WO2002091548A1

WO2002091548A1 - Frequency converter

Info

Publication number: WO2002091548A1
Application number: PCT/SE2002/000889
Authority: WO
Inventors: Gunnar Russberg; Mikael Dahlgren; Stefan Johansson
Original assignee: Abb Ab
Priority date: 2001-05-09
Filing date: 2002-05-08
Publication date: 2002-11-14
Also published as: SE0101645D0; SE0101645L

Abstract

The invention relates to a rotating frequency converter comprising rotor and at least two magnetic cores prvided with windings, as well as at least one machine shaft. The rotor comprises at least two magnetic flux elements arranged radially displaced in relation to the machine shaft. The magnetic flux elements are connected to the machine shaft. The magnetic flux elements are arranged to rotate in a local rotary movement about their axes of rotation. The invention also relates to the use of and a method of controlling such a frequency converter, and also to a system comprising such a frequency converter.

Description

FREQUENCY CONVERTER

Technical field

The present application relates to a rotating frequency converter compris- ing rotor and at least two magnetic cores provided with windings, as well as at least one machine shaft. The rotor of the machine comprises at least two magnetic flux elements arranged to rotate about their own axes of rotation. The axes of rotation of said flux elements are radially displaced in relation to said machine shaft. The flux elements are connected to said machine shaft.

Background art

In many applications it is of particular interest to be able to convert one frequency to another frequency. An example of such an application is when two networks with different frequencies are joined, as in Tokyo for instance, or when one generator operates with a frequency different from that of the drive means. Frequency conversion can also be obtained by means of power electronics or, as in older supply stations for the railway network, via rotary alternators composed of two separate, but connected electrical machines. GB 2 055 515 describes the principle of two electrical machines connected together by a common shaft and supplied via slip rings to the rotor field supply. This older type of alternator is clumsy and entails high losses. The desired frequency control can be obtained through external transmissions or, when a generated frequency shall be higher in an electrical machine, by increasing the number of poles in the machine. This in turn gives increased diameter and thus a larger and heavier generator. The invention defined in the present application aims at providing a compact and flexible rotating frequency converter for a wide power range in a single machine.

Brief description of the invention The present application relates to a compact rotating frequency converter having great flexibility as regards the frequency at which alternating current is generated or consumed. Furthermore, the construction described in the present application permits at least two different types of rotor movement, thereby providing a flexible machine with several degrees of freedom as compared with conven- tional machines. This offers entirely new possibilities for designing electromagnetic machines.

The frequency converter in accordance with the present invention comprises at least two magnetic flux elements that are radially displaced in relation to the machine shaft. The flux elements in the frequency converter are connected to the machine shaft. The flux elements are arranged to rotate in a local rotary movement about their axes of rotation. The excitation directions of the magnetic flux elements are constantly varied in relation to the position vector of the flux element in the rotor construction. The local flux elements generate a global mag- netic flux in the cores. By "global magnetic flux" is meant that the flux from each individual flux element co-operates throughout the construction provided with winding. The direction of the global magnetic field is constantly changed in relation to the relative movement of the rotor.

The global flux described in the invention can be described concisely in the ideal case as a travelling wave with constant amplitude and phase velocity around the magnetic circuit of the machine. This wave has a periodic shape at every instant. In practice elements of pulsing flux also appear, which cause periodically varying velocity and amplitude.

A communication unit consisting of at least one input/output unit with pro- cessor may be included in the invention. Measured values from one or more sensors in the rotor or stator are collected in the processor. Signals from the machine can be sent to the processor via the input/output unit. An output signal from the processor may be sent via the input/output unit to some type of control device fitted in the machine. The communication unit may also be used for sending data from the processor via wires or by means of wireless transmission from the machine for the purpose of control or data collection. The communication unit can be applied on a static part or on some movable part of the invention.

Description of embodiments The frequency converter in accordance with the present application comprises one or more cores, at least two of which are provided with windings. In another embodiment more than two cores are provided with windings. The frequencies of the various cores included in the machine are mutually different.

In a preferred embodiment said flux elements are arranged between the first and the second core.

Furthermore, the frequency converter in another preferred embodiment comprises means for movement of said flux elements such that the axes of rotation of the flux elements follow a global rotary movement about said machine shaft. This means for movement may be a toothed transmission gear, for instance.

Said flux elements are arranged to rotate in a local rotary movement about their axes of rotation with the same or different directions of rotation. The individual angular velocity of the flux elements in this local rotary movement may be the same or different.

In a preferred embodiment the means for movement of said flux elements is arranged so that each flux element in its local rotation acquires varying angular velocity. The angular velocity of each flux element will be highest when the flux element passes a pole giving a higher flux fluctuation per time unit. Depending on the variation in angular velocity, a more or less pulse-shaped voltage with increased peak value is obtained for a generator.

In another preferred embodiment the axes of rotation of the magnetic flux elements are peripherally displaced in relation to each other.

In a preferred embodiment the magnetic flux elements comprise perma- nent magnets. The permanent magnets may be made, for instance, of one of the following materials: Steel, AINiCo, Ba, Sr-ferrites, Sm(Fe,Co), SmCo, SmFeN, NdFeB and nanocomposite permanent magnets.

The excitation directions of the flux elements may be varied around the periphery of the machine.

Brief description of the drawings

Figure 1 shows a preferred embodiment of the frequency converter in accordance with the present invention. Figure 2 shows the machine as illustrated in fig. 1 seen from the side. Figure 3 shows the fundamental principle of frequency conversion in a frequency converter in accordance with the present invention. Figure 4 shows another preferred embodiment of a frequency converter in accordance with the present invention. Figure 5 shows one embodiment of a flux element. The flux elements can transmit movement and/or absorb forces in several directions, e.g. a radially directed force.

In all preferred embodiments said cores are made out of optional magnetic material. A core may be in the form of a laminated sheet iron core or a com- pacted powder core of magnetic material.

One or more windings in the invention as described in the present application may be wound with insulated cable or insulated conductor for low voltage. The insulated cable, which may be a high-voltage or medium-voltage cable, is preferably constructed with an insulating part comprising at least two semi-con- ducting layers that surround an insulating layer. The invention described in the present application is intended for use within an optional power range.

Detailed description of preferred embodiments

Figure 1 shows a preferred embodiment of the frequency converter in ac- cordance with the present application. A first core 10 provided with a winding surrounds a second core 12, also provided with a winding 13. The core windings may be arranged in several ways. The cores may be wound individually, after which the windings may be connected in series or in parallel, or may be galvanically isolated. A number of flux elements 14 are arranged between the first and second cores. The flux elements are provided with permanent magnets 15. The movements of the flux elements are correlated. Figure 1a is a flux image illustrating the magnetic flux of the machine in a preferred embodiment. The flux elements are provided with permanent magnets 15. The excitation directions of the magnets are in this embodiment directed in different directions so that a multipolar machine is obtained. The movements of the flux elements are correlated so that the fluxes from the flux elements co-operate to form a global rotating multipolar flux in the frequency converter, as indicated in the figure by the flux lines 19. Figure 1b illustrates the same embodiment as fig. 1a but at a different time when the magnets have assumed a different position. Figure 2 shows the machine as illustrated in fig. 1 seen from the side. A first core 10 provided with a winding surrounds a second core 12, also provided with a winding 13. A number of flux elements 14 are arranged between the first and second cores.

Figure 3a shows the fundamental principle of frequency conversion in a frequency converter in accordance with the present invention. A number of flux elements 14 are placed between a first fixed core 10 and a second fixed core 12, with a distance d between their centres, and provided with permanent magnets 15 arranged with alternating excitation directions. The permanent magnets 15 give rise to a flux in the first and second cores, respectively. In fig. 3b all the flux elements have been rotated a part of a turn in counter clockwise direction in the figure. The flux image in each core has thus changed and the flux pattern is therefore displaced in one direction in the first core and in the opposite direction in the second core. If a velocity v is simultaneously applied to the set of flux elements the flux pattern in the first core will acquire the velocity fR*2d + v in one direction whereas the flux pattern in the second core will acquire the velocity fR*2d - v in the other direction, where fR is the rotation frequency of the flux elements. The flux wave obtained has thus a higher velocity in the first core than in the second one. The wave length, on the other hand, remains unchanged. The voltage varia- tion induced in the first core thus acquires a frequency that differs from the frequency of the voltage variation induced in the second core. The frequency ratio between the induced voltages will be f : fR = (fR+ v/2d) : (fR-v2d) where f-( is the frequency in the first winding and f2 is the frequency in the second winding. The flux-generating elements have thus create global travelling flux waves having the same wave length but with different velocity in each core.

Figure 4 shows another preferred embodiment of a frequency converter in accordance with the present invention. This comprises a first core 10 provided with a first winding 11 and a second core 12 provided with a winding 13, and also a number of flux elements 14 arranged between the first and second cores. The flux elements are provided with permanent magnets and arranged to rotate about their own axes. A machine shaft is also included which is connected to the flux elements 14. When the flux elements 14 are caused to move, partly in a circular movement with the angular velocity ω about the machine shaft, and partly in a rotary movement about their own axes with the angular velocity COR = 2p * fR, a ro- tary flux wave is obtained in the first and second cores. In accordance with the same principle the flux wave in the first core 10 acquires the angular velocity ωi =

(2COR/N)+ ω, where N is the number of flux elements, whereas the flux wave in the second core 12 acquires the angular velocity ω2= (2 COR/N) - co. Different frequencies are thus obtained in the two windings 11 and 13, respectively. Selection of the number of flux elements and of respective angular velocities ω and ωR enables an optional frequency ratio to be obtained between the two windings. The frequency ratio between the induced voltages will be fi : f _R = (ωR +¹ _N ω):( ωR -

¹ N ω). The number of pairs of poles is determined by 1/2*N.

Figure 5 shows one embodiment of a flux element. The flux element may be of optional shape. A flux element having cylindrical shape is illustrated in the figure but other shapes are feasible within the scope of the appended claims, such as a tapering shape. The element in this embodiment is made out of permanently magnetic material 31, soft magnetic material 32 and non-magnetic material 33.

The invention is naturally not limited to the above embodiments exemplified but can be designed as modifications within the scope of the inventive con- cept defined in the appended claims.

Claims

1. A rotating frequency converter comprising rotor and at least two magnetic cores (10, 12) provided with windings, as well as at least one machine shaft, said rotor comprising at least two flux-generating, variable magnetic flux elements (14) arranged radially displaced in relation to said machine shaft and said magnetic flux elements (14) being connected to said machine shaft, characterized in that said magnetic flux elements (14) are arranged to rotate in a local rotary movement about their axes of rotation.

2. A rotating frequency converter as claimed in claim 1 , characterized in that the flux from the flux elements (14) is superposed to at least two global fluxes moving at different angular velocities in the magnetic parts of the machine.

3. A rotating frequency converter as claimed in the preceding claims, characterized in that at least one of said fluxes moves in substantially opposite direction to the other fluxes.

4. A rotating frequency converter as claimed in claim 2, characterized in that said fluxes move in substantially the same direction.

5. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the frequency converter comprises more than two cores.

6. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said magnetic flux elements (14) are arranged between two cores.

7. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the frequency converter comprises means for movement of said magnetic flux elements (14) such that the axes of rotation of the magnetic flux elements follow a global rotary movement about said machine shaft.

8. A rotating frequency converter as claimed in the preceding claim, characterized in that the means for movement is arranged so that the local rotation of said magnetic flux elements (14) is achieved with varying angular velocity.

9. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said magnetic flux elements (14) comprise permanent magnets (15).

10. A rotating frequency converter as claimed in the preceding claim, charac- terized in that the permanent magnets (15) are made of one of the following materials: Steel, AINiCo, Ba, Sr-ferrites, Sm(Fe,Co), SmCo, SmFeN, NdFeB and nanocomposite permanent magnets.

11. A rotating frequency converter as claimed in any one of claims 1-10, characterized in that said magnetic flux elements (14) comprise a squirrel cage winding.

12. A rotating frequency converter as claimed in any one of claims 1-10, characterized in that said magnetic flux elements (14) comprise a field winding.

13. A rotating frequency converter as claimed in any one of claims 1-10, characterized in that said magnetic flux elements (14) comprise soft magnetic material.

14. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the frequency converter comprises means for varying the magnetic flux of the magnetic flux elements (14) mechanically.

15. A rotating frequency converter as claimed in any one claims 1-13, charac- terized in that the frequency converter comprises means for varying the magnetic flux of the magnetic flux elements (14) electromagnetically.

16. A rotating frequency converter as claimed in any one claims 1-13, characterized in that said magnetic flux elements (14) are arranged so that their time variations are correlated with each other.

17. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the machine is multiphase.

18. A rotating frequency converter as claimed in any one of claims 1-18, characterized in that the axes of rotation of said magnetic flux elements (14) are peripherally displaced in relation to each other.

19. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the winding (11 , 13) of the machine comprises an insulated conductor for low voltage.

20. A rotating frequency converter as claimed in the preceding claim, charac- terized in that the winding (11 , 13) of the machine comprises a cable for high voltage comprising one or more current-carrying conductors surrounded by at least two semiconducting layers and an intermediate insulating layer of solid insulation.

21. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said magnetic flux elements (14) are arranged to absorb forces in several directions.

22. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said magnetic flux elements (14) are arranged to absorb radial forces.

23. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the axis of rotation of the rotor coincides with the machine shaft.

24. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said first core (10) surrounds the rotor.

25. A rotating frequency converter as claimed in any one of claims 1-23, characterized in that said first core (10) is surrounded by the rotor.

26. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said first core (10) is arranged coaxially in relation to the rotor.

27. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said second core (12) is arranged coaxially in rela- tion to the rotor.

28. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said second core (12) surrounds the first core.

29. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that said first and second windings (11 , 14) are arranged having the same number of phases.

30. A rotating frequency converter as claimed in any one of claims 1-28, characterized in that said first and second windings (11 , 13) are arranged having different numbers of phases.

31. A rotating frequency converter as claimed in any one of claims 1-27, characterized in that said second core (12) is surrounded by the first core.

32. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the magnetic flux elements (14) are arranged to rotate in said local rotary movement with different directions of rotation.

33. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that the magnetic flux elements (14) are arranged to rotate in said local rotary movement with varying angular velocity.

34. A rotating frequency converter as claimed in any one of the preceding claims, characterized in that it comprises a communication unit.

35. The use of a frequency converter as claimed in any one of the preceding claims to convert one number of phases to another number of phases.

36. A system comprising a frequency converter as claimed in any one of the preceding claims.

37. A method of controlling a rotating frequency converter as claimed in any one of the preceding claims, wherein a first and a second flux wave are obtained in the first and second core, respectively, characterized in that the angular velocity of respective flux waves is determined by the local rotation and global movement of the flux-generating elements (14), whereby a flux variation with the frequency fi = ((2COR/N) + ω/2p is obtained in a fixed point in the first core and a flux variation with the frequency f2 = (2COR/N) - ω)/2p is obtained in a fixed point in the second core.