JP2005253273A - Dc power supply system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC power supply system that can prevent a trouble even if an arbitrary cell is put into abnormal states including a short-circuit, disconnection, overcharge, and overdischarge. <P>SOLUTION: This system comprises an IGBT 5 that is connected between the output end of a DC power supply 2 and the series circuit of a plurality of lithium ion secondary batteries 1a to 1n, a diode 4 that is connected in parallel to the IGBT 5 in polarity that allows discharging only to a plurality of the lithium ion secondary batteries, IGBTs 6 that are connected in series to each of lithium ion secondary battery, IGBTs 7 that are connected in parallel to each of series circuits of a single lithium ion secondary battery and the single IGBT 6, voltage probes 10 that detect a terminal voltage of each lithium ion secondary battery, voltage regulating circuits 8 that regulate the terminal voltage of each lithium ion secondary battery, and a control unit 9. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power supply system that uses a lithium ion secondary battery for supplying a stable power to a DC load such as a communication device without instantaneous interruption, and in particular, short-circuiting and opening a lithium ion secondary battery, When overdischarge and overcharge occur, these are detected at an early stage, and the DC power supply system having a function of protecting the assembled battery is opened.

  FIG. 7 shows a configuration of a conventional DC power supply system using a lithium ion secondary battery (see Patent Document 1). As shown in FIG. 7, a conventional power supply system includes a battery pack 103 in which a DC power supply 102 that converts commercial power supply 101 into DC power and outputs it, and a plurality of lithium ion secondary batteries 1a to 1n are connected in series. A voltage adjusting circuit 104-1 to 104-n that is provided corresponding to each lithium ion secondary battery constituting the assembled battery and performs voltage adjustment of each lithium ion secondary battery, and a battery disconnecting switch 105, The voltage probe 106 and the control unit 107 are included.

A control line 108 is connected between the control unit 107, the battery disconnect switch 105, and the voltage adjustment circuits 104-1 to 104n. 110 is a DC load.
The direct current power is supplied from the direct current power source 102 or the assembled battery 103 to the direct current load.

In the DC power supply system configured as described above, when charging a plurality of lithium ion secondary batteries connected in series, if the capacity or internal resistance of all the batteries is always the same, the batteries can be charged with good balance.
In practice, however, there is some variation in battery capacity or internal resistance.
Furthermore, even if the internal resistance is the same in the initial stage, the internal characteristics of the battery change as time passes due to long-term charging, and the capacity and internal resistance of the battery also change.

As a result, the balance of each lithium ion secondary battery is lost, and the cell voltage in the assembled battery varies.
Therefore, when charging a plurality of lithium ion secondary batteries 1a to 1n connected in series, each of the lithium ion secondary batteries 1a to 1n is connected to a voltage adjusting circuit 104-1 to 104-n and a terminal voltage of each battery. And a control unit 102 for controlling the voltage adjustment circuits 104-1 to 104-n. When any battery reaches the charge completion voltage, it is provided corresponding to the lithium ion secondary battery that has been charged. The voltage regulation circuit is operated, the charging current is bypassed, and the charging voltage of each lithium ion secondary battery is charged by charging one cell (battery) until all lithium ion secondary batteries reach the charging voltage. It is uniform.

Further, as protection against overcharge and overdischarge, a battery disconnect switch 105 is connected in series with the charge / discharge path of the assembled battery 103. The main purpose of this switch is to disconnect the circuit for protection of the lithium ion secondary battery constituting the assembled battery 103, and the voltage at which the voltage of any lithium ion secondary battery becomes a problem in terms of battery safety (example 4.2) It is released when the voltage rises to V) (overcharge) and when the voltage drops to a voltage that deteriorates before the battery characteristics cannot be recovered (eg 3.0V) (overdischarge).
JP 2003-217675 A

However, the above-described conventional power supply system opens the battery disconnection switch 105 when an arbitrary lithium ion secondary battery in the assembled battery 103 reaches an abnormal voltage, so that a power failure occurs after the battery disconnection switch 105 is opened. Even if this occurs, since the discharge path is disconnected, power cannot be supplied to the DC load 110.
On the other hand, lithium ion secondary batteries need to be connected in parallel to increase battery capacity. In the conventional DC power supply system shown in FIG. 7, a voltage adjustment circuit is required for each lithium ion secondary battery.

Therefore, in order to reduce the number of voltage adjustment circuits, it is effective to provide a voltage adjustment circuit for each assembled battery connected in parallel.
However, when lithium ion secondary batteries (referred to as cells) are connected in series and parallel as described above, when any cell is short-circuited, all the connected batteries connected in parallel are completely discharged and reach an abnormal voltage. Since the battery disconnection switch is opened, there is a problem that power cannot be supplied to the DC load because the discharge path is disconnected even if a power failure occurs after the switch is opened.

  The present invention has been made in view of such circumstances, and an arbitrary circuit of a series circuit of a plurality of secondary batteries or a series / parallel circuit of a plurality of secondary batteries connected in parallel to the output terminal of a DC power supply. It is an object of the present invention to provide a DC power supply system that can prevent a failure even when a cell is in an abnormal state such as a short circuit, an open state, an overcharge, or an overdischarge.

  In order to achieve the above object, the invention described in claim 1 includes a DC power supply and a series circuit of a plurality of secondary batteries connected in parallel to an output terminal of the DC power supply, and the output of the DC power supply. A DC power supply system for supplying DC power to a DC load from an end, wherein the first switch means connected between an output end of the DC power supply and a series circuit of the plurality of secondary batteries, and the plurality A diode that is connected in parallel to the first switch means with a polarity that allows only discharge to the secondary battery, a second switch means that is connected in series to each of the plurality of secondary batteries, and the second battery A third switch means connected in parallel to each of the series circuit of the secondary battery and the second switch means, a voltage detection means for detecting a terminal voltage of each of the plurality of secondary batteries, Adjust the terminal voltage of each secondary battery If it is determined that an abnormal state has occurred in any secondary battery among the plurality of secondary batteries based on the detection output of the pressure adjusting unit and the voltage detecting unit, the abnormality is determined according to the type of the abnormal state. And control means for controlling the on / off states of the first, second and third switch means so as to eliminate the influence of the state.

  Further, according to a second aspect of the present invention, in the DC power supply system according to the first aspect, instead of each single secondary battery in the series circuit of the plurality of secondary batteries, a voltage equalizing line is used in parallel. It is characterized by replacing with a plurality of secondary batteries connected to.

  Further, the invention according to claim 3 is the DC power supply system according to claim 1 or 2, wherein the control means charges the series circuit of the plurality of secondary batteries with the DC power supply. When any secondary battery among the plurality of secondary batteries reaches a predetermined charging voltage, the first switch means is turned off.

  According to a fourth aspect of the present invention, in the DC power supply system according to any one of the first to third aspects, the control means is configured to supply power from a series circuit of the plurality of secondary batteries to a DC load. The second switch means is turned off and the third switch means is turned on when an arbitrary battery among the plurality of secondary batteries drops to a predetermined terminal voltage. To do.

  Further, the invention according to claim 5 is the DC power supply system according to any one of claims 1 to 4, wherein the control means is charging the series circuit of the plurality of secondary batteries with the DC power supply. When any of the plurality of secondary batteries is short-circuited or opened, the first switch unit is turned off.

  The invention according to claim 6 is the DC power supply system according to any one of claims 1 to 5, wherein the control means supplies power from the series circuit of the plurality of secondary batteries to the DC load. In some cases, when any one of the plurality of secondary batteries is short-circuited or opened, the first switch unit is turned off.

  The invention according to claim 7 is the DC power supply system according to any one of claims 1 to 6, further comprising a current detection means for detecting a bypass current during charging in each of the plurality of secondary batteries. And the control means compares the current value of the bypass current of each of the plurality of secondary batteries with a threshold value, and determines that the current value of the bypass current is abnormal when the current value of the bypass current is larger than the threshold value. A signal indicating a state is output.

  As described above, according to the present invention, a DC power supply and a series circuit of a plurality of secondary batteries or a series / parallel circuit of a plurality of secondary batteries connected in parallel to the output terminal of the DC power supply are provided. A DC power supply system for supplying DC power to a DC load from an output terminal of the DC power supply, between the output terminal of the DC power supply and a series circuit or a series-parallel circuit of the plurality of secondary batteries. A first switch means connected, a diode connected in parallel to the first switch means with a polarity that allows only discharge to the plurality of secondary batteries, and each of the plurality of secondary batteries in series Second switch means to be connected, third switch means connected in parallel to each of the series circuit of the secondary battery and the second switch means, and each terminal of the plurality of secondary batteries Voltage detection means for detecting the voltage; It is determined that an abnormal state has occurred in any secondary battery among the plurality of secondary batteries based on the voltage adjustment means for adjusting the terminal voltage of each of the secondary batteries and the detection output of the voltage detection means. And a control means for controlling the on / off states of the first, second and third switch means to remove the influence of the abnormal state according to the type of the abnormal state. Therefore, it is possible to prevent a failure of the DC power supply system when the secondary battery is short-circuited, opened, overcharged, or overdischarged.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The configuration of the DC power supply system according to the first embodiment of the present invention is shown in FIG. In the figure, the DC power supply system according to the first embodiment of the present invention includes a DC power supply 2 and a series of a plurality of lithium ion secondary batteries 1 a to 1 n connected in parallel to the output terminal of the DC power supply 2. And a DC power is supplied to the DC load 3 from the output terminal of the DC power source 2.

  Further, the IGBT 5 as the first switch means connected between the output terminal of the DC power supply 2 and the series circuit of the plurality of lithium ion secondary batteries 1a to 1n, and the plurality of lithium ion secondary batteries 1a to 1n A diode 4 connected in parallel to the IGBT 5 with a polarity allowing only discharge, a IGBT 6 as a second switch means connected in series to each of the plurality of lithium ion secondary batteries 1a to 1n, and a single lithium IGBT 7 as third switch means connected in parallel to each of the series circuit of the ion secondary battery and IGBT 6, and voltage detection means for detecting the terminal voltage of each of the plurality of lithium ion secondary batteries 1 a to 1 n And a voltage adjustment circuit 8 as voltage adjustment means for adjusting the terminal voltage of each of the plurality of lithium ion secondary batteries 1a to 1n. And a control unit 9 as a control means.

  When the control unit 9 determines that an abnormal state has occurred in any lithium ion secondary battery among the plurality of lithium ion secondary batteries 1a to 1n based on the detection output of the voltage probe 10, the control unit 9 Function to switch on / off states of IGBTs 5, 6, and 7 so as to eliminate the influence of these abnormal states according to the type, that is, short circuit, open, overcharge, and overdischarge of the lithium ion secondary battery have.

  The control unit 9 charges a series circuit of the plurality of lithium ion secondary batteries 1a to 1n with the DC power supply 2, and any lithium ion secondary battery among the plurality of lithium ion secondary batteries is charged with a predetermined charging voltage (for example, When the voltage reaches the specified voltage for completion of charging, control is performed so that the IGBT 5 is turned off.

  In addition, the control unit 9 is configured so that an arbitrary lithium ion secondary battery among the plurality of lithium ion secondary batteries 1a to 1n is supplied from the series circuit of the plurality of lithium ion secondary batteries 1a to 1n to the DC load 3. When the voltage decreases to a predetermined terminal voltage (for example, a specified voltage that causes overdischarge), the lithium ion secondary that has been reduced to a predetermined terminal voltage by turning off the IGBT 6 connected in series with the secondary battery. The IGBT 7 connected in parallel to the series circuit of the battery and the IGBT 6 is turned on.

  Further, the control unit 9 is charging the series circuit of the plurality of lithium ion secondary batteries 1a to 1n with the DC power source 2, or the power from the series circuit of the plurality of lithium ion secondary batteries 1a to 1n to the DC load 3. When any of the plurality of lithium ion secondary batteries 1a to 1n is short-circuited or opened, the IGBT 5 is turned off.

In FIG. 1, a DC power source 2 converts AC commercial power into DC and supplies power to the DC load 3.
On the other hand, there are a plurality of lithium ion secondary batteries 1a to 1n connected in series so that electric power can be supplied to the DC load 3 without interruption in the event of a power failure. These lithium ion secondary batteries 1a to 1n are lithium ions. It is connected to the output terminal of the DC power source 2 which is a charging means for charging the secondary batteries 1a to 1n.

  Moreover, the lithium ion secondary batteries 1a to 1n are connected to the control unit 9 that monitors the terminal voltage of each cell (lithium ion secondary battery) with the voltage probe 10, and have reached the charging completion voltage (example .4.1V). In order from the cell, the control unit 9 sends a signal through the control line 12 to operate the voltage adjustment circuit 8 to prevent the terminal voltage of each cell from varying.

A specific configuration of the voltage adjusting circuit 8 is shown in FIG. In the figure, a voltage adjustment circuit 8 includes a lithium ion secondary battery, for example, a series circuit of a semiconductor switch 80 and a current limiting element (for example, a resistor) connected in parallel to a 1a via a current probe 11, a comparator 82.
The comparator 82 compares the voltage between the terminals of the lithium ion secondary battery 1a with the reference voltage when the lithium ion secondary battery is fully charged, and the voltage between the terminals of the lithium ion secondary battery 1a has reached the reference voltage. Sometimes a signal to turn on the semiconductor switch is output.

  Next, the operation of the DC power supply system configured as described above will be described with reference to FIG. The terminal voltage of each cell (lithium ion secondary battery) in the assembled battery in which the lithium ion secondary batteries 1a to 1n are connected in series is monitored, and any cell during charging due to a failure of the voltage adjustment circuit 8 or the like, For example, when the terminal voltage monitored by the voltage probe 10 of the 1n cell reaches a specified value (eg, 4.2V), that is, when 1n cell overcharge is detected, the lithium ion secondary batteries 1a to 1n are connected in series. The IGBT 5 is turned off to prevent the charging current from flowing into the assembled battery.

In this way, the IGBT 5 as the first switch means is turned off, and even if a power failure occurs, power is supplied to the DC load 3 through the diode 4 connected in series with the lithium ion secondary batteries 1a to 1n. Can be supplied.
Further, when any cell, for example, a 1n cell, detects a short circuit or an open state during charging and discharging, the terminal voltage monitored by the voltage probe 10 becomes 0 V, so the lithium ion secondary batteries 1a to 1n. The IGBT 5 connected in series with the 1n cell is turned off, the IGBT 7 connected in parallel with the 1n cell is turned on, and the IGBT 7 connected in series with the 1n cell is turned off. Similarly, power can be supplied to the DC load 3 during a power failure.

However, in this case, since the 1n cell that is short-circuited or opened cannot be discharged, the backup time during which power can be supplied from the lithium ion secondary batteries 1a to 1n to the DC load 3 is reduced. Suspension of supply can be prevented.
By the way, if the assembled battery is charged without providing the IGBT 5 as the first switch means and any cell is short-circuited or opened, V / n (V: assembled battery charging voltage, n: battery connected in series until then) The number of cells charged per unit cell becomes V / (n-1), the charging voltage per unit cell rises, the characteristics of the battery deteriorates significantly, and the safety valve operates and becomes unusable. There is a risk that.

Therefore, it can be seen that providing the IGBT 5 as the first switch means and disconnecting the DC power supply 2 as the charging circuit is an important function in securing the safety of the DC power supply system.
On the other hand, when power is supplied from the lithium ion secondary batteries 1a to 1n to the DC load 3 due to a power failure or the like, the voltage of the lithium ion secondary batteries 1a to 1n decreases, and all the cells are sequentially set to the specified value. A voltage of (eg 3.0V), that is, an overdischarge voltage is reached. For cells that have reached a specified value (eg, 3.0V), battery characteristics may deteriorate until the battery cannot be recovered unless battery discharge is stopped.

  Therefore, in this power supply system, when any cell, for example, 1n cell, reaches the overdischarge voltage, the control unit 9 detects that the terminal voltage monitored by the voltage probe 10 has become 3.0V. The IGBT 7 as the third switch means connected in parallel to the 1n cell is turned on, and the IGBT 6 as the second switch means is turned off. The other cells also have a specified value (eg, 3.0 V). As soon as the voltage is reached, the IGBT 6 is controlled to be turned off and the IGBT 7 is turned on to prevent each cell voltage from becoming 3.0 V or less.

  In this case, since the DC power source 2 and the lithium ion secondary batteries 1a to 1n are not out of order, the IGBT 5, which is the first switch means, is kept on, and the commercial power source 1 recovers, and then the lithium ion secondary The batteries 1a to 1n are on standby so that they can be charged.

So far, the operation of the DC power supply system when any cell is short-circuited, opened, overcharged or overdischarged has been described, but the lithium ion secondary batteries 1a to 1n are in a mode different from the above state. The detection method when a problem occurs is shown below.
If there is no variation in the characteristics of the lithium ion secondary batteries 1a to 1n, the terminal voltage of each cell is equalized to the set charging voltage by the operation of the voltage adjustment circuit 8, but it is maintained and charged due to some battery malfunction. It is possible that the bypass current of an arbitrary cell measured by the current probe 11 during recovery charging is very small compared to the bypass current of other cells. This situation will be described with reference to FIG.

  For example, assuming that the bypass current value of each cell is 6I for the lithium ion secondary battery 1a, 5I for 1b, 1I for 1c, 7I, and 1n for I, the semiconductor switch 80 and the current limiting element of the voltage regulator circuit 8 for the 1n cell The bypass current value flowing in the bypass path (see FIG. 2) including the 81 series circuit is as small as 1/5 or less of the other cells, and a large charge current flows in the 1n cell.

  This is a difference in the magnitude of each bypass current due to the voltage drop of any 1n cell. Therefore, if all the lithium ion secondary batteries 1a to 1b constituting the assembled battery are normal, the difference in the bypass current value does not appear so much, so that it is regarded as an abnormality of the 1n cell and an abnormal signal is transmitted to the outside. In addition, the threshold value of the abnormality determination in the control unit 9 at that time is, for example, the difference between the bypass current of the cell having the smallest bypass current and the other cells in the assembled battery is compared by the control unit 9, and the smallest bypass current is obtained. Although it is assumed that the cell becomes 1/5 or less of other cells, it is needless to say that the present invention is not limited to this.

Next, FIG. 5 shows a configuration of a DC power supply system according to the second embodiment of the present invention.
The direct current power supply system according to the second embodiment shown in FIG. 5 differs from the direct current power supply system according to the first embodiment shown in FIG. 1 in terms of the configuration in series of a plurality of lithium ion secondary batteries 1a to 1n. Instead of each single lithium ion secondary battery in the circuit, it is replaced with a plurality of lithium ion secondary batteries connected in parallel with equalizing wires, and the other functions are the same, so the same function Elements having the same reference numerals are given the same reference numerals, and redundant description is omitted.

  In the case of the DC power supply system according to the first embodiment shown in FIG. 1, a plurality of lithium ion secondary batteries 1a to 1n are connected in series, but the DC power according to the second embodiment shown in FIG. In the supply system, for example, instead of 1a, the lithium ion secondary batteries 1a, 2a, and 3a are connected in parallel by connecting pressure equalizing lines in order to increase the battery capacity. The same applies to the other lithium ion secondary batteries 1b to 1n in the first embodiment.

  Since the lithium ion secondary batteries 1a, 2a, and 3a connected in parallel equalize the voltage of each cell by means of a pressure equalizing line, the battery of a set is considered as one battery whose capacity is tripled. be able to. Therefore, the operation of the DC power supply system configured as shown in FIG. 5 is the same as that of FIG. 3 showing the operation of the DC power supply system according to the first embodiment, as shown in FIG. However, the operation of the control unit 9 at the time of short-circuiting and opening is different from that of the DC power supply system according to the first embodiment shown in FIG.

In the DC power supply system shown in FIG. 5, when any cell, for example, 1n cell is short-circuited, 2n cell and 3n cell are also completely discharged through 1n cell, so n sets monitored by voltage probe 10 The terminal voltage of the parallel circuit of the 1n cell, 2n cell, and 3n cell is 0V.
Accordingly, the IGBT 5 is turned off, the IGBT 7 connected in parallel to the IGBT 7 is turned on, and the IGBT 6 connected in series by the n-th 1n cell, 2n cell, and 3n cell parallel circuit is turned off. By doing so, the power supply to the DC load 3 at the time of a power failure is maintained.

  On the other hand, when an arbitrary cell, for example, a 1n cell is opened, in the DC power supply system according to the first embodiment shown in FIG. 1, the terminal voltage of the 1n cell monitored by the voltage probe 10 becomes 0V. In the DC power supply system according to the second embodiment shown in FIG. 5, since the lithium ion secondary batteries 2n and 3n are connected in parallel, the n-th 1n cell, 2n cell, The terminal voltage of the parallel circuit of 3n cells does not become 0V, but becomes the terminal voltage of 2n cells and 3n cells.

  Therefore, the control unit 9 turns off the IGBT 5 connected in series with the lithium ion secondary battery groups 1a to 1n, 2a to 2n, and 3a to 3n connected in series and parallel as shown in FIG. The IGBT 7 connected in parallel to the 1n cell is turned off, and the IGBT 6 connected in series to the 1n cell is turned on to maintain the power supply to the DC load 3 at the time of power failure. I am doing so.

The block diagram which shows the structure of the direct-current power supply system which concerns on 1st Embodiment of this invention. The block diagram which shows the specific structure of the voltage adjustment circuit in the direct-current power supply system which concerns on 1st Embodiment of this invention shown in FIG. Explanatory drawing which shows the operation state of the direct-current power supply system which concerns on 1st Embodiment of this invention shown in FIG. Explanatory drawing which shows the magnitude | size of the bypass current of each cell in the direct-current power supply system which concerns on embodiment of this invention. The block diagram which shows the structure of the direct-current power supply system which concerns on 2nd Embodiment of this invention. Explanatory drawing which shows the operation state of the DC power supply system which concerns on 1st Embodiment of this invention shown in FIG. The block diagram which shows the structure of the conventional DC power supply system.

Explanation of symbols

1a to 1n ... lithium ion battery (cell)
2 ... DC power supply 3 ... DC load 4 ... Diode 5, 6, 7 ... IGBT
DESCRIPTION OF SYMBOLS 8 ... Voltage adjustment circuit 9 ... Control part 10 ... Voltage probe 11 ... Current probe 12 ... Control line 80 ... Semiconductor switch 81 ... Current limiting element 82 ... Comparator

Claims (7)

A DC power supply system having a DC power supply and a series circuit of a plurality of secondary batteries connected in parallel to the output end of the DC power supply, and supplying DC power from the output end of the DC power supply to a DC load. And
First switch means connected between an output terminal of the DC power supply and a series circuit of the plurality of secondary batteries;
A diode connected in parallel to the first switch means with a polarity that allows only discharge to the plurality of secondary batteries;
A second switch means connected in series to each of the plurality of secondary batteries;
Third switch means connected in parallel to each of the series circuits of the secondary battery and the second switch means;
Voltage detection means for detecting a terminal voltage of each of the plurality of secondary batteries;
Voltage adjusting means for adjusting the terminal voltage of each of the plurality of secondary batteries;
If it is determined that an abnormal state has occurred in any secondary battery among the plurality of secondary batteries based on the detection output of the voltage detection means, the influence of the abnormal state is removed according to the type of the abnormal state Control means for controlling the on / off states of the first, second and third switch means to be switched,
A direct-current power supply system comprising:   2. The direct current according to claim 1, wherein each of the series circuits of the plurality of secondary batteries is replaced with a plurality of secondary batteries connected in parallel with a voltage equalizing line instead of a single secondary battery. Power supply system.   The control means charges the series circuit of the plurality of secondary batteries with the DC power source, and when any secondary battery among the plurality of secondary batteries reaches a predetermined charging voltage, the first means The DC power supply system according to claim 1, wherein the switch means is turned off.   The control means includes a second switch when any battery among the plurality of secondary batteries drops to a predetermined terminal voltage during power feeding from a series circuit of the plurality of secondary batteries to a DC load. The DC power supply system according to any one of claims 1 to 3, wherein a means is turned off and the third switch means is turned on.   When the control means is charging the series circuit of the plurality of secondary batteries with the DC power source, and any of the plurality of secondary batteries is short-circuited or opened, the first switch means The DC power supply system according to claim 1, wherein the DC power supply system is turned off.   The control means may be configured such that when any battery among the plurality of secondary batteries is in a short circuit state or an open state during power supply from the series circuit of the plurality of secondary batteries to the DC load, 6. The DC power supply system according to claim 1, wherein the switch means is turned off. Furthermore, it has a current detection means for detecting a bypass current during charging in each of the plurality of secondary batteries,
The control means compares the current value of the bypass current of each of the plurality of secondary batteries with a threshold value, and determines that the current value of the bypass current is abnormal when the current value of the bypass current is larger than the threshold value. The DC power supply system according to any one of claims 1 to 6, wherein:

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