NO974345L - Double-marked permanent magnet machine - Google Patents

Description

The present invention relates to low-speed electric generators and in particular an electric generator for direct-drive wind turbines.

In recent years, wind turbines have received increased attention as alternative energy sources, since they are safe for the environment and relatively inexpensive. With this growing interest, significant efforts have been made to develop wind turbines that are reliable and efficient.

In general, a wind turbine includes a rotor that has multiple blades. The rotor is mounted horizontally into a housing, which is arranged on top of a truss column or a monotube tower. The turbine blades transform wind energy into rotational power that drives one or more generators that are rotationally connected to the rotor via a gearbox. The gearbox is required to increase the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy into electrical energy, which is fed into a utility grid.

Many conventional wind turbines rotate at a constant speed to produce electricity at sixty cycles per second (60 Hz), which is the US standard for alternating current. Since the wind speed changes continuously, these wind turbines must have a system to maintain a constant rotor speed. In such a system, the rotor speed is kept constant by increasing the pitch of the blades as the wind speed rises and decreasing the pitch of the blades as the wind speed falls.

Some turbines work at a variable speed as a power converter is used to adjust the output. As the speed of the turbine rotor fluctuates, the frequency of the alternating current flowing from the generator will also vary. Power converters, which are arranged between the generator and the utility grid, transform alternating current with a variable frequency into direct current, and then it is transformed back into alternating current which has a constant frequency of sixty periods per second.

A wind turbine must be solid and reliable. Since the gearbox of the turbine is expensive, heavy and requires a lot of maintenance, it is desirable to eliminate the gearbox and connect the generator directly to the turbine rotor. Advantages associated with a direct drive wind turbine are improved reliability, lower costs, reduced weight, quieter operation, greater efficiency and a absence of a torque limit.

However, connecting the turbine rotor directly to the generator is problematic since conventional generators are not able to work efficiently at low rotor speeds in the range of 30 to 50 revolutions per minute. A machine which can be used as a generator at low rotor speeds is described in Weh, H.; May, H.; Shalaby, M.: "Highly Effective Magnetic Circuits for Permanent Magnet Excited Synchronous Machines", Proe. ICEM 1990, Vol. 3, pp. 1040-1045.

This transverse flux (TF) machine, shown in Figure 1, comprises an annular rotor (of which only a section is shown), a stationary outer armature winding 4, a

stationary inner armature winding 6, several outer stator core flux conductors 8, and several inner stator core flux conductors 10. The annular rotor 2 includes a first row of permanent magnets 12 and a second row of permanent magnets 14, a ring 16, made of non-magnetic material such as fiber reinforced resin, is arranged between the two permanent magnet rows. The ring-shaped rotor 2 is constructed so that permanent magnets 12 alternate with iron elements 18 and permanent magnets 14 alternate with iron elements 20.

Although the TF machine can work at low rotor speeds, it has several prominent faults or deficiencies. In particular, the TF machine may be exposed to significant gap flux leakage, which adversely affects performance. To understand the nature of this problem, it will help to look at the relationship between

P = Tto, where

P = the power output of the machine

r = torque

co = angular velocity of the rotor.

From the above relationship, it is clear that in order to achieve a high power output (P) at a low angular velocity (co), the torque (r) produced by the machine should be maximized. It is commonly known in the art that in order to achieve a high torque it is necessary to maximize the flux capacity of the machine and to increase the electric current in the armature windings 4 and 6. To obtain additional current in the windings 4 and 6 unwanted energy loss due to heat generation , the cross-sectional area of the armature windings 4 and 6 must be increased.

Furthermore, it is generally known in the art that the torque produced by a machine is proportional to the diameter of the machine squared (or the third power or some other power higher than one) times the length of the machine. In other words,

r=Kd<2>L, where

r = torque

k = constant

L = the active material length of the machine

d = the active material diameter of the machine

The above relationship indicates that to achieve high torque in a compact design or package, the optimal solution is to increase the diameter of the machine rather than its length. In the known system shown in figure 1, if the diameter of the TF machine is to be increased and the length kept constant, only the gap depth of the stator core flux conductors 8 and 10, which contain the respective armature windings 4 and 6, can be increased to maximize the cross-sectional area of the armature windings 4 and 6 (since the depth D is a function of the diameter of the machine), while the slot width W of the stator core flux conductors 8 and 10 (which is a function of the length of the machine) and remains the same.

Figure 2 shows that when gap depth D increases, cross-sectional areas Aa of the gap air gap and the length of the flux path Ls to the steel of, for example, the outer stator core flux conductor 8 also increase, while the cross-sectional area As of the outer stator core flux conductor 8 and the length of the flux path La through the gap air gap remain constant. Since the reluctance R (the resistance that meets magnetic flux in a magnetic circuit) is equal to L/(oA, where

(a = the permeability of the medium

L = the flux path length

A = cross-sectional area of the medium

it is clear from figure 2 that when the slot depth D increases, the reluctance through the steel of the outer stator core flux conductor 8 will increase, while the reluctance through the slot air gap will decrease. Thus, increasing the gap depth D will lead to increased flux leakage whereby flux connections, instead of following the path Ls through the outer stator core flux conductor 8, pass through the gap air gap along the path La. Any flux leaking through the gap along the path La instead of following the path Ls does not reach all the coils in the winding located in

the gap air gap (for example, winding 4 in Figure 1) and thereby does not contribute to producing the torque output of the machine, which causes the power output of the machine to decrease.

Another disadvantage of the TF machine is that due to the asymmetric placement of the two stators (i.e. outer stator core flux conductor 8 and inner stator core flux conductor 10) the reluctances seen by the outer armature winding 4 and the inner armature winding 6 (Figure 6) will be different, which causes an electromagnetic imbalance between the two phases. The reason for the electromagnetic imbalance of the TF machine can be identified in Figure 3. An outer volume 22, which is defined by the outer stator core flux conductor 8 alternating with the air gap 23 is larger than the inner volume 24, which is defined by the inner stator core flux conductor 10 alternating with the air gap 25. Since both volumes 22 and 24 contain the same number of identical stator core flux conductors made of steel, but the outer volume 22 is physically larger than the inner volume 24, the ratio of steel to air in the outer volume 22 is less than in the inner volume 24. Accordingly, the outer volume 22 has a greater reluctance to magnetic flux than the inner volume 24, which causes a magnetic imbalance between the two phases of the outer armature winding and the inner armature winding 6 (not shown in Figure 3). The magnetic imbalance between the two phases of the TF machine leads to circulating currents that contribute to heat loss, bearing currents that can cause failure of the rotor bearings, and uneven loading on the rotor, leading to difficulties in the mechanical and electrical design of the machine.

Furthermore, the possibility of producing a large TF machine (which may be desirable since increasing the number of poles of the machine, and thus its size, will increase its performance at low rotor speeds) turns out to be a difficult task since maintaining small air gap 26, 28 as illustrated in Figure 4, between the annular rotor 2 and outer and inner stator core flux conductors 8 and 10 becomes more difficult as these components increase in size. (It is common knowledge in the art that air gaps between the moving and stationary components of electrical machines must be minimized for maximum power and efficiency. In addition, the TF machine is unsuitable for high-speed operation since the concentric orientation of the stationary outer core flux conductors 8 and the annular rotor 2 is so that when the rotor speed is increased, radial expansion of the annular rotor 2 will gradually reduce the air gap 26 until the annular rotor 2 collides with the outer stator core flux conductors 8, leading to a catastrophic failure of the TF machine.

Furthermore, the TF machine is relatively expensive since it is difficult to produce the complicated stationary assemblies that perceive outer and inner stator core flux conductors 8 and 10 and armature windings 4 and 6. The TF machine uses a lot of copper in its windings, which in turn increases the manufacturing costs. The copper in the windings was used inefficiently since only the segments of armature windings 4 and 6 having thickness T (Figure 4) are used for torque generation (since only these segments of the windings are coupled with magnetic flux). The function of the remaining segments having thickness G (where G>T) is simply to complete the electrical circuit.

The TF machine also has defects in that, due to lack of access to its inner part, it is difficult to remove the heat generated in the inner stator core flux conductors 10 during the operation of the machine, which reduces the efficiency and reduces the output power.

It is therefore desirable to provide a doubly distinct permanent magnet machine which overcomes the aforementioned disadvantages, for example minimizes gap flux leakage, has electromagnetically balanced winding phases, is simple and inexpensive to manufacture, is capable of both low-speed and high-speed operation, facilitates the removal of heat and is compact and efficient.

It is also desirable for a permanent magnet machine to achieve a high power density at low angular speed, to have a high number of poles, to use a conventional winding design for low inductance windings and to have a simple storage structure.

Further advantages of the invention will become clear after reviewing the description and accompanying drawings.

One embodiment comprises the dual distinct axial flux permanent magnet machine according to the present invention, a rotor mounted between a pair of coaxially and laterally oriented stators. The rotor is constructed of a plurality of permanent magnets that alternate with electromagnetically distinct poles made of steel. Each stator has a plurality of longitudinally oriented salient poles. The stator poles support two pluralities of copper coils, whereby each coil is wound around each stator pole. Each plurality of coils is connected in series and thus forms a two-phase winding.

The present invention is illustrated as an example, and in no way limiting, in the figures in the accompanying drawings, where: Fig. 1 is a perspective drawing of a previously known transverse flux (TF)

machine.

Fig. 2 is a perspective drawing of a stator core flux conductor of the known type

The TF machine in Figure 1.

Fig. 3 is a side view of the previously known TF machine in Fig. 1.

Fig. 4 is a detailed drawing of the previously known TF machine in Fig. 3.

Fig. 5 shows in a separate perspective the main component of a double distinct axial flux permanent magnet machine (DSAFPM) constructed according to the present invention. Fig. 6 is a schematic side view of the rotor of the DSAFPM machine shown

figure 5.

Fig. 7 is a perspective view showing a manufacturing technique for the stators

shown in Figure 5.

Fig. 8 is a perspective and partial cross-section of the DSAFPM machine implemented in

accordance with the present invention.

Fig. 9 is a perspective view of a coil for the DSAFPM machine in figure 8. Fig. 10 is a perspective view of the coil in figure 8 with end windings of

different lengths.

Fig. 11 is a schematic drawing showing a converter topology suitable for connecting the DSAFPM machine of Fig. 8 to a push or utility grid, where the DSAFPM machine is connected to a wind turbine rotor.

Fig. 12 shows the detailed diagram of converter topologies for Fig. 11.

Fig. 13 is an electrical circuit equivalent of the DSAFPM machine of Fig. 8.

Fig. 14 is a diagram illustrating torque production for the DSAFPM machine of Fig. 8 at normal speed. Fig. 15 is a diagram illustrating the torque production of

The DSAFPM machine in Figure 8 at high speed.

Fig. 16 is a cross-section of the DSAFPM machine of Fig. 8.

Figs 17-24 show variations in the flux distribution of the DSAFPM machine in figure 8. Figs 25 and 26 are drawings of flux connection which correspond to variations in the flux distribution of the DSAFPM machine in figures 17 to 24. Fig. 27 schematically shows a doubly distinct axial flux permanent magnet machine where each stator includes coils of phase A and phase B windings. Fig. 28 is a cross section of a doubly pronounced axial flux permanent magnet machine that has a dual rotor configuration. Figs 29 and 30 schematically show different rotor orientations for the machine in figure 28.

Fig. 31 is a cross-section of a doubly pronounced radial flux permanent magnet machine according to the present invention.

For illustration purposes, these figures are not necessarily drawn to the same scale. In all the figures, identical components are named with identical reference numbers.

In the following description, specific details are shown to provide a more

thorough understanding of the invention. However, the invention can be practiced without these particular details. In other cases, well-known elements are not shown or described to avoid unnecessary obscuration of the present invention. Accordingly, the description and drawings are to be considered illustrative rather than restrictive

manner.

Figure 5 shows the main components of a doubly distinct axial flux permanent magnet machine according to the present invention. The machine comprises the first stator 100. A rotor 102, and a second stator 104, all of which have an annular shape. The stators 100 and 104 have an outer diameter D, which is the same as the outer diameter of the rotor 102.

The rotor 102 includes a plurality of longitudinally oriented permanent magnets 106, such as rare earth permanent magnets or ferrite permanent magnets. The permanent magnets 106 are spaced equally around the rotor 102 and alternate with a plurality of electromagnetically distinct rotor poles 108 made of a magnetically permeable material, for example laminated steel, and are identical in number to the permanent magnet 106. Each permanent magnet 106 defines a radial dimension T and an angular dimension 9m. The permanent magnet 106 is polarized in a transverse direction, so that the rotor poles 108 are identically polarized on both sides of the rotor, as shown in figure 6 which illustrates the directions of the flux lines 107.

The stator 100 (Figure 5) has a plurality of longitudinally oriented protruding stator poles 110 and a back iron 111. The stator 104 has a plurality of longitudinally oriented protruding stator poles 112 and a back iron 113. The stator poles 110 and 112 are placed at equal distances around their respective stators 100 and 104. Each stator has a number of stator poles equal to the number of rotor poles 108. Each stator pole defines a radial dimension T and an angular dimension Øs.

The stators 100 and 104 each comprise a plurality of discrete laminated steel layers or screens and can be produced in a reasonable manner by rolling up and punching out a strip of steel laminate, as illustrated in figure 7.

Figure 8 is a perspective cross-section of the double pronounced axial flux permanent magnet machine according to the invention. The rotor 102 of the machine is rigidly attached to a main shaft 114, which may be directly coupled to a wind turbine rotor (not shown). The main shaft 114 is stored inside a cylindrical housing 116, which has end surfaces 118 and 120. The shaft 114 rotates in bearings 122 and 124 which are centrally mounted in the respective end surfaces 118 and 120.

The back iron 11 of the stator 100 is rigidly attached to the inner surface of the end face 118, while the back iron 113 of the stator 104 is rigidly attached to the inner surface of the end face 120. Such a placement of the stators 100 and 104 makes it possible to efficiently remove the heat which is generated in the stators by eddy currents and coil currents by conduction to the housing 116 and then by convection to the surrounding atmosphere.

The stators 100 and 104 are oriented so that when the stator pole 112 is completely aligned with the permanent magnets 106, the stator pole 110 is completely aligned with the rotor poles 108 and vice versa. Stator pole 110 stores copper coils 126 and stator poles 112 stores copper coils 128, whereby a coil is located around the circumference of each stator pole. The coils 126 and 128 are of conventional shape and design, and can therefore be inexpensively and easily manufactured and installed in the slots defined by the stator poles 110 and 112.

As shown in Figure 9, the coil 128 comprises an end winding portion E and a conductor portion C. The length of the end winding portion E (which does not take part in the torque generation) is small compared to the length of the conductor portion C. Such a configuration of coils 126 and 128 reduces the inductance in the coils (the inductance is the property of an electrical circuit that a varying current in the circuit produces a varying magnetic field which induces the voltage in the same circuit or in a nearby circuit), which is advantageous for converter-fed machines where the current is controlled by a pulse width modulated voltage which is applied to the machine terminals. This advantage arises because a low inductance winding allows fast dynamic current control since the current closely follows the applied or generated voltage without significant phase difference. Since the end winding part E is small, the copper in the windings is also used efficiently and the costs of the machine are further reduced. The coils 126 and 128 can also have the design shown in figure 10, where the end windings E, and E2 have different lengths.

As illustrated in Figure 11, the coils 126 are connected in series and comprise a phase-A winding 133. The coils 128 are also connected in series, and comprise a phase-B winding 135. The phase-A and phase-B windings 133 and 135 are coupled to an electronic power converter 128 comprising a three-phase DC to AC inverter 134, such as that described in US Patent No. 5,225,712, to William L. Erdman, and a bipolar two-phase inverter 136, which controls the amount of current in both directions through each phase winding. Power is produced when a wind turbine rotor 235 rotates the shaft 114, which is rigidly connected to the wind turbine rotor 235. The inverter 134 is electrically connected to a utility grid 137 and the inverter 136 is electrically connected to phase-A and phase-B windings 133 and 135. The inverters 134 and 136 is connected by means of a direct current (DC connection 138). The converter 129 provides phase current regulation by a pulse width modulated voltage waveform. Furthermore, the converter 129 allows the machine to operate either as a motor or a generator and also allows a variable voltage, variable frequency operation of the machine while maintaining a constant voltage and constant frequency connection to the utility grid.

Figure 12 is a schematic diagram of the inverter 136, which includes several switches 137, such as insulated gate bipolar transistors (IGBT), several driving diodes 139 and a voltage source 140, for example a battery.

A linear model of the doubly pronounced axial flux

the permanent magnet machine, developed based on a finite element modeling analysis (FEM - Finite Element Modeling) can be used to adjust the performance of the machine and to investigate possible control methods for it. The following assumptions are made for this linear model: (1) variation of the inductance as a function of the rotor angle is linear; and (2) the inductance is independent of the current level. The electrical circuit equivalent of the linear model of the double salient axial flux permanent magnet machine shown in Figure 13 is derived as follows:

where

ua= the terminal voltage of phase A;

ub = the terminal voltage of phase B;

ia = phase current to phase A;

ib = phase current to phase B;

ra = resistance in phase A;

r5= resistance in phase B;

Xa= armature reaction flux connection to phase A;

Xb= armature reaction flux connection to phase B;

Further,

where

Yma= permanent magnet flux coupled of phase A

\|/mb = permanent magnet flux coupled of phase B

than further,

where

Mab= mutual inductance between phase A and phase B (flux connected by phase B

divided by the excitation current of phase A);

Mba = mutual inductance between phase A and phase B (flux connected by phase A

divided by the excitation current of phase B);

From the above

where

qr= mechanical degrees of rotor rotation

cor= the angular velocity of the rotor.

This set of equations is shown schematically in figure 13, where the following definitions apply: ema= induced voltage in phase A produced by permanent magnet flux variety;

emb = induced voltage in phase B produced by permanent magnet flux variation;

era = reluctance voltage in phase A produced by the variation of

the self-inductance in phase A;

erb= reluctance voltage in phase B produced by the variation of

self-inductance in phase B;

erma = reluctance voltage in phase A produced by the variation in mutual

inductance between phase A and phase B;

emb = reluctance voltage in phase B produced by the variation in mutual

inductance between phase A and phase B;

Laa = the self-inductance in phase A;

Lbb= the self-inductance in phase B;

Mab= mutual inductance between phase A and phase B;

The torque is given by:

where

Tma= ia x d^j/door = mechanical torque produced by phase A

Tmb= ib x d^t/de, = mechanical torque produced by phase B

Under normal operating conditions, the self-reluctance torque of phase A and phase B will cancel each other, as shown in Figure 14. The mutual reluctance torque has a zero average value. The peak reluctance torque is small since the variation in mutual inductance is relatively small as a result of the double air gap structure of the double pronounced axial flux permanent magnet machine. As a result, torque production is very smooth.

When the operating speed of the machine is higher than the rated value, the self-reluctance torque can be used to compensate for the power loss due to the irregular current waveform using the control methods illustrated in Figure 15. Therefore, the double pronounced axial flux permanent magnet machine is able to withstand higher speeds than known permanent magnet machines. At higher speeds, the mutual reluctance still contributes to achieving zero average torque.

A non-linear model of the doubly pronounced axial flux permanent magnet machine can be produced if X,a and Xb are defined as follows:

Since the stators 100 and 104 are identically shaped, the reluctances seen by the phase-A winding and the phase-B winding will be equal, and this establishes an electromagnetic balance between the two phases. Electromagnetic balance between the two phases is advantageous as circulating currents, bearing currents and various loads on the rotor are theoretically eliminated, thereby increasing the efficiency and reliability of the machine.

As shown in Figure 16, there is an air gap 130 between the rotor 102 and the poles 110 (indicated by the dotted line) of the stator 100. Similarly, there is an air gap 132, which has the same width as the air gap 130, between the rotor 102 and the stator poles 112 It is well known that by minimizing the air gap between the rotor and the stator of an electric machine, this will lead to increased power and efficiency. The axial configuration of stator 100, rotor 102, and stator 104 allows for small air gaps 130 and 132 regardless of the size of rotor 102 and stators 100 and 104, thus reducing the manufacturing costs of a physically large machine. Such a machine could occupy a large number of poles and make it possible to have a high yield at low rotor speeds. Due to the aforementioned axial configuration, the radial expansion of the rotor 102 does not reduce the air gaps 130 and 132 at high rotor speeds, which, combined with the fact that the uniform shape or form of the rotor 102 reduces wind resistance (loss due to air friction), provides a additional advantage is that high-speed operation is possible.

Furthermore, the gap flux leakage of the dual pronounced axial flux permanent magnet machine is minimized since a folded Wctil coil 126 and 128 is increased rather than a gap depth Ds to achieve high torque generation. As explained in detail in the previous section of the description, minimizing the gap depth Ds leads to reduced gap flux leakage.

The operation of the above-described embodiment of the invention is illustrated with reference to figures 17 to 24. When the rotor pole 108 is fully aligned with the stator poles 110, the permanent magnets 106 are fully aligned with the stator poles 112 (figure 17). This orientation of the rotor 102 (which corresponds to 0 degrees of rotor rotation) brings all the magnetic flux connections 127 produced by the permanent magnets 106 into connection with the phase-A winding (not shown in Figure 17) of the stator 100. No flux connects the phase-B winding (not shown in Figure 17) to stator 104 in this case.

When the rotor 102 has rotated 22.5° (figure 18), the poles 110 and 112 are partially aligned with the poles 108 of the rotor 102, so that flux linkages 127 produced by the permanent magnets 106 are equally distributed between the stator 100 and the stator 104. In this case, the flux connection to the phase-A winding (not shown in figure 18) equal to the connection to the phase-B winding (not shown in figure 18).

At 45° (figure 19), the rotor 102 is located so that the stator poles 110 are fully aligned with the permanent magnet 106 and the stator poles 112 are fully aligned with the rotor pole 108. With this orientation of the rotor 102, all the flux connections 127 produced by the permanent magnets 106 are connected to the phase-B winding (not shown in figure 19) to the stator 104.

Flux distributions at 67.5°, 90°, 112.5°, 135° and 157.5° of the rotor 102 are shown in the respective figures 20, 21, 22, 23 and 24. Drawings of the flux connections 127 to phase-A and the phase-B windings corresponding to from 0 to 180 mechanical degrees of rotation are shown in the respective figures 25 and 26. The phase shift between the phase-A and phase-B currents of the double pronounced axial flux permanent magnet machine is 90° electrical.

Thus, a permanent magnet machine is provided which overcomes the foregoing disadvantages, for example minimizes gap flux leakage, has electromagnetically balanced phases, is simple and inexpensive to manufacture, is capable of being operated at both low speed and high speed, facilitates heat removal, and is compact and efficient.

The double pronounced axial flux permanent magnet machine is also advantageous because of its characteristic of achieving a high power density at low angular speed, of adopting a high pole number, of using a conventional winding design with the low induction winding, and of using a simple storage structure.

Many other modifications of the apparatus, some of which are described here, are possible. For example, it can double pronounced axial flux

permanent magnet machine have any number of stator poles greater than 2. Furthermore, it is not necessary that the ratio between stator poles (for example, stator 100) and rotor poles be equal to 1 to 1. Depending on the size of the machine, this ratio can be changed in accordance with the following formula:

R = S + 2, where

S = number of stator poles

R = number of rotor poles.

In addition, other suitable stator/rotor pole arrangements are possible. For example, it may be appropriate to have a combination of two stator poles and any equal number of rotor poles greater than 4, for example 2/6, 2/8, .... 2/100 etc. Other combinations, for example 4 /8, 4/10, 4/12, etc, 6/10, 6/12, 6/14, etc., etc. can also be used.

Furthermore, the coils of the phase-A and phase-B windings can be positioned so that each stator contains phase-A as well as phase-B coils. Figure 27 schematically illustrates a dual salient axial flux permanent magnet machine having a 16-pole rotor 150. A first two-piece stator 152 and a second two-piece stator 156. The rotor 150 includes permanent magnets 155 and electromagnetically salient poles 157. Stator 152 includes a phase-A portion 160, which has poles 151, and a phase-B part 162, which has poles 153. Stator 156 comprises a phase-B part 164, which has poles 154 and a phase-A part 168 which has poles 158. The poles of phase- A parts 160 and 168 store coils 170 which are connected in series and comprise the phase A winding. Poles of the phase-B parts 162 and 164 carry coils 172 which are connected in series and comprise the phase-B winding. In Figure 27, the orientation of the rotor 150 in relation to the stators 152 and 156 is such that all the magnetic flux connections 127 produced by the permanent magnets 155 connect the coils 170 to the phase-A winding. Another implementation of the topology in this embodiment is where the number of rotor poles, R, is an integer multiple of ten, while the number of stator poles, S, is calculated in accordance with the formula S = R (4/5).

Figure 28 shows an embodiment of the double pronounced axial flux permanent magnet machine which has a dual rotor configuration. The machine comprises a first stator 200, a first rotor 202, a second stator 204, a second rotor 206, and a third stator 208, each of which has an annular shape. Stators 200, 204, and 208 include respective back irons 210, 212, and 214. Stator 200 has a plurality of longitudinally oriented salient stator poles 216 and stator 208 has a plurality of longitudinally oriented salient stator poles 218. Poles 216 and 218 are equally spaced around their respective stators. 200 and 208. The stator 204 has two juxtaposed pluralities of longitudinally oriented salient poles 220(a) and 220(b), where the poles 220(a) and 220(b) are equally spaced around the stator 204.

Several copper coils 222, 224(a) and (b), and 226 are connected so that coils 222 and 226 comprise the phase-A winding and coils 224(a) and (b) comprise the phase-B winding. Individual coils 222 and 226 are arranged around stator poles 216 and 218. Individual coils 224(a) and (b) are arranged around stator poles 220(a) and (b).

Figure 29 illustrates that the rotors 202 and 206 are constructed of several longitudinally oriented permanent magnets, respectively 203 o 2025, which alternate between several electromagnetically distinct rotor poles, respectively 207 and 209, made of, for example, laminated steel. Gaps G1tG2lG3 and G4 separate stator 200 and rotor 202, rotor 202 and stator 204, stator 204 and rotor 206 and rotor 206 and stator 208.

As shown in Figure 28, the rotors 202 and 206 are rigidly attached to a rotor bearing 228, for example by means of screw-type fasteners 230 and 231. The rotor bearing 228 is attached relative to a main axis 232, for example by means of a weld seam (not shown ). The shaft 232 is rotatably supported in a housing 234 which has end surfaces 236 and 238 and a cylindrical body 240, and can be directly connected, for example to the wind turbine rotor 235. The stators 200 and 208 are rigidly attached to the end surfaces 236 and 238, for example by of screw-type fasteners 242 and 244. The stator 204 is rigidly attached to the cylinder body 240, for example by means of screw-type fasteners 246.

In the case when the number of stator poles is equal to the number of rotor poles (figure 29), the stators 200, 204 and 208 are oriented so that when the poles 207 and 209 are fully aligned with the poles 220 of the stator 204, the permanent magnets 203 are fully aligned with the poles 216 and the permanent magnets 205 is fully aligned with poles 218. This orientation of rotors 202 and 206 causes flux linkages 127 produced by permanent magnets 203 and 205 to couple coils 224(a) and (b)

(not shown in figure 28) to the phase-B winding. Similarly, when the permanent magnets 203 and 205 are fully aligned with the poles 220 (Figure 30), the poles 207 and 209 are fully aligned with the respective poles 216 and 218. This orientation of the rotor 202 and 206 causes flux linkages 127 produced by the permanent magnets 203 and 205 to connect the coils 222 and 226 (not shown in figure 30) to the phase-A winding.

The dual distinct axial flux permanent magnet machines are not limited to single or dual rotor configurations. It is also possible with variations that have three or more rotors and different ratios between rotor and stator poles.

Furthermore, a radial flux version of the double pronounced permanent magnet machine can also be implemented, as shown in figure 31. Such a machine comprises an outer stator 300 and an inner stator 302 which is concentrically oriented with respect to the outer stator 300. The stator 300 includes a plurality of radially oriented and equally spaced salient poles 304 facing inwardly. A plurality of copper coils 306, wound around the poles 304 and connected in series, form an A-phase winding. The stator 302 includes a plurality of radially oriented equally spaced salient poles 308, which face outwards. A plurality of copper coils 310, wound around the coils 308 and connected in series, constitute a phase-B winding. The stators 302 have respective back irons 312 and 314.

A concentric rotor 316 is arranged between the outer stator 300 and the inner stator 302. The rotor 316 comprises several permanent magnets 318 which alternate with an equal number of electromagnetically distinct rotor poles 320, made of, for example, laminated steel. Permanent magnets are placed at equal distances around the rotor 316 and in a number equal to the number of poles 304 and 308. The rotor 316 may be directly connected to a wind turbine rotor (not shown). The principle of operation of this embodiment of the invention is the same as that of the double pronounced axial flux permanent magnet machine described above.

As with the axial flux embodiments of the invention, the ratio of the number of rotor poles to the number of stator poles can vary. Furthermore, the coils in this machine do not need to be connected so that the coils of one stator comprise the A-phase winding and the coils of the other stator comprise the B-phase winding.

The above-mentioned embodiments of the double pronounced permanent magnet machine are only given as examples. The scope of the invention must therefore not be established on the basis of the given examples, but is given in the accompanying patent claims and their equivalents.

Claims (30)

1. Double-distinct permanent magnet machine, characterized in that it includes: at least two stators which are coaxially fixed with respect to each other; at least one rotor arranged between the at least two stators; and a two-phase winding carried by the at least two stators. 2. Double-distinct permanent magnet machine according to claim 1, characterized in that each of the at least two stators includes a plurality of distinct stator poles and has an axis of symmetry. 3. Double-pronounced permanent magnet machine according to claim 2, characterized in that the prominent stator poles are shaped longitudinally in relation to the axis of symmetry. 4. Double-pronounced permanent magnet machine according to claim 2, characterized in that the prominent stator poles are shaped radially in relation to the axis of symmetry. 5. Double-distinct permanent magnet machine according to claim 1, characterized in that the at least one rotor includes a plurality of permanent magnets. 6. Double-distinct permanent magnet machine according to claim 5, characterized in that the permanent magnets alternate with electromagnetically distinct rotor poles made of a magnetically permeable material. 7. Double-distinct permanent magnet machine according to claim 6, characterized in that each of the electromagnetically distinct rotor poles has a first and a second side, and the permanent magnets are polarized so that the first side has the same magnetic polarization as said second side. 8. Double-distinct permanent magnet machine according to claim 1, characterized in that the two-phase winding comprises a first and a second plurality of coils. 9. Double-distinct axial flux permanent magnet machine, characterized in that it comprises: at least two stators which are coaxially and laterally arranged relative to each other; at least one rotor arranged between the at least two stators; and a winding having a first phase and a second phase, the winding being carried by the at least two stators. 10. Double-distinct axial flux permanent magnet machine according to claim 9, characterized in that each of the at least two stators has a plurality of distinct stator poles and an axis of symmetry. 11. Double-pronounced axial flux permanent magnet machine according to claim 10, characterized in that the prominent stator poles are equally distributed around each of the at least two stators and shaped longitudinally in relation to the axis of symmetry. 12. Double-pronounced axial flux permanent magnet machine according to claim 9, characterized in that the at least one rotor includes a plurality of permanent magnets which are equally placed around said at least one rotor and inserted between a plurality of electromagnetically distinct rotor poles made of a magnetically permeable material, as each of the electromagnetically distinct rotor poles has a first and a second side, and the converter is polarized so that the first side has the same magnetic polarization as the second side. 13. Double-distinct axial flux permanent magnet machine according to claim 9, characterized in that the first phase comprises a first plurality of coils which are connected in series and the second phase comprises a second plurality of coils which are connected in series. 14. Double-distinct axial flux permanent magnet machine according to claim 13, characterized in that the first plurality of coils is carried by one of the at least two stators, and the second plurality of coils is carried by the other of the at least two stators. 15. Double-distinct axial flux permanent magnet machine, characterized in that it comprises: at least two stators which are coaxially and laterally arranged in relation to each other, each of the at least two stators having an axis of symmetry and S pronounced stator poles, where S is an even integer equal to or greater than two, and the pronounced stator poles are equally distributed around each of the at least two stators, and the distinct stator poles are shaped longitudinally in relation to the axis of symmetry; at least one rotor is inserted between the at least two stators, the at least one rotor including P permanent magnets, where P is an even integer equal to or greater than two, and the permanent magnets are equally distributed around the at least one rotor and alternate with R electromagnetically distinct rotor poles made of a magnetically permeable material, where R is an integer equal to P; and a winding having a first phase and a second phase, the winding being carried by the at least two stators, and the first phase comprising a first plurality of coils connected in series, and the second phase comprising a second plurality of coils connected in series. 16. Double-distinct axial flux permanent magnet machine according to claim 15, characterized by atR = S. 17. Double-distinct axial flux permanent magnet machine according to claim 15, characterized by atR = S + 2. 18. Double-distinct axial flux permanent magnet machine according to claim 15, characterized by R = S + X, where X is an even integer equal to or greater than four. 19. Double-pronounced axial flux permanent magnet machine according to claim 15, characterized in that the first plurality of coils is wound around the prominent stator poles of one of the at least two stators, and the second plurality of coils is wound around the prominent stator poles of the other of the at least two stators. 20. Double-prominent axial flux permanent magnet machine according to claim 15, characterized in that the first plurality of coils is wound around the prominent stator poles of both of the at least two stators, and the second plurality of coils is also wound around the prominent stator poles of both of the at least two stators. 21. Double-distinct axial flux permanent magnet machine according to claim 20, characterized in that R is a multiple of ten and S = R(4/5). 22. Double-distinct axial flux permanent magnet machine according to claim 15, characterized in that the coils consist of copper, the magnetically permeable material consists of steel, and the at least two stators comprise a steel laminate. 23. Double-distinct axial flux permanent magnet machine, characterized in that it comprises: at least three stators coaxially and laterally arranged with respect to each other; at least two rotors interposed among the at least three stators; and a winding which has a first phase and a second phase, the winding being stored by the at least three stators. 24. Double-pronounced axial flux permanent magnet machine according to claim 23, characterized in that the at least three stators define a first lateral lateral stator, a second lateral or lateral stator, and a center stator, and each of the at least three stators has S pronounced stator poles, where S is an even integer equal to or greater than two, and the first phase comprises a first plurality of coils and the second phase comprises a second plurality of coils, and the first plurality of coils are wound around the distinct stator poles of the central stator, and the plurality of coils are wound around the distinct stator poles of the first lateral and the second lateral stator. 25. Double-distinct axial flux permanent magnet machine according to claim 24, characterized in that each of the at least two rotors has P permanent magnets, where P is an even integer equal to or greater than two, and the permanent magnets alternate with R electromagnetically distinct rotor poles made of a magnetic permeable material, where R is an integer equal to P. 26. Double-distinct axial flux permanent magnet machine according to claim 25, characterized in that R = S. 27. Double-distinct axial flux permanent magnet machine according to claim 25, characterized in that R = S +2. 28. Double-distinct axial flux permanent magnet machine according to claim 25, characterized by atR = S + X, where X is an even integer equal to or greater than four. 29. Double-distinct permanent magnet machine for a direct-drive wind turbine, characterized in that it comprises: at least two stators which are coaxially arranged with respect to each other; at least one rotor interposed between the first at least two stators and rigidly connected to a wind turbine rotor; and a two-phase winding stored by the at least two stators and electrically connected to a utility network by means of an electronic converter. 30. Double-distinct permanent magnet machine according to claim 29, characterized in that the electronic converter comprises a three-phase inverter which is electrically connected to the utility grid and a two-phase inverter which is electrically connected to the two-phase winding, and the three-phase inverter is connected to the two-phase inverter by means of a direct current coupling .