Power supply device

Abstract

To avoid prohibition of processing involving opening / closing of a relay when charging is completed.SOLUTION: A power supply device comprises: a connection circuit that forms a parallel circuit that connects a first battery module and a second battery module in parallel when charging them; a variable resistor disposed between the first battery module and the second battery module connected in parallel in the connection circuit; and a control device capable of executing resistance adjustment processing for adjusting a resistance value of the variable resistor when charging the first battery module and the second battery module. The resistance adjustment processing includes processing of: calculating a circulation current generatable between the battery modules on the basis of an open circuit voltage difference being a difference between an open circuit voltage of the first battery module and an open circuit voltage of the second battery module; calculating a heat generation quantity generatable in the variable resistor by multiplying the calculated circulation current by the open circuit voltage difference; and adjusting the resistance value of the variable resistor so as to allow the calculated heat generation quantity to become less than a prescribed allowable value.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The technology disclosed in this specification relates to a power supply device.

Background Art

[0002] Patent Document 1 describes a power supply device. This power supply device includes two battery modules that can be charged by an external power supply, a connection circuit that connects the two battery modules in parallel, and a control device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power supply device as described above, when charging two battery modules with an external power supply, it is conceivable to connect the battery modules in parallel. Thereby, the output voltage required for the external power supply can be lowered, and the time required to charge those battery modules can be shortened. However, since there are individual differences between the two battery modules, even when charging is performed at the same charging voltage, a difference may occur in the state of charge (SOC) between those battery modules. In this case, at the end of charging (specifically, when the energization of the charging current is stopped), an open-circuit voltage difference occurs between the two battery modules, so a circulating current that circulates current between those battery modules is generated. When the relay is opened and closed in a situation where a circulating current is generated, an arc may occur at the contact of the relay, and the relay may be damaged. Therefore, until the open-circuit voltage difference between the battery modules is eliminated, it is necessary to prohibit processing involving the opening and closing of the relay, and the functions and convenience of the power supply device are impaired.

[0005] In light of the above circumstances, this specification provides a technology to avoid the prohibition of processes involving the opening and closing of a relay when charging is complete. [Means for solving the problem]

[0006] The technology disclosed herein is embodied in a power supply device. This power supply device includes a first battery module and a second battery module that can be charged by an external power source; a connection circuit having a plurality of relays that forms a parallel circuit connecting the first battery module and the second battery module in parallel when the first battery module and the second battery module are being charged; a variable resistor provided in the connection circuit and interposed between the first battery module and the second battery module connected in parallel; and a control device that can perform a resistance adjustment process to adjust the resistance value of the variable resistor when the first battery module and the second battery module are being charged. The resistance adjustment process includes a process of calculating a circulating current that may occur between the first battery module and the second battery module based on an open-circuit voltage difference which is the difference between the open-circuit voltage of the first battery module and the open-circuit voltage of the second battery module; a process of calculating the amount of heat that may be generated in the variable resistor by multiplying the open-circuit voltage difference by the calculated circulating current; and a process of adjusting the resistance value of the variable resistor so that the calculated amount of heat is below a predetermined allowable value.

[0007] In the configuration described above, the resistance adjustment process is repeatedly performed while the first and second battery modules are charging. During the resistance adjustment process, the open-circuit voltage difference between the battery modules is monitored, for example, based on the respective charge levels of the first and second battery modules. If an open-circuit voltage difference occurs between the battery modules, and charging is terminated at that point (more specifically, the flow of charging current is stopped), a circulating current will be generated between the battery modules, causing heat to be generated in the variable resistor. Therefore, the resistance adjustment process calculates the circulating current that may occur between the battery modules based on the open-circuit voltage difference, and further calculates the amount of heat that may be generated in the variable resistor. The resistance value of the variable resistor is then adjusted so that the amount of heat generated in the variable resistor falls below a predetermined tolerance value. The predetermined tolerance value here is, for example, a value that can withstand current flow for an unlimited amount of time when the amount of heat generated in the variable resistor is less than that value. With this configuration, the generation of an open-circuit voltage difference between the two battery modules is suppressed while the two battery modules are charging. This avoids the prohibition of processes involving the opening and closing of relays after charging is complete.

[0008] In a second embodiment, the resistance adjustment process in the first embodiment may include: a process for calculating a first corrected voltage obtained by correcting the open-circuit voltage of the first battery module with a voltage change due to circulating current; a process for calculating a second corrected voltage obtained by correcting the open-circuit voltage of the second battery module with a voltage change due to circulating current; and a process for adjusting the resistance value of a variable resistor so that the first corrected voltage and the second corrected voltage are within a predetermined allowable range. With such a configuration, the open-circuit voltage difference between the two battery modules is suppressed so that the circulating current that may occur between the two battery modules is within an allowable range for each battery module.

[0009] In a third embodiment, the resistance adjustment process in the first or second embodiment may further include a process for estimating the open-circuit voltage of the first battery module based on the charge level of the first battery module, and a process for estimating the open-circuit voltage of the second battery module based on the charge level of the second battery module.

[0010] In a fourth embodiment, in any of the first to third embodiments, the control device may, upon completion of charging of the first and second battery modules, set the resistance value of the variable resistor to approximately its maximum value and then execute a process involving the opening and closing of multiple relays. With this configuration, even if an open-circuit voltage difference occurs between the two battery modules at the end of charging, the circulating current flowing between them is greatly reduced by setting the resistance value of the variable resistor to approximately its maximum value. As a result, the control device can quickly execute a process involving the opening and closing of relays without waiting for the open-circuit voltage difference to be eliminated after charging is complete.

[0011] The technology disclosed herein can also be embodied in other power supply devices. This power supply device includes a first battery module and a second battery module that can be charged by an external power source; a connection circuit having a plurality of relays that selectively forms a parallel circuit connecting the first battery module and the second battery module in parallel and a series circuit connecting the first battery module and the second battery module in series; a variable resistor provided in the connection circuit and interposed between the first battery module and the second battery module connected in parallel; and a control device that controls the opening and closing of the plurality of relays and adjusts the resistance value of the variable resistor. The control device is configured to perform the following processes: when charging of the first battery module and the second battery module begins, control the plurality of relays to form the parallel circuit in the connection circuit; when charging of the first battery module and the second battery module ends, set the resistance value of the variable resistor to approximately its maximum value; and after setting the resistance value of the variable resistor to approximately its maximum value, control the plurality of relays to form the series circuit in the connection circuit.

[0012] In the configuration described above, the two battery modules are connected in parallel at the start of charging, and at the end of charging, the resistance value of the variable resistor interposed between the two parallel-connected battery modules is set to approximately its maximum value. As a result, even if an open-circuit voltage difference occurs between the two battery modules at the end of charging, the circulating current flowing between them is greatly reduced because the resistance value of the variable resistor is set to approximately its maximum value. This allows the power supply to connect the two battery modules in series without waiting for the open-circuit voltage difference to be eliminated after charging is complete. [Brief explanation of the drawing]

[0013] [Figure 1] A schematic diagram showing the configuration of the power supply unit 10 and the vehicle 100 on which it is mounted in the embodiment. [Figure 2] A schematic circuit diagram showing the series circuit formed by the connecting circuit 16. [Figure 3] A schematic circuit diagram showing the parallel circuit formed by the connecting circuit 16. [Figure 4] A flowchart showing an example of the resistance adjustment process performed by the control device 18. [Figure 5] Figure 5 shows the changes over time of various indicators in the resistance adjustment process. Figure 5(A) shows the resistance value RV of the second pre-charge resistor 42. Figure 5(B) shows the open-circuit voltage OCV1 of the first battery module 12, the open-circuit voltage OCV2 of the second battery module 14, the closed-circuit voltage CCV1 of the first battery module 12, and the closed-circuit voltage CCV2 of the second battery module 14, respectively. Figure 5(C) shows the open-circuit voltage difference (OCV1-OCV2) between the open-circuit voltage OCV1 of the first battery module 12 and the open-circuit voltage OCV2 of the second battery module 14. Figure 5(D) shows the charging current I1 flowing through the first battery module 12 and the charging current I2 flowing through the second battery module 14, respectively. [Modes for carrying out the invention]

[0014] (Example 1) Referring to the drawings, the power supply unit 10 of the embodiment and the vehicle 100 in which it is employed will be described. The power supply unit 10 is a device that supplies power to multiple motors 102, 104, 106, and 108 of the vehicle 100. The power supply unit 10 in this embodiment is equipped with multiple battery modules 12 and 14 and is sometimes referred to as a battery pack. Each of the battery modules 12 and 14 is configured to be rechargeable. The vehicle 100 referred to here is an electric vehicle that travels on the road surface, and is a so-called electric vehicle (BEV: Battery Electric Vehicle). However, the vehicle 100 is not limited to electric vehicles, and may be a hybrid vehicle (HEV: Hybrid Electric Vehicle), a plug-in hybrid vehicle (PHEV: Plug-in Hybrid Electric Vehicle), or a fuel cell vehicle (FCEV: Fuel Cell Electric Vehicle). Also, the motors 102, 104, 106, and 108 in this embodiment are examples of loads mounted on the vehicle 100.

[0015] As shown in Figure 1, the vehicle 100 comprises multiple motors 102, 104, 106, and 108, and multiple inverters 110, 112, 114, and 116. Each of the motors 102, 104, 106, and 108 is a drive motor that drives the wheels of the vehicle 100. The multiple motors 102, 104, 106, and 108 include a first motor 102, a second motor 104, a third motor 106, and a fourth motor 108. The first motor 102 drives the right front wheel, the second motor 104 drives the left front wheel, the third motor 106 drives the right rear wheel, and the fourth motor 108 drives the left rear wheel. Each of the inverters 110, 112, 114, and 116 is a device that performs DC-AC power conversion between the power supply unit 10 and the corresponding motors 102, 104, 106, and 108. The multiple inverters 110, 112, 114, and 116 include the first inverter 110, the second inverter 112, the third inverter 114, and the fourth inverter 116. The first inverter 110 is installed between the power supply unit 10 and the first motor 102, and can convert DC power from the power supply unit 10 into three-phase AC power and supply it to the first motor 102. The first inverter 110 can also convert three-phase AC power from the first motor 102 into DC power and supply it to the power supply unit 10. The configurations of the second inverter 112, the third inverter 114, and the fourth inverter 116 are the same as those of the first inverter 110, so their explanation is omitted. While not particularly limited, if the rated voltage of the power supply unit 10 and the rated voltages of each motor 102, 104, 106, and 108 are different, a DC-DC converter may be further provided between the power supply unit 10 and each inverter 110, 112, 114, and 116.

[0016] Furthermore, each motor 102, 104, 106, and 108 does not necessarily have to drive only one wheel. For example, one motor may drive a pair of front or rear wheels. Therefore, the number of motors 102, 104, 106, and 108 in vehicle 100 is not limited to four, but can be one or more. Also, the number of inverters 110, 112, 114, and 116 can be appropriately changed depending on the number and arrangement of the motors 102, 104, 106, and 108.

[0017] As shown in Figure 1, the vehicle 100 further includes a charging inlet 118. The charging inlet 118 is configured to allow the connection of an external power supply. For example, when charging the battery modules 12 and 14 of the power supply unit 10 mounted on the vehicle 100, the external power supply and the charging inlet 118 of the vehicle 100 are connected via a power supply connector. This supplies AC power from the external power supply to the battery modules 12 and 14. In this way, the vehicle 100 can charge the battery modules 12 and 14 using an external power supply. As an example, the external power supply is a power source that supplies AC power, such as a household commercial power supply or a charging station. Although not particularly limited, the charging inlet 118 is connected to the power supply unit 10 via charging relays 120 and 122.

[0018] As mentioned above, the power supply unit 10 comprises a first battery module 12 and a second battery module 14. Each battery module 12 and 14 has multiple battery cells arranged in a stacked configuration. Each battery cell is a rechargeable secondary battery cell, such as a lithium-ion battery cell, a solid-state battery cell, or a nickel-metal hydride battery cell. The specific number of battery cells is not particularly limited and can be changed as appropriate according to the output voltage required for each battery module 12 and 14. Furthermore, the power supply unit 10 does not necessarily have to have two battery modules; it may have three or more.

[0019] As shown in Figure 1, the power supply unit 10 further comprises a connection circuit 16 and a control device 18. The connection circuit 16 comprises a plurality of relays 20, 22, 24, 26, 28, 30, 32, 34, and 36. The control device 18 controls the opening and closing of the plurality of relays 20-36.

[0020] The plurality of relays 20 - 38 includes a first relay 20, a second relay 22, and a third relay 24. These relays 20, 22, 24, together with a first pre - charge resistor 38, constitute a first system main relay 40. The third relay 24 and the first pre - charge resistor 38 are connected in series, and they are connected in parallel to the second relay 22. Thus, the first system main relay 40 is provided with a first pre - charge resistor 38 to avoid excessive inrush current. The first system main relay 40 is interposed between the battery modules 12, 14 and the first motor 102, and can electrically connect and disconnect the battery modules 12, 14 and the first motor 102. Also, the first system main relay 40 is interposed between the battery modules 12, 14 and the second motor 104, and can electrically connect and disconnect the battery modules 12, 14 and the second motor 104. In addition, when the first system main relay 40 electrically connects the battery modules 12, 14 and the motors 102, 104, it can avoid excessive inrush current by interposing the pre - charge resistor 38 therebetween.

[0021] The relays 20-36 further include a fourth relay 26, a fifth relay 28, and a sixth relay 30. These relays 26, 28, and 30, together with a second precharge resistor 42, constitute a second system main relay 44. The second precharge resistor 42 is a variable resistor. The resistance value of the second precharge resistor 42 is controlled by a control device 18. The sixth relay 30 and the second precharge resistor 42 are connected in series, and they are connected in parallel to the fifth relay 28. That is, the second system main relay 44, like the first system main relay 40, is also provided with a second precharge resistor 42 to avoid excessive inrush current. The second system main relay 44 is interposed between the battery modules 12 and 14 and the third motor 106, and can electrically connect and disconnect the battery modules 12 and 14 and the third motor 106. Furthermore, the second system main relay 44 is also interposed between the battery modules 12 and 14 and the fourth motor 108, allowing for the electrical connection and disconnection of the battery modules 12 and 14 and the fourth motor 108. In addition, when the second system main relay 44 electrically connects the battery modules 12 and 14 to the motors 106 and 108, it interposes the second precharge resistor 42 between them, thereby preventing excessive inrush current.

[0022] The plurality of relays 20 - 36 further includes a seventh relay 32, an eighth relay 34, and a ninth relay 36. These relays 32, 34, 36 are provided to switch the connection mode between the first battery module 12 and the second battery module 14. That is, the control device 18 is configured to selectively form a series circuit shown in FIG. 2 and a parallel circuit shown in FIG. 3 in the connection circuit 16 by controlling the opening and closing of the plurality of relays 20 - 36. Specifically, when the control device 18 closes the relays 20, 22, 26, 30, 32 and opens the other relays, the connection circuit 16 forms the series circuit shown in FIG. 2. In this series circuit, the first battery module 12 and the second battery module 14 are connected in series. Further, the first battery module 12 and the second battery module 14 connected in series are electrically connected to four inverters 110, 112, 114, 116 and four motors 102, 104, 106, 108.

[0023] On the other hand, when the control device 18 closes the relays 26, 30, 34, 36 and opens the other relays, the connection circuit 16 forms the parallel circuit shown in FIG. 3. In this parallel circuit, the first battery module 12 and the second battery module 14 are connected in parallel. Further, the first battery module 12 and the second battery module 14 connected in parallel are electrically connected to a charging inlet 118 via charging relays 120, 122. Thereby, when an external power source is connected to the charging inlet 118 via a power supply connector, the two battery modules 12, 14 can be charged by the external power source. Further, in the parallel circuit shown in FIG. 3, a second pre - charge resistor 42 is interposed between the first battery module 12 and the second battery module 14 connected in parallel. As described above, the second pre - charge resistor 42 is a variable resistor, and the resistance value of the second pre - charge resistor 42 is controlled by the control device 18.

[0024] The control device 18 monitors the State of Charge (SOC) of the first battery module 12 and the State of Charge (SOC) of the second battery module 14, respectively. The method of monitoring is not particularly limited. For example, the control device 18 can calculate the State of Charge of the first battery module 12 by integrating the charging current and discharging current of the first battery module 12 over time. The same applies to the second battery module 14. Based on the State of Charge of the first battery module 12, the control device 18 estimates the open-circuit voltage of the first battery module 12, and based on the State of Charge of the second battery module 14, it estimates the open-circuit voltage of the second battery module 14. Then, using these two open-circuit voltages, the control device 18 estimates the open-circuit voltage difference between the first battery module 12 and the second battery module 14, and the circulating current flowing between the first battery module 12 and the second battery module 14 in a parallel circuit (see Figure 3). Since the total resistance of the parallel circuit (i.e., the internal resistances of battery modules 12 and 14, the resistance of the second pre-charge resistor 42, and the resistances of other circuit components) are known, the circulating current can be determined by dividing the open-circuit voltage difference by these resistances.

[0025] With the above configuration, when the vehicle 100 is running, the power supply unit 10 is electrically connected to the motors 102, 104, 106, and 108. In this case, the control device 18 causes the connection circuit 16 to form a series circuit as shown in Figure 2. As a result, the first battery module 12 and the second battery module 14 are connected in series to the multiple motors 102, 104, 106, and 108. This allows the power supply unit 10 to supply power to the multiple motors 102, 104, 106, and 108 at a relatively high voltage. On the other hand, when the power supply unit 10 is charged by an external power source, the power supply unit 10 is electrically connected to the charging inlet 118. In this case, the control device 18 causes the connection circuit 16 to form a parallel circuit as shown in Figure 3. As a result, the first battery module 12 and the second battery module 14 are connected in parallel to the charging inlet 118. This allows the power supply unit 10 to be charged at a relatively low charging voltage, and the output voltage required from the external power source can be reduced.

[0026] Next, the resistance adjustment process performed by the control device 18 will be described with reference to Figures 4 and 5. In this resistance adjustment process, the resistance value RV of the second pre-charge resistor 42 is adjusted. The control device 18 repeatedly performs the resistance adjustment process while the first battery module 12 and the second battery module 14 are charging. Prior to the resistance adjustment process shown in Figure 4, the control device 18 controls the opening and closing of multiple relays 20-36 at the start of charging of the first battery module 12 and the second battery module 14, thereby forming the parallel circuit shown in Figure 3 in the connection circuit 16. In this parallel circuit, the first battery module 12 and the second battery module 14 are connected in parallel, with the second pre-charge resistor 42 interposed between them.

[0027] As shown in Figure 4, the control device 18 determines whether the difference between the charge level SOC1 of the first battery module 12 and the charge level SOC2 of the second battery module 14 (|SOC1-SOC2|) is greater than a predetermined charge level difference dSOC (step S10). As mentioned above, the control device 18 monitors the charge level SOC1 of the first battery module 12 and the charge level SOC2 of the second battery module 14, respectively. If the result in step S10 is YES, the control device 18 sets the resistance value RV of the second pre-charge resistor 42 to the initial resistance value RV0 (step S12). The initial resistance value RV0 here is zero, although it is not particularly limited. On the other hand, if the result in step S10 is NO, the control device 18 terminates the resistance adjustment process shown in Figure 4.

[0028] Next, the control device 18 calculates the circulating current (|I|) that may occur between the first battery module 12 and the second battery module 14 (step S14). The circulating current that may occur between the first battery module 12 and the second battery module 14 refers to the circulating current that may occur due to the open-circuit voltage difference between the two battery modules 12 and 14 if charging were to be completed at that point (more specifically, if the supply of charging current were to be stopped). Based on the charge level SOC1 of the first battery module 12, the control device 18 estimates the open-circuit voltage OCV1 of the first battery module 12, and based on the charge level SOC2 of the second battery module 14, it estimates the open-circuit voltage OCV2 of the second battery module 14. Here, the resistance value R1 of the first battery module 12, the resistance value R2 of the second battery module 14, the resistance value RV of the second pre-charge resistor 42, and the resistance values ​​RT of other circuit components are known, and the sum of these values ​​is the total resistance value of the parallel circuit. Therefore, the control device 18 can determine the circulating current (|I|) that may occur between the first battery module 12 and the second battery module 14 by dividing the open-circuit voltage difference (|OCV1-OCV2|), which is the difference between the open-circuit voltage OCV1 of the first battery module 12 and the open-circuit voltage OCV2 of the second battery module 14, by the total resistance value of the parallel circuit (R1+R2+RV+RT).

[0029] The control device 18 then determines whether the first correction voltage of the first battery module 12 and the second correction voltage of the second battery module 14 are within a predetermined allowable range (step S16). The first correction voltage of the first battery module 12 is calculated by correcting the open-circuit voltage OCV1 of the first battery module 12 with the voltage change due to the circulating current. Similarly, the second correction voltage of the second battery module 14 is calculated by correcting the open-circuit voltage OCV2 of the second battery module 14 with the voltage change due to the circulating current.

[0030] For example, when charging is stopped, if the open-circuit voltage OCV1 of the first battery module 12 is higher than the open-circuit voltage OCV2 of the second battery module 14, a circulating current may be generated from the first battery module 12 towards the second battery module 14. Therefore, the first correction voltage of the first battery module 12 is calculated by subtracting the voltage change, which is the product of the resistance value R1 of the first battery module 12 and the circulating current (|I|), from the open-circuit voltage OCV1 of the first battery module 12. The second correction voltage of the second battery module 14 is calculated by adding the voltage change, which is the product of the resistance value R2 of the second battery module 14 and the circulating current (|I|), to the open-circuit voltage OCV2 of the second battery module 14. These correction voltages are essentially equivalent to the closed-circuit voltages (CCV1 and CCV2 in Figure 5).

[0031] If the first correction voltage of the first battery module 12 and the second correction voltage of the second battery module 14 are greater than a predetermined allowable lower limit Vmin and less than a predetermined allowable upper limit Vmax, the control device 18 determines YES in step S16 and proceeds to the process in step S20. On the other hand, if the result in step S16 is NO, the control device 18 increases the resistance value RV of the second precharge resistor 42 from the initial resistance value RV0 by a predetermined resistance value dRV (step S18) and returns to the process in step S14. Thus, the processes from step S14 to step S18 are repeated until YES is determined in step S16, and the resistance value RV of the second precharge resistor 42 increases. In this way, the resistance value RV of the second precharge resistor 42 is adjusted so that the first correction voltage and the second correction voltage are within a predetermined allowable range.

[0032] Next, the control device 18 calculates the amount of heat W that may be generated in the second pre-charge resistor 42 (step S20). This amount of heat W is calculated by multiplying the open-circuit voltage difference (|OCV1-OCV2|) between the two battery modules 12 and 14 by the circulating current (|I|) calculated in step S14. If the amount of heat W that may be generated in the second pre-charge resistor 42 is less than a predetermined allowable value Wmax (YES in step S22), the control device 18 terminates the resistance adjustment process shown in Figure 4. On the other hand, if the result in step S22 is NO, similar to the case in step S16 where NO is obtained, the control device 18 increases the resistance value RV of the second pre-charge resistor 42 from the initial resistance value RV0 by a predetermined resistance value dRV (step S18) and returns to the process in step S14. Therefore, the resistance value RV of the second pre-charge resistor 42 continues to increase until it is determined to be YES in both step S16 and step S22. In this way, the resistance value RV of the second precharge resistor 42 is adjusted so that the amount of heat W that may be generated in the second precharge resistor 42 is less than a predetermined allowable value Wmax. The predetermined allowable value Wmax here is, for example, a value that can withstand energization for an unlimited time when the amount of heat generated in the second precharge resistor 42 is less than that value.

[0033] When charging of the first battery module 12 and the second battery module 14 is complete, the control device 18 sets the resistance value RV of the second precharge resistor 42 to approximately its maximum value and then executes a process involving the opening and closing of multiple relays 20-36. Here, "approximately maximum value" means the maximum value to which the resistance value RV of the second precharge resistor 42 can be set, or a value of 70% or more of that maximum value. The process involving the opening and closing of multiple relays 20-36 includes, for example, the process of forming the series circuit shown in Figure 2 in the connection circuit 16, and the process of opening the second system main relay 44, etc., in order to power down the power supply device 10.

[0034] In the above configuration, the resistance adjustment process shown in Figure 4 is repeatedly performed while the first battery module 12 and the second battery module 14 are charging, thereby adjusting the resistance value RV of the second pre-charge resistor 42 as shown in Figure 5(A). In the resistance adjustment process, the open-circuit voltages OCV1, OCV2 and closed-circuit voltages CCV1, CCV2 of each battery module 12 and 14 are estimated or calculated based on the respective charge levels SOC1 and SOC2 of the first battery module 12 and the second battery module 14, as shown in Figure 5(B). As a result, the open-circuit voltage difference (OCV1-OCV2) between the battery modules 12 and 14 is monitored, as shown in Figure 5(C). If an open-circuit voltage difference (OCV1-OCV2) exists between the battery modules 12 and 14, and charging is terminated at that point (more specifically, the supply of charging current is stopped), a circulating current I will be generated between the battery modules 12 and 14, causing heat to be generated in the second pre-charge resistor 42. Therefore, in the resistance adjustment process, the circulating current I that may occur between the battery modules 12 and 14 is calculated based on the open-circuit voltage difference (OCV1-OCV2), and the amount of heat W that may occur in the second pre-charge resistor 42 is also calculated. Then, the resistance value RV of the second pre-charge resistor 42 is adjusted so that the amount of heat W in the second pre-charge resistor 42 falls below a predetermined allowable value Wmax.

[0035] That is, as shown in Figure 5(C), at time t0 when charging of the two battery modules 12 and 14 begins, the open-circuit voltage difference (OCV1-OCV2) between the open-circuit voltage OCV1 of the first battery module 12 and the open-circuit voltage OCV2 of the second battery module 14 is relatively large. In contrast, the resistance value of the second pre-charge resistor 42 is adjusted to increase once after charging begins, and then decrease, as shown in Figure 5(A). Therefore, as shown in Figure 5(D), after charging begins, the charging current I2 flowing through the second battery module 14 is larger than the charging current I1 flowing through the first battery module 12, which is connected in series with the second pre-charge resistor 42. When the open-circuit voltage difference between the two battery modules 12 and 14 is eliminated by the difference between these charging currents I1 and I2, the resistance value of the second pre-charge resistor 42 is set to a small value (for example, a resistance value close to zero), and the charging current I2 flowing through the first battery module 12 and the charging current I2 flowing through the second battery module 14 become approximately equal. As described above, the generation of an open-circuit voltage difference between the two battery modules 12 and 14 is suppressed during charging. This prevents the prohibition of processes involving the opening and closing of relays 20-36 after charging is complete.

[0036] As an example, in the control device 18 of Embodiment 1, as shown in Figure 4, the resistance value RV of the second precharge resistor 42 is adjusted in the resistance adjustment process so that the first correction voltage and the second correction voltage are within a predetermined allowable range (i.e., greater than a predetermined allowable lower limit Vmin and less than a predetermined allowable upper limit Vmax). With this configuration, the open-circuit voltage difference (OCV1-OCV2) between the two battery modules 12 and 14 is suppressed so that the circulating current I that may occur between the two battery modules 12 and 14 is within an allowable range for each battery module 12 and 14.

[0037] In Embodiment 1, the control device 18 estimates the open-circuit voltage OCV1 of the first battery module 12 based on the charge level SOC1 of the first battery module 12, and estimates the open-circuit voltage OCV2 of the second battery module 14 based on the charge level SOC1 of the second battery module 14. In other embodiments, the control device 18 may directly detect the open-circuit voltages OCV1 and OCV2 of each battery module 12 and 14 using a voltage sensor.

[0038] As an example, in Embodiment 1, the control device 18 sets the resistance value RV of the second pre-charge resistor 42 to approximately its maximum value when charging of the first battery module 12 and the second battery module 14 is complete, and then executes a process involving the opening and closing of multiple relays 20-36. With this configuration, even if an open-circuit voltage difference (OCV1-OCV2) occurs between the two battery modules 12 and 14 when charging is complete, the circulating current I flowing between the battery modules 12 and 14 is greatly reduced by setting the resistance value RV of the second pre-charge resistor 42 to approximately its maximum value. As a result, the control device 18 can quickly execute a process involving the opening and closing of relays 20-36 without waiting for the open-circuit voltage difference (OCV1-OCV2) to be resolved after charging is complete.

[0039] (Example 2) Next, the power supply unit of Example 2 will be described. Compared with the power supply unit 10 of Example 1, the power supply unit of Example 2 is characterized in that the control device 18 performs the following series of processes instead of the resistance adjustment process shown in Figure 4.

[0040] In Embodiment 2, the control device 18 controls a plurality of relays 20-36 to form a parallel circuit as shown in Figure 3 in the connection circuit 16 when charging of the first battery module 12 and the second battery module 14 begins. This allows the two battery modules 12 and 14 to be charged while connected in parallel. When charging of the first battery module 12 and the second battery module 14 is completed, the control device 18 sets the resistance value of the second precharge resistor 42 to approximately its maximum value. Here, "approximately maximum value" means the maximum value to which the resistance value RV of the second precharge resistor 42 can be set, or a value of 70% or more of that maximum value. After setting the resistance value of the second precharge resistor 42 to approximately its maximum value, the control device 18 controls a plurality of relays 20-36 to form a series circuit as shown in Figure 2 in the connection circuit 16.

[0041] In the configuration described above, the second pre-charge resistor 42 is interposed between the two battery modules 12 and 14 connected in parallel in the parallel circuit shown in Figure 3. Therefore, even if an open-circuit voltage difference occurs between the two battery modules 12 and 14 at the end of charging, the resistance value of the second pre-charge resistor 42 is set to approximately its maximum value, which significantly reduces the circulating current flowing between the battery modules 12 and 14. For example, depending on the type of battery modules 12 and 14 and the level of charge of the battery modules 12 and 14, the accuracy of the estimated open-circuit voltage for the battery modules 12 and 14 may be low. Even in such cases, the power supply device of Embodiment 2 can connect the two battery modules 12 and 14 in series without waiting for the open-circuit voltage difference to be eliminated after charging is complete. Furthermore, since the resistance value of the second pre-charge resistor 42 can be set to zero while the battery modules 12 and 14 are charging, the charging power supplied from an external power source can be used as charging power for the battery modules 12 and 14 without being consumed by the second pre-charge resistor 42.

[0042] Although several specific examples have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or in the drawings exhibit technical usefulness individually or in combination. [Explanation of symbols]

[0043] 10: Power supply unit, 12: First battery module, 14: Second battery module, 16: Connection circuit, 18: Control device, 20-36: Relays, 38: First pre-charge resistor, 40: First system main relay, 42: Second pre-charge resistor, 44: Second system main relay, 100: Vehicle, 102-108: Motor, 110-116: Inverter, 118: Charging inlet, 120, 112: Charging relay

Claims

1. A first battery module and a second battery module that can be charged by an external power source, A connection circuit having multiple relays, which forms a parallel circuit that connects the first battery module and the second battery module in parallel when the first battery module and the second battery module are being charged, A variable resistor is provided in the aforementioned connection circuit and is interposed between the first battery module and the second battery module, which are connected in parallel. A control device capable of performing a resistance adjustment process to adjust the resistance value of the variable resistor when charging the first battery module and the second battery module, Equipped with, The aforementioned resistance adjustment process is, A process for calculating a circulating current that may occur between the first and second battery modules based on the open-circuit voltage difference, which is the difference between the open-circuit voltage of the first battery module and the open-circuit voltage of the second battery module, A process to calculate the amount of heat that may be generated in the variable resistor by multiplying the open-circuit voltage difference by the calculated circulating current, The process includes adjusting the resistance value of the variable resistor so that the calculated heat generation falls below a predetermined allowable value. power supply.

2. The aforementioned resistance adjustment process is, A process for calculating a first corrected voltage by correcting the open-circuit voltage of the first battery module with the voltage change caused by the circulating current, A process for calculating a second corrected voltage by correcting the open-circuit voltage of the second battery module with the voltage change caused by the circulating current, The power supply device according to claim 1, further comprising the process of adjusting the resistance value of the variable resistor so that the first correction voltage and the second correction voltage are within a predetermined allowable range.

3. The aforementioned resistance adjustment process is, A process for estimating the open-circuit voltage of the first battery module based on the charge level of the first battery module, The power supply device according to claim 1, further comprising a process for estimating the open-circuit voltage of the second battery module based on the charge level of the second battery module.

4. The power supply device according to any one of claims 1 to 3, wherein the control device sets the resistance value of the variable resistor to approximately its maximum value when charging of the first battery module and the second battery module is completed, and then performs a process involving opening and closing the plurality of relays.

5. A first battery module and a second battery module that can be charged by an external power source, A connection circuit having multiple relays, which selectively forms a parallel circuit connecting the first battery module and the second battery module in parallel, and a series circuit connecting the first battery module and the second battery module in series, A variable resistor is provided in the aforementioned connection circuit and is interposed between the first battery module and the second battery module, which are connected in parallel. A control device that controls the opening and closing of the plurality of relays and adjusts the resistance value of the variable resistor, Equipped with, The control device is The process involves controlling the plurality of relays to form the parallel circuit in the connection circuit when charging of the first battery module and the second battery module begins, The process of setting the resistance value of the variable resistor to approximately its maximum value when the charging of the first battery module and the second battery module is complete, The system is configured to perform the following steps: setting the resistance value of the variable resistor to the approximate maximum value, and then controlling the plurality of relays to form the series circuit in the connection circuit. power supply.

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