JP2013223354A - Rectifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rectifier that can operate in an extremely low temperature range such as a liquid nitrogen temperature and has low loss.SOLUTION: A rectifier (1) rectifying an alternating current from an AC power supply (8) includes a first magnetic yoke (2) around which a first coil (4) and a second coil (5) are wound, and a second magnetic yoke (3) around which a third coil (6) and a fourth coil (7) are wound. The first and third coils are connected in series to the AC power supply, and the second and fourth coils are connected in series to a DC power supply (9). The rectifier generates a bias magnetic field to the first and second yokes by causing the DC power supply to output a DC bias current I, and performs rectifying operation using a magnetic saturation phenomenon.

Description

  The present invention relates to a technical field of a rectifier that rectifies an alternating current supplied from an alternating current power source and outputs it as a direct current to a load side, particularly a rectifier that can operate even in a cryogenic region such as liquid nitrogen temperature.

  In recent years, attempts have been made to apply a superconductor having an electric resistance value of substantially zero in an extremely low temperature region to various technical fields. Superconductors can achieve excellent transmission efficiency when transmitting DC power with an extremely low electric resistance value, but loss is increased when AC power is transmitted. Therefore, in a device using a superconductor (hereinafter, referred to as “superconducting device” as appropriate), DC power is mainly used.

  On the other hand, even when such a superconductor is used, commercial AC power having a frequency of 50 Hz or 60 Hz is often used as a power supply source. For this reason, after converting commercial AC power to DC at room temperature, it is generally performed to transmit power to a superconducting device in a cryogenic state via a current lead. However, in such an embodiment in which the normal temperature side and the cryogenic temperature side are electrically connected, a large power supply facility and a current lead are indispensable, and the size and cost of the facility increase. In particular, current leads invite enormous heat penetration from the normal temperature side to the low temperature side, so a large refrigeration system is required, which is one of the factors that hinder the spread of superconducting equipment.

  In order to avoid such an increase in the size and cost of the apparatus, it is considered that it is an effective solution to allow an alternating current from a commercial power source to be directly used in an internal electric circuit even in a superconducting device. . For this purpose, it is necessary to realize a rectifier that converts an alternating current from a commercial power source into a direct current even in a cryogenic state.

  For example, Patent Document 1 discloses a rectifier that performs DC conversion from a general AC system in a normal temperature state, although the application target is not a superconducting device. In particular, the rectifier according to Patent Document 1 is formed of a semiconductor element such as a diode.

JP 2001-177985 A

  In the cryogenic region where superconducting equipment is used, there is a high risk of element destruction due to thermal contraction during cooling and thermal expansion due to local heating during operation. Therefore, it is difficult to ensure sufficient reliability with a rectifier made of a semiconductor element such as a diode as in Patent Document 1. Since a semiconductor element having a small capacity has a small heat capacity, there is a possibility that such element destruction risk can be reduced. However, since it is assumed that a large current is mainly used in superconducting equipment, it is necessary to prepare an enormous number of elements when such a small-capacitance element is used. There is concern over the occurrence of a large voltage drop on the V order. This is a loss larger than the heat load when the current lead is used, and lacks practicality.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a rectifier that can operate even in an extremely low temperature region such as liquid nitrogen temperature and has little loss.

  In order to solve the above problems, a rectifier according to the present invention is a rectifier that rectifies an alternating current supplied from an alternating current power source and outputs the rectified current to a load side as a direct current, wherein the first coil and the second coil are A wound first magnetic yoke and a second magnetic yoke wound with a third coil and a fourth coil are provided, and the first and third coils are in series with the AC power source. The second and fourth coils are connected in series to a DC power source, and a DC bias current is output from the DC power source, whereby the first and second magnetic yokes are output. A bias magnetic field is generated, and an inductance in one of the positive and negative directions of the first and third coils is made smaller than an inductance in the other direction.

  According to the present invention, a bias magnetic field is applied to the first and second magnetic yokes by supplying a DC bias current from a DC power source to the second and fourth coils. Since the magnetic yoke is made of a magnetic material, the permeability of the first and second magnetic yokes made of the magnetic material changes when a bias magnetic field is applied. Here, when a bias magnetic field of a predetermined value or more is applied due to the magnetic saturation phenomenon of the magnetic material, the inductances of the first and second coils change in one direction among the alternating currents whose direction of flow changes periodically. On the other hand, it becomes smaller and larger in the other direction. As a result, a component that flows substantially in one direction from the alternating current can be extracted, and a rectifying effect can be obtained.

  As described above, according to the rectifier according to the present invention, it is possible to realize a rectification operation without using a semiconductor element in which it is difficult to ensure sufficient reliability in a cryogenic environment. In other words, it is possible to provide a rectifier that can operate even in a cryogenic region such as liquid nitrogen temperature and has little loss.

  A primary side that receives an alternating current supplied from the alternating current power source and a primary side that is arranged on a low temperature side, and that is arranged on the high temperature side and transforms the alternating current transferred as magnetic energy from the primary side to the load side A transformer having a secondary side that outputs to the power source may be provided. In this case, the alternating current supplied from the alternating current power source can be transmitted as magnetic energy in a non-contact manner from the primary side to the secondary side. Therefore, for example, even when the AC power source is a commercial power source in a room temperature environment, it can be introduced into a rectifier circuit in a low temperature environment without heat intrusion.

  In this case, the transformer has a plurality of secondary sides, and each of the plurality of secondary sides is provided with the first and second magnetic yokes to form a double-wave rectifier circuit. It may be. In this way, by combining the above-described half-wave rectifier circuits, energy that has been wasted in a single half-wave rectifier circuit can be effectively used without being discarded, so that a more efficient rectifier can be realized.

  The second and fourth coils may be wound in opposite directions. As a result, the electromotive voltages induced from the AC coils are canceled each other, and the DC power supply can control the DC bias current without being affected by the AC current, and adjusts the magnetic characteristics of the magnetic yoke to output a high-quality rectified current. can do.

  The first and second magnetic yokes may be made of an iron-based amorphous magnetic material. Since the iron-based amorphous magnetic material has small hysteresis, it is easy to realize rectification control by a bias magnetic field using a DC bias current.

  The load may comprise a resistor. If a load having a very low resistance value such as a superconducting device (for example, a superconducting magnet) is used as a load, the loss of the system becomes very small. On the other hand, if an alternating current continues to be supplied from the alternating current power supply, the total energy of the system continues to increase, and the operation may run out of control. Therefore, by including a resistor having an appropriate resistance value in the load as in this aspect, it is possible to avoid a runaway operation and realize a stable rectification operation.

According to the present invention, a bias magnetic field is applied to the first and second magnetic yokes by supplying a DC bias current from a DC power source to the second and fourth coils. Since the magnetic yoke is made of a magnetic material, the permeability of the first and second magnetic yokes made of the magnetic material changes when a bias magnetic field is applied. Here, when a bias magnetic field of a predetermined value or more is applied due to the magnetic saturation phenomenon of the magnetic material, the inductances of the first and second coils change in one direction among the alternating currents whose direction of flow changes periodically. On the other hand, it becomes smaller and larger in the other direction. As a result, a component that flows substantially in one direction from the alternating current can be extracted, and a rectifying effect can be obtained.
As described above, according to the rectifier according to the present invention, it is possible to realize a rectification operation without using a semiconductor element in which it is difficult to ensure sufficient reliability in a cryogenic environment. In other words, it is possible to provide a rectifier that can operate even in a cryogenic region such as liquid nitrogen temperature and has little loss.

It is a schematic diagram which shows the whole structure of the rectifier which concerns on this embodiment. It is a graph which compares and shows the BH characteristic curve of a silicon steel plate and an iron-type amorphous magnetic body. It is a graph which shows the operating point of a magnetic yoke at the time of applying a direct current bias current to the 2nd and 4th coil in a rectifier. It is a circuit diagram which shows the example which comprised the double wave rectifier circuit combining the rectifier of FIG. It is a graph which shows the time change of the rectification current of the rectifier shown in FIG. It is the graph which expanded and showed the rectification current of the rectifier shown in FIG. 5 about the time axis. FIG. 7 is a graph showing the change over time of the rectified current when the supply voltage from the AC power supply is kept constant when the resistance value of the resistor is set to substantially zero in the rectifier of FIG. FIG. 4 is a graph corresponding to FIG. 3 showing operating points when the rectified current increases in a runaway manner.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

FIG. 1 is a schematic diagram showing an overall configuration of a rectifier 1 according to the present embodiment. The rectifier 1 includes a first magnetic yoke 2 and a second magnetic yoke 3, and both have a cross-sectional area S _mag and a magnetic circuit length L _mag . A first coil 4 and a second coil 5 are wound around the first magnetic yoke 2, and a third coil 6 and a fourth coil 7 are wound around the second magnetic yoke 3. Has been.

The first coil 4 and the third coil 6 are connected in series with each other, and an AC power supply 8 that is a commercial power supply for supplying 50 Hz or 60 Hz AC power is connected to one end side. The second coil 5 and the fourth coil 7 are connected in series with the DC power source 9. As a result, in FIG. 1, the alternating current I _AC is supplied from the alternating current power supply 8, and the direct current bias current I _{DC_BIAS} is supplied from the direct current power supply 9.

In particular, the second coil 5 and the fourth coil 7 to which the DC bias current _{IDC_BIAS} is supplied are _{wound around} the first magnetic yoke 2 and the second magnetic yoke 3 in opposite directions, respectively. . This makes it possible to cancel each other electromotive voltage AC current I _AC from the AC power source 8 is induced from the first and third coil 4 and 6 to be supplied. As a result, the DC power supply 9 can control the magnetic characteristics of the magnetic yokes 2 and 3 by adjusting the DC bias current value I _{DC_BIAS} without being affected by the _AC current I _AC from the AC power supply 8 at all. It is like that.

  The first and second magnetic yokes 2 and 3 are made of an iron-based amorphous magnetic material instead of a silicon steel plate, which is a kind of magnetic material used for general transformers and electric motors. Here, in FIG. 2, the continuous line has shown the iron-type amorphous magnetic body, and the broken line has shown the silicon steel plate. Thus, the iron-based amorphous magnetic material has a small hysteresis. For this reason, even if a magnetic material loss occurs, the amount of heat is exhausted to room temperature, which is suitable for a rectifier capable of operating at a cryogenic temperature.

Here, the DC bias current _I second and fourth coil 5, 7 _{DC_BIAS} flows has a same number of turns, while the number of turns and _{N DC,} first and third coil 4 alternating current flows , 6 has a same number of turns and the number of turns and N _AC. Further, it is assumed that the magnetic field lines leaking from the magnetic yokes 2 and 3 are small enough to be ignored. In this case, the inductance _{L AC} of the first and second coil 4, 6 alternating current flows _{I AC} is expressed by the following equation ^{_{L AC = 4π10 -7 μ r N}} AC 2 S mag / L mag (1)
Is obtained. The DC bias current _I inductance _{L DC} of the second and fourth coil 5, 7 _{DC_BIAS} flows following equation ^{_{L DC = 4π10 -7 μ r N}} DC 2 S mag / L mag (2)
Is obtained.

Incidentally, mu _r in the above equation (1) (2) is the relative permeability of the magnetic material constituting the magnetic yoke 2 and 3 (iron-based amorphous magnetic material), the following equation μ _r = ∂B / ∂H (3 )
Is required. As shown in the above equation (3), the relative permeability μ _r corresponds to the slope of the BH curve shown in FIG. 2, and when the magnetic yokes 2 and 3 are in a region where the slope is large, the inductances L _DC and L _{When AC} is large and the inclination is in a small region, the inductances L _DC and L _AC also tend to be small.

FIG. 3 is a graph showing operating points of the magnetic yokes 2 and 3 when the DC bias current _{IDC_BIAS} is applied to the second and fourth coils 5 and 7 in the rectifier 1. When a DC bias current I _{DC_BIAS} is applied to the second and fourth coils 5 and 7, a bias magnetic field H _BIAS = N _DC / L _mag (4) is applied to the magnetic yokes 2 and 3.
Is applied. As a result, the operating point of the magnetic yokes 2 and 3 moves to the H _BIAS point shown in FIG. When the operating point moves in one direction (positive side in the example of FIG. 3) in this way, the first and third are caused by the magnetic saturation phenomenon of the iron-based amorphous magnetic material constituting the magnetic yokes 2 and 3 shown in FIG. while relative permeability mu _r is small for the inductance L _AC is the positive side current of the coil 4 and 6, it shows that the relative permeability mu _r is increased with respect to the negative side of the current . That is, the alternating current I _AC flowing through the first and third coils 4 and 6 tends to flow because the inductance L _AC is small for the positive side, whereas the inductance L _AC is large for the negative side current. It becomes difficult to flow. As a result, the first to fourth coils constitute a magnetic saturation reactor, and the circuit shown in FIG. 1 functions as a rectifier circuit.

  Returning to FIG. 1 again, a load 10 is connected to the output side of the rectifier 1. As described above, the rectifier 1 substantially functions as a current operation type rectifier circuit. Therefore, unlike a voltage-operated rectifier using a general semiconductor element, it is necessary for a current exceeding a certain level to flow (in other words, a rectifying operation cannot be performed with a minute current). . Considering this, as the load 10, for example, a superconducting magnet or a resistor that needs to be constantly energized is preferable.

Rectifier 1 shown in FIG. 1 rectifies the negative one of the code alternating current I _AC in the first and third coil 4,6, which functions as a so-called half-wave rectifier circuit. FIG. 4 is a circuit diagram showing an example in which the double-wave rectifier circuit 20 is configured by combining such rectifiers 1. In FIG. 4, the normal temperature region 21 is surrounded by a solid line, and the cryogenic region 22 is surrounded by a broken line.

AC current I _AC input to the rectifier 20 is supplied from the AC power source 8, which is installed in the normal temperature region 21 (e.g., commercial AC power supply). The AC current I _AC input from the AC power supply 8 is input to the primary side L1 of the transformer 23, converted into a predetermined AC voltage, and then output to the secondary side L2. In particular, the transformer 23 has a primary side L1 disposed in the normal temperature region 21 and a secondary side L2 disposed in the cryogenic region 22. Thus, since energy transfer from the normal temperature region 21 side to the cryogenic region 24 side is performed by magnetic energy, heat intrusion to the cryogenic region 24 side can be avoided. That is, conventionally, energy transfer from the room temperature region 21 side to the cryogenic region 22 side is performed in a material contact state such as a power lead, etc., in order to solve the heat intrusion to the cryogenic region 24 side. Although a large-scale cooling device or the like is necessary, in the present embodiment, they can be eliminated by performing energy transfer in a non-contact manner.

Further, the rectifier 20 shown in FIG. 4 uses a nonlinear saturation of the magnetic saturation reactors L _X1 and L _X2 (each of which is composed of the first to fourth coils shown in FIG. 1) on the secondary side L2 of the transformer 23. A double-wave rectifier circuit that inputs to the characteristic element and supplies the load 10 is configured. In FIG. 4 in particular, the load 10 is a superconducting magnet 26 and a resistor 27 connected in series with each other, but it goes without saying that the present invention is not limited to this. By configuring the double-wave rectifier circuit in this way, there is less pulsation than in the case of the half-wave rectifier circuit, and rectification can be performed efficiently.
In the present embodiment, the case where the double-wave rectifier circuit is configured will be described in detail below. However, it goes without saying that the case where the dual-wave rectifier circuit is configured is the same.

FIG. 5 is a graph showing the change over time of the output current of the rectifier 20 shown in FIG. 4 (the direct current I _DC supplied to the load 10). The alternating current I _AC output from the alternating current power source 8 is rectified to the direct current power I _DC by the above-described rectifying action in the rectifier 20. In this example, since the superconducting coil 26 and the resistor 27 are used as the load 10, the time constant is long, and it takes time to reach a steady state. Thus, a substantially complete DC current _IDC is obtained in this way. be able to.

In this embodiment, in particular, AC power of 50 Hz, 100 V _rms is input from the AC power supply 8, the self-inductance of the primary side L1 and the secondary side L2 of the transformer 23 is L1 = L2 = 0.01 (H), and the load 10 The inductance of the superconducting coil 26 is L0 = 0.05 (H), the resistance value of the resistor 27 is RL = 0.01 (Ω), and the cross-sectional area of the two magnetic yokes 2 and 3 is S _mag. = 0.1 (m ² ), the magnetic circuit length is L _mag = 1 (m), the number of turns of the second and fourth coils 5 and 7 is N _DC = 50 (turns), and the first through which the alternating current I _AC flows The number of turns of the third coils 4 and 6 is N _AC = 25 (turns), and the DC bias current is I _{DC_BIAS} = 65 (A). As a result, it was experimentally verified that a substantially direct current of about 20 A was obtained about 60 seconds after the start of operation.

Note that the DC bias current (DC current flowing through the second and fourth coils 5 and 7) I _{DC_BIAS} may be separately rectified by preparing a similar rectifier 20 separately. The DC bias current _{IDC_BIAS} does not need to change the current value with time in order to obtain the above-described rectifying action. Therefore, even the rectifier 20 having a long time constant can be used effectively. When the rectifier 20 is used to rectify the DC bias current I _{DC_BIAS} , the second and fourth coils 5 and 7 constituting the rectifier have N _DC = 3000 (turns) and I _DC = 1 ( A) is preferable, and in this case, it is advantageous in that the heat intrusion of the current lead supplying the control direct current bias current _{IDC_BIAS} can be ignored.

6 is a graph showing an enlarged for the time axis rectified current I _DC shown in FIG. When the rectified current is viewed on a short time scale, pulsation (ripple) is present. Ripple factor of the rectifier current I _DC is determined by the time constant of the coil inductance and the resistor 27 of the superconducting magnet 26 is a load 10. In the rectifier 20 according to the present embodiment, the pulsating current value was about 0.2 A, and the ripple rate was about 0.01%.

In the present embodiment, in particular, the resistor 27 is included as the load 10 of the rectifier 20. The reason will be described below with reference to FIGS.
Resistor 27 plays an important role in limiting the capacity of the rectified current I _DC. If the resistor 10 is not included as the load 10 and is composed of only the superconducting magnet 26, the resistance value of the superconducting magnet 26 is substantially zero. Therefore, the resistance value of the load 10 as a whole is also substantially zero. Therefore, the energy (DC current) output from the rectifier 20 is not consumed on the load 10 side. On the other hand, energy continues to be supplied from the AC power supply 8 side, and the total amount of energy held by the system rapidly increases and diverges. As a result, if the total amount of energy continues to increase in this way, the operation of the rectifier 20 may be abnormal.

According to the inventors' research, when the total resistance value of the load 10 is substantially zero, the rectified current I _DC runaway manner increases, the rectification operation of the rectifier 20 becomes impossible is known . Figure 7 illustrates the rectifier 20 shown in FIG. 4, the resistance value of the resistor 27 has when set to substantially zero, the temporal variation of the rectified current I _DC in the case of maintaining the supply voltage from the AC power supply to a constant It is a graph. Figure 8 is a graph corresponding to Figure 3 showing an operating point in a case where commutation current I _DC increases in runaway. 7 and 8, the load resistance RL is set to be as small as 0.001 (Ω), the input AC power supply voltage is kept constant at 100 (V _rms ), and the inductance of the superconducting coil is set to L ₀ = 0.01 (H).

If the resistance value resistor 27 has, as shown in FIG. 7 is substantially zero, after rectified current I _DC is that increased to around 100 (A), it begins to increase rapidly, reach the vicinity of 200 (A) . Thereafter, the rectified current decreases rapidly and gradually goes to zero. The reason why the rectified current _IDC becomes unstable in this way is considered to be because the capacity limit of the magnetic circuit formed by the magnetic yokes 2 and 3 has been exceeded as shown in FIG. That is, when the rectified current _IDC increases and the input alternating current _IAC increases, both the positive and negative sides of the magnetic yokes 2 and 3 reach the saturation region. As a result, the rectification mechanism described above fails and the rectification operation cannot be performed normally. According to the inventor's study, when the iron yoke amorphous magnetic material having a sectional area S _mag of 0.1 (m ² ) and a magnetic circuit length L _mag of 1 (m) is used as the magnetic yokes 2 and 3, The maximum current value that can be rectified was about 100 (A).

  In addition, as for the various coils and wiring in the rectifier 20 which concerns on this embodiment, both a normal electric wire and a superconducting wire can be used. In particular, the present embodiment aims to operate the rectifier 20 at an extremely low temperature (liquid nitrogen temperature), and thus the coil and the wiring are configured to reduce the loss of the rectifier 20 by using a superconducting wire.

As described above, according to the rectifiers 1 and 20 according to the present embodiment, the first and second coils 5 and 7 are supplied with the DC bias current _{IDC_BIAS} from the DC power supply. A bias magnetic field H _BIAS is applied to the magnetic yokes 2 and 3. Since the magnetic yoke 2 and 3 is made of a magnetic material, by applying a bias magnetic field H _BIAS, permeability mu _r of the first and second magnetic yokes 2,3 made of a magnetic material is changed. Here, when a bias magnetic field H _BIAS greater than or equal to a predetermined value is applied due to a magnetic saturation phenomenon of the magnetic material, the inductance of the first and second coils 4 and 6 changes the alternating current I in which the flowing direction changes periodically. Of _AC , it decreases in one direction and increases in the other direction. As a result, it is possible to extract the component flowing from the substantially alternating current I _AC flows in one direction, to obtain the rectification effect.
As described above, according to the rectifier according to the present invention, it is possible to realize a rectification operation without using a semiconductor element in which it is difficult to ensure sufficient reliability in a cryogenic environment. In other words, it is possible to provide a rectifier that can operate even in a cryogenic region such as liquid nitrogen temperature and has little loss.

  INDUSTRIAL APPLICABILITY The present invention can be used for a rectifier that rectifies an alternating current supplied from an alternating current power source and outputs it as a direct current to the load side, particularly a rectifier that can operate even in an extremely low temperature region such as liquid nitrogen temperature.

DESCRIPTION OF SYMBOLS 1 Rectifier 2 Magnetic yoke 3 Magnetic yoke 4 1st coil (alternating current coil)
5 Second coil (DC coil)
6 Third coil (AC coil)
7 Fourth coil (DC coil)
8 AC Power Supply 9 DC Power Supply 10 Load 20 Rectifier 21 Room Temperature Area 22 Cryogenic Area 23 Transformer 26 Superconducting Magnet 27 Resistor

Claims (6)

A rectifier that rectifies an alternating current supplied from an alternating current power source and outputs it as a direct current to the load side,
A first magnetic yoke around which a first coil and a second coil are wound;
A second magnetic yoke around which a third coil and a fourth coil are wound,
The first and third coils are connected in series to the AC power source,
The second and fourth coils are connected in series to a DC power source,
By outputting a DC bias current from the DC power source, a bias magnetic field is generated for the first and second magnetic yokes, and the inductance in one of the positive and negative directions of the first and third coils is changed. A rectifier characterized in that it is smaller than the inductance in the direction of. A primary side which is arranged on a low temperature side and receives an alternating current supplied from the alternating current power source;
The transformer according to claim 1, further comprising a secondary side arranged on the high temperature side and having a secondary side that transforms an alternating current transferred as magnetic energy from the primary side and outputs the transformed alternating current to the load side. The rectifier described.   The transformer has a plurality of secondary sides, and a double-wave rectifier circuit is formed by providing the first and second magnetic yokes for each of the plurality of secondary sides. The rectifier according to claim 2.   The rectifier according to any one of claims 1 to 3, wherein the second and fourth coils are wound in opposite directions.   The rectifier according to any one of claims 1 to 4, wherein the first and second magnetic yokes are made of an iron-based amorphous magnetic material.   The rectifier according to any one of claims 1 to 5, wherein the load includes a resistor.

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