Battery unit

Abstract

To prevent a circulating current during parallel charging.SOLUTION: In a battery unit, a series circuit of a first battery and a first switch and a series circuit of a second battery and a second switch are connected between a plus wiring and a minus wiring. A diode is connected in parallel to the first switch in an orientation in which an anode of the diode is on a positive wiring side. A third switch connects the first battery and the second battery in series in an ON state. When external charging facilities are connected, a control device performs: processing of turning off the third switch; processing of turning on the second switch; processing of starting charging by the charging facilities; and processing of turning on the first switch when a voltage detected by a voltage detection circuit (a voltage applied to the first switch) exceeds a reference voltage after charging by the charging facilities is started.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a battery unit.

[0002] Patent Document 1 discloses a battery unit in which two batteries can be connected in either parallel or series. By connecting the two batteries in parallel, the two batteries can be charged at a relatively low voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-078393 Summary of the Invention [Problem to be solved by the invention]

[0004] If there is a difference in output voltage (e.g., open circuit voltage: hereinafter referred to as OCV) between two batteries, a circulating current will occur when the two batteries are connected in parallel. The circulating current will deteriorate the switches and batteries. This specification proposes a technology to prevent circulating current when charging two batteries in parallel. [Means for solving the problem]

[0005] The battery unit disclosed in this specification includes a positive wiring, a negative wiring, a first battery, a second battery, a first switch, a second switch, a third switch, a diode, a voltage detection circuit, and a control device. A series circuit of the first battery and the first switch is connected between the positive wiring and the negative wiring. The diode is connected in parallel to the first switch with the anode of the diode facing the positive wiring. A series circuit of the second battery and the second switch is connected between the positive wiring and the negative wiring. The third switch is configured such that, when in an on state, the series circuit of the first battery and the second battery is connected between the positive wiring and the negative wiring. The voltage detection circuit detects the voltage applied to the diode. When an external charging facility is connected to the positive wiring and the negative wiring, the control device performs the following processes: turning off the third switch; turning on the second switch after turning off the third switch; starting charging by the charging facility after turning on the second switch; and turning on the first switch when the voltage detected by the voltage detection circuit after starting charging by the charging facility exceeds a forward reference voltage.

[0006] In this battery unit, when the output voltage of the first battery is higher than the output voltage of the second battery, circulating current is prevented as follows: The control device turns off the third switch and then turns on the second switch. When the second switch is turned on, the second battery is electrically connected between the positive and negative wires. At this time, the output voltage of the first battery is higher than the output voltage of the second battery, but the diode prevents circulating current. When charging by the charging equipment begins, the second battery, which has a lower output voltage, is charged first. In this state, voltage is applied to the diode in the reverse direction (i.e., in the direction in which the cathode has a higher potential than the anode), so the voltage detected by the voltage detection path is the reverse voltage. After that, when the supply voltage from the charging equipment increases, a charging current begins to flow through the series circuit of the first battery and the diode. Then, a voltage drop occurs in the diode in the forward direction (i.e., in the direction in which the anode has a higher potential than the cathode), so the voltage detected by the voltage detection circuit becomes the forward voltage. As a result, the voltage detected by the voltage detection circuit exceeds the forward reference voltage, and the control device turns on the first switch. Turning on the first switch allows a high charging current to flow to the first battery. This allows the first battery and the second battery to be charged in parallel. In this way, this battery unit can prevent circulating current when charging two batteries in parallel. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a circuit diagram of a battery unit 10 (when charging). [Figure 2] 10 is a flowchart showing a process during charging. [Figure 3] 1 is a circuit diagram of the battery unit 10 (when power is being supplied). DETAILED DESCRIPTION OF THE INVENTION

[0008] The battery unit 10 of the embodiment shown in FIG. 1 is mounted on an electric vehicle. The battery unit 10 has a positive wiring 12, a negative wiring 14, a capacitor 16, a first battery 21, a second battery 22, a first relay switch 31, a second relay switch 32, and a third relay switch 33. The capacitor 16 is connected between the positive wiring 12 and the negative wiring 14. The positive electrode of the first battery 21 is connected to the positive wiring 12. The negative electrode of the first battery 21 is connected to one terminal of the first relay switch 31. The other terminal of the first relay switch 31 is connected to the negative wiring 14. In other words, a series circuit of the first battery 21 and the first relay switch 31 is connected between the positive wiring 12 and the negative wiring 14. One terminal of the second relay switch 32 is connected to the positive wiring 12. The other terminal of the second relay switch 32 is connected to the positive electrode of the second battery 22. The negative electrode of the second battery 22 is connected to the negative wiring 14. That is, a series circuit of the second battery 22 and the second relay switch 32 is connected between the positive wiring 12 and the negative wiring 14. One terminal of the third relay switch 33 is connected to the negative electrode of the first battery 21. The other terminal of the third relay switch 33 is connected to the positive electrode of the second battery 22. When the third relay switch 33 is turned on, a series circuit of the first battery 21 and the second battery 22 is formed between the positive wiring 12 and the negative wiring 14.

[0009] A switching circuit and a voltage detection circuit 51 are connected in parallel to the first relay switch 31. The switching circuit has diodes 41a and 41d and IGBTs (insulated gate bipolar transistors) 41b and 41c. The cathode of the diode 41a is connected to the negative electrode of the first battery 21. The anode of the diode 41a is connected to the anode of the diode 41d. The cathode of the diode 41d is connected to the negative wiring 14. The collector of the IGBT 41b is connected to the cathode of the diode 41a. The emitter of the IGBT 41b is connected to the anode of the diode 41a. The emitter of the IGBT 41c is connected to the anode of the diode 41d. The collector of the IGBT 41c is connected to the cathode of the diode 41d. The voltage detection circuit 51 detects the voltage applied to the first relay switch 31. When the IGBT 41b is turned on, the voltage detection circuit 51 detects the voltage applied to the diode 41d.

[0010] A switching circuit and a voltage detection circuit 52 are connected in parallel to the second relay switch 32. The switching circuit has diodes 42a and 42d and IGBTs 42b and 42c. The cathode of the diode 42a is connected to the positive wiring 12. The anode of the diode 42a is connected to the anode of the diode 42d. The cathode of the diode 42d is connected to the positive electrode of the second battery 22. The collector of the IGBT 42b is connected to the cathode of the diode 42a. The emitter of the IGBT 42b is connected to the anode of the diode 42a. The emitter of the IGBT 42c is connected to the anode of the diode 42d. The collector of the IGBT 42c is connected to the cathode of the diode 42d. The voltage detection circuit 52 detects the voltage applied to the second relay switch 32. When the IGBT 42b is turned on, the voltage detection circuit 52 detects the voltage applied to the diode 42d.

[0011] The battery unit 10 has a positive terminal 62, a negative terminal 64, a relay switch 66, and a relay switch 68. The positive wiring 12 is connected to the positive terminal 62 via the relay switch 66. The negative wiring 14 is connected to the negative terminal 64 via the relay switch 68. An external charging facility 100 is connected to the positive terminal 62 and the negative terminal 64. The charging facility 100 is a relatively low-voltage charging facility for charging the batteries 21, 22 in parallel.

[0012] The battery unit 10 includes a control device 70. The control device 70 controls each part of the battery unit 10.

[0013] Normally, relay switches 31, 32, 66, and 68 and IGBTs 41b, 41c, 42b, and 42c are off, and third relay switch 33 is on. Therefore, a series circuit of batteries 21 and 22 is connected between positive wiring 12 and negative wiring 14. The voltage output from the series circuit of batteries 21 and 22 is supplied to a traction motor (not shown). When charging equipment 100 is connected to positive terminal 62 and negative terminal 64, control device 70 executes the parallel charging process shown in FIG. 2. Note that the OCVs of batteries 21 and 22 differ depending on the usage state of batteries 21 and 22. Generally, connecting batteries with different OCVs in parallel generates a circulating current, which deteriorates the batteries and the relay switches. In contrast, the parallel charging process shown in FIG. 2 can be executed while preventing a circulating current, even when the OCV of first battery 21 (hereinafter referred to as OCV1) and the OCV of second battery 22 (hereinafter referred to as OCV2) differ.

[0014] In step S2, the control device 70 turns the third relay switch 33 off.

[0015] In step S4, the control device 70 turns on the relay switch connected to the battery with the lower OCV out of the relay switches 31 and 32. That is, the control device 70 turns on the second relay switch 32 when OCV1 is higher than OCV2, and turns on the first relay switch 31 when OCV2 is higher than OCV1.

[0016] In step S6, the control device 70 turns on one of the IGBTs 41b and 42b that is connected in parallel to the relay switch that is turned off. That is, the control device 70 turns on the IGBT 41b when the first relay switch 31 is turned off, and turns on the IGBT 42b when the second relay switch 32 is turned off.

[0017] For example, if OCV1 is higher than OCV2, the second relay switch 32 is turned on in step S4, and the IGBT 41b is turned on in step S6. In this state, the negative electrode of the first battery 21 is electrically connected to the anode of the diode 41d, the positive electrode of the first battery 21 is electrically connected to the positive electrode of the second battery 22, and the negative electrode of the second battery 22 is electrically connected to the cathode of the diode 41d. In this state, a voltage corresponding to the difference between OCV1 and OCV2 is applied to the diode 41d in the reverse direction (i.e., in the direction in which the cathode has a higher potential than the anode). Therefore, the diode 41d is turned off, and no circulating current is generated. Note that if OCV2 is higher than OCV1, the circulating current is prevented by the diode 42d.

[0018] In step S8, the control device 70 starts charging by the charging equipment 100. That is, the control device 70 turns on the relay switches 66 and 68. The control device 70 also communicates with the charging equipment 100 and turns on the charging relay switches 100a and 100b within the charging equipment 100. As a result, the output voltage V100 of the power supply 100c within the charging equipment 100 is applied between the positive wiring 12 and the negative wiring 14. The charging equipment 100 gradually increases the output voltage V100.

[0019] When charging by the charging equipment 100 starts, the control device 70 determines in step S10 whether a charging current is flowing to the battery with the higher OCV. The control device 70 repeatedly executes step S10 after charging starts. The control device 70 makes the determination in step S10 based on the detected values ​​of the voltage detection circuits 51 and 52. More specifically, the control device 70 determines whether a charging current is flowing to the first battery 21 by determining whether the detected value of the voltage detection circuit 51 is higher than a reference voltage in the forward direction of the diode 41d. The control device 70 also determines whether a charging current is flowing to the second battery 22 by determining whether the detected value of the voltage detection circuit 52 is higher than a reference voltage in the forward direction of the diode 42d. The reference voltage is a voltage lower than the forward voltage drops of the diodes 41d and 42d.

[0020] As described above, the charging equipment 100 gradually increases the output voltage V100. For example, if OCV1 is higher than OCV2 at the start of the process shown in FIG. 2, when the output voltage V100 reaches OCV2, a charging current flows to the second battery 22, and the second battery 22 is charged. At this stage, the output voltage V100 is lower than OCV1, so no charging current flows to the first battery 21. In this state, a reverse voltage corresponding to the difference between OCV1 and the output voltage V100 is applied to the diode 41d. This reverse voltage is detected by the voltage detection circuit 51. The charging equipment 100 increases the output voltage V100 as the output voltage of the second battery 22 increases. When the output voltage V100 becomes higher than OCV1, a forward voltage is applied to the diode 41d, and a charging current flows through the series circuit of the first battery 21 and the diode 41d. This causes the voltage applied to the diode 41d to be equal to the forward voltage drop of the diode 41d. As a result, a forward voltage that is equal to the forward voltage drop of diode 41d is detected by voltage detection circuit 51. That is, the detection value of voltage detection circuit 51 increases from a reverse voltage to a forward voltage that is higher than the reference voltage. Then, control device 70 determines YES in step S10.

[0021] If the answer is YES in step S10, the control device 70 turns on the relay switch 31, 32 that is connected to the battery with the higher OCV in step S12. For example, if OCV1 is higher than OCV2 at the start of the processing in FIG. 2, the control device 70 turns on the first relay switch 31 in step S12. This allows a charging current to flow through the first relay switch 31. Because the first relay switch 31 is turned on while the voltage is clamped by the diode 41d, the voltage fluctuation occurring in the first relay switch 31 is extremely small. This suppresses the inrush current in the first relay switch 31 and suppresses deterioration of the first relay switch 31.

[0022] In step S14, the controller 70 turns off the IGBT 41b, 42b that is on. For example, if OCV1 is higher than OCV2 at the start of the process in Figure 2, the controller 70 turns off the IGBT 41b in step S14.

[0023] In step S16, the control device 70 commands the charging equipment 100 to increase the output voltage V100. As a result, the batteries 21 and 22 are charged in parallel with a high charging current. Thereafter, when the batteries 21 and 22 are fully charged, the control device 70 stops the parallel charging.

[0024] As described above, according to the battery unit 10 of the embodiment, parallel charging of the batteries 21 and 22 can be performed while preventing circulating current. Furthermore, in the battery unit 10 of the embodiment, the charging current increased in step S16 flows to the first relay switch 31, and does not flow to the diode 41d. Because a high current does not flow to the diode 41d, a small diode can be used as the diode 41d. Similarly, because a high current does not flow to the diode 42d, a small diode can be used as the diode 42d. Therefore, the battery unit 10 can be made smaller.

[0025] When charging is completed, the control device 70 turns on the IGBT 41b and then turns off the first relay switch 31. When the IGBT 41b is turned on, a charging current flows through the diode 41d, and the voltage applied to the first relay switch 31 is clamped. This prevents a high voltage from being applied to the first relay switch 31 when the first relay switch 31 is turned off. By turning off the IGBT 41b after turning off the first relay switch 31, the negative electrode of the first battery 21 can be disconnected from the negative wiring 14.

[0026] As shown in FIG. 3 , the positive terminal 62 and the negative terminal 64 can be connected to an external power supply target facility 200 (a facility that operates using power supplied from the battery unit 10), and power can be supplied in parallel from the batteries 21 and 22 to the power supply target facility. The following description will be given assuming that OCV1 is higher than OCV2 at the start of power supply. The control device 70 first turns off the third relay switch 33. Next, the control device 70 turns on the first relay switch 31 connected to the first battery 21, which has a higher OCV. Next, the control device 70 turns on the IGBT 42c of the switching circuit, which is connected in parallel to the second relay switch 32. In this state, a voltage corresponding to the difference between OCV1 and OCV2 is applied in the reverse direction to the diode 42a, preventing circulating current. Next, the relay switches 66 and 68 are turned on to start power supply to the power supply target facility 200. Immediately after the start of power supply, current flows from the first battery 21, which has a high OCV1, to the power supply target facility 200. In this state, a reverse voltage is applied to the diode 42a, so no current flows from the second battery 22 to the power supply target facility 200. Thereafter, when the output voltage of the first battery 21 drops to approximately the same as the OCV2, current flows from the second battery 22 to the power supply target facility 200. Then, the voltage detected by the voltage detection circuit 52 (i.e., the voltage applied to the diode 42a) changes from a reverse voltage to a forward voltage (i.e., a voltage equivalent to the forward voltage drop of the diode 42a). Then, the control device 70 turns on the second relay switch 32 and turns off the IGBT 42c. This allows parallel power supply by the batteries 21 and 22.

[0027] As described above, the battery unit 10 can perform parallel power feeding while preventing circulating current.

[0028] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0029] 12: Positive wiring, 14: Negative wiring, 21: First battery, 22: Second battery, 31: First relay switch, 32: Second relay switch, 33: Third relay switch, 42d: Diode, 51: Voltage detection circuit

Claims

[Claim 1] A battery unit, The positive wire and The negative wire and A first battery; A second battery; A first switch; A second switch; A third switch; A diode and a voltage detection circuit; control device, and a series circuit of the first battery and the first switch is connected between the positive wiring and the negative wiring; The diode is connected in parallel to the first switch with the anode of the diode facing the positive wiring side, a series circuit of the second battery and the second switch is connected between the positive wiring and the negative wiring; the third switch is configured such that, in an on state, a series circuit of the first battery and the second battery is connected between the positive wiring and the negative wiring, the voltage detection circuit detects a voltage applied to the diode; When an external charging facility is connected to the positive wiring and the negative wiring, the control device a process of turning off the third switch; a process of turning on the second switch after turning off the third switch; a process of starting charging by the charging facility after turning on the second switch; a process of turning on the first switch when the voltage detected by the voltage detection circuit exceeds a forward reference voltage after the charging by the charging equipment is started; A battery unit that carries out the above.

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