Power supply device

Abstract

To provide a power supply device that simply and stably suppresses a circulating current generated in a battery pack.SOLUTION: A power supply device 1 has: a first battery 11; a second battery 12 connected in parallel with the first battery 11 and having a higher degree of deterioration than the first battery 11; and a circulating current prevention unit 13 for preventing a current from being input to or output from the second battery 12 until the current input to or output from the first battery 11 is greater than an unusable current range set for the second battery 12. The circulating current prevention unit 13 has a charge / discharge control unit 21, a total current measurement unit 22, a branch current measurement unit 23, and a switch 24.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power supply device in which, for example, a plurality of batteries are connected in parallel.

Background Art

[0002] In recent years, there has been a technique of increasing the output power and storage capacity of a battery pack by combining a plurality of batteries in series and parallel to form a battery pack. In such a battery pack, when batteries with different degrees of deterioration are connected in parallel, a circulating current is generated between the parallel-connected batteries. The circulating current is a charge and discharge current flowing between the parallel-connected batteries. Therefore, techniques for preventing the generation of this circulating current are disclosed in Patent Documents 1 and 2.

[0003] In the power supply device described in Patent Document 1, a current detection circuit and a switch are connected in series to each battery module connected in parallel, and the output of the current detection circuit is calculated by a control circuit to control the switch. The control circuit switches off the switch connected to a battery module in which the direction of the flowing current becomes opposite to the normal direction or the current imbalance becomes larger than a set value to cut off the current.

[0004] The circulating current prevention device described in Patent Document 2 includes a current measurement unit that measures the current flowing into the secondary battery, a charging switching element, and a discharging switching element, and determines the direction of the current to perform control so as to exclusively conduct the charging and discharging switching elements.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when connecting batteries with significantly different degrees of degradation, such as new batteries and reused batteries, in parallel, there is a problem in controlling the on / off state of the switch connected in series with the batteries.

[0007] This invention has been made in view of the above circumstances, and aims to easily and stably suppress the circulating current generated in a battery pack. [Means for solving the problem]

[0008] One embodiment of the power supply device according to the present invention includes a first battery, a second battery connected in parallel with the first battery and having a higher degree of degradation than the first battery, and a circulating current prevention unit that prevents current from being input to and output to the second battery until the current input to and output to the first battery exceeds the unusable current range set for the second battery.

[0009] Another embodiment of the power supply device according to the present invention includes a first battery, a second battery connected in parallel with the first battery and having a higher degree of degradation than the first battery, a total current measuring unit for detecting the total current value of the currents input and output to the first battery and the second battery, a branch current measuring unit for measuring branch current values ​​which are the currents input and output to the second battery, a switch provided between the branch current measuring unit and the second battery, and a charge / discharge control unit that turns the switch into a conductive state when the total current value exceeds a preset unusable current range, and maintains the switch in a conductive state when the branch current value indicates the same direction of current flow as the total current value.

[0010] Another embodiment of the power supply device according to the present invention includes a first battery, a second battery connected in parallel with the first battery and having a higher degree of degradation than the first battery, a common wiring provided in common to the first battery and the second battery, a first diode whose cathode is connected to the second battery and whose anode is connected to the common wiring, and a second diode whose cathode is connected to the common wiring and whose anode is connected to the second battery. [Effects of the Invention]

[0011] According to the power supply device of the present invention, circulating current generated in a battery pack can be easily and stably suppressed. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram of the power supply device according to Embodiment 1. [Figure 2] This diagram illustrates the unusable current range of the power supply according to Embodiment 1. [Figure 3] This is a flowchart illustrating the operation of a power supply device including a circulating current prevention unit according to Embodiment 1. [Figure 4] This is a block diagram of the power supply device according to Embodiment 2. [Figure 5] This figure illustrates that in the power supply device according to Embodiment 2, no circulating current flows when no charge / discharge current is flowing. [Figure 6] This diagram illustrates the current flow in the power supply device according to Embodiment 2 when a charging current is being supplied. [Figure 7] This is a block diagram of the power supply device according to Embodiment 3. [Figure 8] This is a block diagram of the power supply device according to Embodiment 4. [Figure 9] This is a block diagram of the power supply device according to Embodiment 5. [Figure 10] This diagram illustrates the unusable current range of the power supply according to Embodiment 5. [Modes for carrying out the invention]

[0013] For clarity of explanation, the following descriptions and drawings have been omitted and simplified as appropriate. Furthermore, each element shown in the drawings as a functional block performing various processes can be composed of a CPU (Central Processing Unit), memory, and other circuits in hardware terms, and implemented in software terms by programs loaded into memory. Therefore, it will be understood by those skilled in the art that these functional blocks can be implemented in various ways using hardware alone, software alone, or a combination thereof, and are not limited to any one of these. In each drawing, the same elements are denoted by the same reference numeral, and redundant explanations have been omitted where necessary.

[0014] Furthermore, the program described above includes, when loaded into a computer, a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored in a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disc (DVD), Blu-ray® disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically, or otherwise propagating signals.

[0015] Embodiment 1 Fig. 1 shows a block diagram of the power supply device 1 according to Embodiment 1. As shown in Fig. 1, the power supply device 1 according to Embodiment 1 includes a first battery (for example, battery 11), a second battery (for example, battery 12), and a circulating current prevention unit 13. In Fig. 1, two batteries are shown as the batteries connected in parallel, but the number of parallel-connected batteries may be any number as long as it is 2 or more.

[0016] The batteries 11 and 12 are connected in parallel to a common power line Wc that transmits the charge / discharge current to the batteries 11 and 12. In the following description, the wiring branched from the common power line Wc and connected to the battery 11 is referred to as a branched power line Wb1, and the wiring branched from the common power line Wc and connected to the battery 12 is referred to as a branched power line Wb2. The battery 11 is a battery that has not deteriorated or has a small degree of deterioration. On the other hand, it is assumed that the battery 12 has the same degree of deterioration as the battery 11 or a higher degree of deterioration than the battery 11. Here, as the degree of deterioration of the battery progresses, the OCV (Open Circuit Voltage) of the battery becomes low and the internal resistance becomes high.

[0017] The circulating current prevention unit 13 prevents current from being input to and output from the battery 12 until the current input to and output from the battery 11 exceeds the unusable current range set for the battery 12. In Embodiment 1, the circulating current prevention unit 13 includes a charge / discharge control unit 21, a total current measurement unit 22, a branched current measurement unit 23, and a switch 24.

[0018] The total current measurement unit 22 is located on the common power line Wc and detects the total current value of the currents input and output to batteries 11 and 12. The branch current measurement unit 23 is located on the branch power line Wb2 and measures the branch current value, which indicates the magnitude of the currents input and output to battery 12. The switch 24 is located on the branch power line Wb2 where the branch current measurement unit 23 is located, and is installed in series with the branch current measurement unit 23. The charge / discharge control unit 21 turns the switch 24 into a conductive state when the total current value measured by the total current measurement unit 22 exceeds the unusable current range, and maintains the switch 24 in a conductive state when the branch current value indicates the same direction of current flow as the total current value. In other words, the charge / discharge control unit 21 maintains the switch 24 in an off state during the period when the total current value measured by the total current measurement unit 22 is within the unusable current range. Furthermore, the charge / discharge control unit 21 conducts the switch 24 when the total current value measured by the total current measurement unit 22 exceeds the unusable current range. However, if the branch current value indicates a current flow direction opposite to that of the total current value, the switch 24 switches from the conduction state to the disconnection state.

[0019] Here, we will explain the unusable current range. Figure 2 shows a diagram illustrating the unusable current range of the power supply device according to Embodiment 1. As shown in Figure 2, in Embodiment 1, for a battery 11 that has not deteriorated significantly, the entire current range from the maximum discharge current (100% charge / discharge current) to the maximum charge current (-100% charge / discharge current) is usable. In other words, the charge / discharge current for battery 11 is never interrupted. On the other hand, for a battery 12 that has deteriorated significantly, the range in which the charge / discharge current is less than 10% of the maximum discharge current and less than 10% of the maximum discharge current is defined as the unusable current range for battery 12. The charge / discharge control unit 21 then keeps the switch 24 in the off state during the period when the total current measured by the total current measurement unit 22 is within the unusable current range.

[0020] Furthermore, the size of the unusable current range can be set to a range other than that shown in Figure 2, depending on the product specifications, the degree of degradation of the battery, etc.

[0021] Next, the operation of the circulating current prevention unit 13 will be explained in detail. Figure 3 shows a flowchart illustrating the operation of the power supply device 1 including the circulating current prevention unit 13 according to Embodiment 1. As shown in Figure 3, when the circulating current prevention unit 13 starts battery control, it first turns off the switch 24 (step S1). Subsequently, the charge / discharge control unit 21 acquires the total current value measured by the total current measurement unit 22 (step S2). Then, the charge / discharge control unit 21 determines whether the current flowing through the common power line Wc is in the charging direction or the discharging direction (step S3).

[0022] Then, in step S3, if it is determined that the current flowing through the common power line Wc is in the discharge direction, the charge / discharge control unit 21 determines whether the State of Charge (SOC) of the battery 12 is above the lower limit (step S4). If the SOC of the battery 12 is below the lower limit in step S4, the charge / discharge control unit 21 disables the battery 12 and performs the total current measurement in step S2 (NO branch of step S4). On the other hand, if it is determined in step S4 that the SOC of the battery 12 is above the lower limit (YES branch of step S4), the battery 12 is set to discharge mode (step S5).

[0023] Next, the charge / discharge control unit 21 determines whether the total current value measured by the total current measurement unit 22 is within the usable range (outside the unusable current range) of the battery 12 (step S6). In step S6, if the total current value is outside the usable range (i.e., within the unusable current range), the charge / discharge control unit 21 returns to step S2 and continues measuring the total current value by the total current measurement unit 22. On the other hand, if it is determined in step S6 that the total current value is within the usable range (i.e., outside the unusable current range), the charge / discharge control unit 21 switches the switch 24 from the off state to the on state (step S7). Then, with the switch 24 on, the charge / discharge control unit 21 measures the branch current value flowing to the battery 12 using the branch current measurement unit 23 (step S8).

[0024] Subsequently, the charge / discharge control unit 21 determines whether the direction of the current indicated by the branch current value matches the direction of the current indicated by the total current value (step S9). If, in step S9, the direction of the current indicated by the branch current value is the opposite charging direction to that of the total current value (charging branch of step S9), the charge / discharge control unit 21 returns to step S1 and switches the switch 24 from the ON state to the OFF state. On the other hand, if, in step S9, the direction of the current indicated by the branch current value is the same discharge direction as the total current value (discharge branch of step S9), the charge / discharge control unit 21 uses the battery 12 as a power source for discharging (step S10). The charge / discharge control unit 21 then repeatedly performs the process from measuring the total current value (step S2) until the State of Charge (SOC) of the battery 12 falls below the lower limit (NO branch of step S11). Furthermore, if the State of Charge (SOC) of battery 12 falls below the lower limit, the charge / discharge control unit 21 returns to step S1 and switches switch 24 from the ON state to the OFF state (YES branch of step S11).

[0025] Furthermore, in step S3, if it is determined that the current flowing through the common power line Wc is in the charging direction, the charge / discharge control unit 21 determines whether the state of charge (SOC) of the battery 12 is below the upper limit (step S12). If the SOC of the battery 12 exceeds the upper limit in step S12, the charge / discharge control unit 21 maintains the off state of the switch 24 to prevent the battery 12 from being charged, and performs the total current measurement in step S2 (NO branch of step S12). On the other hand, if it is determined in step S12 that the SOC of the battery 12 is below the upper limit (YES branch of step S12), the battery 12 is set to charging mode (step S13).

[0026] Next, the charge / discharge control unit 21 determines whether the total current value measured by the total current measurement unit 22 is within the usable range (outside the unusable current range) of the battery 12 (step S14). In step S14, if the total current value is outside the usable range (i.e., within the unusable current range), the charge / discharge control unit 21 returns to step S2 and continues measuring the total current value by the total current measurement unit 22. On the other hand, if it is determined in step S14 that the total current value is within the usable range (i.e., outside the unusable current range), the charge / discharge control unit 21 switches the switch 24 from the off state to the on state (step S15). Then, with the switch 24 on, the charge / discharge control unit 21 measures the branch current value flowing to the battery 12 using the branch current measurement unit 23 (step S16).

[0027] Subsequently, the charge / discharge control unit 21 determines whether the direction of the current indicated by the branch current value matches the direction of the current indicated by the total current value (step S17). If, in step S17, the direction of the current indicated by the branch current value is the opposite discharge direction to that of the total current value (discharge branch of step S17), the charge / discharge control unit 21 returns to step S1 and switches the switch 24 from the ON state to the OFF state. On the other hand, if, in step S17, the direction of the current indicated by the branch current value is the same charging direction as the total current value (charging branch of step S17), the charge / discharge control unit 21 uses the battery 12 as a power source for charging (step S18). Then, for the period until the State of Charge (SOC) of the battery 12 exceeds the upper limit, the charge / discharge control unit 21 repeatedly performs the process from measuring the total current value (step S2) (NO branch of step S19). Furthermore, if the State of Charge (SOC) of battery 12 exceeds the upper limit, the charge / discharge control unit 21 returns to step S1 and switches switch 24 from the ON state to the OFF state (YES branch of step S19).

[0028] In secondary batteries, as degradation progresses, the OCV (Overcurrent Voltage) decreases and the internal resistance increases. Due to this characteristic, a circulating current is generated when secondary batteries with different degrees of degradation are connected in parallel. However, when the charge and discharge currents to the secondary batteries connected in parallel are sufficiently large, the current distribution among the connected secondary batteries will only deviate from being equal, and a circulating current will not be generated.

[0029] As described above, in the power supply device 1 according to Embodiment 1, the circulating current prevention unit 13 cuts off the input and output of current to the battery 12, which is a deteriorated battery, unless the total current value flowing through the common power line Wc becomes large enough to fall outside the unusable current range set for the battery 12. As a result, in the power supply device 1 according to Embodiment 1, charging and discharging to the battery 12 is stopped during periods when the total current value is small, thus preventing the generation of circulating current.

[0030] Furthermore, in the power supply device 1 according to Embodiment 1, the current flowing through the branch power lines Wb1 and Wb2 is not measured separately. Instead, the occurrence of circulating current is detected by comparing the direction of the total current with the direction of the current flowing through the battery 12, thereby preventing errors in determining the occurrence of circulating current.

[0031] Furthermore, in the power supply device 1 according to Embodiment 1, the charging and discharging current to the battery 12 is switched on and off based on the magnitude of the total current value and the difference in direction between the total current value and the branch current value. As a result, in the power supply device 1 according to Embodiment 1, the on / off switching of the switch does not occur frequently. In other words, the power supply device 1 according to Embodiment 1 can control the switch with simple switch control while improving the stability of the switch control.

[0032] Embodiment 2 Embodiment 2 describes a circulating current prevention unit 33, which is another form of the circulating current prevention unit 13. Therefore, Figure 4 shows a block diagram of the power supply device 2 according to Embodiment 2, which includes the circulating current prevention unit 33.

[0033] As shown in Figure 4, the power supply unit 2 does not have a charge / discharge control unit 21, a total current measurement unit 22, a branch current measurement unit 23, or a switch 24. Instead, a circulating current prevention unit 33 is provided on the branch power line Wb2. The circulating current prevention unit 33 has a first diode (e.g., diode D1) and a second diode (e.g., diode D2). Diode D1 has its cathode connected to the battery 12 and its anode connected to the common power line Wc. Diode D2 has its cathode connected to the common power line Wc and its anode connected to the battery 12. Diodes D1 and D2 each have a forward bias voltage VF of approximately 0.7V. Due to this forward bias voltage VF, diodes D1 and D2 maintain an interrupted state for the period during which the voltage difference between the anode and cathode is less than or equal to the forward bias voltage VF. Furthermore, in the circulating current prevention unit 33, since diodes D1 and D2 are connected so that current flows in opposite directions to each other, current will not flow unless the voltage difference between battery 11 and battery 12 is greater than or equal to the forward bias voltage VF, regardless of the direction of charging or discharging.

[0034] Next, the operation of the power supply device 2 according to Embodiment 2 will be described. In the following description using Figures 5 and 6, an example will be described in which battery 11 has an OCV voltage Vb11 of 50.5V and an internal resistance Ri11 of 0.1Ω, and battery 12 has an OCV voltage Vb12 of 50.0V and an internal resistance Ri12 of 0.15Ω.

[0035] First, Figure 5 shows a diagram illustrating that no circulating current flows in the power supply device 2 according to Embodiment 2 when no charge / discharge current is flowing. As shown in Figure 5, when no current is flowing, the output voltage of battery 11 is approximately 50.5V, which is about the same as the voltage Vb11, and the output voltage of battery 12 is approximately 50.0V, which is about the same as the voltage Vb12. The difference in output voltage between battery 11 and battery 12 is 0.5V, which is smaller than the forward bias voltage VF of diodes D1 and D2, so no circulating current is generated from battery 11 to battery 12.

[0036] Next, Figure 6 shows a diagram illustrating the current flow in the power supply device 2 according to Embodiment 2 when a charging current is applied. As shown in Figure 6, in the power supply device 2 according to Embodiment 2, during periods when the common power line Wc is small (period when the charging current IC in Figure 6 is 1A), a branch current ICb1 of 1A flows to the battery 11, and the output voltage of the battery 11 becomes 50.6V, which is the sum of 50.5V Vb11 and the voltage generated by the 1A branch current flowing through the internal resistance Ri11 = 0.1V. Therefore, the output voltage of the battery 11 does not exceed 50.7V, which is necessary to activate the circulating current prevention unit 33 provided in correspondence with the battery 12. Therefore, during periods when the charging current IC shown on the right side of Figure 6 is about 1A, the entire charging current IC flows to the battery 11, and no circulating current is generated from the battery 11 to the battery 12.

[0037] On the other hand, when the charging current IC exceeds 2A, the output voltage of battery 11 exceeds 50.7V, causing the circulating current prevention unit 33 to conduct when the charging current IC is 2A or higher. When the circulating current prevention unit 33 conducts, the charging current IC flows to both battery 11 and battery 12 as branch currents ICb1 and ICb2. The right diagram of Figure 6 shows the case when the charging current IC is approximately 12A. In this case, the output voltage of battery 11 is 51.3V, which is the sum of 50.5V Vb11 and the voltage generated by the 8A branch current ICb1 flowing through the internal resistance Ri11 = 0.8V. The output voltage of battery 12 is 50.6V, which is the sum of 50.0V Vb12 and the voltage generated by the 4A branch current ICb2 flowing through the internal resistance Ri12 = 0.6V. The sum of the output voltage of battery 12 and the forward bias voltage VF is 51.3V. In other words, in the power supply device 2 according to Embodiment 2, the charging current IC is distributed to batteries 11 and 12 so that the voltage at the branching point of the branch power lines Wb1 and Wb2 is the same.

[0038] As described above, the power supply device 2 according to Embodiment 2 prevents circulating current from flowing between battery 11 and battery 12 without switch control. Furthermore, in Embodiment 2, the unusable current range in which the current flowing to battery 12 is interrupted is determined by the magnitude of the internal resistance Ri11 of battery 11 and the magnitude of the OCV voltage Vb11 of battery 11. In the example shown in Figure 6, the unusable current range is the range in which the charging current and discharge current are 2A or less.

[0039] Furthermore, in the power supply device 2 according to Embodiment 2, the circulating current prevention unit 33 has a configuration that prevents the generation of circulating current without relying on a switch, thus eliminating the complexity of switch control and enabling stable prevention of circulating current.

[0040] Embodiment 3 Embodiment 3 describes a power supply device 3, which is another example of the power supply device 1 according to Embodiment 1. In the description of Embodiment 3, the components described in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and their descriptions are omitted.

[0041] Figure 7 shows a block diagram of the power supply device 3 according to Embodiment 3. As shown in Figure 7, in Embodiment 3, multiple batteries are provided as second batteries. In Figure 7, n batteries, numbered 121 to 12n, are shown as multiple second batteries.

[0042] Furthermore, as shown in Figure 7, the circulating current prevention unit 13a according to Embodiment 3 has branch current measuring units 231 to 23n and switches 241 to 24n, corresponding to the number of second batteries. Each of the branch current measuring units 231 to 23n and switches 241 to 24n is provided on the branch power supply line of the second battery.

[0043] Thus, when multiple second batteries are provided, the charge / discharge control unit 21a sets a range as the unusable current range in which it is considered that no circulating current will be generated from any of the second batteries due to the incorporation of multiple second batteries. Setting this unusable current range becomes easier by keeping the degree of degradation of the second batteries within a certain range. In Embodiment 3, the unusable current range needs to be increased in proportion to the number n of second batteries when the number of second batteries increases.

[0044] The operation of the power supply device 3 according to Embodiment 2 can be performed by replacing the battery 12 in the operation of the power supply device according to Embodiment 1 shown in Figure 3 with batteries 121 to 12n.

[0045] Thus, even when multiple second batteries are provided whose degree of degradation is less than or equal to that of the first battery, the generation of circulating current can be suppressed in the power supply device 3 according to Embodiment 2 by setting an unusable current range in which no circulating current occurs in any of the multiple second batteries.

[0046] Furthermore, by setting a common unusable current range for multiple second batteries, it is not necessary to individually control batteries 121 to 12n. Therefore, the power supply device 3 according to Embodiment 2 can achieve a simplified device configuration and simplified control.

[0047] Embodiment 4 Embodiment 4 describes a power supply device 4, which is another example of the power supply device 2 according to Embodiment 2. In the description of Embodiment 4, the components described in Embodiments 1 and 2 are denoted by the same reference numerals as in Embodiments 1 and 2, and their descriptions are omitted.

[0048] Figure 8 shows a block diagram of the power supply device 4 according to Embodiment 4. As shown in Figure 8, in Embodiment 4, multiple batteries are provided as second batteries. In Figure 8, n batteries, numbered 121 to 12n, are shown as multiple second batteries.

[0049] Furthermore, as shown in Figure 8, in the power supply device 4 according to Embodiment 4, circulating current prevention units 331 to 33n are provided for each of the batteries 121 to 12n. Each of the circulating current prevention units 331 to 33n is provided on the branch power line of the second battery. The configuration of the circulating current prevention units 331 to 33n is the same as that of the circulating current prevention unit 33 shown in Figure 4.

[0050] In the power supply device 4 according to Embodiment 4, by providing each of the multiple second batteries with circulating current prevention units 331 to 33n having the same configuration as the circulating current prevention unit 33, the generation of circulating current can be prevented by disconnecting the second batteries from the common power line Wc until the current range flowing through the common power line exceeds a certain size, similar to Embodiment 2.

[0051] Embodiment 5 Embodiment 5 describes another form of the method for determining the unusable current range described in Embodiment 1. In the description of Embodiment 5, the components described in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1 and their descriptions are omitted.

[0052] Figure 9 shows a block diagram of the power supply unit 5 according to Embodiment 5. As shown in Figure 9, the power supply unit 5 according to Embodiment 5 has a circulating current prevention device 13b instead of the circulating current prevention unit 13 of the power supply unit 1 according to Embodiment 1. The circulating current prevention device 13b replaces the charge / discharge control unit 21 of the circulating current prevention unit 13 with a charge / discharge control unit 21b.

[0053] Similar to the charge / discharge control unit 21, the charge / discharge control unit 21b conducts the switch 24 when the total current value measured by the total current measurement unit 22 exceeds the unusable current range, and maintains the conduction state of the switch 24 when the branch current value measured by the branch current measurement unit 23 indicates the same direction of current flow as the total current value. Here, the charge / discharge control unit 21b differs from the charge / discharge control unit 21 in its method of determining the unusable current range.

[0054] Specifically, the charge / discharge control unit 21b is equipped with a function to acquire output voltages from the first battery (e.g., battery 11) and the second battery (e.g., battery 12). Based on the acquired output voltages from each battery, the charge / discharge control unit 21b determines the range in which no circulating current occurs between battery 11 and battery 12 as the unusable current range. Hereinafter, the method for determining the unusable current range according to Embodiment 5 will be described in detail.

[0055] Therefore, Figure 10 shows a diagram illustrating the unusable current range of the power supply device 5 according to Embodiment 5. As shown in Figure 10, the output voltages of batteries 11 and 12 change with a constant slope with respect to the charge and discharge current. This change in output voltage can be expressed by equation (1) for the output voltage Vo1 of battery 11 and by equation (2) for the output voltage Vo2 of battery 12. Vo1 = Rin1 × I1 + Voc1 ... (1) Vo2 = Rin2 × I2 + Voc2 ... (2) Here, in equation (1), Rin1 is the internal resistance of battery 11, I1 is the charge / discharge current of battery 11, and Voc1 is the open-circuit voltage of battery 11. Also, in equation (2), Rin2 is the internal resistance of battery 12, I2 is the charge / discharge current of battery 12, and Voc2 is the open-circuit voltage of battery 12.

[0056] From equations (1) and (2) above, it can be seen that the internal resistance Rin1 of battery 11 and the internal resistance Rin2 of battery 12 can be calculated if the output voltages obtained during charging and discharging of batteries 11 and 12, and the open-circuit voltages of batteries 11 and 12 are known, respectively.

[0057] Therefore, the charge / discharge control unit 21b stores the open-circuit voltage Voc1 of the battery 11, which was measured before the battery 11 was incorporated into the power supply unit 5. Then, the charge / discharge control unit 21b calculates the internal resistance Rin1 from the slope of the change in the output voltage of the battery 11 with respect to the total current value when the switch 24 is in the off state.

[0058] Furthermore, the charge / discharge control unit 21b obtains the open-circuit voltage Voc2 of the battery 12 from the battery voltage measured when the switch 24 is in the off state. The charge / discharge control unit 21b then calculates the internal resistance Rin2 from the slope of the change in the output voltage of the battery 12 with respect to the branch current value when the switch 24 is in the connected state.

[0059] The charge / discharge control unit then calculates the discharge current value Idischg, which is the lower limit of the unusable current range, and the charge current value Ichg, which is the upper limit of the unusable current range, using equations (3) and (4). Idischg=(Voc2-Voc1) / Rin1···(3) Ichg=(Voc1-Voc2) / Rin2···(4)

[0060] In the example shown in Figure 9, battery 12 is a more degraded battery than battery 11, and its open-circuit voltage Voc2 is lower than the open-circuit voltage Voc1 of battery 11. Also, in the example shown in Figure 9, as the battery performance deteriorates, the slope of the voltage change of battery 12 is steeper than that of battery 11. In such a case, in the range where the charging current is less than or equal to the charging current value Ichg, the open-circuit voltage Voc1 of battery 11 becomes higher than the output voltage of battery 12, resulting in a circulating current flowing from battery 11 to battery 12. Similarly, in the range where the discharge current is less than or equal to the discharge current value Idischg, the open-circuit voltage Voc2 of battery 12 becomes lower than the output voltage of battery 11, resulting in a circulating current flowing from battery 11 to battery 12. In other words, a circulating current occurs when the total current value falls within the unusable current range, with the discharge current Idischg as the lower limit and the charging current Ichg as the upper limit. However, the charge / discharge control unit 21b suppresses the generation of this circulating current by controlling the switch 24 to the off state in this unusable current range.

[0061] As shown in Figure 9, in the power supply device 5 according to Embodiment 5, the battery 11 can be used for the entire range of charge and discharge currents.

[0062] As described above, in the power supply device 5 according to Embodiment 5, the unusable current range is set based on the characteristics of the battery incorporated into the power supply device 5. This makes it possible to suppress the generation of circulating current while making more effective use of the battery performance than the power supply device 1 according to Embodiment 1.

[0063] Furthermore, in the power supply device 5 according to Embodiment 5, the slope of the change in output voltage of batteries 11 and 12, as well as the open-circuit voltage, can be acquired while the device is in use. As a result, in the power supply device 5 according to Embodiment 5, the unusable current range can be updated during operation in accordance with the state of the batteries, so that the batteries can be used at the efficiency considered to be the most efficient according to the degree of battery degradation. In addition, in the power supply device 5 according to Embodiment 5, it is also possible to update the open-circuit voltage Voc1 of battery 11 when the measurement result by the total current measurement unit 22 shows a total current value of 0.

[0064] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0065] 1~5 Power supply 11, 12 Batteries 13, 33, 13a, 13b, 331~33n Circulating current prevention section 21, 21a, 21b Charge / Discharge Control Unit 22 Total current measurement section 23, 231~23n Branch current measurement section 24, 241~24n switches D1, D2 diodes D2 Diode Wc common power line Wb1, Wb2 Branch Power Lines

Claims

1. The first battery and A second battery is connected in parallel with the first battery and has a higher degree of degradation than the first battery, A circulating current prevention unit prevents current from being input to and output to the second battery until the current input to and output to the first battery exceeds the unusable current range set for the second battery, A power supply device having the following features.

2. The aforementioned circulating current prevention unit is A total current measuring unit that detects the total current value of the currents input to and output from the first battery and the second battery, A branch current measuring unit that measures a branch current value indicating the magnitude of the current input and output to the second battery, A switch is provided on the branch power line on which the branch current measuring unit is located, in series with the branch current measuring unit, A charge / discharge control unit that turns the switch into a conductive state when the total current value exceeds the unusable current range, and maintains the switch in a conductive state when the branch current value indicates the same direction of current flow as the total current value, A power supply device according to claim 1, having the following features.

3. The power supply device according to claim 2, wherein the charge / discharge control unit sets the unusable current range by setting the total current value at which the output voltage of the first battery is less than or equal to the discharge current value that exceeds the open circuit voltage of the second battery as a lower limit, and the total current value at which the output voltage of the second battery is less than or equal to the charge current value that exceeds the open circuit voltage of the first battery as an upper limit, and controls the switch to a conductive state when the total current value exceeds the unusable current range.

4. The open-circuit voltage of the first battery is the value measured before the first battery was incorporated into the power supply device. The open-circuit voltage of the second battery is the value measured by the charge / discharge control unit when the switch is in the off state. The charge / discharge control unit, The lower limit is set to the value obtained by dividing the internal resistance of the first battery, calculated from the slope of the output voltage of the first battery with respect to the charge / discharge current measured when the switch is in the off state, by the difference between the open-circuit voltage of the second battery and the open-circuit voltage of the first battery. The power supply device according to claim 3, wherein the upper limit is set to the value obtained by dividing the internal resistance value of the second battery, which is calculated from the slope of the output voltage of the second battery with respect to the charge / discharge current measured when the switch is in a conductive state, by the difference between the open-circuit voltage of the first battery and the open-circuit voltage of the second battery.

5. The system further includes a common power line provided for both the first battery and the second battery, The aforementioned circulating current prevention unit is A first diode whose cathode is connected to the second battery and whose anode is connected to the common power line, A second diode whose cathode is connected to the common power line and whose anode is connected to the second battery, The power supply device according to claim 1.

6. The power supply device according to any one of claims 1 to 5, wherein the second battery includes a plurality of batteries connected in parallel with each other.

7. The first battery and A second battery is connected in parallel with the first battery and has a higher degree of degradation than the first battery, A total current measuring unit that detects the total current value of the currents input to and output from the first battery and the second battery, A branch current measuring unit that measures the branch current value which is the current input and output to the second battery, A switch is provided between the branch current measuring unit and the second battery, A charge / discharge control unit that turns the switch into a conductive state when the total current value exceeds a preset unusable current range, and maintains the switch in a conductive state when the branch current value indicates the same direction of current flow as the total current value, A power supply device having the following features.

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