JPS59230169A - Direct current measuring circuit of dc converting device - Google Patents

Abstract

PURPOSE:To measure a direct current with high accuracy and high stability without being influenced by an interphase reactor of the secondary winding side by forming the other by a delta connection in case other one of the primary winding of a stepdown transformer 1, or the secondary winding of a current transformer for detecting a current of each phase is a star shape. CONSTITUTION:A current in each phase of a primary side winding 11a of a star connection of stepdown transformer 11 whose secondary side is connected to a DC converting device with a reactor 2 is detected by current transformers 5-7. The secondary winding of the current transformers 5-7 forms a three phase bridge circuit of a delta connection through rectifiers 8a-8f, and an ammeter 9 is connected to its output side. In case of currents KIx, KIw, etc. being proportional to a DC current of this DC converting device flow to the ammeter 9, a current (kit), etc. being proportional to an energizing current by the reactor 2 different by 180 degrees in phase flow in the forward and reverse directions through the rectifiers 8a, 8c, etc., and do not flow to the ammeter 9. Accordingly, a direct current of the DC converting device is measured with high accuracy and high stability without being influenced by the interphase reactor. In this regard, even when the primary winding and the secondary winding bridge are formed by delta and star connections, respectively, the same result is obtained.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to the detection of the DC output current of a device that converts three-phase father current power into DC power by detecting the current flowing into the AC winding of a transformer. Concerning circuits for equivalent measurement.

[Prior art and its problems]

The following methods are conventionally known as methods for measuring the DC output current of a DC converter that converts AC power into DC power via a transformer and a rectifier. That is, the first method is to directly detect the DC output current using an electromagnetic type or a DC current transformer using a magnetic device such as a Hall element. The third method is to provide a current transformer on the input side of the rectifier, rectify the secondary winding current of this current transformer, and detect a current proportional to the DC output current of the converter. For example, a current transformer is provided on the input side of an AC winding, that is, a transformer, and the secondary winding current of the current transformer is rectified to detect a current proportional to the DC output current of the converter.

However, when the DC output current is a large current exceeding 10,000 amperes, the first. The second method requires a large and expensive current transformer to directly detect large currents, a large and expensive DC current measuring device, and requires a large installation space and large support. There are disadvantages such as the need for a structure. On the other hand, the third method requires only a current transformer that detects the high-voltage side winding current of a step-down transformer, for example, an alternating current of several tens to hundreds of amperes, so a small and inexpensive bushing current transformer is used. It is advantageous to be able to do so.

For this reason, electrolysis can be used to refine non-ferrous metals, chlorine,
Low voltage used for manufacturing caustic soda, etc.

In large current DC converters, the third method is often used to measure the DC output current.

FIG. 1 is a connection diagram of a conventional DC converter and its current measuring circuit. In the figure, 1 is a step-down transformer, which has a star-connected AC winding (minusary winding) 1a and two star-connected DC windings (secondary windings) 1b and 1°. An interphase reactor 2 having a midpoint terminal is connected between the neutral points of the two sets of DC windings 'b + 'c, and the output side of each phase winding is connected to a six-phase single-current system. Rectifier 3
is provided.

Further, a load 4 is connected between the DC output side (positive electrode) of the rectifier 3 and the midpoint terminal of the interphase reactor 2, and the load 4 is configured to be supplied with the DC output current Id. On the other hand, 5, 6.7 are three current transformers installed on the AC winding la side of the step-down transformer 1, and the secondary winding side thereof is star-connected and consists of rectifiers 8a...f. It is connected to the rectifier circuit 8. Reference numeral 9 denotes a current measuring section provided in the DC output circuit of the rectifier circuit 8 and configured to detect a DC current KId proportional to the DC output current Id of the DC converter.

In the circuit shown in Figure 1, the double star-shaped six-phase rectifier circuit has two sets of three-phase rectifier circuits that input three-phase AC power with a phase difference of 60 electrical degrees from each other, and uses the interphase reactor 2 as a pressure equalizer. The DC windings lb group and 1° group rectifier ``Ll + 3V + 3W + and 3x, 3 are operated in parallel.
A current having a waveform as shown in FIG. 2 flows through each of y and 3□. In other words, a geometric wave-like current cut into a rectangle of 120 electrical degrees with a magnitude of one-half of the DC output current d of the converter is applied to each rectifier repeatedly with a blocking time of 240 electrical degrees. A DC current Id, which is a composite value of the intermittent DC currents flowing through each rectifier, continuously flows through the load 4 provided on the DC output side. However, an excitation current it based on the difference between the instantaneous values of the voltages of the DC winding 1b and 1° flows in the interphase reactor 2, and the intermittent DC current flowing through each rectifier has a second
As shown in the figure, this excitation current (an alternating current such as a sine wave or triangular wave with a frequency three times the source frequency) is superimposed.

In FIG. 1, at time 11 in FIG. 2, the directions of the direct current and excitation current flowing through each part of the apparatus are shown with solid line arrows representing the DC current and broken line arrows representing the excitation current it. At other times, only the current distribution and polarity are different, but essentially the same. Among the intermittent DC currents indicated by solid arrows in the figure, the current Iw passing through the W phase of the DC winding 1b flows through the rectifier 3w, the load 4. Circulating the circuit called the neutral point of the interphase reactor 22 winding 1b,
The current x passing through the six phases of the winding 1° is the rectifier 3ry load 4.
The two currents Ix and Iw flowing through the neutral point of the 1° winding of the interphase reactor 22 are added at the load 4 to form a DC output current Id. On the other hand, the excitation current it of the interphase reactor shown by the broken line arrow circulates to the interphase reactor 2 through the W phase of the interphase reactor 22 winding 1b, the rectifier 3w, and the six phases of the rectifier a- with the winding 1°, It doesn't flow. That is, only the DC current Id flows through the load 4, and the exciting current it of the interphase reactor does not flow. On the other hand, a current corresponding to the intermittent DC current Id flowing to the DC converter side and the excitation current it of the interphase reactor flows also in the rectifier provided on the AC winding la side of the transformer 1 via the current transformers 5 to 7. .

Harmonic current kit8 corresponding to the excitation current indicated by the broken line arrow
f, current transformer 7. It circulates through the path of the current transformer neutral point and the current transformer 5, and a component corresponding to the exciting current also flows to the current detection section 9. That is, the harmonic current kit corresponding to the excitation current it of the interphase reactor 2, which is not included in the current flowing through the load 4 of the DC converter 8, is detected by the current measurement unit 9 provided on the primary side of the transformer. I end up.

There is no problem if the excitation current of the interphase reactor is very small and can be ignored in terms of the measurement accuracy of the DC output current Id of the converter, but if you want to measure the current with particularly high accuracy, or due to the structure of the interphase reactor, for example, the magnetic circuit If there is an air gap and the excitation current is large, or if magnetic saturation occurs in the interphase reactor for some reason, a current component corresponding to the excitation current of the interphase reactor will be superimposed on the current measurement section, which will cause the target DC output current to This is a fatal flaw in that measurement equivalence is lost. Further, when the detected current of the current ITI measuring section is used to control the phase angle of the control rectifier, there is a drawback that the phase angle constantly changes due to fluctuations in the detected current waveform.

[Purpose of the invention]

The present invention was made in view of the situation of multiple connections, and it is an object of the present invention to provide a current measurement circuit for a DC converter that has high accuracy and stability and eliminates the influence of the excitation current of the mutual reactor.

[Key points of the invention]

According to the present invention, the above-mentioned object is to provide a current transformer that transforms each phase current to the primary winding side, which cannot be grounded, of a transformer having an interphase reactor on the secondary side and a double star-shaped six-phase rectifier circuit. Three units are installed, and a three-phase bridge-connected rectifier circuit is installed on the secondary side of each current transformer, which inputs the secondary winding current of each current transformer, and a current measurement unit is installed on the DC output side of the rectifier circuit. and when either the primary winding of the transformer or the secondary winding of the current transformer is connected in an ungrounded star shape, the other winding is By forming the wires to be triangularly connected, harmonic current components transformed by the current transformer in response to the excitation current of the phase reactor are circulated only to the rectifier circuit, and do not flow to the current measuring section. This was achieved by configuring it as follows.

[Embodiments of the invention]

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

FIG. 3 is a connection diagram of a current measuring circuit of a DC converter according to an embodiment of the present invention. In the figure, a step-down transformer 11 has a star-connected primary winding (AC winding) 11 with an ungrounded neutral point.
a and two sets of star-connected secondary windings (DC windings) 11
b and 11o, and includes a DC winding 114.b and 11o. and 11
A rectifier 3 connected in a double star shape with an interphase reactor is provided on the load side of o.

The configuration of the secondary side of the transformer and the flow-through operation of the rectifier are the same as those described in FIGS. 1 and 2, and will therefore be omitted.

Transformer 11 The secondary windings of three current transformers 5, 6.7 that transform the current flowing into the AC winding 11a connected in a star shape are triangularly connected to each other, and a three-phase bridge is installed on the output side. The connected rectifier circuit 8 and current measuring section 9 are connected. In the figure, the current flowing through each part of the device at time t1 in Fig. 2 is shown by the solid line arrow, the current related to the output DC current IdK of the rectifier 3 is shown by the solid line arrow, and the harmonic current related to the excitation current port of the interphase reactor 2 is shown by the broken line arrow. The directions in which the current flows are shown in the figure.

Even at times other than tl, the current distribution differs only in the portion and direction in which the current flows, but is essentially the same. Therefore, the current distribution at time t1 will be described in detail below.

At time 11, rectifiers 3w and 3x are in a conducting state as shown in Fig. 2, and correspondingly, W of the DC winding is
Current and Ix flow through the phase and X phase, respectively.
An excitation current it of the mutual reactor 2 flows superimposed on this. In addition, the AC winding 11a of the transformer 11 has a current ■W * ■ whose phase is 180 degrees different from the current flowing through the DC winding.
11 flows into the W phase and the U phase, respectively, and superimposed on this, a current corresponding to the harmonic current it flows as indicated by the broken line arrow. In the secondary windings of the three current transformers 5, 6 and 7, there is a current induced by the current flowing in the negative secondary winding, that is, a current on the output side of the DC winding ■wI'' + 'd r
A current proportional to It flows. In the figure, these currents are K
IW, K1. z: , KId , kit ,
KIw, K1. The solid line arrows indicate the paths and directions in which the water flows. As is clear from the figure, KIw, K1. both flow in the same direction through the current measuring section 9 and are added, and a current KId proportional to the output current Id of the rectifier flowing through the load 4 is detected.

There are still direct currents KIw, KI in the rectifiers 8a and 8°.
Since x is flowing, the harmonic current kit flows through the rectifier 8a.
.

8° in forward or reverse direction to each current transformer 5, 6.7
The current flows back to the secondary winding of , but does not flow to the current measuring section 9 . In this way, the current measuring section has a DC current Id flowing through the load 4.
Since only the current KId proportional to
By converting into DC output current Id, the rectifier 3
The DC output current Id can be determined accurately.

FIG. 4 is a connection diagram of a current measuring circuit of a DC converter showing a modification of the above-described embodiment. The connection diagram in Fig. 4 differs from Fig. 3 in that the primary winding (AC winding) of the step-down transformer 12 is triangularly connected, and correspondingly, the current transformer 5
, 6.7, the secondary windings are star-connected.

In the figure, the DC current flowing through each part at time t1 in Fig. 2 is shown by a solid line arrow, and the harmonic current generated corresponding to the excitation current of the interphase reactor 2 is shown by a broken line arrow. At time t1 in FIG. 2, the rectifiers 3W and 3. r and are in a state of flow.

The output current Id flows through the load 4 by adding the currents F and Ix flowing through the rectifier, and the AC winding 12a of the transformer 12 receives currents Iw and Iu corresponding to the Iw and Ix.
is supplied from the U phase and the W phase as shown by the solid line arrow, and the harmonic current is superimposed on this and circulates between the W phase and the U phase. As a result, the secondary windings of the current transformers 5, 6.7 have a current KIW induced by said current flowing into and out of the transformer.
Kx, KId, and harmonic current kit flow as shown by the arrows. Among these, the currents flowing through the rectifiers 3w and 3x, the DC currents KIw and KIa- proportional to Ix.
is a current K that flows in the same direction through the current measurement unit 9 along a path as indicated by a solid arrow and is added, and is proportional to the current Id flowing through the load 4.
Id is detected by the current measuring section 9. Also, since the DC current KIwlKI,z' is flowing through the rectifiers 8a and 8°, the harmonic current kit flows through the rectifiers 8a and 8c in the forward direction or in the opposite direction, respectively, and flows through the current transformers 5, 6, . The current flows back to the secondary winding 7 and does not flow to the current measuring section 9. Even if the current measurement circuit is configured in this way as shown in FIG.
As described in the figure, the output current IdK of the rectifier 3
Only the proportional DC current component can be detected and measured.

Note that although the above description has been made regarding an example in which the rectifier is configured with a semiconductor rectifier, the present invention can also be applied to a current measurement circuit of a device using a semiconductor-controlled rectifier.

〔Effect of the invention〕

According to the present invention, as described above, the current transformers 5 to 7 provided on the AC winding side of the interphase reactor, and the three-phase bridge-connected rectifier provided on the secondary winding side of the current transformer. It includes a circuit 8 and a current measuring section 9 provided on the DC side of the rectifier circuit, and when one of the AC winding of the transformer and the secondary winding of the current transformer is triangularly connected, the other The wires were configured so that they were connected in a star shape with the neutral point not grounded. As a result, a harmonic current KIw is induced in the secondary windings of the current transformers 5 to 7 in response to the excitation current IT of the phase reactor, and a DC current KIw flowing through the rectifier circuit 8 is proportional to the optical output current Id. K1. v
% conduction kit can be prevented from flowing through the current measuring section 9,
A current measuring section generates a current KI proportional to the DC output current Id.
We were able to provide a current measurement circuit that can detect only d. Therefore, the problem of conventional current measurement circuits in which sufficient measurement accuracy could not be obtained due to the influence of the harmonic current kit has been solved, and measurement accuracy has been improved. We were able to contribute to the provision of a DC converter that incorporates an inexpensive and highly accurate current measurement circuit using .

When the current KId detected by the current measurement unit 9 is used to control the output current of a DC converter, conventionally the output current is controlled based on the influence of the harmonic current kit superimposed on the detected current waveform. However, according to the present invention, this problem can be avoided and the output current can be controlled with high precision.

[Brief explanation of the drawing]

Figure 1 is a connection diagram of the current measurement circuit of a conventional DC converter.
Figure 2 is a conceptual diagram of the output current waveform of each phase rectifier connected in six phases, Figure 3 is a connection diagram of a current measurement circuit showing an embodiment of the present invention, and Figure 4 is a modification of Figure 3. FIG. In the figure, 1, 11, 12... step-down transformer, 1
1a. 12a-AC winding, Ilb, c, 12b, c-
DC winding, 2... Interphase reactor, 3... Rectifier, 4... Load, 5.6.7... Current transformer, 8... Rectifier circuit, 9... Current measurement unit, Id ...Current output current, 1t
... Excitation current of interphase reactor (harmonic current j, K
Id: detection current, kit: harmonic current. Figure 1 Figure 2

Claims (1)

[Claims] 1) In a converter having a double star-shaped six-phase rectifier circuit with an interphase reactor on the secondary side of a step-down transformer, a current transformer that respectively detects currents flowing in and out of the primary side of the step-down transformer; The primary winding of the step-down transformer includes a three-phase bridge-connected rectifier circuit commonly provided on the secondary side of the current transformer, and a current measuring section provided on the DC output side of the rectifier circuit. A direct current conversion device characterized in that when one of the windings is connected in an ungrounded star shape, the other winding is connected in a triangular manner. DC current measurement circuit.