WO2010063140A1

WO2010063140A1 - A controllable reactor and fabrication method thereof

Info

Publication number: WO2010063140A1
Application number: PCT/CN2008/001972
Authority: WO
Inventors: Xiaobo Yang; Jin Zhang
Original assignee: ABB Research Ltd Switzerland
Current assignee: ABB Research Ltd Switzerland
Priority date: 2008-12-05
Filing date: 2008-12-05
Publication date: 2010-06-10
Anticipated expiration: 2011-06-05
Also published as: CN102203885A

Abstract

A controllable reactor and a method of assembling it are disclosed. The controllable reactor (1) comprises a core structure (2) surrounded by a main winding (3), and a control winding(201) for controlling an inductance of the core structure (2), and the core structure (2) comprises a control element (20) with a control core (200) surrounded by the control winding (201). The method includes prefabrication control elements (20) with a control core (200) surrounded by the control winding (201), and stacking a plurality of prefabricated control elements (20) and uncontrolled elements (21) to form the core structure of the reactor (1), so as to simplify design, fabrication, and assembling of a controllable reactor with a transverse DC winding.

Description

A controllable reactor and fabrication method thereof

Technical Field The invention relates to the field of power transmission, and more particularly to a controllable reactor and a method of fabricating the controllable reactor.

Background Art

Controllable reactor has very big potential market as a cost effective solution in many areas, such as reactive power compensation, voltage regulation, power quality enhancement. High speed of its regulation (< 100 ms) requires a high power DC converter for the regulation current, which will suffer from one or more of the following disadvantages: difficulty of design and fabrication, high cost, larger harmonics, and the unavailability of auxiliary power of the controllable reactor. A lower speed of regulation (500 - 1000 ms) requires considerably less power for the DC control winding but with limited market applications as well.

Brief Summary of the Invention

It is therefore an objective of the invention to simplify design and fabrication of a controllable reactor with a transverse DC winding.

According to an embodiment of the invention, a controllable reactor for electric power systems comprises a core structure surrounded by a main winding which is connectable to the electric power system, as well as a control winding connectable to a control power source. The control winding controls a magnetic inductance of the core structure by generating a variable magnetic field in the core structure. The control winding is wound around a control core of a control element that is itself part of the core structure. Hence, the control winding is entirely surrounded by the main winding, and the two windings can be assembled separately and independently of each other.

According to another embodiment of the invention, the field produced by the control winding is essentially perpendicular to the field from the main winding. In this way, an induced AC current ripple in the control winding is suppressed. According to another embodiment of the invention, the core structure comprises uncontrolled elements, i.e. elements of which the inductance is not deliberately altered by applying dedicated control fields. These uncontrolled elements comprise disks of conventional magnetic core material such as iron, or air gaps provided in-between the former and adjacent control elements. Suppose that the core structure consists of an air gap, a control element, and an uncontrolled element. In this condition, if one desires to change the control range of the reactor by changing the volume of the control element, the volume of the air gap or that of the uncontrolled element should be changed accordingly. In this connection, with a variation of the volume of the air gap or the uncontrolled element and a corresponding variation of the volume of the control element, the control range of the reactor is variable.

According to another embodiment of the invention, the control winding comprises at least one turn wound around the control core. With a variation of the number of the turns wound around the control core, its magnetic field may be changed accordingly even without change of the value of current flowing through the control winding.

According to an embodiment of the invention, a controllable reactor for electric power systems comprises two core structures, either of which is surrounded by a main winding which is connectable to the electric power system, as well as two control windings connected in series or in parallel to a control power source, or even respectively connected to two control power sources. Therefore, the size of the controllable reactor can be reduced.

According to another aspect of the invention, a method of assembling a controllable reactor is provided. The controllable reactor comprises a core structure surrounded by a main winding and a control winding for controlling an inductance of the core structure. The method comprises the steps of: prefabricating control elements with a control core surrounded by the control winding, and stacking a plurality of prefabricated control elements together with a number of uncontrolled elements to form the core structure of the reactor. From this, the main winding is assembled to surround the resulting core structure as whole.

Brief Description of the Drawings

The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the drawings, in which: Fig.l shows a structure of a controllable reactor according to an embodiment of the invention.

Fig.2 shows the structure of a control element of the core structure according to an embodiment of the invention; Fig. 3 shows a composed flux in the control core according to an embodiment of present invention;

Fig. 4 shows magnetic curves of the core structure under different control current according to an embodiment of the invention;

Fig.5 shows a structure of a controllable reactor according to another embodiment of the invention;

Fig.6A and Fig. 6B show a structure of a controllable reactor according to further embodiments of the invention; and

Fig.7 shows a structure of a controllable reactor according to further embodiments of the invention. The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

Preferred Embodiments of the Invention Fig.1 shows the structure of a controllable reactor according to an embodiment of the invention. The controllable reactor 1 schematically illustrated in Fig. 1 has a core structure 2 surrounded by a main winding 3 and a yoke 4. The cross section area of the core structure 2 is shaped like round, ellipse, or rectangle and it comprises a control element. The cross section area of the yoke 4 is shaped like round, ellipse, or rectangle, and its purpose is to close the magnetic circuit of the core structure 2. Preferably, the controllable reactor 1 further includes a concentrating flux plate 5 disposed between the core structure 2 and the yoke 4, which reduces the leakage of flux from the magnetic circuit. The cross section area of the concentrating flux plate 5 is shaped like round, ellipse, or rectangle and the concentrating flux plate 5 is made up of magnetic material, such as silicon steel and amorphous alloy. As shown in Fig. 1 , the core structure 2 is fixed coaxially with the other elements of the controllable reactor 1, such as the concentrating flux plate 5, but other relative positions of the core structure 2 against the concentrating flux plate 5 are possible. For example, the core structure 2 may also be arranged to deviate from the axial of the concentrating flux plate 5.

Fig. 2 shows a structure of the control element 20 with a control core 200 surrounded by a control winding 201 according to an embodiment of the invention. As shown in Fig. 2, the control core 200 is shaped like a ring and can be made of a magnetic material such as silicon steel and amorphous alloy. The control winding 201 comprises at least one turn wound around the control core 200. For a ring-shaped control core 200 with a central opening, the turns of the winding 201 pass through the central opening as depicted in Fig. 2, such as to produce a circular magnetic control field in the control core 200. With more turns, lower control current in the control winding 201 is required for producing the same control field and thus smaller DC power supply is needed. Preferably, the turns are essentially evenly spaced around a circumference of the ring-shaped control core.

By having the control winding 201 and the control core 200 designed independently as one module, namely the control element 20, the control winding 201 is entirely surrounded by the main winding 3 and the two windings can be assembled separately and independently of each other, thus design and fabrication of elements of the controllable reactor, such as the control winding and the control core, can be simplified and the cost thereof can be reduced. Also, the controllable reactor according to the embodiment of present invention can operate in a way of single phase reactor and thus can be easily transported. By having the yoke 4, leakage flux is reduced.

Although the control element 20 has been described in considerable detail with reference to Fig. 2, other versions are possible. For example, the control core 200 is shaped like toroidal, U-shaped, I-shaped, E-shaped, C-shaped, Pot, El-shaped, EE-shaped, and at least one turn of the control winding 201 is wound around at least one limb of these control core structures such as to produce a suitable magnetic control field in the control core 200 .

Preferably, the control core 200 may further comprise grooves for accommodating the control winding 201, or a space between adjacent turns of the control winding may be filled with electrical isolation material or cooling liquid. With the grooves, the air gap due to the finite thickness of the wires of the control winding goes away and the control range of the controllable reactor is increased. The cross section areas of the control core 200 of the control elements 20 with the grooves are different that those of the other parts of the control core 200, such that the flux density generated by the control winding 201 is variable along the direction of the main flux in the control element. Fig. 3 shows a composed flux in the control core according to an embodiment of present invention. As shown in Fig. 3, the control winding 201 generates, in the core structure 2, a perpendicular magnetic field essentially perpendicular to a magnetic field generated by the main winding 3. By having such relative orientation of the main flux against the control flux, less magnetic coupling to the control winding 201 from the main winding 3.

Particularly, during operation, a control current is injected into the control winding 201 so as to change an equivalent inductance of the controllable reactor 1. In the control element 20, the magnetic flux has two components: a main flux by the main winding 3 and a control flux by the control winding 201 with an essentially perpendicular orientation and generated by the control current. The composed magnetic flux as well as magnetic circuit is spiral, as shown in Fig. 2. Meanwhile, permeability of the control core 200 decreases a lot because of the saturation caused by the control current.

Considering two critical cases, control current is very large and make the controllable disk deeply statured and control current is equal to zero. When the control current is very large, the controlled disk is deeply saturated. The control element 20 is similar to an air gap. The inductance is decided by the permeability, length, and cross section of deep saturated control element 20. Under such condition, it is close to a fixed value reactor and the inductance is also similar.

When control current is equal to zero, the control element 20 is normal iron disk. The core of the reactor has not any air gap. The inductance is decided by the permeability, length and cross section of iron core, namely the control core 200. Under this condition, it is similar to a no-load transformer and the inductance is very large since the permeability of silicon steel is thousands times of air gap in conventional shunt reactor.

Fig. 4 shows magnetic curves of the core structure under different control current according to an embodiment of the invention. As shown in Fig. 4, four magnetic curves A,

B, C, and D are illustrated as example. With the increase of the control current Ic, the magnetic curve of the core shifts through the curve A, B, C, and D. In ideal condition, the working point of the core is always located in linear area of magnetic curves. Each of the four magnetic curves A, B, C, and D has a linear portion. For example, magnetic curve A has a linear portion extends from 0 to H₁, magnetic curve B has a linear portion extends from 0 to H₂, magnetic curve C has a linear portion extends from 0 to H₃, and magnetic curve D has a linear portion extends from 0 to H₄. The linear portion of magnetic curve A is of the narrowest range among the four magnetic curves A, B, C, and D, while the linear portion of magnetic curve D is the widest. Suppose taking magnetic curve A as working curve of the controllable reactor. With the increase of value of magnetizing strength H, its working point may move out of its linear portion to nonlinear portion where working point H₅ is an instance. According to electromagnetism theory, harmonics are generated when the controllable reactor works in nonlinear portion of its working curve. In this connection, if the controllable reactor works at point H₅ on magnetic curve A, then harmonics are induced. In order to remove the harmonics, one may shift working curve from curve A to curve D by changing the value of the control current in the control winding, where point H₅ on curve D resides in linear portion, so that the controllable reactor works in linear portion again. Thus, the working point of the controllable reactor falls under the linear portion again and harmonics are suppressed.

The control current is supplied by a control power source for pushing or pulling energy to or from the control element 20. By using such a bidirectional converter as the control power source, in consideration of AC current induced in the control winding by AC current in the main winding, the control winding is fed a bidirectional current so as to suppress the effect of the induced AC current therein and maintain a DC current and render fast response. Other versions of the control power source are possible, for example unidirectional converter for pushing energy to the control element 20.

Fig. 5 shows a structure of a controllable reactor according to another embodiment of present invention. As shown in Fig. 5, the core structure 2 further comprises an uncontrolled element 21 with an uncontrolled core. The uncontrolled core is shaped like a ring or a disk and can be made of a magnetic material such as silicon steel and amorphous alloy. The control elements 20 and the uncontrolled elements 21 are arranged such that an average value of a magnetic flux density of the perpendicular magnetic field in the control core 200 of the control element 20 is higher than an average value of a magnetic flux density of the perpendicular magnetic field in the uncontrolled core of the uncontrolled element 21. Particularly, the core structure 2 comprises a succession of the control elements 20 and the uncontrolled elements 21 aligned coaxially as illustrated in Fig. 5. By having such configurations of the core structure 2, leakage inductance is reduced. Other relative positions of the control elements 20 against the uncontrolled elements 21 are possible, for example, the axial of the control element 20 may deviate from that of the uncontrolled element 21. In addition, the person skilled in the art shall appreciate they could also be of different sizes. Fig. 6A and Fig. 6B shows a structure of a controllable reactor according to another embodiment of present invention. As shown in Fig. 6A, the core structure 2 may comprise an air gap 22 between the yoke 4 and the control elements 20. As shown in Fig. 6B, the core structure 2 may further comprise an air gap 22 between the control elements 20, between the uncontrolled elements 21, or between the control element 20 and the uncontrolled element 21. By having one or more of the above configurations of the core structure 2 as shown in Fig. 6A or Fig. 6B, if one desires to change the control range of the reactor by changing the volume of the control element, the volume of the air gap 22 or that of the uncontrolled element should be changed accordingly. In this connection, with a variation of the volume of the air gap 22 or the uncontrolled element and a corresponding variation of the volume of the control element, the control range of the reactor is variable.

The above embodiments concern a controllable reactor with one leg, namely one core structure. Fig.7 shows a structure of a controllable reactor according to further embodiments of the invention, which relates to a controllable reactor with two legs. According to Fig.7, the controllable reactor 1 comprises: a first leg and a second leg, namely the core structure 2 according to any of the previous embodiments and a further core structure 2'. For example, the further core structure 2 is surrounded by a further main winding 3 and comprises a control element. Also, the further core structure T may be configured in a similar way to a core structure according to any of the previous embodiments. For example, the further core structure 2' is surrounded by a further main winding 3' and comprises a control element. The control element comprises a further control core surrounded by a further control winding for controlling an inductance of the further core structure 2'. A yoke 4a magnetically links one end of the first leg and one end of the second leg and a yoke 4b magnetically link the other end of the first leg and the other end of the second leg, such that the yokes 4a, 4b close a magnetic circuit of the two core structures 2, 2' thus a flux flows through the yokes 4a, 4b, the core structure 2 and the further core structure 2'. And, the two main windings 3, 3' are electrically connected in series or in parallel. By having such configuration of two core structures, because the capacity of the controllable reactor depends on the volume of the control element, the capacity of the controllable reactor can be increased by introducing more control elements while maintaining the volume of the controllable reactor, for example by combining the two legs of the yokes of Fig. 1 and replacing the combined legs with core structure. In other words, with such configuration of two core structures, the volume of the controllable reactor can be reduced while maintaining its capacity. In addition, the control winding may be connected in series, connected in parallel, or even powered by two different power supplies. By having them connected in series, current ripple in the control windings can be suppressed.

Preferably, a concentrating flux plate 5, 5' is disposed between the core structure 2, 2' and the yoke 4a, 4b, which reduces the leakage of flux from the magnetic circuit.

A method according to an embodiment of present invention for fabricating a controllable reactor with a core structure 2 surrounded by a main winding 3 and a control winding for controlling an inductance of the core structure 2, comprising prefabricating control elements 20 with a control core 200 surrounded by the control winding 201, and stacking a plurality of prefabricated control elements 20 and uncontrolled elements 21 to form the core structure of the controllable reactor 1.

Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no way limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims

1. A controllable reactor (1), with a core structure (2) surrounded by a main winding (3) and a control winding (201) for controlling an inductance of the core structure (2), characterized in that the core structure (2) comprises a control element (20) with a control core (200) surrounded by the control winding (201).

2. The controllable reactor according to claim 1, characterized in that the control winding (201) generates, in the core structure (2), a perpendicular magnetic field essentially perpendicular to a magnetic field generated by the main winding (3).

3. The controllable reactor according to claim 2, characterized in that the core structure (2) comprises an uncontrolled element (21) with an uncontrolled core, wherein an average value of a magnetic flux density of the perpendicular magnetic field in the control core (200) is higher than an average value of a magnetic flux density of the perpendicular magnetic field in the uncontrolled core.

4. The controllable reactor according to claim 3, characterized in that the core structure (2) comprises a succession of control elements (20) and uncontrolled elements (21).

5. The controllable reactor according to claim 3, characterized in that the core structure (2) comprises an air gap (22) between two control elements (20), between two uncontrolled elements (21), or between a control element (20) and an uncontrolled element (21).

6. The controllable reactor according to claim 1, characterized in that the control core (200) is ring shaped and the control winding (201) comprises at least one turn wound around the control core (200).

7. The controllable reactor according to claim 6, wherein the turns are essentially evenly spaced.

8. The controllable reactor according to claim 6, characterized in that the control core (200) comprises groves for accommodating the control winding, or in that a space between adjacent turns of the winding is filled with electrical isolation material or cooling liquid.

9. The controllable reactor according to claim 5, characterized in that the cross section areas of the control core (200) of the control elements (20) with the grooves are different that those of the other parts of the control core (200).

10. The controllable reactor according to claim 1 or 2, wherein the material of the control core (200) is silicon steel or amorphous alloy.

11. The controllable reactor according to claim 1 or 2, characterized in that the controllable reactor comprises a bidirectional converter, for inputting or withdrawing energy to or from the control element (20).

12. The controllable reactor according to claim 1 or 2, characterized in that the controllable reactor comprises a yoke (4), for closing the magnetic circuit of the core structure(2).

13. The controllable reactor according to any of claims 1 to 8, characterized in that the controllable reactor comprises: a further core structure (2'), which is surrounded by a further main winding (3'); a further control winding, for controlling an inductance of the further core structure (2'); and a yoke (4a, 4b), for closing a magnetic circuit of the two core structures (2, 2'); wherein the further core structure (2') comprises a further control element with a further control core surrounded by the further control winding.

14. The controllable reactor according to claim 12, characterized in that the two main windings (3, 3') are connected in series or parallel and the two control windings are connected in series or parallel.

15. A method of fabrication of a controllable reactor with a core structure (2) surrounded by a main winding (3) and a control winding for controlling an inductance of the core structure (2), comprising - prefabricating control elements (20) with a control core (200) surrounded by the control winding (201), and

- stacking a plurality of prefabricated control elements (20) and uncontrolled elements (21) to form the core structure of the reactor.