Motor generator with improved gas gap flux alignment

Abstract

The present invention is a rotating electromagnetic machine, such as an electric motor or generator, in which flux direction changes adjacent to a gas gap are avoided. The disclosed improvements are applicable to permanent magnet alternators, induction motors and generators, doubly fed induction generators, and the like. Coils are disclosed that are adapted and fixed within a desired slot geometry. An excitation system co-located within a main rotor core and a main stator core is also disclosed. The use of rubber vulcanized to the rotor in combination with a stainless steel rotor sleeve is also disclosed.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is an application entering the national phase of PCT application PCT / US2020 / 035616 filed on June 1, 2020. This application claims priority to U.S. Provisional Application No. 62 / 855,908 filed on May 31, 2019. Each of the above applications is incorporated by reference into this application. Technical Field

[0003] The present invention relates to electromagnetic motors and generators. Summary of the invention

[0004] The present invention reduces hysteresis losses in the iron of motors and generators by improving the alignment of the magnetic flux paths in the rotor and stator with the direction of the magnetic flux in the air gap when the machine is operating at rated torque.

[0005] Conventional motors and generators typically provide radial flux paths in the iron core between the coil slots. This arrangement results in good alignment of the magnetic flux in the iron and the magnetic flux in the gas gap under no-load, zero-torque conditions. Perhaps this non-optimal design persists because acceptance testing of many large machines is performed under no-load, zero-torque conditions. Maximum torque occurs when the magnetic flux crosses the gas gap at an angle of approximately 45 degrees. When the magnetic flux crossing the gas gap is at a non-radial angle (e.g., 45 degrees), the flux distribution in the radial stator teeth (the iron between the coils) is very uneven. High flux areas result in high hysteresis losses. Low flux areas represent wasted iron or wasted space that could have been used for larger, lower-loss conductors.

[0006] The present invention maintains the continuity of flux direction as it passes between the stator, the gas gap and the rotor. The continuity of flux direction leads to more uniform flux density, lower hysteresis losses and more efficient use of core material while providing space for larger cross-section low-loss coils.

[0007] The present invention is applicable to various motor and generator types, including induction motors, synchronous motors, salient pole synchronous motors, doubly fed induction motors, permanent magnet alternators, etc.

[0008] According to another aspect of the present invention, a hybrid machine may be provided in which the magnetic field of the rotor is established by a combination of direct current (DC) excitation and permanent magnets.

[0009] According to another aspect of the machine, the coil may be formed of a conductor having a stepwise adjusted width to thickness aspect ratio combined with a constant conductor cross section to allow multiple turns of the same conductor cross section to effectively fill the tapered slots.

[0010] According to another aspect of the present invention, an AC electric machine (e.g., 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 entering and exiting the rotor, generating an AC excitation power in the non-rotating magnetic field. The AC excitation power is then rectified to establish a DC power supply in the rotor. For example, rectification can be accomplished by ordinary diodes or by means of externally controlled diodes, rectifiers, or transistors. For example, the control can be electrical, magnetic, or optical. An optically controlled rectifier is preferred. This establishes a non-alternating magnetic field in and between the rotor and the stator. This field can act alone, or this field can act in conjunction with a permanent magnetic field. The use of permanent magnets can improve the overall efficiency of the machine, and a controllable portion of the field strength can be used for voltage and power factor control. The rotating DC excitation coil can share a slot with a rotating AC coil that collects energy for the non-rotating field established by the DC stator DC winding.

[0011] According to another aspect of the invention, a conical coil can be provided that can be axially inserted into a stator slot with an appropriate amount of spacing. Once in place, a stretchable elastic spacer can be inserted in a stretched and thin state. For example, this can be inserted while connected to a tensioned rope. Once in the correct axial position, the tension can be reduced, allowing the elastic spacer to shorten and expand laterally to fill the slot and press the coil radially inward to make close contact with the sides of the stator slot. This method is particularly suitable for "hairpin" coils that are inserted like a staple with only one end bent.

[0012] According to another aspect of the present invention, an inflatable tube may be used instead of the elastic spacer.

[0013] According to another aspect of the present invention, the inflatable tube may be inflated with a fusible substance.

[0014] According to another aspect of the invention, the meltable substance may also be elastic so as to allow removal of the spacer by stretching.

[0015] According to another aspect of the invention, alignment of the magnetic field at the gas gap can be established by using adjacent magnet segments, each magnet segment being magnetized to provide optimal flux alignment. The magnetization of each magnet segment can be constant throughout the segment, or the magnetization of each magnet segment can (preferably) be constant in successive directions across the surface of each segment.

[0016] According to another aspect of the invention, the segments may be electrically isolated from each other in order to minimize eddy current losses.

[0017] According to another aspect of the invention, the magnet may be secured by a metal sleeve that is shrunk into place.

[0018] According to another aspect of the invention, the magnets may be secured with a fiber reinforced plastic, such as carbon fibers in an epoxy, vinyl ester or polyester matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the prior art.

[0020] Figure 2 It is the prior art.

[0021] Figure 3 It is the prior art.

[0022] Figure 4a , Figure 4b and Figure 4c Shown is a cross section of a permanent magnetic machine incorporating a winding Roebel bar coil suitable for forming the present invention. Figure 4b Shows Figure 4a Detail of the circled area B shown in FIG. Figure 4c Shows Figure 4b Details inside area E are shown in .

[0023] Figure 5a , Figure 5b , Figure 5c , Figure 5d , Figure 5e and Figure 5f A cross section of a permanent magnet machine with shaped coils according to an aspect of the invention is shown. Figure 5b Shows Figure 5a Detail of area A shown in . Figure 5c Shows Figure 5a Detail of area D shown in FIG. Figure 5d Shows Figure 5a Details inside area E are shown in . Figure 5e Shows Figure 5b Detail of area B shown in . Figure 5f Shows Figure 5a Details inside region C are shown in FIG.

[0024] Figure 6a and Figure 6b A cross section of a random winding permanent magnet machine according to an aspect of the invention is shown. Figure 6b Shown in Figure 6a Detail of area A shown in .

[0025] Figure 7A cross section of a permanent magnet machine according to an aspect of the invention is shown, wherein slots in the rotor core laminations are provided to allow insertion of conductors when the permanent magnet segments have to be remagnetized.

[0026] Figure 8a A cross section of a machine with a rotor (rotatable in the directions 64 and 65) having external permanent magnets according to an aspect of the invention is shown. Figure 8b Shown in Figure 8a Detail of the circled area B shown in FIG.

[0027] Figure 9a and Figure 9b A machine with external rotor permanent magnets is depicted. Figure 9b Shown in Figure 9a Detail of the circled area A shown in FIG.

[0028] Fig.10 It is a hybrid permanent magnet machine with an excitation coil.

[0029] Fig.11a A prior art high voltage rotating electric machine coil is shown. Figure 11b to Figure 11d The coil fixing method is depicted. Fig.11b and Fig.11d Detail of circular area C as it appears in an embodiment of the present technology is shown.

[0030] Fig.12 It is a schematic diagram of a brushless excitation system combined with the present invention. DETAILED DESCRIPTION

[0031] Figure 1 , Figure 2 and Figure 3 A prior art configuration of magnets and slots in electric motors and generators is shown.

[0032] refer to Figure 4a , Figure 4b and Figure 4c, shows a cross section of a rotating electric machine with an AC stator that can operate in either motor or generator mode. The stator core 30 carries a sinusoidally varying magnetic flux, as shown by flux lines 21a, 21b, 21c, 21d, 21e, 21f, 21g and 21h. This machine is asymmetric and functions differently in all four quadrants. It is optimized for two-quadrant operation, which is required, for example, for elevators or in combination with reversible pump turbines. The power generation and drive that occur in these two examples have torques in the same direction but rotations in opposite directions. In each of the two quadrants, the flux lines cross the gas gap 49 with the same angular sign. For maximum power, the angle of the flux lines crossing the gas gap can be in the range of 30 degrees to 45 degrees from the radial direction. Flux angles greater than 45 degrees may cause slippage or loss of synchronization between the poles of the permanent magnets and the poles generated by the coils in the stator. According to one aspect of the invention, the coil current phase angle can be adjusted to prevent loss of synchronization. Now also refer to Figure 5f , the unidirectional tapered stator slots 51 shown before coil insertion (as shown, tapering in one direction) are aligned with this angle to minimize flux concentration at the tip 55 of the stator tooth 56. Similarly, the permanent magnet segments 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 and 19 are magnetized so that flux can leave the magnets, pass through the gas gap and enter the stator core without changing direction. The magnetization direction of the permanent magnet segments can be uniform across the discrete magnet segments, or in the case of a single magnet per pole, it is preferred to magnetize in a continuous direction to maintain the designed angle through which the gas gap passes. The required field strength varies with angular position, and the magnet thickness should also vary accordingly to achieve economical use of expensive magnetic materials. The change in flux direction within the gas gap in the prior art machine results in a larger effective gas gap. The longer indirect flux path through the gas gap of the prior art machine results in a lower magnetic field strength or the need for larger magnets. The coil 60 shown may be similar to a Robe wire bar, except that the conductor cross-sectional shape changes with each pass through the slot so that the assembled bar fits within the unidirectional tapered stator slots 51 .

[0033] refer to Figure 5a , Figure 5b , Figure 5c , Figure 5d , Figure 5e and Figure 5f , showing Figure 4a , Figure 4b and Figure 4cA variation of a rotating electric machine. The windings 28 (e.g., windings 28a to 28ab) are composed of wires that are flattened according to the order in which they are placed in each slot. The flattening is preferably accomplished using automated equipment configured to establish the desired thickness over the length of each individual wire. This allows the coils to have a tapered shape that matches the shape of the unidirectional tapered stator slots 51, which provide a constant core cross-sectional area and flux density as a function of radius. This constant flux density configuration minimizes hysteresis losses while also optimizing the use of iron and copper. The unidirectional tapered stator slots 51 also allow the coils to be inserted from one end of the slot with a generous clearance. Once the coils are fully inserted, the elastically stretched packer 25 penetrates the back-iron end 54 of the slot under tension. The back-iron 57 is Figure 6a . The tension-induced, stretched "packer" 25 presents a reduced cross-section compared to the unstretched packer 26. Once the stretched packer 25 is in place, the tension is released and the tensioning device can be disconnected. This causes the unstretched packer 26 to fully occupy the available space and apply a positioning preload against the rear edge of the coil. The coil can be removed by tensioning the packer 26 again. The preload provided suppresses coil vibrations. The resulting close contact between the coil and the slot improves heat transfer. The permanent magnet segments 4 to 19 can be fixed with carbon fiber windings 27.

[0034] refer to Figure 6a and Figure 6b , shows an example arrangement of randomly wound coils 58 and 59 in slots. Coil insulator 62 separates coils 58 and 59. Slot insulator 63 insulates the coils from stator core 30.

[0035] refer to Figure 7 The purpose of providing remagnetization slots 31 in the rotor core 20 is to remagnetize the permanent magnet segments 4 to 19 when demagnetization occurs due to an external short circuit or overheating of the magnets for any reason. The conductors placed in such slots for remagnetization will preferably be used in combination with conductors located and fixed outside the rotor, removed from the stator.

[0036] refer to Figure 8a and Figure 8b, showing a cross section of an external magnet rotating electric machine similar to that used for a permanent magnet UAV motor. The spline shaft 22 prevents the stator core 30 from rotating. The spline shaft 22 is preferably non-magnetic so as to minimize eddy current losses that would otherwise be caused by the alternating flux through the spline shaft 22. The spline shaft 22 may include holes 23 that can be used to enhance cooling, for example as part of a heat pipe. In the two-pole configuration shown, the flux must pass through the diameter of the stator core 30. The spline connection between the spline shaft 22 and the stator core 30 minimizes the required diameter of the spline shaft 22, thereby minimizing the magnetic resistance of the diameter flux path through the assembly consisting of the spline shaft 22 and the stator core 30. The permanent magnet segments 4 to 19 are all magnetized with a flux direction that is aligned with the nominal rated load flux direction through the gas gap. Again, flux lines that do not change direction when passing through the gas gap result in a shorter effective gas gap, minimizing the magnetic resistance of the magnetic circuit and allowing the use of minimal magnetic material (e.g., rare earth). Figure 8b Example coils 58, 59 are shown in slots (e.g., non-tapered slots 50) designed to direct magnetic flux lines between the rated torque direction in the gas gap and the diametric flux path on the two-pole machine shown. It should be noted that different numbers of poles require different flux paths through the rotor.

[0037] refer to Figure 9a and Figure 9b , showing Figure 8a and Figure 8b In this case, the bidirectional tapered slots 24 are shaped to avoid magnetic flux concentration at either end of the slots 24 (as shown, tapering in both directions).

[0038] refer to Fig.10 , a hybrid synchronous machine is shown in cross section. The machine combines permanent magnet segments 4 to 19 with rotor field coils 29 to provide control of voltage and power factor while retaining some of the efficiency advantages of the permanent magnetic field. The rotor field coils 29 can be energized in either direction to increase or decrease the field provided by the permanent magnet segments. The rotor field coils 29 can be energized by conventional slip rings, by conventional (prior art) brushless exciters, or, in accordance with another aspect of the invention, by a brushless exciter co-located and superimposed with the main synchronous alternator shown.

[0039] refer to Fig.11a , Fig.11b , Fig.11c and Fig.11d, the unstretched packer 26 can take the shape of a flat rubber band. The stretched packer 25 can penetrate the circular portion of the high-voltage stator slot 52 when stretched. In this way, the circular coil 61 can be fixed in the circular portion of the high-voltage stator slot 52 in the stator core 30. This can be combined with high-voltage rotating electric machine coils (for example, ABB High voltage generator) (see Fig.11a ).

[0040] refer to Fig.12 , the excitation system may include an auxiliary winding (stator DC excitation coil) 41 co-located with the AC power stator winding 48 to produce a non-rotating magnetic field having a magnetic path through the stator 72 and the rotor 45. This results in the generation of AC power in the auxiliary winding 44 in the rotor 45. This AC power available in the rotor 45 is rectified to provide DC power to the rotor field coil 29. The optical rectifier controller 46 controls the optically controlled rectifier 70 via the optical link 71. The optically controlled rectifier 70 can switch the polarity of the rotor field coil 29 and adjust the rotor field coil 29. The optically controlled rectifier 70 can be replaced by a functionally similar device, such as a small photodiode or functional equivalent that controls a conventional thyristor rectifier. This configuration overcomes the complexity of mounting a separate exciter to a larger AC generator, where the larger AC generator may have a large gas gap and a large bearing spacing that are incompatible with those exciters. The present invention in this regard provides a cheaper, more rugged and more compact exciter configuration. The exciter magnetic circuit is superimposed on, i.e. co-located with, the main magnetic circuit of the motor or generator. This configuration eliminates the need for a separate exciter generator. Separate exciter generators tend to be smaller, may require a smaller air gap, and have tighter positioning tolerances for the rotor within the stator. The elimination of a separate magnetic circuit for the rotor reduces part count, machine weight, machine size, and machine cost.

[0041] refer to Fig.12 , the excitation controller 40 supplies direct current DC current to the auxiliary winding 41 (stator DC excitation coil), which causes the power of the alternating current to be delivered to the auxiliary winding 44 in the rotor 45. The generated alternating AC power is rectified with an optically controlled rectifier 46. The generated direct current DC power can be of either polarity, depending on whether the optical rectifier control is activated. The direct current DC power is applied to the rotor field coil 29. This power can be used to generate a field alone, or it can be used in conjunction with the permanent magnet segments in the rotor to generate a rotor magnetic field. The output power is obtained from the generator through the alternating AC power stator winding 48. Please note that the system can be configured as a generator, a synchronous motor, or a synchronous capacitor.

[0042] According to another aspect of the invention, the machine may be designed for submersible use. Its end coils may be embedded in rubber. Its stator pole faces may also be embedded in rubber. Preferably, a rubber such as Lord Chemical Company The rubber is vulcanized to the surface of the stator core laminations using an adhesive such as PTFE. In addition, the stainless steel sleeve mounted on the rotor can slide on the rubber bonded to the stator using water lubrication with minimal wear. The assembly acts as a rubber bearing, similar to the rubber bearings used for ship stern tubes. This is superior to covering the pole surface with stainless steel because, unlike stainless steel, rubber does not generate eddy current losses. The rubber-covered stator in combination with the stainless steel-covered rotor can also be used in the case of a structure where the rotor is located outside the stator.

[0043] It should be noted that the improvements disclosed herein are applicable to rotating electromagnetic machines having different numbers of poles and phases. The two-pole machine shown here is only an example.

Claims

1. A rotating electric machine comprising an alternating current stator, a rotor, and a gas gap, the rotor rotating relative to the alternating current stator and comprising permanent magnet segments, each of the permanent magnet segments being magnetized to have a flux direction substantially aligned with a non-radial nominal rated load flux direction at the gas gap, the gas gap being between the stator and the rotor.

2. The rotating electric machine according to claim 1, wherein: For maximum power of the rotating electric machine, the angle of the flux lines passing through the gas gap is in the range of 30 to 45 degrees to the radial direction.

3. The rotating electric machine according to claim 2, wherein: The alternating current stator also includes stator slots accommodating coil windings, the stator slots being positioned at a non-radial angle aligned with the angle.

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