JP2000224862A - Power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power conversion apparatus which prevents rise in the voltage rating of a device to be connected to a current intermediate circuit, even when a circuit is constituted by adding a neutral conductor to an AC circuit to be output by the power conversion apparatus, or even when an output AC current becomes high, whose weight and dimension are reduced and which prevents a drop in reliability. SOLUTION: A neutral-phase output arm 21, which is composed of a series circuit consisting of two sets of semiconductor switching elements is connected to the DC intermediate circuit of this power conversion apparatus. They are operated to be turned on and off alternately. The other end of a reactor 23 connected to the intermediate point of the neutral-phase output arm is pulled out as a neutral conductor 12. Thereby, a three-phase four-wire system three-phase alternating current or a single- phase three-wire system single-phase alternating current is obtained. In addition, when a smoothing capacitor is constituted by connecting an even number of pieces of capacitors in series, their intermediate point is connected to the neutral conductor 12. Alternatively, a battery 4 is connected across the intermediate point of the smoothing capacitor formed by connecting the even number of pieces of capacitors in series and the positive or negative pole of the DC intermediate circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention provides an AC circuit having a neutral conductor, and maintains a low voltage rating of a device connected to a DC intermediate circuit even when an output voltage of a power converter increases. The present invention relates to a power conversion device that can

[0002]

2. Description of the Related Art When transmitting and distributing three-phase AC power,
In Japan, a three-phase three-wire circuit configuration is generally used. However, if a three-phase four-wire circuit is formed by adding a neutral wire to the circuit, two types of voltages can be obtained, which is convenient. For example, if the line voltage in a three-phase four-wire circuit is 380 V, the phase voltage is 220 V. Therefore, in Europe and the like, power is often distributed using a three-phase four-wire circuit. Normal single-phase electrical products are used at 220V, but large-capacity single-phase or three-phase electrical products such as heaters are used at 380V. are doing. If the single-phase AC circuit is also a single-phase three-wire circuit with a neutral wire, for example,
Since a double voltage of 00 V and 200 V can be obtained, in recent years, most of the distribution circuits in Japan have a single-phase 3
A wire circuit is employed.

[0003] The commercial AC power supply may fluctuate in voltage and frequency, or may fail. Therefore, a load that may be adversely affected by fluctuations in voltage and frequency receives AC power from a so-called CVCF inverter (constant voltage constant frequency inverter) connected to a commercial AC power supply to avoid fluctuations in voltage and frequency. I have. Also, if you do not want to interrupt the power supply to the load,
A so-called UPS (uninterruptible power supply) is connected to a commercial AC power supply, and AC power is received via the UPS, thereby avoiding the risk of power failure. These CVCF inverters and UPS output by a three-wire circuit for three-phase AC, and output by a two-wire circuit for single-phase AC.

FIG. 7 is a main circuit connection diagram showing a general example of a power converter for outputting a three-phase three-wire three-phase AC, and shows a case of an uninterruptible power supply. 7, a rectifier 2 as a power supply converter for converting AC power from the AC power supply 1 into DC power, and a three-phase inverter 5 as a load converter for converting this DC power into three-phase AC power. The three-phase uninterruptible power supply 10 is composed of the smoothing capacitor 3 and the battery 4 connected to a DC intermediate circuit connecting the DC side of the rectifier 2 and the DC side of the three-phase inverter 5. The three-phase AC power output from the three-phase uninterruptible power supply 10 is supplied to the three-phase three-wire load 8 after being shaped by a filter circuit including the filter reactor 6 and the filter capacitor 7. The operation of the three-phase uninterruptible power supply 10 is irrelevant to the present invention, and a description thereof will be omitted.

FIG. 8 is a main circuit connection diagram showing a conventional example of obtaining a three-phase four-wire three-phase AC from a three-phase three-wire three-phase AC output from a power converter. In the conventional circuit of FIG. 8, the reactor 11 for neutral point generation, which is a star-connected reactor, is connected to the AC output side of the general uninterruptible power supply described in FIG. This is the configuration. A line drawn from the star connection point of the reactor 11 for generating a neutral point is a neutral line 12, and the neutral line 1 is connected to a three-phase three-wire circuit on the output side of the three-phase uninterruptible power supply 10.
By combining the two, a three-phase four-wire circuit is obtained, which may be connected to the three-phase four-wire load 13.

Although not shown, if three sets of autotransformers are star-connected in place of the reactor 11 for generating a neutral point, the neutral wire 12 can be drawn from the star connection point. A three-phase four-wire circuit is obtained. If the tap of the star-connected autotransformer is connected to the three-phase four-wire load 13, a voltage different from the output voltage of the three-phase uninterruptible power supply 10 is generated. It can be applied to the phase 4 wire load 13. Although not shown, the three-phase uninterruptible power supply 1
Between the zero and the three-phase four-wire load 13, for example, a three-phase transformer in which the primary winding has a delta connection and the secondary winding has a star connection is inserted, and a star connection point of the secondary winding is drawn. Neutral line 12
The three-phase uninterruptible power supply 10 and the three-phase four-wire load 13
And a three-phase four-wire circuit in which the voltage of the three-phase four-wire load 13 is different from the output voltage of the three-phase uninterruptible power supply 10 is obtained. A single-phase two-wire circuit is provided with a single-phase neutral point generating reactor, a single-phase single-turn transformer or a two-winding transformer in the same manner as described above.
Although a linear circuit is obtained, its illustration and description are omitted.

[0007]

The output circuit of a three-phase inverter is usually a three-phase three-wire system, and the output circuit of a single-phase inverter is also usually a single-phase two-wire system. In order to obtain a three-phase four-wire circuit or a single-phase three-wire circuit, it is necessary to use a reactor for generating a neutral point, an autotransformer, or a two-winding transformer. Because iron and copper are the main materials,
Since a large weight and size are required, there is a disadvantage that the whole apparatus becomes large and heavy, and there is a disadvantage that the price becomes high. When the output voltage of the power converter is, for example, 40
When the voltage rises to about 0 V, the DC intermediate circuit voltage rises to approximately 600 V in proportion to this. Since a smoothing capacitor connected to a DC intermediate circuit requires an extremely large capacitance, an aluminum electrolytic capacitor is generally used. However, it is difficult to manufacture an aluminum electrolytic capacitor having a high withstand voltage. Therefore, multiple aluminum electrolytic capacitors are connected in series and used.In this case, resistors are connected to equalize the voltage shared by each capacitor. This lowers the efficiency of the apparatus and raises the temperature.

Furthermore, in the case of an uninterruptible power supply, the voltage of a battery for backing up a power failure must be increased with an increase in the DC intermediate circuit voltage. As a result, the number of battery cells connected in series increases, causing a problem that reliability is reduced.
There is a problem of high price.

Accordingly, an object of the present invention is to provide a circuit configuration in which a neutral wire is added to an AC circuit output from a power converter, or to reduce the voltage of equipment connected to a DC intermediate circuit even if the output AC voltage increases. An object of the present invention is to reduce the weight and size of the device and avoid a decrease in reliability by avoiding an increase in rating.

[0010]

In order to achieve the above object, a power converter according to the present invention comprises a neutral phase output arm having a structure in which two sets of semiconductor switch elements are connected in series, and a DC intermediate of the power converter. These two elements are alternately turned on and off by connecting between the positive and negative electrodes of the circuit.The other end of the reactor connected to the neutral point of the neutral phase output arm is pulled out as a neutral line, so that the three-phase power In the case of a converter, a three-phase four-wire three-phase AC is obtained, and in the case of a single-phase power converter, a single-phase three-wire single-phase AC is obtained.

Alternatively, the smoothing capacitor connected between the positive and negative electrodes of the DC intermediate circuit forming the power conversion device is formed by connecting an even number of capacitors in series, and the neutral phase is formed by connecting two sets of semiconductor switch elements in series. An output arm is connected between the positive and negative electrodes of the DC intermediate circuit to turn on and off these two elements alternately, but the other end of the reactor connected to the intermediate point of the neutral phase output arm and an intermediate point of the smoothing capacitor By short-circuiting the point and the other end of this reactor as a neutral wire, a three-phase power converter can obtain a three-phase four-wire three-phase AC, and a single-phase power converter can obtain a single-phase three-phase AC. Wire-type single-phase alternating current shall be obtained.

Alternatively, the smoothing capacitor connected between the positive and negative electrodes of the DC intermediate circuit constituting the power conversion device is formed by connecting an even number of capacitors in series, and the neutral phase is formed by connecting two sets of semiconductor switch elements in series. An output arm is connected between the positive and negative electrodes of the DC intermediate circuit to turn on and off these two elements alternately, but the other end of the reactor connected to the intermediate point of the neutral phase output arm and an intermediate point of the smoothing capacitor Point, a battery is connected between the intermediate point of the smoothing capacitor and either the positive or negative pole of the DC intermediate circuit, and the other end of the reactor is pulled out as a neutral line, thereby providing three-phase power conversion. If the device is a three-phase four-wire type three-phase alternating current, a single-phase power converter is used to obtain a single-phase three-wire type single-phase alternating current.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a main circuit connection diagram showing a first embodiment of the present invention, and corresponds to claim 1. The AC power supply 1, the rectifier 2, and the smoothing circuit shown in FIG. The names, uses, and functions of the capacitor 3, the battery 4, the three-phase inverter 5, the filter reactor 6, the filter capacitor 7, and the three-phase four-wire load 13 are the same as those of the general circuit described above with reference to FIG. The description of the same parts is omitted.

In the circuit of the first embodiment shown in FIG. 1, a three-phase uninterruptible power supply 20 is constructed by adding a neutral phase output arm 21, a neutral phase arm drive circuit 22, and a neutral point output reactor 23. I have. That is, the neutral phase output arm 21 connecting two sets of semiconductor switch elements such as IGBTs (insulated gate bipolar transistors) in series is connected between the positive and negative electrodes of the DC intermediate circuit, and the positive and negative IGBTs are neutralized. The on / off operation is performed alternately by a signal from the phase arm drive circuit 22. The neutral point output reactor 23 is provided at an intermediate point of the neutral phase arm drive circuit 22 (a junction point between the positive side IGBT and the negative side IGBT). And the other end of the neutral point output reactor 23 is set to the neutral
Connect to line load 13.

The positive side I
The GBT and the negative electrode IGBT are alternately turned on and off at a time ratio of 1: 1. The on / off frequency at this time is arbitrary. Since the high frequency components generated by the on / off operation are absorbed by the neutral point output reactor 23, the output voltage of the neutral point output reactor 23 becomes equal to the virtual neutral point potential. Although the three-phase inverter 5 only controls the line voltage of the AC output, the three-phase uninterruptible power supply 20 can control the phase voltage with respect to the virtual neutral point potential. Phase alternating current can be provided to the three-phase four-wire load 13.

FIG. 2 is a main circuit connection diagram showing a second embodiment of the present invention, and corresponds to claim 2. This second embodiment is a circuit for realizing a single-phase three-wire circuit. The three-phase inverter 5 of the circuit of the first embodiment is replaced with a single-phase inverter 35.
The single-phase uninterruptible power supply 30 can be obtained by replacing the three-phase filter reactor 6 and the filter capacitor 7 with the single-phase filter reactor 36 and the filter capacitor 37. Although the phase AC power can be supplied to the single-phase three-wire load 14, the description of these operations will be omitted.

FIG. 3 is a main circuit connection diagram showing a third embodiment of the present invention, which corresponds to claim 3. The circuit of the third embodiment is the same as that of the first embodiment shown in FIG. As the smoothing capacitor 3 connected to the DC intermediate circuit of the circuit, an even number (FIG.
The three-phase uninterruptible power supply 40 is configured by adopting a series connection of the two smoothing capacitors 43P and 43N, which is different from the circuit of the first embodiment of FIG. Except for the above, the description is omitted for the same parts.

In the circuit of the third embodiment, the connection between the smoothing capacitors 43P and 43N is connected to the neutral point output reactor 23.
(That is, the neutral line 12), the potential at this point becomes the virtual neutral point potential as described above.
Therefore, the voltage of the smoothing capacitor 43P and the smoothing capacitor 4
This is equal to the voltage of 3N, so that a resistor for balancing voltage sharing is not required.

FIG. 4 is a main circuit connection diagram showing a fourth embodiment of the present invention, which corresponds to claim 4. The circuit of the fourth embodiment is a single-phase three-wire circuit which is the same as that of the first embodiment. In the third embodiment, the single-phase uninterruptible power supply 50 in which the three-phase inverter 5 of the circuit is changed to the single-phase inverter 35, and the three-phase filter reactor 6 and the filter capacitor 7 are replaced with the single-phase filter reactor 36 and the filter capacitor 37. This can be achieved by: Therefore, description of the operation of the fourth embodiment will be omitted.

FIG. 5 is a main circuit connection diagram showing a fifth embodiment of the present invention, and corresponds to claim 5. The circuit of the fifth embodiment is the same as that of the third embodiment shown in FIG. The battery 4 connected to the DC intermediate circuit of the circuit is connected to a smoothing capacitor 43P.
And the connection point 43N and the negative terminal of the DC intermediate circuit (the same applies between the connection point and the positive terminal of the DC intermediate circuit) to constitute a three-phase uninterruptible power supply. Except for this point, all of them are the same.

In the circuit of the fifth embodiment, since the voltages of the smoothing capacitors 43P and 43N are both half of the DC intermediate circuit voltage as described above, the voltage of the battery 4 can be reduced as compared with the prior art. .

FIG. 6 is a main circuit connection diagram showing a sixth embodiment of the present invention, and corresponds to claim 6. This sixth embodiment circuit is a three-phase circuit of the fifth embodiment circuit. Inverter 5
-Phase uninterruptible power supply 70 in which
By replacing the three-phase filter reactor 6 and the filter capacitor 7 with the single-phase filter reactor 36 and the filter capacitor 37, a single-phase three-wire circuit can be realized. Therefore, description of the operation of the sixth embodiment will be omitted.

[0023]

Since the ordinary power converter is configured to output a three-phase three-wire type or a single-phase two-wire type alternating current, a three-phase four-wire type or a single-phase three-wire type having a neutral wire is provided. To obtain AC, large and heavy equipment such as transformers and reactors made mainly of iron and copper was required. Also, since the DC intermediate circuit voltage also increases with the increase in the output AC voltage of the power converter, the voltage of the smoothing capacitor using an aluminum electrolytic capacitor connected to this DC intermediate circuit and the voltage of the battery that backs up the power failure is reduced. As the temperature increases, various inconveniences such as a decrease in the efficiency of the device, an increase in heat generation, a decrease in the reliability, and an increase in the size and the price of the protection device are occurring.

According to the present invention, a neutral phase output arm composed of a semiconductor switch element is connected to a DC intermediate circuit of a power conversion device, and this is turned on and off alternately at a time ratio of 1: 1. As a result, a virtual neutral point potential can be obtained via the neutral point output reactor connected to the intermediate point of the neutral phase output arm. Since three-phase four-wire or single-phase three-wire AC can be easily obtained without using large-sized and heavy equipment, the effect of avoiding large and heavy equipment and reducing costs can be achieved. can get.

Further, if the smoothing capacitor connected to the DC intermediate circuit is formed by connecting an even number of capacitors in series, and the intermediate point thereof is connected to the virtual neutral point potential generation point, a voltage balancing resistor can be used. Even without this, the voltages of the capacitors connected in series can be equalized, so that even if the voltage of the DC intermediate circuit is increased, the effect that the efficiency of the device is reduced and heat generation can be avoided can be obtained.

Further, since a backup battery at the time of power failure can be connected in parallel to a part of the divided smoothing capacitor, the battery voltage can be kept low even if the DC intermediate circuit is increased in voltage. Therefore, the battery protection device can be simplified, and the number of battery cells connected in series can be reduced.

[Brief description of the drawings]

FIG. 1 is a main circuit connection diagram showing a first embodiment of the present invention.

FIG. 2 is a main circuit connection diagram showing a second embodiment of the present invention.

FIG. 3 is a main circuit connection diagram showing a third embodiment of the present invention.

FIG. 4 is a main circuit connection diagram showing a fourth embodiment of the present invention.

FIG. 5 is a main circuit connection diagram showing a fifth embodiment of the present invention.

FIG. 6 is a main circuit connection diagram showing a sixth embodiment of the present invention.

FIG. 7 is a main circuit connection diagram showing a general example of a power converter that outputs a three-phase three-wire three-phase AC.

FIG. 8 is a main circuit connection diagram showing a conventional example of obtaining a three-phase four-wire three-phase AC from a three-phase three-wire three-phase AC output from a power converter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier as power supply side converter 3 Smoothing capacitor 4 Battery 5 Three phase inverter as load side converter 6,36 Filter reactor 7,37 Filter capacitor 8 Three phase three wire load 10 Three phase uninterruptible power supply 11 Neutral point generating reactor 12 Neutral wire 13 Three phase four wire load 14 Single phase three wire load 20, 40, 60 Three phase uninterruptible power supply 21 Neutral phase output arm 22 Neutral phase arm drive circuit 23 Neutral point Output reactor 30, 50, 70 Single-phase uninterruptible power supply 35 Single-phase inverter 43P, 43N as load-side converter Smoothing capacitor

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takahiro Nonaka 1-1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term in Fuji Electric Co., Ltd. 5H007 AA06 BB05 CA01 CB05 CC01 CC09 HA02

Claims (7)

[Claims] A power converter for converting AC to DC, a load converter for converting DC to three-phase AC, and a DC side of the power converter and a DC side of the load converter are coupled. In a power converter that outputs a three-phase three-wire three-phase alternating current, which is composed of a DC intermediate circuit and a smoothing capacitor connected to the DC intermediate circuit, two sets of semiconductor switch elements are connected in series. A neutral phase output arm is connected between the positive and negative electrodes of the DC intermediate circuit constituting the power conversion device, and both elements are alternately turned on and off, and a reactor is provided at an intermediate point of the neutral phase output arm. One end is connected and the other end of this reactor
A power converter characterized by obtaining a three-phase alternating current of a wire type. 2. A power converter for converting AC to DC, a load converter for converting DC to single-phase AC, and a DC side of the power converter and a DC side of the load converter are coupled. In a power converter that outputs a single-phase two-wire single-phase alternating current constituted by a DC intermediate circuit and a smoothing capacitor connected to the DC intermediate circuit, two sets of semiconductor switch elements are connected in series. A neutral phase output arm is connected between the positive and negative electrodes of the DC intermediate circuit constituting the power conversion device, and both elements are alternately turned on and off, and a reactor is provided at an intermediate point of the neutral phase output arm. One end is connected and the other end of this reactor is
A power converter characterized by obtaining a single-phase AC of a wire system. 3. A power converter for converting AC into DC, a load converter for converting DC into three-phase AC, and a DC side of the power converter and a DC side of the load converter are coupled. A DC intermediate circuit, and a smoothing capacitor connected to the DC intermediate circuit, to output a three-phase three-wire three-phase AC, wherein the smoothing capacitor includes an even number of capacitors connected in series. A neutral phase output arm consisting of a series connection of two semiconductor switch elements is connected between the positive and negative electrodes of a DC intermediate circuit constituting the power converter, and both elements are alternately turned on and off. Operate, connect one end of the reactor to the middle point of this neutral phase output arm, short-circuit the middle point of the smoothing capacitor and the other end of the reactor, make the other end of the reactor a neutral wire, Obtaining 4-wire three-phase AC A power converter characterized by the above-mentioned. 4. A power converter for converting AC to DC, a load converter for converting DC to single-phase AC, and a DC side of the power converter and a DC side of the load converter are coupled. A DC intermediate circuit, and a smoothing capacitor connected to the DC intermediate circuit, and outputs a single-phase two-wire single-phase alternating current, wherein the smoothing capacitor includes an even number of capacitors connected in series. A neutral phase output arm consisting of a series connection of two sets of semiconductor switch elements is connected between the positive and negative electrodes of a DC intermediate circuit constituting the power converter, and both elements are turned on and off alternately. Operate, connect one end of the reactor to the middle point of this neutral phase output arm, short-circuit the middle point of the smoothing capacitor and the other end of the reactor, make the other end of this reactor a neutral wire, Obtaining 3-wire single-phase AC A power converter characterized by the above-mentioned. 5. A power converter for converting AC to DC, a load converter for converting DC to three-phase AC, and connecting a DC side of the power converter and a DC side of the load converter. A DC intermediate circuit, and a smoothing capacitor connected to the DC intermediate circuit, to output a three-phase three-wire three-phase AC, wherein the smoothing capacitor includes an even number of capacitors connected in series. A neutral phase output arm consisting of a series connection of two semiconductor switch elements is connected between the positive and negative electrodes of a DC intermediate circuit constituting the power converter, and both elements are alternately turned on and off. One end of the reactor is connected to the intermediate point of the neutral phase output arm, the intermediate point of the smoothing capacitor is short-circuited to the other end of the reactor, and the intermediate point of the smoothing capacitor and the positive and negative of the DC intermediate circuit are connected. With either pole A power conversion device, wherein a battery is connected between the two reactors, and the other end of the reactor is set to a neutral wire to obtain a three-phase four-wire three-phase alternating current. 6. A power converter for converting AC to DC, a load converter for converting DC to single-phase AC, and connecting a DC side of the power converter and a DC side of the load converter. A DC intermediate circuit, and a smoothing capacitor connected to the DC intermediate circuit. The power conversion device outputs a single-phase two-wire single-phase alternating current. A neutral phase output arm consisting of a series connection of two semiconductor switch elements is connected between the positive and negative electrodes of a DC intermediate circuit constituting the power converter, and both elements are alternately turned on and off. The intermediate point of the neutral phase output arm is connected to one end of the reactor, the intermediate point of the smoothing capacitor is short-circuited to the other end of the reactor, and the intermediate point of the smoothing capacitor and the positive and negative of the DC intermediate circuit are connected. With either pole A power conversion device characterized in that a battery is connected between the two reactors, and the other end of the reactor is used as a neutral wire to obtain a single-phase three-wire single-phase alternating current. 7. The power converter according to claim 1, wherein the two sets of semiconductor switch elements connected in series constituting the neutral phase output arm are alternately turned on and off and turned on and off. An electric power conversion device, wherein an operation is performed such that an off time is equal.