Motor generator with improved air gap magnetic flux alignment

Abstract

To provide a rotating electric machine such as a motor or a generator which avoids a change in a magnetic flux direction adjacent to an air gap.SOLUTION: The disclosed improvements may be applied to a permanent magnet alternator, an induction motor and a generator, a doubly fed induction generator etc. Adaptation of coils to and fixation within required slot geometries are disclosed. Excitation systems collocated within a primary stator core and a primary stator core are also disclosed. Use of rubber vulcanized to the rotor in conjunction with a stainless steel rotor sleeve is also disclosed.SELECTED DRAWING: Figure 4a

Description

[Technical Field]

[0001] This application is an international phase application of and claims priority to U.S. Provisional Application No. 62 / 855,908, filed May 31, 2019, which is incorporated herein by reference. Please note that May 31, 2020, was a Sunday, so the deadline for this patent application is June 1, 2020.

[0002] The present invention relates to electromagnetic motors and generators. Summary of the Invention [Means for solving the problem]

[0003] The present invention reduces iron hysteresis losses in motors and generators with improved matching of the magnetic flux paths in the rotor and stator and the magnetic flux orientation in the air gap with the machine operating at rated torque.

[0004] Conventional motors and generators generally provide radial magnetic paths within the iron core between the coil slots. This arrangement results in a good match between the magnetic flux in the iron and the magnetic flux in the air gap under no-load, zero-torque conditions. This non-optimized design likely persists because acceptance testing for many large machines is performed under no-load, zero-torque conditions. Maximum torque occurs when the magnetic flux crosses the air gap at an angle of approximately 45 degrees. The flux distribution in the radial stator teeth (iron between the coils) is very non-uniform when the magnetic flux across the air gap is at a non-radial angle, such as 45 degrees. High flux areas result in high hysteresis losses. Low flux area represents wasted iron or wasted space that could be used for larger, lower-loss conductors.

[0005] The present invention maintains flux directional continuity as the flux passes through the stator, air gap, and rotor, resulting in more uniform flux density, lower hysteresis losses, and more efficient use of iron core material, while providing space for larger cross-section, lower loss coils.

[0006] The present invention is applicable to a variety of motor and generator types, including induction motors, synchronous motors, salient pole synchronous motors, doubly fed induction motors, permanent magnet alternators, and the like.

[0007] According to a further aspect of the invention, a hybrid machine may be provided, in which the rotor's magnetic field is established by a combination of DC excitation and permanent magnets.

[0008] According to a further aspect of the machine, the coil may be formed from a conductor having a stepped width / thickness aspect ratio in conjunction with a constant conductor cross section to allow multiple turns of the same conductor cross section to efficiently fill the tapered slot.

[0009] According to a further aspect of the present invention, an AC-electrical machine, such as a motor or generator, is provided in which an excitation magnetic circuit is superimposed on the magnetic circuit of the electric machine. In this case, a DC excitation current is provided to an auxiliary DC winding in the stator. This results in a non-rotating magnetic field passing in and out of the rotor, generating AC excitation power. This AC excitation power is then rectified to establish a DC power source in the rotor. Rectification may be accomplished, for example, by conventional diodes or using externally controlled diodes, rectifiers, or transistors. Control may be, for example, electrical, magnetic, or optical. Optically controlled commutation is preferred. This establishes a non-alternating magnetic field in and between the rotor and stator. This field may act by itself or in conjunction with a permanent magnetic field. The use of a penetrating magnet may improve the overall efficiency of the machine, while a controllable portion of the magnetic field strength may be used for voltage and power factor control. The rotating DC excitation coil may share a slot with the rotating AC coil, which collects energy for the non-rotating magnetic field established by the DC stator winding.

[0010] According to a further aspect of the present invention, a tapered coil may be provided that can be inserted axially into a stator slot with a convenient amount of clearance. Once in place, a stretchable elastomeric shim may be inserted in a stretched, thin state. This may be inserted while attached to a tensioned cord, for example. Once in the correct axial position, the tension may be reduced, allowing the elastomeric shim to contract and expand laterally, filling the slot and sealing against the sides of the stator slot and forcing the coil radially inward. This approach is particularly well-suited for "hairpin" coils, which have a bend on only one end and are inserted like a staple.

[0011] In accordance with a further aspect of the present invention, an inflatable tube may be used in place of the elastomeric shim.

[0012] In accordance with a further aspect of the present invention, the inflatable tube may be inflated with a soluble substance.

[0013] In accordance with a further aspect of the present invention, the soluble material may also be elastomeric to allow the shim to be removed by stretching.

[0014] According to a further aspect of the invention, magnetic field alignment in the air gap may be established by using adjacent magnet segments that are each magnetized to provide optimal flux alignment. The magnetization of each magnet segment may be constant across the segment, or (preferably) over a range of orientations across the face of each segment.

[0015] In accordance with a further aspect of the invention, the sections may be electrically insulated from one another to minimize eddy current losses.

[0016] In accordance with a further aspect of the invention, the magnet may be secured with a metal sleeve that is shrunk into place.

[0017] In accordance with a further aspect of the invention, the magnets may be secured with a fiber reinforced plastic, such as, for example, carbon fiber in an epoxy, vinyl ester, or polyester matrix. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is prior art. [Figure 2] FIG. 2 is prior art. [Figure 3] FIG. 3 is prior art. [Figure 4a] FIG. 4a illustrates a cross section of a permanent magnet machine incorporating form wound Leber-Bar coils adapted for the present invention. [Figure 4b] FIG. 4b illustrates a cross section of a permanent magnet machine incorporating form wound Leber-Vall coils adapted for the present invention. [Figure 4c] FIG. 4c illustrates a cross section of a permanent magnet machine incorporating form wound Leber-Bar coils adapted for the present invention. [Figure 5a] FIG. 5a illustrates a cross section of a permanent magnet machine with coils formed in accordance with one aspect of the present invention. [Figure 5b] FIG. 5b illustrates a cross section of a permanent magnet machine with coils formed in accordance with one aspect of the present invention. [Figure 5c] FIG. 5c illustrates a cross section of a permanent magnet machine with coils formed in accordance with one aspect of the present invention. [Figure 5d] FIG. 5d illustrates a cross section of a permanent magnet machine with coils formed in accordance with one aspect of the present invention. [Figure 5e] FIG. 5e illustrates a cross section of a permanent magnet machine with coils formed in accordance with one aspect of the present invention. [Figure 5f] FIG. 5f illustrates a cross section of a permanent magnet machine with coils formed in accordance with one aspect of the present invention. [Figure 6a] FIG. 6a illustrates a cross section of a randomly wound permanent magnet machine according to one aspect of the present invention. [Figure 6b]FIG. 6b illustrates a cross section of a randomly wound permanent magnet machine according to one aspect of the present invention. [Figure 7] FIG. 7 illustrates a cross section of a permanent magnet machine in accordance with one aspect of the present invention, where slots in the rotor laminations are provided to allow conductors to be inserted when the permanent magnets need to be remagnetized. [Figure 8a] FIG. 8 illustrates a cross section of a machine with an external permanent magnet rotor according to one aspect of the invention. [Figure 8b] FIG. 8 illustrates a cross section of a machine with an external permanent magnet rotor according to one aspect of the invention. [Figure 9a] FIG. 9a depicts an external rotor permanent magnet machine. [Figure 9b] FIG. 9b depicts an external rotor permanent magnet machine. [Figure 10] FIG. 10 is a hybrid permanent magnet machine with an excitation coil. [Figure 11] FIG. 11 depicts the coil fixation method. [Figure 12] FIG. 12 is a schematic diagram of a brushless excitation system in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1, 2, and 3 illustrate prior art configurations of magnets and slots in motors and generators.

[0020] Referring to Figures 4a, 4b, and 4c, a cross section of a rotating electric machine with an alternating current stator is shown, which can operate in either motor or generator mode. Stator core 21 carries a sinusoidally varying magnetic flux, illustrated by flux lines 21a, 21b, 21c, 21d, 21e, 21f, 21g, and 21h. The machine is asymmetric and does not function identically in all four quadrants. It is optimized for two-quadrant operation, as required, for example, for raising and lowering elevators or for use in conjunction with reversible pump-turbines. Electricity generation and motor power occur in these two embodiments with torque in the same direction but rotation in opposite directions. In each of these two quadrants, the magnetic flux lines traverse air gap 49 at angles of the same sign. For maximum power, the angle of the magnetic flux lines traversing the air gap can be within a range of 30 to 45 degrees from the radial direction. Flux angles greater than 45 degrees can result in slippage or loss of synchronization between the permanent magnet poles and the coil-generating poles in the stator. According to one aspect of the present invention, the coil current phase angle may be adjusted to prevent loss of synchronization. Referring again to FIG. 5f, the tapered stator slot 51, shown prior to coil insertion, is aligned at this angle to minimize flux concentration at the tips 55 of the stator teeth 56. Similarly, permanent magnets 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19 are magnetized so that flux exits the magnets, crosses the air gap, and enters the stator core without unnecessary changes in direction. The magnetization orientation of the permanent magnets may be uniform across the discrete magnet segments, or, in the case of a single magnet per pole, may preferably be magnetized in a range of directions to maintain the design angle across the air gap. The required magnetic field strength varies with angular position, and magnet thickness is therefore varied to achieve economical use of expensive magnetic materials. The change in flux direction within the air gap of prior art machines results in a larger effective air gap. The longer indirect magnetic path across the air gap of prior art machines results in either lower magnetic field strength or the requirement for larger magnets.The coil shown is similar to a Roebel burl, except that the conductor cross section changes with each pass through the slot as the assembled burl fits into the tapered stator slot 51.

[0021] Referring to Figures 5a, 5b, 5c, 5d, 5e, and 5f, a variation of the rotating electric machine of Figures 4a, 4b, and 4c is shown. The windings 28a-28w are composed of wires that are flattened according to their placement order in each slot. Flattening is preferably performed using automated equipment configured to establish the required thickness across the length of each individual wire. This allows the coils to assume a tapered shape that matches the shape of the tapered stator slot 51, providing a constant core cross-sectional area and flux density as a function of radius. This constant flux density configuration minimizes hysteresis losses while optimizing the use of both iron and copper. The tapered stator slot 51 also allows for coil insertion from one end of the slot with wide clearance. Once the coils are fully inserted, an elastomeric "packer" 26 is threaded under tension through the back iron end 54 of the slot. Back iron 57 is identified in Figure 6a. The tension causes the "packer" 26 to assume a reduced cross-section as the packer 25 is stretched. Once the stretched packer 25 is in place, the tension may be released and the tensioning means disconnected. This results in the packer 26 fully occupying the available space and applying a positioning preload against the trailing edge of the coil. Coil removal may be accomplished by again tensioning the packer 26. The preload provided damps coil vibration. The resulting intimate contact between the coil and slot improves heat transfer. The magnet 4-19 may be secured with a carbon fiber winding 27.

[0022] 6a and 6b, an exemplary arrangement of randomly wound coils 58 and 59 within the slots is illustrated. Coil insulation 62 separates coils 58 and 59. Slot insulation 63 insulates the coils from stator 21.

[0023] 7, slots 31 are provided in the rotor core 20 for the purpose of remagnetizing the permanent magnets 4-19 in the event that demagnetization occurs due to an external short circuit or overheating of the magnets for any reason. Conductors installed in such slots for remagnetization will preferably be used in conjunction with conductors located and secured outside the rotor that are removed from the stator.

[0024] 8a and 8b, a cross section of an external magnet rotating electric machine similar to that used for a permanent magnet UAV motor is shown. A splined shaft 22 prevents rotation of the stator core 25. The splined shaft 22 is preferably non-magnetic to minimize eddy current losses that might otherwise be caused by the AC flux passing through it. The splined shaft 22 may include holes 23, which can be used to augment cooling, for example, as part of a heat pipe. In the two-pole configuration shown, the flux must pass across the diameter of the core 21. The splined connection between the splined shaft 22 and the stator core 25 minimizes the required diameter of the splined shaft 22, thereby minimizing the reluctance of the diametral magnetic path through the assembly consisting of the splined shaft 22 and the stator core 25. The magnet sections 4-19 are each magnetized with a flux orientation that is aligned with the nominal load-rated flux orientation across the air gap. Again, magnetic flux lines that do not change direction as they traverse the air gap result in a shorter effective air gap, minimizing magnetic circuit reluctance and allowing the use of minimal magnetic material, such as rare earths. Figure 8b illustrates example coils in slots designed to guide magnetic flux lines between the rated torque orientation in the air gap and the diametric magnetic path traversing the illustrated two-pole machine. Note that different numbers of poles require different magnetic paths through the rotor.

[0025] 9a and 9b, a variation of the machine of Figures 8a and 8b is shown in which the slots 24 are shaped to avoid flux concentration at either end of the slots 24.

[0026] Referring to Figure 10, a hybrid synchronous machine is illustrated in cross section. This machine combines permanent magnets 4-19 with rotor field coils 29 to provide voltage and power coefficient control while retaining some of the useful advantages of a permanent magnetic field. The rotor field coils 29 may be energized in either direction to either add to or subtract from the field provided by the permanent magnets. The rotor field coils 29 may be energized through a conventional sliding ring, through a conventional (prior art) brushless exciter, or, in accordance with a further aspect of the invention, through a brushless exciter co-located with and superimposed on the illustrated primary synchronous alternator.

[0027] 11a, 11b, 11c, and 11d, the packer 26 may take the form of a flat rubber band. The packer 26 may be stretched and threaded through the circular portions of the slots 28. In this way, the circular coils 27 may be secured within the circular portions of the slots 28 in the stator core 21. This may be used in conjunction with high voltage rotating electrical machine coils, such as those incorporated into ABB Powerformer® high voltage generators.

[0028] Windings 28a-28w, power stator windings, and rotor field windings are listed. Are these different elements?

[0029] Referring to FIG. 12 , the excitation system may include a DC coil 41 co-located with the AC power stator winding 48 to produce a non-rotating magnetic field using a magnetic circuit passing through both the stator 72 and the rotor 45. This results in AC power being generated in an auxiliary winding 44 in the rotor 45. This AC power available at the rotor 45 is rectified to provide DC power to the rotor field coils 29. An optical rectifier controller 46 controls an optically controlled rectifier 70 through an optical link 71. The optically controlled rectifier 70 may switch and adjust the polarity of the rotor field coils 29. The optically controlled rectifier 70 may be substituted using functionally similar means, such as a small photodiode controlling a conventional silicon-controlled rectifier or a functional equivalent. This configuration overcomes the complexity of mounting a separate exciter on a larger alternator, which may have large air gaps and bearing clearances that are incompatible with those of the exciter. In this regard, the present invention provides a cheaper, more robust, and more compact exciter configuration. The excitation magnetic circuit is superimposed on, i.e., co-located with, the primary magnetic circuit of the motor or generator. This configuration eliminates the need for a separate excitation generator. Separate excitation generators tend to be smaller, require smaller air gaps, and can have smaller positioning tolerances for the rotor within the stator. Eliminating a separate magnetic circuit for the rotor reduces part count, machine weight, machine size, and machine cost.

[0030] Referring to FIG. 12, an excitation controller 40 supplies DC current to an auxiliary winding 41 in a stator DC excitation coil 42, which results in AC power being delivered to a winding 44 in a rotor 45. The resulting AC power is rectified with an optically controlled rectifier 46. The resulting DC power can be of either polarity, depending on which optical rectifier control is activated. This DC power is applied to a DC rotor coil 47. This power can be used to generate a field by itself or in conjunction with permanent magnets in the rotor to generate a rotor magnetic field. Output power is drawn from the generator through the stator coil 48. Note that the system may be configured as a generator, a synchronous motor, or a synchronous condenser.

[0031] According to a further aspect of the present invention, the machine may be designed for submersible use. The end coils may be embedded in rubber. The stator pole face surfaces may also be embedded in rubber. The rubber is preferably vulcanized onto the surface of the stator core laminations using an adhesive such as Lord Chemical Company ChemLok®. Furthermore, a stainless steel sleeve fitted to the rotor can slide on the rubber bonded to the stator with very little wear and water lubrication. The assembly acts as a rubber bearing similar to those used for ship stern tubes. This is superior to coating the pole face surfaces in stainless steel because, unlike stainless steel, rubber does not suffer from eddy current losses. In configurations where the rotor is on the outside of the stator, a rubber-coated stator may also be used in conjunction with a stainless steel-coated rotor.

[0032] It should be noted that the improvements disclosed herein apply to rotating electromagnetic machines of varying pole numbers and phases, however the two-pole machines illustrated herein are exemplary.

Claims

1. A rotating electrical machine comprising a permanent magnet rotor and an alternating current stator, the stator slots being substantially aligned with magnetic flux across the air gap at rated load conditions.

2. A rotating electrical machine comprising a permanent magnet rotor and an alternating current stator, wherein the rotor magnetization is substantially aligned with the magnetic flux across the air gap at rated load.

3. 1. A rotating electric machine comprising a permanent magnet rotor and an alternating current stator, wherein the stator slots are substantially aligned with magnetic flux traversing an air gap at a rated load condition, and wherein rotor magnetization is substantially aligned with the magnetic flux traversing the air gap at rated load.

4. The rotating electrical machine of claim 3 further comprising a rotor field excitation coil (rotor field excitation coil not included herein).

5. A rotating electric machine excitation system co-located with a rotating electric machine, wherein DC coils in an otherwise AC stator generate AC power in a rotor that is otherwise non-alternating magnetic flux, the AC power in the rotor being rectified to DC power in the rotor and used to excite rotor field windings (rotor field windings not defined herein).

6. The rotating electric machine of claim 5 , wherein commutation is controlled through an optical link between the steady-state controller and the rotating rectifier.

7. The rotary machine of claim 5 , wherein a portion of the rotor magnetic field is provided by one or more permanent magnets.

8. A coil fixation system for a rotating electrical machine in which an electrical coil is stretched thin for assembly and then secured using an elastomeric packer that can be allowed to return to a thick, tight-fit state after the coil is assembled and positioned.

9. A submersible rotating electrical machine comprising a rubber coated rotor in an air gap (water gap) in conjunction with a stainless steel coated rotor.

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