WO2012137245A1

WO2012137245A1 - Power conversion device

Info

Publication number: WO2012137245A1
Application number: PCT/JP2011/002004
Authority: WO
Inventors: 理津田; 高太郎濱島
Original assignee: 国立大学法人東北大学
Priority date: 2011-04-04
Filing date: 2011-04-04
Publication date: 2012-10-11

Abstract

A power conversion device according to the present invention uses a superconductor as a power conversion element and is excellent in the stability of continuous operation, instantaneous responsiveness, and the reliability of switching operation. The power conversion device comprises: an iron core (1) having a primary-side iron core region (1_C) and two secondary-side iron core regions (1_L, 1_R) and constituting closed magnetic paths (2) having two routes that pass through the primary-side iron core region (1_C) and respective different regions including secondary-side iron core regions (1_L, 1_R); a primary winding (3) wound around the primary-side iron core region (1_C); secondary windings (4_L, 4_R) wound around the respective secondary-side iron core regions (1_L, 1_R) and having one ends connected in such a relationship that the outputs are inverted to each other; and magnetic path changing switches (5) for shielding the closed magnetic paths per each of the closed magnetic paths of the secondary-side iron core regions (1_L, 1_R). Further, the magnetic path changing switches (5) each have: a cylindrical superconductor (6) covering the iron core (1) and imparting a magnetic shielding effect to the iron core; and a magnetic field applying coil (7) conducting switching current (13) having an AC waveform and applying a magnetic field that is greater than or equal to a critical magnetic field to the cylindrical superconductor (6). An exciting current is flowed through a primary winding (3), and a magnetic field that is greater than or equal to the critical magnetic field is alternately applied to the magnetic field applying coils (7) and the magnetic path changing switches (5) are alternately switched, thereby passing a magnetic flux (2) alternately through the two-channel closed magnetic paths and generating induced electromotive force at the secondary windings (4_L, 4_R) to output secondary current.

Description

Power converter

The present invention relates to a power conversion device. More specifically, the present invention relates to an apparatus that converts, for example, alternating current power into direct current power or direct current power into alternating current power by a switching action by applying a magnetic field of a critical magnetic field or higher.

As a power conversion technology, power conversion devices using semiconductor switching elements have already been used in a wide range of fields from home appliances to large electric motors. In the future, power conversion technology is expected to become indispensable for energy saving of various power devices, the spread and promotion of natural energy, and the realization of highly stable, high quality and highly reliable power supply. In particular, a DC interconnection system that links between distribution AC systems, such as radial AC distribution systems in a factory area, is considered to be a very useful system that enables energy saving and high reliability of the distribution system in the factory area. Therefore, its realization is desired.

Currently, power converters use gate turn-off thyristors (GTO thyristors) and insulated gate bipolar transistors (IGBTs) as power conversion elements, and also for active filters that suppress harmonics generated by the switching operation of the power conversion elements. GTO thyristors and IGBTs are used. However, in power converters using semiconductor elements, it is difficult to increase the speed if emphasizing large capacity, and it is difficult to increase the capacity if emphasizing high speed. Has the problem of being difficult. For example, when using a high-voltage, high-current GTO thyristor to increase the capacity of a power converter, the loss of the snubber circuit increases, and many small-capacity high-speed switching elements such as IGBTs are connected in series Causes problems such as a complicated circuit configuration and reduced reliability. Moreover, since the GTO thyristor that has been used as an on / off device for a large-capacity power converter can only be used at a switching frequency of several hundred Hz or less, it is a power converter for a power active filter that requires high-speed current control. Difficult to apply. In addition, when a large number of high-speed switching devices such as IGBTs are connected in series and a power converter capable of high-capacity high-frequency switching is configured, it is difficult to apply to power transmission and distribution systems from the viewpoint of efficiency and reliability. ing. Moreover, it is not sufficient to use a GTO thyristor or IGBT for a large-capacity active filter for power, and it is necessary to use an LC filter to suppress harmonics. For this reason, installation costs and operation costs are very expensive. It will be something. Thus, the high cost of the large-capacity semiconductor power conversion device becomes a bottleneck, and it is not easy to satisfy the economic conditions. Therefore, the DC interconnection system has not yet been put into practical use.

Therefore, it has been proposed that by using a superconductor as a power conversion element, it is possible to reduce the cost, size and efficiency of the power conversion device and to promote the spread of the DC system. For example, a superconducting device is incorporated in a part of a circuit, and a resistance type conversion device (Patent Documents 1-4) for controlling the presence or absence of resistance of the superconductor by applying a magnetic field to the superconductor, or a superconducting switching element (cryotron) and an LC There is a superconducting inverter (Patent Document 5) that generates a continuous oscillating current by changing the resistance of a superconducting switching element at the same frequency as the resonant frequency using a resonant circuit and obtains an alternating current output.

Also, a power conversion device using the magnetic shielding effect of a superconductor has been proposed (Patent Document 6). In this power converter, the magnetic flux generated in the iron core by the primary coil is switched by the magnetic path switching element using the magnetic shielding effect of the superconductor, thereby causing the magnetic flux to be alternately linked to the two secondary coils and electromagnetic induction. Thus, a secondary current is generated in the two electric circuits. The iron core is divided at four locations to form a gap, and a structure in which a superconductor element is inserted into the gap is adopted, so that the flow of the two magnetic circuits can be switched. And the on / off of the superconductor inserted in the middle of the magnetic circuit of the iron core is controlled by the magnetic field generated by the control coil installed in the iron core region through which the two magnetic circuits pass in common, or using the drive unit This is to be realized by mechanically replacing the superconductor and the normal conductor.

JP-A-1-194310 Japanese Patent Laid-Open No. 1-160065 JP-A 64-78017 JP-A 64-26365 JP 2005-116921 JP 2008-72886

However, since all the inventions described in Patent Documents 1-4 utilize the presence or absence of resistance caused by the transition between the superconducting state and the normal conducting state of the superconductor, The intended switching operation (commutation operation) cannot be obtained unless the generation resistance of the current increases. However, if the resistance generated during the normal conduction transition is large, the temperature rise due to Joule heat generation during the normal conduction transition increases, so it takes time to return from the normal conduction state to the superconducting state. Therefore, it is difficult to perform a stable continuous operation and a reliable switching operation. The invention described in Patent Document 5 is also similar to the invention described in Patent Document 1-4 in that a superconductor is incorporated in a part of the circuit and the presence or absence of resistance is controlled by transition between the superconducting state and the normal conducting state. It has the problem of.

In addition, although the power conversion device described in Patent Document 6 uses the magnetic shielding effect of the superconductor, the structure of inserting the superconductor element in the middle of the magnetic path by dividing the iron core and the transition of the superconductor element A structure in which a magnetic field for control is applied through the iron core is adopted, so that the magnetic shielding effect of the superconductor cannot be sufficiently obtained due to the influence of the leakage magnetic field and the shape of the superconductor, and the reliability of the switching operation is insufficient. It has become.

In other words, in order to be able to switch the flow of the two magnetic circuits, the iron core is divided at four locations to form a gap, and a superconductor element is inserted into the gap between the iron cores. The magnetic circuit is not a closed circuit, and the energy transfer efficiency decreases due to the leakage magnetic field between the iron cores. Also, if the area of the superconductor element inserted between the iron cores is larger than the cross section of the iron core, it is impossible to apply a magnetic field to the entire superconductor, and the magnetic shielding current in the superconductor cannot be reduced to zero. On the other hand, if it is small, a sufficient magnetic shielding effect cannot be obtained. For this reason, since the amount of magnetic flux passing through the superconductor element cannot be easily controlled, there is a problem that it is difficult to achieve high efficiency.

Also, since the magnetic field for controlling the transition of the superconductor element is applied through the iron core, it is always necessary to control the magnetic field generation according to the amount of alternating current. However, it is not easy to increase the speed of switching between magnetic circuits near the zero-cross point of the alternating current. Inductance also exists in the control coil itself that applies a magnetic field for controlling the transition of the superconductor element in the iron core, so even if you try to change the coil current at high speed for the transition control of the superconductor element, Cannot change at high speed. For this reason, it is very difficult to perform discontinuous superconducting bulk passage magnetic flux amount control. Therefore, it is difficult to control the switching operation, and it is difficult to reliably perform the switching operation.

Therefore, an object of the present invention is to provide a power conversion device that uses a superconductor as a power conversion element and has excellent continuous operation stability, instantaneous response, and switching operation reliability.

In order to achieve such an object, the power conversion device of the present invention has a primary side core region and two secondary side core regions, and passes through the primary side core region and different regions of the secondary side core region, respectively. An iron core that forms a two-path closed magnetic path, a primary winding wound around the primary iron core region, and a secondary winding that is wound around the secondary iron core region and has one end connected to each other so that the output is inverted. And a magnetic path changeover switch that shields the closed magnetic path for each closed magnetic path in the secondary core region, and the magnetic path changeover switch covers the iron core and provides a magnetic shielding effect on the iron core. And a magnetic field applying coil that applies a switching current having an AC waveform to apply a magnetic field higher than the critical magnetic field to the cylindrical superconductor, and energizes the primary winding with the exciting current and Critical magnetic field By alternately applying the upper magnetic field and alternately switching the magnetic path changeover switch, the magnetic flux is alternately passed through the two closed magnetic paths so that an induced electromotive force is generated in the secondary winding to cause the secondary current to flow. ing.

In the power conversion device of the present invention, the material of the cylindrical superconductor may be limited depending on the purpose of operation, but basically the same structure and the current waveform of the switching current flowing in the magnetic field application coil By switching the magnitude and further the current flowing through the primary winding, a power conversion device having different functions can be configured. For example, in the power conversion device of the present invention, a sinusoidal alternating current is input to the primary winding, and a pulse wave having the same duration as the half wave of the sinusoidal alternating current input to the primary winding is input to the magnetic field application coil. In addition, a switching current greater than or equal to a current that generates a magnetic field corresponding to the critical magnetic field of the cylindrical superconductor is alternately applied in synchronism with the sine wave AC current to alternately apply a magnetic field higher than the critical magnetic field to the cylindrical superconductor. It is possible to function as a rectifier by alternately switching the magnetic paths of the system and inducing a positive AC half-wave voltage alternately in the secondary windings of each closed magnetic path to output a DC current.

Further, in the power conversion device of the present invention, the cylindrical superconductor is a type II superconductor, and a waveform corresponding to an AC waveform to be input from the secondary winding and input a DC current to the primary winding. In addition, a switching current having a half-wave waveform having a time width half that of the AC waveform is alternately supplied to the magnetic field application coils of the two magnetic paths, so that a cylindrical superconductivity is applied to the magnetic path where no switching current is applied. The magnetic flux on the side where the switching current is flowing is blocked by the magnetic shielding by the body, but the magnetic field strength is half-wave between the upper critical magnetic field and the lower critical magnetic field of the cylindrical superconductor. By applying a magnetic field that changes to a cylindrical superconductor to induce a half-wave voltage, positive and negative AC half-wave voltages are alternately induced in the secondary windings of each closed magnetic circuit to output an AC current. To function as an inverter It is possible.

Here, the cylindrical superconductor may be formed into a cylindrical shape by a single superconducting bulk or may be formed into a cylindrical shape by joining a plurality of superconducting bulks, but a single crystal bulk is used. It is preferable that a plurality of superconducting bulks are joined to be formed into a cylindrical shape. In addition, the cylindrical superconductor should be a polycrystalline bulk, whether it is formed into a cylinder by a single superconducting bulk or formed into a cylinder by joining a plurality of superconducting bulks. Is preferred.

Further, the magnetic field application coil is preferably wound around the cylindrical superconductor in a toroidal shape, more preferably the same number of turns in both the clockwise and counterclockwise directions in the circumferential direction of the cylindrical superconductor. It is wound in a toroidal shape.

According to the power conversion device of the present invention, the magnetic path switching switch for switching the flow of magnetic flux generated in the iron core is composed of the cylindrical superconductor covering the periphery of the iron core and the magnetic field application coil, and flows through the magnetic field application coil. By controlling the magnetic shielding effect of each superconductor by current control, the flow of magnetic flux in the iron core is interrupted or controlled, so a stable continuous switching operation with a simple structure and good responsiveness, and Realized reliably.

That is, the power conversion device according to the present invention uses the superconductor as a derivative rather than as a resistor, and performs switching with or without inductance, so that heat generation can be suppressed. Since the switching operation is not obtained using the resistance generated during the normal conduction transition, the temperature rise due to Joule heat generation during the normal conduction transition is not a problem, and it takes time to return from the normal conduction state to the superconducting state. I don't need it. That is, it can respond instantaneously as a switching element and can be stably operated continuously, and it is easy to obtain an intended switching operation.

Moreover, the power converter device concerning this invention is a core which comprises the closed magnetic circuit of 2 paths | paths which pass either one of a primary side core area | region provided with a primary winding, and two secondary side core area | regions provided with a secondary winding. And a simple magnetic circuit configuration including a magnetic path changeover switch that shields the closed magnetic circuit for each closed magnetic circuit in the secondary core region, the structure is simple. Moreover, since it does not have a drive unit, it can be expected to improve continuous stable operation and save labor for maintenance.

Moreover, the power converter according to the present invention employs a magnetic closed circuit to block or control the flow of magnetic flux in the iron core by the magnetic shielding effect of a cylindrical superconductor covering the periphery of the magnetic path. Therefore, the switching operation can be executed instantly and reliably, and the switch performance is high. In other words, the cylindrical superconductor having a hollow portion is arranged so as to cover the outside of the iron core, so there is no part where the iron core is divided, and the magnetic circuit becomes a closed circuit. A decrease in transmission efficiency can be avoided, and high efficiency can be achieved. Further, when the state is changed to the normal conducting state, the magnetic shielding current in the cylindrical superconductor can be reduced to zero. In addition, since the magnetic field application coil is separated from the magnetic circuit, magnetic field generation control according to the amount of alternating current is unnecessary, and switch control is easy. In addition, switching of the magnetic circuit near the zero cross point of the alternating current can be performed at high speed and reliably. Therefore, the switching operation as the magnetic path changeover switch or the passing magnetic flux amount control element can be easily controlled, and the responsiveness is good and the function can be surely performed.

Furthermore, when functioning as an inverter, the cylindrical superconductor in the secondary core region on the side where magnetic flux is to be passed functions as a passing magnetic flux amount control element. Continuous DC / AC conversion is possible by simply passing an electric current. In addition, by controlling the waveform of the switching current flowing in the magnetic field application coil, secondary currents having various waveforms or frequencies that can only be obtained by a complicated circuit using a semiconductor element can be easily obtained.

Therefore, since the power conversion device of the present invention can control the current flowing in the secondary side circuit with high accuracy and high speed, for example, a DC interconnection system that links between radial AC distribution systems in a factory area or the like. Even in the case of being used for the above, it is possible to promote the spread of the DC system without requiring a very expensive large capacity active filter for power.

Also, in the power conversion device of the present invention, when using a superconductor formed by joining a plurality of superconducting bulks into a cylindrical shape, each superconducting bulk is as high performance as a single crystal bulk. However, since the characteristics of the joint portion deteriorate, the critical magnetic field as a superconductor formed in a cylindrical shape can be made small. This makes it possible to construct a magnetic superconducting switching element with a low critical magnetic field while improving the magnetic shielding characteristics by increasing the volume of the superconductor, so that the amount of magnetic flux in the iron core can be rapidly changed between zero and a finite value. . In addition, this becomes more effective by using a polycrystalline bulk. That is, the polycrystalline bulk is a low-performance superconducting bulk having a small critical current density and a small critical magnetic field because the crystal boundary is originally weakly coupled. By joining them and obtaining a superconductor formed into a cylindrical shape, a magnetic superconducting switching element having a low critical magnetic field can be constructed while improving the magnetic shielding characteristics by increasing the volume.

Further, in the power conversion device of the present invention, when the magnetic field application coil is wound around the cylindrical superconductor in a toroidal shape, magnetic field leakage to the outside can be suppressed. Furthermore, when the cylindrical superconductor is wound in a toroidal shape with the same number of turns in both the clockwise and counterclockwise directions in the circumferential direction, the equivalent current paths flowing in the circumferential direction of the cylindrical superconductor are opposite to each other. Since it becomes the direction and cancels out, it becomes apparently zero, and the leakage magnetic field can be made extremely small. This reduction of the leakage magnetic field can reduce noise generated in the waveform of the secondary current. In particular, in the inverter, when controlling the magnitude of the magnetic field applied to the type II superconductor, a clean AC waveform without disturbance is obtained.

It is a figure which shows the principle of the magnetic switching element used for the power converter device of this invention, (A) shows an OFF state, (B) shows an ON state. It is a figure explaining the transient phenomenon of the magnetic shielding effect of a type II superconductor. It is a perspective view which shows an example of the cylindrical superconductor which comprises a magnetic switching element. It is a temperature process figure which shows an example of oxygen annealing conditions at the time of preparation of a YBCO polycrystal bulk. It is a perspective view which shows an example of the toroidal winding of the coil for a magnetic field application with respect to a cylindrical superconductor. 1 is a front view of a superconductingly connected cylindrical superconductor, showing an embodiment in which one cylindrical superconductor is configured by superconducting YBCO polycrystalline bulk. FIG. It is a principle figure which shows one Embodiment which comprised the power converter device of this invention as a rectifier. It is a principle figure which shows the operation | movement state of the rectifier, (A) is the flow of the magnetic flux in the state where the left switching current is off and the right switching current is on, and (B) is the magnetic flux in the state where the left switching current is on and the right switching current is off. Show the flow. It is a wave form diagram when carrying out full wave rectification of the alternating current of 60 Hz in the rectifier. It is a wave form diagram when carrying out full wave rectification of the alternating current of 500 Hz in the rectifier. It is a principle figure showing one embodiment which constituted the power converter of the present invention as an inverter. It is a principle figure which shows the operation | movement state of the inverter, (A) is the flow of the magnetic flux in the state where the left switching current is off and the right switching current is on, and (B) is the magnetic flux in the state where the left switching current is on and the right switching current is off. Show the flow.

Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings. The power converter according to the present invention can have functions such as a transformer, a circuit breaker, a power storage function, and a frequency converter in addition to a power conversion function from AC to DC and from DC to AC. A basic configuration and function as a power conversion device will be described, and then other functions will be described.

FIG. 1 shows the operating principle of a magnetic field type superconducting switch element constituting the power converter of the present invention. This magnetic field type superconducting switch element 5 pays attention to the magnetic shielding characteristic which is a difference between the superconducting state and the normal conducting state, and is a cylindrical superconductor having a hollow portion 10 in the center (referred to as a cylindrical superconductor). 6 is used to enclose part of the iron core 1 forming a closed magnetic circuit, and for example, a magnetic field 11 greater than the critical magnetic field is applied to the cylindrical superconductor 6 by energizing the magnetic field application coil. The critical magnetic field applied to the cylindrical superconductor 6 when the energization of the magnetic field application coil is stopped when the magnetic shielding effect is lost by switching to the state and the magnetic flux flowing through the iron core is not hindered (see FIG. 1B). The application of the magnetic field is stopped and the state is changed to the superconducting state, thereby turning off the magnetic flux 2 in the iron core 1 by the magnetic shielding effect (see FIG. 1A). That is, when the coil 3 is wound around the annular core 1 and energized, the magnetic flux 2 generated from the coil 3 flows in the core 1. However, when the coil 3 is energized while a part of the annular core 1 is covered with the cylindrical superconductor 6, the magnetic flux 2 generated in the coil 3 is generated inside the superconductor 6 due to the magnetic shielding effect of the superconductor 6. The magnetic flux in the iron core 1 becomes zero because it is canceled by the magnetic flux 9 caused by the magnetic shielding current 8 flowing through the core. In this state, when a magnetic field 11 higher than the critical magnetic field is applied to the superconductor 6, the superconductor 6 undergoes a normal conduction transition, and the magnetic shielding current 8 becomes zero, as if the superconductor 6 does not exist. A magnetic flux 2 flows in the iron core 1. In this way, whether or not the cylindrical superconductor 6 covering the iron core 1 is switched between the superconducting state and the normal conducting state by whether or not the magnetic field application coil is energized, and the magnetic shielding effect is applied to the iron core 1. A switching operation is performed.

Here, the magnetic shielding effect of the superconductor 6 does not necessarily mean that the magnetic field of the hollow portion 10 is zero if it is a cylinder, but the magnetic flux distribution applied to the hollow portion 10 and the cylindrical shape of the superconductor 6. Dependent. For example, when the magnetic flux density passing through the hollow portion 10, that is, the magnetic flux density flowing through the iron core 1 is high and the volume of the cylindrical superconductor 6 is small, the shielding current amount is insufficient, so the net magnetic flux of the hollow portion 10 is It will not be zero. Further, since the magnetic flux 9 is only a magnetic field generated by the shielding current 8 flowing in the superconductor 6, the net magnetic flux in all regions of the hollow portion 10 with respect to any magnetic field distribution in the hollow portion 10 of the cylindrical superconductor 6. In some cases, the density cannot be reduced to zero. Therefore, it is preferable that the cylindrical superconductor 6 has a small gap with the iron core 1 passing through the hollow portion 10, and more preferably is in contact with the outer surface of the iron core 1. In this case, since the leakage magnetic field is reduced, the cancellation rate of the magnetic field of the hollow portion 10, that is, the magnetic field passing through the iron core 1, is increased, and the magnetic shielding effect is increased. That is, as the air gap between the iron core 1 and the cylindrical superconductor 6 covering the iron core 1 is smaller, the magnetic flux 9 generated by the circumferential shielding current 8 flowing inside the superconductor 6 due to the magnetic shielding effect of the cylindrical superconductor 6. Flows into the iron core 1 and is absorbed by the iron core 1 in the case of the iron core 1 having substantially the same size as the hollow portion 10 of the cylindrical superconductor 6. Since the magnetic flux 9 produced by the shield current 8 and the magnetic flux 2 in the iron core 1 produced by the primary winding 3 are opposite and have the same size, the inner iron core 1 of the cylindrical superconductor 6 is The net magnetic flux that flows is zero. Further, it is important that the cylindrical superconductor 6 has a hollow portion 10 for covering so as to surround a part of the iron core 1 forming a closed magnetic circuit, and the shape is not particularly limited to a cylinder, It may be a square tube or a polygonal tube. Of course, when the inner peripheral contour shape, that is, the shape of the hollow portion 10 is round like a cylinder, the inside of the cylindrical superconductor 6 is larger than the case of the square hollow portion 10 where current tends to concentrate on the corner portion. The distribution of the shielding current 8 is uniform in the circumferential direction and the magnetic flux canceling efficiency in the iron core 1 is expected to be improved. However, since the cross-sectional shape of a normally used iron core is rectangular, The shape of the hollow portion 10, that is, the cylindrical shape is appropriately selected in consideration of the air gap between the cylindrical superconductor 6 covering the cylindrical superconductor 6.

As a superconducting material, it is possible to use either a type I superconductor or a type II superconductor in the case of functioning only as a magnetic path switching element that controls the amount of magnetic flux by simple on / off. In the case of functioning as a passing magnetic flux amount control element that is continuously increased or decreased, the use of a type II superconductor is preferred. An alloy-based superconductor or a high-temperature superconductor such as YBCO is a type II superconductor, and therefore, as shown in FIG. 2, the state where the Meissner state called the vortex state and the normal conducting state are mixed is lower. It exists between the critical magnetic field H _c1 and the upper critical magnetic field H _c2 . In the vortex state of the type II superconductor, unlike the type I superconductor that immediately shifts from the Meissner state to the normal conducting state, the magnetic shielding effect is accompanied by a transient phenomenon. In other words, the magnetic shielding effect changes depending on the magnitude of the magnetic field applied to the cylindrical superconductor 6 by the magnetic field application coil 7, so that the magnetic shielding effect changes between the state where the magnetic shielding effect is sufficiently obtained and the state where the magnetic shielding effect is zero. The amount can be adjusted. Therefore, the amount of magnetic flux passing through the iron core 1 can be arbitrarily controlled by the amount of magnetic field applied to the cylindrical superconductor 6, that is, the amount of current of the magnetic field applying coil 7 to the cylindrical superconductor 6. This is because the magnetic shielding current amount of the cylindrical superconductor 6 decreases as the magnetic field applied to the cylindrical superconductor 6 increases, and this characteristic is useful when performing inverter operation. And it has been clarified by the rectification experiment at 500 Hz by the present inventors that the control of the magnetic shielding amount has sufficient response for realizing high-speed switching. The experimental results are shown in FIG.

Here, in the case of the rectifying operation, the magnetic path changeover switch 5 only needs to function as a switching element for switching the magnetic path by simply controlling the amount of magnetic flux, but in the case of functioning as an inverter. There are cases where the magnetic flux path functions as a switching element that switches the magnetic path by simply controlling on / off of the magnetic flux passing through, and functions as a magnetic flux amount control element that performs continuous increase / decrease of the magnetic flux volume. Therefore, in the case of a power conversion device that performs an inverter operation, the superconductor 6 needs to be a type II superconductor, preferably an yttrium superconductor, more preferably a polycrystalline yttrium superconductor. The use of the body. Of course, it is only necessary to be able to switch between the superconducting state and the normal conducting state during the rectifying operation, so that it is possible to use either a type II superconductor or a type I superconductor. That is, the magnetic path switching element can also be constituted by a type I superconductor. It should be noted that the responsiveness of the control of the magnetic shielding amount of the superconductor is considered to depend on the size of the cylindrical superconductor 6, the size of the magnetic field application coil 7, and strictly speaking the size of the inductance.

Also, the cylindrical superconductor 6 needs to change the amount of magnetic flux in the iron core at high speed between zero and a finite value. For this purpose, it is necessary to transfer the cylindrical superconductor 6 to normal conduction at high speed by applying a magnetic field to the cylindrical superconductor 6. For this purpose, it is desirable that the critical magnetic field of the cylindrical superconductor is as small as possible. When the critical magnetic field of the cylindrical superconductor 6 is large, the magnetic field applying coil 7 to the cylindrical superconductor 6 becomes large, the entire apparatus is enlarged, and the conduction loss in the magnetic field applying coil 7 is increased. This is because the efficiency of the magnetic field application coil 7 is increased and the inductance of the magnetic field application coil 7 is increased, and the switching speed is decreased. Generally, when the critical magnetic field is small, the critical current density is also small, that is, the magnetic shielding current in the superconducting state is often small. However, the magnetic shielding property can be improved by increasing the volume of the superconductor having the magnetic shielding property. For this reason, when configuring a magnetic field type superconducting switching element, it is most important to use a superconductor having a low critical magnetic field. However, the superconducting bulk currently on the market is only a single crystal superconducting bulk such as YBCO (yttrium-based superconductor; Y-Ba-Cu-O-based superconductor), and it is only a material with a large critical current density and critical magnetic field. is there. Even if the cylindrical superconductor 6 is configured using such a superconducting bulk, a large magnetic shielding effect can be obtained, but since the critical magnetic field is high, it is not easy to transfer the superconductor to normal conduction. It becomes difficult to realize a target switching phenomenon as a switching element. Therefore, attention was focused on a polycrystalline YBCO bulk produced by a sintering method. In the polycrystalline bulk, since the crystal boundary is weakly coupled, the overall critical current density of the cylindrical superconductor 6 is small, and the critical magnetic field is also small. Further, unlike single crystal bulk, it is not manufactured by crystal growth, but can be easily manufactured by sintering the mixed material, so that significant reduction in material cost and manufacturing cost can be expected. In this way, the power converter of the present invention is unique in that it intends to actively utilize a low-performance superconducting bulk, contrary to the direction of aiming to improve the performance of current superconducting material development. Innovative.

Here, as shown in FIG. 3, the cylindrical superconductor 6 is formed into a cylindrical shape with a single superconducting bulk, and as shown in FIG. 6, a plurality of superconducting bulks 6a are joined to form a cylindrical shape. It may be molded into a shape. In particular, in the case of high voltage applications, since the iron core becomes thick, a large cylindrical superconductor 6 is required. However, when forming a cylindrical superconductor 6 by joining a plurality of superconducting bulks 6a. As shown in FIG. 6, for example, a large cylindrical superconductor 6 can be easily manufactured by superconducting connection of a trapezoidal superconducting bulk 6a. In addition, the superconducting characteristics of the joint 14 connecting the superconducting bulks 6a are deteriorated as compared with the inside of the superconducting bulk 6a. Therefore, by adjusting the superconducting bulk joining condition, the superconducting characteristics of the joint 14 can be controlled to the characteristics required for the cylindrical superconductor 6. Therefore, when a single crystal bulk is used, it is preferable that a plurality of superconducting bulks are joined and formed into a cylindrical shape. In this case, even if each bulk 6a is as high performance as a single crystal bulk, the characteristics of the junction are deteriorated, so that the critical current density as a whole of the superconductor formed in a cylindrical shape is reduced. The critical magnetic field can be reduced. Furthermore, it is preferable to use a polycrystalline superconducting bulk in any case where it is formed into a cylindrical shape by a single superconducting bulk or in a case where a plurality of superconducting bulks are joined and formed into a cylindrical shape.

Here, the magnetic field type superconducting switching element 5 of the present embodiment is composed of the cylindrical superconductor 6 and the iron core 1, but the on / off control of the switching element 5, that is, the superconducting state and the normal conducting state of the cylindrical superconducting conductor 6. The transition control is executed by energizing a magnetic field applying coil 7 wound around the cylindrical superconductor 6 in a toroidal manner and applying a magnetic field higher than the critical magnetic field. During the switching operation, the entire cylindrical superconductor 6 in the superconducting state needs to be quickly transferred to normal conduction, and therefore, it is necessary to apply a necessary magnetic field to the entire cylindrical superconductor 6. In addition, it is necessary that the applied magnetic field for causing the cylindrical superconductor 6 to make a normal conducting transition does not affect the magnetic field distribution in the iron core 1. From this, as a magnetic field application method to the cylindrical superconductor 6, a method of directly applying a magnetic field by the magnetic field applying coil 7 wound around the cylindrical superconductor 6 in a toroidal manner was adopted. If the coil can be densely wound in the circumferential direction in a toroidal shape, a toroidal magnetic field is applied only to the cylindrical superconductor 6, and leakage of the magnetic field to the outside can be suppressed. Further, the magnetic field application coil 7 is preferably wound in a toroidal shape with the same number of turns in both the clockwise and counterclockwise directions in the circumferential direction of the cylindrical superconductor. For example, as shown in FIG. 5, when one conductor is wound around the cylindrical superconductor 6 in a toroidal shape, the winding amount is reversed in the middle of the winding, and the same amount is rewound. At this time, the direction in which the conductor of the magnetic field applying coil 7 is wound around the cylindrical superconductor 6 is the same both in the clockwise direction and in the counterclockwise direction. In this case, since the equivalent current paths 12 formed in the circumferential direction are opposite to each other and cancel each other, the apparent current path becomes zero, and the leakage magnetic field can be extremely reduced. This has been clarified by a rectifying operation experiment using a small model of the present inventors. Therefore, as shown in FIG. 5, the magnitude of the magnetic field applied to the type II superconductor by the magnetic field application coil wound with the same number of turns in both the counterclockwise direction and the clockwise direction is within the range of the vortex state. When controlling with, a clean AC waveform without disturbance is obtained. Of course, when a clean AC waveform is not required, for example, in the case of a rectifying operation that requires only a simple on / off operation, the magnetic field application coil is simply wound around the cylindrical superconductor in a toroidal shape. There is no problem. In order to obtain the number of ampere turns necessary for the magnetic field applying coil 7, not only one reciprocation in the circumferential direction of the cylindrical superconductor 6 but also a number of reciprocations by rewinding as many times as necessary. However, it can be wound, and in some cases, a plurality of conductors may be used.

Further, the switching current 13 flowing through the magnetic field application coil 7 needs to be at least an AC waveform accompanied by a change in the magnetic field, not a DC waveform. However, the sine wave waveform is not particularly limited, and differs depending on the operation mode of rectifying operation or inverter operation and the current waveform desired to be obtained after conversion. For example, in the case of a rectifying operation, if the pulse height is equal to or greater than the current that creates a magnetic field corresponding to the critical magnetic field of the cylindrical superconductor 6 with a pulse wave having the same time width as the half wave of the input sinusoidal alternating current The waveform is not particularly required to be a rectangular wave, but is preferably a rectangular wave with little sag at the rise and fall in order to reliably apply a magnetic field above the critical magnetic field. In the case of inverter operation, the switching current 13 is not passed through one of the magnetic path changeover switches 5 or only the switching current 13 having a magnitude that generates only a magnetic field below the lower critical magnetic field is passed and maintained in a superconducting state. In order to function as a switching element that cuts off the magnetic path, the other magnetic path changeover switch 5 functions as a passing magnetic flux amount control element that performs continuous increase / decrease control of the passing magnetic flux amount. A switching current 13 having a magnitude that forms a magnetic field in which the strength of the magnetic field changes in a half-wave shape between the upper critical magnetic field H _c2 and the lower critical magnetic field H _c1 and a half-wave shape of an arbitrary AC waveform flows. It is. The waveform of the switching current 13 flowing through the magnetic field application coil 7 determines the current waveform obtained after conversion. Therefore, normally, the waveform of the switching current 13 flowing through the magnetic field application coil 7 is determined according to the current waveform desired to be obtained after the conversion. For example, when a sine wave AC waveform is created from DC, it is necessary to apply a half-wave rectified waveform having a time width corresponding to the half wave of the target sine wave AC waveform, for example, a current having a waveform as shown in FIG. . In other words, the current waveform on the secondary side in the case of inverter operation can be controlled by the waveform of the switching current that flows through the magnetic field application coil to the cylindrical superconductor 6.

By using the magnetic field type superconducting switching element 5 configured as described above, the current waveform and magnitude of the switching current 13 flowing through the magnetic field applying coil 7, and further the current waveform of the primary current or switching to AC or DC In addition, it is possible to configure a power converter that can be arbitrarily switched to a rectifying operation or an inverter operation.

FIG. 7 shows an embodiment in which the power converter of the present invention is configured as a rectifier. This power converter has a primary side core region 1 _C and two secondary

side core regions

1 _L , 1 _R , passes through the primary side core region 1 _C , and has a secondary

side core region

1 _L , 1 _R. The core 1 constituting the two closed magnetic paths passing through different regions, the primary winding 3 wound around the primary side core region 1 _C , and the secondary

side core regions

1 _L and 1 _R are wound on the respective outputs. Secondary windings 4 _L and 4 _R , one end of which is connected to each other, and a magnetic path changeover switch 5 that shields the closed magnetic path for each closed magnetic path of the secondary side core regions 1 _L and 1 _R. I have. Specifically, using a tripod iron core, the primary winding 3 through which an alternating current flows is connected to the central iron core 1 _C , and the secondary windings 4 _L and 4 _R for taking out a direct current are connected to the

iron cores

1 _L and 1 _R at both ends. Each of them is arranged to constitute a magnetic circuit in which two

secondary windings

1 _L and 1 _R are connected in parallel to the primary winding. A cylindrical superconductor 6 is disposed on the magnetic circuits connected in parallel so as to cover the iron core 1. The magnetic path changeover switch 5 includes a cylindrical superconductor 6 that covers the iron core 1 and gives a magnetic shielding effect to the iron core 1, and a switching field 13 having an alternating waveform is applied to the cylindrical superconductor 6. A magnetic field applying coil 7 for applying the above magnetic field, and alternately supplying a switching current 13 for energizing the primary winding 3 with an alternating current as a primary current and generating a magnetic field higher than the critical magnetic field in the magnetic field applying coil 7. By applying the magnetic path changeover switch 5 alternately, the magnetic flux is alternately passed through the two closed magnetic paths to generate an induced electromotive force in the secondary windings 4 _L and 4 _R, and a DC current as a secondary current is generated. It is configured to flow.

Although not shown, at least of the magnetic path changeover switch 5, the cylindrical superconductor 6 and the magnetic field application coil 7 are accommodated in a heat insulating container in which a cooling medium is enclosed, and are applied by the magnetic field application coil 7. Unless a magnetic field greater than the critical magnetic field is applied, the superconducting state is maintained. The heat insulating container is called a cryogenic vessel or cryostat which is formed into a double wall structure by, for example, FRP or a polymer insulating material, and the space between the double walls is evacuated. Therefore, the inside and outside of the heat insulating container are placed in a vacuum heat insulating state, and a cryogenic state sufficient to maintain the superconducting state of the cylindrical superconductor 6 by a cooling medium such as liquid nitrogen sealed or circulated inside the container. Can be easily retained. A superconducting conductor can also be used for the magnetic field application coil 7. *

In order to efficiently use the magnetic shielding effect of the cylindrical superconductor 6, the gap between the inner surface of the hollow portion 10 at the center of the cylindrical superconductor 6 and the outer surface of the iron core 1 is made as small as possible. Is desirable. The outer diameter and length of the cylindrical superconductor 6 are determined according to the maximum magnetic flux density in the iron core 1. Increasing the outer diameter and the superconducting bulk length of the cylindrical superconductor 6 can improve the magnetic shielding effect. Here, the critical magnetic field of the YBCO polycrystalline bulk changes depending on the temperature and time at the time of superconducting bulk fabrication (during sintering) and the oxygen annealing conditions. Therefore, the superconducting bulk having a critical magnetic field suitable for the capacity of the transducer is used. Fabrication is possible. The cylindrical superconductor 6 of FIG. 3 is a YBCO polycrystalline bulk produced by the present inventors. A cylindrical superconductor having an outer diameter of 18 mm, an inner diameter of 10 mm, and a length of 9.5 mm is processed by processing a cylindrical superconductive bulk. YBCO polycrystalline bulk was produced. Moreover, the temperature process which produced this superconducting bulk is shown in FIG. This oxygen annealing condition is not a general optimum condition, but only one condition suitable for producing a superconducting bulk used in the power conversion device of this embodiment. As shown in FIG. 5, the magnetic field application coil 7 is wound directly on the cylindrical superconductor 6 in a toroidal shape so as to reciprocate in the circumferential direction.

The magnetic field applying coils 7 are connected to different power sources and excited in accordance with the waveform of the primary current flowing through the primary winding. The two power supplies are linked so that they can be turned on and off alternately. In the conversion from alternating current to direct current, the cylindrical superconductor 6 only needs to be repeatedly realized in the normal conducting state and the superconducting state. Therefore, when using a type II superconducting bulk such as YBCO, a magnetic field higher than the upper critical magnetic field H _c2 is used. It is sufficient to pass a current that can generate the current. Of course, when a type I superconductor is used, a current that can generate a magnetic field higher than the critical magnetic field Hc may be applied. In order to increase the response speed at this time, it is necessary to reduce the inductance of the magnetic field application coil to the cylindrical superconductor 6 as much as possible and increase the amount of current flowing to the coil. The number of windings on the primary side and the secondary side is determined according to the voltage class on the primary side and the secondary side.

The operation method of this superconducting rectifier is as follows. For each half wave of the sinusoidal alternating current flowing through the primary winding 3, the switching current 13 is alternately supplied to the magnetic field applying coil 7 of the left and right cylindrical superconductors 6 to alternately generate the magnetic field on the cylindrical superconductor 6. So that the voltage between the terminals of the secondary windings 4 _L and 4 _R always has the same sign. At this time, the waveform of the magnetic field applied to the cylindrical superconductor 6, that is, the waveform of the switching current 13 flowing through the magnetic field application coil 7 is, for example, a rectangular wave that can be clearly controlled on and off. In FIG. 8A, since no magnetic field is applied to the left cylindrical superconductor 6 for the first half wave, the left superconductor 6 maintains the superconducting state. Accordingly, the magnetic flux passing through the core 1 _L of the left side of the flux 2 generated in primary winding 3 side, the magnetic flux generated in the core 1 _L by the magnetic shielding current 9 flowing through the tubular superconductor 6 (not shown) Is canceled (magnetic shielding effect), and the apparent magnetic flux becomes zero. Therefore, the voltage becomes the core 1 secondary winding 4 _L in flux linkage _L of the left zero does not occur. On the other hand, in the right magnetic circuit, a rectangular wave magnetic field is applied to the right cylindrical superconductor 6, so that the cylindrical superconductor 6 undergoes normal conduction transition and the magnetic shielding effect becomes zero. Therefore, all the flux 2 generated in the primary side passes through the right side of the iron core 1 in _R. Therefore, in the secondary winding 4 _R wound around the right core 1 _R, voltage is generated with respect to the magnetic flux change, the addition amount of the zero voltage of the voltage and the left becomes the full secondary voltage. As shown in FIG. 8 (B), in the next half-wave, through the flux 2 on the left side of the iron core 1 in _L by which a magnetic field is applied to the rectangular wave to the left of the cylindrical superconductor 6 normal conductive transition, opposite Further, by making the magnetic field applied to the right cylindrical superconductor 6 zero, the cylindrical superconductor 6 is returned to the superconducting state and the magnetic shielding effect is applied. Accordingly, the magnetic flux apparent on the right side of the iron core 1 in _R is zero, the voltage at the right side of the secondary winding 4 _R does not occur. In contrast, in the left side of the secondary winding 4 _L, since the total amount of magnetic flux 2 generated in the primary side passes, a voltage corresponding to the time variation of the magnetic flux 2 is generated. Which zero voltage of the left secondary winding 4 _L of voltage and right of the secondary winding 4 _R is applied is a total voltage of the secondary winding. As described above, a full-wave rectified waveform can be obtained by alternately repeating the magnetic field application to the superconducting bulk every half wave.

In order to verify the above conversion principle, a model device shown in FIG. 7 was produced and an experiment of rectification operation was attempted. In this device, a 5 × 7 mm iron leg is combined to form a tripod iron core having a width of 105 mm and a height of 84 mm, and the primary winding 3 for flowing 20 turns of alternating current is placed in the center iron core 1 _C and 1000 turns. the secondary winding 4 _L, 4 _R retrieve the DC current is arranged to the core 1 _L, 1 _R at both ends, the two secondary windings 1 _L, 1 _R of the output terminal is connected via a resistor . The switching current 13 flowing through the magnetic field application coil 7 was 5.5 A, and the magnetic field applied to the cylindrical superconductor 6 was 10 mT.
One of the experimental results is shown below. FIG. 9 shows a waveform when full-wave rectification is performed on an alternating current of 60 Hz. The broken line is the primary side alternating current, and the solid line is the secondary side full-wave rectified current waveform. The lower rectangular wave is a waveform of energization to the magnetic field application coil 7. From this result, it was confirmed that the sine wave alternating current can be full-wave rectified by the power conversion device of the present invention. In addition, in order to investigate the responsiveness of the device, a full-wave rectification experiment was attempted when the frequency of the sinusoidal AC waveform was increased. As one of the results, a full-wave rectified waveform of a 500 Hz sine wave alternating current is shown in FIG. From this result, it was confirmed that even when a pulse magnetic field of 1 ms was applied, the transition between the normal conducting state and the superconducting state of the left and right cylindrical superconductors 6 can be controlled, and high-speed switching can be handled.

FIG. 11 shows an embodiment in which the power converter of the present invention is configured as an inverter. The inverter can be configured using a core 1, the primary winding 3, the secondary winding 4 _L, 4 _R, tubular superconductor 6 and the magnetic field applying coils 7 having the same structure as the rectifier shown in FIG. 7 . However, it is necessary to use a type II superconductor such as YBCO polycrystalline bulk as the material of the cylindrical superconductor 6. Moreover, contrary to the case of the superconducting rectifier, the DC current is inputted to the primary winding 3, alternating current is outputted from the secondary winding 4 _L, 4 _R (see FIG. 12). Further, the waveform of the switching current 13 flowing through the magnetic field application coil 7 indicates that the strength of the magnetic field is between the upper critical magnetic field H _c2 and the lower critical magnetic field H _c1 of the cylindrical superconductor 6 composed of YBCO polycrystalline bulk. A switching current 13 having a size that forms a magnetic field that changes to a half-wave shape and a half-wave shape of an arbitrary AC waveform is passed. For example, a switching current 13 having a half-wave rectified waveform having a time width corresponding to a half-wave of a waveform desired to be obtained from the secondary winding and a frequency AC waveform is applied.

The specific operation is as follows. In FIG. 12A, when the magnetic field applied to the left cylindrical superconductor 6 is zero, the magnetic flux 2 passing through the left iron core 1 _L is zero due to the influence of the shielding magnetic field generated by the cylindrical superconductor 6. Become. When applying a positive magnetic field of the half-wave sine wave to the tubular superconductor 6 to the right of the core 1 _R, magnetic shielding effect of the tubular superconductor 6 is reduced in accordance with the magnitude of the applied magnetic field increases , voltage and current corresponding to the amount of magnetic flux passing through the right side of the iron core 1 _R is generated on the right side of the secondary winding 4 _R. Further, while the applied field is reduced beyond the peak, increase the magnetic shielding effect of the tubular superconductor 6 gradually, the voltage and current decreases little by little generated on the right side of the secondary winding 4 _R . A sine wave AC voltage / current can be generated by performing the same operation alternately with the right cylindrical superconductor 6 and the left cylindrical superconductor 6. Since the half wave of the sine wave alternately generated on the left and right secondary windings 4 _L and 4 _R has a positive and negative relationship, it is output as a continuous sine wave. In addition, since the frequency of the sinusoidal alternating current obtained on the secondary side becomes equal to the frequency of the magnetic field application waveform to the cylindrical superconductor 6, by changing the frequency of the switching current 13 flowing through the magnetic field application coil 7, An AC voltage / current having an arbitrary frequency can be obtained. That is, it can function as a frequency converter. Further, since the secondary side current waveform can be controlled by the current waveform of the switching current 13 flowing through the magnetic field application coil 7, not only a sine wave but also a square wave or a triangular wave can be easily generated. In this way, it is possible to easily create various AC waveforms without using a complicated circuit manufactured using a semiconductor element. Inverters that use semiconductor elements that are widely used nowadays, a square wave pulse is generated by turning on and off the switch and DC / AC conversion is performed. However, since harmonics are generated at the same time, an active filter or the like is used to remove this. Expensive harmonic countermeasure devices are required. In contrast, in the superconducting inverter of this embodiment, the magnitude of the magnetic field applied to the superconducting bulk, that is, the magnetic shielding effect of the superconducting bulk, is controlled by controlling the amount of current supplied to the magnetic field application coil wound around the superconducting bulk. Since the amount of magnetic flux in the iron core can be controlled arbitrarily and continuously, an expensive harmonic countermeasure device such as an active filter becomes unnecessary.

The power conversion device of the present invention configured as described above has one primary-side core region and two secondary-side core regions, passes through the primary-side core region and has different secondary-side core regions. By adding a superconducting bulk to the iron core that constitutes the two closed magnetic paths that pass through each of them, bidirectional conversion between AC and DC, including transformation and frequency conversion, becomes possible. As the size increases, the effect of space saving increases. When a DC system is introduced into a power distribution system such as a factory, the power conversion device of the present invention is effective because the installation location is limited. Moreover, since the structure of the power converter device of this invention is very simple and there are not many components, it is anticipated that it will contribute greatly to the breakthrough of the cost reduction which has become the bottleneck of the power converter.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, the number of turns of the secondary winding relative to the number of turns of the primary winding becomes the transformation ratio of the DC half-wave voltage to the AC half-wave voltage, so that the transformer function can be given by these turns ratio, Depending on the turns ratio, step-up / step-down voltage transformation or equal pressure conversion is possible, and further, current flows by connecting the secondary winding to an external circuit (not shown). Since the secondary winding has an inductance corresponding to the number of windings, the secondary winding itself becomes a smooth winding, and the half wave is smoothed. Furthermore, although the description of the power conversion device of the present invention has been described mainly taking the case of a single phase as an example, it goes without saying that it can be applied to a three-phase AC power conversion device. Moreover, since the magnetic field application coil is housed in a heat insulating container together with the cylindrical superconducting bulk and cooled, it can be composed of a superconductor conductor or a normal conductor.

Furthermore, it is possible to construct a superconducting DC power transmission system that converts the generated AC power into DC using the power conversion device of the present invention, transmits the AC power, and supplies it back to AC near the customer. For example, three power converters that function as rectifiers and three power converters that function as inverters are arranged at both ends of a DC transmission line composed of superconducting cables, and three-phase alternating current is temporarily converted to direct current using the power converter as a rectifier. After the power is converted into power and transmitted, a direct current power transmission system can be configured to return to three-phase alternating current with a power conversion device that functions as an inverter. This DC power transmission system is configured by directly connecting a secondary winding of a power converter that performs a rectifying operation and a primary baseline of the power converter that performs an inverter operation with a superconducting cable. If the primary windings of the three rectifiers are respectively coupled to the three-phase alternating current phases, the alternating current of each phase is converted into a direct current, and then direct current is transmitted via the superconducting cable. Then, in the three power converters on the inverter side, a half wave of a sine wave is applied to each magnetic field applying coil 7 at a period in which the magnetic flux generated by the direct current passed through each primary winding is shifted by 120 degrees in electrical angle. By flowing the waveform switching current 13, the secondary winding of each power converter can be supplied to the consumer after returning to a three-phase alternating current having a phase of 120 ° in electrical angle. In addition, since the frequency of the three-phase alternating current at the time of reverse conversion can be set freely, it can be converted into a three-phase alternating current of an arbitrary frequency. Moreover, this DC power transmission system can function not only as a circuit breaker but also as a power storage system (SMES) if the magnetic circuit selector switch 5 is controlled to disconnect the magnetic circuit from the electric circuits at both ends. In both rectifier operation and inverter operation, in the case of a failure of the connected DC system, the power conversion function is stopped by stopping energization of the switching current to the magnetic field application coil of the magnetic path switching switch of each magnetic path. By doing so, the DC circuit can be cut off. When the AC system fails, the AC line is interrupted by an AC circuit breaker as in the conventional case, and the DC system is stopped by the above method as necessary. In addition, since the cylindrical superconducting bulk of the magnetic path changeover switch is maintained in the superconducting state, the operation can be immediately resumed by starting energization of the switching current to the magnetic field application coil. In addition, if a superconducting rectifier and a superconducting inverter are combined, the frequency converter can be easily configured.

A power converter according to the present invention is suitable as an AC / DC converter incorporated in a DC power transmission system, and can have functions of a transformer, a circuit breaker, a power storage device, and a frequency converter, and the power converter It can be used for a direct current power transmission system and an electric power storage system.

Claims

An iron core that has a primary core region and two secondary core regions, and that constitutes a two-path closed magnetic path that passes through the primary core region and passes through different regions of the secondary core region; and A primary winding wound around the primary side core region, a secondary winding wound around the secondary side core region and having one end connected in a relationship in which the outputs are inverted with each other, and each closed magnetic field of the secondary side core region A magnetic path changeover switch that shields the closed magnetic path for each path, the magnetic path changeover switch covering the iron core and giving a magnetic shielding effect to the iron core, and an alternating current switching current And a magnetic field application coil for applying a magnetic field of a critical magnetic field or higher to the cylindrical superconductor, and energizing the primary winding with an excitation current and a magnetic field application coil of the magnetic field application coil higher than the critical magnetic field. Magnetism Are alternately applied and the magnetic path changeover switch is alternately switched to pass a magnetic flux alternately through the two closed magnetic paths, thereby generating an induced electromotive force in the secondary winding and causing a secondary current to flow. A power converter.
A cylindrical superconductor having a pulse wave having the same time width as a half wave of the sine wave alternating current input to the primary winding, the sinusoidal alternating current being input to the primary winding, and the magnetic field applying coil to the primary winding. The switching current greater than or equal to the current that generates a magnetic field corresponding to the critical magnetic field is alternately flowed in synchronization with the sinusoidal alternating current to alternately apply a magnetic field greater than or equal to the critical magnetic field to the cylindrical superconductor. The power converter according to claim 1, wherein the magnetic path of the system is alternately switched, and a positive AC half-wave voltage is alternately induced in the secondary winding of each closed magnetic path to output a DC current.
The cylindrical superconductor is a type II superconductor, and is a waveform corresponding to an AC waveform to be output from the secondary winding and inputting a DC current to the primary winding, and of the AC waveform. By passing the switching current having a half-wave waveform having a half time width through the magnetic field application coils of the two magnetic paths alternately, the cylindrical magnetic path on the side where the switching current is not passed is provided. The magnetic flux between the upper and lower critical magnetic fields of the cylindrical superconductor is in the magnetic path on the side where the switching current is passed while the magnetic flux is blocked by the magnetic shielding of the superconductor. Is applied to the cylindrical superconductor by inducing a half-wave voltage to alternately induce positive and negative AC half-wave voltages in the secondary windings of each closed magnetic circuit. To output alternating current Power converter of one claim 1, wherein.
The power converter according to any one of claims 1 to 3, wherein the cylindrical superconductor is a polycrystalline bulk.
4. The power conversion device according to claim 1, wherein the magnetic field application coil is wound in a toroidal shape around the cylindrical superconductor. 5.
6. The power converter according to claim 5, wherein the magnetic field application coil is wound in a toroidal shape with the same number of turns in both the clockwise and counterclockwise directions in the circumferential direction of the cylindrical superconductor.