The machine that is claimed pertains to the technical field of electromagnetic generators and motors. It is a device to transform mechanical power, i.e. a moving force, into electrical energy, and vice-versa. It is an electrical machine in which the magnetic flow enters the rotor by transference through a passive air gap from a source of static magnetic flow.
There are automotive alternators in which electromagnetic excitation is static, but whose magnetic flow passes through four air gaps and the shape of the magnetic circuit thereof in the stator is of the conventional type, all of which make them completely different from the one that is claimed.
The utility model U 200402396 owned by one of the applicants of this invention patent, has static electromagnetic excitation, with a single central axial coil and only two air gaps per pole, as claimed in this invention patent.
However, the proposal in this patent includes excitation by means of only one central permanent axial magnet 12 and by several 10, on the disk or on the axial armature, alone or combined with multiple excitation coils 11 with their cores incorporated between the central part of the disk 8 and the outer ring-shaped crown of the disk 8 or between the two rings of the axial armature 6; the shape and distribution of the rotor and stator poles is specific to this patent; there is multiple flow variation, triple in the embodiment presented; all of which makes it substantially different from the aforementioned utility model in the structure thereof and the effects produced.
It is also different from the aforementioned utility model because, with the addition of the squirrel cage 18 on the rotor 2, the new basic synchronous alternator is transformed into an asynchronous motor-alternator, one of those identified as being preferred for driving electric and hybrid vehicles, and for wind turbines, without the problems that this addition causes in conventional synchronous alternators.
The technical problems of the conventional machines and the reasoned solutions that the proposed invention brings are presented below.
a). In all generators, and especially those aimed at automotives and wind generation, obtaining power at low speeds without increasing the size of the machine is a problem, since at high speeds the voltage is more than sufficient and therefore must be limited by the chosen regulation system.
The voltage calculations, applying the relevant electro-technical formulas show this assertion.
The basic formula:
Voltage=Flow variation/Time taken for variation to take place
Applied correctly, the formula proves it and the experiment confirms it.
b). Cooling at low speeds is also a problem for conventional alternators, because it limits the power that may be obtained. The cross-section of the electrical conductor of the stator winding determines the number of turns per coil and this determines the coil voltage. The greater the voltage per turn obtained, the less ohmic loss there is because fewer turns per coil are needed for the same coil voltage.
It is clear that the innovation reduces the unwanted heat produced as the voltage is considerably increased and the length of the coil wire is reduced, and thus the ohmic resistance thereof.
c). Another problem that conventional automotive alternators have is the amount of copper that the excitation coils require, and the heat these generate.
It may be seen in
The calculations show that for the same number of ampere-turns and equal copper wire diameter, this arrangement requires a fraction of the copper wire length of a conventional one and has a much larger outer cooling surface and much less ohmic resistance than a conventional one because a central coil on a large-diameter core is substituted for several on small cores. The amount of heat generated by the excitation current is less due to the lower ohmic resistance. Moreover, and very importantly, the amount of copper used in excitation, in the case of electromagnets, is much less than in conventional ones. In the multiple coil version, it is one third. Therefore, they generate much less heat. The calculations show that for the same induction in the active air gap, the amount of copper is approximately a third and the heat dissipated is half or less. In addition, the cost is lower, despite there being several coils, because they are smaller and have much less copper.
The excitation coil cooling is much better because they generate less heat and because they are joined to a significant mass of iron, situated on the outside of the machine and the exposure thereof to the cooling medium, generally air, is much greater and more efficient due to having a greater surface than a single, large-diameter central coil. A simple calculation shows that the surface of automotive alternators equally exposed to induction in the active air gap is much greater with multiple coils than with one central coil.
The air cooling fan 28 does not necessarily need to be mounted only on the rotor. There may be another 21, with a larger diameter and more efficient, mounted on the outside of the magnetic keeper, but inside the armature 27 of the machine.
This enables the heat created when electrical power is generated to be slowly expelled outside. This is very important.
Likewise, the number of ampere-turns may be increased because there is space for it, without affecting the size of the rotor and stator due to scale. This is also very important.
d). In conventional and automotive alternators,
In the innovation there are no rings nor the brushes thereof because the excitation coils are static. This, too, reduces cost.
e). The use of permanent magnets instead of excitation coils is highly valued, because it does not use copper in the excitation, but it has the drawback that the permanent magnets in the known generators are placed on the rotor. Voltage regulation must be done through the stator by complicated and expensive means because the permanent magnets give a certain, fixed induction and rotate with the rotor.
f). Wind turbines with conventional permanent magnets have a certain start-up torque called “cogging”, which prevents them from starting up at certain wind speeds, even though it is sufficient to generate energy once started-up.
The innovation that is proposed resolves these two problems, e) and f), since the excitation magnet or magnets 10 are not on the rotor; they are static since they are on the outer core and the magnetic field acting upon them may be adjusted via a coil of electricity-conducting filament 13 wrapped around them or via the combination of permanent magnets and electromagnets to regulate and eliminate cogging. This is achieved in the following way: see
The magnetic polarity of the permanent magnets 10 and the electromagnets 11 faces in the same direction, for example, towards the periphery of the disk 8. See
If there were only permanent magnets, 10 and 12, as the windings 13 that are on them are excited with an inverse current, they subtract their own flow from that of the magnets until they are cancelled out. The windings 13 are also used to restore the magnetism of the magnets in the event that they have lose it.
The use of electromagnets combined with permanent magnets, with or without coils on the latter, to produce excitation, which is claimed in this patent, may also be applied to generators in which excitation is installed in the rotor,
In both cases, the form described above enables very simple and low-cost regulation to be carried out, as well as removing the cogging or start-up torque due to the presence of the permanent magnets. This is very important for wind turbines, especially those with power between 3 and 8 kW.
g). Conventional synchronous alternators cannot be converted into asynchronous motors because they have the problem that during start-up and, to a lesser extent, normal operation, the rotation field of the stator induces dangerous currents in the windings of the inductor, because the magnetic circuit closes through the poles of the rotor where the inductor coils are located. See
Generators with excitation by magnetic transference technology, have a secondary or passive air gap 4, as stated in the description,
When operating as a hypo-asynchronous motor or hyper-asynchronous generator, only the existing dispersion flow and the regulation flow pass through the secondary air gap 4. It has been demonstrated experimentally this it is very small.
This essentially differentiates the machine claimed as a synchronous generator and asynchronous machine, with conventional synchronous alternators with squirrel cage or coil rotor start-up, in which the two air gaps are active. This difference is very important, as explained below:
The rotation field produced by the stator, supplied by the appropriate polyphase voltage and current system, produces high induced voltage in the excitation coils in conventional synchronous alternators, because they are in the rotor and are crossed by it. See
h). In the case of generators with conventional permanent magnets placed in the rotor, the conversion to an asynchronous motor is not possible because it demagnetises the magnets.
The innovation proposed does not have this problem because the magnets are not in the rotor but rather in the external core where the flow induced by the stator coils does not reach, which coils close over the keeper of the rotor as in a conventional asynchronous machine. See
FIG. 1.—Cross-section of the innovated alternator, with coils and permanent magnets in the disk, in the axial armature and the central core.
FIG. 2.—Arrangement of magnets and electromagnets and regulation and anti-cogging coils on the disk.
FIG. 3.—Flows in the innovated alternator.
FIG. 4.—Flows in the conventional alternator.
Below is a description of an embodiment and of the various possibilities with the technology contained in the explanation and in the claims, without this entailing any restriction on the scope of the patent.
All the components that form part of the innovation have been included, for a better understanding thereof, even if their number and presence are not the same as those in other embodiments.
The machine has an aluminium front shield 22 that houses the rolling front bearing 23, for the shaft 24 of the machine, which rotates at its other end on another bearing 25 whose support 26 is held in the disk of the external magnetic core 3 to guarantee the air gaps 4 and 5. An aluminium outer cover 27 closes the protective armature, which contains the main fan 21. There are another two internal fans, 28.
The stator 1 is joined by mechanical contact to the external core 3, which in turn is facing the rotor 2 through the secondary or passive air gap 4.
The inducing coils 11 and the permanent magnets 10 are inserted in the magnetic circuit 29, with the polarities thereof facing in the same direction as the field, 30,
The poles 16 of the rotor 2 face the poles 14 of the stator, through the active air gap 5. See
In
The electromagnet 12 is situated in the central area surrounded by a coil 13, in the same way as the other permanent magnets 10 situated in the disk 8.
The magnetic flow path in
There are several ways to operate as a synchronous generator:
All of them have the advantage of being able to transform into an asynchronous machine by adding a squirrel cage 18 on the rotor.
The appropriately supplied electromagnets are equivalent to a permanent magnet, both with equal polarity facing, for example, towards the periphery of the disk 8, see
As the excitation is removed from the electromagnets, the flow of the permanent magnets closes on itself, cogging is eliminated and the voltage is easily regulated and at a low cost. This play of magnetic fields is represented in
This requires the number of electromagnets and permanent magnets to be the same.
The cost of several excitation coils with the cores thereof is lower than that of the single central coil used by automotive alternators because it has much less copper as the diameter of the core is much smaller. A simple calculation demonstrates this.
With regard to the poles or projections of the keepers of appropriate magnetic material, for example a thin magnetic sheet to reduce losses due to hysteresis,
In the innovated alternator,
Each stator pole faces one rotor pole, and as each turn of the coil comprises three stator poles, the flow variation, for equal speed and flow, is triple, the voltage thereby being triple.
In the conventional alternator,
The rotor of a conventional synchronous machine with permanent magnets,
The same effect is achieved by combining permanent magnets and electromagnets in a manner similar to that explained above for the excitation mounted on the disk 8 of
Position 34,
Number | Date | Country | Kind |
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P201200334 | Mar 2012 | ES | national |
Filing Document | Filing Date | Country | Kind |
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PCT/ES2013/070184 | 3/21/2013 | WO | 00 |