DRIVE SYSTEM WITH ELECTROMAGNETIC ENERGY TRANSFER

Abstract

The invention relates to a drive system (1) with electromagnetic energy transfer. The system (1) comprises a track (3) comprising a plurality of stators (4), each stator (4) having at least one winding adapted to generate a magnetic field having a fundamental harmonic (8) and at least one further harmonic (9) when fed with an varying current, and a movable element (2) comprising a primary magnetic element (5) adapted to receive said fundamental harmonic (8) to drive said movable element (2) along said track. The system (1) is characterized in that said movable element (2) further comprises a secondary magnetic element (6a-6c) adapted to receive said at least one further harmonic (9) to generate power onboard of said movable element (2). The invention also relates to a linear fractional slot synchronous machine and a rotational synchronous machine.

Claims

1-14. (canceled)

15. A drive system for electromagnetic energy transfer, comprising: a movable magnetic device that is configured to move based upon an applied magnetic flux; a track defining a predetermined path along which the movable magnetic device follow based upon the applied magnetic flux, the track comprising a plurality of stators, each stator having at least one electrical winding configured to generate a magnetic field having a fundamental harmonic signal and at least one further harmonic signal when supplied with a varying current; wherein the movable magnetic device further comprises: a primary magnetic component configured to receive the fundamental harmonic signal and configured to drive the movable magnetic device along the track; a secondary magnetic component configured to receive the at least one further harmonic signal and to generate power for the movable magnetic device, wherein the at least one further harmonic is a sub harmonic signal; and a control unit configured to modulate a current in each of the stators to affect the at least one further harmonic such that the generation of power for the movable magnetic device is increased.

16. The drive system according to claim 15, wherein the varying current is an alternating current.

17. The drive system according to claim 15, wherein at least one of the primary magnetic component and the secondary magnetic component comprise a winding.

18. The drive system according to claim 15, wherein the movable magnetic device comprises a plurality of primary magnetic components and secondary magnetic components alternately arranged along the movable magnetic device.

19. The drive system according to claim 15, wherein the width of the windings of the secondary magnetic component substantially scales to the distance between subsequent primary magnetic components based on the frequency ratio between the fundamental harmonic to the at least one further harmonic received by the secondary magnetic component.

20. The drive system according to claim 15, wherein the movable magnetic device further comprises a mounting plate on which the primary magnetic component and the secondary magnetic component are mounted, the mounting plate comprising a slot for receiving the secondary magnetic component.

21. The drive system according to claim 20, wherein the mounting plate is made of a material having a high magnetic permeability.

22. The drive system according to claim 21, wherein the mounting plate is made of iron.

23. The drive system according to claim 15, wherein the stators are successively supplied with successive phases of the varying current.

24. A linear fractional slot synchronous machine, comprising the drive system according to claim 15.

25. A rotational synchronous machine, comprising the drive system according to claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

[0024] FIGS. 1a and 1b are side views of a linear synchronous machine with a drive system according to known prior art.

[0025] FIG. 2 is a side view of a linear synchronous machine with a drive system according to one exemplary embodiment of the invention.

[0026] FIG. 3 is a cross-sectional view along the plane A-A in FIG. 2.

[0027] FIG. 4 is a diagram that shows the fundamental harmonic and the sub harmonic generated by a stator of the drive system.

[0028] FIG. 5 is a schematic drawing of the inductive power transfer according to the invention.

[0029] FIG. 6 is a drawing of one possible embodiment of a track for moveable elements using the drive system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0030] FIG. 1a and FIG. 1b show side views of a linear synchronous machine with a drive system according to known prior art. The drive system 1 for movable elements 2 comprises a track 3 with a plurality of stators 4, wherein each stator 4 has a winding (not shown) fed with a current so as to generate a magnetic field and therefore a magnetic flux. The magnetic flux affects a magnetic element 5 in the movable element 2 so as to pull the movable element 2 in a direction along said track 3. The current that is fed to the stator windings is an alternating current, e.g. a sinusoidal current with three phases and with a frequency that controls the speed of the moving element 2. In FIG. 1a and FIG. 1b the three phases are referenced as A, B and C. The phases A, B, C, are fed to succeeding stator windings in the drive system 1 to accomplish a successive movement of the magnetic pull on the moving element 2 and thereby a continuous movement of the moving element 2.

[0031] FIG. 2 is a side view of a linear synchronous machine with a drive system 1 according to one exemplary embodiment of the invention. The drive system 1 for movable elements 2 comprises a track 3 with a plurality of stators 4, wherein each stator has windings (not shown) fed with a current so as to generate a magnetic field and a magnetic flux. The magnetic flux affects a magnetic element 5 in the movable element 2 so as to pull the movable element 2 in a direction along said track 3. The current that is fed to the stator winding is an alternative current, e.g. with three phases with a frequency that controls the speed of the moving element 2. The frequency of the alternating current is typically in the range of 0.2-10 Hz. The phases are fed to succeeding stator windings 4 in the drive system 1 to accomplish a successive movement of the magnetic pull on the moving elements 2.

[0032] The moving element in FIG. 2 is further equipped with a secondary electro-magnetic element 6a-6c, which is a winding designed to pick up the energy of the sub-harmonic magnetic wave frequency of the fundamental harmonic of the magnetic field that is used for the movement of the moving element 2. The winding of the secondary magnetic element is designed so as to pick up the variable magnetic flux produced of the sub-harmonic. The parts of the moving element 2 are mounted on an iron plate 12.

[0033] The secondary magnetic element 6a-6c is preferably an inductor comprising a coil for collecting the magnetic field of said sub-harmonic. A flux concentrating material of high magnetic permeability is arranged around the coil for increasing the power transfer. In FIG. 2 the flux concentrating material is the mounting plate of the moveable element. Cut-outs 7 in the mounting plate are made to facilitate the winding/coil of the secondary magnetic element 6a-6c.

[0034] The windings of the secondary magnetic elements 6a-6c are preferably placed in the space in between the primary magnetic elements 5 so that they can link the flux produced by the sub-harmonic at the same time as the flux produced by the fundamental harmonic is used for pulling the moving element 2. The use of the space in between the primary magnetic elements 5 for the wires of the windings of the secondary magnetic elements 6a-6c makes it possible to place the receiving secondary magnetic elements as close to the stators as the primary magnetic elements 5, thereby increasing efficiency of the energy transfer since the amplitude of the magnetic field from the stators decreases exponentially with the distance from the stators. The moveable element may thus be made very compact since the primary magnetic elements and the secondary magnetic elements 6a-6c are interlaced.

[0035] FIG. 3 is a cross-sectional view along the plane A-A in FIG. 2. The windings 6a-6c of the secondary magnetic element 6a-6c are placed in the space in between the primary magnetic elements 5. The primary magnetic elements 5 are separated by a distance d. In the embodiment of FIG. 3, three windings 6a-6c are shown to pick up the sub-harmonic of the stators 4. The use of the space in between the primary magnetic element will ensure a good link of the sub-harmonic if the width W of the windings 6a-6c of the secondary magnetic element substantially is chosen as the frequency ratio between the fundamental harmonic to the further harmonic. For example, if the first sub-harmonic has half the frequency of the fundamental harmonic (as shown in FIG. 4), the width of the windings 6a-6c of the secondary magnetic element should be chosen so as to enclose two primary magnetic elements. The magnetic pull from the fundamental harmonic on the primary magnetic elements 5 will then be synchronized with the inductive reception of the sub-harmonic by the secondary magnetic element.

[0036] The current that is induced by the winding of the secondary magnetic elements 6a-6c is fed to a rectifier (not shown) via the connection cables 11a-11c so that a direct current may be used by any electrical equipment on the moveable element 2.

[0037] FIG. 4 is a diagram that shows the fundamental harmonic 8 and the further harmonics 9, 10 generated by a stator 4 of the drive system 1. The further harmonics 9, 10 in prior art solutions are imperfections that consume energy that will be lost in iron losses, since only the fundamental harmonic 8 is used for movement of the moving element 2. Energy losses are due to induced eddy currents in materials with magnetic permeability. Because of that, the stator windings configurations of prior art are optimized to minimize the sub-harmonics 9, and higher order harmonics 10, so that the only energy of the alternating current transmitted in form of magnetic field energy is transmitted in the fundamental harmonic 8. It is, however, not possible to build a fractional slot stator winding without having unwanted harmonics and to produce a perfect feeding alternating current, making some losses due to sub-harmonics 9, and higher order harmonics 10, unavoidable.

[0038] In the present invention, however, the unavoidable side effects of the sub-harmonics 9 and higher order harmonics 10 are used to transfer energy via the secondary magnetic element 6a-6c of the moving element 2. The previously lost energy of the strongest sub-harmonic 9 of the magnetic field created by the stator windings of the track 3 is recovered by windings of the secondary magnetic element 6a-6c of the moving element 2 and inductively converted to electricity. The power supply (not shown) supplying the stator windings of the track 3 with alternating current may also be controlled to modify the alternating current so as to be less optimal for the movement of the moving element 2 and to create a bigger sub-harmonic that can be used for energy transfer to the moving element 2 instead. The strongest sub-harmonic 9 is often, as shown in FIG. 4, the one having half the frequency of the fundamental harmonic 8.

[0039] The modification of the feed current and thereby the sub-harmonic 9 can be made manually to transfer a static amount of electrical power to the moving element 2, but it may also be controlled by a control unit or a computer software so as to be able to adjust the power of the energy transferred to the moving element 2. In that case energy may be saved when electricity is not needed on the moving element 2. Some equipment on the moving element 2 could also be directly controlled by the amount of power transferred to the moving element 2.

[0040] By using a sub-harmonic 9 of the magnetic field created by the stator windings, no extra parts are needed except for the receiving second magnetic element of the moving element 2. The electrical power transferred to the moving element 2 may e.g. be used for tool in a machine, like sealing jaws of a packaging machine, for cooling of a tool etc. The electrical power generated in said manner, can be further conditioned with electrical means, such as filters and/or DC-DC converters, in order to create DC or AC power usable for industrial purposes onboard the movable element 2.

[0041] FIG. 5 is a schematic drawing of the inductive energy transfer. The stator windings of the stators 4 of the drive system 1, located in the track 3 are fed with a three phase alternating current (AC) produced by a DC/AC converter. The AC current in the stators 4 produces a magnetic field with the same frequency of its fundamental harmonic 8 as the frequency of the AC current. The fundamental harmonic 8 is adapted to be linked to the primary magnetic element 5 of the moveable element so as to move the moveable element. Since the frequency of the alternating current feeding the stators 4 determines the speed of the moveable elements 2 of the drive system, the main line fed is arranged to control the frequency of the produced AC and thereby controls the speed of the moveable elements 2 on the track 3 of the drive system of the present invention. As described above, a sub-harmonic 9 to the fundamental harmonic 8 is adapted to be received by the secondary magnetic element 6 via its windings. The current induced in the windings of the secondary magnetic element 6 is rectified and fed to a DC/AC converter to drive any electrical load in need of electrical energy on the moveable element 2. Naturally the DC current from the rectifier may be used by a load directly if required.

[0042] FIG. 6 is a drawing of one possible embodiment of a track for moveable elements 2 using the drive system 1 according to the present invention. Moveable elements 2 move along a track 3 in the direction R. The stators are integrated in the side 3 facing the mounting plates 12 of the moveable elements 2. The mounting plates 12 of each moveable element are of the type shown in FIGS. 2 and 3, i.e. they are equipped with both primary magnetic elements 5 in form of permanent magnets and secondary magnetic element 6a-6c for inductive energy transfer via the first sub-harmonic 9 of the magnetic field produced by the stators 4 in the track 3. The moveable elements 2 may be equipped with electrical tools like moulds, induction sealing jaws, cooling systems for other equipment or any other equipment. Electrical energy is thus wireless transmitted to the moveable elements 2 using the normally unwanted effects of the sub-harmonic of the magnetic field from the stators 4 of the synchronous machine drive system 1.