Power supply system

Abstract

To improve voltage conversion efficiency of a power supply system.SOLUTION: A power supply system comprises: a high-voltage battery; a low-voltage battery with nominal voltage lower than that of the high-voltage battery, which is electrically connected with a load; a first converter which is electrically connected between the high-voltage battery and the low-voltage battery to perform voltage conversion between the high-voltage battery and the low-voltage battery; a second converter which is electrically connected between the high-voltage battery and the low-voltage battery to perform the voltage conversion between the high-voltage battery and the low-voltage battery, and with rated power smaller than that of the first converter; and a control device which controls operations of the first converter and the second converter. The control device can selectively execute a plurality of operation modes according to the total value of output currents of the first converter and the second converter.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 describes a power supply system. This power supply system includes a battery that supplies power to a load, a first converter that converts voltage between the load and the battery, a second converter that converts voltage between the load and the battery and has a lower rated power than the first converter, and a control device that controls the operation of the first converter and the second converter. The control device is configured to operate either or both of the first converter and the second converter depending on the magnitude of the output current to the load. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-117454 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above power supply system, the first converter is used when the output current to the load is in a first range, and the second converter is used when the output current to the load is in a second range that is smaller than the first range. This improves voltage conversion efficiency. However, in the intermediate region between the first and second ranges, a decrease in voltage conversion efficiency cannot be avoided regardless of whether the first or second converter is used.

[0005] In view of the above, the present specification provides techniques for improving voltage conversion efficiency in a power supply system. [Means for solving the problem]

[0006] The technology disclosed in this specification is embodied in a power supply system that supplies power to a load. The power supply system includes a high-voltage battery, a low-voltage battery having a lower nominal voltage than the high-voltage battery and electrically connected to the load, a first converter electrically connected between the high-voltage battery and the low-voltage battery and converting voltage between the high-voltage battery and the low-voltage battery, a second converter electrically connected between the high-voltage battery and the low-voltage battery and converting voltage between the high-voltage battery and the low-voltage battery and having a lower rated power than the first converter, and a control device that controls operation of the first converter and the second converter. The control device is capable of selectively executing a plurality of operating modes depending on the total value of the output currents of the first converter and the second converter. The plurality of operating modes include a first operating mode that can be selected when the total value of the output current is within a first current range, and in which only the first converter supplies power; a second operating mode that can be selected when the total value of the output current is within a second current range that is smaller than the first current range, and in which only the second converter supplies power; and a third operating mode that can be selected when the total value of the output current is within a third current range that is located between the first current range and the second current range, and in which neither the first converter nor the second converter supplies power.

[0007] In the first operating mode, the operation of the second converter may be stopped so that only the first converter supplies power. Alternatively, the output voltage of the second converter may be set to a value lower than the output voltage of the first converter, thereby substantially stopping the power supply by the second converter. Similarly, in the second operating mode, the operation of the first converter may be stopped so that only the second converter supplies power. Alternatively, the output voltage of the first converter may be set to a value lower than the output voltage of the second converter, thereby substantially stopping the power supply by the first converter.

[0008] In the above configuration, when the total output current is in a relatively high range (first current value range), power is supplied from the first converter with a high rated power, and when the total output current is in a relatively low range (second current value range), power is supplied from the second converter with a low rated power. This increases the voltage conversion efficiency of the power supply system. When the total output current is in an intermediate range (third current value range), the voltage conversion efficiency of both the first and second converters decreases. Therefore, power is not supplied from the first and second converters, and power is supplied to the load from the low-voltage battery. This prevents a decrease in voltage conversion efficiency even when the total output current is in the intermediate range (third current value range).

[0009] In one embodiment of the present technology, the control device may be configured to prohibit execution of the third operating mode when the degradation index of the low-voltage battery is within a predetermined degradation range, regardless of the total value of the output current. With this configuration, even when the total value of the output current is within the third current range, at least one of the first converter and the second converter does not stop operating, and power is supplied from the high-voltage battery to the load. As a result, when degradation of the low-voltage battery is progressing, discharge of the low-voltage battery is prohibited or suppressed, thereby suppressing further degradation of the low-voltage battery.

[0010] In one embodiment of the present technology, the plurality of operating modes may further include a fourth operating mode and a fifth operating mode. The fourth operating mode is selectable when the total output current is within a third current range, and is an operating mode in which only the first converter supplies power intermittently. The fifth operating mode is selectable when the total output current is within the third current range, and is an operating mode in which the second converter supplies power and the first converter supplies power intermittently. In this case, when a degradation indicator of the low-voltage battery is within a predetermined degradation range, the control device may execute either the fourth operating mode or the fifth operating mode depending on the degradation level indicated by the degradation indicator.

[0011] According to the above configuration, the fourth operating mode is selected when the degree of degradation of the low-voltage battery is relatively small. In the fourth operating mode, the first converter intermittently supplies power, allowing the first converter to operate at an operating point with high voltage conversion efficiency even when the total output current is in the intermediate region (third current value range). At this time, the low-voltage battery is complementarily discharged in response to the intermittent power supply from the first converter, thereby supplying the required current to the load. On the other hand, in the fifth operating mode, power supply from the second converter is added compared to the fourth operating mode. The discharge current of the low-voltage battery is reduced by the amount of the current output by the second converter, thereby suppressing further degradation of the low-voltage battery.

[0012] In one embodiment of the present technology, a power supply system may include a high-voltage battery, a low-voltage battery having a lower nominal voltage than the high-voltage battery and electrically connected to a load, a first converter electrically connected between the high-voltage battery and the low-voltage battery and converting voltage between the high-voltage battery and the low-voltage battery, a second converter electrically connected between the high-voltage battery and the low-voltage battery and converting voltage between the high-voltage battery and the low-voltage battery and having a lower rated power than the first converter, and a control device controlling operation of the first converter and the second converter. The control device is capable of selectively executing a plurality of operation modes depending on a total value of output currents of the first converter and the second converter. The plurality of operation modes may include a sixth operation mode selectable when the total value of the output currents is within a fourth current range and in which power is not supplied from the first converter and the second converter.

[0013] According to the above configuration, when the total output current is in a very low range (fourth current range), the voltage conversion efficiency is low even when the second converter with a low rated power is used. In such a situation, power supply from the first converter and the second converter is stopped, so that power can be supplied to the load from the low-voltage battery. This makes it possible to avoid a decrease in voltage conversion efficiency even when the total output current is in a very low range (fourth current range).

[0014] In one embodiment of the present technology, the control device may be capable of executing a degradation determination process that calculates one or more of an internal resistance of a low-voltage battery or a capacity of the low-voltage battery as a degradation indicator of the low-voltage battery. In this case, when executing the degradation determination process while executing the first operation mode, the control device may further operate the second converter to supply a charge current or a discharge current to the low-voltage battery. Alternatively, when executing the degradation determination process while executing the second operation mode, the control device may further operate the first converter to supply a charge current or a discharge current to the low-voltage battery.

[0015] When calculating the internal resistance of the low-voltage battery, if the current flowing through the low-voltage battery fluctuates, the internal resistance may not be calculated correctly. Similar concerns exist regarding the capacity of the low-voltage battery. In this regard, the above-described configuration allows for the additional operation of the unused converter between the first and second converters, thereby enabling a stable current to flow through the low-voltage battery regardless of fluctuations in power consumption by the auxiliary equipment. This allows for accurate calculation of the internal resistance of the low-voltage battery, enabling more accurate determination of the degree of degradation of the low-voltage battery. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a block diagram showing the configuration of a power supply system 2 in the present embodiment. [Figure 2] 4 is a graph showing the relationship between the output current and the voltage conversion efficiency of the first converter 20 and the second converter 22 in this embodiment. [Figure 3] 3 is a flowchart showing a series of processes executed by a control device 30 in a power supply system 2 in the first embodiment. [Figure 4] 3 is a flowchart showing a series of processes in a low-voltage battery output mode executed by a control device 30 in a power supply system 2 in the first embodiment. [Figure 5]10 is a flowchart showing a series of processes executed by a control device 30 in a power supply system 2 according to a second embodiment. [Figure 6] 10 is a graph showing the output current of the low-voltage battery 12 and the operating states of the first converter 20 and the second converter 22 in a fourth operation mode and a fifth operation mode in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] (First Example) A power supply system 2 according to a first embodiment will be described with reference to the drawings. As an example, the power supply system 2 according to the first embodiment can be adopted in an electric vehicle (BEV: Battery Electric Vehicle). Furthermore, the configuration described in this embodiment is not limited to electric vehicles, but can also be adopted as a power source for other types of devices and equipment that use electricity as a power source.

[0018] As shown in FIG. 1, the power supply system 2 includes a high-voltage battery 10, a low-voltage battery 12, a first converter 20, a second converter 22, a control device 30, an electrical load 40, and current sensors 50A, 50B, and 50C. The high-voltage battery 10 is a high-voltage battery that supplies power to the electrical load 40. Note that the term "high voltage" here refers to a nominal voltage exceeding 60 V DC. The high-voltage battery 10 incorporates multiple secondary battery cells and is configured to be chargeable and dischargeable. The secondary battery cells are not particularly limited, but may be, for example, lithium-ion batteries or all-solid-state batteries. The low-voltage battery 12 is a battery with a lower nominal voltage than the high-voltage battery 10. The low-voltage battery 12 can supply power to the electrical load 40 in the same way as the high-voltage battery 10. The low-voltage battery 12 is not particularly limited, but may be, for example, a lead-acid battery.

[0019] The first converter 20 (hereinafter referred to as the first DDC 20) is electrically connected between the high-voltage battery 10 and the low-voltage battery 12. The first DDC 20 is configured to step down the output power from the high-voltage battery 10 between the high-voltage battery 10 and the low-voltage battery 12. Note that the specific configuration of the first DDC 20 is not particularly limited. As an example, the first DDC 20 may be a non-insulated converter using a switching element and a coil.

[0020] The second converter 22 (hereinafter referred to as the second DDC 22) is electrically connected between the high-voltage battery 10 and the low-voltage battery 12, similar to the first DDC 20. The second DDC 22 is configured to step down the output power from the high-voltage battery 10 between the high-voltage battery 10 and the low-voltage battery 12, similar to the first DDC 20. The second DDC 22 is configured to have a lower rated power than the first DDC 20. As shown in the graph of FIG. 2, the voltage conversion efficiency for each output current value is different. As shown in the graph of FIG. 2, the second DDC 22 has a higher voltage conversion efficiency than the first DDC 20 in the low output current value range (from Th0 to Th1), and the first DDC 20 has a higher voltage conversion efficiency than the second DDC 22 in the high output current value range (from Th1B to Th2).

[0021] The control device 30 controls the operation of the first DDC 20 and the second DDC 22. That is, by controlling the operation of the first DDC 20 and the second DDC 22, the control device 30 can adjust the voltage and current output by each of the first DDC 20 and the second DDC 22. Furthermore, since the first DDC 20 and the second DDC 22 in this embodiment have different rated powers, voltage conversion efficiency can be improved by switching the operation of each DDC according to the range of output current values ​​for which voltage conversion efficiency is high. The control device 30 is connected to the first DDC 20 and the second DDC 22 via signal lines. The control device 30 is also connected to current sensors 50A, 50B, and 50C via signal lines, and monitors the output current values ​​of the first DDC 20 and the second DDC 22 and the low-voltage battery 12, as well as the output voltage value from a voltage sensor (not shown) provided inside the low-voltage battery 12. The control device 30 in this embodiment includes a processor and a memory (not shown), and controls the operations of the first DDC 20 and the second DDC 22 by executing various programs stored in the memory with the processor.

[0022] The electric load 40 is a device that is driven by power supplied from the high-voltage battery 10 or the low-voltage battery 12. There are no particular limitations on the specific configuration of the electric load 40. As an example, the electric load 40 is a drive device for an electric vehicle, and may include an electric motor that drives the wheels and an inverter that controls the power supplied to the electric motor.

[0023] The current sensors 50A, 50B, and 50C are devices that detect the current values ​​output from the first DDC 20, the second DDC 22, and the low-voltage battery 12. The specific configurations of the current sensors 50A, 50B, and 50C are not particularly limited.

[0024] Referring to FIG. 3, a series of processes executed by the control device 30 in the power supply system 2 of the first embodiment will be described. The control device 30 is configured to start a series of processes shown in FIG. 2 when supplying power from the high-voltage battery 10 of the power supply system 2 to the electrical load 40. First, the power supply system 2 operates the first DDC 20 to start supplying power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S10). Then, the control device 30 determines whether the total value (IL) of the output currents of the first DDC 20 and the second DDC 22 is less than the first current value (Th1) (S12). If the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the first current value (IL < Th1) (S12: Yes), the control device 30 stops the operation of the first DDC 20, starts the operation of the second DDC 22, and starts supplying power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S20). On the other hand, if the total value of the output currents of the first DDC 20 and the second DDC 22 is greater than or equal to the first current value (IL ≧ Th1) (S12: No), the control device 30 determines whether the internal resistance value (Ri) of the low-voltage battery 12 is less than the first resistance value (Ra) (S14).

[0025] If the internal resistance value of the low-voltage battery 12 is greater than or equal to the first resistance value (Ri ≧ Ra) (S14: No), the control device 30 proceeds to the processes after step S18 described in the following paragraphs. If the internal resistance value of the low-voltage battery 12 is less than the first resistance value (Ri < Ra) (S14: Yes), the control device 30 determines whether the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the second current value (Th1B) (S16). Note that the second current value is greater than the first current value described in the above paragraph (i.e., Th1B > Th1). If the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the second current value (IL < Th1B) (S16: Yes), the control device 30 stops the operations of the first DDC 20 and the second DDC 22, and starts the low-voltage battery output mode in which power is output from the low-voltage battery 12 to supply power to the electrical load 40. Details of the low-voltage battery output mode will be described in the following paragraphs using FIG. 4.

[0026] On the other hand, when the total value of the output currents of the first DDC 20 and the second DDC 22 is equal to or greater than the second current value (IL ≥ Th1B) (S16: No), the control device 30 determines whether the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the third current value (Th2) (S18). Note that the third current value is greater than the third current value described in the above paragraph (i.e., Th2 > Th1B). When the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the third current value (IL < Th2) (S18: Yes), the control device 30 continues the operation of the first DDC 20 and continues to supply power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S40). When the total value of the output currents of the first DDC 20 and the second DDC 22 is equal to or greater than the third current value (IL ≥ Th2) (S18: No), the control device 30 operates both the first DDC 20 and the second DDC 22 and supplies power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S50). When the processes of respective steps S20, S30, S40, and S50 are started, the power supply system 2 ends a series of processing procedures shown in FIG. 3 (end). Further, after ending (end) the series of processing procedures shown in FIG. 3, the power supply system 2 may restart the series of processing procedures shown in FIG. 3 again from step S12.

[0027] Referring to FIG. 4, a series of processes when the control device 30 executes the low-voltage battery output mode in the power supply system 2 of the first embodiment will be described. When the low-voltage battery output mode is executed (S30), the control device 30 determines whether the output current value (IB) of the low-voltage battery 12 is greater than or equal to the first current value and less than or equal to the second current value based on the detection value sent from the current sensor 50C (S32). If the output current value of the low-voltage battery 12 is not greater than or equal to the first current value and less than or equal to the second current value (IB < Th1 or IB > Th1B) (S32: No), the control device 30 ends the series of processing procedures of the low-voltage battery output mode shown in FIG. 4 (End). On the other hand, if the output current value of the low-voltage battery 12 is greater than or equal to the first current value and less than or equal to the second current value (Th1 ≦ IB ≦ Th1B) (S32: Yes), the control device 30 determines whether the state of charge (SOC) of the low-voltage battery 12 is greater than or equal to the first state of charge (SOC1) (S34). If the state of charge of the low-voltage battery 12 is less than the first state of charge (SOC < SOC1) (S34: No), the control device 30 ends the series of processing procedures of the low-voltage battery output mode shown in FIG. 4 (End). If the state of charge of the low-voltage battery 12 is greater than or equal to the first state of charge (SOC ≧ SOC1) (S34: Yes), the control device 30 continues the low-voltage battery output mode (S36). Further, the control device 30 calculates the internal resistance value (Ri) of the low-voltage battery 12 based on the detected current value and voltage value from the current sensor 50C and the voltage sensor provided inside the low-voltage battery 12 (S38). Thereafter, the control device 30 returns to step S32 and repeatedly executes the series of processing procedures of the low-voltage battery output mode shown in FIG. 4 to supply power from the low-voltage battery 12 to the electrical load 40.

[0028] As shown in FIGS. 2, 3, and 4, in a series of processes executed by the control device 30 of the power supply system 2 in the first embodiment, when in a region where the total value of the output current is relatively high (Th1B≦IL<Th2), the first DDC 20 with a large rated power is used, and when in a region where the total value of the output current is relatively low (IL<Th1), the second DDC 22 with a small rated power is used. And when the total value of the output current is in the intermediate region (Th1≦IL<Th1B), since the voltage conversion efficiency of both the first DDC 20 and the second DDC 22 decreases, the operations of the first DDC 20 and the second DDC 22 are stopped, and a low-voltage battery output mode (S30) for supplying power from the low-voltage battery 12 to the load is executed. With such a configuration, the voltage conversion efficiency can be increased in a wide range of output current value regions in the power supply system 2. Also, when the deterioration index of the low-voltage battery 12 is within a predetermined deterioration range (Ri≧Ra), further deterioration of the low-voltage battery 12 can be suppressed by avoiding the execution of the low-voltage battery output mode (S30) regardless of the total value of the output current. As shown in FIG. 2, in the processing procedure of step S20, when the total value of the output current is equal to or less than a fourth current value (Th0) that is even smaller than the first current value (Th1), the second DDC 22 may not be used and the mode may be switched to the low-voltage battery output mode (S30). By adopting such a configuration, even when in a region where the total value of the output current is very low (IL≦Th0) such that the voltage conversion efficiency becomes low even when the second DDC is used, a decrease in the voltage conversion efficiency can be avoided.

[0029] (Second Embodiment) Referring to FIGS. 5 and 6, the power supply system of the second embodiment will be described. The power supply system of this embodiment has the content of the processing executed by the control device 30 changed as compared with the power supply system 2 of the first embodiment. That is, the control device 30 in this embodiment is configured to execute a series of processes shown in FIG. 5 instead of the series of processes shown in FIG. 3. In other respects, the power supply system of this embodiment has the same configuration as the power supply system 2 of the first embodiment shown in FIG. 1. That is, the power supply system of this embodiment also includes a high-voltage battery 10, a low-voltage battery 12, a first DDC 20, a second DDC 22, a control device 30, an electrical load 40, and current sensors 50A, 50B, and 50C (see FIG. 1). The configurations and functions of these are as described in the first embodiment, and redundant descriptions will be avoided here.

[0030] Also in the power supply system of this embodiment, the control device 30 is configured to start a series of processes shown in FIG. 5 when supplying power from the high-voltage battery 10 of the power supply system 2 to the electrical load 40. First, the power supply system operates the first DDC 20 to start supplying power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S100). After that, the control device 30 determines whether the total value (IL) of the output currents of the first DDC 20 and the second DDC 22 is less than the first current value (Th1) (S102). When the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the first current value (IL < Th1) (S102: Yes), the control device 30 stops the operation of the first DDC 20 and starts the operation of the second DDC 22 to start supplying power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S120).

[0031] On the other hand, when the total value of the output currents of the first DDC 20 and the second DDC 22 is greater than or equal to the first current value (IL≧Th1) (S102: No), the control device 30 determines whether the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the second current value (Th1B) (S104). Here, as described in the above-mentioned first embodiment, Th1B>Th1. When the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the second current value (IL<Th1B) (S104: Yes), the control device 30 determines whether the internal resistance value (Ri) of the low-voltage battery 12 is greater than or equal to the first resistance value (Ra) (S112). When the internal resistance value of the low-voltage battery 12 is greater than or equal to the first resistance value (Ri≧Ra) (S112: Yes), the control device 30 proceeds to the process of step S106 described in the following paragraph. When the internal resistance value of the low-voltage battery 12 is less than the first resistance value (Ri<Ra) (S112: No), the control device 30 determines whether the internal resistance value (Ri) of the low-voltage battery 12 is greater than or equal to the second resistance value (Rb) (S114). Note that the second resistance value is smaller than the first resistance value described in the above paragraph (i.e., Rb<Ra). When the internal resistance value (Ri) of the low-voltage battery 12 is greater than or equal to the second resistance value (Rb) (Ri≧Rb) (S114: Yes), the control device 30 operates the second DDC 22, intermittently operates the first DDC 20, and starts executing the small-output mode in which power is output from the low-voltage battery 12 at a value equal to or less than the eleventh current value (I1) (S150).

[0032] When the internal resistance value of the low-voltage battery 12 is less than the second resistance value (Ri < Rb) (S114: No), the control device 30 determines whether the internal resistance value (Ri) of the low-voltage battery 12 is greater than or equal to the third resistance value (Rc) (S116). Note that the third resistance value is smaller than the second resistance value described in the above paragraph (i.e., Rc < Rb). When the internal resistance value of the low-voltage battery 12 is greater than or equal to the third resistance value (Ri ≥ Rc) (S116: Yes), the control device 30 does not operate the second DDC 22, intermittently operates the first DDC 20, and starts executing the medium output mode in which power is output from the low-voltage battery 12 at a current value equal to or less than the twelfth current value (I2) (S160). As shown in FIG. 6, the twelfth current value (I2) is greater than the eleventh current value (I1) (i.e., I2 > I1). Also, when the internal resistance value of the low-voltage battery 12 is less than the third resistance value (Ri < RC) (S116: No), the control device 30 stops the operations of the first DDC 20 and the second DDC 22, similar to step S30 in the first embodiment, and starts the high output mode in which power is output from the low-voltage battery 12 at a current value equal to or greater than the twelfth current value to supply power to the electrical load 40 (S170).

[0033] On the other hand, when the total value of the output currents of the first DDC 20 and the second DDC 22 is greater than or equal to the second current value (IL > Th1B) (S104: No), the control device 30 determines whether the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the third current value (Th2) (S106). Here, as described in the first embodiment above, Th2 > Th1B. When the total value of the output currents of the first DDC 20 and the second DDC 22 is less than the third current value (IL < Th2) (S106: Yes), the control device 30 continues the operation of the first DDC 20 and continues to supply power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S130). Further, when the total value of the output currents of the first DDC 20 and the second DDC 22 is greater than or equal to the third current value (IL ≧ Th2) (S106: No), the control device 30 operates both the first DDC 20 and the second DDC 22 and supplies power to the electrical load 40 while voltage-converting the power output from the high-voltage battery 10 (S140). When the processes of steps S120, S130, S140, S150, S160, and S170 are started, the power supply system in the second embodiment ends a series of processing procedures shown in FIG. 5 (end). Further, after the power supply system in the second embodiment ends the series of processing procedures shown in FIG. 5 (end), the series of processing procedures shown in FIG. 5 may be started again from step S102.

[0034] According to the configuration of the second embodiment described above, the effect of improving the voltage conversion efficiency in the power supply system 2 described in the first embodiment can be further enhanced. That is, when the total value of the output current is in the output current region (Th1 ≦ IL < Th1B) where the voltage conversion efficiency of the first DDC 20 and the second DDC 22 is low, and the degree of deterioration of the low-voltage battery 12 is relatively small (Rc ≦ Ri < Rb), the medium output mode (S160) is selected. In the medium output mode, by operating the first DDC 20 intermittently, even when the total value of the output current is in the intermediate region (Th1 ≦ IL < Th1B), the first DDC 20 can be operated at an operating point with high voltage conversion efficiency. At this time, in response to the intermittent operation of the first DDC 20, the low-voltage battery 12 is discharged complementarily, so that the current required for the electrical load 40 is supplied. On the other hand, when the degree of deterioration of the low-voltage battery 12 is medium (Rb ≦ Ri < Ra), the low output mode (S150) is selected. In the low output mode, the second DDC 22 is operated while the first DDC 20 is operated intermittently. That is, compared with the medium output mode, in the low output mode, the second DDC 22 operates further. Since the discharge current of the low-voltage battery 12 decreases by the amount of the current output by the second DDC 22, further deterioration of the low-voltage battery 12 is suppressed. Note that the medium output mode (S160) and the low output mode (S150) described in the second embodiment correspond to the fourth operation mode and the fifth operation mode described in the above paragraph.

[0035] 6 shows graphs illustrating the change over time in the output current value of the low-voltage battery 12 and the operational states of the first DDC 20 and the second DDC 22 when the low power mode (S150) and the medium power mode (S160) are executed in the second embodiment. The graphs shown in (A) of FIG. 6 show the change over time in the output current value of the low-voltage battery 12 and the operational states of the first DDC 20 and the second DDC 22 when the medium power mode is executed in step S160 in the second embodiment. The graphs shown in (B) of FIG. 6 show the change over time in the output current value of the low-voltage battery 12 and the operational states of the first DDC 20 and the second DDC 22 when the low power mode is executed in step S150 in the second embodiment. Furthermore, when executing the small output mode (S150) and the medium output mode (S160) shown in Figure 5, as in the low-voltage battery output mode of the first embodiment shown in Figure 4, the output current value of the low-voltage battery 12 and the charging rate of the low-voltage battery 12 may be determined before determining whether or not to continue each output mode.

[0036] In steps S20, S40, S120, and S130 in the first and second embodiments, when a request for determining deterioration of the low-voltage battery 12 is received, the control device 30 may calculate the internal resistance value by repeatedly charging and discharging the low-voltage battery 12 using the DDC that is not operating during execution of each process. This improves the accuracy of the deterioration determination process for the low-voltage battery 12. Specifically, when the first DDC 20 is not operated and the second DDC 22 is operated to supply power to the electrical load 40, as in step S20 in the first embodiment or step S120 in the second embodiment, charging and discharging between the first DDC 20 and the low-voltage battery 12 may be repeated, and the internal resistance value may be calculated based on the output current value and output voltage value of the low-voltage battery 12 detected during the charging and discharging, and the deterioration determination process may be performed. Furthermore, when power is supplied to the electrical load 40 by operating the first DDC 20 without operating the second DDC 22, as in step S40 of the first embodiment or step S130 of the second embodiment, charging and discharging between the second DDC 22 and the low-voltage battery 12 may be repeated, and the internal resistance may be calculated based on the output current and output voltage values ​​of the low-voltage battery 12 detected during charging and discharging, and the deterioration determination process may be performed. In this way, by performing the deterioration determination process as described above in steps S20, S40, S120, and S130 of the first and second embodiments, by additionally operating unused DDCs, a stable current can be supplied to the low-voltage battery 12 regardless of fluctuations in power consumption by the electrical load 40. This allows the internal resistance of the low-voltage battery 12 to be correctly calculated, and the degree of deterioration of the low-voltage battery 12 to be more accurately determined.

[0037] Furthermore, in the first and second embodiments, the high-voltage battery 10 is configured by stacking multiple secondary battery cells, and the nominal voltage may be 400 volts or 600 volts. In other embodiments, the high-voltage battery 10 may be configured by connecting multiple batteries, each with a nominal voltage of 200 volts or 300 volts, in series. In this case, each battery connected in series may be connected in parallel to the first DDC 20 and the second DDC 22, respectively. With such a configuration, the amount of voltage drop in the power supplied from each battery can be reduced, further reducing power loss.

[0038] As a further embodiment of this embodiment, a power generation device such as a solar panel may be connected to the electrical load 40 of the power supply system. With this configuration, the power generated by the solar panel is boosted by the first DDC 20 or the second DDC 22, and the power is supplied to the high-voltage battery 10, thereby charging the high-voltage battery 10.

[0039] Although specific examples of the technology disclosed in this specification have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0040] 2: Power supply system, 10: High voltage battery, 12: Low voltage battery, 20: First converter, 22: Second converter, 30: Control device, 40: Electric load, 50A, 50B, 50C: Current sensors,

Claims

1. A power supply system for supplying power to a load, comprising: A high-voltage battery, a low-voltage battery having a nominal voltage lower than that of the high-voltage battery and electrically connected to the load; a first converter electrically connected between the high-voltage battery and the low-voltage battery, for converting voltage between the high-voltage battery and the low-voltage battery; a second converter electrically connected between the high-voltage battery and the low-voltage battery, converting voltage between the high-voltage battery and the low-voltage battery, and having a rated power lower than that of the first converter; a control device that controls operations of the first converter and the second converter; Equipped with the control device is capable of selectively executing a plurality of operation modes in accordance with a total value of output currents of the first converter and the second converter; The plurality of operation modes include: a first operating mode selectable when the sum of the output currents is within a first current range, in which only the first converter supplies power; a second operating mode selectable when the sum of the output currents is within a second current range smaller than the first current range, in which only the second converter supplies power; a third operating mode selectable when the sum of the output currents is within a third current range located between the first current range and the second current range, in which the first converter and the second converter do not supply power; Power supply system.

2. 2. The power supply system according to claim 1, wherein the control device is configured to prohibit execution of the third operating mode when a deterioration index of the low-voltage battery is within a predetermined deterioration range, regardless of the total value of the output current.

3. The plurality of operation modes include: a fourth operating mode selectable when the total output current is within the third current range, in which only the first converter supplies power intermittently; a fifth operating mode selectable when the sum of the output currents is within the third current range, in which the second converter supplies power and the first converter supplies power intermittently; When a deterioration index of the low-voltage battery is within the deterioration range, the control device executes either the fourth operation mode or the fifth operation mode depending on a deterioration level indicated by the deterioration index. The power supply system according to claim 2 .

4. A power supply system for supplying power to a load, comprising: A high-voltage battery, a low-voltage battery having a nominal voltage lower than that of the high-voltage battery and electrically connected to the load; a first converter electrically connected between the high-voltage battery and the low-voltage battery, for converting voltage between the high-voltage battery and the low-voltage battery; a second converter electrically connected between the high-voltage battery and the low-voltage battery, converting voltage between the high-voltage battery and the low-voltage battery, and having a rated power lower than that of the first converter; a control device that controls operations of the first converter and the second converter; Equipped with the control device is capable of selectively executing a plurality of operation modes in accordance with a total value of output currents of the first converter and the second converter; The plurality of operation modes include: a sixth operating mode selectable when the sum of the output currents is within a fourth current range, in which the first converter and the second converter do not supply power. Power supply system.

5. the control device is capable of executing a deterioration determination process that calculates at least one of an internal resistance of the low-voltage battery and a capacity of the low-voltage battery as a deterioration index of the low-voltage battery; When the control device executes the deterioration determination process while the first operation mode is being executed, the control device further operates the second converter to pass a charge current or a discharge current through the low-voltage battery; 5. The power supply system according to claim 1, wherein when the control device executes the deterioration determination process while the second operating mode is being executed, the control device further operates the first converter to pass a charging current or a discharging current through the low-voltage battery.

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