CN104956573A - motor - Google Patents

Abstract

An electric machine comprising a plurality of removable modular stator components (1, 50, 51, 200, 201, 210, 211, 220, 260, 390, 400, 410) configured to be assembled to form a stator and a plurality of rotor components (2, 52, 221, 261, 391, 401, 411) configured to be assembled to form a rotor. One of the stator and rotor components has a first radial component and a second radial component and the other of the stator and rotor components has a third radial component. A separation gap is defined between the first radial assembly and the second radial assembly. A third radial assembly is positioned within the separation gap. The rotor is movable relative to the stator. The motor can produce a sinusoidal air gap MMF profile with minimal distortion.

Description

motor

technical field

The present invention relates to electric machines, and in particular but not limited to direct drive electric machines, such as like generators with windings, which allow the stator to be modularized in order to facilitate the production, testing and assembly process.

Background technique

Most wind turbine generators and tidal hydro generators are driven by mechanical gearboxes that amplify the speed of rotation to increase their power generation without substantially increasing their size. The variable speed gearbox itself has considerable weight and size. Despite a long history of technological development, today's gearboxes still suffer from reliability issues, which increase the overall cost of energy.

In response to the weakness of gearboxes, it has been proposed to dispense with gearboxes by using direct-drive generators in conjunction with solid-state power converters. Without a gearbox, direct drive generators would have to be much larger generators than those using a gearbox for the same power generation capacity, because direct drive generators have lower rotational speeds. Direct drive generators are not without their problems, as reliability is transferred to the generator in the absence of a gearbox. The outer diameter of direct drive generators poses a challenge in engineering development as well as in manufacturing, production management and logistics.

A direct drive tidal hydroelectric generator may have a seawater flooded air gap between the stator and rotor. Mechanical rolling element bearings are not suitable for subsea applications and are expensive for such larger diameter machines. Instead, the stator and rotor of this "wet" generator are supported by marine-grade low-friction journal bearings that operate based on hydrodynamic lubrication. Wet generators with journal bearings typically have relatively large mechanical clearances between the stator and rotor compared to electric machines supported by rolling element bearings.

For ease of manufacture and also for economical reasons, large direct drive generators are usually constructed by assembling together a number of small machine sections. Several separate, parallel pairs of stator segments may be distributed around the periphery of the machine to form an axial flux generator. Each stator segment may include an electronic magnetic core, concentrated coils and some electrical components enclosed in a watertight case. One disadvantage of this arrangement is the limited power capacity due to the considerable spacing between the stator segments which would otherwise be filled with active magnetic material. Conventional three-phase double-layer windings would result in a higher power density machine, but since the phase windings overlap each other around the machine, the stator cannot be segmented without having overhanging coils.

Non-overlapping concentrated coils and/or fractional slot windings are very common in permanent magnet motors. However, they are not used in induction motors because they induce opposing field harmonics in the rotor, which results in very low torque. Squirrel-cage and solid steel rotors are essentially short-circuited conductive structures without any pre-defined current paths, so that the induced currents will generate harmonics rich in magnetomotive force (MMF). One remedy to this problem is to use a wound rotor with the same number of poles as the fundamental stator MMF so as not to induce other harmonics. While it is not impractical to use a wound rotor for a wet induction generator, its construction would be somewhat complicated.

Linear induction motors have been proposed having two opposing stators sandwiching electrically conductive rotor disks. The two stators are offset from each other such that the concentrated coils from the second stator are displaceable by an odd number of half wavelengths of the undesired number of poles or by an odd number of whole wavelengths of the undesired number of poles and have reversed current direction. This arrangement cancels even integer harmonics of the magnetic field while enhancing the desired fundamental magnetic field. This harmonic cancellation requires equal and balanced sharing from the offset stator. If either stator fails to operate, the even harmonics are not cancelled, resulting in a large negative torque which counteracts the predominant positive torque. The air gap on both sides of the rotor should also be nominally equal. Undesired MMF harmonics are not completely canceled when there is a relatively large rotor offset in the axial direction.

Wet generators are slightly more complex to construct than dry generators because water must be prevented from intruding into critical electrical components. The coil can be resin encapsulated and the assembly further protected by a stainless steel case. Alternatively, the stator segments and coils may be encapsulated in resin within a plastic case. For total removal of resin and air voids in the coil, the entire assembly would need to be infused under vacuum pressure, which increases the production cost of the coil. Once a failure is detected or the assembly is deemed unfit for use, the entire coil assembly is discarded.

Contents of the invention

According to one aspect, an electrical machine is provided that may be used in tidal energy harvesting applications, wherein the only rotating component is an annular rotor. The absence of a gearbox, drive shaft and mechanical rolling element bearings reduces cost and simplifies the overall system. The air gap of the machine can be filled with sea water.

Axial flux induction generators are available having double-sided annular stators sandwiching annular conductive discs. The rotor discs may be ironless to reduce corrosion from direct exposure to seawater. Another additional benefit is that the weight of the rotor disc can be less than that of a permanent magnet mounted rotor and this results in a lighter, lower static friction and lower inertia rotor suitable for a turbomachine. The use of an annular disk structure as the rotor considerably simplifies the manufacturing process compared to wound or squirrel-cage rotors.

Modular or segmented stators and rotors are available which can be assembled in a side-to-side manner to form a continuous annular stator and a continuous annular rotor respectively. The modular stators can be identical so that they can be tested independently during production. Any module in the generator can be easily replaced. A subsea housing housing power conversion equipment can be integrated into each modular stator.

Modular stators can have a winding scheme that yields substantially equal MMFs to those of conventional motors with distributed and overlapping windings. Coils may not overlap between two adjacent modular stators, and may not be in an overhanging position. The MMF magnetic field can be characterized as substantially sinusoidal in shape. The fundamental component may be most dominant.

The winding scheme can be such that the sinusoidal waveform of the induced MMF is substantially preserved even when there are large rotor excursions. Winder solutions can be configured for single-phase or multi-phase motors for generators.

Concentric or overlapping coils can be pre-prepared prior to insertion into the stator slots. The number of coil turns will vary as they are spread across multiple slots. The coils may be sufficiently insulated that they need not be encapsulated in resin. The coils can also be directly exposed to seawater to facilitate heat dissipation.

There may be general axial flux induction machines with a double-sided annular rotor sandwiching an annular stator. The stator may include discrete ferromagnetic poles, which may be held and spaced apart by annular disks. Each rotor may include a conductive plate and an iron plate (back iron).

Winding arrangements are available which are suitable for linear motors, radial flux and axial flux rotary motors which can be induction, permanent magnet, field synchronous, doubly fed induction or synchronous reluctance motors.

Description of drawings

In order that the invention may be readily understood and put into practical effect, it will now be described by way of non-limiting examples of merely exemplary embodiments, the description referring to the accompanying drawings. In the attached picture:

Figure 1 is an exploded perspective view of an axial flux machine having a modular stator and a modular rotor assembled to form a whole continuous stator and rotor, respectively;

Figure 2 shows a modular double-sided stator arrangement and a modular rotor as shown in Figure 1;

Figure 3 shows a watertight box containing the stack of stator laminations shown in Figure 1;

Figure 4 shows a prior art single-phase induction motor with symmetrical windings distributed in a 16-slot stator, where (a) is a radial flux motor, (b) is an axial flux motor, and (c ) is the equivalent representation of slots and coils;

Figure 5 shows a single-phase, axial flux induction motor in which,

(a) is a layout with concentric windings;

(b) is a layout with lapped windings; and

(c) is an equivalent winding scheme including multiple basic units;

Figure 6 shows:

(a) Single-phase, axial flux induction motors comprising double-sided stators in which the auxiliary winding of the stator serves as the center pole winding;

(b) the air-gap magnetic field generated by the main winding; and

(c) the air gap magnetic field generated by the auxiliary winding;

Figure 7 shows:

(a) Equivalent full-span winding schemes for single-phase, axial flux induction motors; and

(b) its air-gap magnetic field and harmonics;

Figure 8 shows:

(a) Equivalent short-pitch winding schemes for single-phase, axial flux induction motors; and

(b) its air-gap magnetic field and harmonics;

Figure 9 shows:

(a) Winding schemes for single-phase, axial flux induction motors with sinusoidal windings; and

(b) its air-gap magnetic field and harmonics;

Figure 10 shows:

(a) Winding schemes for single-phase, axial-flux induction motors with sinusoidal windings and higher number of coils per elementary unit; and

(b) its air-gap magnetic field and harmonics;

Figure 11 shows:

(a) Equivalent full-span winding schemes for three-phase, axial flux induction motors; and

(b) The same winding scheme, but with coils of overlapping phases;

Figure 12 shows:

(a) an equivalent short-pitch winding scheme for a three-phase, axial flux induction motor; and

(b) Equivalent short-pitch double-layer winding;

Figure 13 shows:

(a) Equivalent 8/9 short-pitch winding scheme for three-phase, axial flux induction motors; and

(b) Equivalent 8/9 short-pitch double-layer winding;

Figure 14 shows:

(a) Equivalent 7/9 short-pitch winding scheme for three-phase, axial flux induction motors; and

(b) Equivalent 7/9 short-pitch double-layer winding;

Figure 15 shows:

(a) An equivalent short-pitch winding scheme for a three-phase, axial flux induction motor with better slot utilization;

(b) a phase A coil having an average coil pitch of 4; and

(c) all phase coils with an average coil pitch of 6;

Figure 16 shows a winding scheme for a three-phase, axial flux induction motor with an asymmetric double-sided stator;

Figure 17 shows a winding scheme for a three-phase, axial flux induction motor, where the windings of one phase are split between symmetrical double-sided stators;

Figure 18 shows a winding scheme for a three-phase, axial flux induction motor, where the windings of one phase are split between symmetrical double-sided stators and the turns of all phase coils are distributed;

Figure 19 shows a winding scheme for a five-phase, axial flux induction motor;

Figure 20 shows a winding scheme for a five-phase, axial flux induction motor with overlapping coils;

Figure 21 shows:

(a) Winding schemes for six-phase, axial flux induction motors; and

(b) a power converter feeding a phase coil;

Figure 22 is an exploded perspective view of an axial flux machine in which 8 modular stators and 8 modular rotors are assembled to form a complete continuous stator and rotor, respectively;

Figure 23 shows a modular stator and a modular double-sided rotor;

Figure 24 shows:

(a) Stator poles comprising a stack of ferromagnetic laminations;

(b) Stator poles comprising non-ferrous or ferrous blocks of rectangular cross-section; and

(c) a stack of laminations contained in a waterproof case;

Figure 25 shows staggered ends of a modular stator;

Figure 26 shows a single phase, axial flux induction motor where:

(a) is a layout with concentric windings;

(b) is a layout with lapped windings; and

(c) is an equivalent winding scheme including multiple basic units;

Figure 27 shows a winding scheme for a single-phase, axial flux induction motor with the auxiliary winding wound as the center pole winding;

Figure 28 shows a winding scheme for a single phase axial flux induction motor with sinusoidal windings;

Figure 29 shows a winding scheme for a single phase axial flux induction motor with sinusoidal windings and with higher turns coils per elementary unit;

Figure 30 shows a winding scheme for a three-phase, axial flux induction motor;

Figure 31 shows a winding scheme for a three-phase, axial flux induction motor with higher turns coils per elementary unit;

Figure 32 shows a winding scheme for a three-phase, axial flux induction motor with overlapping coils;

Figure 33 shows an equivalent 8/9 short-pitch winding scheme for a three-phase, axial flux induction motor;

Figure 34 is an equivalent short-pitch winding scheme for a three-phase, axial flux induction motor with better slot utilization;

Figure 35 is a winding scheme for a three-phase, axial flux induction motor with its turns assigned;

Figure 36 is a modified winding scheme for a three-phase, axial flux induction motor with its turns assigned;

Figure 37 shows:

(a) a winding scheme for a five-phase, axial flux induction motor; and

(b) have overlapping windings;

Figure 38 shows:

(a) Winding schemes for six-phase, axial flux induction motors; and

(b) a power converter feeding a phase coil;

According to another embodiment of the present invention;

Figure 39 shows:

(a) Radial-flux, rotating induction machines including a double-sided stator; and

(b) its modular stator and modular rotor;

Figure 40 shows:

(a) Radial-flux, rotating induction machines including a double-sided rotor; and

(b) its modular stator and modular rotor;

Figure 41 shows:

(a) Radial-flux, single-air-gap rotary induction machines; and

(b) its modular stator and modular rotor;

Figure 42 shows a permanent magnet motor with a double-sided stator;

Figure 43 shows a permanent magnet motor with a double-sided rotor;

Figure 44 shows a Halbach array permanent magnet motor with a double-sided rotor;

Figure 45 is a field-wound synchronous motor with a double-sided stator;

Figure 46 is a field-wound synchronous motor with double-sided rotors;

Figure 47 shows a synchronous reluctance machine with a double-sided stator; and

Figure 48 shows a synchronous reluctance machine with a double-sided rotor.

Detailed ways

The preferred embodiments disclosed herein relate primarily to large underwater turbines employing direct drive generators, but are equally applicable to wind turbines, wave powered machines and/or electric vehicles.

first embodiment

There is provided an axial flux induction generator having an annular double-sided stator sandwiching a single annular rotor. Both the double sided stator and rotor are modular for ease of production and are assembled circumferentially end to end to form a complete electric machine. Figure 1 is an example of such an assembly, where 12 modular stators 1 and 12 modular rotors 2 spanning a mechanical angle of 30 degrees each form a complete annular stator and rotor, respectively. Any number of modular stators 1 or modular rotors 2 may also be provided as practical. The support structure 3 of the modular stators has mounting points to facilitate fitting to adjacent modular stators. The assembled modular stator provides a seamless distribution of current links equivalent to a motor constructed from continuous ring stators. This results in a non-destructive rotating magnetic field within the air gap with essentially the same peak amplitude and spatial relationship throughout the toroidal machine.

Figure 2 shows an example of a modular stator 1 and a modulo-spanning rotor 2 according to a first embodiment of the invention. An axial flux machine with a double-sided stator 4 has two radially extending and substantially parallel stator assemblies defining an air gap between them from which the energy originates. The rotor has a radially extending rotor assembly 5 positionable between and rotatable relative to the coils 6 such that the MMF component induced in the rotor 2 is caused by the two stators 4 when the induced MMF component is sinusoidal The stator is the most efficient. An ironless rotor can be used in a symmetrical manner if a suitable current link can be provided through the coils 6 so that magnetic flux from one side of the stator pole can traverse the air gap to reach the opposite side of the stator pole. This arrangement is advantageous because corrosion of the iron caused by direct exposure to seawater is avoided and a simple conductive plate 5 can be used. The rotor disk 5 may be made of metals including copper and aluminum with low electrical resistivity. The modular rotor disks 5 may be connected or linked together circumferentially, such that a continuous short circuit is created around the rotor.

FIG. 3 shows one side of the double-sided stator 4 . The stator may comprise stacks of ferromagnetic material 8, such as electrical or mild steel, suitably laminated and generally insulated to facilitate dry axial flux machine applications. The entire stack of stator irons can be painted or coated with multiple layers of waterproof protective coating 9 for marine applications. The coated laminations of the stator laminations are preferably housed inside a plastic case 10 for added protection against accidental wear and against water intrusion, as shown in FIG. 3 . The void 11 in the box can be replaced with a waterproof resin compound or for a ferrous material, which results in a groove with parallel sides. The box 10 has toothed features on its front face which match the physical protrusions 12 and slots 13 of the axial flux stator. The surface at the back flat is hermetically sealed. In the example shown in FIG. 3 , the box completely covers the width of the stator poles including the pole tips 14 . While there may be thrust or journal bearings preventing direct contact and friction between the stator and rotor, it is still preferred to cover and reinforce the stator pole faces of the case with protective covers which serve as secondary protection from wear. The protective cover may be made of a substantially strong and non-metallic material including fiberglass. The double-sided stator is fixed to the support structure 3 .

Coils 6 may be wound in situ, or pre-prepared coils may be inserted into stator slots 13 defined by box 10 and external to stator iron 8 . This arrangement is advantageously easier to manufacture than the process of encapsulating both the stator iron and the enamelled copper coils in resin. Direct exposure to seawater means more efficient heat dissipation through the conductor insulation jacket. The conductors of the coil 6 are preferably insulated with a high dielectric strength plastic sheath impermeable to seawater. Winding wires insulated with a sheath of PVC, PE2+PA and HT4 commonly found in submersible pumps can be used. The modular stator 1 may have staggered ends such that the coils 6 are fully contained within the assembly. Coil 6 may be a concentric or lap coil. The number of turns can also be scaled across multiple slots 13 to obtain a more sinusoidal MMF.

In FIG. 2 , the waterproof underwater housing 7 can be made integral to the support structure 3 . The coil terminals may enter the subsea housing 7 via suitable compression glands, where they may be interconnected with other coils 6 . Alternatively, the coil terminals may be jointed on the outside of the submerged housing. The underwater housing 7 can also house the power conversion equipment responsible for converting the power generated within the module. The integration of power conversion equipment into the stator simplifies production and pre-deployment, where each modular stator can be tested independently and configured in a 'plug and play' style. Faulty modular stators can also be easily replaced without affecting normal modules.

The winding scheme defining the phases of an axial flux induction generator will now be described with reference to FIGS. 5 to 21 . The term "basic unit" will be used frequently in order to define a section with a basic winding spanning the length of a pole pair. The modular stator 1 may comprise one base unit or a plurality of base units to suit the application.

Figure 4(a) and Figure 4(b) show the single-phase 2-pole winding schemes of radial flux and axial flux induction motors of the prior art, respectively. The term "single phase" refers to a winding connected to a single phase AC grid or a single phase power converter, but for practical reasons they usually have two phase windings. The 16-slot cylindrical stators are cut and unfolded imaginary (as shown by dashed lines and arrows) so that their slots and coils lie flat as in Fig. 4(c). A single phase induction motor has two phase windings, one main and the other auxiliary, denoted "M" and "A" respectively. The purpose of the auxiliary winding is to provide assistance in starting the induction motor, since exciting only the main winding with a sinusoidal voltage at zero rotor speed will create a pulsating air gap MMF at the frequency of the source. This is due to the canceling positive sequence torque (forward travel due to MMF) and negative sequence torque (reverse travel due to MMF), which are equal in magnitude but opposite in direction.

Referring now to the two-phase single layer winding of Figure 4(c), the auxiliary winding is spatially orthogonal with respect to the main winding. The main winding and the auxiliary winding each occupy 8 slots, and the number of conductors in each slot may or may not be the same. The main and auxiliary windings have the same number of slots per pole per phase (number of slots/pole/phase), ie qM=qA=4. Even though the main and auxiliary windings have the same number of turns and the same wire gauge, their phase resistances are not the same because the end windings can be slightly different for the two phases. Because the machine has a single-layer winding structure, the end windings of the main and auxiliary coils overlap each other around the stator. There is no place in the machine where the stator and coils can be physically divided into equiangular sections without cutting off at least some of the coils.

Figure 5(a) shows how the two-phase windings can be split in a modular fashion while maintaining the conventional features of the main and auxiliary windings according to the first embodiment of the invention. In this double-sided stator configuration, the auxiliary coil is wound at one side of the stator 50 and the main coil is wound at the opposite side of the stator 51 . The two phases are spatially orthogonal with respect to each other. A rotor disk 52 is sandwiched between opposing stators 50 and 51 . Arc 53 represents the end winding on the link coil side. For example, the coil side (M) at slot 1 is linked to the coil side (M') at slot 8. Both the main and auxiliary phases comprise concentric windings 53 with a coil pitch of 5 and 7. This gives an average coil pitch of 6, which is the same as the prior art winding scheme of FIG. 4 . Figure 5(b) shows that lap windings 54 with a coil pitch of 6 can also be used, giving the same current link distributions as those shown in Figure 5(a). The winding schemes disclosed below are shown as concentric windings, but it will be understood by those skilled in the art that lapped windings may be used.

Fig. 5(c) is a schematic winding diagram equivalent to Fig. 5(a), in which a plurality of basic units 55 are connected end to end to form a multi-pole motor. This schematic equivalent is shown without stator iron and will facilitate the discussion below. Each elementary cell 55 spans 16 slots as separated by thick lines. A modular stator 1 as previously defined may comprise one base unit 55 or a plurality of base units 55 . The two opposing stators 50 and 51 are offset relative to each other by 4 slots so that they can be disassembled without cutting or jamming the coils. The teeth and slots of opposing stators are aligned across the axial air gap. It can be seen from Figure 5(a) that not all stator slots are filled with conductors. Since there is only one phase per stator side, the stator back iron can be extended to fill these slots.

To operate as a generator, the induction machine is connected to a power converter where reactive power comes from the energized AC line (in the opposite direction to active power delivered to the AC line). As the tidal flow causes the turbine/rotor to spin, the auxiliary winding for start-up can be omitted in the stator, leaving only the main winding to be used. A disadvantage of this arrangement is that the induction motor cannot be operated as a motor to start the turbine during periods of low tidal flow. It is preferred that there are two windings in the generator to assist the turbine in overcoming static friction between the bearings of the stator and rotor. Furthermore, the functions of the auxiliary and main windings can be interchanged similarly to bidirectional induction motors.

Start-up of the turbine can be accomplished by injecting current in the auxiliary winding which temporarily offsets the current ahead of the main winding. This current injection sequence causes the rotor to rotate from the auxiliary winding to the main winding. The phase lead in current can be achieved by connecting a series capacitor between the auxiliary winding and the single-phase AC supply. Alternatively, the auxiliary winding may be directly connected to a variable frequency converter, such as a pulse width modulated voltage source inverter or a current source inverter with a controlled rectifier. The voltage of the auxiliary winding can be varied to mitigate torque ripple across all operating points.

An alternative variant of a single phase axial flux induction generator is shown in Figure 6(a). Such a winding scheme arises from the fact that the current links in radial direction (inward and outward) are responsible for generating the magnetic field in the air gap, regardless of how the end windings are organized around the perimeter. The auxiliary coil is manipulated such that an intermediate pole is obtained across the boundary between two adjacent elementary units. Such a winding arrangement enables the stator to be disassembled into aligned modules, as shown in Fig. 6(a). A modular stator may comprise one or more basic units as defined by bold lines. Figure 6(b) and Figure 6(c) are the air-gap magnetic fields generated by the main winding and the auxiliary winding, respectively, where the latter phase leads by 90 degrees. The variant in FIG. 6( a ) is identical to FIG. 5( c ) with respect to the current connection and the air-gap magnetic field. However, the auxiliary end winding will be correspondingly longer, which makes the winding of the machine slightly asymmetrical. The resistance increase on the auxiliary phase can be accommodated by using conductors with a larger cross-sectional area, if desired. However asymmetrical windings are common in practical single phase induction motors in order to generate high starting torque.

The winding scheme of Fig. 6(a) can be extended to a two-layer winding structure, where each stator side includes both main and auxiliary windings, as shown in Fig. 7(a). The auxiliary winding occupies the bottom layer of the slot, while the main winding resides at the upper layer of the slot. The stator teeth and coils of the main and auxiliary windings on one side of the modular stator are aligned to the stator teeth and coils on the opposite side, and they combine to produce an equivalent full-span winding. Figure 7(b) shows the corresponding air gap flux density and harmonics generated by the main winding. If the machine is symmetrical, the auxiliary winding also produces the same result. If the main and auxiliary windings at the upper stator are connected to a power converter independent of the windings at the bottom stator, there may be redundant fault tolerance. Any failure in the power converter or in the coils in either side of the modular stator will not cause an overall failure because the other side is still functional (at lower power rating).

In Figure 7(b), the fundamental component is the most dominant, but there are also some third and fifth harmonics. Space harmonic content can be reduced by current links similar to those produced by short pitch windings. It is common to find conventional double layer windings with short or spaced pitch coils, where each coil turn starts from the bottom layer of one slot and returns via the top layer of the other slot. An equivalent short pitch effect can be produced by offsetting the full pitch coils of the top stator to the left or right relative to the bottom stator. This configuration is shown in Figure 8(a), where the bottom stator offsets one slot to the right, creating a staggered base unit. A modular stator may comprise a base unit or base units as defined by the thick separation line in Figure 8(a). Figure 8(b) compares the harmonics generated by the full-pitch and short-pitch winding schemes. The spatial harmonic content has been reduced by the latter, so its fundamental component has also been reduced.

The current link distribution in a two-phase winding motor can be made to resemble a sinusoid by properly distributing the turns in the slots. Figure 9(a) shows how an electric machine can be adapted to incorporate approximately sinusoidal windings. The difference in text size specifies the number of conductors in the slot, where bold font indicates a higher number of conductors. Figure 9(b) shows the resulting air gap flux density and harmonics for a scheme similar to that in Figure 8(a). A better sinusoidal air gap magnetic field can be obtained by increasing the number of coils per base unit. Figure 10(a) is an example where 6 concentric coils per phase form a basic unit, as opposed to 4 concentric coils per phase in the winding scheme of Figure 9(a). Larger fonts represent higher numbers of conductors, while smaller fonts represent fewer conductors. The resulting magnetic fields of the two poles are closer to ideal sinusoidal curves, as shown in Fig. 10(b). The undesired harmonics common to the motors in Fig. 5(c), Fig. 6(a), Fig. 7(a), 8(a) and Fig. 9(a) are reduced by the winding scheme of Fig. 10(a).

The concept of a modular stator arrangement is also applicable to three-phase motors. Three-phase motors naturally produce a more sinusoidal air gap MMF than single-phase motors without the need for sinusoidal windings. Figure 11(a) shows a three-phase axial flux machine constructed by multiple basic unit stators. A modular stator may comprise one or more base units. The stator is subdivided into three layers, and the coils of one phase are confined to one layer without overlapping the other. A-phase, B-phase, and C-phase coils are spaced apart at an electrical angle of 120 degrees, and they occupy the top, middle, and bottom layers of the slots, respectively. Each basic unit spans 12 slots, where the number of slots/poles/phases and average coil pitch are equal to 2 and 6, respectively (e.g., slots 1-8 and 2-7 for concentric coils, and slots 1-8 for shingled coils slots 1-7 and 2-8). Alternatively, the phase coils can be overlapped in one single layer winding, as shown in Fig. 11(b). The teeth and slots of the two opposing stators are aligned with each other. The current link distribution at one side of the stator is a mirror image of the opposite side, and they combine to create an air gap MMF. Although the fundamental component is highest in relative magnitude, the resulting air-gap MMF also contains some non-tripling higher harmonics (5, 7, 11, 13, etc.), which is very difficult for a full-span coil. common.

Since the phase coils on one side of the stator do not physically overlap the coils on the opposite side of the stator, it is possible to offset one stator relative to the other by one slot or a higher number of slots, resulting in a single chord or short distance effect. In Fig. 12(a), the winding arrangement at the upper and bottom stators is the same as in Fig. 11(a), but the bottom stator is shifted one slot pitch to the left relative to the upper stator, resulting in an equivalent 5/6 short distance winding. The base units are staggered, but the stator teeth and slots from two opposing stators are aligned. The staggered stator in Fig. 12(a) can be equivalently mapped to a prior art double-layer winding, as shown in Fig. 12(b). A conventional 5/6 short pitch double layer winding has coils spanning 5 slot pitches measured from inward current at the slots of the upper layer to outward current at the slots of the bottom layer. For example, phase "A" current flows inward through slot 5 in the upper tier and outward through slot 10 in the bottom tier. For clarity, only the chords of the phase A coil are shown in Fig. 12(b). It is evident that the phase coils of the prior art double winding overlap all around the stator and there is no point at which the stator is segmented without cutting off the coil end windings or having overhanging coils. However the invention can be segmented and the coil still fully contained therein. This staggered stator arrangement advantageously results in a better sinusoidal air gap MMF than the full-pitch arrangement.

Using the same winding concept, the 18-slot double-sided stator can be shifted by one slot pitch or two slot pitches for 8/9 and 7/9 short-pitch arrangements, respectively. Fig. 13(a) and Fig. 13(b) respectively show the winding arrangement of the 8/9 short-pitch axial flux induction motor and its equivalent prior art 8/9 short-pitch double-layer winding. Figure 14(a) and Figure 14(b) respectively show the winding arrangement of a 7/9 short-pitch axial flux induction motor and its equivalent prior art 7/9 short-pitch double-layer winding. Boundaries between identical basic units are shown in bold lines. Modular stators can consist of one or more base unit numbers. Due to their slot number/pole/phase equal to 3, the motors in Fig. 13(a) and Fig. 14(a) have even lower space harmonic content than the motor in Fig. 12(a).

The coil can be made to occupy more slots in order to increase the slot utilization of the motor. Figure 15(a) shows a double sided stator arrangement with three layer coils occupying 67% of the slot. Each phase winding has eight coils, resulting in pole pairs in 12 slots. Since each slot of the stator has coil sides from two phases, the stator cannot be segmented without dismantling the coil set for one of the phases. The basic unit defined by the thick line in Fig. 15(a) encapsulates the coils of phase B and phase C, but separates the coil of phase A. Any attempt to offset the phase A coils so that they are packaged in separate units will distort the spatial relationship between the phases. However, the end windings of phase A can be manipulated so that the same current link distribution with respect to phases B and C can be achieved. Figure 15(b) is a three-phase winding of a basic unit. Phases B and C each have a set of windings comprising four concentric coils with an average coil pitch of six. The phase A coil can be split into two smaller groups of windings, where each group comprises two concentric coils in a unit of twelve slots without changing the inward and outward current distribution.

With an average of four coil pitches, the end windings of phase A are shorter than those of phases B and C, which means that phase A will have less phase resistance. The number of turns in the phase A coil is preferably constant in order to keep the machine's current links balanced. But in phase A the length of the coil interconnection or its conductor size can be adjusted in order to obtain the same resistance as that of phase B and phase C. Alternatively, the concentric coils of phase A can be made to span the same coil pitch as phases B and C, as shown in Figure 15(c). Spanning six coil pitches means that the end windings of phase A necessarily overlap. Nevertheless, the end winding of phase A does not overlap the end windings of phases B and C, which represents a clear advantage.

Another winding arrangement can also be provided where the coil pitch is equal between phases and no phase coils or end windings overlap. Since the MMF of the air gap is caused independently by each opposing stator, it is possible to have an asymmetrical stator arrangement, which enables convenient segmenting of the three-phase windings. Figure 16 shows an asymmetric double sided stator with A phase coils wound on one side of the stator and B and C phase coils wound on the other side. Each basic unit spanning 12 slots is defined by a thick line. A modular stator may comprise one or more base units. Regardless of the phase, each set of windings has the same coil pitch (τ = 6 slot pitches). Such an arrangement is phase balanced and has the advantage of maximizing slot utilization while maintaining non-overlapping windings.

If geometrically symmetrical stators are desired, one of the stators may be wound with all sets of coils of the first phase and half the number of turns of the coils of the second phase, while the other stator may be wound with all sets of coils of the third phase and half the number of turns of the coils of the second phase. Half the number of turns of the two-phase coil. Figure 17 shows such a winding arrangement according to a first embodiment of the invention. The upper stator has all the phase C coils and half the turns of the phase B coils, and the bottom stator has all the phase A coils and half the turns of the phase B coils. Within each side of the stator, the winding layers of phases A and C are twice the size of phase B, but when the two sides are combined, the total area of the slots of phase B is equal to the total area of the slots of phases A and C. The axes of the B-phase coils from both sides of the stator match each other in space and direction, and the coils are connected in series to obtain the same number of turns as the A-phase and C-phase. The coils of Figures 16 and 17 may have different numbers of turns in their respective layers in order to create a short distance effect. By way of example, Figure 18 shows an equivalent short pitch winding scheme where phase coils designated in bold font have twice the number of conductors as phase coils designated in normal font.

Modular stators suitable for axial flux machines with a higher number of phases (4, 5, 6, 7 phases, etc.) can be derived using the winding arrangement principles disclosed above. There are many permutations of coil arrangements. For example, each side of a double-sided stator may have all or half of the phases. An asymmetric split of the phase coils can also be realized, in which the phase is split unequally between two opposing stators. Furthermore, all phases can be connected at the same neutral point, or each phase can be connected to the power converter as an independent circuit.

Figure 19 is an example of a five phase motor with an asymmetric double sided stator, where the upper stator has three phases and the bottom stator has the remaining two phases. The spatial angle between each two phases is 72 degrees apart in electrical degrees. The base unit is defined by the segments (shown in bold lines) of the stator segment enclosing the 10 slots. A modular stator can consist of one basic unit or several basic units. Five phases can be connected to a neutral point, and the terminals are connected to a five-phase power converter. For fault tolerance, the phases can be connected as independent circuits with five individual power converter feeding phase coils A to E. The phase coils can also be compressed into a single layer and placed on both sides of the stator. As shown in Figure 20, the phase coils of the upper stator 200 are mirror images of the phase coils of the bottom stator 201, and they may be connected together in series or in association to the power converter. Alternatively, the phase coils of the upper stator 200 and the bottom stator 201 may be respectively connected to independent power converters.

Multiphase axial flux motors can also be constructed with two or more sets of symmetrical phase windings. Figure 21(a) is an example of a six-phase motor composed of two sets of symmetrical three-phase windings A1, B1, C1 and A2, B2, C2, which are offset by an electrical angle of 30 degrees. A first set of windings is wound at the upper stator 210 and a second set is wound at the bottom stator 211 . The winding arrangement at the upper stator 210 is a mirror image of that of the bottom stator 211, but the latter is shifted one slot to the right, resulting in a phase shift of 30 electrical degrees. The base unit spans 12 slots as defined by the bold lines in Figure 21(a). A modular stator can consist of one base unit or a plurality of base units. Since the coil side occupies odd slots at the upper stator and even slots at the bottom stator, a double sided stator with six slots per base unit can be used. The shaded area in Fig. 21(a) may be an empty slot for a 12-slot base unit or a ferromagnet for a 6-slot base unit. The latter has non-aligned stator teeth between opposing stators.

Figure 21(b) shows a first set of three-phase windings fed by a three-phase power converter 212, while a second set is fed by a separate three-phase power converter 213, the phase of the power converter 213 being relative to the power converter 212 30 degrees electrical angle of delay. This six-phase winding configuration has the advantage of eliminating lower harmonics and is more fault tolerant due to its dual power converter layout. The windings in Figures 19, 20 and 21 can be extended to a scheme where the coil side occupies multiple slots in order to improve the distribution of the MMF.

Features common to the above winding schemes will now be described. Each side of the stator produces an approximately sinusoidal current distribution independent of the other side. When two stators are arranged to sandwich nonmagnetic and conductive rotor disks, the MMF of the total air gap is the superposition of the air gap magnetomotive forces produced by the corresponding stators. For axial flux wet generators with hydrodynamic journal bearings, there is an air gap separation between the rotor and stator that is equal throughout the machine. Any rotor deflection in the axial direction within the allowed mechanical clearance will still result in a predominantly sinusoidal induced air gap MMF. This is a clear advantage of the present invention.

Although the axial flux induction generator disclosed in this invention utilizes a slotted stator, the winding scheme is also applicable to a slotless machine. The term "slotless" refers to the smooth magnetic air gap separating the stator and rotor. The Lorentz force applied to the conductors during operation can remove the coils in slotless motors, so the coils must be mechanically held in place by non-magnetic clamps that consist of shapes similar to actual stator teeth protrusions. Alternatively, the coil may also be resin impregnated in a suitable mounting housing. The coils encapsulated within the resin can be widened to fill the space that would otherwise be occupied by the resin. Slotless induction motors require very high magnetizing currents due to their large air gap. In the absence of stator teeth, the number of coil turns can be increased to compensate for the reduction in magnetization MMF.

second embodiment

According to a second embodiment, an axial flux machine is provided having a pair of radially extending and substantially parallel annular rotor assemblies 221 sandwiching a radially extending annular stator assembly 220 . A continuous annular stator is formed by assembling a number of modular stators circumferentially end to end. Figure 22 shows an example of such an assembly, where 8 modular stators 220 and 8 modular rotors 221 each spanning a mechanical angle of 45 degrees form a complete annular stator. Similar to the machine disclosed in the first embodiment, any number of modular stators 220 and modular rotors 221 may be provided. The rotor 221 may or may not have the same number of modules as the stator 220 . When assembled, the modular stator 220 provides a seamless current link distribution equivalent to a motor built from continuous ring stators. The air gap magnetic field has essentially the same peak magnitude and spatial relationship throughout the toroidal machine.

Fig. 23 shows by way of example what a modular stator 220 and rotor section 221 may comprise. In this single stator configuration, magnetic flux traverses primarily axially along the stator poles 233 and returns circumferentially via the rotor disc 237 . Because there is a nominally zero flux circumferentially traversing in the stator, the stator iron yoke can be omitted, leaving only the stator poles 233 . This is particularly advantageous since laminated stators suitable for axial flux machines are difficult to manufacture. In the absence of a yoke, the stator poles 233 may be fabricated from discretely stacked laminations having the same cross-sectional profile across the machine axial depth. The discrete stator poles are spaced apart by inserting them through the slots of the rigid annular disk 235 and clamping together in place. The stator assembly is secured to a support structure 222 .

Discrete stator poles suitable for three different axial flux machines are shown in FIG. 24 . Figure 24(a) shows a stator pole comprising a stack of ferromagnetic laminations 240 comprising electrical and mild steel, which are typically insulated for dry environment applications such as wind turbines and Electric vehicles. The coil 234 is wound on or around the lamination surface of the stator magnetic poles. Figure 24(b) shows that the discrete stator poles can be blocks 241 of simple rectangular cross-section made of non-ferromagnetic material. Such stator poles whose sole purpose is to support the coils are particularly suitable for air core slotless motors. The block of simple rectangular cross-section may also be iron in order to concentrate and direct the magnetic flux through the smallest effective air gap. FIG. 24( c ) shows an example of a stator pole suitable for marine applications, where the stacked laminations 240 are housed in a waterproof case 242 . The hermetically sealed top cover is removed to reveal the lamination face 240 . The entire stack of ferromagnetic laminations 240 may be painted or coated with multiple layers of waterproof protective coatings. Waterproof box 242 provides added protection against accidental wear and water intrusion. The void 243 in the tank (if any) may be filled with a resin compound or iron core to provide structural strength to the assembly.

Coils 234 may be wound in situ, or pre-prepared coils may be inserted into slots between stator poles 233 . For marine applications, the conductors suitable for coil 234 are preferably insulated with a high dielectric strength plastic sheath impermeable to seawater. Insulated winding wires can be used with sheaths of PVC, PE2+PA and HT4 commonly found in submersible pumps. Coils 234 may be concentric or lap coils and are fully housed within modular stator 220 . Coil 234 can also span multiple slots, and the number of turns can also be scaled across multiple slots to obtain a more sinusoidal MMF.

The support structure 222 can be offset so that the coil 234 can be fully contained within the assembly. Figure 25 shows an example where the upper part 250 of the support structure is offset to the left relative to the bottom part 251 by one stator pole. The first stator pole 252 on the left side extends axially from top to center, while the last stator pole 253 on the right side extends axially from bottom to center. When the first modular stator is assembled to the second modular stator, the last stator pole 253 of the first modular stator combines with the first stator pole 252 of the second modular stator to form a full length stator pole. Such a structure enables easy assembly and removal of the modular stator. The upper part 250 and lower part 251 of the support structure may be offset by a number of stator poles depending on the winding scheme.

For marine applications, a waterproof underwater housing 236 can be made integral to the support structure 222 (FIG. 23). The coil terminals may enter the subsea housing via appropriate compression glands and within the housing 236 itself may be interconnected with other coils within the modular stator. The subsea enclosure 236 may also house the power conversion equipment responsible for converting the power generated within the module. This modular stator 220 simplifies the production process, where each module can be built and tested independently before being fully assembled. They can be configured as "plug and play" to facilitate the exchange and replacement of failed modules.

The modular rotor assembly 221 in FIG. 23 includes two opposing rotors 237 . Each opposing rotor 237 also includes a conductive disc 238 for carrying the induced current and an iron disc (back iron) 239 adapted for magnetic flux return to the stator. The electrically conductive rotor disk 238 may be made of metals with low electrical resistance including copper and aluminum. When assembled, each modular rotor disk 237 may be circumferentially connected to its adjacent rotor disk to form a continuous short circuit path. The ferrous disk 239 may be formed from a discrete stack of ferromagnetic laminations. For applications exposed to corrosive environments, the laminations can be coated with multiple layers of waterproof protective coating and can be housed in a waterproof case. The voids may be filled with a resin compound.

The winding scheme defining the motor phases will now be described with reference to FIGS. 26 to 38 . The term "elementary unit" will be frequently used in order to define a section of elementary windings having a length spanning a pole pair. The modular stator 220 may comprise one or more base units to suit the application.

Fig. 26(a) shows a single-phase axial flux induction motor with an opposing rotor 261 sandwiching a stator 260 according to a second embodiment of the present invention. In this axial flux, single stator configuration, the auxiliary winding is wound at the first layer of the stator 260 while the main winding is wound at the second layer. The two phases are spatially orthogonal to each other. Shaded areas represent stator ferromagnetic poles. Arc 262 represents the end winding link coil side. For example, the coil side (M) at slot 1 is linked to the coil side (M') at slot 8. This motor has non-overlapping concentric windings 262 with an average coil pitch of 6, similar to the prior art motor in FIG. 4 . The top and bottom of the stator 260 are offset by four slots in order to avoid coil splitting or jamming. Figure 26(b) shows that lapped windings 263 with a coil pitch of 6 can also be used, giving the same current link distribution as those shown in Figure 26(a). The winding schemes disclosed below are concentric windings, but it will be understood by those skilled in the art that lapped windings may be used. Fig. 26(c) is a schematic diagram of a winding equivalent to Fig. 26(a), where a plurality of elementary units 264 are connected end to end to form a multi-pole motor. Stator iron and rotor are omitted for clarity. Each elementary cell 264 of the stator 260 spans 16 slots as indicated by bold lines. A modular stator can consist of one or more basic units.

The end windings on the stator side can be manipulated without changing the distribution of the current links. Figure 27 shows an alternative variant of a single phase axial flux induction machine in which an intermediate pole is derived across the boundary between two adjacent elementary cells. Such a winding arrangement enables the stator to be disassembled into aligned modules. A modular stator may comprise one or more basic units defined by the bold lines in FIG. 27 . The corresponding air-gap magnetic fields generated by the main and auxiliary windings are similar in shape to those of Fig. 6(b) and Fig. 6(c). Since the auxiliary coil shown in Figure 27 has 8 coil pitches, as opposed to 6 in Figure 26, the end windings of the former will be correspondingly longer, which makes the machine winding slightly asymmetrical. The resistance increase in the auxiliary phase can be accommodated by using conductors with larger cross-sectional areas, if desired. However asymmetrical windings are common in practical single phase induction motors in order to generate high starting torque.

Appropriately distribute the number of conductors in the slots to resemble a sinusoid. Figure 28 is a winding schematic diagram of a single-phase axial flux motor with approximately sinusoidal windings. Bold fonts represent higher number conductors. The air gap flux density and harmonics for this winding scheme are similar to those of Fig. 9(b). To further reduce unwanted harmonics, the number of concentric coils per elementary unit per phase can be increased to 6, as shown in FIG. 29 . Such a winding scheme increases slot utilization and produces a more sinusoidal magnetic field in the air gap in a manner similar to Fig. 10(a). The fundamental component of the air gap magnetic field is highest and all other higher harmonics are reduced.

The winding principle disclosed in the second embodiment can be extended to three-phase motors. Figure 30 shows a three-phase axial flux machine constructed from multiple basic unit stators. The stator is subdivided into three layers, and the coils of one phase are confined to one layer without overlapping the other. A-phase, B-phase, and C-phase coils are spaced apart at an electrical angle of 120 degrees, and they occupy the top, middle, and bottom layers of the slots, respectively. Each elementary unit spans 12 slots with slot number/pole/phase and average coil pitch equal to 2 and 6 respectively (eg, slots 1-8 and 2-7). Another example of a winding scheme with number of slots/poles/phases and average coil pitch equal to 3 and 9 respectively is shown in FIG. 31 .

The winding scheme of Figures 30 and 31 is equivalent to a full-pitch winding with its phase coils occupying one-third of the total stator slots. The phase coils can be compressed into one layer by having overlapping coils as shown in FIG. 32 . An equivalent short-pitch or single-chord winding is obtained if a second layer with the same coil pitch as the first layer is wound and offset relative to the first layer by a number of slot pitches. Figure 33 shows an example where the upper layer is shifted to the right relative to the lower layer so as to result in an equivalent 8/9 short pitch double layer winding. A basic unit for generating a dual pole pair magnetic field is defined by a thick line. Modular stators can be constructed to include one or more basic units. The windings can be fully contained and defined within the modular stator. This short pitch winding produces an even better sinusoidal air gap MMF than the full pitch solution of FIG. 32 .

The slot utilization of a three-phase axial flux machine can be increased to 67% with the winding scheme shown in Figure 34. Each basic unit has four concentric coils (slots 1-10, 2-9, 3-8 and 4-7) with an average coil pitch of 6 per phase. If lapped coils are used, they occupy slots 1-7, 2-8, 3-9 and 4-10. This winding scheme requires the stator to have staggered ends in order to accommodate the coil side of one of the phases.

Another variant of the winding scheme is shown in FIG. 35 with the same slot utilization as in FIG. 34 but with shorter end windings. Each phase of this winding scheme also occupies one layer and has eight coil sides resulting in pole-pair magnetic fields within 12 stator slots. Within a basic unit, the eight coil sides are split into two sets of concentric coils (slots 1-4 & 2-3 and slots 7-10 & 8-9), which effectively shorten the end windings. A variation of this winding scheme can have a distributed number of turns for a better sinusoidal air gap magnetic field. In FIG. 35, bold text represents slots with a higher number of conductors, eg, the phase A coil spanning slots 1 and 4 has a higher number of turns than its concentric counterpart spanning slots 2 and 3. Another variant of a three-phase axial flux induction machine is shown in FIG. 36 . There are two sets of concentric coils, with each set spanning an average of three slots (eg, slots 1-5 & 2-4 and slots 7-11 & 8-10). The concentric coils can have different numbers of turns to produce a more sinusoidal MMF than using the same number of turns in each coil. Phase coils designated in bold font indicate higher turns.

The concept of a modular stator arrangement can also be applied to axial flux machines with a higher number of phases (4, 5, 6, 7 phases, etc.) according to the second embodiment of the invention. All phases can be connected to a neutral point or can be independent of each other. Fig. 37(a) is an example of a five-phase motor in which phase coils are arranged in five layers (one phase per layer). Figure 37(b) is yet another example of a five-phase motor where all phase coils are compressed into a single layer. A basic unit encapsulates 10 stator slots as shown in bold lines, and one modular stator can include one or more basic units. The spatial angle between each two phases is an electrical angle separated by 72 degrees. Such a machine may have a neutral point and may be fed through a single power converter. Alternatively, the phase coils can also be separate circuits, where each phase is connected to a separate power converter.

A polyphase motor may also include two or more sets of symmetrical phase windings. Figure 38(a) is an example of a six-phase motor composed of two sets of symmetrical three-phase windings A1, B1, C1 and A2, B2, C2. A first set of windings is wound at the upper layer of the stator, while a second set is wound at the bottom layer. The winding arrangement at the upper layer is a mirror image of that at the bottom layer, but the latter is shifted one slot to the right, resulting in a phase shift of 30 electrical degrees. In this example, the base unit spans 12 slots as defined by the bold lines. A modular stator can consist of one base unit or a plurality of base units.

In Figure 38(b), the first set of three-phase windings is fed by a three-phase power converter 380, while the second set is fed by a separate three-phase power converter 381, the phase of which is relative to the power converter 380 30 degrees electrical angle of delay. This six-phase winding configuration has the advantage of eliminating lower harmonics and is more fault tolerant due to its dual power converter layout. In order to further improve the distribution of the MMF, the windings in Fig. 37 and Fig. 38 can be extended to a solution where the coil side occupies multiple slots. Axial flux machines with a higher number of phases can be obtained by using the winding arrangement principles disclosed in the first and second embodiments of the present invention.

third embodiment

The features of the modular axial flux induction motor described above in the first and second embodiments can be extended to other types of motors.

The modular winding scheme can also be extended to linear induction motors. Intuitively, the winding arrangements of Figures 5-21 and 26-38 are similar to linear induction motors. The stator and rotor can be manufactured as a modular unit and assembled together to form a linear motor. If a linear motor rolls on an imaginary line so that one end meets the other, you get a cylindrical radial flux motor. FIG. 39( a ) and FIG. 40( a ) respectively show a radial flux motor having a double-sided stator 390 sandwiching a rotor 391 and a double-sided rotor 401 sandwiching a stator 400 . Such a motor is constructed from the modular stator and rotor of Figure 39(b) and Figure 40(b). Cylindrical single air gap radial flux machines are also available where one side of the double sided stator is omitted and a suitable flux return path is provided. FIG. 41 shows a single air gap radial flux machine constructed from a modular stator 410 and a modular rotor 411 .

Although the features disclosed are specific to axial flux induction machines, the features are still applicable to axial flux or radial flux permanent magnet machines. It is preferred to have a sinusoidal MMF distribution by using greater than or equal to one slot per pole per phase. For high performance, induction motors require an almost sinusoidal current link distribution. The winding schemes described in the previous embodiments are mainly integer slot windings (number of slots/poles/phases are integers). Fractional slot windings (fractional number of slots per pole per phase) offer more degrees of freedom in choosing the number of slots and poles, and are segmented more directly than integer slot windings. However, fractional slot windings are uncommon in induction motors because of the high undesired harmonics associated with the non-sinusoidal current link distribution. These harmonics are not a problem in permanent magnet motors because the air gap flux density is mainly generated by the permanent magnet rotor. As regards current link distribution, any stator winding scheme that meets the requirements of a high performance induction electric machine, including those disclosed above, will more often than not exceed the requirements of a permanent magnet motor than that of a permanent magnet motor.

Figures 42 and 43 show a permanent magnet motor with a double-sided stator and a permanent magnet motor with a double-sided rotor, respectively. The rotor iron of a double sided rotor can be eliminated by using Halbach array permanent magnets as shown in FIG. 44 . The same modular stator and windings can be used in wound field synchronous motors. The air gap field of the motor is generated by the rotor field windings supplied with DC current via slip rings or via a brushless excitation system. 45 and 46 schematically show a field-wound synchronous machine with a double-sided stator and a field-wound synchronous machine with a double-sided rotor, respectively. The wound rotor may also be a set of multi-phase windings connected to the power converter eg via multi-phase slip rings. This type of motor layout is known as a doubly-fed induction motor, where the stator and rotor windings participate in the energy conversion process. An actual synchronous reluctance motor has the same stator and windings as an induction motor, but has a rotor comprising a stack of iron laminations shaped so that they tend to align themselves with the stator magnetic field. 47 and 48 show a synchronous reluctance machine with a double-sided stator and a synchronous reluctance machine with a double-sided rotor, respectively.

Direct drive tidal generators can use rare earth magnets to increase the power density of the generator. Typically, NdFeB magnets are of interest due to their high remanence, high coercivity and high energy yield. However, the sharp rise in the price of rare earth elements in recent years has prompted many industries to consider rare earth-free solutions in order to remain competitive on price. In addition to cost, assembling the stator and permanent magnet rotor together will require specific fixtures due to the unbalanced magnetic pull when the magnets are close to the stator iron. Another disadvantage from a safety point of view is the generator electromotive force (EMF), which exists at the terminals when there is relative movement between the stator and rotor. To avoid risk of electric shock, the rotor must come to a complete stop and remain stationary before any service or repair can be performed.

Embodiments of the present invention may provide an electric machine, particularly a direct drive electric machine, that does not involve the use of gearboxes, drive shafts, and mechanical rolling element bearings. Eliminating these components simplifies the system and reduces cost. Additionally, the motor does not involve the use of rare earth magnets, which could add cost and cause electric shock. The motor in the present invention can be assembled from multiple modular stators and modular rotors. This significantly increases the ease of manufacture and maintenance and further reduces costs. More importantly, the motor of the present invention can generate a sinusoidal air gap magnetomotive force distribution with minimal distortion.

It will be appreciated by those skilled in the art that the above-described embodiments have been described by way of example only and not in any limiting sense, and that design, construction and Various changes and modifications in operational details are possible.

Claims (41)

1. A motor comprising: a plurality of detachable modular stator components configured to be assembled to form a stator; a plurality of rotor components configured to be assembled to form a rotor; One of the stator part and the rotor part having a first radial assembly and a second radial assembly, and the other of the stator part and the rotor part having a third radial assembly ; a separation gap between and defined by the first radial assembly and the second radial assembly; the third radial assembly is positionable within the separation gap between the first radial assembly and the second radial assembly; The rotor is movable relative to the stator. 2. The electric machine according to claim 1, wherein, The first radial assembly includes a first stator assembly, and the second radial assembly includes a stator assembly spaced from, parallel to, and connected to the first stator assembly. a second stator assembly opposite the subassembly; The first stator assembly and the second stator assembly are each configured to receive a plurality of windings therein for generating a substantially sinusoidal magnetic field; and wherein, The third radial assembly includes a stator assembly configured to be positioned within a separation gap and between the first stator assembly and the second stator assembly and further configured to be positioned relative to the first stator assembly. The stator assembly and said second stator assembly move. 3. The motor according to claim 2, wherein the first stator assembly and the second stator assembly respectively comprise iron cores having a plurality of slots. 4. An electric machine according to claim 2 or 3, wherein said first stator assembly and said second stator assembly each have a single phase winding; and said single phase winding of said first stator assembly is at Spatially orthogonal to the single phase winding of the second stator assembly. 5. An electric machine according to claim 2 or 3, wherein said first stator assembly has at least one phase winding and said second stator assembly has at least one phase winding, said first stator assembly and said Said windings of the second stator assembly are substantially geometric mirror images of each other. 6. An electric machine according to claim 2 or 3, wherein said first stator assembly has at least one phase winding and said second stator assembly has at least one phase winding, said first stator assembly and said Said windings of the second stator assembly are offset relative to each other by at least one slot pitch to generate a magnetomotive force equivalent to that generated by short pitch windings. 7. The electric machine of claim 1, wherein: said third radial assembly includes a stator assembly; each of said modular stator components includes a plurality of stator teeth and stator slots; Each of said modular stator components is configured to receive therein a plurality of windings for generating a substantially sinusoidal magnetic field; and wherein, The first radial assembly includes a first rotor assembly and the second radial assembly includes a second rotor assembly, the first rotor assembly configured to be positionable on a first side of the stator assembly and the first rotor assembly. a second rotor assembly configured to be positionable on a second opposite side of the stator assembly, The first rotor assembly and the second rotor assembly define a separation gap therebetween adapted to receive the stator assembly therein such that the first rotor assembly and the second rotor assembly are positioned relative to the The stator assembly moves. 8. An electric machine according to claim 7, wherein the stator teeth and slots are formed from a plurality of discrete iron or non-iron cores. 9. An electric machine as claimed in any one of claims 2, 7 or 8, wherein the magnetic field has substantially the same peak magnitude and spatial relationship throughout the machine. 10. An electric machine as claimed in claim 3 or 8, wherein the iron or non-iron core is watertight. 11. An electrical machine as claimed in any one of claims 2, 3 or 7 to 10, wherein the windings are fully contained and bounded within the modular stator. 12. An electrical machine as claimed in any one of claims 7 to 11, wherein the windings are connected as two phase windings. 13. An electric machine as claimed in any one of claims 7 to 11, wherein the windings are connected as polyphase windings. 14. An electrical machine as claimed in any one of claims 4-6 or 12-13, wherein at least one of said phase windings has a center pole winding arrangement. 15. An electric machine as claimed in any one of claims 2 to 14, wherein the winding is a coil spanning a plurality of stator slots. 16. The electric machine of claim 15, wherein the number of turns of the coil varies proportionally across a plurality of the stator slots. 17. An electrical machine as claimed in any one of claims 2 to 16, wherein the windings are insulated and waterproof. 18. An electrical machine as claimed in any one of claims 1 to 17, wherein an enclosure adapted to accommodate power conversion equipment is integrated into the modular stator. 19. An electrical machine according to any one of claims 1 to 18, wherein each said rotor member comprises at least one selected from the group consisting of: conductive components, permanent magnets, field windings, multiple phase winding or core. 20. An electric machine as claimed in any one of claims 1 to 19, wherein the stator and the rotor are linear. 21. An electric machine as claimed in any one of claims 1 to 19, wherein the stator and the rotor are cylindrical. 22. An electric machine comprising: a plurality of detachable modular stator components configured to be assembled to form a stator; each of said modular stator components includes a first stator assembly spaced apart from, parallel to, and opposite to a second stator assembly; a separation gap between and defined by said first stator assembly and said second stator assembly; each of the first stator assembly and the second stator assembly are respectively configured to receive a plurality of windings therein for generating a substantially sinusoidal magnetic field; and A plurality of rotor components configured to be assembled to form a rotor, and wherein each of said rotor components is configured to be positioned within said separation gap between said first stator assembly and said second stator assembly, and further configured to move relative to the first stator assembly and the second stator assembly. 23. The electric machine of claim 22, wherein the first stator assembly and the second stator assembly each include a core having a plurality of slots. 24. An electric machine according to claim 22 or 23, wherein said first stator assembly and said second stator assembly each have a single phase winding; and said single phase winding of said first stator assembly is at Spatially orthogonal to the single phase winding of the second stator assembly. 25. An electric machine according to claim 22 or 23, wherein said first stator assembly has at least one phase winding and said second stator assembly has at least one phase winding, said first stator assembly and said Said windings of the second stator assembly are substantially geometric mirror images of each other. 26. An electric machine according to claim 22 or 23, wherein said first stator assembly has at least one phase winding and said second stator assembly has at least one phase winding, said first stator assembly and said Said windings of the second stator assembly are offset relative to each other by at least one slot pitch to generate a magnetomotive force equivalent to that generated by short pitch windings. 27. An electric machine comprising: a plurality of detachable modular stator components configured to be assembled to form a stator; each of said modular stator components includes a plurality of stator teeth and stator slots; each of said modular stator components is configured to receive therein a plurality of windings for generating a substantially sinusoidal magnetic field; and a plurality of rotor components configured to be assembled to form a rotor; Each of the plurality of rotor components includes a first rotor assembly configured to be positionable on a first side of the modular stator component and a second rotor assembly configured to be positionable on a second, opposite side of the modular stator component. two rotor assemblies, the first rotor assembly and the second rotor assembly defining a separation gap therebetween adapted to receive the modular stator components therein such that the first rotor assembly and the A second rotor assembly moves relative to the modular stator component. 28. An electric machine as claimed in claim 27, wherein the stator teeth and slots are formed from a plurality of discrete iron or non-iron cores. 29. An electric machine as claimed in any one of claims 22, 27 or 28, wherein the magnetic field has substantially the same peak magnitude and spatial relationship throughout the machine. 30. An electrical machine as claimed in claim 23 or 28, wherein the iron or non-iron core is watertight. 31. An electric machine as claimed in any one of claims 22, 23 or 27 to 30, wherein the windings are fully contained and bounded within the modular stator. 32. An electric machine as claimed in any one of claims 27 to 31 , wherein the windings are connected as two phase windings. 33. An electrical machine as claimed in any one of claims 27 to 31 , wherein the windings are connected as polyphase windings. 34. An electric machine as claimed in any one of claims 24-26 or 32-33, wherein at least one of said phase windings has a center pole winding arrangement. 35. An electric machine as claimed in any one of claims 22 to 34, wherein the winding is a coil spanning a plurality of stator slots. 36. The electric machine of claim 35, wherein the number of turns of the coil varies proportionally across a plurality of the stator slots. 37. An electric machine as claimed in any one of claims 22 to 36, wherein the windings are insulated and waterproof. 38. An electric machine as claimed in any one of claims 22 to 37, wherein an enclosure adapted to house power conversion equipment is integral to the modular stator. 39. An electrical machine as claimed in any one of claims 22 to 38, wherein each said rotor member comprises at least one selected from the group consisting of: conductive components, permanent magnets, field windings, multiple phase winding or core. 40. An electric machine as claimed in any one of claims 22 to 39, wherein the stator and the rotor are linear. 41. An electric machine as claimed in any one of claims 22 to 39, wherein the stator and rotor are cylindrical.