JP4101267B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device including a DC ground fault detection circuit that detects a DC ground fault current of a DC power supply whose output voltage varies.

  An AC ground fault detection circuit that detects a ground fault current of an AC power supply has already been proposed (see, for example, Patent Document 1).

  However, such an AC ground fault detection circuit cannot be used as a DC ground fault detection circuit that detects a ground fault current of a DC power supply.

  Therefore, the applicant is examining a power conversion device including a DC ground fault detection circuit as shown in FIG.

  The power converter 1 provided with this DC ground fault detection circuit includes a power converter 5 such as an inverter that converts DC power output from a DC power source 3 such as a solar battery into AC power. An insulating transformer 9 is provided between the power converter 5 and an AC load (not shown) for converting the output voltage of the power converter 5 into a required voltage required by the AC load. A normally open switch 11 is provided between the insulating transformer 9 and an AC load (not shown). The switch 11 is configured to be opened and closed by a switch drive circuit 13. The power converter 5 includes a control signal generation circuit 7. The control signal generation circuit 7 outputs a control signal to the power converter 5 and a switch control circuit 13 that controls opening / closing of the switch 11. The power converter 5 is supplied with a control signal from the control signal generating circuit 7 and converts DC power into AC power.

In such a power conversion device 1, the switch 11 is closed when the operation starts. When it is detected that a DC ground fault has occurred on the output side of the DC power source 3 such as a solar battery, the control signal generating circuit 7 stops outputting the control command and the switch drive circuit 13 of the switch 11 is opened. A DC ground fault detection circuit 15 is provided.
The DC ground fault detection circuit 15 includes a first current limiting resistor Ra, and is provided between a positive terminal P of a DC power source 3 such as a solar cell whose output voltage varies and a ground point E. A current detection circuit 17 is provided. In addition, a second current detection circuit 19 provided with a second current limiting resistor Rb and provided between the negative terminal N of the DC power supply 3 and the ground point E is provided. In this example, the ground point E is provided at a connection point 20 that connects the first current detection circuit 17 and the second current detection circuit 19 to each other on the ground point E side. These first current detection circuit 17 and second current detection circuit 19 are arranged in the direction of positive terminal P → first current detection circuit 17 → ground point E → second current detection circuit 19 → negative terminal N. A current flows. This is because the insulation transformer 9 is connected to the load side of the power converter 5 and is practical unless a ground fault occurs at the positive terminal P or the negative terminal N at the output terminal of the DC power source 3 such as a solar battery. This is because a circuit is not formed, and the output current of the DC power supply 3 cannot be a return path of the current even if the grounding point E is in the middle of the flow path and the grounding point E is grounded. This is because the current returns to the negative terminal N. Further, a zero-phase current detection circuit 21 for detecting a difference current ΔI between the first detection current Ia flowing through the first current detection circuit 17 and the second detection current Ib flowing through the second current detection circuit 19 includes: It is provided in the middle of these circuits. In this case, equal current flows through the first and second current limiting resistors Ra and Rb when no DC ground fault occurs on the terminals P and N side of the DC power supply. The DC ground fault detection circuit 15 further includes a ground fault determination circuit 23 that determines that a DC ground fault has occurred when the difference current ΔI exceeds a predetermined reference value.

  When such a power converter 1 does not generate a DC ground fault on the side of the positive terminal P and the negative terminal N of the DC power source 3 such as a solar cell, the first current limiting resistor Ra and the second current limiting resistor The first detection current Ia and the second detection current Ib that are equal to the resistor Rb flow as described above. When these currents Ia and Ib are input to the zero-phase current detection circuit 21, the difference current ΔI (= Ia−Ib) is output from the zero-phase current detection circuit 21. This difference current ΔI is input to the ground fault determination circuit 23. The ground fault determination circuit 23 determines that no DC ground fault has occurred because the difference current ΔI is less than the reference value. When a DC ground fault has not occurred, the ground fault determination circuit 23 does not output a control command to the control signal generation circuit 7, so the control signal generation circuit 7 gives a control signal to the power converter 5, and the power converter 5 Converts DC power to AC power. At this time, since the control signal generation circuit 7 does not give an open command to the switch drive circuit 13, the switch 11 remains closed and supplies AC power to an AC load (not shown).

  However, when a DC ground fault occurs at the negative terminal N of the DC power source 3 as shown in FIG. 7, a grounding resistance Rx appears at the ground fault point. In this case, since the negative terminal N of the DC power source 3 is grounded, the ground point E becomes a return path of the current, and the current flows in the direction of the positive terminal P → the first current detection circuit 17 → the ground point E until halfway. Flowing. The current is branched into two at the ground point E, one flows from the ground point E → the second current detection circuit 19 → the negative terminal N, and the other flows from the ground point E → the ground resistance Rx → the negative terminal N.

At this time, if the current flowing through the ground resistor Rx is Ix, and the currents flowing through the first current limiting resistor Ra and the second current limiting resistor Rb are Ia and Ib, then Ia = Ib + Ix and the currents Ia and Ib The balance is lost, the current Ia becomes larger than the current Ib (Ia> Ib), and the difference current ΔI generated in the zero-phase current detection circuit 21 exceeds the reference value. For this reason, the ground fault determination circuit 23 determines a DC ground fault. When the ground fault determination circuit 23 determines a DC ground fault, the ground fault determination circuit 23 gives a control command to the control signal generation circuit 7. As a result, the control signal generation circuit 7 gives an open command to the switch drive circuit 13 to open the switch 11, stops supply of the control command to the power converter 5, and the power converter 5 stops power conversion. To do. For this reason, it is possible to detect an abnormal state of the DC power supply and safely stop power supply to an AC load (not shown).
JP-A-61-150615

  In the DC power source 3 such as a solar battery, the voltage fluctuation of the DC power generation output of the solar battery is large, for example, from DC 200 V to DC 500 V depending on the amount of solar radiation and the temperature. Therefore, in the power conversion device 1 shown in FIG. 6, when the DC output voltage of the lower limit solar cell that can be operated is set to DC 250 V as shown in FIG. 4, when the amount of solar radiation and temperature are large and the load factor used is small. The direct current output voltage of the solar cell rises to DC500V, and the current flowing through the first current limiting resistor Ra and the second current limiting resistor Rb is doubled, so that it is output from the zero-phase current detection circuit 21. The difference current ΔI is doubled. Therefore, as shown in FIG. 4, although the ground fault does not occur, the reference value at the time of the occurrence of the ground fault is exceeded. There is an inviting problem.

  Further, in order not to cause a malfunction at DC500V, if the reference value at the time of occurrence of the ground fault is increased from the value shown in FIG.

  The objective of this invention is providing the power converter device which can prevent the misjudgment and malfunction by a ground fault determination circuit, and can prevent the fall of the detection sensitivity of a ground fault determination circuit.

  Another object of the present invention is to provide a power conversion device that can easily obtain a series connection and non-connection state of first and second additional resistors with respect to the first and second current limiting resistors. .

  A power conversion device according to the present invention includes a power converter that converts DC power output from a DC power source such as a solar battery into AC power, an insulation transformer provided between the power converter and a load, A control signal generation circuit that outputs a control signal to the converter, and a DC ground fault detection circuit that stops the output of a control command from the control signal generation circuit when it detects that a DC ground fault has occurred on the output side of the DC power supply And. The DC ground fault detection circuit has a first current limiting resistor, a first current detection circuit provided between a positive terminal of a DC power source whose output voltage varies and a ground point, and a second current A second current detection circuit including a limiting resistor and provided between the negative terminal of the DC power supply and the ground; a first detection current flowing through the first current detection circuit; and a second current detection circuit A zero-phase current detection circuit that detects a difference current from the second detection current flowing through the ground, and a ground fault determination circuit that determines that a DC ground fault has occurred when the difference current exceeds a predetermined reference value. Yes.

  In particular, in the power converter of the present invention, the DC ground fault detection circuit is configured so that the first additional resistor having a predetermined value can be selectively connected in series to the first current limiting resistor. The first resistance adding circuit is provided. Further, a second resistance addition circuit configured to selectively connect a second additional resistance having a predetermined value in series with the second current limiting resistance is provided. Further, a voltage detection circuit for detecting a DC output voltage of the DC power supply is provided. In addition, a voltage determination circuit that determines whether or not the DC output voltage exceeds a predetermined reference voltage is provided. Further, when the voltage determination circuit detects that the DC output voltage exceeds the reference voltage, the first and second additional resistors are connected in series to the first and second current limiting resistors, respectively. When the command is output to the first and second resistance adding circuits and the state where the DC output voltage does not exceed the reference voltage is detected, the first and second additional resistors are connected to the first and second current limiting circuits. There is provided a command generation circuit for outputting a command not connected in series to the resistor for use to the first and second resistance addition circuits.

  In such a DC ground fault detection circuit of the power conversion device, the DC output voltage of the DC power supply is detected by the voltage detection circuit, and if the DC output voltage of the DC power supply exceeds a predetermined reference voltage, the first and first Since the two additional resistors are connected in series to the first and second current limiting resistors, the current flowing through the first and second current limiting resistors even when the DC output voltage is greatly increased. Can be suppressed. Therefore, even when the lower limit of the DC output voltage for DC ground fault detection is considered to be DC250V, for example, and the reference value of the zero-phase current detection circuit is set, according to the present invention, when the DC output voltage rises to DC500V, for example. The difference current ΔI output from the zero-phase current detection circuit does not double, and the ground fault determination circuit does not cause erroneous determination or malfunction. Also, in this DC ground fault detection circuit, even if the DC output voltage rises to, for example, DC 500 V, the difference current ΔI output from the zero-phase current detection circuit does not increase in proportion to the voltage rise. Sensitivity is not reduced. On the other hand, when the output voltage of the DC power supply does not increase, the first and second additional resistors are not connected in series with the first and second current limiting resistors, so that the first and second additional resistors have an influence. Never give.

  The present invention can also be applied to a power conversion device in which a switch is provided on the secondary side of an insulating transformer and a switch drive circuit for driving the switch is provided. When the present invention is applied to a power converter having this switch, when a DC ground fault occurs, it is possible to prevent the switch from being opened and supplying abnormal power to the load.

  Further, the DC ground fault detection circuit can be specifically configured as follows. That is, the DC ground fault detection circuit is connected in parallel to the first additional resistor having a predetermined value connected in series with the first current limiting resistor and in parallel with the first additional resistor. And a first resistance adding circuit including a first short circuit having a first switch that can be controlled to open and close accordingly. A second additional resistor having a predetermined value connected in series to the second current limiting resistor and a second additional resistor connected in parallel to the second additional resistor and capable of opening and closing in accordance with a command. A second resistance adding circuit including a second short circuit having two switches. Further, a voltage detection circuit for detecting a DC output voltage of the DC power supply is provided. In addition, a voltage determination circuit that determines whether or not the DC output voltage exceeds a predetermined reference voltage is provided. Further, when the voltage determination circuit detects that the DC output voltage exceeds the reference voltage, the first and second additional resistors are connected in series to the first and second current limiting resistors, respectively. A command to open the first and second switches of the first and second short circuit so as to maintain the state is output to the first and second resistance adding circuits, and the DC output voltage does not exceed the reference voltage Is detected, the first and second short-circuits of the first and second short-circuits are short-circuited so as to short-circuit the first and second additional resistors connected in series to the first and second current-limiting resistors. A command generation circuit is provided for outputting a command to close the second switch to the first and second resistance adding circuits.

  In such a DC ground fault detection circuit of the power conversion device, the DC output voltage of the DC power supply is detected by the voltage detection circuit, and if the DC output voltage of the DC power supply exceeds a predetermined reference voltage, the first and first 2 is opened, and the first and second additional resistors are connected in series to the first and second current limiting resistors, respectively. Therefore, even if the DC output voltage rises greatly, the first In addition, an increase in current flowing through the second current limiting resistor can be suppressed. Therefore, even when the lower limit of the DC output voltage for DC ground fault detection is considered to be DC250V, for example, and the reference value of the zero-phase current detection circuit is set, according to the present invention, when the DC output voltage rises to DC500V, for example. The difference current ΔI output from the zero-phase current detection circuit does not double, and the ground fault determination circuit does not cause erroneous determination or malfunction. Also, in this DC ground fault detection circuit, even if the DC output voltage rises to, for example, DC 500 V, the difference current ΔI output from the zero-phase current detection circuit does not increase in proportion to the voltage rise. Sensitivity is not reduced. On the other hand, when the output voltage of the DC power supply does not increase, the first and second switches are closed and the first and second additional resistors are not connected in series with the first and second current limiting resistors. The first and second additional resistors are not affected.

  A zero-phase current detection circuit includes a detection core in which a magnetic flux due to a current flowing in the first current detection circuit and a magnetic flux due to a current flowing in the second current detection circuit flow, a detection coil wound around the detection core, and a detection A first current detection circuit and a second current detection are provided when an excitation core arranged so as to be linked to the core and an excitation coil for passing an alternating magnetic flux by an excitation current Iex having a frequency f are provided in the excitation core. Even if a direct current flows through the circuit, the difference current can be detected.

  In the power converter according to the present invention, when the DC output voltage of the DC power supply is detected by the voltage detection circuit and the DC output voltage of the DC power supply exceeds a predetermined reference voltage, the first and second additional resistors are added. Since each of the first and second current limiting resistors is connected in series, the increase in the current flowing through the first and second current limiting resistors can be suppressed even when the DC output voltage is greatly increased. Can do. Therefore, even when the lower limit of the DC output voltage for DC ground fault detection is considered to be DC250V, for example, and the reference value of the zero-phase current detection circuit is set, according to the present invention, when the DC output voltage rises to DC500V, for example. The difference current ΔI output from the zero-phase current detection circuit does not double, and the ground fault determination circuit does not cause erroneous determination or malfunction. Also, in this DC ground fault detection circuit, even if the DC output voltage rises to, for example, DC 500 V, the difference current ΔI output from the zero-phase current detection circuit does not increase in proportion to the voltage rise. Sensitivity is not reduced. On the other hand, when the output voltage of the DC power supply does not increase, the first and second additional resistors are not connected in series with the first and second current limiting resistors, so that the first and second additional resistors have an influence. Never give.

  Hereinafter, an example of the best mode for carrying out a power conversion apparatus using a DC ground fault detection circuit according to the present invention will be described in detail with reference to FIGS. 1 to 3. FIG. 1 is a block diagram of a power converter using the DC ground fault detection circuit of this example, FIG. 2 is a schematic configuration diagram of a zero-phase current detection circuit used in this example, and FIGS. (C) is an operation explanatory view of FIG. Note that portions corresponding to those in FIG. 6 described above are denoted by the same reference numerals.

  In the power conversion device 1 using the DC ground fault detection circuit 15 of this example, the DC ground fault detection circuit 15 selectively selects a first additional resistor having a predetermined value with respect to the first current limiting resistor Ra. A second additional resistor Rd having a predetermined value is selectively connected in series to the first resistance adding circuit 25 configured to connect Rc in series and the second current limiting resistor Rb. And a second resistance adding circuit 27 configured to be able to be connected.

  The first and second resistance addition circuits 25 and 27 are connected in parallel to the first and second addition resistances Rc and Rd and to the first and second addition resistances Rc and Rd in response to a command. The first and second current limiting resistors Ra, comprising a parallel circuit having first and second short circuits 33, 35 having first and second switches 29, 31 that can be opened and closed. It is connected in series with Rb.

  The DC ground fault detection circuit 15 includes a voltage detection circuit 37 that detects the DC output voltage of the DC power supply 3 and a voltage that determines whether or not the DC output voltage exceeds a reference voltage predetermined in the reference voltage generation circuit 39. And a determination circuit 41. Further, when the voltage determination circuit 41 detects that the DC output voltage exceeds the reference voltage, the first and second additional resistors Rc and Rd are connected to the first and second current limiting resistors Ra and Rb. Are output to the first and second resistance adding circuits 25 and 27, respectively, and when it is detected that the DC output voltage does not exceed the reference voltage, the first and second addition A command generation circuit 43 that outputs a command not to connect the resistors Rc and Rd in series to the first and second current limiting resistors Ra and Rb to the first and second resistance adding circuits 25 and 27; .

  The first and second switches 29 and 31 that can be controlled to be opened and closed can be configured by contacts of an electromagnetic relay switch having a normally closed contact. The command generation circuit 43 can be constituted by an electromagnetic relay switch excitation circuit. In this case, a state where no excitation current flows in the excitation circuit of the electromagnetic relay switch is a state where a command not connected in series is output from the command generation circuit 43, and an excitation current flows in the excitation circuit of the electromagnetic relay switch. Is a state in which a command for series connection is output from the command generation circuit 43.

  In this case, the zero-phase current detection circuit 21 can be configured as shown in FIG. That is, a detection core 21a in which a magnetic flux caused by a current flowing in the first current detection circuit 17 and a magnetic flux caused by a current flowing in the second current detection circuit 19 flow, a detection coil 21e wound around the detection core 21a, and a detection The exciting core 21b is arranged so as to be linked to the core 21a, and the exciting coil 21d is configured to flow an alternating magnetic flux with an exciting current Iex having a frequency f through the exciting core 21b. The output of the detection coil 21e is supplied to the ground fault determination circuit 23.

  In such a zero-phase current detection circuit 21, since direct current flows through the first current detection circuit 17 and the second current detection circuit 19, there is no time variation of the magnetic flux as shown in FIG. . Therefore, as shown in FIG. 2, an excitation core 21b orthogonal to the detection core 21a is provided, and an excitation current Iex having a frequency f is supplied from the AC power supply 21c to the excitation coil 21d wound around the excitation core 21b. When attention is paid to the orthogonal portion (hatched portion) of the detection core 21a with respect to the excitation core 21b, the magnetization direction gradually rotates from the circumferential direction to the right angle (width) direction as the excitation current Iex increases, and finally completely aligns in the right angle direction. . At this time, the magnetic resistance in the circumferential direction increases extremely, and the magnetic flux of the detection core 21a becomes almost zero.

  Accordingly, the magnetic flux changes at a frequency 2f as shown in FIG. 3C, and an alternating induced voltage corresponding to the difference current ΔI is generated in the detection coil 21e.

  This induced voltage is given to the ground fault determination circuit 23.

  In the power conversion device 1 having such a configuration, the DC ground fault detection circuit 15 detects the DC output voltage of the DC power source 3 made of a solar battery with the voltage detection circuit 37, and the DC output voltage of the DC power source 3 is predetermined. When the reference voltage is exceeded, the command generation circuit 43 issues a command to connect the first and second additional resistors Rc and Rd in series with the first and second current limiting resistors Ra and Rb, respectively. Since the first and second additional resistors Rc and Rd are connected in series to the first and second current limiting resistors Ra and Rb, which are output to the second resistor adding circuits 25 and 27, respectively, the first and second Increase in current flowing through the current limiting resistors Ra and Rb can be suppressed. As a result, even if the reference value of the zero-phase current detection circuit 21 is determined based on the lower limit of the DC output voltage of the solar cell being, for example, DC 250 V, the amount of solar radiation is increased and the DC output of the solar cell is increased. When the voltage rises to, for example, DC 500 V, the first and second resistance addition circuits 25 and 27 are added, so that the difference current ΔI output from the zero-phase current detection circuit 21 does not become extremely large. Therefore, no erroneous determination or malfunction occurs in the ground fault determination circuit 23. On the other hand, when the output voltage of the DC power supply 3 does not increase, the additional resistor Rc is not connected in series to the first current limiting resistor Ra, and also to the second current limiting resistor Rb. The additional resistor Rd is not connected in series. Therefore, in such a case, the presence of the additional resistors Rc and Rd does not cause erroneous determination or malfunction.

  In this example, the first and second resistance addition circuits 25 and 27 are connected in parallel to the additional resistances Rc and Rd and the additional resistances Rc and Rd, and switches 29 and 31 that can be controlled to open and close according to commands. It is comprised with the parallel circuit provided with the short circuit 33,35 which has. The parallel circuit is connected in series to the first and second current limiting resistors Ra and Rb. By adopting such a configuration, it is possible to easily obtain a series connection and a non-connection state of the additional resistors Rc and Rd with respect to the first and second current limiting resistors Ra and Rb only by opening and closing the switches 9 and 31. .

  FIG. 4 is a diagram illustrating the relationship between the DC input voltage and the difference current. This figure explains the difference between the configuration of this example when the DC output voltage rises above the set value and the conventional configuration.

  In the case of the conventional configuration, when the DC output voltage of the solar cell is set to DC250V, for example, if the solar radiation amount or the temperature increases and the DC output voltage of the solar cell rises to DC500V, for example, the difference current ΔI causes a ground fault. In spite of this, there is a problem that it becomes larger than the reference value and causes erroneous detection. However, in the case of the configuration of the present invention, when the DC output voltage of the solar cell rises to, for example, DC500V, the additional resistors Rc and Rd are connected in series to the first and second current limiting resistors Ra and Rb, and the differential current ΔI does not increase by a factor of about 2, and erroneous detection is not caused.

  FIG. 5 is a block diagram of another example implementing a power converter using a DC ground fault detection circuit according to the present invention. Note that portions corresponding to those in FIG. 1 are indicated by using reference numerals obtained by adding 100 to the reference numerals used in FIG. A power conversion device 101 using the DC ground fault detection circuit 115 of the present example includes a power converter 105 that converts DC power output from a DC power source 103 such as a solar battery into AC power, and the power converter 105 illustrated in the figure. Control is performed when it is detected that a DC ground fault has occurred on the output side of the DC power supply 103, and an isolation transformer 109 provided between the DC power supply 103 and the isolation transformer 109 provided between the DC power supply 103 and the insulation transformer 109. A DC ground fault detection circuit 105 for stopping output of a control command from the signal generation circuit 107.

  The DC ground fault detection circuit 115 selectively connects a first current limiting resistor Ra and a first additional resistor Rc having a predetermined value in series to the first current limiting resistor Ra. And a first current circuit 117 provided between the positive terminal P of the DC power supply 103 whose output voltage varies and the ground point E. ing. In addition, the second current limiting resistor Rb and the second additional resistor Rd having a predetermined value can be selectively connected in series to the second current limiting resistor Rb. And a second current adding circuit 127, and a second current circuit 119 provided between the negative terminal N of the DC power source 103 and the ground point E. In addition, a voltage detection circuit 137 that detects a DC output voltage of the DC power supply 103 and a voltage determination circuit 141 that determines whether or not the DC output voltage exceeds a predetermined reference voltage. When the voltage determination circuit 141 detects that the DC output voltage exceeds the reference voltage, the first and second additional resistors Rc and Rd are connected to the first and second current limiting resistors Ra and Rb. Are output to the first and second resistance adding circuits 125 and 127, respectively, and when it is detected that the DC output voltage does not exceed the reference voltage, the first and second addition A command generation circuit 143 is provided for outputting a command to the first and second resistance adding circuits 125 and 127 that the resistors Rc and Rd are not connected in series to the first and second current limiting resistors Ra and Rb. Further, a zero-phase current detection circuit 121 provided between the first and second current circuits 117 and 119 and the ground point E is provided. In this example, a zero-phase current detection circuit 121 is provided on the grounding circuit 144 that connects the grounding point E and the connection point 120 that connects the first and second current circuits 117 and 119 to each other on the grounding point E side. ing. Furthermore, a ground fault determination circuit 123 that determines that a DC ground fault has occurred based on the output of the zero-phase current detection circuit 121 is provided.

  In this case, the circuit configuration when a DC ground fault occurs at the negative terminal N of the DC power supply 103 is indicated by a broken line.

  Even in such a power converter 101, a ground fault current flows through the grounding circuit 144 only when a DC ground fault occurs, and the zero phase current detection circuit 121 detects this, and based on the output of the zero phase current detection circuit 121. The ground fault determination circuit 123 determines that a DC ground fault has occurred. At this time, if the output voltage of the DC power source 103 such as a solar cell has risen to DC500V higher than the lower limit DC output voltage DC250V, the voltage determination circuit 141 determines this via the voltage detection circuit 137, and the command generation circuit 143 According to the command, the first additional resistor Rc is connected in series to the first current limiting resistor Ra, and the second additional resistor Rd is connected in series to the second current limiting resistor Rb. As a result, the ground fault current can be reduced.

  The DC power sources 3 and 103 whose output voltage fluctuates are not limited to solar cells, and the present invention can be applied to any DC power sources 3 and 103 whose output voltage fluctuates.

It is a block diagram which shows an example of the power converter device using the direct-current ground fault detection circuit which concerns on this invention. It is a schematic block diagram which shows operation | movement of the zero phase current detection circuit used in this example. (A), (B), and (C) are operation | movement explanatory drawings of FIG. It is a figure which shows the relationship between the DC input voltage of a prior art example and this invention example, and a difference current. It is a block diagram which shows the other example of the power converter device using the direct-current ground fault detection circuit which concerns on this invention. It is a block diagram which shows the power converter device using the conventional DC ground fault detection circuit. It is a block diagram which shows the state in which the DC ground fault generate | occur | produced with the power converter device using the conventional DC ground fault detection circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power converter 3 DC power supply 5 Power converter 7 Control signal generation circuit 9 Isolation transformer 11 Switch 13 Switch drive circuit 15 DC ground fault detection circuit 17 1st current detection circuit 19 2nd current detection circuit 21 Zero phase Current detection circuit 23 Ground fault determination circuit 25 First resistance addition circuit 27 Second resistance addition circuit 29, 31 First and second switches 33, 35 First and second short circuit 37 Voltage detection circuit 39 Reference voltage Generating circuit 41 Voltage determining circuit 43 Command generating circuit Ra, Rb First and second current limiting resistors Rc, Rd First and second additional resistors

Claims (5)

A power converter that converts DC power output from a DC power source such as a solar battery into AC power, an isolation transformer provided between the power converter and a load, and a control signal is output to the power converter A control signal generation circuit, and a DC ground fault detection circuit for stopping the output of the control command from the control signal generation circuit when detecting that a DC ground fault has occurred on the output side of the DC power supply,
The DC ground fault detection circuit is
A first current detection circuit comprising a first current limiting resistor and provided between the positive terminal of the DC power supply and the ground point, the output voltage of which varies;
A second current detection circuit comprising a second current limiting resistor and provided between the negative terminal of the DC power supply and the ground point;
A zero-phase current detection circuit for detecting a difference current between a first detection current flowing through the first current detection circuit and a second detection current flowing through the second current detection circuit;
When the difference current exceeds a predetermined reference value, a power converter including a ground fault determination circuit that determines that a DC ground fault has occurred,
The DC ground fault detection circuit is
A first resistance adding circuit configured to selectively connect a first additional resistor having a predetermined value in series with the first current limiting resistor;
A second resistance addition circuit configured so that a second additional resistance having a predetermined value can be selectively connected in series to the second current limiting resistance;
A voltage detection circuit for detecting a DC output voltage of the DC power supply;
A voltage determination circuit for determining whether or not the DC output voltage exceeds a predetermined reference voltage;
When the voltage determination circuit detects a state where the DC output voltage exceeds the reference voltage, the first and second additional resistors are respectively connected to the first and second current limiting resistors. A command for series connection is output to the first and second resistance adding circuits, and when it is detected that the DC output voltage does not exceed the reference voltage, the first and second additional resistors are A power conversion apparatus comprising: a command generation circuit that outputs a command not connected in series to the first and second current limiting resistors to the first and second resistance addition circuits. A power converter that converts DC power output from a DC power source such as a solar battery into AC power, an insulating transformer provided between the power converter and a load, and a secondary side of the insulating transformer A switch, a switch drive circuit for driving the switch, a control signal generating circuit for outputting a control signal to the power converter and the switch drive circuit, and a DC ground fault on the output side of the DC power supply. A DC ground fault detection circuit for stopping the output of the control command from the control signal generating circuit and sending the open command from the switch drive circuit when detecting that it has occurred,
The DC ground fault detection circuit is
A first current detection circuit comprising a first current limiting resistor and provided between the positive terminal of the DC power supply and the ground point, the output voltage of which varies;
A second current detection circuit comprising a second current limiting resistor and provided between the negative terminal of the DC power supply and the ground point;
A zero-phase current detection circuit for detecting a difference current between a first detection current flowing through the first current detection circuit and a second detection current flowing through the second current detection circuit;
When the difference current exceeds a predetermined reference value, a power converter including a ground fault determination circuit that determines that a DC ground fault has occurred,
The DC ground fault detection circuit is
A first resistance adding circuit configured to selectively connect a first additional resistor having a predetermined value in series with the first current limiting resistor;
A second resistance addition circuit configured so that a second additional resistance having a predetermined value can be selectively connected in series to the second current limiting resistance;
A voltage detection circuit for detecting a DC output voltage of the DC power supply;
A voltage determination circuit for determining whether or not the DC output voltage exceeds a predetermined reference voltage;
When the voltage determination circuit detects a state where the DC output voltage exceeds the reference voltage, the first and second additional resistors are respectively connected to the first and second current limiting resistors. A command for series connection is output to the first and second resistance adding circuits, and when it is detected that the DC output voltage does not exceed the reference voltage, the first and second additional resistors are A power conversion apparatus comprising: a command generation circuit that outputs a command not connected in series to the first and second current limiting resistors to the first and second resistance addition circuits. A power converter that converts DC power output from a DC power source such as a solar battery into AC power, an isolation transformer provided between the power converter and a load, and a control signal is output to the power converter A control signal generation circuit, and a DC ground fault detection circuit for stopping the output of the control command from the control signal generation circuit when detecting that a DC ground fault has occurred on the output side of the DC power supply,
The DC ground fault detection circuit is
A first current detection circuit including a first current limiting resistor and provided between a positive terminal of a direct current power source and a ground point, the output voltage of which varies;
A second current detection circuit comprising a second current limiting resistor and provided between the negative terminal of the DC power supply and the ground point;
A zero-phase current detection circuit that detects a difference current between a first detection current flowing through the first current detection circuit and a second detection current flowing through the second current detection circuit;
When the difference current exceeds a predetermined reference value, a power converter including a ground fault determination circuit that determines that a DC ground fault has occurred,
The DC ground fault detection circuit is
A first additional resistor having a predetermined value connected in series to the first current limiting resistor and a first additional resistor connected in parallel to the first additional resistor and capable of opening and closing in response to a command. A first resistance adding circuit comprising: a first short circuit having a switch;
A second additional resistor having a predetermined value connected in series to the second current limiting resistor and a second additional resistor connected in parallel to the second additional resistor and capable of opening and closing in response to a command. A second short circuit having a second switch, and a second resistance adding circuit,
A voltage detection circuit for detecting a DC output voltage of the DC power supply;
A voltage determination circuit for determining whether or not the DC output voltage exceeds a predetermined reference voltage;
When the voltage determination circuit detects a state where the DC output voltage exceeds the reference voltage, the first and second additional resistors are respectively connected to the first and second current limiting resistors. A command to open the first and second switches of the first and second short circuit so as to maintain the state of being connected in series is output to the first and second resistance adding circuits, and the DC output voltage is When detecting a state in which the reference voltage is not exceeded, the first and second additional resistors connected in series with the first and second current limiting resistors are short-circuited. And a command generation circuit for outputting a command to close the first and second switches of the first and second short circuit to the first and second resistance adding circuits.   The zero-phase current detection circuit includes a detection core through which a magnetic flux caused by a current flowing through the first current detection circuit and a magnetic flux caused by a current flowing through the second current detection circuit, and a detection coil wound around the detection core The power conversion device according to claim 1, further comprising: an excitation core disposed so as to interlink with the detection core; and an excitation coil that causes an alternating magnetic flux generated by an excitation current Iex having a frequency f to flow through the excitation core. A power converter that converts DC power output from a DC power source such as a solar battery into AC power, an isolation transformer provided between the power converter and a load, and a control signal is output to the power converter A power comprising: a control signal generation circuit; and a DC ground fault detection circuit that stops the output of the control command from the control signal generation circuit upon detecting that a DC ground fault has occurred on the output side of the DC power supply A conversion device,
The DC ground fault detection circuit is
A first resistor configured such that a first additional resistor having a predetermined value can be selectively connected in series to the first current limiting resistor and the first current limiting resistor. A first current circuit provided between the positive terminal of the DC power supply and the ground point, the output voltage of which varies,
A second resistor configured such that a second additional resistor having a predetermined value can be selectively connected in series to the second current limiting resistor and the second current limiting resistor. A second current circuit provided between the negative terminal of the DC power supply and the ground point, and an additional circuit;
A voltage detection circuit for detecting a DC output voltage of the DC power supply;
A voltage determination circuit for determining whether or not the DC output voltage exceeds a predetermined reference voltage;
When the voltage determination circuit detects a state in which the DC output voltage exceeds the reference voltage, the first and second additional resistors are respectively connected to the first and second current limiting resistors. A command for series connection is output to the first and second resistance adding circuits, and when it is detected that the DC output voltage does not exceed the reference voltage, the first and second additional resistors are A command generating circuit for outputting a command not connected in series to the first and second current limiting resistors to the first and second resistance adding circuits;
A zero-phase current detection circuit provided between the first and second current circuits and the ground point;
A power converter comprising: a ground fault determination circuit that determines that a DC ground fault has occurred based on an output of the zero-phase current detection circuit.

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