conversion device

Abstract

In the conversion device (10), a second conversion circuit (44) is connected to a second winding (48B) of a transformer (48) and is capable of bidirectional power conversion. Another second conversion circuit (54) is connected to a second winding (58B) of another transformer (58) and is capable of bidirectional power conversion. A third conversion circuit (46) converts alternating current power input to another second winding (48C) of the transformer (48) and is capable of outputting direct current power to the common path (62). Another third conversion circuit (56) converts alternating current power input to another second winding (58C) of the other transformer (58) and is capable of outputting direct current power to the common path (62).

Description

Technical Field

[0001] This disclosure relates to a conversion device. Background Technology

[0002] Patent document 1 illustrates an energy storage system mounted in a vehicle. This energy storage system includes multiple energy storage modules capable of switching between series and parallel connections, and an onboard charger capable of charging the multiple energy storage modules based on power supplied from an external charger.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-80473 Summary of the Invention

[0006] Summary of the invention

[0007] The problem that the invention aims to solve

[0008] The energy storage system disclosed in Patent Document 1 performs voltage equalization processing before the parallel switching of multiple energy storage modules, ensuring that the potential difference between the multiple energy storage modules is below a predetermined threshold so that the power converter operates. However, during the voltage equalization process, this energy storage system requires the power to return through the primary-side switching circuit and capacitors. Since there is a large pulsating current flowing through the capacitors, a large capacitor capacity is required. Therefore, this energy storage system raises concerns about the large size and high cost of the capacitors.

[0009] One of the objectives of this disclosure is to provide a technique that can suppress the load on the capacitor and reduce the difference between the output voltage of the first battery section and the output voltage of the second battery section.

[0010] Solution for solving the problem

[0011] As one of the present disclosures, the conversion device is used in a power supply system, the power supply system having:

[0012] The power supply unit switches between a series connection and a parallel connection between the first battery section and the second battery section;

[0013] The first conversion circuit converts the DC power input to the DC terminal into AC power output to the AC terminal.

[0014] A transformer that magnetically couples a first coil connected to the AC terminal of the first conversion circuit with a plurality of second coils; and

[0015] A capacitor is connected to the DC terminal of the first conversion circuit, wherein...

[0016] The conversion device includes:

[0017] Multiple first conversion circuits;

[0018] The plurality of transformers are respectively connected to the plurality of the first conversion circuits;

[0019] Multiple second conversion circuits; and

[0020] Multiple third conversion circuits,

[0021] A second conversion circuit performs a first operation and a second operation. The first operation is to convert the alternating current generated by a second coil of the transformer into direct current (DC) power output to the first battery section. The second operation is to convert the DC power input from the first battery section into alternating current (AC) power generated by a second coil of the transformer.

[0022] Another second conversion circuit performs a third and a fourth operation. The third operation converts the AC power generated by one of the second coils of the other transformer into DC power output to the second battery section. The fourth operation converts the DC power input from the second battery section into AC power generated by one of the second coils of the other transformer.

[0023] One of the third conversion circuits performs a fifth operation, which is to convert the AC power input to the other second coil of one of the transformers into DC power output to a common path.

[0024] Another of the third conversion circuits performs a sixth operation, which is to convert the AC power input to another second coil of another transformer into DC power output to the common path.

[0025] Invention Effects

[0026] The conversion device disclosed herein can suppress the load on the capacitor and reduce the difference between the output voltage of the first battery section and the output voltage of the second battery section. Attached Figure Description

[0027] Figure 1 This is a block diagram that schematically illustrates a vehicle-mounted system incorporating a power supply system according to a first embodiment of the present disclosure.

[0028] Figure 2 This is an illustrative example of having Figure 1 A schematic diagram of a vehicle with an in-vehicle system.

[0029] Figure 3 This is an example Figure 1 A circuit diagram showing the specific structure of a part of the power conversion section in a power supply system.

[0030] Figure 4 This is an example Figure 1 Part of the power conversion section in the power supply system (with) Figure 3 The circuit diagram showing the specific structure of the different parts.

[0031] Figure 5 This is an explanation Figure 1 An illustration of an example of the operation during external charging in a power supply system.

[0032] Figure 6 This is a flowchart illustrating the process of adjusting control based on the voltage difference of the control device.

[0033] Figure 7 This means that in Figure 1 A diagram illustrating the state of the first charge / discharge control in the power supply system.

[0034] Figure 8 This means that in Figure 1 A diagram illustrating the state of simultaneous first and second discharge control in a power supply system.

[0035] Figure 9 This means that in Figure 1 A diagram illustrating the state of the second charge / discharge control in the power supply system. Detailed Implementation

[0036] The following are examples of embodiments of this disclosure. It should be noted that the features of [1] to [7] illustrated below can be combined arbitrarily without contradiction.

[0037] [1] A conversion device for use in a power supply system, the power supply system having:

[0038] The power supply unit switches between a series connection and a parallel connection between the first battery section and the second battery section;

[0039] The first conversion circuit converts the DC power input to the DC terminal into AC power output to the AC terminal.

[0040] A transformer that magnetically couples a first coil connected to the AC terminal of the first conversion circuit with a plurality of second coils; and

[0041] A capacitor is connected to the DC terminal of the first conversion circuit, wherein...

[0042] The conversion device includes:

[0043] Multiple first conversion circuits;

[0044] The plurality of transformers are respectively connected to the plurality of the first conversion circuits;

[0045] Multiple second conversion circuits; and

[0046] Multiple third conversion circuits,

[0047] A second conversion circuit performs a first operation and a second operation. The first operation is to convert the alternating current generated by a second coil of the transformer into direct current (DC) power output to the first battery section. The second operation is to convert the DC power input from the first battery section into alternating current (AC) power generated by a second coil of the transformer.

[0048] Another second conversion circuit performs a third and a fourth operation. The third operation converts the AC power generated by one of the second coils of the other transformer into DC power output to the second battery section. The fourth operation converts the DC power input from the second battery section into AC power generated by one of the second coils of the other transformer.

[0049] One of the third conversion circuits performs a fifth operation, which is to convert the AC power input to the other second coil of one of the transformers into DC power output to a common path.

[0050] Another of the third conversion circuits performs a sixth operation, which is to convert the AC power input to another second coil of another transformer into DC power output to the common path.

[0051] When the first battery section and the second battery section are connected in series, the conversion device of [1] can charge or discharge the first battery section and the second battery section using different paths when a difference in output voltage between the first battery section and the second battery section occurs. Thus, the conversion device can reduce the difference in output voltage. Furthermore, when charging or discharging the first battery section and the second battery section using different paths, the conversion device can suppress the influence on the capacitor connected to the DC terminal of the first conversion circuit. Therefore, the conversion device can suppress the load on the capacitor and reduce the difference in output voltage between the first battery section and the second battery section.

[0052] [2] Among the conversion devices described in [1] above, the conversion device of [2] has the following characteristics: It includes a control device that controls a plurality of second conversion circuits and a plurality of third conversion circuits. When the first battery section and the second battery section are connected in series, the control device performs a first discharge control, which is a control that causes one of the second conversion circuits to perform a second operation and causes one of the third conversion circuits to perform a fifth operation. The control device performs a second discharge control, which is a control that causes another second conversion circuit to perform a fourth operation and causes another third conversion circuit to perform a sixth operation. The control device reduces the difference between the output voltage of the first battery section and the output voltage of the second battery section by adjusting the output current generated by the first discharge control and the output current generated by the second discharge control.

[0053] The conversion device described in [2] above can perform a first discharge control based on power from the first battery unit to the common path, and a second discharge control based on power from the second battery unit to the common path, and can adjust the discharge current respectively. Furthermore, the conversion device can suppress the load on the capacitor and perform the first discharge control and the second discharge control.

[0054] [3] Among the conversion devices described in [1] or [2] above, the conversion device of [3] has the following characteristics: One of the third conversion circuits performs at least a seventh operation, which is an operation of converting DC power from the common path to output AC power to another second coil of one of the transformers. Another of the third conversion circuits performs at least an eighth operation, which is an operation of converting DC power from the common path to output AC power to another second coil of another transformer.

[0055] The conversion device described in [3] can also perform a charging operation, supplying power to the first battery unit from the common path side via a third conversion circuit, a transformer, and a second conversion circuit. Furthermore, the conversion device can also perform a charging operation, supplying power to the second battery unit from the common path side via another third conversion circuit, another transformer, and another second conversion circuit. Moreover, the conversion device can suppress the load on the capacitors and perform their charging operation.

[0056] [4] Among the conversion devices described in [3] above, the conversion device of [4] has the following characteristics. The conversion device of [4] includes a control device that controls a plurality of second conversion circuits and a plurality of third conversion circuits. The control device selectively performs a first charge-discharge control and a second charge-discharge control. The first charge-discharge control is, when the first battery section and the second battery section are connected in series, simultaneously controlling one second conversion circuit to perform the second operation and one third conversion circuit to perform the fifth operation, and controlling another third conversion circuit to perform the eighth operation and another second conversion circuit to perform the third operation. The second charge-discharge control is, simultaneously controlling another second conversion circuit to perform the fourth operation and another third conversion circuit to perform the sixth operation, and controlling one third conversion circuit to perform the seventh operation and one second conversion circuit to perform the first operation.

[0057] The conversion device described above [4] can charge the second battery unit based on the power from the first battery unit by performing a first charge-discharge control. Furthermore, the conversion device can charge the first battery unit based on the power from the second battery unit by performing a second charge-discharge control.

[0058] [5] Among the conversion devices described in any one of [1] to [4] above, the conversion device of [5] has the following characteristics: The conversion device of [5] includes a control device that controls a plurality of second conversion circuits and a plurality of third conversion circuits. When the difference between the output voltage of the first battery section and the output voltage of the second battery section is a certain value or more, the control device causes the plurality of second conversion circuits and the plurality of third conversion circuits to perform an operation that reduces the voltage difference between the output voltage of the first battery section and the output voltage of the second battery section.

[0059] When the difference between the output voltage of the first battery section and the output voltage of the second battery section is a certain value or higher, the conversion device described above (5) can reduce the voltage difference of the output voltage by control.

[0060] [6] Of the conversion devices described in any of [1] to [5] above, the conversion device of [6] has the following characteristics: The conversion device of [6] includes a switching unit that switches the first battery unit and the second battery unit between a series connection and a parallel connection. The switching unit switches from the series connection to the parallel connection based on the condition that the difference between the output voltage of the first battery unit and the output voltage of the second battery unit is less than a threshold.

[0061] The conversion device described above (6) switches the power supply device from series connection to parallel connection when the difference between the output voltage of the first battery section and the output voltage of the second battery section is less than a threshold. Therefore, it can prevent the switch to parallel connection when the output voltage difference is greater than the threshold.

[0062] [7] Of the conversion devices described in any of [1] to [6] above, the conversion device of [7] has the following characteristics: The conversion device of [7] is connected to the energy storage unit in the common path.

[0063] The conversion device described above [7] can perform the operation of discharging power from the first battery unit to the energy storage unit and the operation of discharging power from the second battery unit to the energy storage unit using different paths.

[0064] <First Implementation Method>

[0065] Figure 1 The conversion device 10 according to the first embodiment of this disclosure is shown. The conversion device 10 constitutes a power supply system for a vehicle.

[0066] (Structure of the power supply system)

[0067] like Figure 2 As shown, the conversion device 10 is used as part of the vehicle-mounted system 2 installed in vehicle 1. Vehicle 1 is a vehicle equipped with the conversion device 10, such as a PHEV or EV vehicle. Figure 2 Thus, the vehicle-mounted system 2 includes a power supply system 3, a high-voltage load 4, auxiliary loads 6, etc. The power supply system 3 includes a conversion device 10, a low-voltage battery 32, and a high-voltage battery 34. The vehicle 1 has connection terminals for electrically connecting to an external AC power source 190. Figure 1 Conversion device 10, such as Figure 1 That way, it is possible to switch between a state where an external AC power supply 190 is electrically connected and a state where an external AC power supply 190 is not connected.

[0068] like Figure 1 Thus, the conversion device 10 includes a power control device 12 and a switch section 14. The power control device 12 includes a power conversion section 16 and a control device 18.

[0069] The conversion device 10 is a system that charges the high-voltage battery 34 and the low-voltage battery 32 based on the AC power supplied from the external AC power source 190 when the vehicle 1 is connected to an external AC power source 190. Furthermore, the conversion device 10 is a system that can supply power to the high-voltage load 4 or auxiliary load 6 while the vehicle is in motion.

[0070] Figure 2The high-voltage load 4 shown is a load that operates by receiving power from the high-voltage battery 34. The high-voltage load 4 includes, for example, a drive unit 8 and a PCU (Power Control Unit) not shown. The PCU is a device that converts the output power of the high-voltage battery 34 into power for driving the drive unit 8 and supplies it to the drive unit 8. The PCU includes, for example, an inverter that generates alternating current (e.g., three-phase alternating current) from direct current and supplies it to the drive unit 8. The drive unit 8 is an electrical drive device such as a main motor. The drive unit 8 is a device that provides driving force to rotate the wheels of the vehicle 1 based on the power supplied from the high-voltage battery 34.

[0071] Auxiliary load 6 refers to auxiliary equipment required to operate engines and electric motors, such as unit motors, alternators, and radiator cooling fans. Auxiliary load 6 may also include electric power steering systems, electric parking brakes, lighting, wiper drives, navigation devices, etc.

[0072] In this specification, "vehicle in motion" includes, but is not limited to, the state in which the vehicle is moving. "Vehicle in motion" also includes the state in which the vehicle moves when the accelerator is pressed. "Vehicle in motion" also includes the state in which the vehicle is stationary and supplying power to any one or all of the auxiliary loads 6. If vehicle 1 is a PHEV, "vehicle in motion" also includes the state in which the engine is idling.

[0073] The high-voltage battery 34 is an example of a power supply device. The high-voltage battery 34 is a power supply device that switches between a first battery section 34A and a second battery section 34B in a series connection and a parallel connection. The high-voltage battery 34 is configured to be chargeable and dischargeable. The high-voltage battery 34 outputs a high voltage (e.g., approximately 300V) for driving the drive unit 8. The output voltage of the high-voltage battery 34 when fully charged is higher than the output voltage of the low-voltage battery 32 when fully charged. The high-voltage battery 34 can be made of lithium-ion batteries or other types of batteries.

[0074] The low-voltage battery 32 is an example of an energy storage unit. The low-voltage battery 32 is configured to be chargeable and dischargeable. The low-voltage battery 32 supplies power to the auxiliary load 6. The low-voltage battery 32 can be made of lead-acid batteries or other types of batteries. When fully charged, the low-voltage battery 32 outputs a specified voltage (e.g., 12V). The high-potential electrode of the low-voltage battery 32 is electrically connected to one conductive path 62A of the common path 62, and the low-potential electrode is electrically connected to the other conductive path 62B.

[0075] The control device 18 is a device that performs various controls on the devices within the vehicle system 2. The control device 18 can be composed of multiple electronic control devices or a single electronic control device. The control device 18 is a device capable of controlling the power conversion unit 16. Specifically, the control device 18 can control the PFC (Power Factor Correction) converters 40 and 50, the first conversion circuits 42 and 52, the transformers 48 and 58, the second conversion circuits 44 and 54, and the third conversion circuits 46 and 56.

[0076] The switching unit 14 includes multiple switches 14A, 14B, and 14C. The switching unit 14 is a switching circuit that switches between a first battery unit 34A and a second battery unit 34B in a series connection and a parallel connection. When switch 14A is in the ON state and switches 14B and 14C are in the OFF state, the switching unit 14 connects the first battery unit 34A and the second battery unit 34B in series. When switch 14A is in the OFF state and switches 14B and 14C are in the ON state, the switching unit 14 connects the first battery unit 34A and the second battery unit 34B in parallel. The switching unit 14 is controlled by a control device 18. The control device 18 controls the switching of the switching unit 14, and can control whether switch 14A is in the ON state and switches 14B and 14C are in the OFF state, or control whether switch 14A is in the OFF state and switches 14B and 14C are in the ON state. The switching unit 14 and the control device 18 are an example of a switching unit.

[0077] If the vehicle equipped with the conversion device 10 is an EV, then through Figure 1 , Figure 2 The EV can travel with the structure shown. If the vehicle equipped with the conversion device 10 is a PHEV, then the vehicle has an engine in addition to the drive unit 8. Therefore, if the vehicle is a PHEV, it can travel as a PHEV by coordinating the operation of the engine and the drive unit 8.

[0078] The power conversion unit 16 mainly includes PFC converters 40 and 50, first conversion circuits 42 and 52, transformers 48 and 58, second conversion circuits 44 and 54, and third conversion circuits 46 and 56. In addition, the power conversion unit 16 includes noise filter units 91, 92, 94, and 96. Noise filter units 91, 92, 94, and 96 are components that remove noise from the path.

[0079] The power conversion unit 16 constitutes a vehicle-mounted charging device. The power conversion unit 16 functions as an OBC (On Board Charger). When an external AC power source 190 (e.g., commercial power) located outside the vehicle 1 is connected to the vehicle 1, the power conversion unit 16 can charge the high-voltage battery 34, which serves as the main power source, based on the power supplied from the external AC power source 190. When the external AC power source 190 is connected to the vehicle 1, the power conversion unit 16 can also charge the low-voltage battery 32 based on the power supplied from the external AC power source 190. Figure 3 , Figure 4 An example of a specific circuit for a portion of the power conversion unit 16 is shown.

[0080] PFC converters 40 and 50 function as power factor correction circuits, forming a bidirectional AC / DC converter that converts AC power to DC power. Figure 1 In this context, PFC converters 40 and 50 are also known as bidirectional AC / DC PFC. For example... Figure 3 Thus, the PFC converter 40 includes inductors 40A and 40B, and switching elements 40C, 40D, 40E, and 40F forming a full-bridge circuit. The two input terminals of the full-bridge circuit formed by the switching elements 40C, 40D, 40E, and 40F are electrically connected to inductors 40A and 40B, respectively. The two output terminals of this full-bridge circuit are electrically connected to the two ends of capacitor 41. When externally charged, the PFC converter 40 generates a DC voltage based on the AC voltage input from the external AC power supply 190 to terminals 40M and 40N, and applies the DC voltage to the two ends of capacitor 41. The PFC converter 40 applies a DC voltage between terminals 42M and 42N of the first conversion circuit 42 depending on the DC voltage applied between the two ends of capacitor 41.

[0081] like Figure 4 Thus, PFC converter 50 has the same structure as PFC converter 40. PFC converter 50 includes inductors 50A and 50B, and switching elements 50C, 50D, 50E, and 50F. The two input terminals of the full-bridge circuit formed by switching elements 50C, 50D, 50E, and 50F are electrically connected to inductors 50A and 50B, respectively. When PFC converter 40 is externally charged, it generates a DC voltage based on the AC voltage input from the external AC power supply 190 to terminals 50M and 50N, and applies the DC voltage between the two ends of capacitor 51 and between terminals 52M and 52N of the first conversion circuit 52.

[0082] like Figure 3Thus, capacitor 41 is electrically connected to terminals 42M and 42N, which are examples of the DC terminals of the first conversion circuit 42. One electrode of capacitor 41 is electrically connected to terminal 42M, and the other electrode of capacitor 41 is electrically connected to terminal 42N.

[0083] like Figure 4 In this way, capacitor 51 is electrically connected to terminals 52M and 52N, which serve as the DC terminals of the first conversion circuit 52. One electrode of capacitor 51 is electrically connected to terminal 52M, and the other electrode of capacitor 51 is electrically connected to terminal 52N.

[0084] The first conversion circuits 42 and 52 function as a DC / AC inverter circuit. Figure 1 In this circuit, the first conversion circuits 42 and 52 are also referred to as DC / AC full-bridge circuits 42 and 52, respectively. The first conversion circuit 42 functions as a power conversion circuit that converts the DC power input from the PFC converter 40 into AC power for output. Figure 3 Thus, the first conversion circuit 42 includes switching elements 42C, 42D, 42E, and 42F constituting a full-bridge circuit. Terminal 42Q of one of the two output terminals of the full-bridge circuit formed by switching elements 42C, 42D, 42E, and 42F is electrically connected to one end of the first transformer 48 (the two ends of the coil 48A). Terminal 42R of the other of the two output terminals is electrically connected to the other end of the end 48M. Terminals 42Q and 42R correspond to an example of the AC terminals of the first conversion circuit 42. The first conversion circuit 42 converts the DC voltage input from the PFC converter 40 to terminals 42M and 42N into an AC voltage and outputs it from terminals 42Q and 42R, applying this AC voltage to the first coil 48A of the transformer 48.

[0085] like Figure 4 Thus, the first conversion circuit 52 has the same structure as the first conversion circuit 42. The first conversion circuit 52 electrically connects one output terminal 52Q of the full-bridge circuit composed of switching elements 52C, 52D, 52E, and 52F to one end of the first coil 58A of the transformer 58, and electrically connects the other terminal 52R to the other end of the coil 58A. Terminals 52Q and 52R correspond to an example of the AC terminals of the first conversion circuit 52. The first conversion circuit 52 converts the DC voltage input from the PFC converter 50 to terminals 52M and 52N into AC voltage and outputs it from terminals 52Q and 52R, applying this AC voltage to the first coil 58A of the transformer 58.

[0086] like Figure 3 , Figure 4 Thus, multiple transformers 48 and 58 are respectively connected to multiple first conversion circuits 42 and 52. For example... Figure 3Thus, transformer 48 includes a first coil 48A and a plurality of second coils 48B and 48C. The first coil 48A is electrically connected to the AC terminal of the first conversion circuit 42. The first coil 48A is magnetically coupled to the plurality of second coils 48B and 48C. In the following description, transformer 48 is also referred to as a transformer 48. The second coil 48B is also referred to as a second coil 48B. The second coil 48C is also referred to as another second coil 48C.

[0087] like Figure 4 Thus, transformer 58 includes a first coil 58A and a plurality of second coils 58B and 58C. The first coil 58A is electrically connected to the AC terminal of the first conversion circuit 52. The first coil 58A is magnetically coupled to the plurality of second coils 58B and 58C. In the following description, transformer 58 is also referred to as another transformer 58. Second coil 58B is also referred to as one second coil 58B. Second coil 58C is also referred to as another second coil 58C.

[0088] The second conversion circuits 44 and 54 function as bidirectional AC / DC converters, capable of bidirectionally converting AC power to DC power. Figure 1 In this circuit, the second conversion circuits 44 and 54 are also referred to as AC / DC full-bridge circuits 44 and 54, respectively.

[0089] The second conversion circuit 44 is an example of a second conversion circuit and is also referred to as a second conversion circuit 44. The second conversion circuit 44 includes switching elements 44C, 44D, 44E, 44F and a capacitor 44H constituting a full-bridge circuit. One terminal of a pair of terminals of the full-bridge circuit formed by the switching elements 44C, 44D, 44E, 44F is electrically connected to one end of the second coil 48B, and the other terminal is electrically connected to the other end of the second coil 48B. The second conversion circuit 44 is capable of performing a first operation to convert the AC power generated in the second coil 48B of the transformer 48 to output DC power to the first battery section 34A. During the first operation, the output voltage (AC voltage) applied to the end 48N of the transformer 48 (the two ends of the coil 48B) is converted into a DC voltage, which is applied to terminals 44M and 44N. Terminal 44M is a conductive path that can be electrically connected to the electrode with the highest potential in the first battery section 34A. Terminal 44N is a conductive path that can be electrically connected to the electrode with the lowest potential in the first battery section 34A. It should be noted that a relay or fuse (not shown) may also be inserted between terminals 44M, 44N and the first battery section 34A. The second conversion circuit 44 also performs a second operation, converting the DC power input from the first battery section 34A to generate AC power in the second coil 48B of the transformer 48. During this second operation, the DC voltage applied to terminals 44M, 44N is converted into AC voltage and applied to the second coil 48B of the transformer 48.

[0090] The second conversion circuit 54 is equivalent to another example of a second conversion circuit, and is also referred to as another second conversion circuit 54. The second conversion circuit 54 has the same circuit structure as the second conversion circuit 44. The second conversion circuit 54 includes switching elements 54C, 54D, 54E, 54F and a capacitor 54H that constitute a full-bridge circuit. One of the terminals of the full-bridge circuit formed by the switching elements 54C, 54D, 54E, 54F is electrically connected to one end of the second coil 58B, and the other terminal is electrically connected to the other end of the second coil 58B. The second conversion circuit 54 can perform a third operation to convert the AC power generated in the second coil 58B of the transformer 58 to output DC power to the second battery section 34B. In the third operation, the output voltage (AC voltage) applied to the end 58N of the transformer 58 (the two ends of the coil 58B) is converted into a DC voltage, and this DC voltage is applied to the terminals 54M, 54N. Terminal 54M is a conductive path that can be electrically connected to the electrode with the highest potential in the second battery section 34B, and terminal 54N is a conductive path that can be electrically connected to the electrode with the lowest potential in the second battery section 34B. It should be noted that a relay or fuse (not shown) may also be interposed between terminals 54M, 54N and the second battery section 34B. The second conversion circuit 54 can also perform a fourth operation to convert the DC power input from the second battery section 34B to generate AC power in the second coil 58B of the transformer 58. In this fourth operation, the DC voltage applied to terminals 54M, 54N is converted into AC voltage and applied to the second coil 58B of the transformer 58.

[0091] The third conversion circuits, 46 and 56, function as bidirectional AC / DC converters, capable of bidirectionally converting AC power to DC power. Figure 1 In this circuit, the third conversion circuits 46 and 56 are also called AC / DC full-bridge circuits 46 and 56, respectively.

[0092] The third conversion circuit 46 is an example of a third conversion circuit and is also referred to as a third conversion circuit 46. The third conversion circuit 46 includes switching elements 46C, 46D, 46E, 46F and a capacitor 46H constituting a full-bridge circuit. One terminal of a pair of terminals of the full-bridge circuit formed by switching elements 46C, 46D, 46E, 46F is electrically connected to one end of the second coil 48C, and the other terminal is electrically connected to the other end of the second coil 48C. The third conversion circuit 46 can perform a fifth operation to convert the AC power generated in the second coil 48C of the transformer 48 to output DC power to the common path 62. In the fifth operation, the output voltage (AC voltage) applied to the end 48P of the transformer 48 (the two ends of the coil 48C) is converted into a DC voltage, and this DC voltage is applied to terminals 46M and 46N. Terminal 46M is the terminal electrically connected to the conductive path 62A of one of the common paths 62 and is the terminal electrically connected to the electrode with the highest potential in the low-voltage battery 32. Terminal 46N is electrically connected to the conductive path 62B of the other side of the common path 62, and is also electrically connected to the electrode with the lowest potential in the low-voltage battery 32. It should be noted that a relay or fuse (not shown) may also be interposed between terminals 46M, 46N and the low-voltage battery 32. The third conversion circuit 46 can also perform a seventh operation to convert the DC power input to the common path 62 to generate AC power in the second coil 48C of the transformer 48. In the seventh operation, the DC voltage applied to terminals 46M, 46N is converted into AC voltage and applied to the second coil 48C of the transformer 48.

[0093] The third conversion circuit 56 is equivalent to another example of a third conversion circuit, and is also referred to as another third conversion circuit 56. The third conversion circuit 56 has the same circuit structure as the third conversion circuit 46. The third conversion circuit 56 includes switching elements 56C, 56D, 56E, 56F and a capacitor 56H that constitute a full-bridge circuit. One of the terminals of the full-bridge circuit formed by the switching elements 56C, 56D, 56E, 56F is electrically connected to one end of the second coil 58C, and the other terminal is electrically connected to the other end of the second coil 58C. The third conversion circuit 56 can perform a sixth operation to convert the AC power generated in the second coil 58C of the transformer 58 to output DC power to the common path 62. In the sixth operation, the output voltage (AC voltage) applied to the end 58P of the transformer 58 (the two ends of the coil 58C) is converted into a DC voltage, and this DC voltage is applied to the terminals 56M and 56N. Terminal 56M is electrically connected to conductive path 62A, which forms one side of the common path 62, and is also electrically connected to the electrode with the highest potential in the low-voltage battery 32. Terminal 56N is electrically connected to conductive path 62B, which forms the other side of the common path 62, and is also electrically connected to the electrode with the lowest potential in the low-voltage battery 32. It should be noted that a relay or fuse (not shown) may also be present between terminals 56M, 56N and the low-voltage battery 32. The third conversion circuit 56 can also perform an eighth operation, converting the DC power applied to the common path 62 to generate AC power in the second coil 58C of the transformer 58. In this eighth operation, the DC voltage applied to terminals 56M, 56N is converted to AC voltage and applied to the second coil 58C of the transformer 58.

[0094] (Basic actions during external charging)

[0095] The following description explains the operation of the conversion device 10 during external charging. During external charging, the conversion device 10 can be electrically connected to an external AC power source 190 located outside the vehicle, via cables (not shown). For vehicle 1 ( Figure 2 An external AC power source 190 is connected. When the external AC power source 190 is electrically connected to the conversion device 10, for example, power is supplied to the control device 18 from the low-voltage battery 32. The detection of the external AC power source 190 being electrically connected to the conversion device 10 and the control of the power supply to the control device 18 are performed by a control device (not shown) that is different from the control device 18.

[0096] When power is supplied to the control device 18 upon connection to the external AC power source 190, the control device 18 activates the power conversion unit 16. Specifically, the control device 18 causes the PFC converter 40, the first conversion circuit 42, and the second conversion circuit 44 to perform power conversion operations respectively, converting the AC voltage from the external AC power source 190 into a high-voltage DC voltage for supplying to the first battery unit 34A. Thus, when a power conversion operation (first path conversion operation) is performed in the path of the PFC converter 40, the first conversion circuit 42, and the second conversion circuit 44, the first battery unit 34A is charged based on the power from the external AC power source 190 (see reference). Figure 5 (See arrow A). Furthermore, the control device 18 causes the PFC converter 50, the first conversion circuit 52, and the second conversion circuit 54 to perform power conversion operations respectively, converting the AC voltage from the external AC power source 190 into a high-voltage DC voltage and supplying it to the second battery unit 34B. Thus, when a power conversion operation (second path conversion operation) is performed in the path of the PFC converter 50, the first conversion circuit 52, and the second conversion circuit 54, the second battery unit 34B is charged based on the power from the external AC power source 190 (see reference). Figure 5 Arrow B).

[0097] During external charging of the high-voltage battery 34, which is powered by an external AC power source 190, the first battery unit 34A and the second battery unit 34B are connected in series. The first battery unit 34A is charged via the aforementioned first path switching operation. The second battery unit 34B is charged via the aforementioned second path switching operation. The control device 18 controls the increase or decrease of the output current supplied to the first battery unit 34A due to the aforementioned first path switching operation. The control device 18 also controls the increase or decrease of the output current supplied to the second battery unit 34B due to the aforementioned second path switching operation. In other words, the control device 18 can independently control the output current for the first battery unit 34A and the second battery unit 34B, respectively.

[0098] When the first battery unit 34A and the second battery unit 34B are connected in parallel, charging is performed on either or both of the aforementioned first path switching operation and the aforementioned second path switching operation. It should be noted that charging based on the aforementioned series connection of the high-voltage battery 34 can be performed when the first charging condition is met (e.g., when the voltage of the external AC power supply 190 is a relatively high 800V). Furthermore, charging based on the aforementioned parallel connection of the high-voltage battery 34 can be performed when the second charging condition is met (e.g., when the voltage of the external AC power supply 190 is a relatively low 400V).

[0099] During the aforementioned external charging, the low-voltage battery 32 can also be charged. In this case, the control device 18 can also perform power conversion operations (third path conversion operations) on the PFC converter 40, the first conversion circuit 42, and the third conversion circuit 46 by converting the AC voltage from the external AC power supply 190 into a low-voltage DC voltage and supplying it to the low-voltage battery 32 (see reference). Figure 5 (Arrow C). Alternatively, the control device 18 can also perform power conversion operations (third path conversion operation) on the PFC converter 50, the first conversion circuit 52, and the third conversion circuit 56 by converting the AC voltage from the external AC power source 190 into a low-voltage DC voltage to supply to the low-voltage battery 32 (see...). Figure 5 Arrow D).

[0100] (The typical operation during series connection)

[0101] The control device 18 can perform the following when the high-voltage battery 34 is connected in series as described above: Figure 6 The voltage difference adjustment control is shown. For example, the control device 18 can also repeatedly perform this control during vehicle starting when the vehicle's start switch is turned on (e.g., during the aforementioned vehicle operation). Figure 6 Control. Alternatively, control device 18 can also be started when external AC power supply 190 is electrically connected to conversion device 10. Figure 6 Control.

[0102] Control device 18 started Figure 6 Under controlled conditions, in step S1, the output voltage value V1 of the first battery unit 34A and the output voltage value V2 of the second battery unit 34B are detected. The detection method for output voltage values ​​V1 and V2 can employ various methods for detecting the output voltage of the vehicle battery. After step S1, in step S2, the control device 18 determines whether the difference between output voltage values ​​V1 and V2 is greater than or equal to a certain value α. If the control device 18 determines in step S2 that the difference between output voltage values ​​V1 and V2 is greater than or equal to a certain value α, then in step S3, it determines whether output voltage value V1 is greater than output voltage value V2.

[0103] When the control device 18 determines that the output voltage value V1 is greater than the output voltage value V2, in step S4, it lowers the upper limit of the output current value of the second DC-DC converter compared to the current value, while the upper limit of the output current value of the first DC-DC converter remains the current value. The first DC-DC converter is a converter consisting of the second conversion circuit 44, the transformer 48, and the third conversion circuit 46, and is used for charging and discharging the first battery unit 34A. The second DC-DC converter is a converter consisting of the second conversion circuit 54, the transformer 58, and the third conversion circuit 56, and is used for charging and discharging the second battery unit 34B. Regarding the output current, the current value flowing from the third conversion circuit 46 to the low-voltage battery 32 is a positive output current value for the first DC-DC converter, and the current value flowing from the low-voltage battery 32 to the third conversion circuit 46 is a negative output current value. Furthermore, the current value flowing from the third conversion circuit 56 to the low-voltage battery 32 is a positive output current value of the second DC-DC converter, while the current value flowing from the low-voltage battery 32 to the third conversion circuit 56 is a negative output current value. With the upper limit of the output current value of the second DC-DC converter remaining at its current value, and the upper limit of the output current value of the first DC-DC converter decreasing compared to the current value, the charging voltages of the first battery unit 34A and the second battery unit 34B are adjusted so that the output voltage value V2 is close to the output voltage value V1.

[0104] In step S6 following step S4, control device 18 may also simultaneously control the second conversion circuit 44 to perform the aforementioned second operation and the third conversion circuit 46 to perform the aforementioned fifth operation, as well as control the third conversion circuit 56 to perform the aforementioned eighth operation and the second conversion circuit 54 to perform the third operation. When the first charge / discharge control is performed in this way, as... Figure 7 Thus, in the first DC-DC converter, control is performed to supply DC power to the common path 62 based on the power from the first battery unit 34A. Furthermore, in the second DC-DC converter, control is performed to supply DC power to the second battery unit 34B based on the power from the common path 62.

[0105] In step S6 following step S4, control device 18 may also simultaneously perform the first discharge control (causing the second conversion circuit 44 to perform the aforementioned second operation and the third conversion circuit 46 to perform the aforementioned fifth operation) and the second discharge control (causing the second conversion circuit 54 to perform the aforementioned fourth operation and the third conversion circuit 56 to perform the aforementioned sixth operation). In this case, such as Figure 8In this way, in the first DC-DC converter, the supply of DC power to the common path 62 is controlled based on the power from the first battery unit 34A. Furthermore, in the second DC-DC converter, the supply of DC power to the common path 62 is controlled based on the power from the second battery unit 34B. In this case, the current output to the common path 62 by the first DC-DC converter is greater than the current output to the common path 62 by the second DC-DC converter. That is, the control device 18 can reduce the difference between the output voltage of the first battery unit 34A and the output voltage of the second battery unit 34B by adjusting the output current generated by the first discharge control and the output current generated by the second discharge control.

[0106] If, in step S3, the control device 18 determines that the output voltage value V1 is lower than the output voltage value V2, then in step S5, it lowers the upper limit of the output current value of the first DC-DC converter compared to the current value, while keeping the upper limit of the output current value of the second DC-DC converter at the current value. If the upper limit of the output current value of the first DC-DC converter remains the current value, but the upper limit of the output current value of the second DC-DC converter is lowered compared to the current value, the charging voltages of the first battery unit 34A and the second battery unit 34B are adjusted to bring the output voltage value V2 closer to the output voltage value V1.

[0107] In step S6 following step S5, control device 18 may also simultaneously control the second conversion circuit 54 to perform the aforementioned fourth operation and the third conversion circuit 56 to perform the aforementioned sixth operation, as well as control the third conversion circuit 46 to perform the aforementioned seventh operation and the second conversion circuit 44 to perform the aforementioned first operation. When performing the second charge / discharge control in this way, as... Figure 9 In this way, in the second DC-DC converter, control is performed to supply DC power to the common path 62 based on the power from the second battery unit 34B. Furthermore, in the first DC-DC converter, control is performed to supply DC power to the first battery unit 34A based on the power from the common path 62.

[0108] In step S6 following step S5, control device 18 may also simultaneously perform the first discharge control (causing the second conversion circuit 44 to perform the second operation described above and the third conversion circuit 46 to perform the fifth operation described above), and the second discharge control (causing the second conversion circuit 54 to perform the fourth operation described above and the third conversion circuit 56 to perform the sixth operation described above). In this case, such as Figure 8In this way, in the first DC-DC converter, the supply of DC power to the common path 62 is controlled based on the power from the first battery unit 34A. Furthermore, in the second DC-DC converter, the supply of DC power to the common path 62 is controlled based on the power from the second battery unit 34B. In this case, it is sufficient to ensure that the current output to the common path 62 by the first DC-DC converter is less than the current output to the common path 62 by the second DC-DC converter. That is, the control device 18 can reduce the difference between the output voltage of the first battery unit 34A and the output voltage of the second battery unit 34B by adjusting the output current generated by the first discharge control and the output current generated by the second discharge control.

[0109] In this way, when the difference between the output voltage of the first battery unit 34A and the output voltage of the second battery unit 34B is a certain value α or higher, the control device 18 causes the multiple second conversion circuits 44, 54 and the multiple third conversion circuits 46, 56 to perform an operation that reduces the difference in the output voltage values.

[0110] The control device 18 continues the control of step S6 after step S4 or step S6 after step S5 until the difference between the output voltage value V1 and the output voltage value V2 is less than a certain value α. When the difference between the output voltage value V1 and the output voltage value V2 is less than a certain value α, the setting of the upper limit current value set by step S4 or step S5 is released.

[0111] (Parallel switching action)

[0112] The control device 18 can also start when the high-voltage battery 34 is in a series connection state and the "prescribed conditions for switching from series connection to parallel connection" are met. Figure 6 This situation is also controlled through the process described above. Figure 6 The control device 18 controls the switching from a series connection to a parallel connection. The "prescribed conditions for switching from a series connection to a parallel connection" are not specifically limited; examples include charging via a specified charging method (charging via an external AC power supply 190 with a 400V output as described above). In this case, the control device 18... Figure 6 After the processing of steps S1 to S8 in the control is completed, simply switch the switch unit 14 to parallel connection after step S8.

[0113] In this case, the control device 18 and the switch unit 14, which are equivalent to an example of the switching unit, switch the high-voltage battery 34 from the series connection described above to the parallel connection described above, based on the condition that the difference between the output voltage of the first battery unit and the output voltage of the second battery unit is less than a threshold (a certain value α).

[0114] (Serial switching action)

[0115] When the predetermined conditions for switching the high-voltage battery 34 from the parallel connection to the series connection are met, the control device 18 sets the first battery section 34A and the second battery section 34B to a series connection by turning switch 14A on and turning switches 14B and 14C off. The "prescribed conditions for switching the high-voltage battery 34 from the parallel connection to the series connection" are not particularly limited, and examples include charging using a predetermined charging method (charging based on the external AC power supply 190 with an output of 800V as described above) and the completion of external charging in a parallel connection.

[0116] The following description concerns the effects of the first embodiment.

[0117] When a voltage difference arises between the output voltage of the first battery section 34A and the output voltage of the second battery section 34B, the conversion device 10 can charge or discharge the first battery section 34A and the second battery section 34B through different paths. Therefore, the conversion device 10 can reduce the voltage difference. Furthermore, when charging or discharging the first battery section 34A and the second battery section 34B through different paths, the conversion device 10 can suppress the impact on the capacitors 41 and 51 connected to the DC terminals of the first conversion circuits 42 and 52. Therefore, the conversion device 10 can suppress the load on the capacitors 41 and 51 and reduce the voltage difference between the first battery section 34A and the second battery section 34B.

[0118] The conversion device 10 is capable of performing a first discharge control based on power from the first battery unit 34A to the common path 62, and a second discharge control based on power from the second battery unit 34B to the common path 62, and can adjust the discharge current accordingly. Furthermore, the conversion device 10 can suppress the load on capacitors 41 and 51 and perform the first and second discharge controls.

[0119] The conversion device 10 can also perform a charging operation, supplying power from the common path 62 side to the first battery unit 34A via a third conversion circuit 46, a transformer 48, and a second conversion circuit 44. Furthermore, the conversion device 10 can also perform a charging operation, supplying power from the common path 62 side to the second battery unit 34B via another third conversion circuit 56, another transformer 58, and another second conversion circuit 54. Moreover, the conversion device 10 can suppress the load on capacitors 41 and 51 and charge them.

[0120] The conversion device 10 can charge the second battery unit 34B based on the power from the first battery unit 34A by performing a first charge-discharge control. Furthermore, the conversion device 10 can charge the first battery unit 34A based on the power from the second battery unit 34B by performing a second charge-discharge control.

[0121] The conversion device 10 can reduce the voltage difference of the output voltage when the difference between the output voltage of the first battery unit 34A and the output voltage of the second battery unit 34B is greater than a certain value.

[0122] The conversion device 10 can switch the high-voltage batteries 34 (power supply units) from a series connection to a parallel connection when the difference between the output voltage of the first battery unit 34A and the output voltage of the second battery unit 34B is less than a threshold. Therefore, the conversion device 10 can prevent switching to a parallel connection when the output voltage difference is greater than or equal to the threshold.

[0123] The conversion device 10 can perform the operation of discharging power from the first battery unit 34A to the low-voltage battery 32 (energy storage unit) and the operation of discharging power from the second battery unit 34B to the low-voltage battery 32 (energy storage unit) using different paths.

[0124] <Other Implementation Methods>

[0125] This disclosure is not limited to the embodiments described above and the accompanying drawings. For example, the features of the embodiments described above or later can be combined in any way without contradiction. Moreover, any feature of the embodiments described above or later can be omitted as long as it is not explicitly stated as an essential feature. Furthermore, the embodiments described above can also be modified as follows.

[0126] In the above embodiment, two first conversion circuits are provided, but three or more first conversion circuits may also be provided. In this case, it is sufficient to provide three or more transformers corresponding to the three or more first conversion circuits respectively. Furthermore, it is sufficient to provide three or more second conversion circuits and three or more third conversion circuits corresponding to the three or more transformers respectively.

[0127] It should be noted that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of this invention is not limited to the embodiments disclosed herein, and is intended to include all modifications within the scope disclosed in the claims or their equivalents.

[0128] Label Explanation

[0129] 1: Vehicle

[0130] 2: Vehicle system

[0131] 3: Power System

[0132] 4: High-voltage load

[0133] 6: Auxiliary loads

[0134] 8: Drive Unit

[0135] 10: Conversion device

[0136] 12: Power control device

[0137] 14: Switch section

[0138] 14A, 14B, 14C: Switches

[0139] 16: Power Conversion Department

[0140] 18: Control device

[0141] 32: Low-voltage storage battery

[0142] 34: High-voltage storage battery (power supply device)

[0143] 34A: First Battery Section

[0144] 34B: Second Battery Section

[0145] 40, 50: PFC converter

[0146] 40A, 40B: Inductors

[0147] 40C, 40D, 40E, 40F: Switching elements

[0148] 40M, 40N: terminal

[0149] 41, 51: Capacitors

[0150] 42, 52: First conversion circuit

[0151] 42C, 42D, 42E, 42F: Switching elements

[0152] 42M, 42N: Terminals (DC terminals)

[0153] 42Q, 42R: Terminals (AC terminals)

[0154] 44, 54: Second conversion circuit

[0155] 44C, 44D, 44E, 44F: Switching elements

[0156] 44H: Capacitor

[0157] 44M, 44N: Terminal

[0158] 46, 56: Third conversion circuit

[0159] 46C, 46D, 46E, 46F: Switching elements

[0160] 46H: Capacitor

[0161] 46M, 46N: Terminal

[0162] 48, 58: Transformer

[0163] 48A: First coil

[0164] 48B, 48C: Second coil

[0165] 48M: End

[0166] 48N: End

[0167] 48P: End

[0168] 50A, 50B: Inductors

[0169] 50C, 50D, 50E, 50F: Switching elements

[0170] 50M, 50N: terminal

[0171] 52C, 52D, 52E, 52F: Switching elements

[0172] 52M, 52N: Terminals (DC terminals)

[0173] 52Q, 52R: Terminals (AC terminals)

[0174] 54C, 54D, 54E, 54F: Switching elements

[0175] 54H: Capacitor

[0176] 54M, 54N: Terminal

[0177] 56C, 56D, 56E, 56F: Switching elements

[0178] 56H: Capacitor

[0179] 56M, 56N: Terminals

[0180] 58A: First coil

[0181] 58B, 58C: Second coil

[0182] 58N: End

[0183] 58P: End

[0184] 62: Shared path

[0185] 62A, 62B: Conductive paths

[0186] 91, 92, 94, 96: Noise Filter Section

[0187] 190: External AC power supply.

Claims

1. A conversion device for use in a power supply system, the power supply system having: The power supply unit switches between a series connection and a parallel connection between the first battery section and the second battery section; The first conversion circuit converts the DC power input to the DC terminal into AC power output to the AC terminal. A transformer that magnetically couples a first coil connected to the AC terminal of the first conversion circuit with a plurality of second coils; and A capacitor is connected to the DC terminal of the first conversion circuit, wherein... The conversion device includes: Multiple first conversion circuits; The plurality of transformers are respectively connected to the plurality of the first conversion circuits; Multiple second conversion circuits; and Multiple third conversion circuits, A second conversion circuit performs a first operation and a second operation. The first operation is to convert the alternating current generated by a second coil of the transformer into direct current (DC) power output to the first battery section. The second operation is to convert the DC power input from the first battery section into alternating current (AC) power generated by a second coil of the transformer. Another second conversion circuit performs a third and a fourth operation. The third operation converts the AC power generated by one of the second coils of the other transformer into DC power output to the second battery section. The fourth operation converts the DC power input from the second battery section into AC power generated by one of the second coils of the other transformer. One of the third conversion circuits performs a fifth operation, which is to convert the AC power input to the other second coil of one of the transformers into DC power output to a common path. Another of the third conversion circuits performs a sixth operation, which is to convert the AC power input to another second coil of another transformer into DC power output to the common path.

2. The conversion device according to claim 1, wherein, The conversion device includes a control device that controls a plurality of second conversion circuits and a plurality of third conversion circuits. When the first battery section and the second battery section are connected in series, the control device performs a first discharge control and a second discharge control. The first discharge control causes one of the second conversion circuits to perform the second operation and causes one of the third conversion circuits to perform the fifth operation. The second discharge control causes another second conversion circuit to perform the fourth operation and causes another third conversion circuit to perform the sixth operation. The control device reduces the difference between the output voltage of the first battery section and the output voltage of the second battery section by adjusting the output current generated by the first discharge control and the output current generated by the second discharge control.

3. The conversion device according to claim 1 or 2, wherein, One of the third conversion circuits performs at least a seventh operation, which is the conversion of DC power from the common path to AC power output to another second coil of one of the transformers. The other third conversion circuit performs at least an eighth operation, which is to convert the DC power from the common path to AC power output to another second coil of the other transformer.

4. The conversion device according to claim 3, wherein, The conversion device includes a control device that controls a plurality of second conversion circuits and a plurality of third conversion circuits. When the first battery section and the second battery section are connected in series, the control device selectively performs a first charge-discharge control and a second charge-discharge control. The first charge-discharge control is to simultaneously control one second conversion circuit to perform the second operation and one third conversion circuit to perform the fifth operation, and to simultaneously control another third conversion circuit to perform the eighth operation and another second conversion circuit to perform the third operation. The second charge-discharge control is to simultaneously control another second conversion circuit to perform the fourth operation and another third conversion circuit to perform the sixth operation, and to simultaneously control one third conversion circuit to perform the seventh operation and one second conversion circuit to perform the first operation.

5. The conversion device according to claim 1 or 2, wherein, The conversion device includes a control device that controls a plurality of second conversion circuits and a plurality of third conversion circuits. When the difference between the output voltage of the first battery section and the output voltage of the second battery section is greater than a certain value, the control device causes the plurality of second conversion circuits and the plurality of third conversion circuits to reduce the voltage difference between the output voltage of the first battery section and the output voltage of the second battery section.

6. The conversion device according to claim 1 or 2, wherein, The conversion device includes a switching unit that switches the first battery unit and the second battery unit between the series connection and the parallel connection. The switching unit switches from the series connection to the parallel connection when the difference between the output voltage of the first battery unit and the output voltage of the second battery unit is less than a threshold.

Images