JPS59230168A - Current measuring circuit of dc converting device - Google Patents

Abstract

PURPOSE:To eliminate the influence of an interphase reactor, and to execute a measurement with high accuracy and stably by measuring a current of the primary side of a star connection in which a neutral point of a stepdown transformer provided with a DC converting device on the secondary side is grounded, through a rectifier brought to a single phase bridge connection of a current transformer. CONSTITUTION:A double star type six phase rectifying circuit with an interphase reactor 2 is provided on the secondary side of a stepdown transformer 1, and a DC Id flows to a load 4. A current flowing to each phase of a star connection in which a neutral point of the primary side of this transformer 1 is grounded is measured by current transformers 5-7, three groups of rectifiers 15a-15d, 16a-16d and 17a-17d brought to a single phase bridge connection of the secondry side of the current transformers 5-7, and an ammeter part 19 for measuring a DC composite value of the three groups of rectifiers, and the current is determined equivalently. In this case, a current flowing through a closed circuit of the current transformer 5, the rectifiers 15a, 16b, current transformer 6, rectifiers 16c, 15d, current transformer 5, etc. does not appear in the ammeter part 19, the influence of the interphase reactor is eliminated, and the current of a DC converting device is measured with high accuracy and stably.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention detects the DC output current of a device that converts three-phase AC power into DC power by detecting the current flowing into the AC winding of a transformer. This relates to a circuit 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, Oni's method is a method in which the DC output current is directly detected using a DC current transformer using an electromagnetic type or a magnetic sensor such as a Hall element. The third method is to install a current transformer on the input side of the transformer, rectify the secondary winding current of this current transformer, and detect a current proportional to the DC output current of the transformer. That is, there is a method in which a current transformer is provided on the input side of the transformer, the secondary winding current of the current transformer is rectified, and a current proportional to the DC output current of the converter is detected.

However, when the DC output current is a large current exceeding 10,000 amperes, the second method requires a large and expensive current transformer to directly detect the large current. The current measuring device has drawbacks such as being bulky and expensive, and requiring a large installation space and a large support 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 transformer, which includes an AC winding (minusary winding) 1a connected in a star shape, and two sets of DC windings (secondary windings) 1b and 1° connected in a star shape. , the neutral point of the AC winding 1a is grounded. Two sets of DC windings'
A phase reactor 2 having a neutral terminal is connected between the neutral points of b + 'c, and a single-current type rectifier 3 connected to six phases is provided on the output side of each phase winding. .

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 a DC output circuit. On the other hand, 5, 6.7 are 3 provided on the AC winding la side of the transformer 1.
The secondary winding side of the current transformer is star-connected and connected to a rectifier circuit 8 consisting of rectifiers 8a to 8h. 9 is provided in the DC output circuit of the rectifier circuit 8, and is a DC current KId proportional to the DC output current Id of the DC converter.
This is a current measuring section formed to detect.

In the circuit shown in Figure 1, the double star-shaped six-phase rectifier circuit has two sets of three-phase rectifier circuits that receive three-phase AC power with a phase difference of 60 electrical degrees from each other, and uses interphase reactor 2 as a pressure equalizer. Rectifiers 9 + 3V + 3W and 3x with DC windings LB and LC groups operated in parallel; 3. ,3
．． A current with a waveform as shown in Fig. 2 flows through each of them.

That is, in each rectifier, a layered wave-like current cut every 120 electrical degrees with a magnitude of 1/2 of the DC output current Id of the converter flows repeatedly with a blocking time of 240 electrical degrees, A DC current Id, which is a composite value of intermittent DC currents flowing through each rectifier, continuously flows through the load 4 provided on the DC output side. However, an exciting current flows through the interphase reactor 2 based on the difference in the instantaneous voltage values of the DC windings 1b and 1c, and the intermittent DC current flowing through each rectifier has this current as shown in Figure 2. An excitation current (an alternating current such as a sine wave or L triangular wave with a frequency three times the power supply 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, the current distribution and polarity are essentially the same. Among the intermittent DC currents indicated by solid arrows in the figure, the current (2) passing through the W phase of the DC winding 1b flows through the rectifier 3w and the load 4. Interphase reactor 2° volume #j! The current error that circulates through the circuit called the neutral point of 1b and passes through the t-phase of winding 1° is rectifier 3X + load 4. Two currents I, , I, , flow in the load 4 through the circuit called the neutral point of the 1° winding of the correlation reactor 22, respectively.
are added to form a DC output current Id. On the other hand, the excitation current it of the interphase reactor indicated by the broken arrow is the W phase of the interphase reactor 29 winding lb, rectifier 3Wl, rectifier 3
x.

It flows back to the interphase reactor 2 via the X phase of the winding lc,
It does not flow to load 4. In other words, the load 4 has a DC current Id
The note flows, but the excitation ionization IT of the somon 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 also flows to the rectifier provided on the AC winding la side of the transformer 1 via current transformers 5 to 7. flows.

The excitation current corresponding current kit indicated by the broken line arrow is the current transformer 5,
Rectifier 8a, current measurement section 9. Rectifier 8h, current transformer neutral point, current transformer 6. It circulates through the paths of the rectifier 8f, the rectifier 8hv, 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 exciting current component kit of the interphase reactor 2, which is not included in the DC output current Id of the DC converter, is detected by the current measurement unit 9 provided on the primary side of the transformer.

There is no problem if the excitation current of the interphase reactor is very small and can be ignored from the measurement point 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 If there is an air gap in the circuit and the excitation current is large, and if magnetic saturation occurs in the interphase reactor for some reason, the current component corresponding to the excitation current of the interphase reactor will be superimposed on the current measurement section, which will prevent the desired DC output. This is a fatal flaw in that the equivalence of current measurements is lost. Furthermore, when the detected current of the current side 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 has been made in view of the above-mentioned situation, and it is an object of the present invention to provide a DC current measuring circuit for a DC converter that eliminates the influence of the excitation current of the phase reactor and has high accuracy and stability.

[Key points of the invention]

According to the present invention, the above-mentioned object is to transform each phase current to the neutral-grounded primary winding of a transformer having a double star-shaped six-phase rectifier circuit with an interphase reactor on the secondary side. Three current transformers are installed, and three sets of single-phase bridge-connected rectifiers are installed on the secondary side of each current transformer, and the secondary winding current of each current transformer is input. By connecting the output side in parallel and forming a measurement circuit to be connected to the current measurement section, the harmonic current components transformed by the current transformer in response to the excitation current of the correlation reactor can be controlled by the three sets of harmonic current components. This was achieved by configuring the current to circulate only through the rectifier and not to flow through the current measuring section.

[Embodiments of the invention]

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

FIG. 3 is a connection diagram of a current detection circuit of a DC converter according to an embodiment of the present invention. In the figure, a transformer 1, an interphase reactor 2. The configuration and flow operation of the six-phase connected rectifier 3 and the DC load 4 are the same as those described in FIG. 1 and FIG. 2, and will therefore be omitted.

On the secondary side of the three current transformers 5, 6.7 that transform each phase current flowing into the AC winding la of the transformer 1, a single-phase bridge connection corresponding to the current transformer 5 is connected. Rectifiers 15a to 15d+i
Rectifiers 16a to 16d are provided corresponding to the current transformer 6, and rectifiers 17a to 17d are provided corresponding to the current transformer 7, and a current measuring section is provided in common on the DC output side of each single-phase bridge-connected rectifier circuit. 19 is configured to measure the composite current of the DC output currents of the respective rectifier circuits.

In the figure, each phase rectifier "u+" V+ of the DC converter
3 W + 3
When current flows, an exciting current it and a DC output An alternating current proportional to the current Id flows and also circulates through each rectifier forming the single-phase bridge rectifier circuits 15, 16, and 17 connected to the secondary side of each current transformer. In the figure, the current in each part at the same instant (time 11 in Figure 2) as explained in Figure 1 is expressed by a solid arrow, which is proportional to the DC output current Id of the converter.
A current kit proportional to the excitation current it of the interphase reactor is indicated by a broken line arrow. At other times, only the current distribution and polarity are different, but essentially the same.

In the figure, if we first focus on the solid arrows and follow the circulation path, we can see that the current flowing into the W phase of the AC winding 1a is transformed by the current transformer 5, and the current flowing into the W phase of the AC winding 1a is transformed by the current transformer 5, and the A current KIw that differs from the primary current by 1800 electrical angles flows through the rectifier 15a and the current detection unit 19. The current flows back to the rectifier 15d and the current transformer 5. In addition, the current flowing out from the U phase of the AC winding 1a is transformed to KIu by the current transformer 6, and then the current flows through the rectifier 16b and the current measuring section 19.
．． The current flows back to the rectifier 16o and current transformer 6. In this way, the current measurement unit 19 has the current KI flowing through the two closed circuits.
u and KIw are added, and the output current I of the DC converter is
A current KId proportional to d is detected. On the other hand, the current ki corresponding to the excitation current of phase reactor 2 indicated by the broken line arrow
If you follow the circulation path of t, you will see that W is operating in parallel.
A closed circuit, that is, a current transformer, in which the secondary windings of the phase and U-phase current transformers 5 and 6 are connected by rectifiers 16b, 16c, 15a, and 15d through which a current corresponding to the DC output current Id flows. 5. Rectifier 15a, rectifier 16
b. Current transformer 6. The current flows through a closed circuit consisting of the rectifier 16o, the rectifier 15d, and the current transformer 5, and does not flow into the current measuring section 19.

As described above, according to the current measuring circuit shown in FIG. 3, the influence of the excitation current of the interphase reactor is removed, and only the DC current proportional to the DC output current Id of the DC converter is transmitted to the t-flow side measuring section 1.
9 can be detected.

〔Effect of the invention〕

According to the present invention, as described above, a step-down transformer 1 has a DC converter connected in a double star six-phase rectifier with an interphase reactor on the secondary side, and the primary Current transformers 5 to 7 that transform the current flowing in and out of the winding 1a are provided, and the DC output side of the single-phase bridge-connected rectifier circuits 15 to 17 provided on the secondary side of each current transformer is By configuring the current measuring section 19 to be provided in common, the alternating current kit proportional to the excitation current of the interphase reactor 2 is prevented from flowing in the current measuring section in a superimposed manner, and the alternating current kit proportional to the DC output current Id of the DC converter is prevented from flowing in the current measuring section. We were able to provide a current measurement circuit for a DC converter that can detect only the DC current KId.

As a result, the measurement accuracy of the current measurement circuit installed on the primary side of the transformer, which was previously unable to obtain sufficient measurement accuracy due to the influence of the excitation current of the interphase reactor, has been improved, and the bushing installed on the primary side of the transformer has been improved. We were able to contribute to the provision of a DC converter equipped with an inexpensive and highly accurate current measurement circuit that uses a current transformer.

Furthermore, when the current detected by the current measurement unit 19 is used to control the output current of a DC converter, conventionally, the control of the output current becomes unstable due to the influence of harmonic components superimposed on the detected current waveform. Although there were drawbacks, the present invention avoids these problems and provides the advantage of being able to control the output current with high precision. Note that the present invention can also be applied to a DC converter using semiconductor-controlled rectifying elements.

[Brief explanation of drawings]

Figure 1 is a connection diagram of the current measurement circuit of a conventional DC converter.
FIG. 2 is an output current waveform of each phase rectifier connected in six phases a, and FIG. 3 is a connection diagram of a current measuring circuit showing an embodiment of the present invention. In the figure, 1... step-down transformer; l...-Secondary winding, 1b, 1゜...Secondary winding, 2...Interphase reactor, 3-Six-phase rectifier circuit, 4...Load, 5, 6.7...
・Current transformer, 15゜16, 17... Single-phase bridge, di-wired rectifier, 9, 19 current measurement section, "u + 3V
+ 3W + ”

Claims (1)

[Claims] l) In a conversion device that forms a double star-shaped six-phase rectifier circuit with an interphase reactor on the secondary side of a step-down transformer whose secondary windings are star-connected, each phase current of the secondary winding is A current transformer that transforms current, three sets of single-phase bridge-connected rectifiers provided corresponding to the secondary sides of the current transformers, and a common DC output circuit of the three sets of rectifiers. 1. A current measuring circuit for a DC converter, comprising: a current measuring section that measures a composite value of DC output currents of the respective rectifiers, and is formed to equivalently measure the DC output current of the converter.