Battery pack

Abstract

In a battery pack comprising multiple batteries connected in parallel, the aim is to extend the lifespan of the relays while suppressing limitations on the overall capacity of the battery pack, and to suppress relatively long charging times. [Solution] The battery pack BP comprises batteries Ba and Bb connected in parallel to each other, and a control unit Cnt that controls the charging current command value so that the charge levels of batteries Ba and Bb become equal during charging. When the maximum current among the currents flowing through batteries Ba and Bb becomes greater than or equal to a first current threshold Ith1, the control unit Cnt reduces the charging current command value by a first predetermined current.

Description

Technical Field

[0001] The present invention relates to a battery pack including a plurality of batteries connected in parallel to each other.

Background Art

[0002] As a battery pack, for example, after starting charging of two batteries connected in parallel to each other, if the difference in state of charge between the respective batteries becomes equal to or greater than a threshold value, a relay connected between the battery with the larger state of charge and a charger is switched from a conductive state to a disconnected state to continue charging only the other battery, and when the state of charge of the other battery approaches the state of charge of the one battery, the relay is switched from the disconnected state to the conductive state to resume charging of the one battery. Thereby, since a relatively large difference in the state of charge of each battery can be suppressed, it is possible to suppress the capacity of the entire battery pack from being limited. Patent Document 1 is known as related art.

[0003] Meanwhile, if the number of times of switching the relay between the disconnected state and the conductive state increases, the service life of the relay may be shortened.

[0004] In the above battery pack, since the relay is switched between the disconnected state and the conductive state each time the difference in state of charge becomes equal to or greater than the threshold value, there is a concern about the shortened service life of the relay.

[0005] Further, in the above battery pack, since charging of the battery is temporarily stopped, the charging time may become longer as compared with a case where charging of the battery is not stopped.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0007] One aspect of the present invention is to provide a battery pack comprising multiple batteries connected in parallel with each other, which aims to extend the lifespan of the relays while suppressing limitations on the overall capacity of the battery pack, and to suppress relatively long charging times. [Means for solving the problem]

[0008] A battery pack in one embodiment of the present invention comprises a plurality of batteries connected in parallel to each other, and a control unit that controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, wherein the control unit reduces the charging current command value by a first predetermined current when the maximum current among the currents flowing through the plurality of batteries becomes equal to or greater than a first current threshold.

[0009] In this way, when the maximum current flowing through each battery exceeds the first current threshold, the charging current command value is reduced by the first predetermined current, thereby suppressing an increase in the temperature difference between each battery and suppressing an increase in the difference in the internal resistance of each battery. As a result, an increase in the difference in the current flowing through each battery is suppressed, and therefore a relatively large difference in the charge level of each battery is suppressed. This prevents the charging control from ending while the difference in the charge level of each battery is still relatively large, thus preventing the usable capacity of the entire battery pack from being limited. In addition, since there is no need to switch between the interrupted and conductive states of the relay, the relay life can be extended. Furthermore, because the configuration keeps current flowing through each battery, the charging time of the battery pack can be kept relatively long compared to a configuration in which the current flowing through the batteries temporarily drops to zero.

[0010] Furthermore, the control unit may be configured to increase the charging current command value by a second predetermined current amount when the maximum current falls below a second current threshold, which is lower than the first current threshold.

[0011] This allows for an increase in the current flowing through each battery, further increasing the charge level of each battery and shortening the charging time of the battery pack.

[0012] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold, and the maximum temperature among the multiple batteries is equal to or greater than the temperature threshold.

[0013] This prevents the battery pack charging time from being extended by unnecessarily reducing the current flowing through each battery, especially when the maximum temperature among the individual batteries is relatively low and the charge levels of each battery are likely to naturally become equal.

[0014] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold, and the temperature difference between the maximum temperature and the minimum temperature among the multiple batteries is equal to or greater than the temperature difference threshold.

[0015] This prevents the battery pack charging time from being extended by unnecessarily reducing the current flowing through each battery, especially when the difference between the maximum and minimum temperatures of each battery is relatively small and the charge levels of each battery are likely to naturally become equal.

[0016] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the plurality of batteries are not being cooled.

[0017] This prevents the battery pack charging time from being extended by unnecessarily reducing the current flowing to each battery when the charge levels of each battery are likely to naturally equalize due to cooling of each battery.

[0018] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the plurality of batteries are being cooled.

[0019] This allows for a reduction in the temperature of individual batteries when it is clear that their temperatures are relatively high, thereby more reliably preventing limitations on the overall usable capacity of the battery pack.

[0020] A battery pack according to one embodiment of the present invention comprises a plurality of batteries connected in parallel with each other, and a control unit that controls the charging current command value so that the charge levels of the plurality of batteries are equal during charging, wherein the control unit reduces the charging current command value by a first predetermined current when the maximum temperature among the temperatures of the plurality of batteries is equal to or greater than a first temperature threshold.

[0021] In this way, when the maximum temperature of each battery exceeds the first temperature threshold, the charging current command value is reduced by the first predetermined current, thereby suppressing an increase in the maximum temperature and preventing an increase in the difference in the internal resistance of each battery. As a result, an increase in the difference in the current flowing through each battery is suppressed, and therefore a relatively large difference in the charge level of each battery is suppressed. This prevents the charging control from ending while the difference in the charge level of each battery is still relatively large, thus preventing the usable capacity of the entire battery pack from being limited. In addition, since there is no need to switch between the interrupted and conductive states of the relay, the relay life can be extended. Furthermore, because the configuration keeps current flowing through each battery, the charging time of the battery pack can be kept relatively long compared to a configuration in which the current flowing through the batteries temporarily drops to zero.

[0022] Furthermore, the control unit may be configured to increase the charging current command value by a second predetermined current when the maximum temperature falls below a second temperature threshold, which is lower than the first temperature threshold.

[0023] This allows for an increase in the current flowing through each battery, further increasing the charge level of each battery and shortening the charging time of the battery pack.

[0024] Further, the control unit may be configured to reduce the charging current command value by the first predetermined current when the maximum temperature is equal to or higher than the first temperature threshold and the plurality of batteries are not being cooled.

[0025] Accordingly, when there is a possibility that the state of charge of each battery naturally becomes equal due to the cooling of each battery, it is possible to suppress an increase in the charging time of the battery pack caused by unnecessarily reducing the current flowing through each battery.

[0026] Further, the control unit may be configured to reduce the charging current command value by the first predetermined current when the maximum temperature is equal to or higher than the first temperature threshold and the plurality of batteries are being cooled.

[0027] Accordingly, when it is clear that the temperature of each battery is relatively high, the temperature of each battery can be lowered, so that it is possible to more reliably suppress the limitation of the usable capacity of the entire battery pack.

[0028] A battery pack according to one embodiment of the present invention includes a plurality of batteries connected in parallel to each other, and a control unit that controls a charging current command value so that the state of charge of the plurality of batteries becomes equal to each other during charging of the plurality of batteries, wherein the control unit reduces the charging current command value by a first predetermined current when a current difference between a maximum current and a minimum current among currents flowing through the plurality of batteries is equal to or greater than a first current difference threshold.

[0029] In this way, when the current difference between the maximum and minimum currents flowing through each battery exceeds a first current difference threshold, the charging current command value is reduced by a first predetermined current, thereby suppressing an increase in the temperature difference between each battery and suppressing an increase in the difference in the internal resistance of each battery. As a result, an increase in the difference in current flowing through each battery is suppressed, and therefore a relatively large difference in the charge level of each battery is suppressed. This prevents the charging control from ending while the difference in the charge level of each battery is still relatively large, thus preventing the usable capacity of the entire battery pack from being limited. In addition, since there is no need to switch between the interrupted and conductive states of the relay, the relay life can be extended. Furthermore, because the configuration keeps current flowing through each battery, the charging time of the battery pack can be kept relatively long compared to a configuration in which the current flowing through the batteries temporarily drops to zero.

[0030] Furthermore, the control unit may be configured to increase the charging current command value by a second predetermined current amount when the current difference falls below a second current difference threshold, which is lower than the first current difference threshold.

[0031] This allows for an increase in the current flowing through each battery, further increasing the charge level of each battery and shortening the charging time of the battery pack.

[0032] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold, and the maximum temperature among the multiple batteries is equal to or greater than the temperature threshold.

[0033] This prevents the battery pack charging time from being extended by unnecessarily reducing the current flowing through each battery, especially when the maximum temperature among the individual batteries is relatively low and the charge levels of each battery are likely to naturally become equal.

[0034] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold, and the temperature difference between the maximum temperature and the minimum temperature among the multiple batteries is equal to or greater than the temperature difference threshold.

[0035] This prevents the battery pack charging time from being extended by unnecessarily reducing the current flowing through each battery, especially when the difference between the maximum and minimum temperatures of each battery is relatively small and the charge levels of each battery are likely to naturally become equal.

[0036] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold and the plurality of batteries are not being cooled.

[0037] This prevents the battery pack charging time from being extended by unnecessarily reducing the current flowing to each battery when the charge levels of each battery are likely to naturally equalize due to cooling of each battery.

[0038] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold and the plurality of batteries are being cooled.

[0039] This allows for a reduction in the temperature of individual batteries when it is clear that their temperatures are relatively high, thereby more reliably preventing limitations on the overall usable capacity of the battery pack.

[0040] A battery pack according to one embodiment of the present invention comprises a plurality of batteries connected in parallel with each other, and a control unit that controls the charging current command value so that the charge levels of the plurality of batteries are equal during charging, wherein the control unit reduces the charging current command value by a first predetermined current when the temperature difference between the maximum temperature and the minimum temperature among the plurality of batteries is greater than or equal to a first temperature difference threshold.

[0041] In this way, when the temperature difference between the maximum and minimum temperatures of each battery exceeds a first temperature difference threshold, the charging current command value is reduced by a first predetermined current, thereby suppressing an increase in the temperature difference between each battery and suppressing an increase in the difference in the internal resistance of each battery. As a result, an increase in the difference in the current flowing through each battery is suppressed, and therefore a relatively large difference in the charge level of each battery is suppressed. This prevents the charging control from ending while the difference in the charge level of each battery is still relatively large, thus preventing the usable capacity of the entire battery pack from being limited. In addition, since there is no need to switch between the interrupted and conductive states of the relay, the relay life can be extended. Furthermore, because the configuration keeps current flowing through each battery, the charging time of the battery pack can be kept relatively long compared to a configuration in which the current flowing through the batteries temporarily drops to zero.

[0042] Furthermore, the control unit may be configured to increase the charging current command value by the first predetermined current amount when the temperature difference between the maximum and minimum temperatures among the multiple batteries is less than or equal to the second temperature difference threshold.

[0043] This allows for an increase in the current flowing through each battery, further increasing the charge level of each battery and shortening the charging time of the battery pack.

[0044] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current amount if the temperature difference between the maximum and minimum temperatures among the multiple batteries is greater than or equal to a first temperature difference threshold and the multiple batteries are not being cooled.

[0045] This prevents the battery pack charging time from being extended by unnecessarily reducing the current flowing to each battery when the charge levels of each battery are likely to naturally equalize due to cooling of each battery.

[0046] Furthermore, the control unit may be configured to reduce the charging current command value by the first predetermined current when the temperature difference between the maximum and minimum temperatures among the multiple batteries is greater than or equal to a first temperature difference threshold and the multiple batteries are being cooled.

[0047] This allows for a reduction in the temperature of individual batteries when it is clear that their temperatures are relatively high, thereby more reliably preventing limitations on the overall usable capacity of the battery pack.

[0048] Furthermore, the battery may be composed of a lithium iron phosphate battery. [Effects of the Invention]

[0049] According to the present invention, in a battery pack comprising multiple batteries connected in parallel to each other, it is possible to extend the lifespan of the relay while suppressing limitations on the overall capacity of the battery pack, and to suppress relatively long charging times. [Brief explanation of the drawing]

[0050] [Figure 1] This figure shows an example of a battery pack according to the embodiment. [Figure 2] This diagram shows an example of the charge-voltage characteristics, the relationship between battery temperature and internal resistance, and the relationship between the current flowing through the battery and battery temperature. [Figure 3] This figure shows an example of the current flowing through the battery and the battery's charge level in a comparative example, and an example of the current flowing through the battery and the battery's charge level in Example 1. [Figure 4] This is a flowchart showing an example of the operation of the control unit in Example 1. [Figure 5] This flowchart shows an example of the operation of the control unit in Modification 1 of Example 1. [Figure 6] This figure shows an example of the current flowing through the battery, the battery's charge level, and the battery's temperature in Modification 1 of Example 1. [Figure 7]This flowchart shows an example of the operation of the control unit in a modified example 2 of Example 1. [Figure 8] This flowchart shows an example of the operation of the control unit in Modification 3 of Example 1. [Figure 9] This flowchart shows an example of the operation of the control unit in Modification 4 of Example 1. [Figure 10] This flowchart shows an example of the operation of the control unit in Modification 5 of Example 1. [Figure 11] This flowchart shows an example of the operation of the control unit in Example 2. [Figure 12] This flowchart shows an example of the operation of the control unit in Modification 1 of Example 2. [Figure 13] This flowchart shows an example of the operation of the control unit in a modified example 2 of Example 2. [Figure 14] This flowchart shows an example of the operation of the control unit in modified example 3 of Example 2. [Figure 15] This flowchart shows an example of the operation of the control unit in modified example 4 of Example 2. [Figure 16] This flowchart shows an example of the operation of the control unit in modified example 5 of Example 2. [Modes for carrying out the invention]

[0051] The embodiments will be described in detail below based on the drawings.

[0052] Figure 1 shows an example of a battery pack according to the embodiment.

[0053] The battery pack BP shown in Figure 1 is installed in vehicles such as electric forklifts and electric vehicles, and supplies power to loads Lo such as the drive motor and electrical equipment installed in the vehicle. In addition, power output from a charger Ch installed outside the vehicle is supplied to the battery pack BP.

[0054] The battery pack BP also comprises two batteries Ba and Bb connected in parallel, relays Rea, Reb, ReCh, and ReLo, current detection units Sia and Sib, voltage detection units Sva1 and Sva2, voltage detection units Svb1 and Svb2, temperature detection units Sta1 and Sta2, temperature detection units Stb1 and Stb2, a cooler F, a memory unit Str, and a control unit Cnt. If there is no need to distinguish between batteries Ba and Bb, they are simply referred to as battery B. Similarly, if there is no distinction between voltage detection units Sva1 and Sva2 and voltage detection units Svb1 and Svb2, they are simply referred to as voltage detection unit Sv. Similarly, if there is no distinction between relays Rea, Reb, ReCh, and ReLo, they are simply referred to as relay Re. Furthermore, the number of batteries B connected in parallel in the battery pack BP is not limited to two, but may be three or more.

[0055] Battery Ba comprises two battery cells BCa1 and BCa2 connected in series, and battery Bb comprises two battery cells BCb1 and BCb2 connected in series. When battery cells BCa1, BCa2, BCb1, and BCb2 are not distinguished, they are simply referred to as battery cells BC. Furthermore, the number of battery cells BC connected in series in battery B is not limited to two; there may be three or more.

[0056] Furthermore, each battery cell BC is composed of, for example, one or more ternary lithium-ion batteries or one or more lithium iron phosphate batteries. When battery cell BC is composed of ternary lithium-ion batteries, for example, as shown in Figure 2(a) (a characteristic showing the correspondence between the charge rate, which is the ratio of the remaining capacity of battery cell BC to the fully charged capacity of battery cell BC [%], and the voltage of battery cell BC), the amount of change in voltage per unit charge rate is relatively large in the range of charge rates from 0% to 100%, making it relatively easy to uniquely determine the charge rate from the voltage. Alternatively, when battery cell BC is composed of lithium iron phosphate batteries, for example, as shown in Figure 2(b) (a characteristic showing the characteristics of battery cell BC), there is a plateau region in a part of the charge rate range from 0% to 100% where the amount of change in voltage per unit charge rate is relatively small, making it relatively difficult to uniquely determine the charge rate from the voltage in that plateau region.

[0057] Furthermore, each battery cell BC is assumed to have different rates of decrease in charge rate per unit time due to self-discharge, as well as different rates of decrease in full charge capacity per unit time due to aging degradation, and the charge rates of each battery B when no charging or discharging is taking place (for example, the average value of the charge rates of each battery cell BC) are assumed to be different.

[0058] Furthermore, as shown in Figure 2(c), for example, the higher the temperature of the battery cell BC, the lower the internal resistance of the battery cell BC, and the lower the temperature of the battery cell BC, the higher the internal resistance of the battery cell BC. Also, as shown in Figure 2(d), the higher the current flowing through the battery cell BC, the higher the temperature of the battery cell BC, and the lower the current flowing through the battery cell BC, the lower the temperature of the battery cell BC. In other words, generally, "heat generation of battery cell BC [W] = (current flowing through battery cell BC)" 2From the formula "internal resistance of battery cell BC", the amount of heat generated by battery cell BC varies in accordance with the square of the current flowing through battery cell BC. For example, even if the difference between current I4 and current I2 and the difference between current I3 and current I1 shown in Figure 2(d) are equal, the difference between temperature T4 and temperature T2 corresponding to the difference between current I4 and current I2 will be greater than the difference between temperature T3 and temperature T1 corresponding to the difference between current I3 and current I1. Assume that current I1 < current I2 < current I3 < current I4 and temperature T1 < temperature T2 < temperature T3 < temperature T4.

[0059] Furthermore, the difference between the maximum and minimum temperatures of each battery cell BC during charging control will increase over time due to factors such as differences in the placement of the battery cells BC. Therefore, the difference between the maximum and minimum internal resistances of each battery cell BC during charging control will also increase over time.

[0060] The relays Rea, Reb, ReCh, and ReLo shown in Figure 1 are each composed of semiconductor relays or electromagnetic relays, and their conduction and disconnection states are controlled by the control unit Cnt. For example, when relays Rea, Reb, ReCh, and ReLo are all in the disconnection state, batteries Ba and Bb are not connected in parallel, power cannot be supplied from batteries Ba and Bb to load Lo, and power cannot be supplied from charger Ch to batteries Ba and Bb. When relays Rea and Reb switch from the disconnection state to the conduction state, batteries Ba and Bb become connected in parallel. Furthermore, when relay ReLo switches from the disconnection state to the conduction state, power can be supplied from batteries Ba and Bb to load Lo, and power can be regenerated from load Lo to batteries Ba and Bb. Alternatively, when relay ReCh switches from the disconnection state to the conduction state, power can be supplied from charger Ch to batteries Ba and Bb.

[0061] The current detection unit Sia is composed of a shunt resistor and the like, and detects the current flowing through the battery Ba (battery cells BCa1, BCa2), and sends the detected current to the control unit Cnt.

[0062] The current detection unit Sib is composed of a shunt resistor or the like, and detects the current flowing through the battery Bb (battery cells BCb1 and BCb2), and sends the detected current to the control unit Cnt. When current detection units Sia and Sib are not distinguished, they are simply referred to as current detection unit Si. Furthermore, if the battery pack BP is equipped with three or more batteries B, the same number of current detection units Si as batteries B are provided in the battery pack BP.

[0063] Here, we will explain the connections between each battery cell BC and each relay Re. The positive terminal of battery cell BCa1 is connected to the positive terminal of battery cell BCb1, the negative terminal of battery cell BCa1 is connected to the positive terminal of battery cell BCa2, and the negative terminal of battery cell BCa2 is connected to the negative terminal of battery cell BCb2 via the current detection unit Sia, relay Rea, relay Reb, and current detection unit Sib. Also, the positive terminal of battery cell BCb2 is connected to the negative terminal of battery cell BCb1. Furthermore, the connection point between the positive terminal of battery cell BCa1 and the positive terminal of battery cell BCb1 is connected to the positive terminal of load Lo, and the connection point between relay Rea and relay Reb is connected to the negative terminal of load Lo via relay ReLo. Furthermore, when the battery pack BP and the charger Ch are connected to each other via the charging cable Ca, the connection point between the positive terminal of battery cell BCa1 and the positive terminal of battery cell BCb1 is connected to the positive terminal of charger Ch, and the connection point between relay Rea and relay Reb is connected to the negative terminal of charger Ch via relay ReCh.

[0064] The voltage detection units Sva1 and Sva2 are each composed of ICs (Integrated Circuits), etc. Voltage detection unit Sva1 detects the voltage of battery cell BCa1 and sends the detected voltage to the control unit Cnt using CAN (Controller Area Network) communication, etc. Voltage detection unit Sva2 detects the voltage of battery cell BCa2 and sends the detected voltage to the control unit Cnt using CAN communication, etc. Furthermore, voltage detection unit Sva1 is driven by the power supplied from battery cell BCa1, and voltage detection unit Sva2 is driven by the power supplied from battery cell BCa2. Therefore, if there is variation in the current consumption of voltage detection units Sva1 and Sva2, the charge levels of battery cells BCa1 and BCa2 may vary as a result of driving voltage detection units Sva1 and Sva2.

[0065] The voltage detection units Svb1 and Svb2 are each composed of ICs or the like. Voltage detection unit Svb1 detects the voltage of battery cell BCb1 and sends the detected voltage to the control unit Cnt using CAN communication or the like. Voltage detection unit Svb2 detects the voltage of battery cell BCb2 and sends the detected voltage to the control unit Cnt using CAN communication or the like. Furthermore, voltage detection unit Svb1 is driven by the power supplied from battery cell BCb1, and voltage detection unit Svb2 is driven by the power supplied from battery cell BCb2. Therefore, if there is variation in the current consumption of voltage detection units Svb1 and Svb2, the charge levels of battery cells BCb1 and BCb2 may vary as a result of driving voltage detection units Svb1 and Svb2.

[0066] The temperature detection units Sta1, Sta2, Stb1, and Stb2 are each composed of thermistors or the like. Temperature detection unit Sta1 is located near battery cell BCa1, detects the temperature of battery cell BCa1, and sends the detected temperature to the control unit Cnt. Temperature detection unit Sta2 is located near battery cell BCa2, detects the temperature of battery cell BCa2, and sends the detected temperature to the control unit Cnt. Temperature detection unit Stb1 is located near battery cell BCb1, detects the temperature of battery cell BCb1, and sends the detected temperature to the control unit Cnt. Temperature detection unit Stb2 is located near battery cell BCb2, detects the temperature of battery cell BCb2, and sends the detected temperature to the control unit Cnt. For example, the control unit Cnt sets the average value of the temperatures detected by temperature detection units Sta1 and Sta2 as the temperature of battery Ba, and the average value of the temperatures detected by temperature detection units Stb1 and Stb2 as the temperature of battery Bb. If temperature detection units Sta1, Sta2, Stb1, and Stb2 are not distinguished, they are simply referred to as temperature detection unit St.

[0067] The memory unit Str is composed of RAM (Random Access Memory) or ROM (Read Only Memory), and stores threshold values ​​and other information, which will be described later.

[0068] The control unit Cnt consists of a processor or programmable device (such as an FPGA (Field Programmable Gate Array) or PLD (Programmable Logic Device)) and performs functions such as power supply and charging control.

[0069] <An example of power supply processing> When the control unit Cnt receives a power supply start instruction from outside the battery pack BP (for example, from a control unit that controls the vehicle's movement), it starts the power supply process, turning relays Rea, Reb, and ReLo into a conductive state and relay ReCh into a disconnected state, thereby enabling power to be supplied from the battery pack BP to the load Lo. Also, when power supply is performed, the control unit Cnt estimates the overall charge level of battery B based on the current flowing through battery B and the voltage of battery B, and displays the estimated charge level on a display (not shown) or the like to inform the user of the battery pack BP's charge status. Furthermore, when the control unit Cnt receives a power supply end instruction from outside the battery pack BP, it turns off relays Rea, Reb, ReLo, and ReCh, thereby preventing power from being supplied from the battery pack BP to the load Lo and ending the power supply.

[0070] <An example of charging control> When the control unit Cnt receives a charging command from outside the battery pack BP, it starts charging control, turns relays Rea, Reb, and ReCh into a conductive state and relay ReLo into a disconnected state, and then periodically sends a charging current command value to the charger Ch. The charger Ch flows a current to the battery pack BP according to the charging current command value sent from the battery pack BP. Of the current flowing from the charger Ch to the battery pack BP, a current corresponding to the internal resistance of battery cells BCa1 and BCa2 flows to battery cells BCa1 and BCa2, and a current corresponding to the internal resistance of battery cells BCb1 and BCb2 flows to battery cells BCb1 and BCb2. Furthermore, during charging control, when at least one of the battery cells BC reaches a fully charged state, the control unit Cnt sets the charging current command value to zero and turns relays Rea, Reb, and ReCh into a disconnected state, thereby ending the charging control. In addition, the control unit Cnt, separate from the charging control, performs cooling control processing for batteries Ba and Bb by driving a cooler F, such as a fan, based on the temperature sent from each temperature detection unit St, thereby maintaining the temperature of each battery cell BC within a predetermined temperature range.

[0071] For example, the control unit Cnt performs constant current charging control as part of the charging control. That is, first, when the control unit Cnt starts constant current charging control, it sends a charging current command value indicating a constant current Ic to the charger Ch at each control cycle (for example, the clock cycle of the control unit Cnt). Then, current according to the charge rate and internal resistance of batteries Ba and Bb flows into batteries Ba and Bb respectively, and the voltages of batteries Ba and Bb gradually rise. When the voltages of batteries Ba and Bb reach a certain voltage or higher, the control unit Cnt determines that batteries Ba and Bb are fully charged and terminates the constant current charging control by setting the charging current command value to zero.

[0072] <Comparative Examples of the Embodiments> Here, we assume that during constant current charging control in the comparative example, the temperature of battery Ba (for example, the average value of the temperatures of battery cell BCa1 and battery cell BCa2) increases while the temperature of battery Bb (for example, the average value of the temperatures of battery cell BCb1 and battery cell BCb2) decreases.

[0073] Figures 3(a) and 3(b) schematically show the current flowing through batteries Ba and Bb and the charge levels of batteries Ba and Bb during constant current charging control in a comparative example. In Figure 3(a), the horizontal axis of the two-dimensional coordinate system represents time, and the vertical axis represents current. The solid line in Figure 3(a) shows an example of the current flowing through battery Ba during constant current charging control, and the dashed line shows an example of the current flowing through battery Bb during constant current charging control. In Figure 3(b), the horizontal axis of the two-dimensional coordinate system represents time, and the vertical axis represents the charge level. The solid line in Figure 3(b) shows an example of the charge level of battery Ba during constant current charging control (for example, the average of the charge levels of battery cell BCa1 and battery cell BCa2), and the dashed line in Figure 3(b) shows an example of the charge level of battery Bb during constant current charging control (for example, the average of the charge levels of battery cell BCb1 and battery cell BCb2).

[0074] In the comparative example shown in Figure 3(a), a constant current Ic flows through batteries Ba and Bb during the period from time t0 to time t1 while constant current charging control is in place. Furthermore, during the period from time t1 to time t3, the current flowing through battery Ba increases as its temperature rises, while the current flowing through battery Bb decreases as its temperature falls. Therefore, as shown in Figure 3(b), during the period from time t1 to time t3, the increase in the charge rate per unit time of battery Ba becomes relatively large as the current flowing through battery Ba increases, while the increase in the charge rate per unit time of battery Bb becomes relatively small as the current flowing through battery Bb decreases. In other words, if the temperatures of batteries Ba and Bb vary during charging control, the charge rates of batteries Ba and Bb will also vary. If the charging control ends while the charge rates of batteries Ba and Bb remain varied, the usable capacity of the entire battery pack BP will be limited.

[0075] Therefore, in the comparative example, at time t3 shown in Figure 3(b), when the difference between the charge rate of battery Ba and the charge rate of battery Bb becomes greater than or equal to the first charge rate threshold th1, relay Rea is turned off and relay Reb is turned on, and the charging current command value is adjusted so that a constant current Ic flows only to battery Bb. Then, as shown in Figure 3(a), after time t3, the current flowing to battery Ba becomes zero, and a current corresponding to the internal resistance of battery Bb flows to battery Bb, so as shown in Figure 3(b), after time t3, the charge rate of battery Ba does not increase, and only the charge rate of battery Bb increases. Subsequently, as shown in Figure 3(b), at time t5, when the difference between the charge rate of battery Bb and the charge rate of battery Ba becomes less than or equal to the second charge rate threshold th2, relays Rea and Reb are turned on, and the charging current command values ​​are adjusted so that a constant current Ic flows to batteries Ba and Bb respectively. As shown in Figure 3(a), a constant current Ic flows through batteries Ba and Bb from time t5 onward, and as shown in Figure 3(b), the charge levels of batteries Ba and Bb gradually increase from time t5 onward while maintaining a constant difference. In other words, in the comparative example, even if the temperatures of batteries Ba and Bb vary during charge control, it is possible to suppress the widening of the difference in charge levels between batteries Ba and Bb, thereby suppressing the limitation of the usable capacity of the entire battery pack BP.

[0076] However, in the comparative example, the relay Re switches between the closed and open states each time the difference in charge level exceeds a threshold, which raises concerns about a shortened lifespan for the relay Re.

[0077] Furthermore, in the comparative example, the configuration temporarily reduces the current flowing to battery Ba to zero. This raises concerns that the time it takes for battery Ba to reach a fully charged state will be longer compared to the case where the current flowing to battery Ba is not stopped, thus increasing the charging time of the battery pack BP.

[0078] Therefore, in the battery pack BP of this embodiment, during charge control, a current limiting process is executed to reduce the current flowing to each battery B before the difference in the charge levels of each battery B becomes relatively large.

[0079] Thus, in this embodiment, the battery pack BP limits the current flowing to each battery B before the difference in the charge levels of each battery B becomes relatively large, thereby suppressing an increase in the temperature difference between each battery B and suppressing an increase in the difference in the internal resistance of each battery B. Therefore, since an increase in the difference in the current flowing to each battery B is suppressed, a relatively large difference in the charge levels of each battery B is suppressed. As a result, the charging control is prevented from ending while the difference in the charge levels of each battery B is still relatively large, thus preventing the usable capacity of the battery pack BP as a whole from being limited.

[0080] Furthermore, the battery pack BP of this embodiment does not require switching between the disconnected and conductive states of relay Re when suppressing a relatively large difference in the charge levels of each battery B, thus extending the lifespan of relay Re.

[0081] Furthermore, the battery pack BP of this embodiment is configured to continuously supply current to each battery B in order to suppress a relatively large difference in the charge levels of each battery B. Therefore, compared to a configuration in which the current flowing to each battery B is temporarily reduced to zero, the time it takes for each battery B to reach a fully charged state is suppressed, and the charging time of the battery pack BP is suppressed to be relatively long.

[0082] Furthermore, the battery pack BP of the embodiment is configured to suppress relatively large differences in the charge levels of each battery B by using the current flowing through each battery B, and not by using the voltage of each battery B to suppress relatively large differences in the charge levels of each battery B. Therefore, it is preferable to implement the current control processing of the embodiment for batteries that have a plateau region in a range of charge levels within the range of 0% to 100%, such as lithium iron phosphate batteries.

[0083] <Example 1> Figure 4 is a flowchart showing the operation of the control unit Cnt in Example 1.

[0084] First, if the control unit Cnt determines that charging control is not in progress (step S11: No), it terminates the current limiting process. If it determines that charging control is in progress (step S11: Yes), it determines whether the maximum current among the currents of each battery B is greater than or equal to the first current threshold Ith1 (step S12). The first current threshold Ith1 is a value that can be determined in advance by conducting experiments or simulations, and for example, it is the maximum current that flows through battery B when the maximum temperature among the temperatures of each battery B does not exceed the temperature upper limit value TU.

[0085] Next, if the control unit Cnt determines that the maximum current is less than the first current threshold Ith1 (step S12: No), it returns to step S11 to determine whether or not charging control is in progress.

[0086] On the other hand, if the control unit Cnt determines that the maximum current is greater than or equal to the first current threshold Ith1 (step S12: Yes), it reduces the charging current command value by the first predetermined current (step S13), then returns to step S11 to determine whether or not charging control is in progress. The first predetermined current is a value that can be determined in advance by conducting experiments or simulations, and is, for example, an arbitrary amount of reduction in the current flowing to battery B when the temperature of battery B does not fall below the lower temperature limit TL due to the reduction in the charging current command value, and the charging time of battery pack BP does not exceed a predetermined time due to the reduction in the charging current command value.

[0087] Thus, in the control unit Cnt of Embodiment 1, when the maximum current among the currents flowing through each battery B becomes equal to or greater than the first current threshold Ith1, the charging current command value is reduced by a first predetermined current.

[0088] Here, we assume that during constant current charging control in Example 1, the temperature of battery Ba increases while the temperature of battery Bb decreases.

[0089] Figures 3(c) and 3(d) schematically show the current flowing through batteries Ba and Bb and the charge levels of batteries Ba and Bb during constant current charging control in Example 1. In the two-dimensional coordinate system shown in Figure 3(c), the horizontal axis represents time and the vertical axis represents current. The solid line in Figure 3(c) shows an example of the current flowing through battery Ba during constant current charging control, and the dashed line shows an example of the current flowing through battery Bb during constant current charging control. In the two-dimensional coordinate system shown in Figure 3(d), the horizontal axis represents time and the vertical axis represents the charge level. The solid line in Figure 3(d) shows an example of the charge level of battery Ba during constant current charging control, and the dashed line in Figure 3(d) shows an example of the charge level of battery Bb during constant current charging control.

[0090] In Embodiment 1 shown in Figure 3(c), during the period from time t0 to time t1' while constant current charging control is in place, the current flowing through battery Ba increases as the temperature of battery Ba rises, and the current flowing through battery Bb decreases as the temperature of battery Bb decreases.

[0091] Furthermore, in Example 1 shown in Figure 3(d), at time t2, which is before time t3 when the difference between the charge levels of battery Ba and battery Bb becomes relatively large, if the current flowing through battery Ba exceeds the first current threshold Ith1, the charging current command value is reduced by a first predetermined current. Then, as shown in Figure 3(c), the current flowing through battery Ba decreases by a predetermined current α corresponding to the internal resistance of battery Ba, and the current flowing through battery Bb decreases by a predetermined current β corresponding to the internal resistance of battery Bb. Also, as shown in Figure 3(c), after time t2, the current flowing through battery Ba gradually decreases while the current flowing through battery Bb gradually increases, and after time t4, the current flowing through battery Ba and the current flowing through battery Bb become approximately the same value. Therefore, in Example 1, as shown in Figure 3(d), after time t4, the charge levels of batteries Ba and Bb gradually increase while maintaining an approximately constant difference.

[0092] Thus, in Example 1, by reducing the current flowing through batteries Ba and Bb before the difference in the charge levels of each battery B becomes relatively large, the increase in the temperature difference between batteries Ba and Bb is suppressed, and the increase in the difference in the internal resistance of batteries Ba and Bb is suppressed. Therefore, since the increase in the difference in the current flowing through batteries Ba and Bb is suppressed, the difference in the charge levels of batteries Ba and Bb becomes relatively large. As a result, charging is prevented from ending while the difference in the charge levels of batteries Ba and Bb is still relatively large, and thus the limit on the usable capacity of the entire battery pack BP can be suppressed.

[0093] Furthermore, in Example 1, since it is not necessary to switch between the interrupted and conductive states of relay Re when suppressing a relatively large difference in the charge levels of batteries Ba and Bb, the lifespan of relay Re can be extended.

[0094] Furthermore, in Example 1, in order to suppress the relatively large difference in the charge levels of batteries Ba and Bb, the configuration keeps current flowing to batteries Ba and Bb. Compared to the case where the current flowing to battery Ba is temporarily reduced to zero, this allows the charge level of battery Ba to be continuously increased, thus suppressing the time it takes for battery Ba to reach a fully charged state and preventing the charging time of the battery pack BP from becoming relatively long.

[0095] <Example 1 Modification 1> Figure 5 is a flowchart showing the operation of the control unit Cnt in a modified example 1 of Embodiment 1. Steps S11 to S13 shown in Figure 5 are the same as steps S11 to S13 shown in Figure 4, and their explanation is omitted.

[0096] In Modification 1 of Example 1, the control unit Cnt reduces the charging current command value by a first predetermined current (step S13), and then determines whether the maximum current among the currents of each battery B is less than or equal to the second current threshold Ith2 (step S14). The second current threshold Ith2 is a value smaller than the first current threshold Ith1, which can be determined in advance by experiments or simulations, and is, for example, the maximum current among the currents flowing through each battery B when the difference in currents flowing through each battery B or the difference in charge levels of each battery B becomes relatively small after the charging current command value has decreased by the first predetermined current.

[0097] Next, in the modified example 1 of Embodiment 1, if the control unit Cnt determines that the maximum current is greater than the second current threshold Ith2 (step S14: No), it continues to execute the process of decreasing the charging current command value by the first predetermined current. If it determines that the maximum current is less than or equal to the second current threshold (step S14: Yes), it increases the charging current command value by the second predetermined current (step S15), then returns to step S11 to determine whether or not charging control is in progress. The second predetermined current is a value that can be determined in advance by conducting experiments or simulations. The second predetermined current may be the same value as the first predetermined current, or it may be a different value.

[0098] As described above, in the modified example 1 of Embodiment 1, the control unit Cnt is configured such that when the maximum current flowing through each battery B exceeds a first current threshold, the charging current command value is reduced by a first predetermined current, and then when the maximum current flowing through each battery B falls below a second current threshold, the charging current command value is increased by a second predetermined current.

[0099] Here, we assume a case in which, during constant current charging control in Modification 1 of Example 1, the temperature of battery Ba rises while the temperature of battery Bb decreases.

[0100] Figures 6(a) to 6(c) schematically show the current flowing through batteries Ba and Bb, the charge levels of batteries Ba and Bb, and the temperature of battery Bb during constant current charging control in Modification 1 of Example 1. In the two-dimensional coordinate system shown in Figure 6(a), the horizontal axis represents time and the vertical axis represents current. The solid line in Figure 6(a) shows an example of the current flowing through battery Ba during constant current charging control, and the dashed line shows an example of the current flowing through battery Bb during constant current charging control. In the two-dimensional coordinate system shown in Figure 6(b), the horizontal axis represents time and the vertical axis represents the charge level. The solid line in Figure 6(b) shows an example of the charge level of battery Ba during constant current charging control, and the dashed line in Figure 6(b) shows an example of the charge level of battery Bb during constant current charging control. In the two-dimensional coordinate system shown in Figure 6(c), the horizontal axis represents time and the vertical axis represents temperature. The solid line in Figure 6(c) shows an example of the temperature of battery Bb.

[0101] In Modification 1 of Example 1, as shown in Figures 6(a) and 6(b), during the period from time t1 to time t2 while constant current charging control is in place, the increase in the charge rate per unit time of battery Ba becomes relatively large as the current flowing through battery Ba increases, while the increase in the charge rate per unit time of battery Bb becomes relatively small as the current flowing through battery Bb decreases. Furthermore, in Modification 1 of Example 1, it is assumed that the temperature of battery Bb is maintained between the lower temperature limit TL and the upper temperature limit TU during the period from time t1 to time t2, as shown in Figure 6(c), because the cooling control process is being performed.

[0102] Furthermore, in the modified example 1 of Embodiment 1 shown in Figure 6(b), at time t2, before the difference between the charge rate of battery Ba and the charge rate of battery Bb becomes relatively large, when the current flowing through battery Ba exceeds the first current threshold Ith1, the charging current command value is reduced by a first predetermined current. Then, as shown in Figure 6(a), at time t2, the current flowing through battery Ba decreases by a predetermined current α corresponding to the internal resistance of battery Ba, and the current flowing through battery Bb decreases by a predetermined current β corresponding to the internal resistance of battery Bb. As a result, similar to Embodiment 1, the widening of the difference between the charge rate of battery Ba and the charge rate of battery Bb can be suppressed, thereby preventing the usable capacity of the entire battery pack BP from being limited. In addition, the lifespan of relay Re can be extended. Note that in the example shown in Figure 6(c), it is assumed that during the period from time t2 to time t4, the temperature of battery Bb drops to near the lower temperature limit TL due to the decrease in the current flowing through battery Bb.

[0103] Furthermore, in the modified example 1 of Embodiment 1 shown in Figure 6(a), at time t4, when the current flowing through battery Ba falls below the second current threshold Ith2, which is smaller than the first current threshold Ith1, the charging current command value is increased by the second predetermined current. As a result, as shown in Figure 6(c), from time t4 onward, the temperature of battery Bb is maintained between the lower temperature limit TL and the upper temperature limit TU. In addition, since the current flowing through batteries Ba and Bb can be increased from time t4 onward, the charge rate of batteries Ba and Bb can be further increased, and the charging time of the battery pack BP can be shortened.

[0104] <Modification 2 of Example 1> Figure 7 is a flowchart showing the operation of the control unit Cnt in a modified example 2 of Embodiment 1. Steps S11 to S15 shown in Figure 7 are the same as steps S11 to S15 shown in Figure 5, and their explanation is omitted.

[0105] In the modified example 2 of Embodiment 1, the control unit Cnt, after determining that charging control is in progress (step S11: Yes), determines that the maximum current is greater than or equal to the first current threshold Ith1 (step S12: Yes), and also determines that the maximum temperature among the temperatures of each battery B is greater than or equal to the temperature threshold (step S12-2: Yes), then reduces the charging current command value by a first predetermined current (step S13). The temperature threshold is, for example, the maximum temperature among the temperatures of each battery B when the minimum temperature among the temperatures of each battery B does not fall below the lower temperature limit TL after the charging current command value has decreased by the first predetermined current.

[0106] Furthermore, steps S14 and S15 shown in Figure 7 may be omitted.

[0107] Thus, in the modified example 2 of Embodiment 1, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the maximum current among the currents flowing through each battery B is equal to or greater than a first current threshold, and the maximum temperature among the temperatures of each battery B is equal to or greater than a temperature threshold.

[0108] According to Modification 2 of Example 1, similar to Example 1, it is possible to suppress the limitation of the total usable capacity of the battery pack BP. Furthermore, the lifespan of relay Re can be extended.

[0109] Furthermore, according to Modification 2 of Example 1, when the maximum temperature among the temperatures of each battery B is relatively low and the charge levels of each battery B are likely to naturally become equal, it is possible to suppress the extension of the charging time of the battery pack BP by reducing the current flowing through each battery B more than necessary.

[0110] <Modification 3 of Example 1> Figure 8 is a flowchart showing the operation of the control unit Cnt in modified example 3 of Embodiment 1. Steps S11 to S15 shown in Figure 8 are the same as steps S11 to S15 shown in Figure 5, and their explanation is omitted.

[0111] In Modification 3 of Example 1, after determining that charging control is in progress (Step S11: Yes), the control unit Cnt determines that the maximum current is greater than or equal to the first current threshold Ith1 (Step S12: Yes), and that the temperature difference between the maximum and minimum temperatures of each battery B is greater than or equal to the temperature difference threshold (Step S12-3: Yes), it reduces the charging current command value by a first predetermined current (Step S13). The temperature difference threshold is a value that can be determined in advance by conducting experiments or simulations, for example, it is the difference between the maximum and minimum temperatures of each battery B when the minimum temperature of each battery B does not fall below the lower temperature limit TL after the charging current command value has decreased by the first predetermined current.

[0112] Furthermore, steps S14 and S15 shown in Figure 8 may be omitted.

[0113] Thus, in the modified example 3 of Embodiment 1, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the maximum current among the currents flowing through each battery B is equal to or greater than a first current threshold, and the temperature difference between the maximum temperature and the minimum temperature among the temperatures of each battery B is equal to or greater than a temperature difference threshold.

[0114] According to Modification 3 of Example 1, similar to Example 1, it is possible to suppress the limitation of the usable capacity of the entire battery pack BP. Furthermore, it is possible to extend the lifespan of relay Re.

[0115] Furthermore, according to Modification 3 of Example 1, when the difference between the maximum and minimum temperatures of each battery B is relatively small and the charge levels of each battery B are likely to naturally become equal, it is possible to suppress the extension of the charging time of the battery pack BP by reducing the current flowing through each battery B more than necessary.

[0116] <Modification 4 of Example 1> Figure 9 is a flowchart showing the operation of the control unit Cnt in modified example 4 of Embodiment 1. Steps S11 to S15 shown in Figure 9 are the same as steps S11 to S15 shown in Figure 5, and their explanation is omitted.

[0117] In the modified example 4 of Embodiment 1, after determining that charging control is in progress (step S11: Yes), the control unit Cnt determines that the maximum current is greater than or equal to the first current threshold Ith1 (step S12: Yes), and also determines that cooling control processing is not being performed for each battery B (step S12-4: Yes), and then reduces the charging current command value by the first predetermined current (step S13).

[0118] Steps S14 and S15 shown in Figure 9 may be omitted.

[0119] Thus, in the modified example 4 of Embodiment 1, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the maximum current flowing through each battery B is equal to or greater than a first current threshold, and each battery B is not being cooled.

[0120] According to Modification 4 of Example 1, similar to Example 1, it is possible to suppress the limitation of the usable capacity of the entire battery pack BP. In addition, the lifespan of relay Re can be extended.

[0121] Furthermore, according to Modification 4 of Example 1, when the temperature of each battery B becomes equal due to the cooling of each battery B, and the charge levels of each battery B may naturally become equal, the charging time of the battery pack BP can be suppressed by reducing the current flowing through each battery B more than necessary.

[0122] <Modification 5 of Example 1> Figure 10 is a flowchart showing the operation of the control unit Cnt in modified example 5 of Embodiment 1. Steps S11 to S15 shown in Figure 10 are the same as steps S11 to S15 shown in Figure 5, and their explanation is omitted.

[0123] In Modification 5 of Example 1, after determining that charging control is in progress (Step S11: Yes), the control unit Cnt determines that the maximum current is greater than or equal to the first current threshold Ith1 (Step S12: Yes), and also determines that cooling control processing is being performed for each battery B (Step S12-5: Yes), it reduces the charging current command value by the first predetermined current (Step S13).

[0124] Steps S14 and S15 shown in Figure 10 may be omitted.

[0125] Thus, in the modified example 5 of Embodiment 1, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the maximum current flowing through each battery B is equal to or greater than a first current threshold, and when each battery B is being cooled.

[0126] According to Modification 5 of Example 1, similar to Example 1, it is possible to suppress the limitation of the total usable capacity of the battery pack BP. Furthermore, it is possible to suppress the relatively long charging time of the battery pack BP.

[0127] Furthermore, according to Modification 5 of Example 1, if it is clear that the temperature of each battery B is relatively high, the temperature of each battery B can be reduced, thereby more reliably suppressing the limitation of the usable capacity of the entire battery pack BP.

[0128] Furthermore, according to Modification 5 of Example 1, when it is clear that the temperature of each battery B is relatively high, the temperature of each battery B can be reduced, thereby preventing the temperature of each battery B from falling below the lower temperature limit TL, and thus extending the lifespan of each battery B.

[0129] <Example 2> Figure 11 is a flowchart showing the operation of the control unit Cnt in Example 2.

[0130] First, if the control unit Cnt determines that it is not in charge control mode (step S21: No), it terminates the current limiting process. If it determines that it is in charge control mode (step S21: Yes), it determines whether the current difference between the maximum and minimum currents of each battery B is greater than or equal to the first current difference threshold Idth1 (step S22). The first current difference threshold Idth1 is a value that can be determined in advance by conducting experiments or simulations, and for example, it is the maximum value of the current difference between the maximum and minimum currents of the currents flowing through each battery B when the maximum temperature of each battery B does not exceed the temperature upper limit value TU.

[0131] Next, if the control unit Cnt determines that the current difference is less than the first current difference threshold Idth1 (step S22: No), it returns to step S21 to determine whether or not charging control is in progress.

[0132] On the other hand, if the control unit Cnt determines that the current difference is greater than or equal to the first current difference threshold Idth1 (step S22: Yes), it reduces the charging current command value by the first predetermined current (step S23), then returns to step S21 to determine whether or not charging control is in progress.

[0133] Thus, in the control unit Cnt of Embodiment 2, when the current difference between the maximum current and the minimum current flowing through each battery B becomes greater than or equal to the first current difference threshold Idth1, the charging current command value is reduced by a first predetermined current.

[0134] Thus, in Example 2, by reducing the current flowing through each battery B before the difference in the charge levels of each battery B becomes relatively large, the increase in the temperature difference between each battery B is suppressed, and the increase in the difference in the internal resistance of each battery B is suppressed. Therefore, since the increase in the difference in the current flowing through each battery B is suppressed, the difference in the charge levels of each battery B becomes relatively large. As a result, it is possible to prevent charging from ending while the difference in the charge levels of each battery B is still relatively large, and thus it is possible to prevent the remaining usable capacity of the entire battery pack BP from being limited.

[0135] Furthermore, according to Example 2, when suppressing a relatively large difference in the charge levels of each battery B, it is not necessary to switch between the disconnected and conductive states of relay Re, thus extending the lifespan of relay Re.

[0136] Furthermore, in Example 2, in order to suppress the relatively large difference in the charge levels of each battery B, the configuration keeps current flowing to each battery B. Compared to the case where the current flowing to battery B is temporarily reduced to zero, this allows the charge level of battery B to be continuously increased, thus suppressing the time it takes for battery B to reach a fully charged state and preventing the charging time of the battery pack BP from becoming relatively long.

[0137] <Modification 1 of Example 2> Figure 12 is a flowchart showing the operation of the control unit Cnt in modified example 1 of Embodiment 2. Steps S21 to S23 shown in Figure 12 are the same as steps S21 to S23 shown in Figure 11, and their explanation is omitted.

[0138] In Modification 1 of Example 2, the control unit Cnt reduces the charging current command value by a first predetermined current (step S23), and then determines whether the current difference between the maximum current and the minimum current of each battery B is less than or equal to the second current difference threshold Idth2 (step S24). The second current difference threshold Idth2 is a value that can be determined in advance by conducting experiments or simulations, and for example, after the charging current command value has decreased by the first predetermined current, it is the current difference between the maximum current and the minimum temperature of the current flowing through each battery B when the difference in current flowing through each battery B or the difference in charge rate of each battery B has become relatively small.

[0139] Next, in the modified example 1 of Embodiment 2, if the control unit Cnt determines that the current difference is greater than the second current difference threshold Idth2 (step S24: No), it continues to execute the process of decreasing the charging current command value by the first predetermined current. If it determines that the current difference is less than or equal to the second current difference threshold Idth2 (step S24: Yes), it increases the charging current command value by the second predetermined current (step S25), then returns to step S21 to determine whether or not charging control is in progress.

[0140] Thus, in the modified example 1 of Embodiment 2, the control unit Cnt is configured such that when the current difference between the maximum current and the minimum current flowing through each battery B becomes greater than or equal to the first current difference threshold Idth1, the charging current command value is reduced by a first predetermined current, and then when the current difference between the maximum current and the minimum current flowing through each battery B becomes less than or equal to the second current difference threshold Idth2, the charging current command value is increased by a second predetermined current.

[0141] According to Modification 1 of Example 2, similar to Example 2, it is possible to suppress the limitation of the total usable capacity of the battery pack BP. Furthermore, it is possible to suppress the relatively long charging time of the battery pack BP. Additionally, the lifespan of the relay Re can be extended.

[0142] Furthermore, according to Modification 1 of Example 2, during charge control, when the current difference between the maximum current and the minimum current flowing through each battery B falls below the second current difference threshold Idth2, the charge rate of batteries Ba and Bb is further increased, thereby shortening the charging time of the battery pack BP.

[0143] <Modification 2 of Example 2> Figure 13 is a flowchart showing the operation of the control unit Cnt in a modified example 2 of Example 2. Steps S21 to S25 shown in Figure 13 are the same as steps S21 to S25 shown in Figure 12, and their explanation is omitted.

[0144] In the modified example 2 of Embodiment 2, after determining that charging control is in progress (step S21: Yes), the control unit Cnt determines that the current difference is greater than or equal to the first current difference threshold Idth1 (step S22: Yes), and that the maximum temperature among the temperatures of each battery B is greater than or equal to the temperature threshold (step S22-2: Yes), it reduces the charging current command value by the first predetermined current (step S23).

[0145] Steps S24 and S25 shown in Figure 13 may be omitted.

[0146] Thus, in the modified example 2 of Embodiment 2, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the current difference between the maximum current and the minimum current flowing through each battery B is greater than or equal to the first current difference threshold Idth1, and the maximum temperature among the temperatures of each battery B is greater than or equal to the temperature threshold.

[0147] According to Modification 2 of Example 2, similar to Example 2, it is possible to suppress the limitation of the total usable capacity of the battery pack BP. Furthermore, the lifespan of relay Re can be extended.

[0148] Furthermore, according to Modification 2 of Example 2, when the maximum temperature among the temperatures of each battery B is relatively low and the charge levels of each battery B are likely to naturally become equal, it is possible to suppress the extension of the charging time of the battery pack BP by reducing the current flowing through each battery B more than necessary.

[0149] <Modification 3 of Example 2> Figure 14 is a flowchart showing the operation of the control unit Cnt in modified example 3 of Example 2. Steps S21 to S25 shown in Figure 14 are the same as steps S21 to S25 shown in Figure 12, and their explanation is omitted.

[0150] In the modified example 3 of Example 2, the control unit Cnt, after determining that charging control is in progress (step S21: Yes), determines that the current difference is greater than or equal to the first current difference threshold Idth1 (step S22: Yes), and also determines that the temperature difference between the maximum and minimum temperatures of each battery B is greater than or equal to the temperature difference threshold (step S22-3: Yes), then reduces the charging current command value by the first predetermined current (step S23).

[0151] Steps S24 and S25 shown in Figure 14 may be omitted.

[0152] Thus, in the modified example 3 of Embodiment 2, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the current difference between the maximum current and the minimum current flowing through each battery B is greater than or equal to the first current difference threshold Idth1, and the temperature difference between the maximum temperature and the minimum temperature of each battery B is greater than or equal to the temperature difference threshold.

[0153] According to Modification 3 of Example 2, similar to Example 2, it is possible to suppress the limitation of the total usable capacity of the battery pack BP. Furthermore, the lifespan of relay Re can be extended.

[0154] Furthermore, according to Modification 3 of Example 2, when the difference between the maximum and minimum temperatures of each battery B is relatively small and the charge levels of each battery B are likely to naturally become equal, reducing the current flowing through each battery B more than necessary can suppress the extension of the charging time of the battery pack BP.

[0155] <Modification 4 of Example 2> Figure 15 is a flowchart showing the operation of the control unit Cnt in modified example 4 of Example 2. Steps S21 to S25 shown in Figure 15 are the same as steps S21 to S25 shown in Figure 12, and their explanation is omitted.

[0156] In Modification 4 of Example 2, after determining that charging control is in progress (Step S21: Yes), the control unit Cnt determines that the current difference is greater than or equal to the first current difference threshold Idth1 (Step S22: Yes), and also determines that cooling control processing is not being performed for each battery B (Step S22-4: Yes), it reduces the charging current command value by the first predetermined current (Step S23).

[0157] Steps S24 and S25 shown in Figure 15 may be omitted.

[0158] Thus, in the modified example 4 of Embodiment 2, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the current difference between the maximum current and the minimum current flowing through each battery B is greater than or equal to the first current difference threshold Idth1, and when each battery B is not being cooled.

[0159] According to Modification 4 of Example 2, similar to Example 2, it is possible to suppress the limitation of the total usable capacity of the battery pack BP. Furthermore, it is possible to extend the lifespan of relay Re.

[0160] Furthermore, according to Modification 4 of Example 2, when the temperature of each battery B becomes equal due to the cooling of each battery B, and the charge levels of each battery B may naturally become equal, the charging time of the battery pack BP can be suppressed by reducing the current flowing through each battery B more than necessary.

[0161] <Modification 5 of Example 2> Figure 16 is a flowchart showing the operation of the control unit Cnt in modified example 5 of Example 2. Steps S21 to S25 shown in Figure 16 are the same as steps S21 to S25 shown in Figure 12, and their explanation is omitted.

[0162] In Modification 5 of Example 2, after determining that charging control is in progress (Step S21: Yes), the control unit Cnt determines that the current difference is greater than or equal to the first current difference threshold Idth1 (Step S22: Yes), and also determines that cooling control processing is being performed for each battery B (Step S22-5: Yes), it reduces the charging current command value by the first predetermined current (Step S23).

[0163] Steps S24 and S25 shown in Figure 16 may be omitted.

[0164] Thus, in the modified example 5 of Embodiment 2, the control unit Cnt is configured to reduce the charging current command value by a first predetermined current when the current difference between the maximum current and the minimum current flowing through each battery B is greater than or equal to the first current difference threshold Idth1, and when each battery B is being cooled.

[0165] According to Modification 5 of Example 2, similar to Example 2, it is possible to suppress the limitation of the total usable capacity of the battery pack BP. Furthermore, it is possible to suppress the relatively long charging time of the battery pack BP.

[0166] Furthermore, according to Modification 5 of Example 2, if it is clear that the temperature of each battery B is relatively high, the temperature of each battery B can be reduced, thereby more reliably suppressing the limitation of the usable capacity of the entire battery pack BP.

[0167] Furthermore, according to Modification 5 of Example 2, when it is clear that the temperature of each battery B is relatively high, the temperature of each battery B can be reduced, thereby preventing the temperature of each battery B from falling below the lower temperature limit TL, and further extending the lifespan of each battery B.

[0168] It should be noted that the present invention is not limited to the embodiments described above, and various improvements and modifications are possible without departing from the spirit of the invention.

[0169] In other words, the above embodiments can be modified, for example, as shown in <Appendix 1> to <Appendix 21>. <Note 1> Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, When the maximum current among the currents flowing through the plurality of batteries exceeds a first current threshold, the control unit reduces the charging current command value by a first predetermined current. Battery pack.

[0170] <Note 2> The battery pack described in Appendix 1, When the maximum current falls below a second current threshold, which is lower than the first current threshold, the control unit increases the charging current command value by a second predetermined current. Battery pack.

[0171] <Note 3> A battery pack as described in Appendix 1 or Appendix 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the maximum temperature among the multiple batteries is equal to or greater than the temperature threshold. Battery pack.

[0172] <Note 4> A battery pack as described in Appendix 1 or Appendix 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold, and when the temperature difference between the maximum and minimum temperatures among the multiple batteries is equal to or greater than the temperature difference threshold. Battery pack.

[0173] <Note 5> A battery pack as described in Appendix 1 or Appendix 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the plurality of batteries are not being cooled. Battery pack.

[0174] <Note 6> A battery pack as described in Appendix 1 or Appendix 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the plurality of batteries are being cooled. Battery pack.

[0175] <Note 7> Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, The control unit reduces the charging current command value by a first predetermined current when the maximum temperature among the multiple batteries is equal to or greater than a first temperature threshold. Battery pack.

[0176] <Note 8> The battery pack described in Appendix 7, When the maximum temperature falls below a second temperature threshold, which is lower than the first temperature threshold, the control unit increases the charging current command value by a second predetermined current. Battery pack.

[0177] <Note 9> A battery pack as described in Appendix 7 or Appendix 8, The control unit reduces the charging current command value by the first predetermined current when the maximum temperature is equal to or greater than the first temperature threshold and the plurality of batteries are not being cooled. Battery pack.

[0178] <Note 10> A battery pack as described in Appendix 7 or Appendix 8, The control unit reduces the charging current command value by the first predetermined current when the maximum temperature is equal to or greater than the first temperature threshold and the plurality of batteries are being cooled. Battery pack.

[0179] <Note 11> Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, When the current difference between the maximum and minimum currents among the currents flowing through the plurality of batteries becomes greater than or equal to a first current difference threshold, the control unit reduces the charging current command value by a first predetermined current. Battery pack.

[0180] <Note 12> The battery pack described in Appendix 11, When the current difference falls below a second current difference threshold, which is lower than the first current difference threshold, the control unit increases the charging current command value by a second predetermined current. Battery pack.

[0181] <Note 13> A battery pack as described in Appendix 11 or Appendix 12, The control unit reduces the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold, and the maximum temperature among the multiple batteries is equal to or greater than the temperature threshold. Battery pack.

[0182] <Note 14> A battery pack as described in Appendix 11 or Appendix 12, The control unit reduces the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold, and the temperature difference between the maximum and minimum temperatures among the multiple batteries is equal to or greater than the temperature difference threshold. Battery pack.

[0183] <Note 15> A battery pack as described in Appendix 11 or Appendix 12, The control unit reduces the charging current command value by the first predetermined current amount if the current difference is equal to or greater than the first current difference threshold and the plurality of batteries are not being cooled. Battery pack.

[0184] <Note 16> A battery pack as described in Appendix 11 or Appendix 12, The control unit reduces the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold and the plurality of batteries are being cooled. Battery pack.

[0185] <Note 17> Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, The control unit reduces the charging current command value by the first predetermined current amount if the temperature difference between the maximum and minimum temperatures among the multiple batteries is greater than or equal to the first temperature difference threshold. Battery pack.

[0186] <Note 18> The battery pack described in Appendix 17, The control unit increases the charging current command value by the first predetermined current when the temperature difference between the maximum and minimum temperatures among the plurality of batteries is less than or equal to the second temperature difference threshold. Battery pack.

[0187] <Note 19> A battery pack as described in Appendix 17 or Appendix 18, The control unit reduces the charging current command value by the first predetermined current amount if the temperature difference between the maximum and minimum temperatures of the plurality of batteries is greater than or equal to a first temperature difference threshold and the plurality of batteries are not being cooled. Battery pack.

[0188] <Note 20> A battery pack as described in Appendix 17 or Appendix 18, The control unit reduces the charging current command value by the first predetermined current when the temperature difference between the maximum and minimum temperatures of the plurality of batteries is greater than or equal to a first temperature difference threshold and the plurality of batteries are being cooled. Battery pack.

[0189] <Note 21> A battery pack as described in any one of the following appendices: 1, 4, 11, or 17. The aforementioned battery is composed of a lithium iron phosphate battery. Battery pack. [Explanation of symbols]

[0190] BP Battery Pack Ba, Bb batteries BCa1, BCa2, BCb1, BCb2 battery cells Sva1, Sva2, Svb1, Svb2 Voltage detection unit Sia, Sib current detection unit Rea, Reb, ReCh, ReLo relays Str storage Cnt Control Unit F Cooler Ch charger Lo load Ca charging cable

Claims

1. Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, When the maximum current among the currents flowing through the plurality of batteries exceeds a first current threshold, the control unit reduces the charging current command value by a first predetermined current. Battery pack.

2. A battery pack according to claim 1, When the maximum current falls below a second current threshold, which is lower than the first current threshold, the control unit increases the charging current command value by a second predetermined current. Battery pack.

3. A battery pack according to claim 1 or claim 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the maximum temperature among the multiple batteries is equal to or greater than the temperature threshold. Battery pack.

4. A battery pack according to claim 1 or claim 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold, and when the temperature difference between the maximum and minimum temperatures among the plurality of batteries is equal to or greater than the temperature difference threshold. Battery pack.

5. A battery pack according to claim 1 or claim 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the plurality of batteries are not being cooled. Battery pack.

6. A battery pack according to claim 1 or claim 2, The control unit reduces the charging current command value by the first predetermined current amount when the maximum current is equal to or greater than the first current threshold and the plurality of batteries are being cooled. Battery pack.

7. Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, The control unit reduces the charging current command value by a first predetermined current when the maximum temperature among the multiple batteries is equal to or greater than a first temperature threshold. Battery pack.

8. A battery pack according to claim 7, When the maximum temperature falls below a second temperature threshold, which is lower than the first temperature threshold, the control unit increases the charging current command value by a second predetermined current. Battery pack.

9. A battery pack according to claim 7 or claim 8, The control unit reduces the charging current command value by the first predetermined current when the maximum temperature is equal to or greater than the first temperature threshold and the plurality of batteries are not being cooled. Battery pack.

10. A battery pack according to claim 7 or claim 8, The control unit reduces the charging current command value by the first predetermined current when the maximum temperature is equal to or greater than the first temperature threshold and the plurality of batteries are being cooled. Battery pack.

11. Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, When the current difference between the maximum and minimum currents among the currents flowing through the plurality of batteries becomes greater than or equal to a first current difference threshold, the control unit reduces the charging current command value by a first predetermined current. Battery pack.

12. A battery pack according to claim 11, When the current difference falls below a second current difference threshold, which is lower than the first current difference threshold, the control unit increases the charging current command value by a second predetermined current. Battery pack.

13. A battery pack according to claim 11 or claim 12, The control unit reduces the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold, and the maximum temperature among the multiple batteries is equal to or greater than the temperature threshold. Battery pack.

14. A battery pack according to claim 11 or claim 12, The control unit reduces the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold, and when the temperature difference between the maximum and minimum temperatures among the multiple batteries is equal to or greater than the temperature difference threshold. Battery pack.

15. A battery pack according to claim 11 or claim 12, The control unit reduces the charging current command value by the first predetermined current amount if the current difference is equal to or greater than the first current difference threshold and the plurality of batteries are not being cooled. Battery pack.

16. A battery pack according to claim 11 or claim 12, The control unit reduces the charging current command value by the first predetermined current amount when the current difference is equal to or greater than the first current difference threshold and the plurality of batteries are being cooled. Battery pack.

17. Multiple batteries connected in parallel to each other, A control unit controls the charging current command value so that the charge levels of the plurality of batteries become equal during charging, Equipped with, The control unit reduces the charging current command value by a first predetermined current if the temperature difference between the maximum and minimum temperatures among the plurality of batteries is greater than or equal to a first temperature difference threshold. Battery pack.

18. A battery pack according to claim 17, The control unit increases the charging current command value by the first predetermined current when the temperature difference between the maximum and minimum temperatures among the plurality of batteries is less than or equal to the second temperature difference threshold. Battery pack.

19. A battery pack according to claim 17 or claim 18, The control unit reduces the charging current command value by the first predetermined current amount if the temperature difference between the maximum and minimum temperatures of the plurality of batteries is greater than or equal to a first temperature difference threshold and the plurality of batteries are not being cooled. Battery pack.

20. A battery pack according to claim 17 or claim 18, The control unit reduces the charging current command value by the first predetermined current when the temperature difference between the maximum and minimum temperatures of the plurality of batteries is greater than or equal to a first temperature difference threshold and the plurality of batteries are being cooled. Battery pack.

21. A battery pack according to any one of claims 1, 7, 11, or 17, The aforementioned battery is composed of a lithium iron phosphate battery. Battery pack.

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