BATTERY MANAGEMENT SYSTEM

Field Of The Disclosure

The present disclosure relates to batteries. In particular, the present disclosure relates to batteries for electric work vehicles and the like.

Background

A rechargeable battery (for example a cell or a battery pack) generates heat as it is charged or discharged. As such, the flow of energy from/to the battery causes the battery to heat up due to the inherent resistances of the battery.

In order to prevent overheating of the battery, a Battery Management System (“BMS”) can be provided to control the power input/output of the battery to a level of heating which can be safely dissipated by the battery.

Typically, a battery manufacturer will specify a safe operating limit for continuous power flow from/to the battery. Additionally, a battery manufacturer may specify a pulsed power limit, where a higher amount of power may be output/input to the battery over a specified time period.

Against this background, the present disclosure aims to provide an improved, or at least commercially relevant alternative, battery management system.

Summary

According to a first aspect of the disclosure, a battery management system 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 timestep based on the discharge current and the duration of the timestep; calculate an accumulated discharge energy of the battery based on an accumulated discharge energy calculated for a preceding timestep and the discharge energy for the timestep; determine a maximum discharge pulse current for a pulse having a duration based on a discharge pulse current look-up 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; calculate 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 control the discharge current of the battery such that the discharge current does not exceed the discharge current limit.

The present inventors have realised that the maximum discharge current values provided by look-up tables from battery manufacturers provide a restrictive way of operating a battery. For example, a battery manufacturer may specify a value for a maximum pulse discharge current (where a pulse is typically of a relatively short duration, for example 2 seconds or 30 seconds), and a separate value for a maximum discharge steady state current (i.e. a safe operating limit for steady state current discharge). While the maximum discharge pulse current may be higher than the maximum discharge steady state current, the increased current is only suitable for operation for the specified duration of the current pulse (e.g. 2 or 30 seconds according to the specified pulse duration). In some cases, a battery manufacturer specifies different maximum discharge pulse currents for pulses of different durations (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 can be challenging to determine a suitable operating current for pulses of an intermediate duration (e.g. operating with a 15 second current pulse), or a suitable operating duration for a current of an intermediate magnitude (i.e. a current between the maximum discharge pulse current and the maximum discharge steady state current). According to the first aspect, a BMS is provided which can determine a safe operating limit for a battery for pulse currents of longer durations than specified in the look-up tables provided by a battery manufacturer. The BMS of the first aspect calculates a discharge current limit by comparing the energy accumulated by discharging the battery to a maximum accumulated energy. The maximum accumulated discharge energy is calculated from a maximum discharge pulse current provided by a look-up table of the BMS. The difference between the accumulated discharge energy and the maximum accumulated discharge energy defines the remaining amount of energy the battery can safely accumulate. Based on the said energy difference, the BMS can determine a discharge current limit that the battery can continue to operate at. In effect, the BMS can allow the battery to safely operate at discharge currents higher than a maximum steady state discharge current for a duration which is longer than the duration of the pulse associated with the maximum discharge pulse current.

According to a second aspect of the disclosure, a Battery Management System (BMS) configured to control a charge current of a battery is provided. The BMS is configured to: calculate a charge energy of the battery for a timestep based on the charge current of the battery and the duration of the timestep; calculate an accumulated charge energy of the battery based on an accumulated charge energy calculated for a preceding timestep and the charge energy for the timestep; determine a maximum charge pulse current for a pulse having a duration based on a charge pulse current look-up table of the BMS; calculate a maximum accumulated charge energy based on the maximum charge pulse current and the duration of the pulse; calculate 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 control the charge current of the battery such that the charge current does not exceed the charge current limit.

Accordingly, it will be appreciated that a BMS may be provided to control a charge current of the battery. The BMS may control the charge current by comparing the accumulated charge energy to the maximum accumulated charge energy. Thus, the BMS may control the charge current following a similar strategy to the BMS of the first aspect.

According to a third aspect of the disclosure, a machine is provided. The machine may comprise 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, a method of controlling a discharge current of a battery is provided. The method comprises: calculating a discharge energy of the battery for a timestep based on the discharge current and the duration of the timestep; calculating an accumulated discharge energy of the battery based on an accumulated discharge energy calculated for a preceding timestep and the discharge energy for the timestep; determining a maximum discharge pulse current for a pulse having a duration based on a discharge pulse current look-up 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 such that the discharge current does not exceed the discharge current limit. It will be appreciated 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 charge current of a battery is provided. The method comprises: calculating a charge energy of the battery for a timestep based on the charge current of the battery and the duration of the timestep; calculating an accumulated charge energy of the battery based on an accumulated charge energy calculated for a preceding timestep and the charge energy for the timestep; determining a maximum charge pulse current for a pulse having a duration based on a charge pulse current look-up 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, 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.

It will be appreciated 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 Figures

An embodiment of the disclosure will now be described with reference to the following non-limiting figures in which:

Fig. 1 shows a graph of a discharge current controlled by a BMS according to this disclosure;

Fig. 2 shows a graph of an accumulated discharge energy and a maximum accumulated discharge energy calculated by the BMS according to this disclosure; Fig. 3 shows a graph of 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 graph of a discharge current controlled by a BMS according to this disclosure;

Fig. 7 shows a graph of a battery current controlled by a BMS according to this disclosure;

Fig. 8 shows a graph of an accumulated energy and a maximum accumulated charge energy calculated by the BMS according to this disclosure;

Fig. 9 shows a graph of a battery current controlled by a BMS according to this disclosure;

Fig. 10 shows a graph of a charge current limit calculated by the BMS according to this disclosure

Fig. 11 shows a graph of a battery current controlled by a BMS according to this disclosure;

Fig. 12 shows a graph of a charge current weight and a discharge current weight calculated by the BMS according to this disclosure;

Figs 13a, 13b and 13c shows graphs of different arbitration strategies for the BMS;

Fig. 14 shows a block diagram of a method of controlling a discharge current of a battery according to an embodiment of the disclosure;

Fig. 15 shows a block diagram of a method of controlling a charge current of a battery according to an embodiment of the disclosure; and

Fig. 16 shows a block diagram of a BMS connected to a battery according to this disclosure. Detailed

According to an embodiment of the disclosure, a battery management system (BMS) 10 is provided. The BMS 10 is configured to control a discharge current of a battery 20. A block diagram of the BMS 10 and 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, a machine 30, for example an electric work machine.

The BMS 10 may comprise various sensors (e.g. current sensors, voltage sensors, temperature sensors) in order 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 comprise a processor, controller or the like configured to control the power output of the battery 20. In order to control the power output of the battery 20, the BMS 10 may also comprise suitable circuitry (e.g. transistors, resistors and the like) configured to control the power output of the battery 20 in response to the power demands of an external load (e.g. power demands from a machine connected to the BMS 10 and 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 to 6 which shows various graphs of different variables of the BMS 10 and the battery 20 over time. In the graphs of Figs. 1 to 6, a current which charges the battery 20 (a charge current) is shown as positive current, while a current which discharges the battery 20 (a discharge current) is shown as a negative current.

Fig. 1 shows a graph of the discharge current of the battery 20 (D). The discharge current of the battery 20 varies over time in response to a square wave demanded current (S). The square wave demanded discharge current in the example of Fig. 1 is 3500 A for a duration of 60 seconds. Fig. 1 also shows a maximum discharge steady state current (Mss) and a maximum discharge pulse current (Mp). In the embodiment of Fig. 1, the maximum discharge pulse current Mp is provided for a pulse duration of 30 seconds. The maximum discharge steady state current (Mss) may be a value associated with the battery 20 which is stored in the BMS 10. In some embodiments, the maximum discharge steady state current (Mss) may be a value which varies with one or more of: State of Charge (SOC) of the battery, battery temperature, battery age. Accordingly, in some embodiments, the BMS 10 may use a discharge steady state look-up table of the BMS 10 to determine a value for the maximum discharge steady state current (Mss).

Similarly, the maximum discharge pulse current (Mp) may be a value associated with the battery 20 which is stored in the BMS 10. In some embodiments, the maximum discharge pulse current (Mp) may be a value which varies with one or more of: State of Charge (SOC) of the battery, battery temperature, battery age. The maximum discharge pulse current (Mp) may be provided in combination with a specified pulse duration T _p over which the battery 20 may be operated at the specified maximum discharge pulse current (Mp). In some embodiments, the BMS 10 may comprise a plurality of maximum discharge pulse currents (Mp), each maximum discharge pulse current (Mp) having an associated pulse duration T _p , where the pulse durations are of different lengths (with different associated M _p ). Accordingly, in some embodiments, the BMS 10 may use a discharge pulse look-up table of the BMS 10 to determine a value for the maximum discharge pulse current (Mp) and an associated duration of the pulse T _p .

It will be appreciated that the maximum discharge steady state currents (Mss) and the maximum discharge pulse currents (Mp) provided in the associated look-up tables may be provided by a battery manufacturer for the battery 20 to be used with the BMS 10.

As will be appreciated from Fig. 1, the demanded current S is greater than the maximum discharge steady state current Mss, but less than the maximum discharge pulse current (Mp). As the demanded current S is demanded for a longer duration than the specified length of the maximum discharge pulse current, the BMS 10 is configured to determine for how long the battery 20 can operate at a discharge current above the maximum discharge steady state Mss and at what discharge current magnitude. As will be appreciated from Fig. 1, initially the BMS 10 allows the battery 20 to discharge 100% of the demanded current. As the demand continues, the BMS 10 reduces the discharge current to ensure that the total energy accumulated by the battery 20 (i.e. heat energy) does not become excessive. According to this disclosure, the BMS 10 calculates the maximum energy to be accumulated based on the maximum discharge pulse current for the battery Mp.

As shown in Fig. 2, the BMS 10 calculates an accumulated discharge energy for the battery ED and a maximum accumulated discharge energy MED.

The maximum accumulated discharge energy MED is calculated for the maximum discharge pulse current Mp and the duration of the pulse associated with the maximum discharge pulse current Mp. According to this embodiment, it is assumed that the maximum energy the battery 20 can accumulate is defined by the battery 20 discharging the maximum discharge pulse current Mp for the specified duration of the pulse Tp. As such, a maximum accumulated discharge energy MED may be calculated according to:

MED = Mp ² x Tp

In some embodiments, the maximum accumulated discharge energy of the battery 20 may also take into account a steady-state energy loss associated with the battery 20. As such, 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 steadystate energy loss may be a predetermined value associated with the battery 20 or the BMS 10.

In some embodiments, the steady state energy loss may be determined by the BMS 10 based on the maximum discharge steady state current Mss. For example, in the embodiment of Figs 1 to 6 it is assumed that the battery 20 can dissipate energy resulting from discharging current at the maximum discharge steady state current Mss for the duration of the pulse T _p . As such, the steady state energy loss may be calculated based on Mss ² x Tp.

Thus, in the embodiment of Figs. 1 to 6, the maximum accumulated discharge energy may be calculated as:

MED = ( MP ² x T _P ) - ( Mss ² x T _P )

In the embodiment of Figs. 1 to 6, the accumulated discharge energy ED is calculated as the BMS 10 controls the battery 20. The BMS 10 updates the discharge current to be controlled at regular timesteps. As such, the accumulated discharge energy ED is updated each timestep (At). So, the accumulated discharge energy for the //th timestep Eo(n) (where n is an integer) is calculated based on an accumulated discharge energy calculated for a preceding timestep (Eo(n-l)) and the discharge energy for the timestep (EAI).

In the embodiment of Figs. 1 to 6, the discharge energy for the timestep (EAI) is calculated based on the squared discharge current currently being output by the battery 20 (D) and the duration of the timestep At. For example, in the embodiment of Figs. 1 to 4, the timestep At may have a duration of 0.1 second. As such, the accumulated discharge energy may be calculated as:

Eo(n) = (Eo(n-l)) + EAI

In some embodiments, the accumulated discharge energy Eo(n) is calculated based on the discharge energy, the accumulated discharge energy for the preceding timestep, and a steady-state energy loss of the battery 20 for the timestep. By taking into account the steady state energy loss, in some cases the accumulated discharge energy Eo(n) may decrease between timesteps.

For example, in the embodiment of Figs. 1 to 6, the steady state energy loss of the battery 20 for the timestep is calculated based on a maximum discharge steady state current of the battery Mss. As such, the steady state energy loss may be calculated as Mss ² x At.

Accordingly, in the embodiments of Figs. 1 to 6, the accumulated discharge energy may be calculated as:

Eo(n) = (Eo(n-l)) + ( D ² x At ) - ( Mss ² x At.) As will be appreciated from Fig. 2, the accumulated discharge energy ED increases while the discharge current (D) is output from the battery 20. When the discharge current drops below the maximum steady state discharge current, the accumulated discharge energy decreases as the battery 20 dissipates the accumulated energy. As will be appreciated from Figs. 1 and 2, as the accumulated discharge energy ED increases, the BMS 10 begins to limit the discharge current output by the battery 20. The process by which this control is implemented is discussed further below.

Fig. 3 is a graph showing the variation of accumulated discharge energy ED and the maximum accumulated discharge energy over time (also shown in Fig. 2). Fig. 4 shows a graph of the discharge current limit (LD) against time, following the same time axis as Figs 1 to 3. The discharge current limit LD is calculated based on a ratio of the maximum accumulated discharge energy MED to the accumulated discharge energy ED. The BMS 10 also ensures that the discharge current limit LD 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 ED to the maximum accumulated discharge energy MED (i.e. ED / MED) may be used as an indication of the remaining energy that may be accumulated by the battery 20 without causing excessive heat build-up (i.e. 1- ED / MED). Thus, in some embodiments, the ratio ED / MED may be used to scale the maximum discharge pulse current Mp in order to calculate a discharge current limit LD.

In some embodiments, the ratio ED / MED is used to scale the difference between the maximum discharge pulse current Mp and the maximum discharge steady state current Mss. In some embodiments, the BMS 10 may ensure that that the magnitude of the discharge current limit is not reduced below the magnitude of the maximum discharge steady state current Mss. As such, in some embodiments, the discharge current limit LD may be calculated as:

LD = (1 - ED / MED ) x ( Mp - Mss ) + Mss Thus, as the accumulated discharge energy ED increases from zero, the discharge current limit LD decreases from the maximum discharge pulse current Mp towards the maximum discharge steady state current Mss.

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 discharge steady state current Mss. For example, in some embodiments, it may be desirable for the BMS 10 to smoothly vary the discharge current limit from the maximum discharge pulse current Mp down to the maximum discharge steady state current Mss. As such, the BMS 10 may favour reducing the instantaneously demanded current in order to maintain the ability to continue providing current at a level above Mss for an extended period of time. In the example of a BMS 10 attached to an electric work vehicle, a smooth variation may be desirable when the battery 20 is being used to perform a driving operation of the vehicle. That is to say, sudden drop outs in acceleration due to the maximum accumulated discharge energy MED being reached may provide a “jerky” operating experience for a user. In other embodiments, it may be desirable for the BMS 10 to favour increasing instantaneous power output. Such a strategy may subsequently require sharp decreases in the discharge current limit in order to avoid breaching the maximum accumulated discharge energy MED. In effect, the BMS 10 may provide a means of arbitrating between one or more of the maximum discharge pulse limits Mp and the maximum discharge steady state current Mss. The arbitration strategy followed can be selected/modified to provide different power output profiles, wherein different power output profiles may be tailored to the various tasks to be performed by the machine.

As such, in some embodiments, the discharge current limit may be calculated based on the maximum discharge pulse current Mp and a discharge current weight W. The discharge current weight may be provided by an arbitration strategy lookup table.

The arbitration strategy lookup table may output a discharge current weight WD based on the ratio of the accumulated discharge energy to the maximum accumulated discharge energy ED / MED. In some embodiments, an arbitration strategy parameter (K) may also be input to the arbitration strategy lookup table in combination with the ratio ED / MED in order to determine an arbitration strategy for the discharge current weight WD.

In some embodiments, the arbitration strategy may govern how the BMS 10 ramps the discharge current down from the maximum discharge pulse current Mp (for no accumulated discharge energy) to the maximum discharge steady state current Mss (where ED = MED).

In one possible strategy favouring instantaneous output power, the BMS 10 may provide that for an accumulated discharge energy less than the maximum accumulated discharge energy, the discharge current limit is equal to the maximum discharge pulse current (i.e. where i.e. ED < MED; LD = Mp). When the accumulated discharge energy is equal to the maximum accumulated discharge energy the BMS 10 enacts a step change in the discharge current limit to the maximum discharge steady state current Mss (i.e. where ED = MED; LD = Mss). Such an arbitration strategy may allow the battery 20 to deliver a discharge current above the maximum discharge steady state current for as long as possible. Once the discharge energy accumulated reaches the maximum MED, the arbitration strategy then enacts a step change in the discharge current limit. An example of such a relationship between ED/MED and the discharge current weight WD is shown in Fig. 13a. Such a step change in discharge current may not be suitable for some applications, and so it may be desirable to provide other arbitration strategies which provide a smoother transition (or ramp) between the maximum discharge pulse current and the maximum discharge steady state current.

For example, in another possible strategy favouring smooth variation in discharge current, the discharge current weight WD may track the variation in ED/MED. An example of such a relationship is shown in Fig. 13b. In contrast to the strategy of Fig. 13a, the arbitration strategy of Fig. 13b reduces the discharge current limit LD from the maximum discharge pule current as soon as the battery 20 starts to accumulate energy. This provides for a smoother transition to steady state discharge currents, but may limit the power output by the battery 20 in cases where the demanded power falls away before the maximum accumulated discharge energy is reached.

A further possible arbitration strategy is shown in Fig. 13c, in which the break point at which the discharge current weight WD is decreased from 1 towards zero changes. It will be appreciated that in the strategy of Fig. 13a, the break point at which the discharge current weight decreases towards zero is at ED/MED = 1 (a step change). In the strategy of Fig. 13b, the break point is at ED/MED = 0. In the embodiment of Fig. 13c, the break point is at ED/MED = 0.5. In each case, the discharge current weight WD is scaled linearly from WD = 1 at the break point to WD = 0 at ED/MED = 1.

In some embodiments, an arbitration strategy parameter ko may be used to select the breakpoint at which discharge current weight WD is scaled towards zero. As such, in some embodiments, an arbitration strategy may be:

For ED/MED < ko ; WD = 1; and

For ED/MED > k _D ; WD = (1 - ED/MED) / (1 - ko).

In some embodiments, an arbitration strategy lookup table may be generated based on the above relationship, wherein the arbitration strategy lookup table generates a discharge current weight WD based on ko and ED/MED. It should be noted that in the examples of Figs. 13a to 13c, a linear relationship is used to scale the discharge current weight between the breakpoint k and ED/MED = 1. In other embodiments, a different relationship may be used to scale WD, for example a polynomial or other non-linear function.

In the embodiment of Figs. 1 to 6, the discharge current weight WD is used to scale the difference between the maximum discharge pulse current Mp and the maximum discharge steady state current Mss. As such, in some embodiments, the discharge current limit LD may be calculated as:

LD = WD x ( Mp - Mss ) + Mss

Fig. 4 shows a graph of the discharge current limit LD which reduces from the maximum discharge pulse current Mp as the accumulated discharge energy increases (as shown in Fig. 3). The BMS 10 is configured to control the discharge current of the battery 20 such that the discharge current D does not exceed the discharge current limit LD. Thus, as shown in Figs. 5 and 6, as the discharge current limit LD falls below the demanded current S (see Fig. 1), the BMS 10 limits the discharge current D in line with the discharge current limit LD. Once the discharge current reduces below the maximum discharge steady state current Mss, the discharge current limit LD starts to increase, as shown in Fig. 5.

It will be appreciated that the while the above description focuses on the calculation of a discharge current limit, the ratio ED / MED may also be used to calculate a discharge voltage limit for the battery 20. As such, a voltage limit may be calculated based on the ratio ED / MED and a maximum discharge pulse voltage which is associated with the maximum discharge pulse current Mp. The maximum discharge pulse voltage may be provided by a battery manufacturer and stored in a suitable lookup table of the BMS 10.

The BMS 10 according to this disclosure may also be used to control a charge current of the battery 20. In some embodiments, the BMS 10 may be used to control a charge current and a discharge current of the battery 20. That is to say, the BMS 10 may control the current input to and output from the battery 20. A method of controlling a charge current and a discharge current of the battery 20 with the BMS 10 will now be described with reference to Figs. 7 to 12 which shows various graphs of different variables of the BMS 10 and the battery 20 over time. In the graphs of Figs. 7 to 12, a current which charges the battery 20 (a charge current) is shown as positive current, while a current which discharges the battery 20 (a discharge current) is shown as a negative current. According to the following description, the charge current and associated variables of the BMS 10 are distinguished from the discharge current and associated variables of the BMS 10, as the BMS 10 may apply different control strategies for charging and discharging of the battery 20.

Fig. 7 shows a graph of the current of the battery (I). The current of the battery 20 varies over time in response to a square wave demanded current (S). The square wave demanded current S in the example of Fig. 7 includes a square wave of demanded discharge current similar to that of Fig. 1, and a square wave of demanded charge current. The square wave of demanded current has a magnitude of 750 A for a duration of 60 seconds. Fig. 7 also shows, a maximum discharge pulse current (Mp), a maximum charge steady state current (Mssc), and a maximum charge pulse current (MPC). In the embodiment of Fig. 7, the maximum discharge pulse current Mp and the maximum charge pulse current MPC are each provided for a pulse duration Tp of 30 seconds. In other embodiments, the pulse durations for the maximum discharge pulse current Mp and the maximum charge pulse current MPC may be different.

The maximum charge steady state current (Mssc) may be a value associated with the battery 20 which is stored in the BMS 10. In some embodiments, the maximum charge steady state current (Mssc) may be a value which varies with one or more of: State of Charge (SOC) of the battery, battery temperature, battery age. Accordingly, in some embodiments, the BMS 10 may use a charge steady state look-up table of the BMS 10 to determine a value for the maximum charge steady state current (Mssc).

Similarly, the maximum charge pulse current (MPC) may be a value associated with the battery 20 which is stored in the BMS 10. In some embodiments, the maximum charge pulse current (MPC) may be a value which varies with one or more of: State of Charge (SOC) of the battery, battery temperature, battery age. For example, as shown in Fig. 7, the maximum charge pulse current (MPC) increases as the battery 20 is discharged (i.e. as the SOC of the battery is reduced). The maximum charge pulse current MPC) may be provided in combination with a specified pulse duration T _p over which the battery 20 may be operated with the specified maximum charge pulse current (MPC). In some embodiments, the BMS 10 may comprise a plurality of maximum charge pulse current (MPC), each maximum charge pulse current (MPC) having an associated pulse duration T _p , where the pulse durations are of different lengths (with different associated MPC). Accordingly, in some embodiments, the BMS 10 may use a charge pulse look-up table of the BMS 10 to determine a value for the maximum charge pulse current (MPC) and an associated duration of the pulse T _P .

It will be appreciated that the maximum charge steady state currents (Mssc) and the maximum charge pulse current limits (MPC) provided in the associated look-up tables may be provided by a battery manufacturer for the battery to be used with the BMS 10.

As will be appreciated from Fig. 7, the demanded current S when charging the battery 20 is greater than the maximum charge steady state current Mss, and also greater than the maximum charge pulse current (MPC). As the demanded current S is demanded for a longer duration than the specified duration Tp of the maximum charge pulse current, the BMS 10 is configured to determine for how long the battery 20 can operate at a charge current above the maximum charge steady state current Mssc and at what charge current magnitude. As will be appreciated from Fig. 7, initially the BMS 10 allows the battery 20 to charge at 100% of the maximum charge pulse current MPC. As the demand continues, the BMS 10 reduces the charge current S to ensure that the total energy accumulated by the battery 20 (i.e. heat energy) does not become excessive. According to this disclosure, the BMS 10 calculates the maximum energy to be accumulated based on the maximum charge pulse current for the battery MPC.

As shown in Fig. 8, the BMS 10 calculates an accumulated energy for the battery E and a maximum accumulated charge energy MEC. The accumulated energy for the battery E may be calculated based on an accumulated discharge energy for the battery ED (as discussed above) and an accumulated charge energy Ec for the battery (i.e. E = Ec + ED). AS such, the charging and discharging of the battery 20 may be taken into account when calculating the charge current limit (or indeed the discharge current limit discussed above).

The maximum accumulated charge energy MEC is calculated the maximum charge pulse current MPC and the duration of the pulse Tp associated with the maximum charge pulse current MPC. Thus, the maximum accumulated charge energy MEC may be calculated in a manner analogous to the maximum accumulated discharge energy MED discussed above. For example, a maximum accumulated charge energy MEC may be calculated according to:

MEC = MPC ² x T _p

In some embodiments, the maximum accumulated charge energy of the battery 20 may also take into account a steady-state energy loss associated with the battery 20. As such, 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 may be determined by the BMS 10 based on the maximum charge steady state current Mssc. For example, it in the embodiment of Figs. 7 to 12 it is assumed that the battery 20 can dissipate energy resulting from charging current at the maximum charge steady state current Mssc for the duration of the pulse T _p . As such, the steady state energy loss may be calculated based on Mssc ² x Tp.

Thus, in the embodiment of Figs. 7 to 12, the maximum accumulated charge energy may be calculated as:

MEC = ( MPC ² x T _p ) - ( Mssc ² x T _p )

In the embodiment of Figs. 7 to 12, the accumulated energy E is calculated as the BMS 10 controls the battery 20. The BMS 10 updates the charge current to be controlled at regular timesteps. As such, the accumulated energy E is updated each timestep (At). So, the accumulated energy for the nth timestep E(n) (where n is an integer) is calculated based on an accumulated discharge energy (Eo(n-l)) and an accumulated charge energy calculated for a preceding timestep (Ec(n-l)) and the discharge/charge energy for the timestep (EAI).

In the embodiment of Figs. 7 to 12, the charge energy for the timestep (EAI) is calculated based on the squared (charge) current currently being output by the battery (I) and the duration of the timestep At. For example, in the embodiment of Figs. 7 to 12, the timestep At may have a duration of 0.1 second. As such, the accumulated energy may be calculated as: E(n) = (E(n-l)) + E _At

In some embodiments, the accumulated energy E(n) is calculated based on the discharge/charge energy, the accumulated energy for the preceding timestep, and a steady-state energy loss of the battery 20 for the timestep. By taking into account the steady state energy loss, in some cases the accumulated energy E(n) may decrease between timesteps.

For example, in the embodiment of Figs. 7 to 12, the steady state energy loss of the battery 20 for the timestep may be calculated based on a maximum discharge steady state current of the battery Mss or a maximum charge steady state current of the battery Mssc depending on whether the battery 20 is discharging or charging respectively. When the battery 20 is charging, the steady state energy loss may be calculated as Mssc ² x At.

As will be appreciated from Fig. 8, the accumulated energy E increases while the battery 20 is charged and when the battery 20 is discharged. When the battery 20 current I drops below the thresholds defined by the maximum steady state discharge current Mss and the maximum steady state charge current Mssc, the accumulated energy decreases as the battery 20 dissipates the accumulated energy. As will be appreciated from Figs. 7 and 8, as the accumulated energy E increases, the BMS 10 begins to limit the current I output by the battery 20. The process by which this control is implemented is discussed further below.

Figs. 9 and 10 shows graphs of the battery current I and the charge current limit (Lc) against time, following the same time axis as Figs. 7 and 8. The charge current limit Lc may be calculated based on a ratio of the accumulated charge energy Ec to the maximum accumulated charge energy MEC. In the embodiment of Figs. 7 to 12, the charge current limit Lc may also take into account any accumulated discharge energy ED. Thus, in the embodiment of Figs. 7 to 12, the accumulated energy E is used instead of the accumulated charge energy Ec. The BMS 10 also ensures that the charge current limit Lc does not exceed the maximum charge pulse current specified by the BMS 10/battery manufacturer. The ratio of the accumulated charge energy Ec to the maximum accumulated charge energy MEC (i.e. Ec / MEC), or the ratio of the accumulated energy E to the maximum accumulated charge energy MEC (i.e. E / MEC), may be used as an indication of the remaining energy that may be accumulated by the battery 20 without causing excessive heat build-up. Thus, in some embodiments, the ratio (Ec / MEC or E / MEC) may be used to scale the maximum charge pulse current MPC in order to calculate a discharge current limit Lc.

In some embodiments, the ratio (Ec / MEC or E / MEC) is used to scale the difference between the maximum charge pulse current MPC and the maximum charge steady state current Mssc. As such, in some embodiments, the charge current limit Lc may be calculated as:

Lc = ( Ec / MEC ) x ( MPC - Mssc ) or

Lc = ( E / MEC ) x ( MPC - Mssc ).

Thus, as the accumulated charge energy Ec increases from zero, the charge current limit Lc decreases from the maximum charge pulse current MPC towards the maximum charge steady state current Mssc.

Similar to the embodiment of Figs. 1 to 6, the embodiment of Figs. 7 to 12 may use an arbitration strategy lookup table to determine a current weight (or a charge current weight), which is used to scale the maximum charge pulse current MPC.

The arbitration strategy lookup table may output a charge current weight Wc based on the ratio of the accumulated energy to the maximum accumulated charge energy E / MEC. In some embodiments, this may involve use of an arbitration strategy parameter kc. In some embodiments, different arbitration strategy parameters ko, kcmay be used for the calculation of discharge current limits and charge current limits respectively, 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 / MEC in order to determine an arbitration strategy for the charge current weight Wc. In the embodiment of Figs. 7 to 12, the charge current weight Wc is used to scale the difference between the maximum charge pulse current MPC and the maximum charge steady state current Mss. As such, in some embodiments, the charge current limit Lc may be calculated as:

Lc = Wc x ( MPC - Mssc )

Fig. 12 shows a graph of the charge current weight Wc and the discharge current weight WD which may be output by the arbitration strategy lookup table based on the ratio of the accumulated energy to the maximum accumulated charge energy (E / MEC) and the ratio of the accumulated energy to the maximum accumulated discharge energy (E / MED) respectively. As will be appreciated from Fig. 12, the ratios E / MEC and E / MED are different during the charging and discharging pulses due to the different values for Mp and MPC.

As shown in Fig. 11, the BMS 10 is configured to control the charge current of the battery 20 such that the battery current I does not exceed the charge current limit Lc and does not exceed the discharge current limit LD. Thus, as shown in Fig. 11, the BMS 10 reduces the current in line with the charge current limit Lc and the discharge current limit LD calculated in accordance with the above-described embodiments.

It will be appreciated that the while the above description focuses on the calculation of a charge current limit, the ratio E / MEC (or Ec / MEC) may also be used to calculate a charge voltage limit for the battery 20. As such, a charge voltage limit may be calculated based on the ratio E / MEC and a maximum charge pulse voltage which is associated with the maximum charge pulse current Mp. The maximum charge pulse voltage may be provided by a battery manufacturer and stored in a suitable lookup table of the BMS 10.

Fig. 14 shows a block diagram of a method 100 of 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 timestep based on the discharge current and a duration of the timestep. 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 preceding timestep and the discharge energy for the timestep.

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 look-up 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 will be appreciated that the method 100 may incorporate additional steps/features in line with the embodiments of the BMS 10 described above.

Fig. 15 shows a block diagram of a method 200 of controlling a charge current of a battery 20 according to an embodiment of the disclosure. The method may be performed by 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 timestep based on the charge current and a duration of the timestep.

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 preceding timestep and the charge energy for the timestep.

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 look-up 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 charge current limit does not exceed the maximum charge pulse current.

In step 206 of the method, the BMS 10 controls the charge current of the battery 20 such that the charge current does not exceed the charge current limit.

It will be appreciated that the method 200 may incorporate additional steps/features in line with the embodiments of the BMS 10 described above.

Industrial Applicability

According to this disclosure, a battery management system (BMS 10) is provided. The BMS 10 is configured to control a 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 a machine 30, for example an electric work machine.

The BMS 10 according to this disclosure determine a safe operating limit for a battery 20 for pulse currents (discharge or charging) of longer durations than specified 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 discharging the battery 20 to a maximum accumulated energy. The maximum accumulated energy is calculated from a maximum pulse discharge current provided by a look-up table of the BMS 10. The difference between the accumulated discharge energy and the maximum accumulated energy defines the remaining amount of energy the battery 20 can safely accumulate. Based on the said energy difference, the BMS 10 can determine a discharge current limit or a charge current limit that the battery 20 can continue to operate at. In effect, the BMS 10 can allow the battery 20 to safely operate at currents (charge or discharge) higher than a specified maximum steady state current for extended time periods (i.e. a time period longer than a duration of a pulse duration). In some embodiments, the BMS 10 may also arbitrate between a maximum charge/discharge pulse current and a maximum charge/discharge steady state current using an arbitration strategy lookup table. In such embodiments, the arbitration strategy followed can be selected/modified to provide different power output profiles, wherein different power output profiles may be tailored to the various tasks to be performed by the machine 30.