharge of power from the battery at a commanded value and in response to a rate of change of a voltage of the battery during discharge increasing to more than a threshold rate, reduce the discharge power to less than the commanded value based on a fraction of a difference between the rate and the threshold rate, and during a discharge of power from the battery at the commanded value and in response to the rate during discharge remaining less than the threshold rate, maintain the discharge of the battery at the commanded value. Vehicle according to claim 1, wherein reducing the discharge power to less than the ordered value corresponds to reducing the discharge power to a percentage of the ordered value, wherein the percentage is complementary to the proportion of the difference between the rate and the threshold rate. Vehicle according to claim 1, wherein the control is further programmed to reduce the discharge power from the commanded value to less than the commanded value on the basis of a proportion of a difference between the voltage threshold and the voltage, in response to the discharge of power from the battery with the commanded value and to the fact that the voltage of the battery decreases to less than a voltage threshold during discharge. Vehicle according to claim 3, wherein the control is further programmed to maintain the discharge of the battery at the commanded value in response to the discharge of power from the battery at the commanded value and to the fact that the voltage of the battery remains greater than the voltage threshold during discharge. Vehicle according to claim 3, wherein reducing the discharge power to less than the ordered value corresponds to reducing the discharge power to a percentage of the ordered value, wherein the percentage is complementary to the proportion of the difference between the voltage threshold and the voltage. Vehicle according to claim 1, wherein the voltage is based on an equivalent circuit model. Vehicle according to claim 1, wherein the threshold rate depends on the temperature of the battery. Vehicle comprising: an electric machine; a battery configured to supply power to the electric machine to propel the vehicle; and a controller programmed to reduce battery discharge power in response to (i) a decrease in battery voltage to less than a first threshold during battery discharge and (ii) an increase in the rate of change of voltage to more than a second threshold during discharge, based on (a) a fraction of a difference between the first threshold and the voltage and (b) a fraction of a difference between the rate and the second threshold. Vehicle according to claim 8, wherein the control is programmed to reduce the battery discharge power only on the basis of the proportion of the difference between the rate and the second threshold in response to (i) the voltage of the battery remaining above the first threshold and (ii) the rate of change of the voltage increasing to more than the second threshold. Vehicle according to claim 8, wherein the control is programmed to reduce the battery discharge power only on the basis of the proportion of the difference between the first threshold and the voltage, in response to (i) the voltage of the battery decreasing to less than the first threshold and (ii) the rate of change of the voltage remaining less than the second threshold. Vehicle according to claim 8, wherein the control is programmed to maintain a current discharge power of the battery in response to (i) the voltage of the battery remaining greater than the first threshold and (ii) the rate of change of the voltage of the battery remaining less than the second threshold. Vehicle according to claim 8, wherein reducing the discharge power corresponds to reducing the discharge power to a percentage of a current value, wherein the percentage is complementary to a sum of (i) the proportion of the difference between the first threshold and the voltage and (ii) the proportion of the difference between the rate and the second threshold. Vehicle, comprising: a battery configured to deliver power to an electric machine for propelling the vehicle; and a controller programmed to, during a discharge of power from the battery at a commanded value and in response to a decrease in the battery voltage to less than a voltage threshold during discharge, reduce the discharge power from the commanded value to less than the commanded value based on a fraction of a difference between the voltage threshold and the voltage, and during a discharge of power from the battery at the commanded value and in response to a decrease in the battery voltage to less than the voltage threshold during discharge, maintain the discharge of the battery at the commanded value. Vehicle according to claim 13, wherein reducing the discharge power to less than the ordered value corresponds to reducing the discharge power to a percentage of the ordered value, wherein the percentage is complementary to the proportion of the difference between the voltage threshold and the voltage. Vehicle according to claim 14, wherein the control unit is further programmed to reduce the discharge power to less than the commanded value based on a fraction of a difference between the rate and the threshold rate in response to the discharge of power from the battery at the commanded value and to the rate of change of the battery voltage increasing to more than a threshold rate during discharge, and wherein reducing the discharge power to less than the commanded value corresponds to reducing the discharge power to a percentage of the commanded value, the percentage being complementary to the fraction of the difference between the rate and the threshold rate.

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