Power supply system

Abstract

The present disclosure relates to a power supply system including a first battery and a second battery capable of charging and discharging based on a series connection and charging and discharging based on a parallel connection using an inverter and a three-phase coil of a motor, when parallel charging is started by turning on an upper branch of the inverter. When an open-circuit voltage difference obtained by subtracting the open-circuit voltage of the second battery from the open-circuit voltage of the first battery is equal to or greater than a predetermined voltage difference, the inverter is switched to reduce the charging power and charge the second battery.

Description

Technical Field

[0001] The present disclosure relates to a power supply system, and more specifically, to a power supply system including two batteries that are capable of being charged and discharged by being connected in series and being charged and discharged by being connected in parallel. Background Art

[0002] As a power supply system of this type, a system has been proposed that includes two batteries that can be charged and discharged in series and in parallel (see, for example, Japanese Patent Application Laid-Open No. 2019-080474). In this system, the batteries are charged and discharged so that the potential difference between the two batteries is below a predetermined threshold. This achieves voltage balancing between the two batteries. Summary of the Invention

[0003] However, in the above power supply system, if the voltages of the two batteries differ for some reason, an excessive current may flow from the higher-voltage battery to the lower-voltage battery when the two batteries are connected in parallel and charged.

[0004] A main purpose of the power supply system of the present disclosure is to suppress an excessive current from flowing when charging two batteries connected in parallel that can be charged and discharged in series and in parallel.

[0005] The power supply system of the present disclosure adopts the following means to achieve the above-mentioned main object.

[0006] The present disclosure provides a power supply system, characterized by comprising:

[0007] First battery;

[0008] Second battery;

[0009] a series connection line connecting the negative terminal of the first battery and the positive terminal of the second battery;

[0010] a series connection relay installed on the series connection line;

[0011] a positive busbar connected to the positive terminal of the first battery;

[0012] a negative busbar connected to the negative terminal of the second battery;

[0013] an inverter connected to the positive bus and the negative bus;

[0014] a three-phase AC motor driven by the inverter;

[0015] A positive-side relay, installed on the positive busbar;

[0016] a negative-side relay, mounted on the negative busbar;

[0017] a first parallel connection line connecting the first battery side and the negative electrode bus bar via the series connection relay of the series connection line;

[0018] a first parallel connection relay installed on the first parallel connection line;

[0019] a second parallel connection line connecting the positive terminal of the second battery and the neutral point of the three-phase AC motor;

[0020] a second parallel connection relay installed on the second parallel connection line in sequence from the second battery side;

[0021] a DC charging connector connected to the inverter side of the positive-side relay of the positive bus bar and to the inverter side of the negative-side relay of the negative bus bar via a power line having a charging relay; and

[0022] A control device controls the relays and the inverter,

[0023] When the control device starts parallel charging of the first battery and the second battery with the positive-side relay, the negative-side relay, the first parallel connection relay, and the second parallel connection relay turned on and the series connection relay turned off, the control device switches the inverter to reduce the voltage of the charging power and charge the second battery when a voltage difference obtained by subtracting the voltage of the second battery from the voltage of the first battery is greater than a predetermined voltage difference.

[0024] In the power supply system disclosed herein, when parallel charging of the first and second batteries begins with the positive-side relay, the negative-side relay, the first parallel connection relay, and the second parallel connection relay turned on and the series connection relay turned off, the control device switches the inverter to step down the charging power and charge the second battery when the voltage difference obtained by subtracting the second battery voltage from the first battery voltage is greater than a predetermined voltage difference. This reduces the voltage difference and prevents excessive current from flowing when the first and second batteries are connected in parallel.

[0025] In the power supply system of the present disclosure, the control device may turn on an upper arm of the inverter to start parallel charging of the first battery and the second battery when the voltage difference is smaller than the predetermined voltage difference.

[0026] In the power supply system of the present disclosure, when the voltage difference is negative, that is, when the voltage of the first battery is less than the voltage of the second battery, the control device disconnects the upper arm of the inverter to charge only the first battery. Furthermore, when it is estimated that the voltage of the first battery is equal to or greater than the voltage of the second battery, the control device connects the upper arm of the inverter to initiate parallel charging of the first and second batteries. Thus, when the voltage of the first battery is equal to or greater than the voltage of the second battery and the voltage difference is less than a predetermined voltage difference, the upper arm of the inverter can be connected to initiate parallel charging of the first and second batteries. In this case, when charging only the first battery, the control device may also estimate that the open-circuit voltage of the first battery is equal to or greater than the open-circuit voltage of the second battery when the voltage of the first battery is equal to or greater than the voltage of the second battery while the charging current of the first battery is limited. This estimate is based on the voltage of the first battery being extremely close to the open-circuit voltage of the first battery while the charging current of the first battery is limited.

[0027] In the power supply system disclosed herein, when the voltage of the first battery becomes lower than the voltage of the second battery during parallel charging of the first and second batteries, the control device disconnects the upper arm of the inverter to charge only the first battery. Furthermore, when it is estimated that the voltage of the first battery is higher than the voltage of the second battery, the control device may connect the upper arm of the inverter to charge the first and second batteries in parallel. This allows the first and second batteries to be charged in parallel while ensuring that the voltage of the first battery is higher than the voltage of the second battery.

[0028] In the power supply system disclosed herein, the control device may also notify the user of battery degradation learning when parallel charging is terminated while current is flowing through the second battery to charge the first battery, if the open circuit voltage of the first battery is higher than that of the second battery according to the relationship map between the battery state of charge and open circuit voltage. This allows the relationship map between the battery state of charge and open circuit voltage to be corrected. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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:

[0030] Figure 1 1 is a schematic configuration diagram showing the configuration of a power supply system according to one embodiment of the present disclosure.

[0031] Figure 2 This is a list showing the status of each relay in various states of the power supply system.

[0032] Figure 3 This is an explanatory diagram showing the flow of current when a first storage battery and a second storage battery are connected in parallel and charged with direct current power from a DC charging station.

[0033] Figure 4 This is a flowchart showing an example of the first half of the parallel charging process.

[0034] Figure 5 This is a flowchart showing an example of the second half of the parallel charging process. DETAILED DESCRIPTION

[0035] Next, a mode (embodiment) for carrying out the present disclosure will be described. Figure 1 This is a schematic diagram showing the configuration of a power supply system 20 according to one embodiment of the present disclosure. The power supply system 20 of this embodiment functions as a device that exchanges power between a battery 26 and an inverter 24 that drives a motor 22, and also functions as a device that charges and discharges the battery 26 using the motor 22 and inverter 24 as needed. The power supply system 20 includes a battery 26, a motor 22, an inverter 24, a main power supply circuit 30, an AC charging circuit 40, a DC charging circuit 50, and an electronic control unit 60.

[0036] The motor 22 is configured, for example, as a known three-phase AC motor with a rotor having permanent magnets attached to its outer surface and a stator wound with three-phase coils. The inverter 24 is composed of six transistors T1 to T6 serving as switching elements and six diodes D1 to D6 connected in parallel with the transistors T1 to T6 in opposite directions. The transistors T1 to T6 are arranged in pairs, two by two, with the inverter 24 serving as the source and sink of the positive and negative busbars 31B and 31G of the battery 26. Each of the connection points between the transistors T1 to T6 pairs is connected to the three-phase coils (U-phase, V-phase, and W-phase) of the motor 22. When voltage is applied between the positive and negative busbars 31B and 31G, the inverter 24 controls the on-time ratio of the transistors T1 to T6 pairs, creating a rotating magnetic field in the three-phase coils and driving the motor 22. A first capacitor 32 for smoothing is provided between the positive bus bar 31B and the negative bus bar 31G.

[0037] The battery 26 includes a first battery 26a and a second battery 26b having the same structure as the first battery 26a. The first battery 26a and the second battery 26b are configured, for example, as lithium-ion secondary batteries or nickel-metal hydride secondary batteries. The positive terminal of the first battery 26a is connected to the positive bus bar 31B, and the negative terminal of the second battery 26b is connected to the negative bus bar 31G. The negative terminal of the first battery 26a is connected to the positive terminal of the second battery 26b via a series power line 35 equipped with a relay DCRNN, which is included in the structure of the main power supply circuit 30. Therefore, when relay DCRNN is turned on, the first battery 26a and the second battery 26b function as a single battery connected in series.

[0038] The main power supply circuit 30 includes a positive busbar 31B, a negative busbar 31G, and a series power line 35. Furthermore, the main power supply circuit 30 includes a first parallel power line 36 connecting the negative terminal of the first battery 26a and the negative busbar 31G, and a second parallel power line 37 connecting the positive terminal of the second battery 26b to the neutral point of the motor 22. A positive-side relay SMRB is attached to the positive busbar 31B, and a negative-side relay SMRG is attached to the negative busbar 31G. Furthermore, a pre-charge circuit comprising a pre-charge relay SMRP and a resistor R is provided in parallel with the negative-side relay SMRG on the negative busbar 31G. These positive-side relay SMRB, negative-side relay SMRG, and pre-charge circuit constitute the system main relay. Specifically, when the first battery 26a and the second battery 26b are connected in series, the positive-side relay SMRB is turned on, and the precharge relay SMRP is turned on to charge the first capacitor 32. Then, when charging of the first capacitor 32 is complete, the negative-side relay SMRG is turned on, and the precharge relay SMP is turned off. This allows power from the battery 26, consisting of the first and second batteries 26a, 26b connected in series, to be supplied to the inverter 24, or conversely, the battery 26 can be charged using power regenerated by the motor 22.

[0039] A relay DCRNG is installed on the first parallel power line 36. A relay DCRNB is installed on the second parallel power line 37 on the second battery 26b side, and a relay DCRN is installed on the neutral point side of the motor 22. A second capacitor 38 is installed between relays DCRNB and DCRN on the second parallel power line 37 and between the negative bus 31G.

[0040] AC charging circuit 40 includes an AC charging power line 41 connected to positive bus bar 31B and negative bus bar 31G, an on-board charger (OBC) 43 connected to AC charging power line 41 via a filter 42, and an AC charging connector 45 connected to on-board charger 43 via a power line 44. Furthermore, AC charging circuit 40 includes a DC / DC converter 46 connected to AC charging power line 41 in parallel with on-board charger 43 via filter 42, and auxiliary equipment 48 and a solar panel 49 connected to DC / DC converter 46 via a power line 47. A relay SSRB is installed on the positive side of AC charging power line 41, and a relay SSRG is installed on the negative side.

[0041] DC charging circuit 50 includes a DC charging power line 51 connected to positive bus bar 31B and negative bus bar 31G, and a DC charging connector 55 connected to DC charging power line 51. A relay DCRB is attached to the positive side of DC charging power line 51, and a relay DCRG is attached to the negative side of DC charging power line 51.

[0042] Although not shown, the electronic control unit 60 is configured as a microcomputer centered around a CPU. Signals from various sensors are input to the electronic control unit 60. Examples of these sensors include a voltage sensor 33 that detects the voltage VH between the terminals of the first capacitor 32 and a voltage sensor 39 that detects the voltage VD between the terminals of the second capacitor 38. Other examples of these sensors include a current sensor 31a that detects the current Ib1 flowing through the first battery 26a, a current sensor 37a that detects the current Id flowing through the second parallel power line 37, and phase current sensors (not shown) that detect the phase currents Iu, Iv, and Iw flowing through the three phases of the motor 22. Other examples of these sensors include a voltage sensor (not shown) that detects the voltage Vb1 between the terminals of the first battery 26a and a voltage sensor (not shown) that detects the voltage Vb2 between the terminals of the second battery 26b. Furthermore, the electronic control unit 60 functions as a control device for driving the motor 22 and therefore receives inputs such as drive commands. Furthermore, when the power supply system 20 is mounted on a vehicle and the motor 22 is used as a driving motor, the accelerator pedal opening and the vehicle speed may be input to the electronic control unit 60 , and the electronic control unit 60 may generate a torque command for the motor 22 .

[0043] The electronic control unit 60 outputs drive control signals to the relays and switch control signals to the inverter 24. Examples of the relays include the positive-side relay SMRB, the negative-side relay SMRG, the precharge relay SMRP, the relay DCRNN, the relay DCRNG, the relay DCRNB, the relay DCRN, the relay SSRB, the relay SSRB, the relay DCRB, and the relay DCRG.

[0044] Figure 2 It is a list showing the states of the relays in various states of the power supply system 20 .

[0045] (1) To drive the motor 22 as a traveling motor, the positive-side relay SMRB, the negative-side relay SMRG, the relay SSRB, the relay SSRG, and the relay DCRNN are turned on. Furthermore, the relays DCRB, the relay DCRG, the relay DCRN, the relay DCRB, and the relay DCRG are turned off.

[0046] (2) When the connection connector from the AC charging station is connected to the AC charging connector 45 and the battery 26 is charged with the AC power from the AC charging station, or when an external electrical load is connected to the AC charging connector 45 and the power from the battery 26 is supplied to the external electrical load as AC power, the relays SSRB, SSRG, and DCRNN are set to the ON state, and the positive-side relay SMRB, the negative-side relay SMRG, the relay DCRB, the relay DCRG, the relay DCRN, the relay DCRB, and the relay DCRG are set to the OFF state.

[0047] (3) When the connection connector from the DC charging station is connected to the DC charging connector 55 and the first battery 26a and the second battery 26b are connected in parallel to charge with DC power from the DC charging station, or when the power from the battery 26 is supplied to the external electrical load as DC power in a state where the external electrical load is connected to the DC charging connector 55 and the first battery 26a and the second battery 26b are connected in parallel, the positive-side relay SMRB, the negative-side relay SMRG, the relay SSRB, the relay SSRG, the relay DCRB, the relay DCRG, the relay DCRN, the relay DCRB, and the relay DCRG are turned on, and the relay DCRNN is turned off.

[0048] (4) When the connection connector from the DC charging station is connected to the DC charging connector 55 and the first battery 26a and the second battery 26b are connected in series to charge with the DC power from the DC charging station, or when the power from the battery 26 is supplied to the external electrical load as DC power in a state where the external electrical load is connected to the DC charging connector 55 and the first battery 26a and the second battery 26b are connected in series, the positive-side relay SMRB, the negative-side relay SMRG, the relay SSRB, the relay SSRG, the relay DCRNN, the relay DCRB, and the relay DCRG are set to an ON state, and the relay DCRNB, the relay DCRNG, and the relay DCRN are set to an OFF state.

[0049] (5) When power is supplied to auxiliary equipment 48 such as a drive recorder while the vehicle is parked, relays SSRB, SSRG, and DCRNN are turned on. Furthermore, positive-side relay SMRB, negative-side relay SMRG, DCRNB, DCRNG, DCRN, DCRB, and DCRG are turned off.

[0050] (6) When the first storage battery 26a and the second storage battery 26b are connected in parallel and charged using the power generated by the solar panel 49, the positive-side relay SMRB, the negative-side relay SMRG, the relay SSRB, the relay SSRG, the relay DCRNB, the relay DCRNG, and the relay DCRN are turned on. Furthermore, the relay DCRNN, the relay DCRB, and the relay DCRG are turned off.

[0051] (7) When the first storage battery 26a and the second storage battery 26b are connected in series and charged using the power generated by the solar panel 49, the relays SSRB, SSRG, and DCRNN are turned on. Furthermore, the positive-side relay SMRB, the negative-side relay SMRG, the relays DCRNB, DCRNG, DCRN, DCRB, and DCRG are turned off.

[0052] Next, the operation of the power supply system 20 of the embodiment thus configured will be described, particularly the operation when the connection connector from the DC charging station is connected to the DC charging connector 55 and the first and second batteries 26a and 26b are connected in parallel to be charged with DC power from the DC charging station. Figure 3This is an explanatory diagram showing the flow of current when the first battery 26a and the second battery 26b are connected in parallel and charged with DC power from a DC charging station. In the figure, the thick solid line with an arrow represents the charging current of the first battery 26a, and the thick dotted line with an arrow represents the charging current of the second battery 26b. In addition, when the connection connector from the DC charging station is connected to the DC charging connector 55 and the first battery 26a and the second battery 26b are connected in parallel and charged with DC power from the DC charging station, as described above, the positive side relay SMRB, the negative side relay SMRG, the relay SSRB, the relay SSRG, the relay DCRB, the relay DCRG, the relay DCRN, the relay DCRB, and the relay DCRG are set to a state of being connected, and the relay DCRNN is set to a state of being disconnected. Moreover, the upper branch of the inverter 24 is connected. As Figure 3 As shown by the thick solid line with an arrow, the first battery 26a is charged by the charging current flowing from the positive side line of the DC charging power line 51 connected to the DC charging connector 55 in the order of the positive side relay SMRB of the positive bus 31B, the first battery 26a, the relay DCRNG of the first parallel power line 36, the negative side relay SMRG of the negative bus 31G, and the negative side line of the DC charging power line 51. Figure 3 As shown by the thick dotted line with an arrow, the second battery 26b is charged by using the charging current flowing from the positive side line of the DC charging power line 51 connected to the DC charging connector 55 via the positive bus 31B in the order of the upper branch of the inverter 24, the neutral point of the motor 22, the relay DCRN and the relay DCRNB of the second parallel power line 37, the second battery 26b, the negative side relay SMRG of the negative bus 31G, and the negative side line of the DC charging power line 51.

[0053] In the power supply system 20 of the embodiment, Figure 4 as well as Figure 5The illustrated parallel charging process performs parallel charging. When executing the parallel charging process, the electronic control unit 60 first inputs the open circuit voltage OCV1 of the first battery 26a and the open circuit voltage OCV2 of the second battery 26b ( S100 ). It then determines whether the open circuit voltage difference ΔOCV (ΔOCV = OCV1 - OCV2), obtained by subtracting the open circuit voltage OCV2 from the open circuit voltage OCV1, is within a range greater than a threshold value Vref1 and less than a threshold value Vref2 ( S110 ). The open circuit voltages OCV1 and OCV2 of the first battery 26a and the second battery 26b can also be derived by applying the charge ratio SOC to a map representing the relationship between the charge ratio SOC and the open circuit voltage OCV of each battery. Threshold Vref1 is a value predetermined so that, even if there are measurement errors in the open-circuit voltages OCV1 and OCV2 of the first and second storage batteries 26a, the open-circuit voltage OCV1 of the first and second storage batteries 26b remains equal to or greater than the open-circuit voltage OCV2 of the second storage battery 26b. Threshold Vref2 is the allowable voltage difference between the open-circuit voltages OCV1 and OCV2 of the first and second storage batteries 26a and is a value greater than threshold Vref1.

[0054] If it is determined in S110 that the open circuit voltage difference ΔOCV (ΔOCV=OCV1-OCV2) is greater than or equal to the threshold value Vref1 and less than or equal to the threshold value Vref2, the upper arm of the inverter 24 is turned on to start parallel charging (S200). Figure 3 As described, the charging circuit for second battery 26b includes the three-phase coil of motor 22. Therefore, the impedance of the charging circuit for second battery 26b is greater than the impedance of the charging circuit for first battery 26a. Consequently, the charging current for first battery 26a is maintained slightly higher than the charging current for second battery 26b, and the voltage Vb1 of first battery 26a is maintained slightly higher than the voltage Vb2 of second battery 26b. The reason for maintaining the voltage Vb1 of first battery 26a slightly higher than the voltage Vb2 of second battery 26b is to prevent the current from flowing through second battery 26b to charge first battery 26a when parallel charging is terminated, due to the voltage Vb2 of second battery 26b being higher than the voltage Vb1 of first battery 26a.

[0055] If it is determined in S110 that the open circuit voltage difference ΔOCV (ΔOCV = OCV1 - OCV2) is less than threshold value Vref1, only first battery 26a is charged until a predetermined time has elapsed (S120, S130). The reason for charging only first battery 26a when open circuit voltage difference ΔOCV is less than threshold value Vref1 is to curb the current that would otherwise flow through second battery 26b to charge first battery 26a when parallel charging begins when open circuit voltage difference ΔOCV is negative. The predetermined time is a relatively short period, such as 1, 2, 5, or 10 seconds. While only first battery 26a is being charged until the predetermined time has elapsed, the charging current to first battery 26a is limited, and voltage Vb1 (CCV1) of first battery 26a is detected (S140). Detected voltage Vb1 (CCV1) is then considered the open-circuit voltage OCV1 of first battery 26a, and the open-circuit voltage difference ΔOCV is calculated (S150). The process then returns to S110 to determine whether the open-circuit voltage difference ΔOCV is greater than threshold Vref1 and less than threshold Vref2. Thus, until the open-circuit voltage difference ΔOCV reaches or exceeds threshold Vref1, charging of only first battery 26a continues.

[0056] If it is determined in S110 that the open-circuit voltage difference ΔOCV (ΔOCV = OCV1 - OCV2) is greater than threshold Vref2, the upper arm of inverter 24 is switched until a predetermined time has elapsed, and parallel charging is performed along with the voltage reduction of the external charging power (S160, S170). After the predetermined time has elapsed, the voltage difference ΔCCV (ΔCCV = CCV1 - CCV2) is calculated using voltage Vb1 (CCV1) of first battery 26a and voltage Vb2 (CCV2) of second battery 26b (S180). Furthermore, a determination is made as to whether the voltage difference ΔCCV is within a range greater than 0 and less than threshold Vref3 (S190). Threshold Vref3 can be the same as threshold Vref2 or slightly less than threshold Vref2. If it is determined that the voltage difference ΔCCV is within a range greater than 0 and less than threshold Vref3, the upper arm of inverter 24 is switched on, and parallel charging begins (S200).

[0057] If it is determined in S190 that the voltage difference ΔCCV is greater than the threshold value Vref3, the process returns to S160 and S170, where the upper arm of the inverter 24 is switched until a predetermined time has elapsed, and parallel charging is performed with the voltage of the external charging power being stepped down. Thus, the upper arm of the inverter 24 is switched until the voltage difference ΔCCV falls below the threshold value Vref3, and parallel charging is continued with the voltage of the external charging power being stepped down.

[0058] If it is determined in S190 that the voltage difference ΔCCV is equal to or smaller than 0, the process of S120 and S130 is performed to charge only the first battery 26 a for a predetermined period of time.

[0059] When parallel charging begins, a process (S210 to S240) is performed to maintain the voltage Vb1 of the first battery 26a slightly higher than the voltage Vb2 of the second battery 26b until the parallel charging is terminated (S250). This process first inputs the voltages Vb1 and Vb2 of the first and second batteries 26a (S210), and then determines whether the voltage difference ΔV (ΔV = Vb1 - Vb2), obtained by subtracting the voltage Vb2 from the voltage Vb1, is negative (S220). If the voltage difference ΔV is negative, the upper arm of the inverter 24 is disconnected, charging only the first battery 26a (S230), and the process returns to S210, where the voltages Vb1 and Vb2 of the first and second batteries are input. In other words, charging only the first battery 26a continues until the voltage difference ΔV reaches or exceeds zero. If it is determined in S220 that the voltage difference ΔV is equal to or greater than 0, the upper arm of inverter 24 is connected to perform parallel charging (S240), and the termination of parallel charging is determined (S250). If the termination of parallel charging cannot be determined, the process returns to S210, where the voltage Vb1 of first battery 26a and the voltage Vb2 of second battery 26a are input. The termination of parallel charging is determined when battery 26 is fully charged, a predetermined charging time has elapsed, the charge fraction SOC of battery 26 reaches a predetermined state indicating the termination of charging, or the user indicates the termination of charging. The reason for maintaining the voltage Vb1 of first battery 26a slightly higher than the voltage Vb2 of second battery 26b is to suppress the current that would otherwise flow from second battery 26b to first battery 26a when parallel charging is terminated, due to the voltage Vb2 of second battery 26b being higher than that of first battery 26a.

[0060] When parallel charging is determined to be complete and charging is terminated, a determination is made as to whether a charging current is flowing through the first battery 26a (S260). If a charging current is determined to be flowing through the first battery 26a, a notification is given indicating the need for deterioration learning of the map of the stored charge ratio (SOC) and the open circuit voltage (OCV) (S270), and this process is terminated. On the other hand, if a charging current is determined not to be flowing through the first battery 26a, the map is determined to be non-degraded, and this process is terminated.

[0061] In the power supply system 20 of the embodiment described above, when parallel charging is initiated by connecting the first and second batteries 26a and 26b in parallel, the following process is performed. When the open-circuit voltage difference ΔOCV, obtained by subtracting the open-circuit voltage OCV2 of the second battery 26b from the open-circuit voltage OCV1 of the first battery 26a, is greater than or equal to threshold Vref2, the upper arm switch of the inverter 24 is switched on, thereby performing parallel charging while stepping down the external charging power until the open-circuit voltage difference ΔOCV falls below threshold Vref3. This prevents excessive current from flowing through the circuit due to a large open-circuit voltage difference ΔOCV when parallel charging is initiated by switching on the upper arm of the inverter 24. Furthermore, when the open-circuit voltage difference ΔOCV is less than threshold Vref1, only the first battery 26a is charged until the open-circuit voltage difference ΔOCV reaches or exceeds threshold Vref1. This allows the current flowing through second battery 26b to charge first battery 26a at the start of parallel charging to be suppressed. At this time, the voltage Vb1 of first battery 26a, detected by limiting the charging current of first battery 26a, is regarded as the open-circuit voltage OCV1 of first battery 26a. The open-circuit voltage difference ΔOCV is calculated, and only first battery 26a is charged until the open-circuit voltage difference ΔOCV reaches a value of zero or greater. This allows the true open-circuit voltage difference ΔOCV to be more reliably kept at a value of zero or greater.

[0062] In the power supply system 20 of the embodiment, during parallel charging, if the voltage difference ΔV, obtained by subtracting the voltage Vb2 of the second battery 26b from the voltage Vb1 of the first battery 26a, is negative, the upper arm of the inverter 24 is disconnected until the voltage difference ΔV reaches or exceeds 0, allowing only the first battery 26a to be charged. After the voltage difference ΔV reaches or exceeds 0, the upper arm of the inverter 24 is connected, allowing parallel charging to continue. This maintains the voltage Vb1 of the first battery 26a slightly higher than the voltage Vb2 of the second battery 26b. This prevents the current flowing through the second battery 26b to charge the first battery 26a when parallel charging is terminated, due to the voltage Vb2 of the second battery 26b exceeding the voltage of the first battery 26a.

[0063] In the power supply system 20 of the embodiment, upon completion of parallel charging, when a charging current is detected flowing through the first battery 26a, a notification is issued indicating the need for degradation learning of the map between the battery charge ratio SOC and the open circuit voltage OCV. This notification enables notification of the need for degradation learning of the map between the battery charge ratio SOC and the open circuit voltage OCV.

[0064] As mentioned above, although this disclosure was described using the embodiment, this disclosure is not limited to such embodiment, and it is needless to say that this disclosure can be implemented in various forms within the scope not departing from the gist of this disclosure.

[0065] The present disclosure can be utilized in the power supply system manufacturing industry and the like.

Claims

1. A power supply system comprising: First battery; Second battery; a series connection line connecting the negative terminal of the first battery and the positive terminal of the second battery; a series connection relay installed on the series connection line; a positive busbar connected to the positive terminal of the first battery; a negative busbar connected to the negative terminal of the second battery; an inverter connected to the positive bus and the negative bus; a three-phase AC motor driven by the inverter; A positive-side relay, installed on the positive busbar; a negative-side relay, mounted on the negative busbar; a first parallel connection line connecting the first battery side and the negative electrode bus bar via the series connection relay of the series connection line; a first parallel connection relay installed on the first parallel connection line; a second parallel connection line connecting the positive terminal of the second battery and the neutral point of the three-phase AC motor; a second parallel connection relay installed on the second parallel connection line in sequence from the second battery side; a DC charging connector connected to the inverter side of the positive-side relay of the positive bus bar and to the inverter side of the negative-side relay of the negative bus bar via a power line having a charging relay; and A control device controls each of the relays and the inverter, When the control device starts parallel charging of the first battery and the second battery with the positive-side relay, the negative-side relay, the first parallel connection relay, and the second parallel connection relay turned on and the series connection relay turned off, the control device switches the inverter to reduce the voltage of the charging power and charge the second battery when a voltage difference obtained by subtracting the voltage of the second battery from the voltage of the first battery is greater than a predetermined voltage difference.

2. The power supply system according to claim 1, wherein: When the voltage difference is smaller than the predetermined voltage difference, the control device turns on the upper arm of the inverter to start parallel charging of the first battery and the second battery.

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