JPH02174562A - Voltage type converter - Google Patents

Abstract

PURPOSE:To protect a semi-conductor element from breakdown by magnetically coupling first and second conductors connected each other with reverse polarity and operating converters in phase at high and low potential sides. CONSTITUTION:First conductor 12 connecting between one end of a high potential side capacitor having the other end connected with positive pole and the negative pole of the high potential side converter 9 is magnetically coupled with second conductor 13 connecting between one end of a low potential side capacitor 5 having the other end connected with the negative pole of the low potential side converter 10 and the positive polarity of the low potential side converter 10, where the high potential side converter 9 and the low potential side converter 10 are operated in phase. The conductors 12, 13 function as normal connecting conductors during steady operation. If trouble occurs, the capacitors 2, 5 are discharged through the conductors 12, 13, and the conductors 12, 13 function as reactors and suppress di/dt of discharge current.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) The present invention relates to a voltage source converter used in an AC/DC converter, etc., and particularly relates to a voltage source converter used in an AC/DC converter, etc.
This invention relates to a voltage source converter that can suppress dt.

(Prior Art) In applications such as direct current power transmission, a method is adopted in which the direct current voltage is increased as much as possible and the current is reduced in order to reduce power transmission loss. For this reason, when using a voltage source converter as an AC/DC converter, it is conceivable to connect the voltage source converters in series.

FIG. 4 is a diagram showing a typical series connection configuration of voltage source converters. In the figure, 1 is a DC circuit, 2 and 5 are DC capacitors, 3A to 3F and 6A to 6F are arms composed of semiconductor elements such as GTO that constitute the voltage source converter, and 4゜7 is a converter. The power transformer 8 is an AC circuit.

In the circuit configured as shown in the figure, forward converter operation and reverse converter operation are performed by turning on and off the bridge arms 38 to 3F and 6A to 6F of the voltage source converter in a predetermined order. is supplied from the DC circuit l to the AC circuit 8,
Conversely, power can be supplied from the AC circuit 8 to the DC circuit 1.

(Problem to be Solved by the Invention) If for some reason in the voltage transformer, arm 3D is short-circuited while arm 3A is on, or point A is grounded, DC capacitor 2 or DC capacitor 2 and 5 are short-circuited through arm 3A. The inductance of this short circuit is small, consisting only of the DC capacitor and the converter bridge, so the short circuit current d
i/d t is extremely large. Incidentally, although the arms 3A to 3F and 68 to 6F constituting the voltage transformer have current interrupting ability, there is a limit to the interrupting current. Therefore,
Even if this type of fault is detected and an attempt is made to interrupt the fault current using a healthy arm 3A, the fault current will exceed the interrupting ability of the arm 3A due to a detection delay due to large di/dt, and the fault current will exceed the breaking capability of the arm 3A. This may lead to destruction of semiconductor switches such as GTO. In addition, if the interruption is not performed, a fault current that is less than the overcurrent withstand capacity of the semiconductor switch forming the arm 3A may flow, leading to destruction of the semiconductor switch forming the arm 3A.

The purpose of the present invention is to suppress the di/dt of the fault current from the DC capacitor in the above-mentioned fault, and to ensure that when a current cutoff command is given to the arm after fault detection, the fault current is below the arm's cutoff current limit. It is an object of the present invention to provide a voltage transformer in which the semiconductor elements constituting the arm are not destroyed by reducing the fault current to less than the overcurrent withstand capacity of the arm.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a high potential side capacitor whose one end is connected to the positive electrode of the high potential side converter 9 as shown in FIG. a first conductor 12 connecting the other end of the conductor 2 and the negative electrode of the high potential side converter 9;
a second conductor 13 connecting the other end of the low potential side capacitor 5 connected to the negative pole of the low potential side converter 10 and the positive pole of the low potential side converter 10;
and a third conductor 14 connecting the negative electrode of the high potential side converter 9 and the other end of the low potential side capacitor 5, and electromagnetically coupling the first conductor 12 and the second conductor 13. circuit 1
The converter 9 on the high potential side and the converter 10 on the low potential side are magnetically coupled with each other at a first order of magnitude, and are operated in the same phase.

(Function) In the voltage transformer of the present invention configured as described above, during steady operation, the first conductor 12 and the second conductor 13
acts as a normal connecting conductor without acting as a reactor, but if an accident such as an arm short circuit or an arm ground fault occurs and the charge in capacitor 2 or capacitor 5 is discharged as a result, the first conductor 12 or second
Since the discharge occurs through the conductor 13, the first conductor or the second conductor 13 acts as a reactor, and the discharge current d
Suppress i/d t.

(Embodiment) Fig. 1 is a configuration diagram showing an embodiment of the present invention, in which 1 is a DC circuit, 2 and 5 are DC capacitors, 3A to 3F, and 6
A to 6F are arms composed of semiconductor elements such as GTO, which constitute the bridge of the voltage transformer, and feedback diodes are connected in antiparallel to each arm. 4 and 7 are converter transformers, and 8 is an AC circuit.

The negative terminal of the high potential side converter 9 consisting of arms 3A to 3F and a feedback diode connected in antiparallel to the arms 3A to 3F and the capacitor 2
The first conductor 12 connects the other end of the first conductor 12 to the other end of the first conductor 12 .

Further, the positive electrode of the low potential side converter 1o consisting of the arms 6A to 6F and a feedback diode connected in antiparallel to the arms 6A to 6F and the other end of the capacitor 5 are connected by a second conductor 13.

Furthermore, the other end of the capacitor 5 and the negative electrode of the high potential side converter 9 are connected by a third conductor J4.

The first conductor I2 and the second conductor 13 are magnetically coupled by a magnetic coupling circuit 11 or the like.

In the voltage transformer of FIG. 1 configured as described above, the high potential side converter 9 and the low potential side converter 1 are connected during steady operation.
0 performs in-phase operation by a control device (not shown).

As shown in FIG. 1, a direct current Id and harmonic currents il and I2 flow through each part of the converter. Here, when converters 9 and 10 perform in-phase operation, 11 and i2 have the same current value.

A harmonic current jl is on the high potential side of the electromagnetic coupling circuit 1, and a harmonic current 12 and Id are on the low potential side of the electromagnetic coupling circuit 11.
flows. Harmonic current 1. Since and 12 are equal, the harmonic magnetic fields of the electromagnetic coupling circuit 11 cancel each other out and are not generated. Further, since the di/dt of the direct current Id is approximately zero, no induced voltage is generated within the electromagnetic coupling circuit 11. Therefore, the existence of the electromagnetic coupling circuit 11 can be ignored under the equality constraint, and the voltage source converter according to the present invention can be operated normally like the conventional converter.

Next, as shown in FIG. 2, it is assumed that a short-circuit accident occurs in the arm 3D for some reason while the arm 3A is energized. Then, a fault current if flows from the DC capacitor 2 through the arm 3A and the high potential side of the electromagnetic coupling circuit 11. At this time, a current if2 flows on the low potential side of the electromagnetic coupling circuit 11 due to electromagnetic induction. Arms 6A, 6E of converter 10
and 6F are on, current lf2 flows from the electromagnetic coupling circuit 1 through the arm 6A, the converter transformer 7, and the arms 6E and 6F. At this time, the current if2 is completely suppressed by the leakage inductance of the converter transformer 2 and the inductance of the AC circuit 8.

Since the fault currents Ifl and if2 must be equal, d i/d t of the fault current if is also suppressed.

Therefore, when an accident is detected by an accident detection circuit (not shown) and a fault current cutoff command is given to arm 3A,
Since d I /d t of the fault current if is suppressed, it can be interrupted before 1fI exceeds the interrupting ability of the arm 3A, and the semiconductor elements constituting the arm 3A can be protected from destruction.

Also, since the inductance of the circuit through which the fault current if flows increases due to the above reason, the fault current ifl is
Since the overcurrent can be suppressed to less than the overcurrent withstand capacity, the semiconductor elements constituting the arm 3A can be protected from destruction.

Although the present invention has been described with respect to the case where the arm of the converter 9 is short-circuited, protection can be similarly provided in the case where the arm of the converter 1O is short-circuited.

Next, suppose that a ground fault occurs in the AC output bus of the converter 9 at point A while the arm 3A is energized, as shown in FIG. Then, the fault current If3 from the DC capacitor 2 flows through the arm 3A, the fault point A, the ground, the DC capacitor 5, and the high voltage side of the electromagnetic coupling circuit 11. At this time, a stain current if4 flows on the low potential side of the electromagnetic coupling circuit 11 due to electromagnetic induction.

Assuming that 6E and 6F are on in arm 6 of converter 10, current if4 flows from electromagnetic coupling circuit 11 to arm 6.
A, flows through converter transformer 7, arms 6A and 6F. At this time, the current 1f4 has its d1/dt suppressed by the leakage inductance of the converter transformer 7 and the inductance of the AC circuit 8. Since the fault currents if3 and lf4 must be equal, the di of fault current 1fs is
/dt is also suppressed.

Therefore, an accident detection circuit (not shown) detects an accident, and a protection circuit (not shown) detects an accident in the arm 3.
When a fault current cutoff command is given to A, d i /d t of the fault current if3 is suppressed, so if3 is
The semiconductor element constituting the arm 3A can be protected from destruction before it exceeds its breaking capacity.

Also, since the inductance of the circuit through which the fault current 1f3 flows increases for the above reason, the fault current if3 is transferred to the arm 3A.
Since the overcurrent can be suppressed to less than the overcurrent withstand capacity, the semiconductor elements constituting the arm 3A can be protected from destruction.

Although the present invention has been described in the case of a ground fault in the AC output bus of the converter 9, protection can be similarly provided in the case of a ground fault in the AC output bus of the converter 10.

[Effects of the Invention] As explained above, according to the present invention, when the voltage source converter is operating normally, the electromagnetic coupling circuit has low impedance and does not affect the current during normal operation. However, in the case of an arm short circuit or an AC output bus ground fault, the fault current d
By suppressing i/dt and making the fault current less than the arm's cutoff limit current when issuing an arm current cutoff command after detecting a fault, or making the fault current less than the arm's overcurrent withstand capacity, the semiconductor elements that make up the arm can A voltage source converter that can be protected without being destroyed can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Figs. 2 and 3 are diagrams showing the path through which fault current flows to explain the present invention in detail, and Fig. 4 is the configuration of a conventional device. FIG. 1... DC circuit, 2, 5... DC capacitor, 3゜6... Arm, 4, 7... Converter transformer, 8...
・AC circuit, 9, 10... converter bri, ji, 11...
・Electromagnetic coupling circuit.

Claims (1)

[Claims] In a voltage source converter configured by connecting in series a high potential side converter and a low potential side converter each equipped with a capacitor on the DC side, the high potential side converter has one end connected to the positive electrode of the high potential side converter. a first conductor connecting the other end of the capacitor and the negative electrode of the high potential side converter; and the other end of the low potential side capacitor, one end of which is connected to the negative electrode of the low potential side converter, and the low potential side converter. and a third conductor that connects the negative electrode of the high potential side converter and the other end of the low potential side capacitor, the first conductor and the second conductor are connected to each other. A voltage source converter characterized by magnetically coupling a conductor and operating a high potential side converter and a low potential side converter in phase.