BATTERY MANAGEMENT SYSTEM

Abstract

A battery management system (BMS) configured to control a discharge current of a battery is provided. The BMS is configured to calculate a discharge energy of the battery for a time step based on the discharge current and the duration of the time step, and to calculate an accumulated discharge energy of the battery based on an accumulated discharge energy calculated for a previous time step and the discharge energy for the time step. The BMS is further configured to determine a maximum discharge pulse current, calculate a discharge current limit, and control the discharge current of the battery such that the discharge current does not exceed the discharge current limit. The BMS can control a charge current of a battery in a similar manner.

Description

FIELD OF DISCLOSUREThe present disclosure relates to batteries. More particularly, the present disclosure relates to batteries for electric work vehicles and the like.Prior ArtA rechargeable battery (e.g., a cell or a battery pack) generates heat upon charging or discharging. The energy flow from / to the battery leads to heating of the battery due to the inherent resistances of the battery.To prevent overheating of the battery, a battery management system ("BMS") may be provided to regulate the power consumption / output of the battery to a level that can be safely drained from the battery.As a rule, a battery manufacturer specifies a safe operating limit for the continuous current flow from / to the battery. In addition, a battery manufacturer may specify a pulsed power limit at which a higher power can be output to the battery / absorbed by the battery over a specific period of time.Against this background, the present disclosure aims to provide an improved or at least commercially relevant alternative battery management system.SummaryAccording to a first aspect of the disclosure, there is provided a battery management system configured to control a discharge current of a battery. The BMS is configured to:calculating a discharge energy of the battery for a time step based on the discharge current and the duration of the time step;calculating an accumulated discharge energy of the battery based on an accumulated discharge energy calculated for a previous time step and the discharge energy for the time step;determining a maximum discharge pulse current for a pulse having a duration based on a discharge pulse current lookup table of the BMS;calculating a maximum accumulated discharge energy of the battery based on the maximum discharge pulse current and the duration of the pulse;calculating a discharge current limit based on a ratio of the accumulated discharge energy to the maximum accumulated discharge energy, the discharge current limit not exceeding the maximum discharge pulse current; andcontrolling the discharge current of the battery so that the discharge current does not exceed the discharge current limit.The present inventors have recognized that the maximum discharge current values from battery manufacturer lookup tables represent a restrictive mode of operation of a battery. For example, a battery manufacturer may specify a value for a maximum pulse discharge current (where a pulse is typically of relatively short duration, e.g., 2 seconds or 30 seconds) and a separate value for a maximum steady-state discharge current (i.e., a safe steady-state discharge operating limit). Although the maximum discharge pulse current may be higher than the maximum stationary discharge current, the increased current is only suitable for operation for the specified duration of the current pulse (e.g., 2 or 30 seconds corresponding to the specified pulse duration). In some cases, a battery manufacturer indicates different maximum discharge pulse currents for pulses of different duration (e.g., a first maximum discharge pulse current for a 2 second current pulse and a second, lower maximum discharge pulse current for a 30 second current pulse). In such cases, it may be difficult to determine an appropriate operating current for medium duration pulses (e.g., operating with a 15 second current pulse) or an appropriate operating time for a medium magnitude current (i.e., a current between the maximum discharge pulse current and the maximum discharge current in the steady state).According to the first aspect, a BMS is provided that can determine a safe operating limit for a battery for impulse currents of longer duration than indicated in the lookup tables provided by the battery manufacturer. The BMS of the first aspect calculates a discharge current limit by comparing the energy accumulated by the discharging of the battery with a maximum accumulated energy. The maximum accumulated discharge energy is calculated from a maximum discharge pulse current provided from a look-up table of the BMS. The difference between the accumulated discharge energy and the maximum accumulated discharge energy defines the amount of remaining energy that the battery can safely accumulate. Based on this energy difference, the BMS may determine a discharge current limit at which the battery may continue to be operated. Indeed, the BMS may enable safe operation of the battery at discharge currents that are higher than a maximum steady-state discharge current for a duration that is longer than the duration of the pulse associated with the maximum discharge pulse current.According to a second aspect of the disclosure, there is provided a battery management system (BMS) configured to control a charging current of a battery. The BMS is configured to:calculating a charge energy of the battery for a time step based on the charge current of the battery and the duration of the time step;calculating an accumulated charge energy of the battery based on an accumulated charge energy calculated for a previous time step and the charge energy for the time step;determining a maximum charge pulse current for a pulse having a duration based on a charge pulse current lookup table of the BMS;calculating a maximum accumulated charge energy based on the maximum charge pulse current and the duration of the pulse;calculating a charge current limit based on a ratio of the accumulated charge energy to the maximum accumulated charge energy, the charge current limit not exceeding the maximum charge pulse current; andcontrolling the charging current of the battery so that the charging current does not exceed the charging current limit.Accordingly, it will be understood that a BMS may be provided to control a charging current of the battery. The BMS may control the charging current by comparing the accumulated charging energy with the maximum accumulated charging energy. Thus, the BMS may control the charging current according to a similar strategy as the BMS of the first aspect.According to a third aspect of the disclosure, a machine is provided. The machine may include a battery and a BMS according to the first and / or second aspect of the disclosure. In some embodiments, the machine may be an electric work vehicle.According to a fourth aspect of the disclosure, there is provided a method of controlling a discharge current of a battery. The method comprises:calculating a discharge energy of the battery for a time step based on the discharge current and the duration of the time step;calculating an accumulated discharge energy of the battery based on an accumulated discharge energy calculated for a previous time step and the discharge energy for the time step;determining a maximum discharge pulse current for a pulse having a duration based on a discharge pulse current lookup table of the BMS;calculating a maximum accumulated discharge energy of the battery based on the maximum discharge pulse current and the duration of the pulse;calculating a discharge current limit based on a ratio of the accumulated discharge energy to the maximum accumulated discharge energy, the discharge current limit not exceeding the maximum discharge pulse current; andcontrolling the discharge current of the battery so that the discharge current does not exceed the discharge current limit.It is understood that the method of the fourth aspect of the disclosure may be performed by the BMS of the first aspect and / or by the machine of the third aspect.According to a fifth aspect of the disclosure, a method of controlling a charging current of a battery is provided. The method comprises:calculating a charge energy of the battery for a time step based on the charge current of the battery and the duration of the time step;calculating an accumulated charge energy of the battery based on an accumulated charge energy calculated for a previous time step and the charge energy for the time step;determining a maximum charge pulse current for a pulse having a duration based on a charge pulse current lookup table of the BMS;calculating a maximum accumulated charge energy based on the maximum charge pulse current and the duration of the pulse;calculating a charging current limit based on a ratio of the accumulated charging energy to the maximum accumulated charging energy, the charging current limit not exceeding the maximum charging pulse current; andcontrolling the charging current of the battery so that the charging current does not exceed the charging current limit.It is understood that the method of the fifth aspect of the disclosure may be performed by the BMS of the second aspect and / or by the machine of the third aspect.Brief Description of the FiguresAn embodiment of the disclosure will now be described with reference to the following non-limiting figures, in which:FIG. 1 shows a diagram of a discharge current controlled by a BMS according to this disclosure;FIG. 2 is a graph of accumulated discharge energy and maximum accumulated discharge energy calculated by the BMS according to this disclosure;FIG. 3 is a graph showing an accumulated discharge energy and a maximum accumulated discharge energy calculated by the BMS;FIG. 4 shows a graph of a discharge current limit calculated by the BMS according to this disclosure;FIG. 5 shows a graph of a discharge current limit calculated by the BMS according to this disclosure;FIG. 6 shows a diagram of a discharge current controlled by a BMS according to this disclosure;FIG. 7 shows a diagram of battery current controlled by a BMS according to this disclosure;FIG. 8 is a graph of an accumulated energy and a maximum accumulated charge energy calculated by the BMS according to this disclosure;FIG. 9 shows a diagram of battery current controlled by a BMS according to this disclosure;FIG. 10 shows a diagram of a charge current limit calculated by the BMS according to this disclosureFIG. 11 shows a diagram of battery current controlled by a BMS according to this disclosure;FIG. 12 is a diagram of a charge current weight and a discharge current weight calculated by the BMS according to this disclosure;FIGS. 13 a, 13 band 13 c show diagrams of different arbitration strategies for the BMS;FIG. 14 is a block diagram of a method for controlling a discharge current of a battery according to an embodiment of the disclosure;FIG. 15 is a block diagram of a method for controlling a charging current of a battery according to an embodiment of the disclosure; andFIG. 16 shows a block diagram of a BMS connected to a battery according to this disclosure.Detailed DescriptionAccording to an embodiment of the disclosure, a battery management system (BMS) 10 is provided. The BMS 10 is configured to control the discharge current of a battery 20. A block diagram of the BMS 10 and the battery 20 is shown in FIG. 16. According to the embodiment, the battery 20 may be a rechargeable battery. The battery 20 and the BMS 10 may be provided as part of or connected to an engine 30, such as an electric machine.The BMS 10 may include various sensors (e.g., current sensors, voltage sensors, temperature sensors) to determine various operating parameters of the battery 20 (e.g., state of charge, battery temperatures, discharge / charge voltage, discharge / charge current, etc.). The BMS 10 may also include a processor, a controller, or the like configured to control the power output of the battery 20. To control the power output of the battery 20, the BMS 10 may also include suitable circuitry (e.g., transistors, resistors, and the like) configured to control the power output of the battery 20 in response to the power output of an external load (e.g., power output of an engine connected to the BMS 10 and the battery 20).A method of controlling a discharge current of a battery 20 with the BMS 10 will now be described with reference to FIGS. 1-6, which show various plots of various variables of the BMS 10 and the battery 20 over time. In the diagrams of FIGS. 1 to 6, a current which charges the battery 20 (a charging current) is represented as a positive current, while a current which discharges the battery 20 (a discharging current) is represented as a negative current.FIG. 1 is a graph showing the discharge current of the battery 20 (D). The discharge current of the battery 20 varies with time in response to a required square wave current (S). The required square wave discharge current in the example of Fig. 1 is 3500 A for a duration of 60 seconds. FIG. 1 also shows a maximum steady state discharge current (M SS) and a maximum discharge pulse current (M P). In the embodiment of FIG. 1, the maximum discharge pulse current M P is provided for a pulse duration of 30 seconds.The maximum discharge persistent current (M SS) may be a value associated with the battery 20 stored in the BMS 10. In some embodiments, the maximum steady-state discharge current (M SS) may be a value that varies with one or more of the following values: battery state of charge (SOC), battery temperature, battery age. Accordingly, in some embodiments, the BMS 10 may use a steady-state discharge current lookup table of the BMS 10 to determine a maximum steady-state discharge current value (M SS).Similarly, the maximum discharge pulse current (M P) may be a value connected to the battery 20 stored in the BMS 10. In some embodiments, the maximum discharge pulse current (M P) may be a value that varies with one or more of the following: state of charge (SOC) of the battery, battery temperature, battery age. The maximum discharge pulse current (M P) can be provided in combination with a specific pulse duration T p via which the battery 20 can be operated with the specified maximum discharge pulse current (M P). In some embodiments, the BMS 10 may include a plurality of maximum discharge pulse currents (M P) each maximum discharge pulse current (M P) having a respective pulse duration T p the pulse durations being of different lengths (with different respective M p). Accordingly, in some embodiments, the BMS 10 may use a discharge pulse current lookup table of the BMS 10 to determine a value for the maximum discharge pulse current (M P) and an associated duration of the pulse T p.It should be appreciated that the steady state maximum discharge current strengths (M SS) and the maximum discharge pulse currents (M P), indicated in the associated look-up tables, may be provided by a battery manufacturer to the battery 20 to be used with the BMS 10.As can be seen from FIG. 1, the demanded current S is larger than the maximum steady-state discharge current M SS, but smaller than the maximum discharge pulse current (M P). Because the demanded current S is demanded for a longer duration than the specified length of maximum discharge pulse current, the BMS 10 is configured to determine how long the battery 20 can be operated at a discharge current above the maximum discharge current M SS in the steady state and at which discharge current magnitude. As can be seen from FIG. 1, the BMS 10 first allows the battery 20 to discharge 100% of the requested current. Upon a continuing demand, the BMS 10 reduces the discharge current to ensure that the total energy (i.e., thermal energy) accumulated by the battery 20 does not become too high. According to this disclosure, the BMS 10 calculates the maximum energy to be accumulated based on the maximum discharge pulse current for the battery M P.As shown in FIG. 2, the BMS 10 calculates an accumulated discharge energy for the battery E D and a maximum accumulated discharge energy M ED.The maximum accumulated discharge energy M ED is calculated for the maximum discharge pulse current M P and the duration of the pulse associated with the maximum discharge pulse current M P. According to this embodiment, it is assumed that the maximum energy that the battery 20 can accumulate is defined by the battery 20 discharging the maximum discharge pulse current M P for the specified duration of the pulse T P. Therefore, a maximum accumulated discharge energy M ED can be calculated as follows:In some embodiments, the maximum accumulated discharge energy of the battery 20 may also account for a steady state energy loss associated with the battery 20. Therefore, in some embodiments, the maximum accumulated discharge energy may be calculated based on the maximum discharge pulse current, the duration of the pulse, and a steady state energy loss of the battery 20 for the duration of the pulse. In some embodiments, the steady state energy loss may be a predetermined value associated with the battery 20 or the BMS 10.In some embodiments, the steady state energy loss through the BMS 10 may be determined based on the maximum steady state discharge current M SS. For example, in the embodiment of FIGS. 1-6, it is assumed that the battery 20 can dissipate energy resulting from the discharge current with the maximum stationary discharge current M SS for the duration of the pulse T p. Therefore, the steady-state energy loss can be calculated based on M SS2 × T P.Thus, in the embodiment of Figs. 1-6, the maximum accumulated discharge energy can be calculated as follows:In the embodiment of Figures 1-6, the accumulated discharge energy E D is calculated when the BMS 10 controls the battery 20. The BMS 10 updates the discharge current to be controlled at regular time steps. Therefore, the accumulated discharge energy E D is updated at each time step (Δt). That is, the accumulated discharge energy for the nth time step ED(n) (where n is an integer) is calculated based on an accumulated discharge energy (E D( n-1)) calculated for a previous time step and the discharge energy for the time step (EΔt).In the embodiment of Figures 1 to 6, the discharge energy for the time step (EΔt) is calculated based on the squared discharge current currently being discharged from the battery 20 (D) and the duration of the time step Δt. For example, in the embodiment of Figures 1 to 4, time step Δt may have a duration of 0.1 seconds. Therefore, the accumulated discharge energy can be calculated as follows:In some embodiments, the accumulated discharge energy E D( n) is calculated based on the discharge energy, the accumulated discharge energy for the previous time step, and a steady-state energy loss of the battery 20 for the time step. By considering the steady-state energy loss, the accumulated discharge energy E D( n) may decrease between the time steps in some cases.For example, in the embodiment of FIGS. 1-6, the steady state energy loss of the battery 20 for the time step is calculated based on a maximum steady state current of the battery M SS. Therefore, the steady-state energy loss can be calculated as M SS2 × Δt.Accordingly, in the embodiments of Figs. 1 to 6, the accumulated discharge energy may be calculated as follows:As can be seen from FIG. 2, the accumulated discharge energy E D increases as the discharge current (D) is output from the battery 20. When the discharge current falls below the maximum stationary discharge current, the accumulated discharge energy decreases because the battery 20 outputs the accumulated energy. As can be seen from FIGS. 1 and 2, as the accumulated discharge energy E D, increases, the BMS 10 starts to limit the discharge current discharged from the battery 20. The process by which this control is implemented is discussed further below.FIG. 3 is a graph showing the change of the accumulated discharge energy E D and the maximum accumulated discharge energy with time (also shown in FIG. 2 ). FIG. 4 is a graph showing the discharge current limit (L D) with time following the same time axis as FIGS. 1 to 3; the discharge current limit L D is calculated based on a ratio of the maximum accumulated discharge energy M ED to the accumulated discharge energy E D. The BMS 10 also ensures that the discharge current limit L D does not exceed the maximum discharge pulse current specified by the BMS 10 / battery manufacturer.In some embodiments, the ratio of the accumulated discharge energy E D to the maximum accumulated discharge energy M ED( i.e., E D / M ED) may be used as an indication of the remaining energy that may be accumulated by the battery 20 without excessive heat buildup (i.e., 1-E D / M ED). Therefore, in some embodiments, the ratio E D / M ED may be used to scale the maximum discharge pulse current M P to calculate a discharge current limit L D.In some embodiments, the ratio E D / M ED is used to scale the difference between the maximum discharge pulse current M P and the maximum steady state discharge current M SS. In some embodiments, the BMS 10 may ensure that the magnitude of the discharge current limit is not reduced below the magnitude of the maximum steady state discharge current M SS. Therefore, in some embodiments, the discharge current limit L D may be calculated as follows:Thus, when the accumulated discharge energy E D increases from zero, the discharge current limit L D decreases from the maximum discharge pulse current M P toward the maximum discharge current in the steady state M SS.In some embodiments, the BMS 10 may vary the manner in which the BMS 10 limits the discharge current when a current demand exceeds the maximum steady state discharge current M SS. For example, in some embodiments, it may be desirable for the BMS 10 to vary the discharge current limit uniformly from the maximum discharge pulse current M P down to the maximum steady state discharge current M SS. Therefore, the BMS 10 may prefer reducing the current demand currently to maintain the ability to provide current at a level above M SS over a longer period of time. In the example of a BMS 10 mounted on an electric work vehicle, smooth change may be desirable when the battery 20 is used for the vehicle's driving operation. That is, sudden acceleration failures due to reaching the maximum accumulated discharge energy M ED may result in a "judder" operational experience for the user. In other embodiments, it may be desirable for the BMS 10 to prefer an increase in instantaneous power output. Such a strategy may then require a great reduction in the discharge current limit in order to avoid exceeding the maximum accumulated discharge energy M ED. Indeed, the BMS 10 may provide a means for intermediary between one or more of the maximum discharge pulse limits M P and the maximum steady state discharge current M SS. The arbitration strategy employed may be selected / altered to provide different power output profiles, where different power output profiles may be tailored to the different tasks to be performed by the engine.Therefore, in some embodiments, the discharge current limit may be calculated based on the maximum discharge pulse current M P and a discharge current strength weight W. The discharge current strength weight may be provided by a arbitration strategy lookup table.The arbitration strategy lookup table may output a discharge current magnitude weight W D based on the ratio of the accumulated discharge energy to the maximum accumulated discharge energy E D / M ED.In some embodiments, an arbitration strategy parameter (K) in combination with the ratio E D / M ED may also be input to the arbitration strategy lookup table to determine an arbitration strategy for the discharge current weight W D.In some embodiments, the arbitration strategy may regulate how the BMS 10 ramps the discharge current from the maximum discharge pulse current M P( with unaccumbered discharge energy) to the maximum discharge persistent current state M SS( at E D= M ED).In one possible strategy that promotes immediate power output, the BMS 10 may provide that at an accumulated discharge energy that is less than the maximum accumulated discharge energy, the discharge current limit is equal to the maximum discharge pulse current (i.e., when E D< M ED; L D= M P). When the accumulated discharge energy is equal to the maximum accumulated discharge energy, the BMS 10 performs stepwise change of the discharge current limit to the maximum discharge continuous current M SS (i.e., when E D= M ED; L D= M SS). Such arbitration strategy may allow the battery 20 to deliver a discharge current over the maximum discharge continuous current as long as possible. Once the accumulated discharge energy reaches the maximum M ED the arbitration strategy performs a stepwise change in the discharge current limit. An example of such a relationship between E D / M ED and the discharge current weight W D is shown in FIG. 13a. Such a sudden change in discharge current may not be suitable for some applications, and therefore it may be desirable to provide other arbitration strategies that allow for a smoother transition (or ramp) between the maximum discharge pulse current and the maximum discharge sustain current.In another possible strategy promoting a smooth change in discharge current, the discharge current weight W D may track the change in E D / M ED for example. An example of such a relationship is shown in Fig. 13b. In contrast to the strategy of FIG. 13 a, the arbitration strategy of FIG. 13 b reduces the discharge current limit L D from the maximum discharge current pulse as the battery 20 begins to accumulate energy. This provides a smoother transition to discharge sustain currents, but may limit the power output of the battery 20 in cases where the demanded power drops before the maximum accumulated discharge energy is reached.A further possible arbitration strategy is shown in FIG. 13c, in which the breakpoint at which the discharge current weight W D is decreased from 1 toward zero changes. It can be seen that in the strategy of FIG. 13 a, the breakpoint at which the discharge current weight decreases towards zero is at E D / M ED= 1 (a step change). In the strategy of Figure 13b, the breakpoint is at E D / M ED= 0. In the embodiment of FIG. 13c, the breakpoint is at E D / M ED= 0,5. In either case, the discharge current weight W D is scaled linearly from W D= 1 at the breakpoint to W D= 0 at E D / M ED= 1.In some embodiments, a arbitration strategy parameter k D may be used to select the breakpoint at which the discharge current weight W D is scaled to zero. Thus, in some embodiments, a arbitration strategy may be as follows:In some embodiments, a arbitration strategy lookup table may be generated based on the above relationship, where the arbitration strategy lookup table generates a discharge current weight W D based on k D and E D / M ED. It should be noted that in the examples of Figures 13a-13c, a linear relationship is used to scale the discharge current weight between breakpoint k and E D / M ED= 1. In other embodiments, another relationship may be used to scale W D such as a polynomial or other non-linear function.In the embodiment of Figures 1-6, the discharge current magnitude weight W D is used to scale the difference between the maximum discharge pulse current M P and the maximum discharge sustain current M SS. Therefore, in some embodiments, the discharge current limit L D may be calculated as follows:FIG. 4 is a graph showing the discharge current limit L D, which decreases as the accumulated discharge energy increases from the maximum discharge pulse current M P (as shown in FIG. 3 ).The BMS 10 is configured to control the discharge current of the battery 20 so that the discharge current D does not exceed the discharge current limit L D. As illustrated in FIGS. 5 and 6, the BMS 10 limits the discharge current D corresponding to the discharge current limit L D, when the discharge current limit L D falls below the required current S (see FIG. 1 ). As soon as the discharge current falls below the maximum discharge continuous current M SS the discharge current limit L D starts to increase, as shown in FIG. 5.It should be understood that although the above description focuses on the calculation of a discharge current limit, the ratio E D / M ED may be used to calculate a discharge voltage limit for the battery 20. The maximum discharge pulse voltage may be provided by a battery manufacturer and stored in an appropriate look-up table of the BMS 10.The BMS 10 may also be used to control a charging current of the battery 20 according to this disclosure. In some embodiments, the BMS 10 may be used to control a charging current and a discharging current of the battery 20. That is, the BMS 10 may control the amount of current flowing into and out of the battery 20. A method of controlling a charging current and a discharging current of the battery 20 with the BMS 10 will now be described with reference to FIGS. 7 to 12 which show various plots of various variables of the BMS 10 and the battery 20 over time. In the diagrams of FIGS. 7 to 12, a current which charges the battery 20 (a charging current) is represented as a positive current, while a current which discharges the battery 20 (a discharging current) is represented as a negative current. As described below, the charging current and associated variables of the BMS 10 are distinguished from the discharging current and associated variables of the BMS 10 because the BMS 10 may apply different control strategies for charging and discharging the battery 20.FIG. 7 is a graph showing the current of the battery (I). The current of the battery 20 varies over time in response to a required square wave current (S). The required square wave current S in the example of FIG. 7 includes a square wave of the required discharge current similar to that in FIG. 1 and a square wave of the required charge current. The square wave of the required current has a strength of 750 A for a duration of 60 seconds. FIG. 7 also shows a maximum discharge pulse current (M P), a maximum charge sustain current (M SSC) and a maximum charge pulse current (M PC). In the embodiment of FIG. 7, the maximum discharge pulse current M P and the maximum charge pulse current M PC are each provided for a pulse duration T P of 30 seconds. In other embodiments, the pulse durations for the maximum discharge pulse current M P and the maximum charge pulse current M PC may be different.The maximum steady-state charging current (M SSC) may be a value connected to the battery 20 stored in the BMS 10. In some embodiments, the maximum steady state charge current (M SSC) may be a value that varies with one or more of the following: state of charge (SOC) of the battery, battery temperature, battery age. Accordingly, in some embodiments, the BMS 10 may use a BMS 10 steady state charge current lookup table to determine a maximum steady state charge current value (M SSC).Similarly, the maximum charge pulse current (M PC) may be a value associated with the battery 20 stored in the BMS 10. In some embodiments, the maximum charge pulse current (M PC) may be a value that varies with one or more of the following: state of charge (SOC) of the battery, battery temperature, battery age. For example, as illustrated in FIG. 7, the maximum charge pulse current (M PC) increases when the battery 20 is discharged (i.e., when the state of charge of the battery is lowered). The maximum charging pulse current (M PC) can be provided in combination with a specific pulse duration T p via which the battery 20 can be operated with the specified maximum charging pulse current (M PC). In some embodiments, the BMS 10 may include a plurality of maximum charge pulse streams (M PC) each maximum charge pulse stream (M PC) having a respective pulse duration T p the pulse durations being of different lengths (with different respective M PC). Accordingly, in some embodiments, the BMS 10 may use a charge pulse lookup table of the BMS 10 to determine a value for the maximum charge pulse current (M PC) and an associated duration of the pulse T p.It should be appreciated that the steady state maximum charging current levels (M SSC) and the maximum charge pulse current limits (M PC), indicated in the associated look-up tables, may be provided by a battery manufacturer for the battery to be used with the BMS 10.As can be seen from FIG. 7, the current intensity S when charging the battery 20 is greater than the maximum stationary charging current M SS and is also greater than the maximum charging pulse current (M PC). Because the demanded current S is demanded for a longer duration than the set maximum charge pulse current duration T P the BMS 10 is configured to determine how long the battery 20 can be operated with a charging current above the maximum charge duration current M SSC and at what charging current level. As can be seen from FIG. 7, the BMS 10 first allows the battery 20 to be charged with 100% of the maximum charge pulse current M PC. When demand continues, the BMS 10 reduces the charging current S to ensure that the total energy (i.e., thermal energy) accumulated by the battery 20 does not become too high. According to this disclosure, the BMS 10 calculates the maximum energy to be accumulated based on the maximum charge pulse current for the battery M PC.As shown in FIG. 8, the BMS 10 calculates an accumulated energy for the battery E and a maximum accumulated charge energy M EC. The accumulated energy for the battery E may be calculated based on an accumulated discharge energy for the battery E D( as discussed above) and an accumulated charge energy E C for the battery (i.e., E=E C+ E D). Therefore, the charging and discharging of the battery 20 can be taken into account in the calculation of the charging current limit (or also the above-explained discharging current limit).The maximum accumulated charge energy M EC is calculated from the maximum charge pulse current M PC and the duration of the pulse T P associated with the maximum charge pulse current M PC. Thus, the maximum accumulated charge energy M EC may be calculated in a similar manner as the maximum accumulated discharge energy M ED. discussed above. For example, a maximum accumulated charge energy M EC may be calculated as follows:In some embodiments, the maximum accumulated charge energy of the battery 20 may also account for a steady state energy loss associated with the battery 20. Therefore, in some embodiments, the maximum accumulated charge energy may be calculated based on the maximum charge pulse current, the duration of the pulse, and a steady state energy loss of the battery 20 for the duration of the pulse. In some embodiments, the steady state energy loss may be a predetermined value associated with the battery 20 or the BMS 10.In some embodiments, the steady state energy loss through the BMS 10 may be determined based on the maximum steady state charging current M SSC. For example, in the embodiment of FIGS. 7-12, it is assumed that the battery 20 can dissipate the energy resulting from the charging current at the maximum charging current M SSC for the duration of the pulse T p. Therefore, the steady-state energy loss can be calculated based on M SSC2 × T P.Thus, in the embodiment of Figures 7 to 12, the maximum accumulated charge energy can be calculated as follows:In the embodiment of Figs. 7 to 12, the accumulated energy E is calculated when the BMS 10 controls the battery 20. The BMS 10 updates the charging current to be controlled at regular time steps. Therefore, the accumulated energy E is updated at each time step (Δt). That is, the accumulated energy for the nth time step E(n) (where n is an integer) is calculated based on an accumulated discharge energy (E D( n-1)) and an accumulated charge energy (E C( n-1)) calculated for a previous time step, and the discharge / charge energy for the time step (EΔt).In the embodiment of Figures 7 to 12, the charge energy for the time step (EΔt) is calculated based on the squared (charge) current currently being output from the battery (I) and the duration of the time step Δt. For example, time step Δt in the embodiment of Figures 7 to 12 may have a duration of 0.1 seconds. The accumulated energy may be calculated as follows:In some embodiments, the accumulated energy E(n) is calculated based on the discharge / charge energy, the accumulated energy for the previous time step, and a steady-state energy loss of the battery 20 for the time step. By considering the steady state energy loss, in some cases, the accumulated energy E(n) may decrease between time steps.For example, in the embodiment of FIGS. 7 to 12, the steady-state energy loss of the battery 20 for the time step may be calculated based on a maximum discharge continuous current of the battery M SS or a maximum charge continuous current of the battery M SSC depending on whether the battery 20 is being discharged or charged. When the battery 20 is charged, the steady-state energy loss may be calculated as M SSC2 × Δt.As can be seen from FIG. 8, the accumulated energy E increases as the battery 20 is charged and as the battery 20 is discharged. When the current I of the battery 20 falls below the threshold values defined by the maximum discharge period current M SS and the maximum charge period current M SSC the accumulated energy decreases because the battery 20 outputs the accumulated energy. As can be seen from FIGS. 7 and 8, as the accumulated energy E increases, the BMS 10 starts to limit the output current I of the battery 20. The process by which this control is implemented is discussed further below.FIGS. 9 and 10 show plots of battery current I and charging current limit (L C) versus time following the same time axis as FIGS. 7 and 8, Charging current limit L C may be calculated based on a ratio of accumulated charge energy E C to maximum accumulated charge energy M EC. In the embodiment of FIGS. 7 to 12, the charging current limit L C can also take into account an accumulated discharge energy E D. Thus, in the embodiment of Figs. 7 to 12, the accumulated energy E is used in place of the accumulated charge energy E C. The BMS 10 also ensures that the charge current limit L C does not exceed the maximum charge pulse current specified by the BMS 10 / battery manufacturer.The ratio of the accumulated charge energy E C to the maximum accumulated charge energy M EC( i.e., E C / M EC) or the ratio of the accumulated energy E to the maximum accumulated charge energy M EC( i.e., E / M EC) may be used as an indication of the remaining energy that can be accumulated by the battery 20 without excessive heat generation. Thus, in some embodiments, the ratio (E C / M EC or E / M EC) may be used to scale the maximum charge pulse current M PC to calculate a discharge current limit L C.In some embodiments, the ratio ( EC / M EC or E / M EC) is used to scale the difference between the maximum charge pulse current M PC and the maximum discharge duration current M SSC. Therefore, in some embodiments, the charge current limit L C may be calculated as follows:Thus, when the accumulated charge energy E C increases from zero, the charge current limit L C decreases from the maximum charge pulse current M PC toward the maximum continuous charge current M SSC.Similar to the embodiments of FIGS. 1-6, the embodiment of FIGS. 7-12 may use a arbitration strategy lookup table to determine a current weight (or a charge current weight) used to scale the maximum charge pulse current M PC.The arbitration strategy lookup table may output a charge current weight Wcbased on the ratio of the accumulated energy to the maximum accumulated charge energy E / M EC. In some embodiments, this may include using an arbitration strategy parameter k C. In some embodiments, different arbitration strategy parameters k D, k C may be used for the calculation of discharge current limits, or the same arbitration strategy may be followed for both charging and discharging.In some embodiments, an arbitration strategy parameter (k) may also be input to the arbitration strategy lookup table in combination with the ratio E / M EC to determine an arbitration strategy for the charge current weight Wc.In the embodiment of Figures 7 to 12, the charge current weight Wc is used to scale the difference between the maximum charge pulse current M PC and the maximum charge sustain current M SS. Therefore, in some embodiments, the charge current limit L C may be calculated as follows:FIG. 12 is a graph of the charge current weight Wc and the discharge current weight W D, which may be output from the arbitration strategy lookup table, based on the ratio of the accumulated energy to the maximum accumulated charge energy (E / M EC) and the ratio of the accumulated energy to the maximum accumulated discharge energy (E / M ED). respectively. As can be seen from FIG. 12, the ratios E / M EC and E / M ED during the charge and discharge pulse currents are different due to the different values for M P and M PC.As shown in FIG. 11, the BMS 10 is configured to control the charging current of the battery 20 so that the battery current I does not exceed the charging current limit L C and the discharging current limit L D. Thus, as shown in FIG. 11, the BMS 10 reduces the current corresponding to the charging current limit L C and the discharging current limit L D, which are calculated according to the above-described embodiments.It will be appreciated that although the above description focuses on the calculation of a charging current limit, the ratio E / M EC( or E C / M EC) may be used to calculate a charging voltage limit for the battery 20. Therefore, a charge voltage limit may be calculated based on the ratio E / M EC and a maximum charge pulse voltage associated with the maximum charge pulse current M P. The maximum charge pulse voltage may be provided by a battery manufacturer and stored in an appropriate look-up table of the BMS 10.FIG. 14 shows a block diagram of a method 100 for controlling a discharge current of a battery 20 according to an embodiment of the disclosure. The method may be performed by the BMS 10 described above.In step 101 of the method, the BMS 10 calculates a discharge energy of the battery 20 for a time step based on the discharge current and a duration of the time step.In step 102 of the method, the BMS 10 calculates an accumulated discharge energy of the battery 20 based on an accumulated discharge energy calculated for a previous time step and the discharge energy for the time step.In step 103 of the method, the BMS 10 determines a maximum discharge pulse current for a pulse having a duration based on a discharge pulse current lookup table of the BMS 10.In step 104 of the method, the BMS 10 calculates a maximum accumulated discharge energy of the battery 20 based on the maximum discharge pulse current and the duration of the pulse.In step 105 of the method, the BMS 10 calculates a discharge current limit based on a ratio of the accumulated discharge energy to the maximum accumulated discharge energy. The discharge current limit does not exceed the maximum discharge pulse current.In step 106 of the method, the BMS 10 controls the discharge current of the battery 20 such that the discharge current does not exceed the discharge current limit.It should be appreciated that the method 100 may include additional steps / features in accordance with the above-described embodiments of the BMS 10.FIG. 15 shows a block diagram of a method 200 for controlling a charging current of a battery 20 according to an embodiment of the disclosure. The method may be performed with the BMS 10 10 described above.In step 201 of the method, the BMS 10 calculates a charge energy of the battery 20 for a time step based on the charge current and a duration of the time step.In step 202 of the method, the BMS 10 calculates an accumulated charge energy of the battery 20 based on an accumulated charge energy calculated for a previous time step and the charge energy for the time step.In step 203 of the method, the BMS 10 determines a maximum charge pulse current for a pulse having a duration based on a charge pulse current lookup table of the BMS 10.In step 204 of the method, the BMS 10 calculates a maximum accumulated charge energy of the battery 20 based on the maximum charge pulse current and the duration of the pulse.In step 205 of the method, the BMS 10 calculates a charge current limit based on a ratio of the accumulated charge energy to the maximum accumulated charge energy. The charging current limit does not exceed the maximum charging current.In step 206 of the method, the BMS 10 controls the charging current of the battery 20 such that the charging current does not exceed the charging current limit.It should be appreciated that the method 200 may include additional steps / features in accordance with the above-described embodiments of the BMS 10.Industrial applicabilityAccording to this disclosure, a battery management system (BMS 10) is provided. The BMS 10 is configured to control the discharge current of a battery 20. According to the embodiment, the battery 20 may be a rechargeable battery. The battery 20 and the BMS 10 may be provided as part of an engine 30, for example an electric machine.The BMS 10, in accordance with this disclosure, determines a safe operating limit for a battery 20 for impulse currents (discharge or charge) of longer duration than indicated in the look-up tables provided by a battery manufacturer. The BMS 10 of the first aspect calculates a discharge current limit and / or a charge current limit by comparing the energy accumulated by the discharge of the battery 20 with a maximum accumulated energy. The maximum accumulated energy is calculated from a maximum pulse discharge current provided from a look-up table of the BMS 10. The difference between the accumulated discharge energy and the maximum accumulated energy defines the amount of remaining energy that the battery 20 can safely accumulate. Based on said energy difference, the BMS 10 may determine a discharge current limit or a charge current limit at which the battery 20 may continue to be operated. Indeed, the BMS 10 may allow the battery 20 to safely operate at currents (charging or discharging current) that are higher than a certain maximum steady-state current for longer periods of time (i.e., for a period longer than the duration of a pulse).In some embodiments, the BMS 10 may also mediate between a maximum charge / discharge pulse current and a maximum charge / discharge sustained current using a arbitration strategy lookup table. In such embodiments, the tracked arbitration strategy may be selected / modified to provide different power output profiles, where different power output profiles may be tailored to the different tasks to be performed by the engine 30.

Claims

A battery management system (BMS) configured to control a discharge current of a battery, the BMS configured to: calculate a discharge energy of the battery for a time step based on the discharge current and a duration of the time step; calculate an accumulated discharge energy of the battery based on an accumulated discharge energy calculated for a previous time step and the discharge energy for the time step; determine a maximum discharge pulse current for a pulse having a duration based on a discharge pulse current lookup table of the BMS; calculate a maximum accumulated discharge energy of the battery based on the maximum discharge pulse current and the duration of the pulse; calculating a discharge current limit based on a ratio of the accumulated discharge energy to the maximum accumulated discharge energy, the discharge current limit not exceeding the maximum discharge pulse current; and controlling the discharge current of the battery so that the discharge current does not exceed the discharge current limit.The BMS of claim 1, wherein the discharge energy is calculated based on the squared discharge current and the duration of the time step.The BMS according to claim 1 or claim 2, wherein the accumulated discharge energy is calculated based on the discharge energy, the accumulated discharge energy for the previous time step, and a stationary energy loss of the battery for the time step; and the maximum accumulated discharge energy of the battery is calculated based on the maximum discharge pulse current, the duration of the pulse, and a stationary energy loss of the battery for the duration of the pulse.The BMS of claim 3, wherein the steady state energy loss of the battery for the time step and / or duration of the pulse is calculated based on a maximum discharge duration current of the battery, optionally wherein the maximum discharge duration current for the battery is determined based on a discharge pulse current lookup table of the BMS.The BMS of any of claims 1 to 4, wherein the discharge current limit is calculated based on the ratio of the maximum accumulated discharge energy to the accumulated discharge energy and a difference between the maximum discharge pulse current and a maximum discharge duration current of the battery, optionally wherein the maximum discharge duration current for the battery is determined based on a discharge pulse current lookup table of the BMS.The BMS according to any one of claims 1 to 5, wherein the calculation of the discharge current limit based on the ratio of the accumulated discharge energy to the maximum accumulated discharge energy comprises: inputting the ratio of the accumulated discharge energy to the maximum accumulated discharge energy into an arbitration strategy lookup table to obtain a discharge current magnitude weight; and calculating the discharge current limit based on the discharge current magnitude weight and the maximum discharge pulse current.The BMS of claim 6, wherein an arbitration strategy parameter in combination with the ratio of the accumulated discharge energy to the maximum accumulated discharge energy is input to the arbitration strategy lookup table to determine an arbitration strategy for the discharge current magnitude weight.A battery management system (BMS) configured to control a charging current of a battery, the BMS configured to: calculate a charging energy of the battery for a time step based on the charging current of the battery and a duration of the time step; calculate an accumulated charging energy of the battery based on an accumulated charging energy calculated for a previous time step and the charging energy for the time step; determine a maximum charging pulse current for a pulse having a duration based on a charging pulse current lookup table of the BMS; calculate a maximum accumulated charging energy based on the maximum charging pulse current and the duration of the pulse; calculating a charge current limit based on a ratio of the accumulated charge energy to the maximum accumulated charge energy, wherein the charge current limit does not exceed the maximum charge pulse current; and controlling the charge current of the battery such that the charge current does not exceed the charge current limit.The BMS of claim 8, wherein the charge energy is calculated based on the squared charge current and the duration of the time step.The BMS of claim 8 or claim 9, wherein the accumulated charge energy is calculated based on the charge energy, the accumulated charge energy for the previous time step, and a stationary energy loss of the battery for the time step; and the maximum accumulated charge energy of the battery is calculated based on the maximum discharge pulse current, the duration of the pulse, and a stationary energy loss of the battery for the duration of the pulse.The BMS of claim 10, wherein the battery steady state energy loss for the time step and / or duration of the pulse is calculated based on a maximum battery steady state charge current, optionally wherein the maximum battery steady state charge current is determined based on a BMS steady state charge current lookup table.The BMS of any of claims 8 to 11, wherein the charge current limit is calculated based on the ratio of the maximum accumulated charge energy to the accumulated charge energy and the difference between the maximum charge pulse current and a maximum charge sustain current of the battery, optionally wherein the maximum charge sustain current for the battery is determined based on a look-up table for the charge sustain current of the BMS.The BMS of any of claims 8 to 12, wherein calculating the charge current limit based on the ratio of the accumulated charge energy to the maximum accumulated charge energy comprises: inputting the ratio of the accumulated charge energy to the maximum accumulated charge energy into a arbitration strategy lookup table to obtain a charge current weight; and calculating the charge current limit based on the charge current weight and the maximum charge pulse current.The BMS of claim 13, wherein a parameter of the charge arbitration strategy in combination with the ratio of the accumulated charge energy to the maximum accumulated charge energy is input to the arbitration strategy lookup table to determine an arbitration strategy for the charge current weight.The BMS of any one of claims 1 to 7, wherein the BMS is further configured to: calculate a discharge voltage limit based on a ratio of the maximum accumulated discharge energy to the accumulated discharge energy, wherein the discharge voltage limit does not exceed a maximum discharge pulse voltage; and / or a BMS of any one of claims 8 to 14, wherein the BMS is further configured to: calculate a charge voltage limit based on a ratio of the maximum accumulated charge energy to the accumulated charge energy, wherein the charge voltage limit does not exceed a maximum charge pulse voltage.A machine comprising a battery; a BMS according to any one of claims 1 to 7; and / or a BMS according to any one of claims 8 to 15.A method of controlling a discharge current of a battery, comprising: calculating a discharge energy of the battery for a time step based on the discharge current and a duration of the time step; calculating an accumulated discharge energy of the battery based on an accumulated discharge energy calculated for a previous time step and the discharge energy for the time step; determining a maximum discharge pulse current for a pulse having a duration based on a discharge pulse current lookup table of the BMS; calculating a maximum accumulated discharge energy of the battery based on the maximum discharge pulse current and the duration of the pulse; calculating a discharge current limit based on a ratio of the accumulated discharge energy to the maximum accumulated discharge energy, wherein the discharge current limit does not exceed the maximum discharge pulse current; and controlling the discharge current of the battery so that the discharge current does not exceed the discharge current limit.A method of controlling a charging current of a battery, comprising: calculating a charging energy of the battery for a time step based on the charging current of the battery and a duration of the time step; calculating an accumulated charging energy of the battery based on an accumulated charging energy calculated for a previous time step and the charging energy for the time step; determining a maximum charging pulse current for a pulse having a duration based on a charging pulse current lookup table of the BMS; calculating a maximum accumulated charging energy based on the maximum charging pulse current and the duration of the pulse; calculating a charging current limit based on a ratio of the accumulated charging energy to the maximum accumulated charging energy, wherein the charging current limit does not exceed the maximum charging pulse current; and controlling the charging current of the battery so that the charging current does not exceed the charging current limit.

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