JP2008278714A - Rectifier circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a parallel 12-pulse rectifier circuit for the purpose of low-voltage large capacity which realizes miniaturization and cost reduction and improves the degree of freedom in design by reduced capacity of AC interphase reactors and small current thereof for the purpose requiring an insulation transformer for voltage step-down. <P>SOLUTION: The rectifier circuit includes an AC interphase reactor 3 having two pairs of three-phase windings 3U<SB>1</SB>, 3V<SB>1</SB>, 3W<SB>1</SB>and 3U<SB>2</SB>, 3V<SB>2</SB>, 3W<SB>2</SB>which are connected between a three-phase input terminal and first, second three-phase output terminals; first and second insulation transformers 2A and 2B having primary sides each connected to the first and second three-phase output terminals, and having a secondary voltage phase difference of substantially 30 degrees; and two three-phase bridge rectifiers 1A and 1B having AC circuits each connected to the secondary side of these insulation transformers and a DC circuit connected in parallel. In the rectifier circuit, the three-phase windings 3U<SB>1</SB>, 3V<SB>1</SB>, 3W<SB>1</SB>and 3U<SB>2</SB>, 3V<SB>2</SB>, 3W<SB>2</SB>have substantially the same number of windings and are wound on the same iron core. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rectifier circuit that rectifies a three-phase AC voltage with a three-phase bridge rectifier through an insulating transformer to obtain a DC voltage, and more specifically, rectification in which the DC sides of two three-phase bridge rectifiers are connected in parallel. It relates to the circuit.

A three-phase bridge rectifier is often used as a power converter that converts three-phase AC power into DC power. Since the three-phase bridge rectifier performs six commutations in one cycle of the power supply, the circuit is also called a six-pulse rectifier circuit. Further, a multi-pulse rectifier circuit such as a 12-pulse rectifier circuit or an 18-pulse rectifier circuit can be configured by combining a plurality of three-phase bridge rectifiers.
Since these multi-pulse rectifier circuits increase the number of commutations, it is well known as an advantage that the harmonic current flowing in the power supply can be reduced and the capacity can be increased.

2 and 3 show a configuration example of a 12-pulse rectifier circuit including two three-phase bridge rectifiers configured by diodes or thyristors. For example, the circuit is basically the same as the circuit described in Non-Patent Document 1. It is.
2 and 3, 1A and 1B are three-phase bridge rectifiers, 2 is one secondary winding is star-connected, the other secondary winding is delta-connected, and the output voltage of both secondary windings is 30 degrees. This is a three-winding insulation transformer having a phase difference of. U, V, and W are three-phase input terminals, and P and N are DC output terminals.

In the circuit of FIG. 2, two three-phase bridge rectifiers 1A and 1B are connected in series, which is suitable mainly for high voltage and large capacity applications.
On the other hand, the circuit of FIG. 3 is a parallel 12-pulse rectifier circuit in which DC circuits of two three-phase bridge rectifiers 1A and 1B are connected in parallel via an interphase reactor 5, and is mainly suitable for low voltage and large capacity applications. . Here, the interphase reactor 5 has the effect | action which suppresses the harmonic current which crosses between the three-phase bridge rectifiers 1A and 1B connected in parallel.
In the circuits of FIGS. 2 and 3, the fifth and seventh harmonics generated by the two three-phase bridge rectifiers 1A and 1B are ideally canceled, so that the harmonics of the power supply are reduced. Can do.

Next, FIG. 4 is a circuit that is theoretically the same as the circuit described in Non-Patent Document 2.
In this circuit, an interphase reactor 31 in which three windings per phase are magnetically coupled is used instead of the insulating transformer 2 shown in FIGS. Hereinafter, this type of reactor is referred to as an AC phase reactor, and the DC side phase reactor 5 illustrated in FIG. 3 is referred to as a DC phase reactor.

In FIG. 4, in the AC interphase reactor 31, windings of different phases are magnetically coupled to each other, so that a phase shift function is generated between the input and output of the reactor 31.
As shown in the figure, the number of turns N ₁ , N ₂ , N ₃ of three windings wound on the same iron core is
N ₁ : N ₂ : N ₃ = 3.73: 2.73: 1.0
Since the output voltages of the two reactors connected to the rectifiers 1A and 1B have a phase difference of 30 degrees, a three-phase AC voltage having a phase difference of 30 degrees is supplied to the rectifiers 1A and 1B, respectively. be able to. Accordingly, the prior art of FIG. 4 attempts to obtain the function of a parallel 12-pulse rectifier circuit similar to the circuit shown in FIG.
In the circuit of FIG. 4, the AC interphase reactor 31 suppresses the cross current flowing between the rectifiers 1 </ b> A and 1 </ b> B, so the DC interphase reactor 5 as shown in FIG. 3 is not necessary.

Next, FIG. 5 is a circuit that is theoretically the same as the circuit described in Patent Document 1. In this circuit, the number of turns N ₁ , N ₂ , N ₃ of three windings wound on the same iron core of the AC interphase reactor 32 is
N ₁ : N ₂ : N ₃ = √3: 1: 1
To design. As a result, the function of the parallel 12-pulse rectifier circuit is obtained as in FIG.

“Electrical Engineering Handbook (6th Edition)”, The Institute of Electrical Engineers of Japan, 20 editions of Power Electronics, pages 846-847 "A New 12-Pulse Rectifier Circuit with Line-Side Interphase Transformer and Nearly Sinusoidal Line Currents" by Manfred Depenbrock and Clemens Niermann, Proc. Of 6th Conference on PEMC, vol.2, pp.374-378 (1990) JP 2000-358372 A (Claims 1 and 4, paragraphs [0019] to [0025], FIG. 1, FIG. 2, etc.)

Now, in a DC power source for inverters applied to the induction heating field of metals and a DC power source for electrolysis used in the production of non-ferrous metals, for example, a voltage of several hundred volts and an output of several thousand kW or more are low voltage and large capacity. A DC power supply is required. Since this type of DC power supply is desirably obtained from a high-voltage commercial power supply of 6 kV class or higher, a step-down transformer is required.
In the field as described above, for example, by using the circuit of FIG. 3 described in Non-Patent Document 1 as the three-winding transformer 2 as a step-down transformer, a low-voltage and large-capacity rectifier circuit (DC power supply) is configured. In addition, the harmonics of the power supply can be reduced. However, in that case, the following problems occur.

For example, when trying to finally obtain a DC voltage of several hundreds V from an AC high voltage of 6 kV or higher, the number of turns of the secondary winding of the three-winding transformer 2 cannot be increased. For this reason, it is necessary to use a step-down three-winding transformer with a large transformation ratio. However, in this type of three-winding transformer, there is an error in effective value between two sets of secondary voltages on the star side and the delta side. It tends to occur.
This voltage effective value error appears as a DC voltage error of the two three-phase bridge rectifiers 1A and 1B. However, since the DC voltage error cannot be compensated for by the DC interphase reactor 5, the DC current flowing between the rectifiers 1A and 1B. Ingredient cross current becomes excessive. As a result, the three-phase bridge rectifiers 1A and 1B and the three-winding transformer 2 having a large capacity are required. At the same time, the secondary current of the three-winding transformer 2 includes many fifth and seventh harmonics, and this harmonic also causes an increase in the capacity of the three-winding transformer 2.

On the other hand, the prior art described in Non-Patent Document 2 and Patent Document 1 is characterized in that an insulating transformer and a DC interphase reactor are not required. However, with these conventional techniques, as described above, when the AC high voltage is stepped down to finally obtain a predetermined DC voltage, a DC interphase reactor is certainly unnecessary, but it is an alternative to a three-winding transformer. Large and expensive AC interphase reactors 31 and 32 are required.
The reason why the AC phase reactor is large and expensive will be described below.

First, as a first reason, the inter-phase reactors 31 and 32 in Non-Patent Document 2 and Patent Document 1 have phase shift characteristics. For this reason, when the phase of the output voltage is changed with respect to the input voltage of the AC phase reactor, a voltage drop of the fundamental wave component caused by the phase shift occurs between the input and output of the coupling reactor in the AC phase reactor, Furthermore, a voltage drop due to the harmonic component occurs.
Here, the capacity of the reactor between the AC phases is determined by the product of the voltage obtained by adding the voltage drop of the fundamental component and the voltage drop of the harmonic component and the current flowing through the reactor between the AC phases.

  The capacity of the AC interphase reactor is determined by the voltage drop of the fundamental wave component. However, in determining the capacity of the DC interphase reactor 5 shown in FIG. 3, the component corresponding to the voltage drop of the fundamental wave component is determined. There is no. That is, when the AC interphase reactors 31 and 32 are used as shown in FIGS. 4 and 5, the capacity of the AC interphase reactors 31 and 32 is set between the DC phases by the voltage drop of the fundamental wave component that is dominant in determining the capacity. It is necessary to increase the capacity of the reactor 5.

As a second reason, a zero-phase component also exists in the cross current that flows between the two three-phase bridge rectifiers 1A and 1B. For example, three single-phase reactors are required to have a cross current suppressing effect on the zero-phase component current. For this reason, an increase in the number of devices compared to the case where the DC interphase reactor 5 is used becomes a factor of an increase in size. Another design problem is that the ratio of the number of turns N ₁ , N ₂ , and N ₃ of the three windings wound on the same iron core of the interphase reactors 31 and 32 does not become an integer.

  Therefore, the problem to be solved by the present invention is to provide a rectifier circuit that is small, inexpensive, and has a high degree of design freedom by solving the above-mentioned problems for low-voltage and large-capacity applications that require an insulating transformer for step-down. is there.

In order to solve the above problems, the invention according to claim 1 is a rectifier circuit that rectifies a three-phase AC voltage and converts it into a DC voltage.
An AC interphase reactor having two sets of three-phase windings connected between the three-phase input terminal and the first and second three-phase output terminals;
First and second isolation transformers each having a primary side connected to the first and second three-phase output terminals and having a phase difference of a secondary voltage of approximately 30 degrees;
Two three-phase bridge rectifiers in which an AC circuit is connected to the secondary side of each of the first and second isolation transformers, and the DC circuits are connected in parallel;
The two sets of three-phase windings in the AC phase reactor are both substantially equal in number of turns and wound on the same iron core.

  In the present invention, two sets of three-phase windings connected to the primary side of these isolation transformers are performed by the first and second isolation transformers in order to realize a phase shift operation for realizing a parallel 12-pulse rectifier circuit. The input current is balanced by an AC interphase reactor. As a result, for low voltage and large capacity applications where an insulation transformer is required for step-down, the capacity and current of the reactor between the AC phases can be reduced to reduce size and price, and increase design flexibility. Can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram of a parallel 12-pulse rectifier circuit according to an embodiment of the present invention. In FIG. 1, reference numeral 3 denotes an AC interphase reactor including two sets of three-phase windings 3U ₁ , 3V ₁ , 3W ₁ and 3U ₂ , 3V ₂ , 3W ₂ .

In this AC interphase reactor 3, the three-phase input terminals U, V, W are connected to a three-phase AC power source (not shown), and the first three-phase output terminals U ₁ , V ₁ , W ₁ and second of 3-phase output terminals _{U 2,} V 2, _{W 2} is the primary winding 2B ₁ and the primary winding 2A ₁ and second 3-phase isolation transformer 2B of the first three-phase isolation transformer 2A Each is connected.
Windings 3U ₁ and 3U ₂ are connected between the input terminal U and the output terminals U ₁ and U _2, and windings 3V ₁ and 3V are connected between the input terminal V and the output terminals V ₁ and V _{2. 2} are connected, and windings 3W ₁ and 3W ₂ are connected between the input terminal W and the output terminals W ₁ and W ₂ . Here, the windings 3U ₁ , 3U ₂ , 3V ₁ , 3V ₂ , 3W ₁ , 3W ₂ are equal in number, and are wound around the same iron core and magnetically coupled.

The first isolation transformer 2A connected to the output terminals U ₁ , V ₁ , W ₁ has a primary winding 2A ₁ having a delta connection, a secondary winding 2A ₂ having a star connection, and the output terminal U _{In the second} three-phase isolation transformer 2B connected to ₂ , V ₂ and W ₂ , the primary winding 2B ₁ and the secondary winding 2B ₂ are delta-connected. Moreover, the transformation ratio of both the transformers 2A and 2B is set equal.
Therefore, the phase difference between the three-phase AC voltages output from the secondary windings 2A ₂ and 2B ₂ is 30 degrees, and these three-phase AC voltages are applied to the AC circuit of the three-phase bridge rectifiers 1A and 1B including diodes. Each is supplied.
4 and 5, the DC circuits of the three-phase bridge rectifiers 1A and 1B are connected in parallel, and the smoothing capacitor 4 is connected between the DC output terminals P and N.

In the above embodiment, assuming that the direction of the current flowing through the three-phase bridge rectifiers 1A and 1B is the positive direction of the AC current, the AC interphase reactors 3 are magnetically coupled to each other in opposite polarities on the same iron core and have a number of turns. Two equal sets of windings 3U ₁ , 3V ₁ , 3W ₁ and 3U ₂ , 3V ₂ , 3W ₂ are wound.

On the other hand, the AC interphase reactor acts so that the resultant magnetomotive force acting on the same iron core becomes almost zero. Therefore, the AC interphase reactor 3 in FIG. 1 is connected to the output terminals U ₁ , V ₁ , W ₁ on the side of the isolation transformer 2A and the output terminals U ₂ , V ₂ , W ₂ on the side of the isolation transformer 2B. It acts so that the flowing current becomes equal.
Another way of looking at this is to increase the primary voltage for isolation transformers whose secondary voltage is lower than the predetermined value, and decrease the primary voltage for isolation transformers whose secondary voltage is higher than the predetermined value. Current can be balanced.

Even if the transformation ratios of the two isolation transformers 2A and 2B are not completely the same and there is an error in the magnitude of the output voltage, the primary input to each isolation transformer 2A and 2B by the AC phase reactor 3 Since the voltage is compensated, the cross current of the DC component flowing between the three-phase bridge rectifiers 1A and 1B as in Non-Patent Document 1 does not occur in principle. Therefore, it is possible to prevent the capacity of the rectifiers 1A and 1B from increasing.
Further, since the AC interphase reactor 3 also functions as a smoothing reactor, the currents of the isolation transformers 2A and 2B are sinusoidal currents with less fifth and seventh harmonic currents. For this reason, the capacity | capacitance reduction of insulation transformer 2A, 2B is possible compared with the prior art of a nonpatent literature 1. FIG.

In the present embodiment, the phase shift for the parallel 12-pulse rectifier circuit is performed by the isolation transformers 2A and 2B as described above. For this reason, since the voltage drop of the fundamental wave component does not occur in the AC interphase reactor 3 as in Non-Patent Document 2 and Patent Document 1, and the capacity is not increased, the capacity of the AC interphase reactor 3 is reduced. Thus, the size can be reduced.
Further, since the AC interphase reactor 3 is connected to the high voltage side of the isolation transformers 2A and 2B, the three-phase bridge rectifier 1A of the same low-voltage and high-current circuit as in Non-Patent Document 2 and Patent Document 1, Compared with the case where it is directly connected to 1B, the current flowing through the AC interphase reactor 3 is reduced, which contributes to downsizing and capacity reduction.

The first three-phase output terminals U _{1 to} W ₁ and the second three-phase output terminals U _{2 to} W ₂ in the AC interphase reactor 3 are insulated from each other by the isolation transformers 2A and 2B. Therefore, zero-phase current does not flow through each terminal, and therefore a three-phase reactor using a three-leg iron core can be used as the AC interphase reactor 3. Therefore, in order to suppress the zero-phase current, for example, the entire apparatus can be miniaturized rather than using three single-phase reactors.

  Furthermore, the AC interphase reactor 3 of the present embodiment can be configured by winding two sets of three-phase windings of the same number of turns on the same iron core, and the ideal turns ratio is as in Non-Patent Document 2 and Patent Document 1. There is no problem of non-integer ratios. Thereby, the number of windings constituting the AC interphase reactor 3 can be freely designed, and the accuracy of current balancing and harmonic reduction can be improved as compared with the prior art. Further, the increase in the degree of freedom of design contributes to the miniaturization of the reactor for interphase AC 3.

It is a circuit diagram showing an embodiment of the present invention. It is a circuit diagram of the prior art described in the nonpatent literature 1. It is a circuit diagram of the prior art described in the nonpatent literature 1. It is a circuit diagram of the prior art described in Non-permitted Document 2. It is a circuit diagram of the prior art described in Patent Document 1.

Explanation of symbols

1A, 1B: Three-phase bridge rectifiers 2, 2A, 2B: Insulation transformers 2A ₁ , 2B ₁ : Primary windings 2A ₂ , 2B ₂ : Secondary windings 3, 31, 32: Reactor 3U ₁ , 3U between AC phases ₂ , 3 V ₁ , 3 V ₂ , 3 W ₁ , 3 W ₂ : Winding 4: Smoothing capacitor 5: DC phase reactor U, V, W: 3-phase input terminals U ₁ , V ₁ , W ₁ , U ₂ , V ₂ , W ₂ : Three-phase output terminal P, N: DC output terminal

Claims (1)

In a rectifier circuit that rectifies three-phase AC voltage and converts it to DC voltage,
An AC interphase reactor having two sets of three-phase windings connected between the three-phase input terminal and the first and second three-phase output terminals;
First and second isolation transformers each having a primary side connected to the first and second three-phase output terminals and having a phase difference of a secondary voltage of approximately 30 degrees;
Two three-phase bridge rectifiers in which an AC circuit is connected to the secondary side of each of the first and second isolation transformers, and the DC circuits are connected in parallel;
The two sets of three-phase windings in the AC interphase reactor have almost the same number of turns and are wound on the same iron core.

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