The invention under consideration concerns a synchronous machine with a stator and a rotor.
Synchronous machines normally comprise a stationary stator and a rotor which can move relative to the stator. The stator of a synchronous machine is usually provided to hold an electrical winding, which can be multiphase. For example, in a three-phase alternating current machine, the windings correlated with the three electrical phases are electrically phase-shifted by 120°, relative to one another.
In the rotor, permanent magnets are frequently used. Alternatively, electromagnets are possible, wherein here a direct current, which flows through coils wound around rotor teeth, is used. The direct current can be transferred into the rotor via brushes or via exciter windings and a rotating rectifier.
A synchronous machine means that the rotor and the rotating field of the stator rotate at the same speed.
An electromagnetic torque on the shaft of the stator is created by the interaction of the magnetic fields of the stator and the rotor.
For some time, synchronous machines with permanent magnets, so-called PM machines, have been on the rise, because they interconnect a high energy density, a compact design, a high efficiency, and a wide rotational speed range. In the last few years, however, the prices for permanent magnet material have gone up considerably. Moreover, there are certain application cases, such as the short circuit case, which limit the use of PM machines in some applications.
Therefore, the current-energized synchronous alternating current machines are an interesting alternative for the future.
A direct current is hereby used, in order to produce the stationary magnetic field of the stator. As already indicated above, the direct current needed for the creation of the field is first transferred from the stator to the rotor. For this, additional windings are usually used in the stator. The additional energy is transferred via the air gap into exciter windings of the rotor and there rectified with the aid of the rectifier and supplied to the field winding(s) which produce the stationary magnetic field of the rotor with the direct current thus obtained. This principle is often designated as self-excitation.
Such self-excited machines are used, for example, in wind generators.
The auxiliary winding in the stator, which the magnetic field makes available for the transfer of the energy into the rotor, is mostly called the exciter field winding and is frequently operated with direct current.
For this, a rectifier is normally also required in the stator. Beyond that, the additional winding is needed in the stator, which is also called the stator auxiliary winding. This leads to the larger stator volume. The auxiliary winding must be sufficiently insulated with respect to the other windings.
Another disadvantage of the described machine type is that windings with q>1, overlapping one another and frequently distributed in the stator, are used, wherein q is the number of the coils per phase and per pole. For the exciter winding in the rotor, a large number of coils per winding are required. A higher engine inertia leads, moreover, to impaired dynamic characteristics of the electric machine. In some known machines, additional slots are needed in the rotor, in order to be able to introduce the field winding and the exciter windings of the rotor into the same rotor core. In this way, the result is also a complex production process.
In the analysis of the harmonics in the air gap, it is evident that the auxiliary winding in the stator produces higher harmonics in the air gap, which form a stationary field. The higher harmonics which are produced by the multiphase main winding of the stator rotate in time, but at different speeds. Thus, there are different harmonics which appear at different rotational speeds, which leads to a fluctuation of the induced voltage in the rotor exciter windings. This leads to a negative influencing of the operating characteristics of the synchronous machine.
The goal of the invention under consideration, therefore, is to make available a synchronous machine with improved characteristics.
In accordance with the invention, the goal is attained by a synchronous machine with the features of the independent patent claim. Developments and refinements are indicated in the dependent patent claims.
In one embodiment, a synchronous machine comprises a stator and a rotor which is situated so it can move relative to the stator. The stator comprises at least one concentrated winding, which is situated in the slots of the stator. An auxiliary winding is not provided separately in the stator. In the rotor, a first winding system is provided, which is set up as the exciter winding and can absorb the energy from the field in the air gap. Furthermore, at least one second winding system is provided, which is set up as the field winding, that is, which is able to produce a stationary magnetic field. Moreover, a rectifier is provided in the rotor, which is connected between the first and the second concentrated winding system, in order to make available the direct current for the production of the magnetic field of the rotor. The first and second winding systems of the rotor comprise a concentric winding.
Since the stator does not have an auxiliary winding, the rectifier bridge for this is also omitted in the stator. With the at least one concentrated winding of the stator, which is normally designed multiphase, both the work harmonic for the synchronous machine is produced as well as, purposefully, a higher harmonic, which serves to supply the rotor via its excitation winding.
Thus, the proposed principle permits a simplified structure of a synchronous machine, which can dispense with the permanent magnets of the rotor.
In one refinement, the at least one concentrated winding of the stator is designed as a multiphase, especially three-phase, concentrated winding. A concentrated winding can be produced at particularly low cost, in comparison to a distributed winding which is made via several teeth and overlapping in phases. In addition, the multiphase design permits a harmonic field distribution and, moreover, a simple connection of the machine to an electrical multiphase system.
Alternatively or additionally, the first winding system of the rotor, that is, the exciter winding, is also designed multiphase as a concentrated winding.
As the work harmonic, the basic harmonic of the magnetomotive force is not used, but rather a higher harmonic of the magnetomotive force which is produced by the stator winding. For example, in a machine with twelve slots in the stator and ten poles in the rotor and a teeth-concentrated winding in the stator, the fifth harmonic can be used as the work harmonic.
Additionally preferred, a higher harmonic of the electromotive force of the stator, different from the work harmonic, is used as the exciter harmonic for the supply of the exciter winding. In the example mentioned for a concentrated winding with twelve slots and ten poles, the seventh harmonic can be advantageously used as the exciter harmonic.
One can clearly see in this example that a higher harmonic of a machine with a concentrated winding in the stator, which is, in fact, undesired, can be advantageously and deliberately used for the purpose, in order to provide the exciter winding in the rotor with electrical energy.
Advantageously, the at least one concentrated winding of the stator produces both the work harmonic as well as the exciter harmonic.
In one embodiment, the field winding in the rotor comprises several coils which are wound around a tooth of the rotor and are connected in series with one another. The serial connection of the field winding is thereby designed in such a way that along the circumference of the rotor, magnetic north poles and magnetic south poles arise with the flow of direct current through the serial connection.
The exciter winding preferably has a high winding factor.
The exciter winding and the field winding are preferably wound around the same teeth of the rotor.
In one refinement, the field winding and the exciter winding have different coil widths and are, insofar, adapted to the different conditions in the air gap with regard to the individually used harmonics. For example, the field winding can have a larger coil width than the exciter winding, since the field winding is adapted to the fifth harmonic and the exciter winding, to the seventh harmonic. The different coil width can, for example, be implemented in a salient pole rotor in that the field winding is wound around the tooth neck of the salient pole, whereas the exciter winding is in the tooth crest with a smaller coil width.
Alternatively or additionally, permanent magnets can be introduced in the rotor, for example, in the leg poles.
Since the proposed synchronous machine has a self-excitation of the rotor via the air gap field of the machine, slip rings and brushes for the galvanic direct current transfer are omitted. In addition, an auxiliary winding and a rectifier in the stator are not needed.
Preferably, the rotor windings—that is, the first and the second winding systems—are made exclusively as concentrated tooth coil windings; that is, all coils of the windings are wound around exactly one tooth.
Preferably, separate tooth coil windings are provided for the excitation winding and the field winding.
The rectification is preferably implemented as a full bridge rectifier circuit.
Preferably, two coils, or multiples thereof, in which the current is induced in the rotor, are connected in series before they are connected to the full bridge rectifier. The excitation winding accordingly always comprises at least two coils in the serial connection.
The invention is explained in more detail, below, on several embodiment examples with the aid of drawings.
The figures show the following:
Rotor 2 is situated relative to this. The rotor comprises a first winding system 3, which is designed as an excitation winding. In the example under consideration, the excitation winding is designed with five strands E1 to E5, which comprise two coils connected in series. The basis in the example is thereby a ten-pole rotor, wherein the exact winding topology of this example will be illustrated later with the aid of
This excitation winding 3 is connected with a rectifier 4 via five terminals X1 to X5; it is designed here as a full bridge diode rectifier. The diode rectifier makes available a direct current to the outlet terminals U1, U2. The direct voltage is smoothed out with a capacitance 5, which comprises a capacitor C. The capacitor C can also be omitted. A field winding 6 is connected in parallel to it; there is a direct current flow through it, which produces a stationary rotor magnetic field and can thus make permanent magnets in the rotor superfluous.
It is remarkable that the stator 1 does not comprise a rectifier or an auxiliary winding. The energy for the excitation of the rotor 2 is rather created by the traditional excitation winding of the stator. The effect is thereby utilized so that the excitation winding of the stator creates both the work harmonic for the synchronous machine as well as at least one upper harmonic—that is, the harmonic of the magnetomotive force, which is used to supply the excitation winding of the rotor.
In the example of
An exemplary mode of action will be explained later with the aid of
A current supply unit 7 is provided to supply the stator winding; it prepares a three-phase supply signal and is controlled by a control unit 8. The machine can be operated with a motor or a generator.
As mentioned, the full bridge rectifier is used to convert the magnetic field supplied to the excitation winding into a direct current to supply the field winding. The field winding, in turn, creates the stationary magnetic field of the rotor.
On an embodiment example,
In detail, the stator 1 in this example has twelve slots, into which a three-phase electrical, concentrated winding is introduced. The stator is shown in
In the lower half of the image of
In the example under consideration, in accordance with
The middle of the image of
The excitation winding of the rotor is supplied by the seventh harmonic. The seventh harmonic of the magnetomotive force produced by the stator winding is therefore used to supply the field winding of the rotor with energy.
An excitation winding is placed in the rotor, below the field winding in the example of
In the embodiment example described, the winding factors for the fifth and the seventh harmonics of the stator winding or its magnetomotive force are the same and are approximately 0.933. Therefore, the flux density in the air gap from these harmonics is also the same. In this way, in turn, as a result of the relatively high fractions of the seventh harmonic and because of the high winding factors of the rotor winding with regard to the seventh harmonic, only a small winding factor is needed, in order to accept this harmonic and to produce sufficient voltage so as to supply the field winding of the rotor by means of the rotating rectifier bridge. The proposed excitation principle in the rotor due to the planned utilization of a harmonic of a concentrated stator winding, which is in any case present, therefore advantageously leads to the dynamic characteristics of the machine and the rotor construction being practically uninfluenced by the proposed self-excitation principle.
In alternative embodiments, it is, of course, possible, to vary the coil width of the excitation of the rotor in such a way that the effect—that is, the fraction of the higher harmonic, such as of the 17th and 19th harmonics, is reduced to the excitation winding of the rotor, with regard to the induced voltage.
The additional permanent magnets have the effect that the characteristic properties of the machine are improved at low speeds.
In contrast,
On an embodiment example,
In detail, the stator 1 shows 18 slots in this example, into which a three-phase electrical, concentrated winding is introduced. The stator is shown in the upper half of the image in
In the lower half of the image of
In the example under consideration, in accordance with
The fifth and the 13th harmonics of the magnetomotive force in the air gap are shown in the middle of the image of
Therefore, one can see that the fifth and the 13th harmonics spread with different orientations and have different speeds. The 13th harmonic is depicted as a dotted line in the middle of the image of
The excitation winding of the rotor is supplied by the 13th harmonic. The 13th harmonic of the magnetomotive force produced by the stator winding is therefore used to supply the field winding of the rotor with energy.
The two following tables show, by way of example, possible additional combinations of a number of stator slots Z and the number of the pole pairs p of the rotor in concentrated windings for self-excited synchronous machines in accordance with the proposed principle. As described above, one harmonic is used as the work harmonic and another harmonic, for the excitation of the rotor winding. Dependent on the combination of the number of stator slots and the number of rotor poles, the available harmonics for the excitation of the rotor field winding are indicated.
Table 1 shows the available harmonics for a two-layer winding.
Table 2, which follows, shows the available harmonics for a one-layer winding.
Of course, it is up to the technical discretion of the expert to apply the principle proposed here to other embodiments of synchronous machines.
Number | Date | Country | Kind |
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10 2013 102 900.0 | Mar 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/055613 | 3/20/2014 | WO | 00 |