JPH08230523A - Method and apparatus for controlling voltage of changeover section in ac feeder circuit - Google Patents

Abstract

PURPOSE: To prevent instant power stoppage during passage in a changeover section and eliminate in-rush current in the change-over of feeder voltage by adjustably equalizing the phase, frequency and amplitude of AC output voltage of an electric power converter to those of the other feeder line voltage. CONSTITUTION: Single phase AC power is once converted to DC power by a single phase self-exciting voltage type power converter 9a connected through a transformer 8a to a M seat feeder line 5. After the DC power is smoothed by a DC capacitor 10, it is converted to the single phase AC voltage having any amplitude, frequency and phase by the single phase self-exciting voltage type power converter 9b to be applied to a changeover section through the transformer 8b. Thus, an electric car passing through the section can be prevented from provisional power stoppage, inflow of inrush current to a load transformer or the like. Also, inrush current to a power system is restrained while a prior changeover breaker is disused to improve substantially the reliability of the changeover section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC feeder circuit using a Scott connection transformer, which is used when a train load is transferred from one feeder wire of the Scott connection transformer to the other feeder wire of the other seat. The present invention relates to a voltage control method and a voltage control device for a switching section.

[0002]

2. Description of the Related Art First, the relationship between the primary and secondary voltages of a Scott connection transformer is shown below. FIG. 13 shows power supplies 16a, 16
Two single-phase AC loads (M seat load 21 and T) from the three-phase AC power supply composed of b and 16c via the Scott connection transformer 2.
An example in which single-phase AC power is supplied to the seat load 22) is shown. In such a power feeding method, the relationship of the single-phase AC voltage supplied to the load side is as follows. First, the power supply voltages E _u , E _v , and E _w are defined as in Equation 1 below.

[0003]

[Number 1] _{E u = √2Esinωt E v = √2Esin} (ωt-2π / 3) E w = √2Esin (ωt-4π / 3)

However, in the equation 1, E: effective value of power supply voltage, ω: angular frequency of power supply, t: time. Here, the output voltages E _M and E _T of the M seat and the T seat of the Scott connection transformer 2 can be expressed by Expression 2.

[0005]

[Number 2] _{E M = E u -E w =} √6Ecos (ωt-2π / 3) E T = √3E v = √6Esin (ωt-2π / 3)

In FIG. 13, 17 is a primary winding of the M-seat transformer, 18 is a secondary winding, 19 is a primary winding of the T-seat transformer, and 20 is a secondary winding. The primary and secondary transformation ratios of the transformer and T-seat transformer are √3 / 2 and 1, respectively. As is clear from the equation 2, it can be seen that the power supply voltages supplied to the M and T seats have a phase difference of 90 degrees in electrical angle.

FIG. 14 shows an AC power feeding type substation in which power is supplied by a Scott connection transformer 2 connected to a three-phase power system 1, and power is supplied when a train load shifts from one seat to another seat. An example of the method is shown. As can be seen from this figure, in such a power feeding method, the train 7 has M
Since there is a 90-degree phase difference between the M seat voltage and the T seat voltage when moving from the T seat wire 6 to the T seat wire 6, it is necessary to always move through the switching section 4.

That is, as shown in the figure, the electric train 7 is fed from the M-seat electric wire 5 and the circuit breaker 3 is running while traveling toward the T-seat.
The train 7 enters the switching section 4 in the state where a is “closed”, the circuit breaker 3b is “open”, and the M seat voltage is applied to the switching section 4. Next, after confirming that the train 7 has completely entered the switching section 4, the circuit breaker 3a is opened and then the circuit breaker 3b is closed after a lapse of a predetermined confirmation time. The T seat voltage is reapplied to section 4.

As a result, the train 7 that was on the M seat electric wire 5
Will pass through the switching section 4 and enter the T-sitting electric wire 6, so that it is possible to move from one feeding electric wire 5 to the other feeding electric wire 6. Similarly, when the train 7 moves from the T-sitting electric wire 6 to the M-sitting electric wire 5, the train 7 can pass through the switching section 4 by a completely opposite operation.

[0010]

In the case of such a section passage method, there is a time during which the feeder 7 is always in a no-voltage state while the train 7 is passing through the switching section 4, and an instantaneous power failure occurs. At the time of reapplying the voltage when switching the applied voltage of the switching section 4 from one feeding voltage to the other feeding voltage, there is a 90-degree phase difference between the voltages, so inrush current or the like may occur in the load transformer of the train 7. Flows and shocks the load transformer. The switching breakers 3a and 3b are opened and closed very often, and a failure or the like is relatively likely to occur. There are problems such as.

The present invention has been made to solve the above problems, and its purpose is to prevent momentary power failure during passage of a switching section and to eliminate inrush current at the time of switching feeding voltage. SUMMARY OF THE INVENTION It is an object of the present invention to provide a voltage control method and a voltage control device for a switching section, in which a failure caused by frequent opening and closing of a switching circuit breaker is prevented and reliability is improved.

[0012]

In order to achieve the above object, the present invention is to connect a voltage type power converter capable of freely adjusting the amplitude, frequency and phase of an output voltage to a switching section and to connect the switching section. The voltage of is adjusted arbitrarily.

That is, the first aspect of the voltage control method according to the present invention is to provide two independent single-phase AC power sources on the secondary side of a Scott connection transformer whose primary side is connected to a three-phase power system. In an AC feeding circuit that feeds two independent feeders, in the voltage control method of the switching section, connect the AC side of the single-phase voltage type power converter to the switching section and proceed from one feeder side. Until the train completely enters the switching section, the phase, frequency, and amplitude of the AC output voltage of the power conversion device, the phase of one feeder voltage feeding the train before entering the switching section, With the same frequency and amplitude, between the time when the train completely enters the switching section and the time when it enters the other feeder, the phase and frequency of the AC output voltage of the power converter,
The amplitude is adjusted to be the same as the phase, frequency and amplitude of the other feeder voltage.

A second invention relating to the voltage control method according to the second aspect is that a train having a single-phase voltage type power conversion device connected to the switching section has an AC side connected thereto, and a train traveling from one feeder line side. Until completely entering the switching section, the amplitude of the AC output voltage of the power converter is set to zero, and the electric power is supplied between the time when the train completely enters the switching section and the other feeder. The amplitude of the AC output voltage of the converter is adjusted to be the same as the amplitude of the other feeder voltage.

According to these inventions, the feeder does not become unvoltaged while passing through the switching section, and the instantaneous power failure of the train is prevented. In addition, there is no phase difference in voltage when exiting from one feeder line and entering the switching section, and when exiting from the switch section and entering the other feeder line, so there is no in-rush current and load transformers, etc. are suppressed. Eliminate the shock to. Furthermore, the switching breaker is also unnecessary.

A third invention relating to the voltage control device according to claim 3 is the voltage control device for carrying out the voltage control method according to the first or second invention, wherein two single-phase self-excited voltage source power converters are used. The DC side of the devices is commonly connected, the AC side of one power converter is connected to one of the two single-phase AC power supplies, and the AC side of the other power converter is connected to the switching section. .

According to a fourth aspect of the voltage control apparatus of the present invention, in the voltage control apparatus for implementing the voltage control method according to the first or second aspect of the invention, two single-phase AC power supplies are connected to Scott connection transformers. The three-phase AC power supply is made by the converter, and the DC side of the single-phase self-excited voltage-type power converter is connected to the DC side of the three-phase self-excited voltage-type power converter in which the AC side is connected to this three-phase AC power supply. The AC side is connected to the switching section.

According to a fifth aspect of the voltage control apparatus of the present invention, in the voltage control apparatus for implementing the voltage control method according to the first or second aspect of the invention, the AC side is connected to the three-phase power system. The DC side of the three-phase self-excited voltage type power converter is connected to the DC side of the single-phase self-excited voltage type power converter, and the AC side is connected to the switching section.

According to a sixth aspect of the voltage control apparatus of the present invention, in the voltage control apparatus for implementing the voltage control method according to the first or second aspect, two ends of each of the two single-phase AC power supplies are connected. The power of two single-phase AC power supplies can be exchanged between these power converters by connecting to the AC side of each of the two single-phase self-excited voltage-type power converters and connecting the DC side of each power converter. In addition to the above, the AC side of another single-phase self-excited voltage type power converter is connected to the switching section, and the DC side thereof is connected to the DC side of the two power converters.

In the third to sixth aspects of the invention, a general-purpose single-phase self-excited voltage type power converter, a three-phase self-excited reactive power compensator, etc. can be used, and a simple circuit configuration can be used in the switching section. A desired voltage control can be performed.

A seventh invention relating to the voltage control device according to claim 7 is the voltage control device according to any one of the third to sixth inventions, wherein the power converter provided on the power supply side is a self-exciting voltage type. Instead of the power converter, a diode rectifier, a thyristor rectifier, or a reversible thyristor rectifier is used. Of these, the diode rectifier and the thyristor rectifier can be applied to a system that does not need to regenerate DC power to the AC power.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 shows the relationship between the M seat voltage E _M and the T seat voltage E _T output by the Scott connection transformer. As is clear from the figure, an electrical angle of 90 between the M seat voltage E _M and the T seat voltage E _T
There is a phase difference in degree, and the M seat voltage E _M leads the T seat voltage E _T and has a phase.

FIG. 2 shows the operation of the first embodiment of the invention. The solid line in the figure indicates the output voltage at each time of the single-phase voltage-type power conversion device in which the AC side is connected to the switching section when the train travels from the M-sitting wire to the T-sitting wire through the switching section. The phase relationship is shown.

That is, ΔT from the time T1 when the train moving from the M seat electric wire completely entered the switching section.
The voltage in the same phase as the M seat wire is output to the switching section until time T2 after ₁ and the phase of the output voltage is 90 degrees at time T3, which is ΔT ₂ earlier than time T4 when the train starts entering the T seat wire. It is delayed and controlled to the same phase as the voltage of the T-seat wire. Note that the frequency and amplitude of the output voltage of the power conversion device are the same as the frequency and amplitude of the M-seat line voltage from time T1 to time T2 after ΔT _1, and are the same as the frequency and amplitude of the T-seat line voltage before time T3. Adjust so that the frequency and amplitude are the same.

On the other hand, the broken line in FIG. 2 indicates the phase relationship of the output voltage at each time of the single-phase voltage type power converter when the electric train travels from the T-seat wire to the M-seat wire through the switching section. Is shown. That is, from the time T1 when the train moving from the T-seat wire completely enters the switching section to the time T2 after ΔT ₁ , the voltage in the same phase as the T-seat wire is output to the switching section, and the train is The output voltage phase is advanced by 90 degrees at time T3, which is ΔT ₂ earlier than time T4 when starting to enter the feeder line, and is controlled to have the same phase as the voltage of the M-seat line. Further, the frequency and amplitude of the output voltage of the power conversion device are the same as the frequency and amplitude of the T-seat line voltage from time T1 to time T2 after ΔT _1, and are the same as those of the M-seat line voltage until time T3. Adjust so that the frequency and amplitude are the same.

In FIG. 2, the amount of change in the output voltage phase of the power conversion device per unit time between time T2 and time T3 is constant, but this need not always be constant.
It does not matter if the amount of change is changed.

FIG. 3 shows the operation of the second embodiment of the invention. This figure shows the output voltage value at each time of the single-phase voltage type power converter with the AC side connected to the switching section when the train enters the other feeding wire through the switching section from one feeding wire. Shows.

For example, when the train travels from the T-seat wire to the M-seat wire through the switching section, the switching section is operated from time T1 when the train completely enters the switching section to time T2 after ΔT _1. 0 is output to the train and the train is M
At time T3, which is ΔT ₂ earlier than time T4 at which entry into the sitting wire is started, control is performed so as to output a voltage having the same phase and amplitude as the M sitting wire. In FIG. 3, the change amount per hour of the output voltage of the power conversion device between time T2 and time T3 is constant, but it is not necessarily constant, and the change amount may be changed.

When the train travels from the M-sitting wire to the T-sitting wire via the switching section, the switching section is operated from time T1 when the train completely enters the switching section to time T2 after ΔT _1. 0 is output at time T, which is earlier than time T4 when the train starts to enter the T-seat wire by ΔT ₂
In 3, the control is performed so as to output a voltage having the same phase and the same amplitude as the T seat wire.

FIG. 4 shows the configuration of an embodiment of the third invention. Each of the following embodiments relates to a voltage control device for directly implementing the voltage control method of the first or second invention. In the embodiment of FIG. 4, the single-phase self-excited voltage-type power converter 9a connected to the M seat wire 5 via the transformer 8a once converts the single-phase AC power into DC power, which is then converted by the DC capacitor 10. After smoothing, the single-phase self-excited voltage-type power converter 9b converts the voltage into a single-phase AC voltage having an arbitrary amplitude, frequency, and phase, and the transformer 8b.
It is applied to the switching section 4 via. In addition,
The same components as those in FIG. 14 are designated by the same numbers.

FIG. 5 shows the structure of the main part of FIG. The single-phase AC power input from the M-seat wire 5 is applied to the transformer 8
A power converter 9 which is insulated by a and is configured by GTO thyristors 13a to 13d as power semiconductor switching elements and freewheeling diodes 14a to 14d respectively connected in anti-parallel to the GTO thyristors 13a to 13d.
It is converted into DC power by a.

This DC power is converted into a power converter 9 having the same structure.
b (composed of GTO thyristors 13e to 13h and freewheeling diodes 14e to 14h) is converted into alternating current power again to apply an alternating voltage of arbitrary amplitude, frequency and phase to the switching section 4 via the transformer 8b. can do. In the present embodiment, the AC side input of the single-phase self-excited voltage source power converter 9a is connected to the M-seat electric wire 5, but this is connected to the T-sitting electric wire 6 to feed power from this electric wire 6. It does not matter as a configuration.

FIG. 6 shows an embodiment of the fourth invention. In this embodiment, two single-phase AC powers of the M-seat wire 5 and the T-seat wire 6 are converted into three-phase AC power by a Scott connection transformer 2b different from the Scott connection transformer 2a on the side of the power system 1. After conversion, the three-phase self-excited voltage-type power converter 12
To convert it to DC power, and then use this DC capacitor 1
After being smoothed by 0, a single-phase self-excited voltage-type power converter 9
Is converted into a single-phase AC voltage having an arbitrary amplitude, frequency, and phase and applied to the switching section 4. The other components are given the same numbers as in the previous embodiments.

FIG. 7 shows the structure of the main part of FIG. Each single-phase AC power input from the M-seat wire 5 and the T-seat wire 6 is converted into a three-phase AC power via the Scott connection transformer 2b, and this three-phase AC power is converted into a GTO thyristor 13
a to 13f and freewheeling diodes 14a to 14f respectively connected in anti-parallel to the a to 13f to convert the power into DC power.

This DC power is supplied to the GTO thyristor 13g-
13j and free-wheeling diodes 14g to 14j each connected in anti-parallel to each other to convert the power into a single-phase AC power by a power converter 9, thereby allowing a desired amplitude in the switching section 4 via a transformer 8b. -A single-phase AC voltage with frequency and phase can be applied.

FIG. 8 shows an embodiment of the fifth invention.
In this embodiment, the three-phase self-excited voltage-type power converter 12 temporarily converts the three-phase AC power into the DC power, which is smoothed by the DC capacitor 10, and then the single-phase self-excited voltage-type power converter 9 is used. Is applied to the switching section 4 after being converted into a single-phase AC voltage having the amplitude, frequency and phase. The other components are given the same numbers as in the previous embodiments.

FIG. 9 is a block diagram of the main part of FIG. The three-phase AC power input from the three-phase power system 1 is insulated via the transformer 8a, and this AC power is isolated from the GTO thyristors 13a to 13a.
The DC power is converted by the power conversion device 12 including 13f and freewheeling diodes 14a to 14f that are respectively connected in anti-parallel to them.

This DC power is supplied to the GTO thyristor 13g-
13j and free-wheeling diodes 14g to 14j each connected in anti-parallel to each other to convert the electric power into a single-phase AC power by a power converter 9, thereby allowing a desired amplitude in the switching section 4 via a transformer 8b. -A single-phase AC voltage with frequency and phase can be applied.

Here, the circuit configuration of the three-phase self-excited voltage type power converter 12 of the embodiment shown in FIGS. 7 and 9 is the same as that of the self-excited reactive power compensator (self-excited SVC) currently put into practical use. Therefore, the three-phase self-excited voltage source power converter 12 may be configured to have both functions. Further, as the power converter for converting the three-phase AC power into the DC power, the six-arm power converter has been described in FIGS. 7 and 9, but the power converter having the 12-arm configuration with three single-phase power converters is used. It may be configured.

FIG. 10 shows an embodiment of the sixth invention. In this embodiment, a single-phase self-excited voltage source power converter 9
The AC side of a and 9b is connected to the M seat electric wire 5 and the T seat electric wire 6 via the transformers 8a and 8b.
By connecting the DC sides of a and 9b to each other via the DC capacitor 10, the single-phase AC power between the M seat and the T seat can be exchanged via the DC circuit.

Further, the direct-current side of another single-phase self-excited voltage type power converter 9c is connected to both ends of the direct-current capacitor 10, and the alternating-current side thereof is connected to the switching section 4 via the transformer 8c, thereby making it optional. The single-phase AC voltage having the amplitude, frequency, and phase is applied to the switching section 4.
The other components are given the same numbers as in the previous embodiments.

FIG. 11 shows the structure of the main part of FIG. The single-phase AC power input from the M-seat wire 5 and the T-seat wire 6 is insulated and stepped up / down through the transformers 8a and 8b, and this AC power is supplied to the GTO thyristors 13a to 13a.
d and a freewheeling diode 14a to 14d respectively connected in anti-parallel to the power converter 9a, and similarly to the GTO thyristors 13e to 13h.
And freewheeling diodes 14e to 14h connected in anti-parallel to each of them and converted into DC power by a power converter 9b, and each DC side is connected via a DC capacitor 10. As a result, the M-seat electric wire 5 and the T-sitting electric wire 6 are connected to each other via the DC circuit, and the single-phase AC power of both is exchanged.

The DC side of the single-phase self-excited voltage source power converter 9c composed of GTO thyristors 13i to 13l and freewheeling diodes 14i to 14l respectively connected in anti-parallel to the both ends of the DC capacitor 10 is provided. By connecting and connecting the AC side to the switching section 4 via the transformer 8c, a single-phase AC voltage of arbitrary amplitude, frequency, and phase can be applied to the switching section 4.

FIG. 12 shows an embodiment of the seventh invention. In this embodiment, as a power converter on the power supply side of each of the above embodiments, that is, a power converter for converting (rectifying) three-phase or single-phase AC power into DC power, a diode rectifier is used instead of the self-excited power converter. (Fig. 12 (a)),
A thyristor (SCR) rectifier (the same (b)) or a reversible thyristor rectifier (the same (c)) is used. In addition, in FIGS. 12B and 12C, 15a to 15l indicate thyristors (SCRs). Here, the configurations of FIGS. 12A and 12B can be applied when it is not necessary to regenerate the electric power on the DC side to the AC side.

In each of the embodiments described above, the GTO thyristor is described as an example of the power semiconductor switching element, but a power transistor, an IGBT (insulated gate bipolar transistor), or other self-extinguishing semiconductor element is used. It may be configured. Further, a plurality of self-extinguishing semiconductor elements are connected in series or in parallel to form one arm of a power converter, or as a power converter, a plurality of power converters are prepared and connected in multiple. It doesn't matter.

[0046]

INDUSTRIAL APPLICABILITY As described above, the present invention provides a switching section through which a train load passes when shifting from one seat of the Scott transformer to the other in an AC feeding circuit that is fed by a Scott connection transformer. A single-phase voltage type power converter is connected and the phase, amplitude, etc. of the voltage output by this power converter are adjusted. As a result, it is possible to prevent an instantaneous power failure of the train passing through the section, an inrush current flowing into the load transformer, and the like. In addition, the reliability of the switching section can be significantly improved by suppressing the inrush current to the power system and eliminating the conventional switching breaker.

[Brief description of drawings]

FIG. 1 is a diagram showing a secondary voltage waveform of a Scott connection transformer.

FIG. 2 is a diagram showing the operation of the embodiment of the first invention.

FIG. 3 is a diagram showing an operation of an embodiment of the second invention.

FIG. 4 is an overall configuration diagram of an embodiment of the third invention.

5 is a configuration diagram of a main part in FIG.

FIG. 6 is an overall configuration diagram of an embodiment of the fourth invention.

7 is a configuration diagram of a main part in FIG.

FIG. 8 is an overall configuration diagram of an embodiment of the fifth invention.

9 is a configuration diagram of a main part in FIG.

FIG. 10 is an overall configuration diagram of an embodiment of the sixth invention.

11 is a configuration diagram of a main part in FIG.

FIG. 12 is a configuration diagram of a main part in an embodiment of the seventh invention.

FIG. 13 is an explanatory diagram of a usage example of a Scott connection transformer.

FIG. 14 is an explanatory diagram of a section switching method according to a conventional technique.

[Explanation of symbols]

1 Three-phase power system 2, 2a, 2b Scott connection transformer 3a, 3b Switching breaker 4 Switching section 5 M sitting wire 6 T sitting wire 7 Train 8a-8c Transformer 9, 9a-9c Single-phase self-excited voltage Type power conversion device 10 DC capacitor 12 three-phase self-excited voltage type power conversion device 13a to 13l Gate turn-off (GTO) thyristor 14a to 14l Diode 15a to 15l Thyristor (SCR) 16a to 16c AC power supply 17 M seat transformer primary winding 18 M seat transformer secondary winding 19 T seat transformer primary winding 20 T seat transformer secondary winding 21 M seat load 22 T seat load

Claims (7)

[Claims] 1. An AC feeding circuit for feeding two independent feeders from two independent single-phase AC power sources on the secondary side of a Scott connection transformer whose primary side is connected to a three-phase power system, In the voltage control method for the switching section, the AC section of the single-phase voltage type power converter is connected to the switching section, and the electric power conversion is performed until the train traveling from one feeder side completely enters the switching section. The phase, frequency, and amplitude of the AC output voltage of the equipment should be the same as the phase, frequency, and amplitude of one feeder voltage feeding the train before entering the switching section, so that the train has completely entered the switching section. From entering the other feeder line, the phase of the AC output voltage of the power converter, the frequency, the amplitude of the other feeder voltage phase,
A voltage control method for a switching section in an AC feeding circuit, characterized by adjusting the frequency and amplitude to be the same. 2. In an AC feeding circuit that feeds two independent feeders from two independent single-phase AC power sources on the secondary side of a Scott connection transformer whose primary side is connected to a three-phase power system, In the voltage control method for the switching section, the AC section of the single-phase voltage type power converter is connected to the switching section, and the electric power conversion is performed until the train traveling from one feeder side completely enters the switching section. The amplitude of the AC output voltage of the device is set to zero, and the amplitude of the AC output voltage of the power converter is adjusted to the voltage of the other feeder line between the time when the train completely enters the switching section and the time when it enters the other feeder line. The voltage control method of the switching section in the AC feeding circuit is characterized in that the voltage is adjusted to be the same as the amplitude of. 3. A voltage control device for implementing the voltage control method according to claim 1 or 2, wherein the DC sides of two single-phase self-excited voltage source power converters are commonly connected, and the AC of one of the power converters is connected. A voltage control device for a switching section in an AC feeding circuit, characterized in that the side is connected to one of the two single-phase AC power supplies and the AC side of the other power converter is connected to the switching section. 4. A voltage control device for implementing the voltage control method according to claim 1 or 2, wherein a three-phase AC power supply is made from two single-phase AC power supplies by a Scott connection transformer, and an AC is applied to the three-phase AC power supply. Side is connected to the DC side of the three-phase self-excited voltage type power converter, the DC side of the single-phase self-excited voltage type power converter is connected, and the AC side is connected to the switching section. Voltage control device for switching section in electric circuit. 5. A voltage control apparatus for implementing the voltage control method according to claim 1 or 2, wherein a single-phase self-excited type is provided on a DC side of a three-phase self-excited voltage source power converter in which an AC side is connected to a three-phase power system. A voltage control device for a switching section in an AC feeding circuit, characterized in that the DC side of an excitation voltage type power converter is connected and the AC side thereof is connected to the switching section. 6. The voltage control device for implementing the voltage control method according to claim 1 or 2, wherein the two ends of each of the two single-phase AC power supplies are respectively connected to the AC sides of the two single-phase self-excited voltage source power converters. In addition to connecting the DC side of each power converter, the power of the two single-phase AC power sources can be exchanged between these power converters, and yet another single-phase self-excited voltage source power converter. A voltage control device for a switching section in an AC feeding circuit, characterized in that the AC side of the device is connected to the switching section and its DC side is connected to the DC side of the two power conversion devices. 7. A voltage control device for a switching section in an AC feeding circuit according to claim 3, 4, 5 or 6, wherein a self-exciting voltage type power is used as a power conversion device provided on the power supply side. A voltage control device for a switching section in an AC feeding circuit, characterized in that a diode rectifier, a thyristor rectifier, or a reversible thyristor rectifier is used instead of the conversion device.