CN118449220A - Power Systems - Google Patents

Abstract

The battery module is composed of single cells connected in series. The battery pack has two battery modules, and the connection mode of the battery modules can be switched to a series connection or a parallel connection by turning on/off the first to third relays. When the charging power or discharging power when the connection mode is switched to a parallel connection is greater than the charging power or discharging power that is reduced due to the increase in the internal resistance of a single cell, the ECU switches the connection mode from a series connection to a parallel connection.

Description

Power Systems

Technical Field

The present disclosure relates to power supply systems.

Background technique

Japanese Patent Application Laid-Open No. 2022-87447 discloses a battery pack in which, in a battery module including a plurality of battery cells connected in parallel, the connection mode of the plurality of battery cells is switched to a series connection during charging.

Summary of the invention

A battery pack is known that has a battery module formed by connecting a plurality of single cells (battery cells) in series, and the plurality of battery modules are connected in series. In such a battery pack, there is also a situation where a single cell contained in the battery module deteriorates rapidly for some reason, thereby increasing the internal resistance. If the internal resistance of a single cell increases, the charging current and discharging current of the single cell will decrease. Therefore, in a battery pack in which a battery module formed by connecting a plurality of single cells in series is connected in series, the charging current and the discharging current will be limited by the single cell with increased internal resistance, and the charging power and the discharging power of the battery pack will be reduced.

An object of the present disclosure is to reduce the amount of reduction in charging power or discharging power of a battery pack even if the internal resistance of a single cell increases in a battery module including a plurality of single cells connected in series.

(1) The power supply system of the present disclosure comprises a battery pack and a control device. The battery pack comprises a plurality of battery modules and a switching circuit. The plurality of battery modules each comprises a plurality of single cells connected in series. The switching circuit is configured to switch the connection mode between the plurality of battery modules to a series connection or a parallel connection. The control device controls the switching circuit. The control device is configured to switch the connection mode from a series connection to a parallel connection according to an increase in the internal resistance of a single cell included in the plurality of battery modules.

According to this configuration, the battery module is composed of single batteries connected in series. The battery pack includes a plurality of battery modules and a switching circuit for switching the connection between the battery modules to a series connection or a parallel connection.

When multiple battery modules are connected in series, if the internal resistance of a single cell included in the battery module increases, the discharge current of the battery pack will decrease. In addition, the charging current relative to the charging voltage of the battery pack decreases. Therefore, if the internal resistance of a single cell increases, the charging power and discharge power of the battery pack will decrease.

The control device switches the connection mode from series connection to parallel connection according to the increase of the internal resistance of a single cell included in the battery module. For example, in the case of series connection, when the charging power or discharging power when the connection mode is switched to parallel connection is greater than the charging power or discharging power reduced due to the increase of the internal resistance of the single cell, the connection mode is switched from series connection to parallel connection. Thus, even if the internal resistance of a single cell increases, the reduction amount of the charging power or discharging power of the battery pack can be reduced.

(2) When the reduction amount ΔPcs of charging power due to the increase of internal resistance when the connection mode is series connection is larger than the reduction amount ΔPcp of charging power when the connection mode is switched to parallel connection, the control device may switch the connection mode from series connection to parallel connection.

According to this configuration, the control device calculates the amount of reduction ΔPcs in charging power caused by the increase in internal resistance when the connection mode is a series connection. In addition, the control device calculates the amount of reduction ΔPcp in charging power when the connection mode is switched to a parallel connection. And when the reduction ΔPcs is greater than ΔPcp, the control device switches the connection mode from a series connection to a parallel connection. When the internal resistance of a single cell increases and the charging power under the series connection is lower than the charging power under the parallel connection, the connection is switched from the series connection to the parallel connection. Therefore, even if the internal resistance of a single cell increases, the reduction in the charging power of the battery pack can be reduced.

(3) In the above (2), the reduction amount ΔPcp of the charging power when the connection mode is switched to the parallel connection may be calculated by also considering the improvement amount of the charger efficiency due to the reduction of the charging voltage caused by the parallel connection.

If the battery modules are connected in parallel, the charging voltage of the battery pack will decrease. If the charging voltage decreases, the boost voltage of the charger becomes smaller, so the efficiency of the charger increases. According to this configuration, since the reduction in charging power ΔPcp is calculated taking into account the improvement in efficiency of the charger, the power of the external power supply can be charged efficiently.

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

According to this configuration, it is possible to reduce the amount of reduction in charging power of the battery pack in the power supply system of the electric vehicle.

(5) When the reduction amount ΔPds of discharge power due to the increase of internal resistance when the connection mode is series connection is larger than the reduction amount ΔPdp of discharge power when the connection mode is switched to parallel connection, the control device may switch the connection mode from series connection to parallel connection.

According to this configuration, the control device calculates the amount of reduction ΔPds in discharge power caused by the increase in internal resistance when the connection mode is a series connection. In addition, the control device calculates the amount of reduction ΔPdp in discharge power when the connection mode is switched to a parallel connection. And when the reduction ΔPds is greater than ΔPdp, the control device switches the connection mode from a series connection to a parallel connection. When the internal resistance of a single cell increases and the discharge power in a series connection is lower than the discharge power in a parallel connection, the connection is switched from a series connection to a parallel connection. Therefore, even if the internal resistance of a single cell increases, the amount of reduction in discharge power of the battery pack can be reduced.

According to the present disclosure, in a battery module including a plurality of cells connected in series, even if the internal resistance of a cell increases, the amount of reduction in charging power or discharging power of the battery pack can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

FIG. 1 is a diagram showing a schematic configuration of a vehicle equipped with a power supply system according to the present embodiment.

FIG. 2 is a flowchart showing an example of a connection switching control process executed by the ECU in the present embodiment.

FIG. 3 is a diagram showing charging current and discharging current of a battery pack connected in series.

FIG. 4 is a diagram showing charging current and discharging current when the internal resistance of the single cells increases in series connection.

FIG. 5 is a diagram showing charging current and discharging current when the internal resistance of the cells increases in parallel connection.

Detailed ways

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are given to the same or corresponding parts in the drawings, and their description will not be repeated.

FIG1 is a diagram showing a schematic configuration of a vehicle 1 equipped with a power supply system according to the present embodiment. The vehicle 1 is an electric vehicle, such as an electric car. The vehicle 1 includes a motor generator (MG: Motor Generator) 40 as a rotating electric machine, a drive wheel 50, a power control unit (PCU: Power Control Unit) 30, a system main relay (SMR: System Main Relay) 20, a battery pack 100, a charging relay 60, a charger 70, and an electronic control unit (ECU: Electronic Control Unit) 200 as an example of a control device.

MG 40 is, for example, an embedded permanent magnet synchronous motor (IPM motor) and has a function as a motor and a function as a generator. Output torque of MG 40 is transmitted to drive wheels 50 via a power transmission device including a speed reducer and a differential device.

When the vehicle 1 is braked, the MG 40 is driven by the driving wheel 50 and operates as a generator. Thus, the MG 40 also functions as a brake device for performing regenerative braking that converts the kinetic energy of the vehicle 1 into electric power. The regenerative electric power generated by the regenerative braking force of the MG 40 is stored in the battery pack 100.

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, a converter and a transformer that operate based on a control signal from the ECU 200. When the battery pack 100 is discharged, the converter boosts the voltage supplied from the battery pack 100 and supplies it to the converter. The converter converts the DC power supplied from the converter into AC power to drive the MG 10. In addition, the PCU 40 may be configured so that the converter is omitted.

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) (i.e., in a conducting state) in response to a control signal from the ECU 200, power can be transferred between the battery pack 100 and the PCU 30. On the other hand, when the SMR 20 is opened (off) (i.e., in a blocking state) in response to a control signal from the ECU 200, the electrical connection between the battery pack 100 and the PCU 30 is blocked.

The vehicle 1 is provided with an input port 71, and the battery pack 100 can be normally charged from an external alternating current (AC) power source 80 as a charging device. The input port 71 is configured to be connected to a connector 81 provided at the front end of a charging cable of the external AC power source (charging device) 80. A charger 70 is provided on the power line between the input port 71 and the battery pack 100, and the AC power supplied from the external AC power source is converted into DC power, and is converted (boosted) into a voltage that can be charged into the battery pack 100. The 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 blocking power between the charger 70 and the battery pack 100 according to a control signal from the ECU 200. When the charging relay 60 is closed, external charging of the battery pack 100 is performed.

The battery pack 100 includes a plurality of battery modules 10. In the present embodiment, the battery pack 100 includes two battery modules 10 (10a, 10b). The battery module 10 is composed of a single cell 11, and the single cell 11 is composed of a secondary battery such as a nickel-metal hydride battery or a lithium-ion battery. The secondary battery can be a battery having a liquid electrolyte between the positive electrode and the negative electrode, or a battery having a solid electrolyte (all-solid-state battery). The battery module 10 is formed by electrically connecting a plurality of single cells 11 in series. The number of single cells 11 can be arbitrary.

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

When the first relay R1 and the second relay R2 are closed (on), and the third relay R3 is disconnected (off), the connection form of the battery module 10a and the battery module 10b becomes a parallel connection. When the first relay R1 and the second relay R2 are disconnected (off), and the third relay R3 is closed (on), the connection form of the battery module 10a and the battery module 10b becomes a series connection. The first relay R1, the second relay R2, and the third relay R3 are controlled by the control device, and these relays are equivalent to an example of the "switching circuit" of the present disclosure. In addition, the battery pack 100 is equivalent to an example of the "battery pack" of the present disclosure.

The battery module 10 is provided with a monitoring unit 15. The monitoring unit 15 includes sensors for detecting the voltage Vb of the single cell 11, the input/output current Im and the temperature TB of the battery module 10, and outputs signals indicating the detection results thereof to the ECU 200. In addition, a voltage sensor 16 for detecting the voltage VB between the positive line PL and the negative 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 are provided, 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 the "power supply system" of the present disclosure.

In the battery pack 100, if the battery modules 10 are connected in series, the output voltage of the battery pack 100 increases, and the system output of the vehicle 1 increases. In addition, if the battery modules are connected in series, as described in Japanese Patent Application Laid-Open No. 2022-87447, the charging time can be expected to be shortened.

There is a case where a single cell 11 included in a battery module 10 rapidly deteriorates for some reason, thereby increasing the internal resistance. If the internal resistance of the single cell 11 increases, the charging current and discharging current of the single cell 11 decrease. Therefore, in a battery pack 100 in which the battery modules 10 in which the single cells 11 are connected in series are connected, the charging current and the discharging current are limited by the single cell 11 in which the internal resistance has increased, and the charging power and the discharging power of the battery pack are reduced.

In the present embodiment, even if the internal resistance of the single cell 11 increases, the amount of reduction in charging power and discharging power can be reduced by switching the connection form of the battery module 10 .

FIG. 2 is a flowchart showing an example of the connection switching control process performed by the ECU 200 in the present embodiment. The flowchart is repeatedly processed for each predetermined period. In addition, in the present embodiment, in the default state, the connection form of the battery module 10 is set to be connected in series. In addition, the default values of the flags F1 and F2 are set to 0.

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

In S11, it is determined whether the flag F1 is 1. Since the default value of the flag F1 is 0, when the process of S11 is performed for the first time, a negative determination is made and the process proceeds to S12. When the flag F1 is 1, an affirmative determination is made and the process proceeds to S16.

In S12, it is determined whether the internal resistance Ri of a certain single cell 11 in the battery module 10 (10a, 10b) is greater than the specified value A. The specified value A is a value such that even if the internal resistance Ri of a certain single cell 11 increases to the specified value A, when the connection form of the battery module 10 is a series connection, the reduction in charging power is significantly smaller than when it is a parallel connection. The specified value A is set in advance through experiments, etc. The internal resistance Ri of the single cell 11 can be calculated based on the voltage Vb, current Im, etc. detected by the monitoring unit 15. For example, in an internal resistance detection routine not shown in the figure, the internal resistance Ri of the single cell 11 can be calculated based on the voltage Vb and current Im when constant current charging or constant current discharging is performed from the battery module 10 (battery pack 100).

When the internal resistance Ri of a certain cell 11 is equal to or greater than the predetermined value A, an affirmative determination is made and the process proceeds to S13. When the internal resistance Ri of all cells 11 is less than the predetermined value A, a negative determination is made and the process proceeds to S22.

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

FIG3 is a diagram showing the charging current and discharging current of the battery pack 100 in series connection. In FIG3, the solid arrows represent the charging current, and the hollow arrows represent the discharging current. The width of the arrows represents the magnitude of the current. In FIG3, all the cells 11 are not degraded and the internal resistance Ri is small. The battery modules 10 are connected in series, and as shown in FIG3, the charging current Ic0 flows in the cells 11 (battery modules 10).

FIG. 4 is a diagram showing the charging current and discharging current when the internal resistance Ri of the single cell 11 increases under series connection. In FIG. 4 , the solid arrow represents the charging current, and the hollow arrow represents the discharging current. The width of the arrow represents the magnitude of the current. FIG. 4 shows a state in which one of the single cells 11 included in the battery module 10a deteriorates rapidly for some reason, so that its internal resistance Ri increases. If the internal resistance Ri of a single cell 11 increases, the charging current of the single cell 11 decreases when the charging voltage is the same. In addition, since the battery module 10 (and the single cell 11) are connected in series, the charging current of the battery pack 100 (battery module 10) decreases from the charging current Ic0 to the charging current Ic1.

FIG. 5 is a diagram showing the charging current and discharging current when the internal resistance Ri of the single cell 11 increases under parallel connection. In FIG. 5, the solid arrow indicates the charging current, and the hollow arrow indicates the discharging current. The width of the arrow indicates the magnitude of the current. FIG. 5, as in FIG. 4, shows a state in which one of the single cells 11 included in the battery module 10a deteriorates rapidly for some reason, thereby increasing its internal resistance Ri. In FIG. 5, the charging voltage (output voltage of the charger 70) is controlled to be approximately 1/2 of that in FIG. 3 and FIG. 4 so that the charging voltage of the single cell 11 is the same as that in FIG. 3 and FIG. 4. Although the charging current is reduced to the charging current Ic1 in the battery module 10a including the single cell 11 with increased internal resistance Ri, the charging current is not reduced in the battery module 10b in which the single cell 11 is not deteriorated and the internal resistance Ri is not increased, and charging is performed by the charging current Ic0.

When the battery modules 10 are connected in series, the charging power (reference charging power) Pcs0 when all the cells 11 are not degraded and the internal resistance Ri is small is set in advance by experiments etc. according to the specifications of the battery pack 100 (battery module 10) etc. The reference charging power Pcs0 varies depending on the SOC (State Of Charge) of the battery pack 100 (battery module 10), so it is stored in the memory of the ECU 200 as a map for each SOC.

In S13, when the connection form of the battery module 10 is a series connection, the reduction amount ΔPcs of the charging power caused by the increase of the internal resistance Ri is calculated as follows. Confirm whether the connection form of the battery module 10 is a series connection. (If it is a parallel connection, switch to a series connection.) When external charging starts, the charging power Pcs1 is calculated by multiplying the voltage VB detected by the voltage sensor 16 and 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 reduction amount ΔPcs of the charging power is calculated by subtracting the charging power Pcs1 from the reference charging power Pcs0 read from the self-map (ΔPcs=Pcs0-Pcs1).

In S13, the reduction amount ΔPcp of the charging power when the connection mode is switched to the parallel connection is calculated as follows. The normal connection state of the battery module 10 is made parallel connection. When external charging starts, the charging power Pcp1 is calculated by multiplying the voltage VB detected by the voltage sensor 16, the current IB detected by the current sensor 17, and the coefficient k. The coefficient k is a coefficient that reflects the improvement in the efficiency of the charger 70 due to the reduction in charging voltage due to the parallel connection, and is set to a value greater than 1. In the present embodiment, it is set to 1.05. Then, the reference charging power Pcs0 corresponding to the current SOC of the battery pack 100 is read from the map. The reduction amount ΔPcp of the charging power is calculated by subtracting the charging power Pcp1 from the reference charging power Pcs0 read from the self-map (ΔPcp=Pcs0-Pcp1). In addition, the coefficient k can be pre-set according to the specifications of the charger 70, or it can be calculated each time based on the charging voltage when connected in series and the charging voltage when connected in parallel.

In the next S14, it is determined whether the reduction amount ΔPcs is greater than the reduction amount ΔPcp. When the reduction amount ΔPcs is greater than the reduction amount ΔPcp (ΔPcs>ΔPsp), an affirmative determination is made and the process proceeds to S15. When the reduction amount ΔPcs is less than the reduction amount ΔPcp (ΔPcs≤ΔPsp), a negative determination is made and the process proceeds to S22.

In S15, the flag F1 is set to 1. Therefore, the next time and thereafter, S11 makes an affirmative determination. In the following S16, the first relay R1 and the second relay R2 are connected (on) and the third relay R3 is blocked (off), so that the connection form of the battery module 10 becomes a parallel connection, and the current routine ends.

In S17, it is determined whether the flag F2 is 1. Since the default value of the flag F2 is 0, when the process of S17 is performed for the first time, a negative determination is made and the process proceeds to S18. When the flag F2 is 1, an affirmative determination is made and the process proceeds to S16.

In S18, it is determined whether the internal resistance Ri of a certain cell 11 in the battery module 10 (10a, 10b) is greater than or equal to a predetermined value B. The predetermined value B is a value such that even if the internal resistance Ri of a certain cell 11 increases to the predetermined value B, the reduction in discharge power is significantly smaller when the connection form of the battery module 10 is a series connection than when it is a parallel connection. The predetermined value B is set in advance through experiments or the like.

When the internal resistance Ri of a certain cell 11 is equal to or greater than the predetermined value B, an affirmative determination is made and the process proceeds to S19. When the internal resistance Ri of all cells 11 is less than the predetermined value A, a negative determination is made and the process proceeds to S22.

In S19, the amount of reduction ΔPds of discharge power caused by the increase of internal resistance Ri when the connection form of the battery module 10 is a series connection, and the amount of reduction ΔPdp of discharge power when the connection form is switched to a parallel connection are calculated. In FIG3 , as indicated by the hollow arrows, when the battery modules 10 are connected in series, all the cells 11 are not degraded, and the internal resistance Ri is small, the discharge current (output current) of the battery module 10 is the current Id0. In the series connection, if the internal resistance Ri of a cell 11 becomes larger, the discharge current of the cell 11 becomes smaller. In addition, since the battery modules 10 (and the cells 11) are connected in series, the discharge current of the battery pack 100 (battery module 10) decreases from the current Id0 to the current Id1 as shown in FIG4 . When the internal resistance Ri of one cell 11 increases, in parallel connection, as shown in FIG. 5 , the discharge current of the battery module 10a including the cell 11 having the large internal resistance Ri becomes the current Id1 , but the discharge current of the battery module 10b is maintained at the current Id0 .

When the battery modules 10 are connected in series, the discharge power (reference output power) Pds0 when all the cells 11 are not degraded and the internal resistance Ri is small is set in advance by experiments, etc., based 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 prescribed load. In the present embodiment, the discharge resistor provided in the PCU 30 is set as the prescribed load.

In S19, when the connection form of the battery module 10 is a series connection, the reduction amount ΔPds of the discharge power caused by the increase of the internal resistance Ri is calculated as follows. Confirm whether the connection form of the battery module 10 is a series connection. (If it is a parallel connection, switch to a series connection.) The power of the battery pack 100 is discharged through the discharge resistor. During this discharge, the discharge power Pds1 is calculated by multiplying the voltage VB detected by the voltage sensor 16 and the current IB detected by the current sensor 17. Then, the reduction amount ΔPds of the discharge power is calculated by subtracting the discharge power Pds1 from the reference output power Pds0 (ΔPds=Pds0-Pds1).

In S19, the reduction amount ΔPdp of the discharge power when the connection mode is switched to the parallel connection is calculated as follows. The connection state of the battery module 10 is set to parallel connection. The power of the battery pack 100 is discharged through the discharge resistor. During this discharge, the discharge power Pdp1 is calculated by multiplying the voltage VB detected by the voltage sensor 16 and the current IB detected by the current sensor 17. Then, the reduction amount ΔPdp of the discharge power is calculated by subtracting the discharge power Pdp1 from the reference output power Pds0 (ΔPdp=Pds0-Pdp1).

In the next S20, it is determined whether the reduction amount ΔPds is greater than the reduction amount ΔPdp. When the reduction amount ΔPds is greater than the reduction amount ΔPdp (ΔPds>ΔPdp), an affirmative determination is made and the process proceeds to S21. When the reduction amount ΔPds is less than the reduction amount ΔPdp (ΔPds≤ΔPdp), a negative determination is made and the process proceeds to S22.

In S21, the flag F2 is set to 1, and the process proceeds to S16. Therefore, a positive determination is made in S17 next time and thereafter. In S22, the first relay R1 and the second relay R2 are set to the blocking (off) state and the third relay R3 is set to the connecting (on) state, so that the connection form of the battery module 10 becomes a series connection, and the current routine ends.

According to this embodiment, when a plurality of battery modules 10 are connected in series, if the internal resistance Ri of a certain single cell 11 included in the battery module 10 increases and the amount of reduction ΔPcs of the charging power is greater than the amount of reduction ΔPcp of the charging power, the connection mode is switched from the series connection to the parallel connection. In addition, if the amount of reduction ΔPds of the discharge power is greater than the amount of reduction ΔPdp of the discharge power, the connection mode is switched from the series connection to the parallel connection. Thus, even if the internal resistance Ri of a certain single cell 11 increases, the amount of reduction of the charging power or the discharge power of the battery pack 100 can be reduced.

According to this embodiment, since the reduction amount ΔPcp is calculated by also taking into account the improvement in efficiency of charger 70 due to the reduction in charging voltage, the electric power of external AC power supply 80 can be efficiently charged.

In the above embodiment, the charging power Pcs1 and the discharging power Pds1 in the case of 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 in the case of parallel connection are calculated. In the case of series connection, the voltage VB and the current IB detected by the monitoring unit 15 can be used to obtain the voltage VB and the current IB. In the case of 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. In addition, the charging power Pcp1 can be obtained by adding the charging power of the battery module 10a and the battery module 10b, and the discharging power Pdp1 can be obtained by adding the discharging power of the battery module 10a and the battery module 10b. Therefore, the voltage sensor 16 and the current sensor 17 may not be required.

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 performed by comparing the charging power Pcs1 with the charging power Pcp1 (Pcs1<Pcp1). Similarly, in S20, the comparison between the reduction amount ΔPds and the reduction amount ΔPdp may be performed by comparing the discharge power Pds1 with the discharge power Pdp1 (Pds1<Pdp1). In this case, the direction of the inequality is opposite to that in the above embodiment. When "Pcs1<Pcp1" is established, it is determined that the reduction amount ΔPcs is larger than the reduction amount ΔPcp, and when "Pds1<Pdp1" is established, it is determined that the reduction amount ΔPds is larger than the reduction amount ΔPdp.

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

The embodiments disclosed herein are illustrative in all aspects and should not be construed as restrictive. The scope of the present disclosure is indicated not by the description of the embodiments described above but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims (5)

1. A power supply system is provided with a battery pack including a plurality of battery modules and a switching circuit,

The plurality of battery modules each include a plurality of unit cells connected in series,

The switching circuit is configured to switch the connection pattern between the plurality of battery modules to a series connection or a parallel connection,

The power supply system further comprises a control device for controlling the switching circuit,

The control means are configured to control the control means,

The connection mode is switched from a series connection to a parallel connection according to an increase in internal resistance of one of the single cells included in the plurality of battery modules.

2. The power supply system according to claim 1, wherein,

When the connection mode is a series connection, Δpcs, which is a decrease in the charging power due to an increase in the internal resistance, is greater than Δpcp, which is a decrease in the charging power when the connection mode is switched to a parallel connection, the control device switches the connection mode from the series connection to the parallel connection.

3. The power supply system according to claim 2, wherein,

The decrease Δpcp is calculated by taking into account the efficiency increase of the charger due to the decrease in the charging voltage caused by the parallel connection.

4. The power supply system according to claim 3, wherein,

The battery pack and the charger are mounted on a vehicle,

The charger converts power from an external ac power source into dc charging power.

5. The power supply system according to claim 1, wherein,

When the connection mode is a serial connection, Δpds, which is a decrease in discharge power due to an increase in the internal resistance, is larger than Δpdp, which is a decrease in discharge power when the connection mode is switched to a parallel connection, the control device switches the connection mode from the serial connection to the parallel connection.