Power System

Abstract

To reduce the amount of decrease of charge power or discharge power of a battery pack even when the internal resistance of a single battery increases.SOLUTION: A battery module 10 comprises single batteries 11, each of which is connected in series. A battery pack 100 comprises two battery modules 10a and 10b. A connection configuration of the battery modules 10 can be switched between series connection and parallel connection by turning a first relay R1 to a third relay R3 ON / OFF. An ECU 200 switches the connection configuration from series connection to parallel connection, when the internal resistance of one of the single batteries 11 increases, and the charge power or discharge power when switching the connection configuration to parallel connection is greater than the decreased charge power or discharge power with the increase of the internal resistance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to power supply systems. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2022-87447 (Patent Document 1) discloses a battery pack in which, in a battery module in which a plurality of battery cells are connected in parallel, the connection of the plurality of battery cells is switched to a series connection during charging. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-87447 Summary of the Invention [Problem to be solved by the invention]

[0004] Battery packs are known that have battery modules in which multiple batteries (battery cells) are connected in series. In such battery packs, one of the batteries included in the battery module may rapidly deteriorate due to some factor, causing an increase in internal resistance. When the internal resistance of a battery increases, the charge and discharge currents of that battery decrease. Therefore, in battery packs in which battery modules are connected in series, each battery module having multiple batteries connected in series, the charge and discharge currents are limited by the battery with increased internal resistance, resulting in a decrease in the charge and discharge power of the battery pack.

[0005] The object of the present disclosure is to reduce the amount of decrease in the charging power or discharging power of a battery pack in a battery module in which multiple cells are connected in series, even if the internal resistance of any of the cells increases. [Means for solving the problem]

[0006] (1) The power supply system disclosed herein includes a battery pack and a control device. The battery pack includes a plurality of battery modules and a switching circuit. Each of the plurality of battery modules includes a plurality of unit cells connected in series. The switching circuit is configured to switch the connection between the plurality of battery modules between a series connection and a parallel connection. The control device controls the switching circuit. The control device is configured to switch the connection from a series connection to a parallel connection based on an increase in the internal resistance of any unit cell included in the plurality of battery modules.

[0007] According to this configuration, the battery module is composed of cells connected in series. The battery pack includes a plurality of battery modules and a switching circuit that switches the connection between the battery modules between a series connection and a parallel connection.

[0008] When multiple battery modules are connected in series, if the internal resistance of any of the cells in the battery modules increases, the discharge current of the battery pack decreases. Also, the charging current relative to the charging voltage of the battery pack decreases. Therefore, if the internal resistance of any of the cells increases, the charging power and discharging power of the battery pack decrease.

[0009] The control device switches the connection configuration from a series connection to a parallel connection based on an increase in the internal resistance of any of the cells included in the battery module. For example, if the internal resistance of the cells increases in a series connection and the charge or discharge power becomes larger when the connection configuration is switched to a parallel connection than the charge or discharge power reduced by the increase in internal resistance, the control device switches the connection configuration from a series connection to a parallel connection. This allows the amount of reduction in the charge or discharge power of the battery pack to be reduced even if the internal resistance of any of the cells increases.

[0010] (2) The control device may switch the connection configuration from a series connection to a parallel connection when the decrease in charging power ΔPcs due to an increase in internal resistance when the connection configuration is a series connection is greater than the decrease in charging power ΔPcp when the connection configuration is switched to a parallel connection.

[0011] With this configuration, the control device calculates the amount of decrease in charging power ΔPcs due to an increase in internal resistance when the connection is in series. The control device also calculates the amount of decrease in charging power ΔPcp when the connection is switched to a parallel connection. When the amount of decrease ΔPcs is greater than ΔPcp, the control device switches the connection from a series connection to a parallel connection. When the internal resistance of the cells increases and the charging power in the series connection falls below the charging power in the parallel connection, the connection is switched from a series connection to a parallel connection. Therefore, even if the internal resistance of any of the cells increases, the amount of decrease in charging power of the battery pack can be reduced.

[0012] (3) In (2) above, the amount of decrease in charging power ΔPcp when the connection type is switched to a parallel connection may be calculated taking into account the improvement in efficiency of the charger due to the decrease in charging voltage caused by the parallel connection.

[0013] When battery modules are connected in parallel, the charging voltage of the battery pack decreases. When the charging voltage decreases, the boost voltage of the charger decreases, and the efficiency of the charger increases. With this configuration, the amount of decrease in charging power ΔPcp is calculated taking into account the improvement in charger efficiency, allowing for efficient charging of the power from the external power source.

[0014] (4) In the above (3), the battery pack and the charger may be mounted on a vehicle, and the charger may convert power from an external AC power supply into DC charging power.

[0015] According to this configuration, it is possible to reduce the amount of decrease in charging power of the battery pack in the power supply system of an electrically powered vehicle.

[0016] (5) The control device may switch the connection configuration from a series connection to a parallel connection when the decrease in discharge power ΔPds due to an increase in internal resistance when the connection configuration is a series connection is greater than the decrease in discharge power ΔPdp when the connection configuration is switched to a parallel connection.

[0017] According to this configuration, the control device calculates the amount of decrease ΔPds in discharge power due to an increase in internal resistance when the connection is in series. The control device also calculates the amount of decrease ΔPdp in discharge power when the connection is switched to a parallel connection. When the amount of decrease ΔPds is greater than ΔPdp, the control device switches the connection from series to parallel. When the internal resistance of the cells increases and the discharge power in the series connection falls below the discharge power in the parallel connection, the connection is switched from series to parallel. Therefore, even if the internal resistance of any of the cells increases, the amount of decrease in discharge power of the battery pack can be reduced. [Effects of the Invention]

[0018] According to the present disclosure, in a battery module in which multiple cells are connected in series, even if the internal resistance of any of the cells increases, the amount of decrease in the charging power or discharging power of the battery pack can be reduced. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram showing a schematic configuration of a vehicle equipped with a power supply system according to an embodiment of the present invention. [Figure 2] 4 is a flowchart showing an example of a connection switching control process executed by an ECU in the present embodiment. [Figure 3] 10A and 10B are diagrams showing charging current and discharging current of a battery pack in a series connection. [Figure 4] FIG. 10 is a diagram showing the charge current and discharge current when the internal resistance of a battery cell increases in a series connection. [Figure 5] FIG. 10 is a diagram showing the charge current and discharge current when the internal resistance of a battery cell increases in a parallel connection. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0021] 1 is a diagram showing a schematic configuration of a vehicle 1 equipped with a power supply system according to this embodiment. The vehicle 1 is an electrically powered vehicle, for example, an electric automobile. The vehicle 1 includes a motor generator (MG) 40, which is a rotating electric machine, drive wheels 50, a power control unit (PCU) 30, a system main relay (SMR) 20, a battery pack 100, a charging relay 60, a charger 70, and an electronic control unit (ECU) 200, which is an example of a control device.

[0022] The MG 40 is, for example, an interior permanent magnet synchronous motor (IPM motor) that functions as both an electric motor (motor) and a generator (generator). The output torque of the MG 40 is transmitted to the drive wheels 50 via a power transmission device that includes a reducer, a differential gear, etc.

[0023] When braking the vehicle 1, the MG 40 is driven by the drive wheels 50, and the MG 40 operates as a generator. This allows the MG 40 to function as a braking device that performs regenerative braking, converting the kinetic energy of the vehicle 1 into electric power. The regenerative power generated by the regenerative braking force in the MG 40 is stored in the battery pack 100.

[0024] The PCU 30 is a power conversion device that converts power bidirectionally between the MG 40 and the battery pack 100. The PCU 30 includes, for example, an inverter and a converter that operate based on a control signal from the ECU 200. When the battery pack 100 is discharging, the converter boosts the voltage supplied from the battery pack 100 and supplies the boosted voltage to the inverter. The inverter converts the DC power supplied from the converter into AC power to drive the MG 10. Note that the PCU 40 may be configured without the converter.

[0025] The SMR 20 is electrically connected to a power line connecting the battery pack 100 and the PCU 30. When the SMR 20 is closed (ON) in response to a control signal from the ECU 200 (i.e., in a conductive state), power can be exchanged between the battery pack 100 and the PCU 30. On the other hand, when the SMR 20 is opened (OFF) in response to a control signal from the ECU 200 (i.e., in a cut-off state), the electrical connection between the battery pack 100 and the PCU 30 is cut off.

[0026] The vehicle 1 is equipped with an inlet 71, and the battery pack 100 can be normally charged from an external alternating current (AC) power source 80, which is a charging facility. The inlet 71 is configured to allow connection to a connector 81 provided at the tip of a charging cable of the external AC power source (charging facility) 80. A charger 70 is provided in the power line between the inlet 71 and the battery pack 100, and converts AC power supplied from the external AC power source into DC power and converts (boosts) the voltage to a level that can charge the battery pack 100. A charging relay 60 is electrically connected to the power line connecting the charger 70 and the battery pack 100. The charging relay 60 switches between supplying and cutting off power between the charger 70 and the battery pack 100 in response to a control signal from the ECU 200. When the charging relay 60 is closed, external charging of the battery pack 100 is performed.

[0027] The battery pack 100 includes a plurality of battery modules 10. In this embodiment, the battery pack 100 includes two battery modules 10 (10a, 10b). The battery module 10 is composed of cells 11, which are secondary batteries such as nickel-metal hydride batteries or lithium-ion batteries. The secondary batteries may be batteries having a liquid electrolyte between the positive and negative electrodes, or may be batteries having a solid electrolyte (all-solid-state batteries). The battery module 10 is composed of a plurality of cells 11 electrically connected in series. The number of cells 11 may be any number.

[0028] The connection between the battery module 10a and the battery module 10b can be switched between a series connection and a parallel connection. In this embodiment, the positive terminal of the battery module 10a and the positive terminal of the battery module 10b are connected to a positive line PL, and the negative terminal of the battery module 10a and the negative terminal of the battery module 10b are connected to a negative line NL. A first relay R1 is provided on the positive line PL between the positive terminal of the battery module 10a and the positive terminal of the battery module 10b. A second relay R2 is provided between the negative terminal of the battery module 10b and the negative line NL. A power line CL connects the positive terminal of the battery module 10a and the first relay R1 and the negative terminal of the battery module 10b and the second relay. A third relay R3 is provided on the power line CL.

[0029] When the first relay R1 and the second relay R2 are closed (ON) and the third relay R3 is opened (OFF), the battery module 10a and the battery module 10b are connected in parallel. When the first relay R1 and the second relay R2 are opened (OFF) and the third relay R3 is closed (ON), the battery module 10a and the battery module 10b are connected in series. The first relay R1, the second relay R2, and the third relay R3 are controlled by a control device, and these relays correspond to an example of a "switching circuit" in the present disclosure. The battery pack 100 corresponds to an example of a "battery pack" in the present disclosure.

[0030] The battery module 10 is provided with a monitoring unit 15. The monitoring unit 15 includes sensors for detecting the voltage Vb of the cells 11, the input / output current Im of the battery module 10, and the temperature TB, and outputs signals indicating the detection results to the ECU 200. The monitoring unit 15 also includes a voltage sensor 16 for detecting the voltage VB between the positive electrode line PL and the negative electrode line NL (the voltage of the battery pack 100), and a current sensor 17 for detecting the input / output current IB of the battery pack 100, and the detection signals thereof are input to the ECU 200. In the present embodiment, the battery pack 100 and the ECU 200 correspond to an example of a "power supply system" of the present disclosure.

[0031] In the battery pack 100, when the battery modules 10 are connected in series, the output voltage of the battery pack 100 increases, thereby improving the system output of the vehicle 1. Furthermore, when the battery modules are connected in series, as explained in Patent Document 1, it is expected that the charging time will be shortened.

[0032] One of the cells 11 included in the battery module 10 may rapidly deteriorate due to some factor, causing an increase in internal resistance. When the internal resistance of a cell 11 increases, the charge current and discharge current of that cell 11 decrease. Therefore, in a battery pack 100 in which battery modules 10, each having cells 11 connected in series, are connected in series, the charge current and discharge current are limited by the cell 11 with increased internal resistance, causing a decrease in the charge power and discharge power of the battery pack.

[0033] In this embodiment, even if the internal resistance of the cells 11 increases, the connection configuration of the battery modules 10 is switched to reduce the amount of decrease in charging power and discharging power.

[0034] 2 is a flowchart showing an example of a connection switching control process executed by the ECU 200 in this embodiment. This flowchart is repeatedly processed at predetermined intervals. In this embodiment, the battery modules 10 are connected in series by default. The default values ​​of flags F1 and F2 are set to 0.

[0035] First, in step (hereinafter, step will be abbreviated as "S") 10, it is determined whether or not the battery pack 100 is in an external charging state. For example, if the connector 81 is connected to the AC inlet 71, it may be determined that the battery pack 100 is in an external charging state. If the battery pack 100 is in an external charging state, a positive determination is made and the process proceeds to S11. If the battery pack 100 is not in an external charging state, a negative determination is made and the process proceeds to S17.

[0036] In S11, it is determined whether or not flag F1 is 1. Since the default value of flag F1 is 0, the first time S11 is processed, a negative determination is made and the process proceeds to S12. If flag F1 is 1, a positive determination is made and the process proceeds to S16.

[0037] In S12, it is determined whether the internal resistance Ri of any of the cells 11 in the battery module 10 (10a, 10b) is equal to or greater than a predetermined value A. The predetermined value A is a value that indicates that even if the internal resistance Ri of any of the cells 11 increases to the predetermined value A, the decrease in charging power is clearly smaller when the battery modules 10 are connected in series than when they are connected in parallel. The predetermined value A is set in advance through experiments, etc. The internal resistance Ri of the cell 11 may be calculated from the voltage Vb, current Im, etc. detected by the monitoring unit 15. For example, in an internal resistance detection routine (not shown), the internal resistance Ri of the cell 11 may be calculated from the voltage Vb and current Im when constant current charging or constant current discharging is being performed from the battery module 10 (battery pack 100).

[0038] If the internal resistance Ri of any of the cells 11 is equal to or greater than the predetermined value A, a positive determination is made and the process proceeds to S13. If the internal resistance Ri of all the cells 11 is less than the predetermined value A, a negative determination is made and the process proceeds to S22.

[0039] In S13, the amount of decrease ΔPcs in charging power due to an increase in internal resistance Ri when the battery modules 10 are connected in series and the amount of decrease ΔPcp in charging power when the connection is switched to parallel connection are calculated.

[0040] FIG. 3 is a diagram showing the charge current and discharge current of the battery pack 100 in a series connection. In FIG. 3, the black arrows represent the charge current, and the white arrows represent the discharge current. The width of the arrows represents the magnitude of the current. In FIG. 3, none of the cells 11 have deteriorated, and the internal resistance Ri is small. The battery modules 10 are connected in series, and as shown in FIG. 3, a charge current Ic0 flows through the cells 11 (battery modules 10).

[0041] FIG. 4 is a diagram showing the charge current and discharge current when the internal resistance Ri of the cells 11 increases in a series connection. In FIG. 4, the black arrows represent the charge current, and the white arrows represent the discharge current. The width of the arrows represents the magnitude of the current. FIG. 4 shows a state in which one of the cells 11 included in the battery module 10a has suddenly deteriorated for some reason, causing its internal resistance Ri to increase. When the internal resistance Ri of one cell 11 increases, the charge current of that cell 11 decreases for the same charge voltage. Because the battery modules 10 (and cells 11) are connected in series, the charge current of the battery pack 100 (battery module 10) decreases from charge current Ic0 to charge current Ic1.

[0042] FIG. 5 shows the charge and discharge currents of parallel-connected cells 11 when their internal resistances Ri increase. In FIG. 5, black arrows represent charge currents, and white arrows represent discharge currents. The width of the arrows indicates the magnitude of the currents. Similar to FIG. 4, FIG. 5 illustrates a state in which one of the cells 11 in a battery module 10a has suddenly deteriorated for some reason, resulting in an increase in its internal resistance Ri. In FIG. 5, the charge voltage (output voltage of the charger 70) is controlled to approximately half that of FIGS. 3 and 4 so that the charge voltage of the cell 11 is the same as that of FIGS. 3 and 4. The charge current of a battery module 10a containing a cell 11 with an increased internal resistance Ri decreases to Ic1. However, the charge current of a battery module 10b containing undegraded cells 11 with no increased internal resistance Ri remains constant and the battery module 10b is charged at Ic0.

[0043] When the battery modules 10 are connected in series, the charging power (reference charging power) Pcs0 when all the cells 11 are not deteriorated and the internal resistance Ri is small is set in advance through experiments or the like depending on the specifications of the battery pack 100 (battery module 10). The reference charging power Pcs0 varies depending on the SOC (State Of Charge) of the battery pack 100 (battery module 10), and is therefore stored in the memory of the ECU 200 as a map for each SOC.

[0044] In S13, the amount of decrease ΔPcs in charging power due to an increase in internal resistance Ri when the battery modules 10 are connected in series is calculated as follows: It is confirmed whether the battery modules 10 are connected in series. (If they are connected in parallel, it is switched to a series connection.) When external charging begins, the charging power Pcs1 is calculated by multiplying the voltage VB detected by the voltage sensor 16 by the current IB detected by the current sensor 17. Then, the reference charging power Pcs0 corresponding to the current SOC of the battery pack 100 is read from the map. The amount of decrease ΔPcs in charging power is calculated by subtracting the charging power Pcs1 from the reference charging power Pcs0 read from the map (ΔPcs = Pcs0 - Pcs1).

[0045] In S13, the amount of decrease in charging power ΔPcp when the connection configuration is switched to the parallel connection is calculated as follows. formare connected in parallel. When external charging begins, charging power Pcp1 is calculated by multiplying voltage VB detected by voltage sensor 16 and current IB detected by current sensor 17 by coefficient k. Coefficient k reflects the improvement in efficiency of charger 70 due to the reduction in charging voltage caused by parallel connection, and is set to a value greater than 1. In this embodiment, it is set to 1.05. Then, reference charging power Pcs0 corresponding to the current SOC of battery pack 100 is read from the map. The charging power Pcp1 is subtracted from the reference charging power Pcs0 read from the map to calculate the reduction amount ΔPcp of charging power (ΔPcp=Pcs0−Pcp1). Coefficient k may be set in advance according to the specifications of charger 70, or it may be calculated each time from the charging voltage in series connection and the charging voltage in parallel connection.

[0046] In the next step S14, it is determined whether the decrease ΔPcs is greater than the decrease ΔPcp. If the decrease ΔPcs is greater than the decrease ΔPcp (ΔPcs>ΔPsp), an affirmative determination is made and the program proceeds to step S15. If the decrease ΔPcs is equal to or less than the decrease ΔPcp (ΔPcs≦ΔPsp), a negative determination is made and the program proceeds to step S22.

[0047] In S15, the flag F1 is set to 1. As a result, from the next time onwards, a positive determination is made in S11. Subsequently, in S16, the first relay R1 and the second relay R2 are connected (ON) and the third relay R3 is disconnected (OFF), so that the connection of the battery modules 10 is changed to a parallel connection, and the current routine ends.

[0048] In S17, it is determined whether or not flag F2 is 1. Since the default value of flag F2 is 0, the first time S17 is processed, a negative determination is made and the process proceeds to S18. If flag F2 is 1, an affirmative determination is made and the process proceeds to S16.

[0049] In S18, it is determined whether the internal resistance Ri of any of the cells 11 in the battery module 10 (10a, 10b) is equal to or greater than a predetermined value B. The predetermined value B is a value at which the decrease in discharge power is clearly smaller when the battery modules 10 are connected in series than when they are connected in parallel, even if the internal resistance Ri of any of the cells 11 increases to the predetermined value B. The predetermined value B is set in advance by experiment or the like.

[0050] If the internal resistance Ri of any of the cells 11 is equal to or greater than the predetermined value B, a positive determination is made and the process proceeds to S19. If the internal resistance Ri of all the cells 11 is less than the predetermined value A, a negative determination is made and the process proceeds to S22.

[0051] In S19, the amount of decrease ΔPds in discharge power due to an increase in internal resistance Ri when the battery modules 10 are connected in series and the amount of decrease ΔPdp in discharge power when the connection is switched to parallel are calculated. As indicated by the white arrow in FIG. 3, when the battery modules 10 are connected in series, none of the cells 11 are degraded, and the internal resistance Ri is small, the discharge current (output current) of the battery module 10 is current Id0. In a series connection, if the internal resistance Ri of one cell 11 increases, the discharge current of that cell 11 decreases. Then, because the battery modules 10 (and the cells 11) are connected in series, the discharge current of the battery pack 100 (battery modules 10) decreases from current Id0 to current Id1, as shown in FIG. 4. When the internal resistance Ri of one battery 11 becomes large, in a parallel connection, as shown in Figure 5, the discharge current of the battery module 10a including the battery 11 with the large internal resistance Ri becomes current Id1, while the discharge current of the battery module 10b is maintained at current Id0.

[0052] When the battery modules 10 are connected in series, the discharge power (reference output power) Pds0 when all the cells 11 are not deteriorated and the internal resistance Ri is small is set in advance by experiments or the like depending on the specifications of the battery pack 100 (battery module 10). The reference output power Pds0 may be the output power (discharge power) when the battery pack 100 is connected to a predetermined load, and in this embodiment, the discharge resistor provided in the PCU 30 is set as the predetermined load.

[0053] In S19, the amount of decrease ΔPds in discharge power due to an increase in internal resistance Ri when the battery modules 10 are connected in series is calculated as follows: It is confirmed whether the battery modules 10 are connected in series. (If they are connected in parallel, the connection is switched to series.) The power of the battery pack 100 is discharged via a discharge resistor. During this discharge, the voltage VB detected by the voltage sensor 16 is multiplied by the current IB detected by the current sensor 17 to calculate the discharge power Pds1. The amount of decrease ΔPds in discharge power is then calculated by subtracting the discharge power Pds1 from the reference output power Pds0 (ΔPds = Pds0 - Pds1).

[0054] In S19, the amount of decrease ΔPdp in discharge power when the connection configuration is switched to the parallel connection is calculated as follows. form are connected in parallel. The power of the battery pack 100 is discharged via a discharge resistor. During this discharge, the voltage VB detected by the voltage sensor 16 is multiplied by the current IB detected by the current sensor 17 to calculate the discharge power Pdp1. Then, the discharge power Pdp1 is subtracted from the reference output power Pds0 to calculate the amount of decrease ΔPdp in the discharge power (ΔPdp=Pds0−Pdp1).

[0055] In the next step S20, it is determined whether the decrease amount ΔPds is greater than the decrease amount ΔPdp. If the decrease amount ΔPds is greater than the decrease amount ΔPdp (ΔPds>ΔPdp), an affirmative determination is made and the process proceeds to step S21. If the decrease amount ΔPds is equal to or less than the decrease amount ΔPdp (ΔPds≦ΔPdp), a negative determination is made and the process proceeds to step S22.

[0056] In S121, the flag F2 is set to 1, and the routine proceeds to S16. As a result, from the next time onwards, a positive determination is made in S17. In S22, the first relay R1 and the second relay R2 are switched to the disconnected (OFF) state, and the third relay R3 is switched to the connected (ON) state, so that the battery modules 10 are connected in series, and the current routine ends.

[0057] According to this embodiment, when multiple battery modules 10 are connected in series, if the internal resistance Ri of any of the cells 11 included in the battery module 10 increases and the decrease in charge power ΔPcs is greater than the decrease in charge power ΔPcp, the connection is switched from series connection to parallel connection. Furthermore, if the decrease in discharge power ΔPds is greater than the decrease in discharge power ΔPdp, the connection is switched from series connection to parallel connection. This makes it possible to reduce the decrease in charge power or discharge power of the battery pack 100 even if the internal resistance Ri of any of the cells 11 increases.

[0058] According to this embodiment, the decrease amount ΔPcp is calculated taking into consideration the improvement in efficiency of the charger 70 due to the decrease in charging voltage, so that the power of the external AC power supply 80 can be used for charging efficiently.

[0059] In the above embodiment, the charging power Pcs1 and the discharging power Pds1 during series connection are calculated using the voltage VB detected by the voltage sensor 16 and the current IB detected by the current sensor 17, and the charging power Pcp1 and the discharging power Pdp1 during parallel connection are calculated. During series connection, the voltage VB and the current IB can be obtained using the voltage Vb and the current Im detected by the monitoring unit 15. Also, during parallel connection, the charging power and the discharging power of the battery module 10a can be calculated using the voltage Vb and the current Im detected by the monitoring unit 15, and the charging power and the discharging power of the battery module 10b can be calculated. Then, the charging power Pcp1 can be obtained by adding the charging powers of the battery module 10a and the battery module 10b, and the discharging power Pdp1 can be obtained by adding the discharging powers of the battery module 10a and the battery module 10b. Therefore, the voltage sensor 16 and the current sensor 17 may not be provided.

[0060] In the above embodiment, the reduction amount ΔPcs and the reduction amount ΔPcp are calculated based on the reference charging power Pcs0, and the reduction amount ΔPds and the reduction amount ΔPdp are calculated based on the reference output power Pds0. Therefore, in S14, the comparison between the reduction amount ΔPcs and the reduction amount ΔPcp may be made by comparing the charging power Pcs1 and the charging power Pcp1 (Pcs1 < Pcp1). Similarly, in S20, the comparison between the reduction amount ΔPds and the reduction amount ΔPdp may be made by comparing the discharging power Pds1 and the discharging power Pdp1 (Pds1 < Pdp1). In this case, the direction of the inequality sign is opposite to that in the above embodiment, and when "Pcs1 < Pcp1" is satisfied, it is determined that the reduction amount ΔPcs is larger than the reduction amount ΔPcp, and when "Pds1 < Pdp1" is satisfied, it is determined that the reduction amount ΔPds is larger than the reduction amount ΔPdp.

[0061] In the above embodiment, the battery pack 100 includes two battery modules 10 (10a, 10b), but the number of battery modules 10 may be three or more.

[0062] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0063] 1 vehicle, 10 battery module, 11 battery cell, 15 monitoring unit, 16 voltage sensor, 17 current sensor, 20 system main relay (SMR), 30 power control unit (PCU), 40 motor generator (MG), 50 drive wheel, 60 charging relay, 70 charger, 71 inlet, 80 external AC power supply, 100 battery pack, 200 electronic control unit (ECU), CL power line, LN negative line, PL positive line, R1 first relay, R2 second relay, R3 third relay.

Claims

1. a battery pack including a plurality of battery modules and a switching circuit; each of the plurality of battery modules includes a plurality of unit cells connected in series; the switching circuit is configured to switch the connection between the plurality of battery modules between a series connection and a parallel connection, and A control device for controlling the switching circuit is provided. The control device the connection configuration is switched from a series connection to a parallel connection based on an increase in the internal resistance of any one of the cells included in the plurality of battery modules, when a decrease amount ΔPcs of charging power due to an increase in the internal resistance when the connection configuration is series connection is larger than a decrease amount ΔPcp of charging power when the connection configuration is switched to parallel connection, the connection configuration is switched from series connection to parallel connection; A power supply system, wherein the decrease amount ΔPcs is the amount of decrease in charging power from a reference charging power Pcs0 when the connection configuration is a series state, and the decrease amount ΔPcp is the amount of decrease in charging power from the reference charging power Pcs0.

2. 2. The power supply system according to claim 1, wherein the amount of decrease ΔPcp is calculated taking into consideration an improvement in efficiency of the charger due to a decrease in charging voltage caused by parallel connection.

3. the battery pack and the charger are mounted on a vehicle; 3. The power supply system according to claim 2, wherein the charger converts power from an external AC power supply into DC charging power.

4. The control device when a decrease ΔPds in discharge power due to an increase in the internal resistance when the connection configuration is series connection is larger than a decrease ΔPdp in discharge power when the connection configuration is switched to parallel connection, the connection configuration is switched from series connection to parallel connection; 2. The power supply system according to claim 1, wherein the decrease amount ΔPds is an amount of decrease in discharge power from a reference output power Pds0 when the connection configuration is a series state, and the decrease amount ΔPdp is an amount of decrease in discharge power from the reference output power Pds0.

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