JP2015162908A - DC voltage supply circuit and ground fault detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC voltage supply circuit and ground fault detection circuit, capable of more completely detecting a ground fault.SOLUTION: The DC voltage supply circuit includes a plurality of DC circuits in which positive lines and negative lines are connected, and a ground fault detection circuit that detects an electric current running through between an intermediate node positioned between the positive line and the negative line and a reference potential node of the respective DC circuits. A voltage of the intermediate node is set to be an absolute value smaller than a minimum absolute value of absolute values of input voltages or output voltages of the respective DC circuits.

Description

  The present invention relates to a DC voltage supply circuit and a ground fault detection circuit, and more particularly to a DC voltage supply circuit and a ground fault detection circuit that perform ground fault detection using a current generated by a ground fault.

  In order to avoid an accident caused by a ground fault, a ground fault is detected using a ground fault detection circuit. A ground fault means the state by which the insulation between an electric circuit and a ground was destroyed and both were electrically connected by low impedance, for example. Ground faults can damage electrical circuits and cause electric shocks and fires.

  As an example of the ground fault detection circuit, for example, the following circuit is disclosed in FIG. 5 of Japanese Patent Application Laid-Open No. 2010-213450. That is, the ground fault detection circuit includes two voltage dividing resistors having the same resistance value connected in series between the P pole and the N pole, and a ground fault connected in series between the neutral point M and the ground point G. It comprises a detection resistor and a ground fault detection relay.

  The ground fault detection circuit is provided between the DC power supply and the load. For example, when the positive side end of the DC power supply has a ground fault, a ground fault current flows from the ground fault location to the ground, and further flows from the ground through the ground point G through the ground fault detection relay. The ground fault detection circuit detects a ground fault using a current flowing through the ground fault detection relay.

JP 2010-213450 A

  Here, in the above circuit including a DC power supply, a load, and a ground fault detection circuit, a configuration in which a non-insulated voltage conversion circuit is newly provided between the DC power supply and the ground fault detection circuit will be considered. The voltage conversion circuit boosts the output of the DC power supply, for example, and supplies it to the load. In addition, since the input and output of the voltage conversion circuit are not insulated, the negative side end of the DC power supply and the N pole are at the same potential.

  Now, it is assumed that the potential difference between both ends of the DC power supply is 100V, and the potential difference between both ends of the load, that is, the potential difference between the P pole and the N pole is 200V. At this time, since the voltage at the neutral point M is the same as the voltage at the ground point G, it is zero volts. Since the resistance values of the two voltage dividing resistors are equal to each other, the voltage at the N pole is minus 100 volts.

  Further, since the negative end of the DC power supply and the N pole are at the same potential, the voltage at the negative end of the DC power supply is also minus 100V. And since the electric potential difference of both ends of DC power supply is 100V, the voltage of the positive side end of DC power supply is zero volt. At this time, the positive side end of the DC power supply and the ground are at the same potential.

  When the positive side end of the DC power supply and the ground are at the same potential, even if the positive side end of the DC power supply has a ground fault for some reason, no ground fault current flows between the ground fault location and the ground. Therefore, since no current flows through the ground fault detection relay, the ground fault detection circuit cannot detect the ground fault.

  This invention was made in order to solve the above-mentioned subject, and the objective is to provide the DC voltage supply circuit and ground fault detection circuit which can detect a ground fault more reliably.

  (1) In order to solve the above-described problem, a DC voltage supply circuit according to an aspect of the present invention includes a plurality of DC circuits each having a positive side line and a negative side line connected to each other, and between the positive side line and the negative side line. A ground fault detection circuit for detecting a current flowing between the intermediate node of each of the DC circuits and a reference potential node of each DC circuit, and the voltage of the intermediate node is an absolute value of an input voltage or an output voltage of each DC circuit The absolute value is set to be smaller than the smallest absolute value.

  (5) In order to solve the above-described problem, a ground fault detection circuit according to an aspect of the present invention includes a first connection node electrically connected to positive lines of a plurality of DC circuits, and each of the DC circuits. A current flowing between a second connection node electrically connected to the negative side line, an intermediate node between the first connection node and the second connection node, and a reference potential node of each DC circuit is detected. The voltage of the intermediate node is set to be an absolute value smaller than the minimum absolute value of the absolute values of the input voltage or output voltage of each DC circuit.

  According to the present invention, a ground fault can be detected more reliably.

FIG. 1 is a diagram showing a schematic configuration of a DC voltage supply circuit according to a first embodiment of the present invention. FIG. 2 is a diagram showing a configuration of the DC voltage supply circuit according to the first embodiment of the present invention. FIG. 3 is a diagram showing an example of a ground fault in the DC voltage supply circuit shown in FIG. FIG. 4 is a diagram showing another example of the ground fault in the DC voltage supply circuit shown in FIG. FIG. 5 is a diagram showing the configuration of a modeled circuit for obtaining the magnitude of the ground fault current of the DC voltage supply circuit in FIGS. 3 and 4. FIG. 6 is a diagram showing a configuration of a DC circuit obtained by modifying the DC circuit of FIG. FIG. 7 is a diagram illustrating replacement of the DC circuit illustrated in FIG. 6 with an equivalent circuit. FIG. 8 is a diagram for explaining the magnitude of the ground fault current in the DC voltage supply circuit according to the first embodiment of the present invention. FIG. 9 is a diagram illustrating an example of setting a threshold used by the ground fault detection circuit according to the first embodiment of the present invention for ground fault detection. FIG. 10 is a diagram illustrating another example of setting of a threshold used by the ground fault detection circuit according to the first embodiment of the present invention for ground fault detection. FIG. 11 is a diagram illustrating a configuration in which the DC voltage supply circuit according to the first embodiment of the present invention includes a noise filter. FIG. 12 is a diagram showing a configuration of a DC voltage supply circuit according to the second embodiment of the present invention. FIG. 13 is a diagram showing an example of a ground fault in the DC voltage supply circuit shown in FIG. FIG. 14 is a diagram showing a configuration of a DC voltage supply circuit according to the third embodiment of the present invention. FIG. 15 is a diagram illustrating an example of a ground fault in the DC voltage supply circuit illustrated in FIG. 14.

  First, the contents of the embodiment of the present invention will be listed and described.

  (1) A DC voltage supply circuit according to an embodiment of the present invention includes: a plurality of DC circuits each having a positive side line and a negative side line connected to each other; an intermediate node between the positive side line and the negative side line; A ground fault detection circuit that detects a current flowing between a reference potential node of the circuit and the voltage of the intermediate node is smaller than the absolute value of the absolute value of the input voltage or the output voltage of each DC circuit. Is set to be a small absolute value.

  With such a configuration, since each positive side line and each negative side line in a plurality of DC circuits have voltages different from the reference potential node, a ground fault occurs in any location of each of the positive side line and each negative side line. Even in this case, a ground fault current flows between the ground fault location and the reference potential node. Therefore, a ground fault can be detected more reliably.

  (2) Preferably, the ground fault detection circuit includes a first resistor electrically connected to the positive side line, a second resistor electrically connected to the negative side line, and the first resistor. And a third resistor connected between the second resistor and the reference potential node.

  With such a configuration, a ground fault can be detected more reliably with a simple circuit.

  (3) Preferably, the DC voltage supply circuit further includes a voltage conversion circuit that is provided corresponding to the DC circuit and converts the voltage of the corresponding DC circuit, and the ground fault detection circuit includes the voltage The conversion circuit is electrically connected to the opposite side of the DC circuit.

  With such a configuration, a plurality of DC circuits having different input voltages or output voltages can be connected to a common ground fault detection circuit, and both the positive side line and the negative side line in each DC circuit are connected to the reference potential node. Since the voltages are different, the ground fault can be detected more reliably even when a ground fault occurs at any location of each positive side line and each negative side line.

  (4) More preferably, in the voltage conversion circuit, the circuit on the DC circuit side and the circuit on the ground fault detection circuit side are not electrically insulated.

  With such a configuration, even if the circuit on the DC circuit side has a ground fault, current flows between the ground fault location and the ground through the ground fault detection circuit, and both the positive side line and the negative side line in each DC circuit are Since the voltage is different from the reference potential node, it is possible to detect the ground fault more reliably even when a ground fault occurs at any location of each positive side line and each negative side line.

  (5) In the ground fault detection circuit according to the embodiment of the present invention, the first connection node in which the positive side lines of the plurality of DC circuits are electrically connected to the negative side line of each of the DC circuits is electrically connected. And a current detection circuit for detecting a current flowing between the first connection node, an intermediate node between the second connection nodes, and a reference potential node of each of the DC circuits. The voltage at the intermediate node is set to an absolute value smaller than the minimum absolute value of the absolute values of the input voltage or output voltage of each DC circuit.

  With such a configuration, since each positive side line and each negative side line of the plurality of DC circuits has a voltage different from the reference potential node, a ground fault occurs at any location of each of the positive side line and each negative side line. Even in this case, a ground fault current flows between the ground fault location and the reference potential node. Therefore, a ground fault can be detected more reliably.

  The present invention can be realized not only as a DC voltage supply circuit or a ground fault detection circuit including such a characteristic processing unit, but also as a method using such characteristic processing as a step, It can be realized as a program to be executed by a computer. Further, it can be realized as a semiconductor integrated circuit that realizes part or all of the DC voltage supply circuit or the ground fault detection circuit, or can be realized as a system including the DC voltage supply circuit or the ground fault detection circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated. Moreover, you may combine arbitrarily at least one part of embodiment described below.

<First Embodiment>
[Configuration and basic operation]
FIG. 1 is a diagram showing a schematic configuration of a DC voltage supply circuit according to a first embodiment of the present invention.

  Referring to FIG. 1, DC voltage supply circuit 10 supplies a voltage to load unit 9. The DC voltage supply circuit 10 includes DC circuits 1 and 2, a ground fault detection circuit 4, and voltage conversion circuits 5 and 6. The load unit 9 includes an inverter 91 and a load 92.

  The DC circuits 1 and 2 are, for example, DC circuits including a solar cell module or a storage battery. For example, the voltage conversion circuit 5 receives a DC voltage from the DC circuit 1, converts the level of the received DC voltage, and supplies it to the load unit 9. For example, the voltage conversion circuit 6 receives a DC voltage from the DC circuit 2, converts the level of the received voltage, and supplies it to the load unit 9. The output side of the voltage conversion circuit 5 and the output side of the voltage conversion circuit 6 are connected to each other.

  For example, when the DC circuit 2 is a circuit including a storage battery and the storage battery is charged, the voltage conversion circuit 6 converts the level of the DC voltage received from the voltage conversion circuit 5 and converts the storage battery. May be supplied.

  The ground fault detection circuit 4 is disposed between the voltage conversion circuit 5 and the voltage conversion circuit 6 and the load unit 9, and is connected between the output side of the voltage conversion circuit 5 and the voltage conversion circuit 6 and the ground. When a ground fault occurs in the DC voltage supply circuit 10, the ground fault detection circuit 4 detects a ground fault based on the current flowing through itself.

  The ground fault detection circuit 4 is not arranged between the voltage conversion circuit 5 and the voltage conversion circuit 6 and the load unit 9, but between the DC circuit 1 and the voltage conversion circuit 5, and between the DC circuit 2 and the voltage conversion. A configuration in which the circuit 6 and the circuit 6 are arranged is also conceivable. However, the configuration in which the ground fault detection circuit 4 is arranged between the voltage conversion circuit 5 and the voltage conversion circuit 6 and the load unit 9 can reduce the number of parts, and can reduce costs, for example.

  FIG. 2 is a diagram showing a configuration of the DC voltage supply circuit according to the first embodiment of the present invention.

  Referring to FIG. 2, DC circuit 1 includes a DC power supply E14. The DC circuit 2 includes a DC power supply E24. DC power supply E14 and DC power supply E24 are, for example, solar cell modules or storage batteries.

  Voltage conversion circuit 5 includes a capacitor C15, an inductor L16, a switch SW17, a diode D18, and a capacitor C29. The switch SW17 is a switch element such as a transistor or FET.

  Voltage conversion circuit 6 includes a capacitor C25, an inductor L26, a switch SW27, a diode D28, and a capacitor C29. The switch SW27 is a switch element such as a transistor or an FET.

  The ground fault detection circuit 4 includes a resistor (first resistor) R31, a resistor (second resistor) R32, and a current detection circuit 36. The current detection circuit 36 includes a resistor (third resistor) R33, a voltage measuring unit 34, and an alarm unit 35.

  The ground fault detection circuit 4 is electrically connected to the side opposite to the DC circuit 1 of the voltage conversion circuit 5 and to the side opposite to the DC circuit 2 of the voltage conversion circuit 6.

  Hereinafter, “connected” of a circuit or a circuit element includes not only a state in which they are directly connected but also a state in which they are electrically connected via another circuit or circuit element.

  In the voltage conversion circuit 5, the positive side end of the DC power supply E14, the first end of the capacitor C15, and the first end of the inductor L16 are connected. The negative side end of the DC power supply E14, the second end of the capacitor C15, and the second end of the switch SW17 are connected. The second end of the inductor L16, the first end of the switch SW17, and the anode of the diode D18 are connected. The cathode of the diode D18 and the first end of the capacitor C29 are connected. The second end of the switch SW17 and the second end of the capacitor C29 are connected. The first end of the capacitor C29 is connected to the positive side end of the load section 9. A second end of the capacitor C <b> 29 is connected to the negative side end of the load unit 9.

  In the voltage conversion circuit 6, the positive side end of the DC power source E24, the first end of the capacitor C25, and the first end of the inductor L26 are connected. The negative side end of the DC power supply E24, the second end of the capacitor C25, and the second end of the switch SW27 are connected. The second end of the inductor L26, the first end of the switch SW27, and the anode of the diode D28 are connected. The cathode of the diode D28 and the first end of the capacitor C29 are connected. The second end of the switch SW27 and the second end of the capacitor C29 are connected.

  The voltage conversion circuit 5 is provided corresponding to the DC circuit 1, and converts the output voltage of the DC circuit 1 by switching the switch SW17.

  The voltage conversion circuit 6 is provided corresponding to the DC circuit 2 and converts the output voltage of the DC circuit 2 by switching the switch SW27.

  More specifically, for example, in the voltage conversion circuit 5, the inductor L16 accumulates energy by increasing the current flowing through the inductor L16 when the switch SW17 is turned on. The energy stored in the inductor L16 is discharged to the capacitor C29 through the diode D18 when the switch SW17 is turned off, and charges the capacitor C29. Thereby, the voltage conversion circuit 5 can convert the DC voltage received from the DC circuit 1 into a DC voltage of a predetermined level and output it. The same applies to the voltage conversion circuit 6.

  In the voltage conversion circuit 5, the circuit on the DC circuit 1 side and the circuit on the ground fault detection circuit 4 side are not electrically insulated. In the voltage conversion circuit 6, the circuit on the DC circuit 2 side and the circuit on the ground fault detection circuit 4 side are not electrically insulated. That is, the voltage conversion circuit 5 and the voltage conversion circuit 6 are non-insulated voltage conversion circuits.

  Hereinafter, the wiring that is connected to the positive output terminal of the DC circuit 1 and has the same potential as the positive output terminal of the DC circuit 1 is also referred to as a positive line of the DC circuit 1. A wire connected to the negative output terminal of the DC circuit 1 and having the same potential as the negative output terminal of the DC circuit 1 is also referred to as a negative line of the DC circuit 1.

  The wiring connected to the positive output terminal of the DC circuit 2 and having the same potential as the positive output terminal of the DC circuit 2 is also referred to as a positive line of the DC circuit 2. The wiring connected to the negative output terminal of the DC circuit 2 and having the same potential as the negative output terminal of the DC circuit 2 is also referred to as a negative line of the DC circuit 2.

  The positive side lines of the DC circuit 1 and the DC circuit 2 are connected to each other. Specifically, the positive side lines of the DC circuit 1 and the DC circuit 2 are connected to each other via the voltage conversion circuit 5 and the voltage conversion circuit 6. Further, the negative side lines of the DC circuit 1 and the DC circuit 2 are connected to each other.

  The resistor R31 is electrically connected to the positive side line. More specifically, the first end of the resistor R31 is connected to the positive side line of the DC circuit 1 via the voltage conversion circuit 5, and is connected to the positive side line of the DC circuit 2 via the voltage conversion circuit 6. ing.

  The first end of the resistor R31 is connected to the positive side line of the DC circuit 1 and the positive side line of the DC circuit 2 at a connection node (first connection node) N41. That is, the connection node N41 is electrically connected to the positive side lines of the DC circuit 1 and the DC circuit 2. More specifically, the connection node N41 is connected to the positive side line of the DC circuit 1 via the voltage conversion circuit 5, and is connected to the positive side line of the DC circuit 2 via the voltage conversion circuit 6. The connection node N41 is, for example, a connection point of a cable connection terminal or a printed circuit board wiring. The connection node N41 is included in the ground fault detection circuit 4.

  The resistor R32 is electrically connected to the negative side line. More specifically, the first end of the resistor R32 is connected to the negative side line of the DC circuit 1 through the voltage conversion circuit 5, and is connected to the negative side line of the DC circuit 2 through the voltage conversion circuit 6. ing.

  The first end of the resistor R32 is connected to the negative side line of the DC circuit 1 and the negative side line of the DC circuit 2 at a connection node (second connection node) N42. That is, the connection node N42 is electrically connected to the negative side lines of the DC circuit 1 and the DC circuit 2. More specifically, the connection node N42 is connected to the negative side line of the DC circuit 1 through the voltage conversion circuit 5, and is connected to the negative side line of the DC circuit 2 through the voltage conversion circuit 6. The connection node N42 is, for example, a connection point of a cable connection terminal or a printed circuit board wiring. Further, the connection node N42 is included in the ground fault detection circuit 4.

  The second end of the resistor R31 and the second end of the resistor R32 are connected at an intermediate node that is an intermediate node between the positive side line and the negative side line. The voltage between the positive side line and the negative side line is divided by the resistor R31 and the resistor R32. Therefore, the voltage of the intermediate node is a voltage between the voltage of the positive side line and the voltage of the negative side line. The intermediate node is, for example, a connection point of a cable connection terminal or a printed circuit board wiring.

  The resistor R33 is connected between the resistors R31 and R32 and the reference potential node N44 of the DC voltage supply circuit 10. More specifically, the second end of the resistor R31, the second end of the resistor R32, and the first end of the resistor R33 are connected at the intermediate node N43. The second end of the resistor R33 and the reference potential node N44 are connected.

  The reference potential node N44 is connected to, for example, the ground, and serves as a reference potential for the DC circuits 1 and 2, the ground fault detection circuit 4, the voltage conversion circuits 5 and 6, and the load unit 9.

  The first end of the voltage measurement unit 34 is connected to the intermediate node N43, and the second end of the voltage measurement unit 34 is connected to the reference potential node N44.

  The current detection circuit 36 detects a current flowing between the intermediate node N43 and the reference potential node N44, that is, a current flowing through the resistor R33. More specifically, the voltage measurement unit 34 measures the voltage at both ends of the resistor R33 that is generated when a current flows through the resistor R33, and outputs the measurement result to the alarm unit 35. The alarm unit 35 determines whether or not a ground fault has occurred based on the measurement result of the voltage across the resistor R33 received from the voltage measurement unit 34. When it is determined that a ground fault has occurred, an alarm is issued.

  For example, the current detection circuit 36 detects a ground fault using a predetermined threshold value. Specifically, for example, the alarm unit 35 compares the measurement result of the voltage across the resistor R33 received from the voltage measurement unit 34 with a predetermined threshold, and detects a ground fault based on the comparison result.

  FIG. 3 is a diagram showing an example of a ground fault in the DC voltage supply circuit shown in FIG.

  Referring to FIG. 3, the negative side line of DC circuit 2 is grounded. More specifically, the negative side end of the DC power supply E24 is connected to the reference potential node N44 via the ground fault resistor R50.

  Thus, when the negative side line of the DC circuit 2 is grounded, the ground fault current I1 flows from the reference potential node N44 through the ground fault resistor 50 to the negative side line of the DC circuit 2. Specifically, for example, the ground fault current I1 is output from the DC power source E24, flows through the resistor R31 and the resistor R33 to the reference potential node N44, and passes from the reference potential node N44 through the ground fault resistor R50 to the DC power source E24. Return to.

  At this time, a potential difference is generated at both ends of the resistor R33 due to the ground fault current I1. The current detection circuit 36 detects a ground fault based on the potential difference generated at both ends of the resistor R33.

  FIG. 4 is a diagram showing another example of the ground fault in the DC voltage supply circuit shown in FIG.

  Referring to FIG. 4, the positive side line of DC circuit 2 is grounded. Specifically, the positive side end of the DC power supply E24 is connected to the reference potential node N44 via the ground fault resistor R50.

  Thus, when the positive side line of the DC circuit 2 has a ground fault, the ground fault current I2 flows from the positive side line of the DC circuit 2 through the ground fault resistor R50 to the reference potential node N44. Specifically, for example, the ground fault current I2 is output from the DC power source E24, flows through the ground fault resistor R50 to the reference potential node N44, and from the reference potential node N44 through the resistors R33 and R32, the DC power source E24. Return to.

  At this time, a potential difference is generated at both ends of the resistor R33 due to the ground fault current I2. The current detection circuit 36 detects a ground fault based on the potential difference generated at both ends of the resistor R33.

  Here, there is no ground fault in any part of the DC voltage supply circuit 10, and the absolute value of the output voltage of the DC power supply E14, that is, the absolute value of the potential difference between both ends of the DC power supply E14 is 50V. The absolute value of the output voltage of the power supply E24, that is, the absolute value of the potential difference between both ends of the DC power supply E24 is 100V, the absolute value of the voltage applied to the load unit 9 is 200V, and the resistance values of the resistors R31 and R32 are Consider the case of 40 kΩ and the resistance value of the resistor R33 is 1 kΩ. Hereinafter, unless otherwise indicated in the text, the potential of the reference potential node N44 is set to zero volts.

  When no part of the DC voltage supply circuit 10 is grounded, no current flows between the intermediate node N43 and the reference potential node N44. That is, since no current flows through the resistor R33, the voltage at the intermediate node N43 is zero volts.

  Since the resistance values of the resistor R31 and the resistor R32 are the same, and the absolute value of the voltage applied to the load unit 9 is 200V, the voltage of the connection node N41 is 100V, and the voltage of the connection node N42 is minus 100V. .

  The voltage at the negative end of the DC power supply E24 is minus 100 V because it is the same as the voltage at the connection node N42.

  Since the voltage at the negative end of the DC power supply E24 is minus 100V, and the absolute value of the output voltage of the DC power supply E24 is 100V, the voltage at the positive end of the DC power supply E24 is the voltage at the negative end of the DC power supply E24. Zero volts higher than 100V. That is, the positive side end of the DC power supply E24 has the same potential as the reference potential node N44.

  In this case, for example, as shown in FIG. 4, even if the positive side line of the DC circuit 2 has a ground fault, since the positive side end of the DC power supply E24 has the same potential as the reference potential node N44, the ground fault current I2 flows. Absent. That is, even if the positive side line of the DC circuit 2 is grounded, the ground side current I2 does not flow through the resistor R33 because the positive side line of the DC circuit 2 and the intermediate node N43 are at the same potential.

  Therefore, since a potential difference does not occur at both ends of the resistor R33, the current detection circuit 36 cannot detect a ground fault.

  In other words, current detection circuit 36 may not be able to detect a ground fault when the absolute value of the voltage at the ground fault location is the same as the absolute value of the potential difference between intermediate node N43 and the negative side line.

  Therefore, in the DC voltage supply circuit 10, the circuit constant of the ground fault detection circuit 4 is set so that the voltage measuring unit 34 can detect the ground fault more reliably when a ground fault occurs. Specifically, in a state where there is no ground fault, the voltage of the intermediate node N43 with respect to the negative side line, that is, the potential difference between the intermediate node N43 and the negative side line is the absolute value of the output voltage of the DC circuit 1 and the DC circuit 2. The absolute value is set to be smaller than the smallest absolute value.

  More specifically, for example, as described above, the absolute value of the output voltage of the DC power supply E14 is 50V, and the absolute value of the output voltage of the DC power supply E24 is 100V. The resistance values of the resistor R31 and the resistor R32 are set so that the absolute value of the potential difference between the intermediate node N43 and the negative side line is smaller than 50 V when none of the locations is grounded.

Here, in a state where no part of the DC voltage supply circuit 10 is grounded, the absolute value of the potential difference between the intermediate node N43 and the negative side line is | Vn |, and the absolute value of the voltage applied to the load unit 9 is When | Vz | is assumed and the resistance values of R31 and R32 are Ra31 and Ra32, respectively, the absolute value | Vn | of the potential difference between the intermediate node N43 and the negative side line is expressed by the following equation.
| Vn | = | Vz | × Ra32 / (Ra31 + Ra32)

  For example, when the absolute value | Vz | of the voltage applied to the load unit 9 is 200 V, when the resistance value Ra31 is set to 82 kΩ and the resistance value Ra32 is set to 12 kΩ, the intermediate node N43 is obtained from the above equation. The absolute value | Vn | of the potential difference between the negative line and the negative side line is about 25.5V, which is smaller than the absolute value of the output voltage of the DC power supply E14, 50V.

  At this time, the voltage of the intermediate node N43 is zero volts, and the absolute value of the potential difference between the intermediate node N43 and the negative side line is 25.5V. Therefore, the voltage of the negative side line is minus 25.5V lower than the voltage of the intermediate node N43. 25.5V.

  Since the voltage at the negative side end of the DC power supply E24 is the same as the voltage at the negative side line, it is minus 25.5V.

  Since the absolute value of the output voltage of the DC power supply E24 is 100V, the voltage at the positive side end of the DC power supply E24 is 74.5V, which is 100V higher than the voltage at the negative side end of the DC power supply E24.

  Further, the voltage at the negative side end of the DC power supply E14 is the same as the voltage at the negative side line, and is minus 25.5V.

  Since the absolute value of the output voltage of the DC power supply E14 is 50V, the voltage on the positive side end of the DC power supply E14 is 24.5V, which is 50V higher than the voltage on the negative side end of the DC power supply E14.

  Thus, for example, the resistance R31 and the resistance R32 are set such that the absolute value of the potential difference between the intermediate node N43 and the negative side line is smaller than the minimum value among the absolute values of the output voltages of the DC circuit 1 and the DC circuit 2. By setting the resistance value, it is possible to prevent the voltages at the positive side end of the DC power supply E14 and the positive side end of the DC power supply E24 from becoming the same zero volt as the reference potential node N44.

  As a result, even when the positive side line of the DC circuit 1 or the DC circuit 2 has a ground fault, a ground fault current flows through the ground fault location, the reference potential node N44 and the resistor R33, and a potential difference occurs between both ends of the resistor R33. The current detection circuit 36 can detect the ground fault current more reliably. That is, the ground fault detection circuit 4 can detect a ground fault more reliably when a ground fault occurs in the DC voltage supply circuit 10.

  When the output voltages of DC circuit 1 and DC circuit 2 vary, that is, when the absolute values of the output voltages of DC circuit 1 and DC circuit 2 vary, the absolute value of the potential difference between intermediate node N43 and the negative side line. However, the resistance values of the resistor R31 and the resistor R32 are set so as to be smaller than the minimum value in the fluctuation range of the absolute value of the output voltage of the DC circuit 1 and the DC circuit 2.

  FIG. 5 is a diagram showing the configuration of a modeled circuit for obtaining the magnitude of the ground fault current of the DC voltage supply circuit in FIGS. 3 and 4.

  Referring to FIG. 5, DC circuit 290 includes a resistor R31, a resistor R32, a resistor R33, a ground fault resistor R50, and a DC power supply E190.

  The positive side end of the DC power supply E190 is connected to the first end of R31. The negative side end of the DC power supply E190 is connected to the positive side end of the resistor R32 via a negative side line. The second ends of the resistor R31 and the resistor R32 are connected to the first end of the resistor R33 at the intermediate node N43. The second end of the resistor R33 is connected to the second end of the ground fault resistor R50 via the reference potential node N44.

  The connection point X corresponds to a connection point between the DC voltage supply circuit 10 and the ground fault resistor R50 in FIGS. 3 and 4, that is, a ground fault point of the DC voltage supply circuit 10. Vx is a voltage at the connection point X with respect to the negative side line. Vdc is a voltage output from the DC power supply E190, and corresponds to the voltage applied to the load unit 9 in FIGS. A voltage Vdc is applied between the connection node N41 and the connection node N42. Further, the ground fault current I9 corresponds to the ground fault current I1 or I2 in FIG. 3 or FIG. 4, and flows through the resistor R33 from the first end side to the second end side of the resistor R33.

  FIG. 6 is a diagram showing a configuration of a DC circuit obtained by modifying the DC circuit of FIG.

  Referring to FIG. 6, DC circuit 291 further includes a DC power supply E191 between connection point X and the negative side line, as compared with DC circuit 290 shown in FIG. 5. The positive end of the DC power supply E191 is connected to the first end of the ground fault resistor R50 at the connection point X. The negative side end of the DC power supply E191 is connected to the negative side line. The DC power supply E191 outputs a voltage Vx. Connection of each circuit element other than the DC power supply E191 in the DC circuit 291 is the same as the connection of each circuit element in the DC circuit 290.

  Hereinafter, the resistance values of the resistors R31, R32, and R33 are referred to as resistance values Ra31, Ra32, and Ra33, respectively, and the resistance value of the ground fault resistor R50 is referred to as Ra50.

  FIG. 7 is a diagram illustrating replacement of the DC circuit illustrated in FIG. 6 with an equivalent circuit.

  FIG. 7A shows a configuration of an equivalent circuit derived from the DC circuit 291 of FIG. FIG. 7B shows a configuration of an equivalent circuit derived from the circuit of FIG. FIG. 7C shows a configuration of an equivalent circuit derived from the circuit of FIG. FIG. 7 (d) shows an equivalent circuit derived from the circuit of FIG. 7 (c).

  Referring to FIG. 7A, equivalent circuit 292 includes a resistor R31, a resistor R32, a DC power supply E190, a DC power supply E191, and a resistor R195.

  In the equivalent circuit 292, the positive side end of the DC power supply E190 and the first end of the resistor R31 are connected. A second end of the resistor R31, a first end of the resistor R32, and a first end of the resistor R195 are connected. A second end of the resistor R195 and the positive side end of the DC power supply E191 are connected. The negative side end of the DC power supply E190, the second end of the resistor R32, and the negative side end of the DC power supply E191 are connected. The ground fault current I9 flows through the resistor R195 from the first end side to the second end side of the resistor R195.

The resistor R195 represents the resistor R33 and the ground fault resistor R50 connected in series in the circuit shown in FIG. 6 as a single resistor. Therefore, when the resistance value of the resistor R195 is Ra195, the resistance value Ra195 is expressed by the following equation.
Ra195 = Ra33 + Ra50

  Referring to FIG. 7B, the equivalent circuit 293 includes a DC current source g1, a DC power source E191, a resistor R31, a resistor R32, and a resistor R195.

  In the equivalent circuit 293, the positive side end of the direct current source g1, the first end of the resistor R31, the first end of the resistor R32, and the first end of the resistor R195 are connected. A second end of the resistor R195 and the positive side end of the DC power supply E191 are connected. The negative side end of the direct current source g1, the second end of the resistor R31, the second end of the resistor R32, and the negative side end of the direct current power source E191 are connected. The ground fault current I9 flows through the resistor R195 from the first end side to the second end side of the resistor R195.

The DC current source g1 and the resistor R31 connected in parallel are equivalently converted from the DC power source E190 and the resistor R31 connected in series in FIG. Therefore, when the output current of the DC current source g1 is Ig, the current Ig is expressed by the following equation.
Ig = Vdc / Ra31

  Referring to FIG. 7C, the equivalent circuit 294 includes a DC current source g1, a DC power supply E191, a resistor R195, and a resistor R196.

  In the equivalent circuit 294, the positive side end of the direct current source g1, the first end of the resistor R196, and the first end of the resistor R195 are connected. The positive side end of the DC power supply E191 and the second end of the resistor R195 are connected. The negative side end of the direct current source g1, the second end of the resistor R196, and the negative side end of the direct current power source E191 are connected. The ground fault current I9 flows through the resistor R195 from the first end side to the second end side of the resistor R195.

The resistor R196 represents the resistors R31 and R32 connected in parallel in FIG. 7B as one resistor. Accordingly, when the resistance value of the resistor R196 is Ra196, the resistance value Ra196 is expressed by the following equation.
Ra196 = Ra31 × Ra32 / (Ra31 + Ra32)

  Referring to FIG. 7D, equivalent circuit 295 includes DC power supply E191, DC power supply E192, resistor R195, and resistor R196.

  In the equivalent circuit 295, the positive side end of the DC power supply E192 and the first end of the resistor R196 are connected. A second end of the resistor R196 and a first end of the resistor R195 are connected. A second end of the resistor R195 and the positive side end of the DC power supply E191 are connected. The negative side end of the DC power source E192 and the negative side end of the DC power source E191 are connected. The ground fault current I9 flows through the resistor R195 from the first end side to the second end side of the resistor R195.

The DC power supply E192 and the resistor R196 connected in series are equivalently converted from the DC current source g1 and the resistor R196 connected in parallel in FIG. 7C. Therefore, when the output voltage of the DC power supply E192 is Vw, the voltage Vw is expressed by the following equation.
Vw = Ig × Ra196
= Vdc × Ra32 / (Ra31 + Ra32)

From the above, the ground fault current I9 is expressed by the following equation (1).

The resistance values Ra31, Ra32, and Ra33 are constant because they are the resistance values of the resistors R31, R32, and R33, respectively. Furthermore, assuming that voltage Vdc and resistance value Ra50 are constant, ground fault current I9 is expressed by the following equation. Here, a and b are constants.
I9 = −a × Vx + b

  That is, when voltage Vdc and resistance value Ra50 are constant, ground fault current I9 is expressed by a linear expression of voltage Vx.

  FIG. 8 is a diagram for explaining the magnitude of the ground fault current in the DC voltage supply circuit according to the first embodiment of the present invention.

  The graph G1 and the graph G2 show the relationship between the ground fault current I9 and the voltage Vx when the voltage Vdc and the resistance value Ra50 in Equation (1) are set to constant values. The graph G1 and the graph G2 have the same voltage Vdc and different resistance values Ra50.

  The gradients of the graph G1 and the graph G2 decrease as the resistance value Ra50 increases. The graph G1 shows the relationship between the ground fault current I9 and the voltage Vx when the resistance value Ra50 is 20 kΩ, for example. Graph G2 shows the relationship between ground fault current I9 and voltage Vx when resistance value Ra50 is 1 MΩ, for example.

  Referring to graph G1, ground fault current I9 is level h11 when Vx = 0, and decreases as Vx increases. The ground fault current I9 becomes zero ampere when Vx = Vxc, and becomes the level h14 when Vx = Vxp.

  The level h11 is a level of the ground fault current I9 when the negative side line has a ground fault. The level h14 is the level of the ground fault current I9 when the positive side line of the voltage Vxp has a ground fault.

  Referring to graph G2, ground fault current I9 is level h12 when Vx = 0, and decreases as Vx increases. The ground fault current I9 becomes zero ampere when Vx = Vxc, and becomes the level h13 when Vx = Vxp.

  The level h12 is the level of the ground fault current I9 when the negative side line has a ground fault. Further, the level h13 is the level of the ground fault current I9 when the location of the voltage Vxp in the circuit is grounded.

The voltage Vx when I9 = 0, that is, the voltage Vxc is expressed by the following equation (2) based on the equation (1).
Vx = Vdc × Ra32 / (Ra31 + Ra32) (2)

  From Equation (2), for example, in the DC circuit 291 shown in FIG. 6, when the voltage at the connection point X is equal to the voltage at the connection point of the resistor R31 and the resistor R32 with respect to the negative side line, the ground fault current I9 is You can see that it doesn't flow.

  Referring to FIGS. 3 and 4 again, the ground fault current I1 that flows through the resistor R33 when the negative side line is grounded and the ground fault current I2 that flows through the resistor R33 when the positive side line is grounded are flowing directions. Is the opposite. Therefore, in the DC circuit 291 shown in FIG. 6, the direction in which the ground fault current I9 flows is opposite in the case where the negative side line is grounded and in the case where the positive side line is grounded.

  Here, when the alarm unit 35 shown in FIG. 3 and FIG. 4 detects a ground fault using the threshold value as described above, the alarm unit 35, for example, uses the first threshold value corresponding to the ground fault current I1 and the ground level. A second threshold value corresponding to the leakage current I2 is used.

  More specifically, the alarm unit 35 generates a ground fault when the ground fault current I1 flowing from the intermediate node N43 toward the reference potential node N44 is larger than the first threshold, or when the ground fault current flows from the reference potential node N44 toward the intermediate node N43. When the current I2 is larger than the second threshold, it is determined that a ground fault has occurred in the DC voltage supply circuit 10. For example, the absolute value of the first threshold level is the same as the absolute value of the second threshold level.

  In FIG. 6, the first threshold corresponds to the case where the ground fault current I9 is positive, and the second threshold corresponds to the case where the ground fault current I9 is negative. In FIG. 8, for example, when the first threshold is set to level h11 and the second threshold is set to level h14, a ground fault is detected when the ground fault current I9 is equal to or higher than level h11 or lower than level h14. Is done.

  FIG. 9 is a diagram illustrating an example of setting a threshold used by the ground fault detection circuit according to the first embodiment of the present invention for ground fault detection.

  The graph G3 and the graph G4 show the relationship between the ground fault current I9 and the voltage Vx when the voltage Vdc and the resistance value Ra50 in the expression (1) are constant values. The graph G3 and the graph G4 have different voltages Vdc and equal resistance values Ra50.

  The graph G3 and the graph G4 move in parallel in the direction in which the ground fault current I9 increases as the voltage Vdc increases. Specifically, for example, the graph G3 moves to the position of the graph G4 when the parameter voltage Vdc is increased by a certain value.

  Referring to graph G3, ground fault current I9 is level h22 when Vx = 0, and decreases as Vx increases. The ground fault current I9 becomes zero ampere when Vx = Vx3, and becomes the level h24 when Vx = Vxp.

  The level h22 is a level of the ground fault current I9 when the negative side line is grounded. The level h24 is the level of the ground fault current I9 when the positive side line of the voltage Vxp has a ground fault.

  Referring to graph G4, ground fault current I9 is level h21 when Vx = 0, and decreases as Vx increases. The ground fault current I9 becomes zero ampere when Vx = Vx4 and becomes level h23 when Vx = Vxp.

  The level h21 is a level of the ground fault current I9 when the negative side line is grounded. The level h23 is the level of the ground fault current I9 when the positive side line of the voltage Vxp has a ground fault.

  Since the value of the ground fault current I9 also changes when the voltage Vdc changes, the first threshold value and the second threshold value may be set in consideration of the change in the voltage Vdc. Specifically, each threshold value is set so that a ground fault can be reliably detected even when Vdc changes. For example, when the ground fault current I9 changes in a range between the graph G3 and the graph G4, the first threshold is set to h22 and the second threshold is set to h23.

  FIG. 10 is a diagram illustrating another example of setting of a threshold used by the ground fault detection circuit according to the first embodiment of the present invention for ground fault detection.

  The graph shows the relationship between the ground fault current I9 and the voltage Vx when the voltage Vdc and the resistance value Ra50 in Equation (1) are set to constant values.

  Referring to the graph, ground fault current I9 is level h31 when Vx = 0, and decreases as Vx increases. The ground fault current I9 becomes level h32 when Vx = Vxp1, and becomes level h33 when Vx = Vxp2.

  The level h31 is the level of the ground fault current I9 when the negative side line has a ground fault. The level h32 is the level of the ground fault current I9 when the voltage at the ground fault location on the positive side line is Vxp1. The level h33 is the level of the ground fault current I9 when the voltage at the ground fault location on the positive side line is Vxp2.

  When the voltage at the ground fault location changes, the second threshold value may be set in consideration of the change in Vx. For example, when the voltage at the ground fault location changes in the range from Vxp1 to Vxp2, the second threshold value is set to the level h32 corresponding to Vxp1.

  FIG. 11 is a diagram illustrating a configuration in which the DC voltage supply circuit according to the first embodiment of the present invention includes a noise filter.

  Referring to FIG. 11, DC voltage supply circuit 13 further includes noise filter 120 between DC circuit 2 and voltage conversion circuit 6, compared to DC voltage supply circuit 10 shown in FIG. 2.

  Noise filter 120 includes capacitors C141, C142, C143, and C144, and inductors L145 and L146.

  In the noise filter 120, the first end of the capacitor C141, the first end of the capacitor C143, the first end of the inductor L145, and the positive side end of the DC power supply E24 in the DC circuit 2 are connected. The first end of the capacitor C142, the second end of the capacitor C143, the first end of the inductor L146, and the negative end of the DC power supply E24 in the DC circuit 2 are connected. The second end of the inductor L146, the second end of the capacitor C144, and the second end of the capacitor C25 in the voltage conversion circuit 6 are connected. The second end of the inductor L145, the first end of the capacitor C144, and the first end of the capacitor C25 in the voltage conversion circuit 6 are connected. A second end of capacitor C141 and a second end of capacitor C142 are connected to reference potential node N44.

  Here, for example, when the output voltage of DC power supply E24 suddenly rises, charging current I10 flows through capacitor C141. Specifically, the charging current I10 is output from the DC power supply E24, flows to the reference potential node N44 through the capacitor C141, and returns from the reference potential node N44 to the DC power supply E24 through the resistor R33, the resistor R32, and the inductor L146. .

  Since the charging current I10 passes through the resistor R33, the current detection circuit 36 may erroneously detect a ground fault.

  However, the charging current I10 flows only for a short time. Therefore, for example, the voltage measurement unit 34 sends the measurement result of the voltage across the resistor R33 to the alarm unit 35 via a low-pass filter. Thereby, the erroneous detection of the ground fault in the current detection circuit 36 can be avoided.

  The voltage measurement unit 34 is not limited to the configuration in which the measurement result of the voltage across the resistor R33 is sent to the alarm unit 35 via the low-pass filter, but is configured to perform an averaging process on the measurement result and send it to the alarm unit 35. Alternatively, the measurement result may be converted to an effective value and sent to the alarm unit 35.

  By the way, in the configuration in which a non-insulated voltage conversion circuit is newly provided between the DC power supply of the circuit shown in FIG. 5 of Patent Document 1 and the ground fault detection circuit, the ground fault detection circuit detects the ground fault. You may not be able to.

  On the other hand, in the DC voltage supply circuit according to the first embodiment of the present invention, the DC circuit 1 and the DC circuit 2 are connected to the positive side line and the negative side line, respectively. The ground fault detection circuit 4 detects a current flowing between the intermediate node N43 between the positive side line and the negative side line and the reference potential node N44 of the DC circuit 1 and the DC circuit 2. The voltage of intermediate node N43 is set to be an absolute value smaller than the minimum absolute value of the absolute values of the output voltages of DC circuit 1 and DC circuit 2.

  With such a configuration, each positive side line and each negative side line in the DC circuit 1 and the DC circuit 2 have a voltage different from that of the reference potential node N44. Even when a fault occurs, a ground fault current flows between the ground fault location and the reference potential node N44. Therefore, a ground fault can be detected more reliably.

  In the DC voltage supply circuit according to the first embodiment of the present invention, in the ground fault detection circuit 4, the resistor R31 is electrically connected to the positive side lines of the DC circuit 1 and the DC circuit 2. Resistor R32 is electrically connected to the negative side lines of DC circuit 1 and DC circuit 2. Resistor R33 is connected between resistors R31 and R32 and reference potential node N44.

  With such a configuration, a ground fault can be detected more reliably with a simple circuit.

  In the DC voltage supply circuit according to the first embodiment of the present invention, the voltage conversion circuit 5 and the voltage conversion circuit 6 are provided corresponding to the DC circuit 1 and the DC circuit 2, respectively. Convert voltage. Ground fault detection circuit 4 is electrically connected to the opposite side of DC circuit 1 and DC circuit 2 of voltage conversion circuit 5 and voltage conversion circuit 6.

  With such a configuration, the DC circuit 1 and the DC circuit 2 having different output voltages can be connected to the ground fault detection circuit 4. In addition, since each positive side line and each negative side line in the DC circuit 1 and the DC circuit 2 have different voltages from the reference potential node N44, a ground fault occurs in any of the positive side line and the negative side line. Even in this case, the ground fault can be detected more reliably.

  In the DC voltage supply circuit according to the first embodiment of the present invention, in the voltage conversion circuit 5 and the voltage conversion circuit 6, a circuit on the DC circuit 1 and DC circuit 2 side, a circuit on the ground fault detection circuit 4 side, Is not electrically isolated.

  With such a configuration, even when a circuit on the DC circuit 1 and DC circuit 2 side has a ground fault, a current caused by the ground fault flows to the ground fault detection circuit 4. In addition, since each positive side line and each negative side line in the DC circuit 1 and the DC circuit 2 have different voltages from the reference potential node N44, a ground fault occurs in any of the positive side line and the negative side line. Even in this case, the ground fault can be detected more reliably.

  In the ground fault detection circuit according to the first embodiment of the present invention, the connection node N41 is electrically connected to each positive side line of the DC circuit 1 and the DC circuit 2. Connection node N42 is electrically connected to each negative side line of DC circuit 1 and DC circuit 2. Current detection circuit 36 detects a current flowing between intermediate node N43 between connection node N41 and connection node N42 and reference potential node N44 of DC circuit 1 and DC circuit 2. Intermediate node N43 is set to have an absolute value smaller than the minimum absolute value of the absolute values of the input voltage or output voltage of DC circuit 1 and DC circuit 2.

  With such a configuration, each of the positive side line and each negative side line of DC circuit 1 and DC circuit 2 has a voltage different from that of reference potential node N44. Therefore, at any location of each positive side line and each negative side line. Even when a ground fault occurs, a ground fault current flows between the ground fault location and the reference potential node N44. Therefore, a ground fault can be detected more reliably.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Second Embodiment>
The present embodiment relates to a DC voltage supply circuit having a configuration of a voltage conversion circuit different from that of the DC voltage supply circuit according to the first embodiment. The contents other than those described below are the same as those of the DC voltage supply circuit according to the first embodiment.

  FIG. 12 is a diagram showing a configuration of a DC voltage supply circuit according to the second embodiment of the present invention.

  Referring to FIG. 12, the DC voltage supply circuit 11 includes a voltage conversion circuit 7 instead of the voltage conversion circuit 5 and a voltage conversion instead of the voltage conversion circuit 6 as compared with the DC voltage supply circuit 10 shown in FIG. A circuit 8 is provided.

  Voltage conversion circuit 7 includes a capacitor C75, an inductor L76, a switch SW77, a diode D78, and a capacitor C89. The switch SW77 is a switch element such as a transistor or FET.

  Voltage conversion circuit 8 includes a capacitor C85, an inductor L86, a switch SW87, a diode D88, and a capacitor C89. The switch SW87 is a switch element such as a transistor or FET.

  The ground fault detection circuit 4 is connected to the side opposite to the DC circuit 1 of the voltage conversion circuit 7 and to the side opposite to the DC circuit 2 of the voltage conversion circuit 8.

  In the voltage conversion circuit 7, the positive side end of the DC power source E14, the first end of the capacitor C75, and the first end of the switch SW77 are connected. A negative side end of DC power supply E14, a second end of capacitor C75, and a first end of inductor L76 are connected. The second end of the inductor L76, the second end of the switch SW77, and the cathode of the diode D78 are connected. The anode of the diode D78 and the second end of the capacitor C89 are connected. The first end of the switch SW77 and the first end of the capacitor C89 are connected. The first end of the capacitor C89 is connected to the positive side end of the load section 9. The second end of the capacitor C89 is connected to the negative side end of the load unit 9.

  In the voltage conversion circuit 8, the positive side end of the DC power supply E24, the first end of the capacitor C85, and the first end of the switch SW87 are connected. A negative side end of DC power supply E24, a second end of capacitor C85, and a first end of inductor L86 are connected. The second end of the inductor L86, the second end of the switch SW87, and the cathode of the diode D88 are connected. The anode of the diode D88 and the second end of the capacitor C89 are connected. The first end of the switch SW87 and the first end of the capacitor C89 are connected.

  The voltage conversion circuit 7 is provided corresponding to the DC circuit 1 and converts the voltage of the DC circuit 1 by switching the switch SW77.

  The voltage conversion circuit 8 is provided corresponding to the DC circuit 2 and converts the voltage of the DC circuit 2 by switching the switch SW87.

  More specifically, for example, in the voltage conversion circuit 7, when the switch SW 77 is turned on, the inductor L 76 increases the current flowing through it and accumulates energy. The energy stored in the inductor L76 is released to the capacitor C89 when the switch SW77 is turned off, and charges the capacitor C89. Thereby, the voltage conversion circuit 7 can convert the DC voltage received from the DC circuit 1 into a DC voltage of a predetermined level and output it. The same applies to the voltage conversion circuit 8.

  In the voltage conversion circuit 7, the circuit on the DC circuit 1 side and the circuit on the ground fault detection circuit 4 side are not electrically insulated. In the voltage conversion circuit 8, the circuit on the DC circuit 2 side and the circuit on the ground fault detection circuit 4 side are not electrically insulated. That is, the voltage conversion circuit 7 and the voltage conversion circuit 8 are non-insulated voltage conversion circuits.

  The positive side lines of the DC circuit 1 and the DC circuit 2 are connected to each other. Further, the negative side lines of the DC circuit 1 and the DC circuit 2 are connected. Specifically, the negative side lines of the DC circuit 1 and the DC circuit 2 are connected via the voltage conversion circuit 7 and the voltage conversion circuit 8.

  The resistor R31 is electrically connected to the positive side line. More specifically, the first end of the resistor R31 is connected to the positive side line of the DC circuit 1 via the voltage conversion circuit 7, and is connected to the positive side line of the DC circuit 2 via the voltage conversion circuit 8. ing.

  The first end of the resistor R31 is connected to the positive side line of the DC circuit 1 and the positive side line of the DC circuit 2 at the connection node N41. That is, the connection node N41 is electrically connected to the positive side lines of the DC circuit 1 and the DC circuit 2. More specifically, the connection node N41 is connected to the positive side line of the DC circuit 1 via the voltage conversion circuit 7, and is connected to the positive side line of the DC circuit 2 via the voltage conversion circuit 8. The connection node N41 is included in the ground fault detection circuit 4.

  The resistor R32 is electrically connected to the negative side line. More specifically, the first end of the resistor R32 is connected to the negative side line of the DC circuit 1 through the voltage conversion circuit 7, and is connected to the negative side line of the DC circuit 2 through the voltage conversion circuit 8. ing.

  The first end of the resistor R32 is connected to the negative side line of the DC circuit 1 and the negative side line of the DC circuit 2 at the connection node N42. That is, the connection node N42 is electrically connected to the negative side lines of the DC circuit 1 and the DC circuit 2. More specifically, the connection node N42 is connected to the negative side line of the DC circuit 1 through the voltage conversion circuit 7, and is connected to the negative side line of the DC circuit 2 through the voltage conversion circuit 8. The connection node N42 is included in the ground fault detection circuit 4.

  The resistor R33 is connected between the resistors R31 and R32 and the reference potential node N44 of the DC voltage supply circuit 10. More specifically, the second end of the resistor R31, the second end of the resistor R32, and the first end of the resistor R33 are connected at the intermediate node N43. The second end of the resistor R33 and the reference potential node N44 are connected.

  The reference potential node N44 is connected to the ground, for example, and serves as a reference potential for the DC circuits 1 and 2, the ground fault detection circuit 4, the voltage conversion circuits 7 and 8, and the load unit 9.

  FIG. 13 is a diagram showing an example of a ground fault in the DC voltage supply circuit shown in FIG.

  Referring to FIG. 13, the negative side line of DC circuit 2 is grounded. Specifically, the negative side end of the DC power supply E24 is connected to the reference potential of the DC voltage supply circuit 11 via the ground fault resistor R50.

  In this way, when the negative side line of the DC circuit 2 is grounded, the ground fault current I3 flows from the reference potential node N44 through the ground fault resistor R50 to the negative side line of the DC circuit 2. Specifically, for example, the ground fault current I3 is output from the DC power source E24, flows through the resistor R31 and the resistor R33 to the reference potential node N44, and passes from the reference potential node N44 through the ground fault resistor R50 to the DC power source E24. Return to.

  At this time, a potential difference is generated at both ends of the resistor R33 due to the ground fault current I3. The current detection circuit 36 detects a ground fault based on the potential difference generated at both ends of the resistor R33.

  Here, there is no ground fault in any part of the DC voltage supply circuit 11, and the absolute value of the output voltage of the DC power supply E14, that is, the absolute value of the potential difference between both ends of the DC power supply E14 is 50V. The absolute value of the output voltage of the power supply E24, that is, the absolute value of the potential difference between both ends of the DC power supply E24 is 100V, the absolute value of the voltage applied to the load unit 9 is 200V, and the resistance values of the resistors R31 and R32 are Consider the case of 40 kΩ and the resistance value of the resistor R33 is 1 kΩ. Hereinafter, unless otherwise indicated in the text, the potential of the reference potential node N44 is set to zero volts.

  When no part of the DC voltage supply circuit 11 is grounded, no current flows between the intermediate node N43 and the reference potential node N44. That is, since no current flows through the resistor R33, the voltage at the intermediate node N43 is zero volts.

  Since the resistance values of the resistor R31 and the resistor R32 are the same, and the absolute value of the voltage applied to the load unit 9 is 200V, the voltage of the connection node N41 is 100V, and the voltage of the connection node N42 is minus 100V. . The voltage at the positive end of the DC power supply E24 is 100 V because it is the same as the voltage at the connection node N41.

  Since the voltage at the positive end of the DC power supply E24 is 100V and the absolute value of the output voltage of the DC power supply E24 is 100V, the voltage at the negative end of the DC power supply E24 is greater than the voltage at the positive end of the DC power supply E24. Zero volts, 100V lower. That is, the negative side end of the DC power supply E24 has the same potential as the reference potential node N44.

  In this case, for example, as shown in FIG. 13, even if the negative side line of the DC circuit 2 is grounded, the ground side current I3 flows because the negative side end of the DC power source E24 is at the same potential as the reference potential node N44. Absent. That is, even if the negative side line of the DC circuit 2 is grounded, the ground side current I3 does not flow through the resistor R33 because the positive side line of the DC circuit 2 and the intermediate node N43 are at the same potential.

  Therefore, since a potential difference does not occur at both ends of the resistor R33, the current detection circuit 36 cannot detect a ground fault.

  That is, the voltage measurement unit 34 may not be able to detect a ground fault when the absolute value of the voltage at the ground fault location is the same as the absolute value of the potential difference between the intermediate node N43 and the positive side line.

  Therefore, in the DC voltage supply circuit 11, the circuit constant of the ground fault detection circuit 4 is set so that the voltage measuring unit 34 can detect the ground fault more reliably when a ground fault occurs. Specifically, in a state where there is no ground fault, the voltage of the intermediate node N43 with respect to the positive side line, that is, the potential difference between the intermediate node N43 and the positive side line is the absolute value of the output voltage of the DC circuit 1 and the DC circuit 2. The absolute value is set to be smaller than the smallest absolute value.

  More specifically, for example, as described above, the absolute value of the output voltage of the DC power supply E14 is 50V, and the absolute value of the output voltage potential difference of the DC power supply E24 is 100V. The resistance values of the resistor R31 and the resistor R32 are set so that the absolute value of the potential difference between the intermediate node N43 and the positive side line is smaller than 50 V when none of the 11 points is grounded.

Here, if the absolute value of the potential difference between the intermediate node N43 and the positive line is | Vm |, the absolute value of the potential difference between both ends of the load section 9 is | Vz |, and the resistance values of R31 and R32 are Rb31 and Rb32, respectively. The absolute value | Vm | of the potential difference between the intermediate node N43 and the positive side line is expressed by the following equation.
| Vm | = | Vz | × Rb31 / (Rb31 + Rb32)

  For example, when the absolute value | Vz | of the voltage applied to the load unit 9 is 200 V, when the resistance value Rb31 is set to 12 kΩ and the resistance value Rb32 is set to 82 kΩ, the intermediate node N43 is obtained from the above equation. The absolute value | Vm | of the potential difference between the positive line and the positive line is about 25.5 V, which is smaller than the absolute value of 50 V of the output voltage of the DC power supply E14.

  At this time, the voltage of the intermediate node N43 is zero volts, and the absolute value of the potential difference between the intermediate node N43 and the positive side line is 25.5V. Therefore, the voltage of the positive side line is 25.5V higher than the voltage of the intermediate node N43. 5V.

  Since the voltage at the positive end of the DC power supply E24 is the same as the voltage at the positive line, it is 25.5V. Since the absolute value of the output voltage of the DC power supply E24 is 100V, the voltage at the negative side end of the DC power supply E24 is minus 74.5V, which is 100V lower than the voltage at the positive side end of the DC power supply E24.

  Further, the voltage at the positive side end of the DC power supply E14 is 25.5V because it is the same as the voltage at the positive side line. Since the absolute value of the output voltage of the DC power supply E14 is 50V, the voltage at the negative side end of the DC power supply E14 is minus 24.5V, which is 50V lower than the voltage at the positive side end of the DC power supply E14.

  Thus, for example, the resistance R31 and the resistance R32 are set such that the absolute value of the potential difference between the intermediate node N43 and the positive side line is smaller than the minimum value among the absolute values of the output voltages of the DC circuit 1 and the DC circuit 2. By setting the resistance value, it is possible to prevent the voltages at the negative side end of DC power supply E14 and the negative side end of DC power supply E24 from becoming the same zero volt as reference potential node N44.

  As a result, even when the negative side line of the DC circuit 1 or the DC circuit 2 has a ground fault, a ground fault current flows through the ground fault location, the reference potential node N44 and the resistor R33, and a potential difference occurs between both ends of the resistor R33. The current detection circuit 36 can detect the ground fault current more reliably. That is, the ground fault detection circuit 4 can detect the ground fault more reliably when a ground fault occurs in the DC voltage supply circuit 11.

  Since other configurations and operations are the same as those of the DC voltage supply circuit according to the first embodiment, detailed description thereof will not be repeated here.

  Next, another embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

<Third Embodiment>
The present embodiment relates to a DC voltage supply circuit in which a voltage is supplied from one DC power source to a plurality of DC circuits as compared with the DC voltage supply circuit according to the first embodiment. The contents other than those described below are the same as those of the DC voltage supply circuit according to the first embodiment.

  FIG. 14 is a diagram showing a configuration of a DC voltage supply circuit according to the third embodiment of the present invention.

  Referring to FIG. 14, DC voltage supply circuit 12 includes DC circuits 101 and 102, voltage conversion circuits 105 and 106, and ground fault detection circuit 4. The DC circuit 101 includes a load Z114. The DC circuit 102 includes a load Z124.

  Voltage conversion circuit 105 includes a capacitor C115, an inductor L116, a switch SW117, a diode D118, and a capacitor C129. The switch SW117 is a switch element such as a transistor or FET.

  Voltage conversion circuit 106 includes a capacitor C125, an inductor L126, a switch SW127, a diode D128, and a capacitor C129. The switch SW127 is a switch element such as a transistor or FET.

  The ground fault detection circuit 4 includes a resistor R31, a resistor R32, and a current detection circuit 36. The current detection circuit 36 includes a resistor R33, a voltage measurement unit 34, and an alarm unit 35. The ground fault detection circuit 4 is connected to the opposite side to the DC circuit 101 of the voltage conversion circuit 105 and to the opposite side to the DC circuit 102 of the voltage conversion circuit 106.

  In the voltage conversion circuit 105, the positive end of the load Z114, the first end of the capacitor C115, and the first end of the inductor L116 are connected. The negative side end of the load Z114, the second end of the capacitor C115, and the anode of the diode D118 are connected. The second end of the inductor L116, the cathode of the diode D118, and the first end of the switch SW117 are connected. The second end of the switch SW117 and the first end of the capacitor C129 are connected. The anode of the diode D118 and the second end of the capacitor C129 are connected. The first end of the capacitor C129 and the positive end of the DC power supply E109 are connected. The second end of the capacitor C129 and the negative end of the DC power supply E109 are connected.

  In the voltage conversion circuit 106, the positive side end of the load Z124, the first end of the capacitor C125, and the first end of the inductor L126 are connected. The negative side end of the load Z124, the second end of the capacitor C125, and the anode of the diode D128 are connected. The second end of the inductor L126, the cathode of the diode D128, and the first end of the switch SW127 are connected. A second end of the switch SW127 and a first end of the capacitor C129 are connected. The anode of the diode D128 and the second end of the capacitor C129 are connected.

  The voltage conversion circuit 105 is provided corresponding to the DC circuit 101, and converts the voltage applied between the input terminals of the DC circuit 101 by switching the switch SW117.

  The voltage conversion circuit 106 is provided corresponding to the DC circuit 102 and converts a voltage applied between the input terminals of the DC circuit 102 by switching the switch SW127.

  More specifically, for example, in the voltage conversion circuit 105, when the switch SW117 is turned on, a self-induced electromotive force is generated in the inductor L116 in the direction opposite to the output voltage of the DC power supply E109. Therefore, the capacitor C115 includes the DC power supply E109. The battery is charged with a voltage lower than the output voltage. The inductor L116 accumulates energy by increasing the current flowing through the inductor L116. When the switch SW117 is turned off, the supply of voltage from the DC power supply E109 to the capacitor C115 is cut off, while the energy accumulated in the inductor L116 charges the capacitor C115. Thereby, the voltage conversion circuit 105 converts the DC voltage received from the DC power supply E109 into a DC voltage of a predetermined level and applies it between the input terminals of the DC circuit 101. The same applies to the voltage conversion circuit 106.

  Hereinafter, the wiring connected to the positive input terminal of the DC circuit 101 and having the same potential as the positive input terminal of the DC circuit 101 is also referred to as a positive line of the DC circuit 101. A wire connected to the negative input terminal of the DC circuit 101 and having the same potential as the negative input terminal of the DC circuit 101 is also referred to as a negative line of the DC circuit 101.

  A wire connected to the positive input terminal of the DC circuit 102 and having the same potential as the positive input terminal of the DC circuit 102 is also referred to as a positive line of the DC circuit 102. A wire connected to the negative input terminal of the DC circuit 102 and having the same potential as the negative input terminal of the DC circuit 102 is also referred to as a negative line of the DC circuit 102.

  In the voltage conversion circuit 105, the circuit on the DC circuit 101 side and the circuit on the ground fault detection circuit 4 side are not electrically insulated. In the voltage conversion circuit 106, the circuit on the DC circuit 102 side and the circuit on the ground fault detection circuit 4 side are not electrically insulated. That is, the voltage conversion circuit 105 and the voltage conversion circuit 106 are non-insulated voltage conversion circuits.

  The positive side lines of the DC circuit 101 and the DC circuit 102 are connected to each other. Specifically, the positive side lines of the DC circuit 101 and the DC circuit 102 are connected via the voltage conversion circuit 105 and the voltage conversion circuit 106. Further, the negative side lines of the DC circuit 101 and the DC circuit 102 are connected to each other.

  The resistor R31 is electrically connected to the positive side line. More specifically, the first end of the resistor R31 is connected to the positive side line of the DC circuit 101 via the voltage conversion circuit 105, and is connected to the positive side line of the DC circuit 102 via the voltage conversion circuit 106. ing.

  The first end of the resistor R31 is connected to the positive side line of the DC circuit 101 and the positive side line of the DC circuit 102 at the connection node N41. That is, the connection node N41 is electrically connected to the positive side lines of the DC circuit 101 and the DC circuit 102. More specifically, the connection node N41 is connected to the positive side line of the DC circuit 101 via the voltage conversion circuit 105, and is connected to the positive side line of the DC circuit 102 via the voltage conversion circuit 106. The connection node N41 is included in the ground fault detection circuit 4.

  The resistor R32 is electrically connected to the negative side line. More specifically, the first end of the resistor R32 is connected to the negative side line of the DC circuit 101 via the voltage conversion circuit 105, and is connected to the negative side line of the DC circuit 102 via the voltage conversion circuit 106. ing.

  The first end of the resistor R32 is connected to the negative side line of the DC circuit 101 and the negative side line of the DC circuit 102 at the connection node N42. That is, the connection node N42 is electrically connected to the negative side lines of the DC circuit 101 and the DC circuit 102. More specifically, the connection node N42 is connected to the negative side line of the DC circuit 101 via the voltage conversion circuit 105, and is connected to the negative side line of the DC circuit 102 via the voltage conversion circuit 106. The connection node N42 is included in the ground fault detection circuit 4.

  The resistor R33 is connected between the resistors R31 and R32 and a reference potential node N44 connected to, for example, the ground. More specifically, the second end of the resistor R31, the second end of the resistor R32, and the first end of the resistor R33 are connected to each other at the intermediate node N43 that is an intermediate node between the positive side line and the negative side line. The second end of R33 and the reference potential node N44 are connected.

  The potential of the reference potential node N44 is the reference potential of the DC voltage supply circuit 12. That is, the reference potential node N44 is a reference potential node for the DC circuit 101 and the DC circuit 102.

  FIG. 15 is a diagram illustrating an example of a ground fault in the DC voltage supply circuit illustrated in FIG. 14.

  Referring to FIG. 15, the positive side line of DC circuit 102 is grounded. Specifically, the positive side end of the load Z124 is connected to the reference potential node N44 via the ground fault resistor R50.

  Thus, when the positive side line of DC circuit 102 has a ground fault, ground fault current I4 flows from the positive side line of DC circuit 102 through ground fault resistor R50 to reference potential node N44. Specifically, for example, the ground fault current I4 is output from the DC power source E109, flows through the ground fault resistor 50 to the reference potential node N44, and passes from the reference potential node N44 through the resistor R33 and the resistor R32 to the DC power source E109. Return to.

  At this time, a potential difference is generated at both ends of the resistor R33 due to the ground fault current I4. The current detection circuit 36 detects a ground fault based on the potential difference generated at both ends of the resistor R33.

  Here, there is no ground fault in any part of the DC voltage supply circuit 12, and the absolute value of the output voltage of the DC power supply E109, that is, the absolute value of the potential difference between both ends of the DC power supply E109 is 200V. The absolute value of the voltage applied to Z114 is 50V, the absolute value of the voltage applied to the load Z124 is 100V, the resistance values of the resistors R31 and R32 are 40 kΩ, and the resistance value of the resistor R33 is 1 kΩ. Think about a case. Hereinafter, unless otherwise indicated in the text, the potential of the reference potential node N44 is set to zero volts.

  When no part of the DC voltage supply circuit 12 is grounded, no current flows between the intermediate node N43 and the reference potential node N44. That is, since no current flows through the resistor R33, the voltage at the intermediate node N43 is zero volts.

  Since the resistance values of the resistor R31 and the resistor R32 are the same and the absolute value of the output voltage of the DC power supply E109 is 200V, the voltage of the connection node N41 is 100V, and the voltage of the connection node N42 is minus 100V.

  Further, the voltage at the negative end of the load Z124 is the same as the voltage at the connection node N42, and thus is minus 100V.

  Since the voltage at the negative side end of the load Z124 is minus 100V and the absolute value of the voltage applied to the load Z124 is 100V, the voltage at the positive side end of the load Z124 is 100V from the voltage at the negative side end of the load Z124. High zero volts. In other words, the positive side end of the load Z124 has the same potential as the reference potential node N44.

  In this case, for example, as shown in FIG. 15, even if the positive side line of the DC circuit 102 is grounded, the ground side current I4 does not flow because the positive side end of the load Z124 has the same potential as the reference potential node N44. . That is, even if the positive side line of the DC circuit 102 is grounded, the ground side current I4 does not flow through the resistor R33 because the positive side line of the DC circuit 102 and the intermediate node N43 are at the same potential.

  Therefore, since a potential difference does not occur at both ends of the resistor R33, the current detection circuit 36 cannot detect a ground fault.

  That is, the voltage measurement unit 34 may not be able to detect a ground fault when the absolute value of the voltage at the ground fault location is the same as the absolute value of the potential difference between the intermediate node N43 and the negative side line.

  Therefore, the DC voltage supply circuit 12 sets the circuit constants of the ground fault detection circuit 4 so that the current detection circuit 36 can detect the ground fault more reliably when a ground fault occurs. Specifically, in a state where there is no ground fault, the voltage of the intermediate node N43 with respect to the negative side line, that is, the potential difference between the intermediate node N43 and the negative side line is the absolute value of the input voltage of the DC circuit 101 and the DC circuit 102. The absolute value is set to be smaller than the smallest absolute value.

  More specifically, for example, as described above, when the absolute value of the voltage applied to the load Z114 is 50V and the absolute value of the voltage applied to the load Z124 is 100V, the DC voltage supply circuit The resistance values of the resistor R31 and the resistor R32 are set so that the absolute value of the potential difference between the intermediate node N43 and the negative side line is less than 50V when none of the 12 points is grounded.

Here, in a state where no part of the DC voltage supply circuit 12 is grounded, the absolute value of the potential difference between the intermediate node N43 and the negative side line is | Vp |, and the absolute value of the output voltage of the DC power supply E109 is | Ve. When | is assumed and the resistance values of R31 and R32 are Rc31 and Rc32, respectively, the absolute value | Vp | of the potential difference between the intermediate node N43 and the negative side line is expressed by the following equation.
| Vp | = | Ve | × Rc32 / (Rc31 + Rc32)

  For example, when the absolute value | Ve | of the output voltage of the DC power supply E109 is 200 V, when the resistance value Rc31 is set to 82 kΩ and the resistance value Rc32 is set to 12 kΩ, the intermediate node N43 and the negative The absolute value | Vp | of the potential difference between the side lines is about 25.5 V, which is smaller than the absolute value of 50 V applied to the load Z114.

  At this time, the voltage of the intermediate node N43 is zero volts, and the absolute value of the potential difference between the intermediate node N43 and the negative side line is 25.5V. Therefore, the voltage of the negative side line is minus 25.5V lower than the voltage of the intermediate node N43. 25.5V.

  Since the voltage on the negative side end of the load Z124 is the same as the voltage on the negative side line, it is minus 25.5V. Since the absolute value of the voltage applied to the load Z124 is 100V, the voltage on the positive side end of the load Z124 is 74.5V, which is 100V higher than the voltage on the negative side end of the load Z124.

  Moreover, since the voltage at the negative side end of the load Z114 is the same as the voltage at the negative side line, it is minus 25.5V. Since the absolute value of the voltage applied to the load Z114 is 50V, the voltage on the positive side end of the load Z114 is 24.5V, which is 50V higher than the voltage on the negative side end of the load Z114.

  Thus, for example, the resistance R31 and the resistance R32 are set such that the absolute value of the potential difference between the intermediate node N43 and the negative side line is smaller than the minimum value among the absolute values of the input voltages of the DC circuit 101 and the DC circuit 102. By setting the resistance value, it is possible to prevent the voltages at the positive side end of the load Z114 and the positive side end of the load Z124 from becoming the same zero volt as the potential of the reference potential node N44.

  As a result, even when the positive side line of the DC circuit 101 or the DC circuit 102 has a ground fault, a ground fault current flows through the ground fault location, the reference potential node N44, and the resistor R33, and a potential difference occurs between both ends of the resistor R33. The current detection circuit 36 can detect the ground fault current more reliably. That is, the ground fault detection circuit 4 can detect a ground fault more reliably when a ground fault occurs in the DC voltage supply circuit 12.

  As described above, in the DC voltage supply circuit according to the third embodiment of the present invention, the DC circuit 101 and the DC circuit 102 are connected to each other on the positive side line and the negative side line. The ground fault detection circuit 4 detects a current flowing between the intermediate node N43 between the positive side line and the negative side line and the reference potential node N44 of the DC circuit 101 and the DC circuit 102. The voltage of intermediate node N43 is set to be an absolute value smaller than the minimum absolute value of the absolute values of the input voltages of DC circuit 101 and DC circuit 102.

  With such a configuration, each of the positive side line and the negative side line in the DC circuit 101 and the DC circuit 102 has a voltage different from that of the reference potential node N44. Even when a fault occurs, a ground fault current flows between the ground fault location and the reference potential node N44. Therefore, a ground fault can be detected more reliably.

  Since other configurations and operations are the same as those of the DC voltage supply circuit according to the first embodiment, detailed description thereof will not be repeated here.

  In the embodiment of the present invention, the ground fault detection circuit 4 has a resistance between the intermediate node N43 and the reference potential node N44 in order to detect a current flowing between the intermediate node N43 and the reference potential node N44. Although the configuration including R33 is not limited to this configuration, for example, a configuration including a current transformer between the intermediate node N43 and the reference potential node N44 or a configuration including a relay may be used. Good.

  Specifically, for example, when the ground fault detection circuit 4 includes a current instead of the resistor R33, the primary winding of the current transformer is connected between the intermediate node N43 and the reference potential node N44. The ground fault detection circuit 4 detects a ground fault based on the current flowing through the secondary winding of the current transformer.

  Further, when the ground fault detection circuit 4 includes a relay instead of the resistor R33, the relay winding is connected between the intermediate node N43 and the reference potential node N44. The ground fault detection circuit 4 detects a ground fault based on the ON or OFF state of the relay contact.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The above description includes the following features.

[Appendix 1]
A plurality of DC power sources each connected to the positive side line and the negative side line;
A ground fault detection circuit for detecting a current flowing between an intermediate node between the positive side line and the negative side line and a reference potential node of each DC power supply;
The DC power supply circuit, wherein the voltage of the intermediate node is set to be an absolute value smaller than a minimum absolute value of absolute values of output voltages of the DC power supplies.

[Appendix 2]
A plurality of loads each having a positive line and a negative line connected to each other;
A ground fault detection circuit for detecting a current flowing between an intermediate node between the positive side line and the negative side line and a reference potential node of each load;
The DC power supply circuit, wherein the voltage of the intermediate node is set to be an absolute value smaller than a minimum absolute value of absolute values of input voltages of the loads.

1, 2, 90, 91, 290, 291 DC circuit 4 Ground fault detection circuit 5, 6, 7, 8, 105, 106 Voltage conversion circuit 9 Load unit 10, 11, 12, 13 DC voltage supply circuit 34 Voltage measurement unit 35 Alarm section 36 Current detection circuit 50 Ground fault resistance 91 Inverter 92 Load 101 DC circuit 102 DC circuit 120 Noise filter 292, 293, 294, 295 Equivalent circuit C15, C25, C29, C75, C85, C89, C115, C125, C129 , C141, C142, C143, C144 Capacitors D18, D28, D78, D88, D118, D128 Diodes E14, E24, E109, E190, E191, E192 DC power supply g1 DC current sources I1, I2, I3, I4 Ground fault current L16, L26, L76, L86, L116, L145, L1 6, L126 inductor N41 connecting node N42 connecting node N43 intermediate node N44 reference potential node R31, R32, R33, R50, R195, R196 resistance SW17, SW27, SW77, SW87, SW117, SW127 switches z114, Z 124 load

Claims (5)

A plurality of DC circuits in which the positive and negative lines are connected to each other;
A ground fault detection circuit for detecting a current flowing between an intermediate node between the positive side line and the negative side line and a reference potential node of each of the DC circuits;
The DC voltage supply circuit, wherein the voltage of the intermediate node is set to be an absolute value smaller than the minimum absolute value of the absolute values of the input voltage or output voltage of each DC circuit. The ground fault detection circuit is
A first resistor electrically connected to the positive side line;
A second resistor electrically connected to the negative side line;
2. The DC voltage supply circuit according to claim 1, comprising: the first resistor, the second resistor, and a third resistor connected between the reference potential node. 3. The DC voltage supply circuit further includes:
A voltage conversion circuit that is provided corresponding to the DC circuit and converts the voltage of the corresponding DC circuit;
The DC voltage supply circuit according to claim 1, wherein the ground fault detection circuit is electrically connected to an opposite side of the voltage conversion circuit with respect to the DC circuit.   4. The DC voltage supply circuit according to claim 3, wherein in the voltage conversion circuit, the circuit on the DC circuit side and the circuit on the ground fault detection circuit side are not electrically insulated. A first connection node electrically connected to the positive side wires of the plurality of DC circuits;
A second connection node electrically connected to the negative side line of each DC circuit;
A current detection circuit for detecting a current flowing between an intermediate node between the first connection node and the second connection node and a reference potential node of each DC circuit;
The ground fault detection circuit, wherein the voltage of the intermediate node is set to be an absolute value smaller than the minimum absolute value of the absolute values of the input voltage or output voltage of each DC circuit.

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