JPH10322883A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent overpotential at the output potential of an inverter by detecting a current flowing between an AC input power supply and the earth or a voltage between them thereby detecting the grounding state of the AC input power supply surely. SOLUTION: When the second phase of a single phase AC power supply 1 is grounded, a ground detection current ieu flows from the first phase of the single phase AC power supply 1 through a second phase loop of a resistor 34, a photocoupler 35, a diode 37, the earth, and the second phase of a single phase AC power supply 1 and a light receiving transistor in the photocoupler 35 is turned on. The ground detection current does not flow into a photocoupler 40 and the light receiving transistor thereof is turned off. Consequently, an overvoltage 15 not applied to a capacitor 29 in case of grounding or nongrounding of the second phase. In case of grounding of the first phase, and an alarm is generated for an apparatus where an inverter is operating in-phase an in synchronism with the AC input power supply and overpotential is prevented by modifying the grounding of the input power supply.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC three-wire circuit composed of a positive phase, a neutral phase, and a negative phase in which both an input and an output are AC. The present invention relates to a power converter having a forward converter and an inverse converter having a common sex phase.

[0002]

2. Description of the Related Art A power converter for converting an AC input into a DC, and further converting the DC into an AC output. The power converter has a common line of input AC, a neutral phase of DC, and a line of output AC. As described in JP-A-5-15171, a forward converter and an inverse converter are formed as a half bridge, and a single-phase AC current connected to a DC neutral phase flows into a capacitor of a DC circuit. Alternatively, the current flows out of the capacitor, but the converter can be downsized compared to a configuration in which the forward converter and the inverse converter are full bridges.

[0003]

Problems of the prior art will be described with reference to FIGS.

FIG. 11 shows a single-phase AC power supply connection 1 as an input, and a single-phase output to a load device connection 32 via a forward converter, a positive-phase, neutral-phase, and negative-phase three-wire DC / inverter. This is a phase AC input type power converter. The forward converter includes a single-phase AC power supply connection unit 1, transistors 7, 8 connected in series between the positive and negative phases of DC, and diodes 11, connected in anti-parallel to each of the transistors 7, 8. 12, a reactor 5 connected between the middle point of the transistors 7 and 8 and the first phase of the single-phase AC power supply connection part 1, and a series connection between the positive phase and the negative phase, and the middle point Two series capacitors 15 connected to the second phase of the single-phase AC power connection 1 and the neutral phase of the DC,
16 and a capacitor 3 connected in parallel to the single-phase AC power supply connection unit 1. That is, a forward converter as a power converter that has one half-bridge type conversion circuit (also referred to as a half-bridge type single-phase forward converter) and converts a single-phase AC to a DC three-wire output is configured. Is done.

The inverter is composed of transistors 17 and 18 connected in series between the positive and negative DC phases and a transistor 1.
Diode 2 connected in anti-parallel to each of 7 and 18
Reactors 25 connected between the middle points of the transistors 17, 18 and the first phase of the load device connection 32.
And two series-connected capacitors 15, 16 connected in series between the positive and negative DC phases and having a midpoint connected to the second phase of the single-phase AC power supply connection 1 and the neutral phase of the DC. And a capacitor 27 connected in parallel to the load device connection part 32.

The capacitor 29 is connected between the first phase of the load device connecting portion 32 and the ground as a noise filter of the load device connecting portion 32, and the capacitor 30 is connected to the load device connecting portion 32.
Is connected between the second phase and the earth.

When the transistors 7, 8, 17, 18 are turned on,
By controlling off, ideally, the AC input current waveform becomes a sine wave and the AC output voltage becomes a sine wave.

In the following description, the single-phase AC power supply connection unit 1 is abbreviated as the single-phase AC power supply 1 and the load device connection unit 32 is abbreviated as the load device 32.

Here, the potential of the first phase of the load device 32 will be described with reference to FIGS.

FIG. 12 shows a vector diagram when the second phase of the single-phase AC power supply 1 is grounded and the output voltage Vuvo of the inverter is in phase with the input voltage Vuvi of the single-phase AC power supply 1.
Since the second phase is grounded, the second phase becomes ground potential, and the output voltage Vuvo of the inverter is in phase with the input voltage Vuvi of the single-phase AC power supply 1, so that the first phase of the load device 32 The maximum potential is the same as the maximum potential of the input voltage of the single-phase AC power supply 1.

FIG. 13 shows a vector diagram when the second phase of the single-phase AC power supply 1 is grounded and the output voltage Vuvo of the inverter is in the opposite phase to the input voltage Vuvi of the single-phase AC power supply 1.
Since the second phase is grounded, the second phase becomes ground potential, and the output voltage Vuvo of the inverter is in the opposite phase to the input voltage Vuvi of the single-phase AC power supply 1, but the output voltage Vuvi of the first phase of the load device 32 is The maximum potential is the same as the maximum potential of the input voltage of the single-phase AC power supply 1.

FIG. 14 is a vector diagram when the first phase of the single-phase AC power supply 1 is grounded and the output voltage Vuvo of the inverter is in the opposite phase to the input voltage Vuvi of the single-phase AC power supply 1.
Since the first phase is grounded, the first phase becomes ground potential, and the output voltage Vuvo of the inverter is in the opposite phase to the input voltage Vuvi of the single-phase AC power supply 1, so that the first phase of the load device 32 The maximum potential is twice the maximum potential of the input voltage of the single-phase AC power supply 1.

The potential of the first phase of the load device 32 is the voltage applied to the capacitor 29. If the input voltage to the load device 32 is 100 V, the voltage applied to the capacitor 29 in FIGS. Although it is 100 V, it becomes 200 V in FIG. 14, and an excessive voltage is applied to the capacitor 29, which may damage the capacitor. An arrester may be connected instead of a capacitor, which can be similarly damaged.

FIG. 15 shows a three-phase AC input type in which a three-phase AC power supply 2 is input and output to a load device 33 via a forward converter, positive-phase, neutral-phase, and negative-phase three-wire DC / inverter. Power conversion device. The forward converter includes a three-phase AC power supply connection 2 and a transistor 7 connected in series between the positive and negative DC phases.
8, a diode 11, 12 connected in anti-parallel to each of the transistors 7, 8, a reactor 5 connected between the midpoint of the transistors 7, 8 and the first phase of the three-phase AC power supply 2, Transistors 9, 10 connected in series between the positive phase and the negative phase, diodes 13, 14 connected in anti-parallel to the transistors 9, 10 respectively, and a three-phase AC Reactor 6 connected to the third phase of power supply 2 is connected in series between the positive and negative phases, and the midpoint is connected to the second phase and the neutral phase of the DC of three-phase AC power supply 2 Two series capacitors 15 and 16
The three-phase AC power supply 2 includes a capacitor 3 connected in parallel to the first and second phases and a capacitor 4 connected in parallel to the second and third phases. That is, a forward converter as a power converter that has two half-bridge type conversion circuits and converts a three-phase AC into a DC three-wire output is configured.

The inverter is composed of transistors 17 and 18 connected in series between the positive and negative DC phases and a transistor 1.
Diode 2 connected in anti-parallel to each of 7 and 18
A reactor 25 connected between the middle point of the transistors 17 and 18 and the first phase of the load device 33; and a transistor 1 connected in series between the positive and negative DC phases.
9, 20, a diode 23, 24 connected in anti-parallel to each of the transistors 19, 20; a reactor 26 connected between the midpoint of the transistors 19, 20 and the third phase of the load device 33; Two series capacitors 15, 16 connected in series between the positive phase and the negative phase and having a middle point connected to the second phase and the neutral phase of the three-phase AC power supply 2.
And a capacitor 27 connected in parallel to the first and second phases of the load device connecting portion 32 and a capacitor 28 connected in parallel to the second and third phases.

As a noise filter of the load device 33, the capacitor 29 is connected between the first phase and the ground of the load device 33, the capacitor 30 is connected between the second phase and the ground of the load device 33, and the capacitor 31 is connected to the third phase of the load device 33. Connected between phase and earth.

Here, the potential of the first phase of the load device 33 will be described with reference to FIGS.

FIG. 16 shows that the second phase of the three-phase AC power supply 2 is grounded and the output voltages Vuvo, Vvwo, Vwu of the inverter are output.
o is the input voltage Vuvi, Vvwi, Vw of the three-phase AC power supply 2
FIG. 4 shows a vector diagram in the case of the same phase as ui. Since the second phase is grounded, the second phase becomes the ground potential, and the output voltage of the inverter is in phase with the input voltage of the three-phase AC power supply 2. Is three-phase AC power supply 2
Is the same as the maximum potential of the input voltage.

FIG. 17 shows that the second phase of the three-phase AC power supply 2 is grounded and the output voltages Vuvo, Vvwo, Vwu of the inverter are output.
o is the input voltage Vuvi, Vvwi, Vw of the three-phase AC power supply 2
FIG. 8 shows a vector diagram in the case of a phase opposite to that of ui. Since the second phase is grounded, the second phase is at ground potential, and the output voltage of the inverter is in phase opposite to the input voltage of the three-phase AC power supply 2, but the maximum potential of the first phase of the load device 33 is Is three-phase AC power supply 2
Is the same as the maximum potential of the input voltage.

FIG. 18 shows that the first phase of the three-phase AC power supply 2 is grounded, and the output voltages Vuvo, Vvwo, Vwu of the inverter are output.
o is the input voltage Vuvi, Vvwi, Vw of the three-phase AC power supply 2
FIG. 8 shows a vector diagram in the case of a phase opposite to that of ui. Since the first phase is grounded, the first phase is at the ground potential, and the output voltage of the inverter is in the opposite phase to the input voltage of the three-phase AC power supply 2. Is three-phase AC power supply 2
Is twice as large as the maximum potential of the input voltage.

The potential of the first phase of the load device 33 is the voltage applied to the capacitor 29. If the input voltage to the load device 33 is 200 V, the voltage applied to the capacitor 29 in FIGS. Although it is 200 V, it becomes 400 V in FIG. 18, and an excessive voltage is applied to the capacitor 29, which may damage the capacitor. An arrester may be connected instead of a capacitor, which can be similarly damaged.

The half-bridge type power converter having a common line of alternating current and the neutral phase of direct current can be downsized. May damage capacitors and arresters between grounds. Conventionally, this problem has been dealt with by checking the ground phase when installing the power converter.However, the input power supply has to be updated and the need to check each time is required. Therefore, proper ground detection and protection are also desired from the viewpoint of the nature.

[0023]

A feature of the present invention that achieves the above object is that an input and an output are both AC and a DC three-wire circuit comprising a positive phase, a neutral phase, and a negative phase is part of the circuit. Capacitors are connected between the positive and neutral phases and between the neutral and negative phases, respectively. In a power converter having a transformer, a current or voltage flowing between an AC input power supply and the ground is detected to detect grounding.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a single-phase power converter according to a first embodiment of the present invention.

Since the configuration of the main circuit is the same as that of FIG.
Description is omitted. A series connection of a resistor 34, a photocoupler 35, and a diode 37 is connected between the first phase of the single-phase AC power supply 1 and the ground.

A diode 36 is connected in anti-parallel to the light emitting diode of the photocoupler 35, and the output of the light receiving transistor is connected to a ground determination circuit 38. A series connection of a resistor 39, a photocoupler 40, and a diode 42 is connected between the second phase of the single-phase AC power supply and the ground. A diode 41 is connected in antiparallel to the light emitting diode of the photocoupler 40, and the output of the light receiving transistor is connected to the ground determination circuit 43.

The ground detection will be described with reference to FIGS.

FIG. 1 shows a case where the second phase of the single-phase AC power supply 1 is grounded.
The ground detection current ieu flows through the second phase loop of the photocoupler 35, the diode 37, the ground, and the single-phase AC power supply 1, and the light receiving transistor of the photocoupler 35 is turned on. No ground detection current flows through the photocoupler 40, and the light receiving transistor of the photocoupler 40 is turned off.

FIG. 2 shows a case where the first phase of the single-phase AC power supply 1 is grounded.
The ground detection current iev flows in the first phase loop of the photocoupler 40, the diode 42, the ground, and the single-phase AC power supply 1, and the light receiving transistor of the photocoupler 40 is turned on. No ground detection current flows through the photocoupler 35, and the light receiving transistor of the photocoupler 35 is turned off.

If the single-phase AC power supply 1 is not grounded, no ground detection current flows, and both photocouplers 35 and 40 are turned off. The single-phase AC power supply 1 is grounded to the second phase, or
If not grounded, excessive voltage is not applied to the capacitor 29, and if grounded in the first phase, excessive voltage may be applied to the capacitor 29. If the inverter is operating in phase with the AC input power supply in synchronization with the AC input power supply, such as an uninterruptible power supply, when the first phase ground is detected, an alarm will be issued and the grounding of the input power supply will be changed. Voltage can be prevented beforehand. In a device in which the inverter does not operate in synchronization with the AC input power, the operation of the device is stopped to prevent application of an excessive voltage to the capacitor 29.

It should be noted that the above can be summarized as follows.
And the output of the photocoupler are as follows.

Photocoupler 35 Photocoupler 40 1st phase grounding off on 2nd phase grounding on off Non-grounding off off As described above, according to the present embodiment, the single-phase power converter is connected to the first phase grounding, It can be distinguished whether it is in a two-phase grounded state or a non-grounded state.

FIG. 3 is a circuit diagram showing a three-phase power converter according to a second embodiment of the present invention.

The structure of the main circuit is the same as that of FIG. Resistance 34, photocoupler 3 between the first phase of three-phase AC power supply and ground
5, a diode 37 connected in series is connected. The diode 36 is connected in anti-parallel to the light emitting diode of the photocoupler 35.
Are connected to the output of the light receiving transistor to the ground determination circuit 38, respectively. Resistance 3 between the second phase of three-phase AC power supply and the earth
9, a photocoupler 40 and a diode 42 connected in series are connected. A diode 41 is connected in antiparallel to the light emitting diode of the photocoupler 40, and the output of the light receiving transistor is connected to the ground determination circuit 43. A resistor 44, a photocoupler 45, and a diode 47 in series are connected between the third phase of the three-phase AC power supply and the ground. The diode 46 is connected in antiparallel to the light emitting diode of the photocoupler 45, and the output of the light receiving transistor is connected to the ground determination circuit 48. FIG. 3 can be applied to a single-phase three-wire power converter as it is.

The ground detection will be described with reference to FIGS.

FIG. 3 shows a case where the second phase of the three-phase AC power supply 2 is grounded.
The ground detection current ieu flows in the second phase loop of the photocoupler 35, the diode 37, the ground, and the three-phase AC power supply 2, and the light receiving transistor of the photocoupler 35 is turned on. From the third phase of the three-phase AC power supply 2, a resistor 44, a photocoupler 45,
The ground detection current iew flows through the second phase loop of the diode 47, the ground, and the three-phase AC power supply 2, and the light receiving transistor of the photocoupler 45 is turned on. No ground detection current flows through the photocoupler 40, and the light receiving transistor of the photocoupler 40 is turned off.

FIG. 4 shows a case where the first phase of the three-phase AC power supply 2 is grounded, and the resistor 39, the photocoupler 40, the diode 42, the ground, and the three-phase AC power supply 2
In the first phase loop, the ground detection current iev flows, and the light receiving transistor of the photocoupler 40 is turned on. From the third phase of the three-phase AC power supply 2, the resistor 44, the photocoupler 45, the diode 47, the ground, and the ground detection current iew flows in the first phase loop of the three-phase AC power supply 2, and the light receiving transistor of the photocoupler 45 is turned on. Become. No ground detection current flows through the photocoupler 35, and the light receiving transistor of the photocoupler 35 is turned off. If the three-phase AC power supply 2 is not grounded,
No ground detection current flows, and the photocouplers 35, 40, 45
Are both turned off. Further, if the three-phase AC power supply 2 is grounded to a neutral point, a ground detection current flows through all the photocouplers, and all of the photocouplers 35, 40, and 45 are turned on.

The three-phase AC power supply 2 is grounded in the second phase, or
If not grounded, no excessive voltage is applied to the capacitors 29 and 31, and excessive voltage is applied to the capacitors 29 and 31 in the case of first-phase grounding, third-phase grounding, and neutral grounding. Sometimes. When the first-phase grounding, the third-phase grounding, and the neutral point grounding are detected, an alarm is issued or protection for stopping the device is performed as in the first embodiment.

It should be noted that the above can be summarized as follows.
And the output of the photocoupler are as follows.

Photocoupler 35 Photocoupler 40 Photocoupler 45 First-phase ground Off On On Second-phase ground On Off On Third-phase ground On On Off Neutral ground On On On Non-ground Off Off Off According to this embodiment, the three-phase power converter determines whether the three-phase power converter is in the ground state of the first-phase ground, the second-phase ground, the third-phase ground, the neutral point ground, or the non-ground. it can.

FIG. 5 is a circuit diagram showing a single-phase power converter according to a third embodiment of the present invention.

The structure of the main circuit is the same as that of FIG. A series connection of a resistor 39 and a photocoupler 40 is connected between the second phase of the single-phase AC power supply connected to the DC neutral phase and the ground. The diode 41 is connected in antiparallel to the light emitting diode of the photocoupler 40, and the output of the light receiving transistor is connected to the ground determination circuit 43.

When the second phase of the single-phase AC power supply 1 is grounded,
No ground detection current flows through the photocoupler 40, and the light receiving transistor of the photocoupler 40 is turned off. When the first phase of the single-phase AC power supply 1 is grounded, the ground detection current flows from the second phase of the single-phase AC power supply 1 to the resistor 39, the photocoupler 40, the ground, and the first phase loop of the single-phase AC power supply 1. As a result, the light receiving transistor of the photocoupler 40 is turned on. If the single-phase AC power supply 1 is not grounded, no ground detection current flows and the photocoupler 40 is turned off. Summarizing the above, the relationship between the ground of the single-phase AC power supply 1 and the output of the photocoupler is as follows.

[0045] If the single-phase AC power supply 1 is the second phase grounded or non-grounded, no excessive voltage is applied to the capacitor 29.
In the case of the first-phase grounding in which the photocoupler 40 is turned on, an alarm can be issued or the device can be stopped to prevent an excessive voltage. In this manner, if the ground current is detected by connecting the ground current detection circuit to at least the second phase of the single-phase AC power supply connected to the neutral phase of the DC, the capacitor 29
Can be identified as being in a ground state in which an overvoltage is applied.

FIG. 6 is a circuit diagram showing a four-phase power converter according to a fourth embodiment of the present invention.

The structure of the main circuit is the same as that of FIG. A series connection of a resistor 39 and a photocoupler 40 is connected between the ground and the second phase of the three-phase AC power supply connected to the neutral phase of the DC. A diode 41 is connected in antiparallel to the light emitting diode of the photocoupler 40, and the output of the light receiving transistor is connected to the ground determination circuit 43.

When the second phase of the three-phase AC power supply 2 is grounded,
No ground detection current flows through the photocoupler 40, and the light receiving transistor of the photocoupler 40 is turned off. When the first phase of the three-phase AC power supply 2 is grounded, the ground detection current flows from the second phase of the three-phase AC power supply 2 to the resistor 39, the photocoupler 40, the ground, and the first phase loop of the three-phase AC power supply 2. As a result, the light receiving transistor of the photocoupler 40 is turned on. If the three-phase AC power supply 2 is not grounded, no ground detection current flows and the photocoupler 40 is turned off. Further, if the three-phase AC power supply 2 is at the neutral point ground, the ground detection current flows, and the photocoupler 40 is turned on.

It should be noted that the three-phase AC power supply 2
And the output of the photocoupler are as follows.

[0050] If the three-phase AC power supply 2 is the second-phase grounded or non-grounded, no excessive voltage is applied to the capacitors 29 and 31, so that the first-phase ground and the third-phase ground when the photocoupler 40 is turned on. In the case of grounding or neutral point grounding, an alarm can be issued or the device can be stopped to prevent excessive voltage. As described above, if the ground current is detected by connecting the ground current detection circuit to at least the second phase of the three-phase AC power supply connected to the neutral phase of DC, the ground in which overvoltage is applied to the capacitors 29 and 31 is obtained. It can be determined whether or not it is in the state.

In the third and fourth embodiments of the present invention, since the ground detection is performed only in the phase of the AC power supply connected to the neutral phase of DC, the number of parts is small, and the reliability and economy are excellent. .
Furthermore, it is also possible to connect a zener diode to the photocoupler in series to increase the ground current detection value.

A detection method other than the photocoupler will be described in the following embodiments.

FIG. 7 is a circuit diagram showing a fifth embodiment of a three-phase power converter according to the present invention.

The structure of the main circuit is the same as that of FIG. A resistor 39 and a current transformer 49 are connected in series between the second phase of the three-phase AC power supply connected to the neutral phase of DC and the ground, and the output of the current transformer 49 is connected to the ground determination circuit 43. I do.

When the second phase of the three-phase AC power supply 2 is grounded,
No ground detection current flows through the current transformer 49, and no current flows through the output of the current transformer 49. When the first phase of the three-phase AC power supply 2 is grounded, the ground detection current flows from the second phase of the three-phase AC power supply 2 to the resistor 39, the current transformer 49, the ground, and the first phase loop of the three-phase AC power supply 2. Flows, and a current flows to the output of the current transformer 49. If the three-phase AC power supply 2 is not grounded, no ground detection current flows and no current flows to the output of the current transformer 49. Furthermore, if the three-phase AC power supply 2 is grounded to a neutral point, a ground detection current flows, and a current flows to the output of the current transformer 49. Ground judgment circuit 4
In step 3, the output current of the current transformer 49 is detected. If no current flows, it can be determined that the second phase is grounded or non-grounded. If a current flows, the first phase is grounded, the third phase is grounded, or It can be determined that the ground is at the neutral point, and an alarm can be issued or the device can be stopped to prevent an excessive voltage, as in the fourth embodiment. Thus, even if the ground current is detected by the current transformer instead of the photocoupler in the embodiment of FIG. 6, the same operation and effect as in the embodiment of FIG. 6 can be obtained.

FIG. 8 is a circuit diagram showing a three-phase power converter of a sixth embodiment according to the present invention.

The structure of the main circuit is the same as that of FIG. The transformer 50 is connected between the second phase of the three-phase AC power supply connected to the DC neutral phase and the ground, and the output of the transformer 50 is connected to the ground determination circuit 43.

When the second phase of the three-phase AC power supply 2 is grounded,
No voltage is applied to the primary of the transformer 50, and no voltage is generated at the output of the transformer 50. When the first phase of the three-phase AC power supply 2 is grounded, a voltage is generated between the second phase of the three-phase AC power supply 2 and the ground, so that a primary voltage is applied to the transformer 50 and the output of the transformer 50 is output. Voltage is generated. In addition, three-phase AC power supply 2
Is not grounded, no voltage is applied to the primary of the transformer 50 and no voltage is generated at the output of the transformer 50. Further, if the three-phase AC power supply 2 is grounded to a neutral point, a voltage is applied to the primary of the transformer 50 and a voltage is generated at the output of the transformer 50.
The output voltage of the transformer 50 is detected by the ground determination circuit 43, and if there is no voltage, it can be determined that the second phase is grounded or non-grounded. If there is a voltage, the first phase ground, the third phase ground, or It can be determined that the ground is at the neutral point, and an alarm can be issued or the device can be stopped to prevent an excessive voltage, as in the fourth embodiment.

FIG. 9 is a circuit diagram showing a seven-phase power converter according to a seventh embodiment of the present invention.

The structure of the main circuit is the same as that of FIG. The capacitor 51 and the transformer 50 are connected in series between the second phase of the three-phase AC power supply connected to the neutral phase of the direct current and the ground, and the output of the transformer 50 is connected to the ground determination circuit 43. The ground detection is the same as in the sixth embodiment. The difference from the sixth embodiment is that when a voltage including a DC component is generated between the second phase and the ground by the capacitor 51, the voltage including the DC component is changed to a primary voltage of the transformer 50 in the sixth embodiment. Is applied, the transformer 50 may be magnetically saturated. However, in the seventh embodiment, a DC component is applied to the capacitor 51, and an AC voltage not including the DC component is applied to the primary of the transformer 50. To be
The transformer 50 is not magnetically saturated. FIG. 10 is a circuit diagram showing a three-phase power converter according to an eighth embodiment of the present invention. The configuration of the main circuit is the same as that of FIG. The capacitor 51 and the resistor 39 are connected between the second phase of the three-phase AC power supply connected to the DC neutral phase and the ground, and the voltage of the resistor 39 is input to the ground determination circuit 43.

When the second phase of the three-phase AC power supply 2 is grounded,
No voltage is generated at the resistor 39. When the first phase of the three-phase AC power supply 2 is grounded, a voltage is generated between the second phase of the three-phase AC power supply 2 and the ground. If the three-phase AC power supply 2 is not grounded, no voltage is generated at the resistor 39. Further, if the three-phase AC power supply 2 is grounded to a neutral point, a voltage is generated at the resistor 39. The ground determination circuit 43 detects the voltage of the resistor 39. If there is no voltage, it can be determined that the second phase is grounded or non-grounded.
It can be determined that the third phase is grounded or the neutral point is grounded, and similarly to the fourth embodiment, an alarm is issued or the device is stopped to prevent an excessive voltage.

Here, the current limiting element is a resistor in the embodiment, but may be a reactor, a capacitor, a transformer, and a composite thereof, for example, a combination of a resistor and a capacitor. Therefore, there is an advantage that the means for detecting current and voltage can be constituted by components that operate only with the AC component.

[0063]

According to the present invention, both the input and the output are AC, and a part of the circuit includes a DC three-wire circuit composed of a positive phase, a neutral phase, and a negative phase. In a power converter having a forward converter and a reverse converter having a common neutral phase, the ground state of the AC input power supply can be reliably detected, and an excessive potential of the output of the reverse converter can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram and an operation explanatory diagram of a first embodiment in which the present invention is applied to a single-phase AC input, single-phase AC output power converter.

FIG. 2 is an operation explanatory view of the first embodiment.

FIG. 3 is a circuit diagram and an operation explanatory diagram of a second embodiment in which the present invention is applied to a three-phase AC input, three-phase AC output power converter.

FIG. 4 is an operation explanatory view of the second embodiment.

FIG. 5 is a circuit diagram of a third embodiment in which the present invention is applied to a single-phase AC input, single-phase AC output power converter.

FIG. 6 is a circuit diagram of a fourth embodiment in which the present invention is applied to a three-phase AC input, three-phase AC output power converter.

FIG. 7 is a circuit diagram of a fifth embodiment in which the present invention is applied to a three-phase AC input, three-phase AC output power converter.

FIG. 8 is a circuit diagram of a sixth embodiment in which the present invention is applied to a three-phase AC input, three-phase AC output power converter.

FIG. 9 is a circuit diagram of a seventh embodiment in which the present invention is applied to a three-phase AC input, three-phase AC output power converter.

FIG. 10 is a circuit diagram of an eighth embodiment in which the present invention is applied to a three-phase AC input, three-phase AC output power converter.

FIG. 11 is a circuit diagram of a single-phase AC input, single-phase AC output half-bridge type power converter.

12 is a vector diagram of an AC input voltage and an AC output voltage of the power converter of FIG. 11 with the AC input second phase grounded and the inverter in phase with the AC input.

13 is a vector diagram of an AC input voltage and an AC output voltage of the power converter of FIG. 11 with the AC input second phase grounded and the inverter being in the opposite phase to the AC input.

FIG. 14 is a vector diagram of an AC input voltage and an AC output voltage of the power converter of FIG. 11 when the AC input is in the first phase ground and the inverter is in the opposite phase to the AC input.

FIG. 15 is a circuit diagram of a three-phase AC input, three-phase AC output half-bridge type power converter.

FIG. 16 is a vector diagram of an AC input voltage and an AC output voltage of the power converter of FIG. 15 with the AC input second phase grounded and the inverter having the same phase as the AC input.

17 is a vector diagram of an AC input voltage and an AC output voltage of the power converter of FIG. 15 with the AC input second phase grounded and the inverter being in the opposite phase to the AC input.

18 is a vector diagram of an AC input voltage and an AC output voltage of the power converter of FIG. 15 with the AC input first phase grounded and the inverter being in the opposite phase to the AC input.

[Explanation of symbols]

1: Single-phase AC power supply, 2: Three-phase AC power supply, 3, 4, 15,
16, 27, 28, 29 to 31, 51 ... capacitors,
5, 6, 25, 26 ... reactor, 7 to 10, 17 to 2
0: Transistor, 11 to 14, 21 to 24, 36, 3
7, 41, 42, 46, 47: diode, 32: single-phase AC load device, 33: three-phase AC load device, 34, 39,
44 ... resistance, 35, 40, 45 ... photocoupler, 38,
43, 48: ground determination circuit, 49: current transformer, 50: transformer.

Claims (11)

[Claims] 1. A positive-side capacitor connected between the positive and neutral phases of a DC three-wire, wherein the input and output are AC and the DC part is a three-wire consisting of a positive phase, a neutral phase, and a negative phase. And a negative-side capacitor connected between the neutral phase and the negative phase of the DC 3 wire, and one end of the forward converter is connected to the positive phase of the DC 3 wire, and the other end is connected to the negative phase of the DC 3 wire. A power converter having at least one half-bridge circuit to be connected, and at least one half-bridge circuit having one end of the inverter connected to the positive phase of the three direct current wires and the other end connected to the negative phase of the three direct current wires. A power conversion device, comprising: means for detecting a current or voltage between the AC input power supply and the ground to detect grounding. 2. The method according to claim 1, wherein the means for detecting ground contact comprises:
Between the AC input and the ground, a current limiting element, a photocoupler, and a diode are connected in series, and between the AC input and the ground connected to the neutral phase of the DC unit, a current limiting element,
A power conversion device comprising: a photocoupler and a diode connected in series; and ground detection is performed at each photocoupler output. 3. The method according to claim 1, wherein the ground detecting means comprises:
A power converter characterized in that a current limiting element, a photocoupler, and a diode are connected in series between an AC input connected to a neutral phase of a DC section and the ground, and ground detection is performed at an output of the photocoupler. . 4. The device according to claim 1, wherein the ground detecting means comprises:
The current limiting element and the photocoupler are connected in series between the AC input connected to the neutral phase of the DC section and the ground, the diode is connected in anti-parallel to the photocoupler, and the ground detection is performed by the photocoupler output. Characteristic power converter. 5. The power converter according to claim 2, wherein the ground detecting means connects a Zener diode in series with the photocoupler. 6. The apparatus according to claim 1, wherein the ground detecting means comprises:
What is claimed is: 1. A power converter, comprising: a current limiting element and a current transformer connected in series between an AC input connected to a neutral phase of a DC section and a ground, and detecting a ground with an output current of the current transformer. 7. The apparatus according to claim 1, wherein the ground detecting means comprises:
A power converter characterized in that a transformer is connected between an AC input connected to a neutral phase of a DC section and the ground, and ground detection is performed with a transformer output voltage. 8. The apparatus according to claim 1, wherein the ground detecting means comprises:
A power converter characterized in that a current limiting element and a transformer are connected in series between an AC input connected to a neutral phase of a DC section and the ground, and ground detection is performed using a transformer output voltage. 9. The method according to claim 1, wherein the ground detecting means comprises:
A power converter, wherein a current limiting element is connected between an AC input connected to a neutral phase of a DC section and the ground, and grounding is detected by a voltage of the current limiting element. 10. The apparatus according to claim 1, wherein an alarm is issued or the apparatus is stopped unless the AC input power supply is not grounded and the AC input phase connected to the neutral phase of the DC section is grounded. Power converter. 11. The power converter according to claim 1, wherein the current limiting element is a resistor, a capacitor, a reactor, a transformer, or a composite thereof.