JP2005130541A - Inverter apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transformerless inverter 3 capable of suppressing fluctuation in a ground voltage to prevent mulfunction of a system protection device 2. <P>SOLUTION: An intermediate connection point 10 of a filter capacitor 8 of a DC intermediate circuit of a transformerless inverter 3, which does not contain a transformer, is grounded between a converter 7 and a zero-phase current transformer 5. The zero-phase current that flows an earth line 11 is detected with a current transformer 12 that penetrates the earth line 11 (1), or a differential current that flows the positive/negative connection line of the DC intermediate circuit is detected with a current transformer 15 or a reactor 17 (2). The output is made to penetrate the zero-phase current transformer 5, in the direction opposite to that of a system 1, through a band pass filter 13 whose impedance is low to a third harmonics 3f<SB>0</SB>frequency of the voltage of the three-phase AC system 1. The transformerless inverter detects a zero-phase current that flows due to grounding, which is offset with the signal detected by the zero-phase current transformer 5, to prevent mulfunction of the system protection device 2 for suppressing fluctuation in a ground voltage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement in an inverter device that receives commercial AC power and converts it into AC power of variable voltage and variable frequency via an intermediate DC circuit.

  In recent years, variable voltage / variable frequency control (hereinafter, abbreviated as a variable speed power supply) using an inverter has been used as a drive power supply for industrial equipment motors from the viewpoint of highly efficient use of energy and energy saving. In addition, with the progress of semiconductor process technology, inverter mounting technology, and motor drive control technology, better inverters will appear and will be used in many devices. In particular, the high withstand voltage, large current capacity, and high speed of power semiconductor elements in recent years are remarkable, and have become a major factor in widespread use of inverter variable speed power supplies for industrial equipment.

  For example, in an inverter using a conventional power semiconductor element, the received voltage is once stepped down by an input transformer, and a variable speed power source is formed by a low voltage inverter, and this is stepped up again by an output transformer to drive the motor. However, if power semiconductors, especially IGBT elements with excellent controllability and high-speed response, have a high breakdown voltage and a large current capacity, inverters that can directly receive the system voltage and control the output voltage become possible. This makes it possible to reduce the loss. As a result, the inverter variable speed power supply was also introduced into the existing motor, which had previously been difficult to install the inverter variable speed power supply due to the problem of installation space, and energy-saving operation of industrial equipment has become possible.

  However, unlike a conventional inverter, a transformerless inverter directly receives a system voltage and supplies power to a motor without insulation. For this reason, there is a possibility that the output voltage waveform of the inverter largely fluctuates due to the balance between the motor (load) and other load devices connected to the system and the influence of the system voltage fluctuation. In particular, when the inverter output voltage is higher than when the motor is driven by a sine wave, the insulation life of the motor may be shorter than before the inverter is introduced, and countermeasures are required.

  Conventionally, for example, as described in Non-Patent Document 1, there is a measure to make the peak of the ground voltage of the inverter constant by grounding the intermediate connection point of the filter capacitor of the intermediate DC circuit of the inverter. It was. Patent Document 1 and the like also disclose that an intermediate connection point of a filter capacitor of an intermediate DC circuit of an inverter is grounded.

  On the other hand, Patent Document 2 discloses a transformerless inverter power supply in which DC power, such as a solar cell having a large stray capacitance, is used as a variable speed power supply with an inverter and power is supplied to a load without a transformer, and countermeasures against malfunction of the earth leakage breaker. It is disclosed.

IEEJ Technical Report No. 739 (P.17-18)

Japanese Patent Laid-Open No. 3-107373 (FIGS. 1, 3, and 8) JP 2002-165461 A (Overall)

  The present invention is directed to a transformerless inverter having no transformer between a zero-phase current transformer inserted in a commercial AC system and an input-side converter constituting the inverter. In such a transformer-less inverter, unlike the conventional inverter, the system and the inverter are not insulated by the transformer. Therefore, as in Non-Patent Document 1 and Patent Document 1, the intermediate connection point of the filter capacitor of the DC intermediate circuit of the inverter Cannot simply be grounded. When grounded, zero-phase current flows from the system side, which may cause malfunction of the system protection device using the zero-phase current transformer. For this reason, in a transformerless inverter, fluctuations in ground voltage cannot be suppressed by a technique such as Non-Patent Document 1 or Patent Document 1, and an output filter is newly installed to suppress overvoltage, or the ground of a motor It is necessary to take measures such as strengthening insulation. As a result, the advantages of transformer-less inverters such as small size, space saving, and low loss cannot be fully utilized.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an inverter device that can suppress fluctuations in ground voltage and prevent malfunction of a system protection device even in a transformerless inverter that receives power from a commercial system.

  In one aspect of the present invention, in a transformer-less inverter having no transformer between the zero-phase current transformer at the power receiving end and the converter on the AC power receiving side of the inverter, grounding for grounding the intermediate connection point of the filter capacitor of the DC intermediate circuit A wire is provided, and the zero-phase current transformer is excited in the reverse direction based on the current flowing through the ground wire.

  According to another aspect of the present invention, in an inverter device including a ground wire that grounds an intermediate connection point of a filter capacitor of an inverter DC intermediate circuit, the transformer is more than the transformer of a three-phase AC system flowing into a converter on the AC power receiving side of the inverter. A zero-phase current transformer is inserted on the converter side, and the zero-phase current transformer is excited in the reverse direction based on the current flowing in the ground line.

  Furthermore, in another aspect of the present invention, a zero-phase current transformer is inserted on the converter side of a transformer of a three-phase AC system flowing into the converter in an inverter device having a ground line for grounding an intermediate connection point of the filter capacitor. Then, a component in a predetermined frequency region is extracted from the current flowing through the ground line, and the zero-phase current transformer is excited in the reverse direction.

  Here, in a preferred embodiment, a frequency component of the third harmonic of the commercial power supply voltage is extracted, and the zero-phase current transformer is excited in the reverse direction by this extracted component.

  According to the present invention, even in a transformer-less inverter in which a zero-phase current transformer is inserted on the input system side of the converter without a transformer, fluctuations in ground voltage are suppressed and malfunction of the system protection device is prevented. An apparatus can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram of an inverter device according to a first embodiment of the present invention. This transformerless inverter system is roughly composed of a commercial AC power supply system 1, a system protection device 2, a transformerless inverter 3, and a motor (load) 4. Here, the system protection device 2 detects a zero-phase current transformer 5 that detects a zero-phase current that flows when the system is grounded, and detects a signal from the zero-phase current transformer 5 to shut off a vacuum circuit breaker or the like. A protection circuit 6 for operating a device (not shown) is provided.

  On the other hand, the transformerless inverter 3 has the following difference from the normal inverter. First, similarly to a normal inverter, a converter 7 for converting a three-phase alternating current of a system into a direct current, a filter capacitor 8 inserted in a direct current intermediate circuit, and a PWM inverter 9 for switching the direct current into an alternating current are provided. In addition, a zero-phase current transformer 5 is inserted into the system 1 without a transformer between the converter 7 and, as a result, a so-called transformer-less inverter 3 is formed. An intermediate connection point 10 of the filter capacitor 8 is grounded by a ground line 11.

  Here, consider a case where the intermediate connection point 10 of the filter capacitor 8 is grounded. First, the current flowing from the system when simply grounded by the ground wire 11 is indicated by a thick arrow in the figure. In the transformerless inverter 3, when the intermediate connection point 10 of the filter capacitor 8 is grounded, a zero-phase current flows into the ground line 11 from the system as indicated by a thick arrow. This is because the DC intermediate circuit voltage obtained by three-phase full-wave rectification by the converter 7 includes a third-order harmonic component of the voltage of the system 1 and is grounded to provide an unbalanced current component. That is, a zero-phase current flows as shown by a thick arrow. In this state, the zero-phase current is detected by the zero-phase current transformer 5 and the protection circuit 6 in the system protection device 2 may be operated.

  However, in the present embodiment, the ground line 11 at the intermediate connection point 10 of the filter capacitor 8 passes through the core of the current transformer 12. The output of this current transformer 12 has a through-wire 14 penetrated through its core so as to excite the zero-phase current transformer 5 in a direction opposite to that of the system 1 via a bandpass filter 13. Therefore, the zero-phase current is detected by the current transformer 12, the frequency component of the third harmonic of the system voltage is extracted by the band pass filter 13, and this is sent to the zero-phase current transformer 5 in the direction opposite to that of the system 1. To penetrate. Thereby, the magnetic field produced by the zero-phase current flowing through the system 1 can be canceled. For this reason, even if the intermediate connection point 10 of the filter capacitor 8 is grounded, the zero-phase current transformer 5 will not erroneously detect the zero-phase current and the protection circuit 6 of the system protection device 2 will not malfunction.

  In particular, in this embodiment, the output of the current transformer 12 is passed through the band-pass filter 13 to extract only the third-order harmonic frequency component of the system voltage.

FIG. 2 is a characteristic diagram of the bandpass filter 13 used in the first embodiment of the present invention. When the frequency of the commercial three-phase AC system is f ₀ , as shown in the figure, the band-pass filter has a small impedance Z in the third harmonic frequency 3 f ₀ region. Therefore, other impedances such as the system voltage frequency f ₀ region, the inverter carrier frequency region, and the pulse rising frequency region have high impedance. For this reason, the high frequency current flowing through the closed circuit connecting the filter capacitor 8, the cable (not shown), the motor load 4, and the ground is removed, and only the current flowing from the system 1 to the ground through the converter 7, the filter capacitor 8, and the intermediate connection point 10 is obtained. Can be detected.

  In this way, in the transformerless inverter in which the zero-phase current transformer 5 is inserted on the AC system 1 side of the converter 7 without a transformer, fluctuations in the ground voltage are suppressed, and the system protection device 2 malfunctions. It is possible to provide an inverter device that prevents this.

  FIG. 3 is an overall configuration diagram of an inverter device according to a second embodiment of the present invention. In FIG. 3, the same elements as those in the embodiment of FIG. In this embodiment, a connecting line connecting the converter 7 and the filter capacitor 8 is passed through the current transformer 15, and the current transformer 15 passes through the zero-phase current transformer 5 in the direction opposite to the system 1. 14 is output. Reference numeral 16 denotes an auxiliary ground line, which is not always necessary if both current transformers 5 and 15 are floating in potential.

  In this embodiment, a connection line connecting the converter 7 and the filter capacitor 8 is passed through the current transformer 15. Thus, the zero-phase current of the system 1 is detected by an unbalanced current, that is, a positive / negative difference current, and the zero-phase current transformer 5 of the system protection device 2 is passed through the system 1 in a direction opposite to the system, thereby flowing through the system 1. The magnetic field generated by the zero phase current can be canceled. For this reason, even if the intermediate connection point 10 of the filter capacitor 8 is grounded, the zero-phase current transformer 5 does not malfunction by detecting the zero-phase current due to the third-order harmonic component.

  Thus, according to the present embodiment, it is possible to provide a transformerless inverter that suppresses fluctuations in ground voltage and prevents malfunction of the system protection device.

  FIG. 4 is an overall configuration diagram of an inverter device according to a third embodiment of the present invention. Also in this embodiment, the same elements as those in the embodiment of FIG. 1 and FIG. This embodiment is different from FIG. 3 in that the output of the current transformer 15 and the output of the zero-phase current transformer 5 are connected in series so as to cancel each other.

  Also according to this embodiment, it is possible to provide a transformerless inverter that suppresses fluctuations in ground voltage and prevents malfunction of the system protection device.

  FIG. 5 is an overall configuration diagram of an inverter device according to a fourth embodiment of the present invention. Also in this embodiment, the same elements as those in FIG. This embodiment differs from FIG. 3 in that a reactor 17 is provided to detect a positive / negative differential current of a DC intermediate circuit connecting the converter 7 and the filter capacitor 8. The reactor 17 includes a positive side coil 18 from the converter 7 toward the filter capacitor 8, a negative side coil 19 in the opposite direction, and an output coil 20. The positive / negative differential current, that is, the zero-phase current appearing in the output coil 20 is output to the through-wire 14 penetrating the zero-phase current transformer 5 in the reverse manner to the system 1 in the same manner as in FIG.

  In this embodiment, a connecting line connecting the positive side and the negative side of the converter 7 and the filter capacitor 8 is wound around the reactor 17 as coils 18 and 19, respectively. These coils 18 and 19 are in the direction of strengthening the magnetic field due to the unbalanced current. For this reason, when a zero-phase current flowing in the ground flows through the connecting line between the two poles connecting the converter 7 and the filter capacitor 8, this is detected by the output coil 20, and the zero-phase current transformer 5 is reversed from the system 1. The magnetic field generated by the zero-phase current flowing through the system 1 is canceled.

  Therefore, similarly to the previous embodiment, it is possible to provide a transformerless inverter that suppresses fluctuations in the ground voltage and prevents malfunction of the system protection device.

  In this embodiment, the output of the output coil 20 of the reactor 17 is passed through the zero-phase current transformer 5 in the direction opposite to the system 1. However, similar to the embodiment of FIG. 4, the same effect can be obtained by connecting this output in series in a direction that cancels the output of the zero-phase current transformer 5.

  The above embodiment is summarized as follows. First, a converter 7 for converting received AC to DC, a filter capacitor 8 connected to the DC side of the converter, and an inverter 9 for converting the DC of the filter capacitor to a three-phase AC of variable voltage and variable frequency are provided. ing. A zero-phase current transformer 5 connected between the load (motor) 4 supplied with the three-phase alternating current from the inverter and the alternating current system 1 flowing into the converter 7 without a transformer. It is intended for transformerless inverters equipped with Here, a ground line 11 for grounding the intermediate connection point 10 of the filter capacitor 8 and a zero-phase current transformer 5 are excited in a direction opposite to that of the AC system 1 based on a current flowing through the ground line 11 or a value corresponding to the current. Excitation means (12-14, 15, or 17) is provided.

  According to these embodiments, the malfunction of the system protection device is prevented by detecting the zero-phase current flowing in the inverter or from the inverter to the ground and canceling this with the signal of the zero-phase current transformer of the system protection device. it can. For this reason, even in a transformerless inverter in which a zero-phase current transformer is inserted on the input system side of the converter without using a transformer, an inverter device is provided that suppresses fluctuations in ground voltage and prevents malfunction of the system protection device. can do.

BRIEF DESCRIPTION OF THE DRAWINGS The whole block diagram of the inverter apparatus by the 1st Example of this invention. The characteristic view of the band pass filter used for the 1st example of the present invention. The whole block diagram of the inverter apparatus by the 2nd Example of this invention. The whole block diagram of the inverter apparatus by the 3rd Example of this invention. The whole block diagram of the inverter apparatus by the 4th Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... System | strain, 2 ... System protection apparatus, 3 ... Transformerless inverter, 4 ... Motor (load), 5 ... Zero phase current transformer, 6 ... System protection circuit, 7 ... Converter, 8 ... Filter capacitor, 9 ... Inverter, DESCRIPTION OF SYMBOLS 10 ... Intermediate connection point of filter capacitor, 11 ... Ground wire, 12 ... Current transformer, 13 ... Band pass filter, 14 ... Through-wire, 15 ... Current transformer, 16 ... Auxiliary ground wire, 17 ... Reactor

Claims (20)

  A converter for converting the received AC to DC, a filter capacitor connected to the DC side of the converter, an inverter for converting the DC of the filter capacitor to a three-phase AC of variable voltage / variable frequency, and from the inverter 3 In a transformerless inverter comprising a load supplied with phase alternating current and a zero-phase current transformer connected between the converter and an alternating current system flowing into the converter without a transformer, intermediate connection of the filter capacitor An inverter device comprising: a ground wire for grounding a point; and means for exciting the zero-phase current transformer in a direction opposite to that of the AC system based on a current flowing through the ground wire or a value corresponding to the current. .   2. The inverter device according to claim 1, wherein the means for exciting the zero-phase current transformer in the reverse direction includes a current transformer for detecting a current flowing through the ground line.   2. The inverter device according to claim 1, wherein the means for exciting the zero-phase current transformer in the reverse direction includes means for detecting a positive / negative current difference in a DC line extending from the converter to the filter capacitor.   The means for exciting the zero-phase current transformer in a reverse direction according to claim 1, further comprising a current transformer having a core penetrating a positive and negative DC line from the converter to the filter capacitor. Inverter device.   2. The inverter device according to claim 1, wherein the means for exciting the zero-phase current transformer in the reverse direction includes a through wire penetrating the core of the zero-phase current transformer.   The means for exciting the zero-phase current transformer in the reverse direction according to claim 1, further comprising: a coil wound with positive and negative DC lines from the converter to the filter capacitor; and a reactor having an output coil. A featured inverter device.   A converter that converts received AC to DC, a filter capacitor that is connected to the DC side of the converter and has an intermediate connection point, an inverter that converts the DC of the filter capacitor to a three-phase AC of variable voltage and variable frequency, and In an inverter device including a load supplied with a three-phase AC output of an inverter and a ground line for grounding an intermediate connection point of the filter capacitor, a transformer is interposed between the converter and an AC system flowing into the converter. The zero-phase current transformer is inserted in a direction opposite to the AC system based on the current flowing from the intermediate connection point of the filter capacitor to the ground line or the equivalent value of the current. An inverter device comprising means for exciting.   8. The inverter device according to claim 7, wherein the means for exciting the zero-phase current transformer in the reverse direction includes a current transformer for detecting a current flowing through the ground line.   8. The inverter apparatus according to claim 7, wherein the means for exciting the zero-phase current transformer in the reverse direction includes means for detecting a positive / negative current difference in a DC line extending from the converter to the filter capacitor.   8. The means for exciting the zero-phase current transformer in a reverse direction according to claim 7, comprising a current transformer having a core penetrating a positive and negative DC line from the converter to the filter capacitor. Inverter device.   8. The inverter device according to claim 7, wherein the means for exciting the zero-phase current transformer in the reverse direction includes a through-wire penetrating the core of the zero-phase current transformer.   8. The means for exciting the zero-phase current transformer in a reverse direction according to claim 7, further comprising: a coil wound with positive and negative DC lines from the converter to the filter capacitor; and a reactor having an output coil. A featured inverter device.   A converter that converts received AC to DC, a filter capacitor that is connected to the DC side of the converter and has an intermediate connection point, and an inverter that converts the DC of the filter capacitor into a three-phase AC of variable voltage and variable frequency, In an inverter device comprising a load supplied with the three-phase alternating current from the inverter and a ground line for grounding an intermediate connection point of the filter capacitor, a transformer is connected between the converter and the alternating current system flowing into the converter. A zero-phase current transformer connected without intervening means, means for extracting a component in a predetermined frequency region from a current flowing from the intermediate connection point of the filter capacitor to the ground line or an equivalent value of the current, and the extraction component And a means for exciting the zero-phase current transformer in a direction opposite to that of the AC system. The other apparatus.   14. The AC system according to claim 13, wherein the AC system is a three-phase AC system, and is based on a third harmonic current of a voltage of the three-phase AC system or a current equivalent value among currents flowing from the intermediate connection point to the ground line. An inverter device comprising means for exciting the zero-phase current transformer in a direction opposite to that of the three-phase AC system.   14. The AC system according to claim 13, wherein the AC system is a three-phase AC system, and the means for exciting the zero-phase current transformer in the reverse direction has a small impedance with respect to the third harmonic frequency of the voltage of the three-phase AC system. An inverter device comprising a bandpass filter.   14. The AC system according to claim 13, wherein the AC system is a three-phase AC system, and the means for exciting the zero-phase current transformer in the reverse direction has a small impedance with respect to the third harmonic frequency of the voltage of the three-phase AC system. An inverter device comprising a bandpass filter having a high impedance in the frequency band of the three-phase AC system, the inverter carrier frequency, and the pulse rise time frequency band.   14. The means for exciting the zero-phase current transformer in the reverse direction according to claim 13 includes: a current transformer that detects a current flowing through the ground line; and the zero-phase current transformer that passes through the output line of the current transformer. An inverter device comprising a core of a container.   14. The inverter device according to claim 13, wherein the means for exciting the zero-phase current transformer in the reverse direction comprises means for detecting a positive / negative current difference in a DC line from the converter to the filter capacitor.   The means for exciting the zero-phase current transformer in the reverse direction according to claim 13 includes a current transformer that detects a current flowing through a ground line that grounds an intermediate connection point of the filter capacitor or a current equivalent value thereof, and a current transformer. An inverter device comprising the zero-phase current transformer having an output line abutted with an output of a current transformer. 14. The means for exciting the zero-phase current transformer in the reverse direction according to claim 13, further comprising: a coil wound with positive and negative DC lines from the converter to the filter capacitor; and a reactor having an output coil. A featured inverter device.

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