WO2016000697A1

WO2016000697A1 - Electric machine having mechanical field weakening

Info

Publication number: WO2016000697A1
Application number: PCT/DE2015/200262
Authority: WO
Inventors: Thomas Schencke; Thomas Pfund
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2014-07-03
Filing date: 2015-04-16
Publication date: 2016-01-07
Also published as: DE102014212871A1

Abstract

A dynamo-electric permanently excited machine having a stator (1), a rotor (2) which is spaced from the stator (1) by an air gap and has magnet pockets (3) and permanent magnets (4) which can be displaced in a radial direction, wherein the permanent magnets (4) at least partially penetrate into the magnetic pockets (3), and wherein the penetration depth of the permanent magnets (4) depends on their radial position, and the density of the magnetic air gap flux generated by the permanent magnets (4) depends on the penetration depth.

Description

Electric machine with mechanical field weakening

The invention relates to a permanent magnet dynamoelectric machine with the ability to operate in the field weakening.

An example of such a dynamo-electric permanent-magnet machine is the permanent-magnet synchronous machine (PSM). PSMs are used in a variety of applications to perform electrical drive tasks. In industrial applications, for example, they are used as servomotors. Due to its high power density compared to other electric machines, the PSM is also considered the preferred drive unit in the field of electromobility. But even as a generator, for example in the field of renewable energy, especially wind power, the PSM is often used.

One reason for the widespread use of permanent-magnet synchronous machines is their high efficiency, which is due to the fact that can be dispensed with an electrical excitation. The excitation field is caused by the permanent magnets usually arranged in the rotor. In addition to the increased efficiency, the permanent excitation over electrical excitation also has the advantage that wear-affected slip ring contacts can be dispensed with to supply a rotating exciter coil.

However, a disadvantage of permanently excited electrical machines compared to electrically excited dynamoelectric machines is that the excitation field in its height can not be changed easily. Thus, for example, a reduction of the magnetic excitation flux is desirable in order to operate a dynamoelectric machine in the so-called field weakening range. In the characteristic field of a dynamoelectric machine, the field weakening area identifies the area of the constant power at which increasing speed decreases the output from the machine torque. By controlling the machine in the field weakening range, it is possible to operate the dynamoelectric machine beyond its rated speed.

In an electrically excited dynamoelectric machine, this characteristic range can be controlled very simply by reducing the excitation current. Although it is also known in permanently excited machines, there is the possibility of producing an air gap field component via suitable energization of the stator of the machine, which counteracts the field of excitation generated by the permanent magnet and thus weakens it. However, such control of the machine is associated with significantly increased losses and a concomitant reduction in the efficiency. In order to be able to operate permanently excited dynamoelectric machines in the field weakening range without significantly impairing the efficiency, methods for mechanical field weakening are known from the prior art. Thus, US20060091752A1 shows a dynamo-electric permanent-magnet machine having the features according to the preamble of patent claim 1. In this document, an external rotor motor is disclosed in which the field weakening is effected by increasing the effective air gap between the rotor and the stator of the machine.

The invention has for its object to provide a permanent-magnet dynamo electric machine with the ability to field weakening, which has a high electrical efficiency.

The object is achieved by a dynamo-electric permanent-magnet machine having the features according to patent claim 1.

Advantageous embodiments can be found in the appended claims. The dynamo-electric pernnan-excited machine according to the invention comprises a stator and a rotor with magnetic pockets spaced apart from the stator via an air gap, as well as permanent magnets which can be displaced in the radial direction.

The special feature of this machine is that the permanent magnets according to the invention at least partially penetrate into the magnetic pockets and in this case the penetration depth of the permanent magnets depends on their radial position, wherein the density of the magnetic air gap flux generated by the permanent magnets in turn depends on the penetration depth. The magnetic pockets guide the permanent magnets in the radial direction. The permanent magnets are preferably magnetized substantially tangentially to the circumferential direction of the rotor. The magnetic pockets preferably extend primarily in the radial and axial directions. Depending on the penetration depth of the permanent magnets into the magnetic pockets serving for guidance, the air gap flow of the dynamoelectric machine changes. Thus, by a suitable radial positioning of the permanent magnets within the magnetic pockets between a normal operation of the dynamoelectric machine with high air gap flux and a field weakening operation of the dynamoelectric machine with reduced air gap flux can be varied.

Preferably, in this case, the rotor is designed such that the density of the air gap flux decreases with decreasing penetration depth. In other words, the field weakening operation is initiated by the fact that the permanent magnets are radi al out of the associated magnetic pockets out.

In a particularly advantageous embodiment of the invention in this case the rotor is designed such that a radially outward displacement of the permanent magnets causes a reduction in the penetration depth. The reduction of the air gap flux when the permanent magnets are brought out of the magnetic pockets can now be realized, preferably, by arranging the magnetic pockets in a ferromagnetic material and, viewed radially outwards, a region of lower permeability to the magnetotapes. see connects. Now, if the permanent magnets are moved from radially inward to radially outward, then a part of the permanent magnets, which was previously surrounded by ferromagnetic material, enters a region of significantly lower magnetic conductivity, so that this latter part experiences a higher magnetic resistance. As a result, the total flux density in the air gap is reduced.

An embodiment of the dynamoelectric machine, in which a radially outward displacement of the permanent magnets has a reduction of the penetration depth, allows in a further particularly advantageous embodiment of the invention, that causes the radially outward displacement of the permanent magnets by increasing centrifugal force with increasing rotor speed becomes. In this way, the field weakening operation can be automatically initiated when the engine is accelerated. An actuator that actively shifts the permanent magnets outwards is not necessary in this case.

For example, the permanent magnets may be biased by a spring in the radial direction inwards. This spring tension is dimensioned such that, starting from a rotational speed which represents the limit rotational speed of the engine at maximum engine torque, a further rotational speed increase can only be realized via the field weakening operation.

In many applications, however, it is also desirable that the excitation of the dynamoelectric machine can be actively reduced or eliminated altogether. This is often the case, for example, in the event of a fault of the machine or of a system operated by the machine. For such an application, an embodiment of the machine is advantageous, which has a signal input for an error signal and an actuator for active displacement of the permanent magnets out of the magnetic pocket in the case of an applied error signal. By a preferred use tangentially to the circumferential direction of magnetized Pernnanentnnagnete it is possible to form the dynamoelekthschen machine as an internal rotor machine, in which a radially outward displacement of the Pernnanentnnagnete has a field weakening result. This can be done, for example, by connecting the magnetic pockets in the radial direction towards the outside to a region of lower permeability and thus higher magnetic resistance. In such an embodiment, the permanent magnets dip in a radially outward displacement in this low-permeability region.

A particularly advantageous application for a dynamoelectric machine according to one of the previously described embodiments can be seen in the field of electromobility. For example, in this case, the dynamoelectric machine can be designed as a permanent magnet synchronous machine, since this has significant advantages over competing machine types, especially in vehicle applications due to their high power density. The inventive method of mechanical field weakening described here further increases the efficiency of such a machine, which is extremely advantageous, especially with regard to the desirable range extension in electric vehicles.

In the following the invention will be described in more detail with reference to the embodiments shown in the figures. Elements with the same function here is assigned the same reference numerals in all figures.

Show it:

1 shows a known from the prior art construction of an electric machine,

Figure 2 shows an embodiment of a rotor of the invention in a first operating state and FIG. 3 shows an embodiment of the rotor according to FIG. 2 in a second operating state. Figure 1 shows a known from the prior art construction of an electrical machine. From a stator 1 with toothed coil technology, only a partial annular cutout is shown. The stator 1 concentrically surrounds a rotor 2 designed as an internal rotor, which is connected in a rotationally fixed manner to a rotor shaft 9. Stator 1 and rotor 2 are spaced apart by an air gap 8.

The machine is a permanent magnet synchronous machine. To generate the exciter field, the rotor 2 has permanent magnets 4 buried in magnetic pockets which are magnetized in the circumferential direction of the rotor 2. Each permanent magnet 4 is adjacent in the circumferential direction on both sides of two Flussleitstücken 6 of highly permeable material, such as stanzpaketierten electrical steel sheets. Within these flux guide pieces 6, the magnetic flux exiting initially from the permanent magnets 4 in the circumferential direction is deflected in a radial direction, so that the magnetic flux lines essentially pass through the air gap 8 in a radial direction.

In addition to the permanent magnets 4, the rotor 2 consists of two further essential elements: an inner rotor part 5 and the flux-conducting pieces 6 positively connected to the inner rotor part 5. During assembly, the flux-conducting pieces 6 can be pushed axially onto corresponding positive-locking elements 7 of the inner rotor part 5 , In the spaces between the flux guide 7, the corresponding pockets for receiving the permanent magnets 4 are formed.

In order to be able to operate such a permanently excited dynamoelectric machine in the field weakening range, a suitable current component must be impressed into the stator current, which counteracts the exciting field generated by the permanent magnets. Such an electric field weakening, for example, using the known field-oriented control is associated with increased losses within the machine and a concomitant reduction in their efficiency.

The two subsequent figures now show by way of example how, based on the invention, the dynamoelectric machine illustrated in FIG. 1 can be modified in order to enable a field weakening operation with a higher electrical efficiency.

FIG. 2 shows an embodiment of a rotor 2 of the invention in a first operating state. In comparison to the electric machine shown in FIG. 1, the magnetic pockets 3 provided for receiving the permanent magnets 4 are radially offset slightly inwards, so that the permanent magnets 4 are slightly further away from the air gap 8 of the machine in the operational situation illustrated in FIG ,

The peculiarity of the electrical machine illustrated in FIG. 2 consists in the fact that the permanent magnets 4 can be pushed out of the magnetic pockets 3 in the radial direction. The permanent magnets 4 are in this case in each operating state at least partially performed by the magnetic pockets 3.

In the operating state shown in FIG. 2, the maximum exciter flux of the machine is established. In the radially inner position of the permanent magnets 4 shown here, they penetrate maximally into the magnetic pockets 3. In this way, a maximum proportion of the magnetic material is arranged in the immediate vicinity of the high-permeability flux guide pieces 6. The magnetic flux generated by the permanent magnets 4 thus opposes a minimum magnetic resistance. The magnetic field lines, which emerge tangentially from the permanent magnets 4 substantially in the circumferential direction of the machine, are deflected in the radial direction within the flux guide pieces 6 and pass through the air gap 8 of the machine. The permanent magnets 3 are biased against the groove bottom of the magnet pockets 3 by spring elements 1 1 shown schematically here. Up to a certain speed of the machine, the biasing force of these springs 1 1 is sufficient to hold the permanent magnets 4 against the centrifugal force in this position maximum penetration depth.

With increasing speed, however, causes the centrifugal force that the permanent magnets 4 radially considered against the biasing force of the springs 1 1 move outward and thus decreases the penetration depth of the permanent magnets 4 in the magnetic pockets 3.

Viewed in the radial direction, the outer side of the magnetic pockets 3 is adjoined by a region of lower permeability 10, which has a significantly lower magnetic conductance in comparison to the flux conducting pieces 6. This may be, for example, air, but also a low-permeability solid, in particular plastic. Now, if the permanent magnets are moved out of the magnetic pockets 3 with increasing speed and thus with increasing centrifugal force, they enter this area of lower permeability 10 and the operating state shown in FIG. 3 is established.

Thus, FIG. 3 shows an embodiment of the rotor according to FIG. 2 in a second operating state in which a field weakening operation occurs. The penetration depth of the permanent magnets 4 in the magnetic pockets 3 has decreased since the permanent magnets 4 have now moved piecemeal into the area of lower permeability 10. The part of the permanent magnets 4, which is located in this region of lower permeability 10, now sees itself confronted with a significantly higher magnetic conductance than the part of the permanent magnets 4 which still lies in the magnetic pockets 3.

As a result of this increase in the magnetic resistance, the air gap flux is finally reduced compared with the situation according to FIG. 2 and the machine can approach a speed range that is above its rated speed range.

LIST OF REFERENCE NUMBERS

1 stator

2 rotor

3 magnetic pockets

4 pernnan magnets

5 inner rotor part

6 flux guides

7 positive locking elements

8 air gap

9 rotor shaft

10 area of lower permeability

1 1 spring

Claims

claims

1 . Having dynamo-electric permanent magnet machine

A stator (1),

A rotor (2) spaced apart from the stator (1) by an air gap and having magnet pockets (3) and

· Movable in the radial direction permanent magnets (4),

characterized in that

the permanent magnets (4) penetrate at least partially into the magnetic pockets (3), wherein the penetration depth of the permanent magnets (4) depends on their radial position and the density of the magnetic air gap flux generated by the permanent magnets (4) depends on the penetration depth.

2. Dynamo-electric permanent-magnet machine according to claim 1, wherein the rotor (2) is designed such that the density of the air gap flux decreases with decreasing penetration depth.

3. Dynamo-electric permanent-magnet machine according to claim 2, wherein the rotor (2) is designed such that a radially outward displacement of the permanent magnets (4) causes a reduction of the penetration depth.

4. Dynamo-electric permanent-magnet machine according to claim 3, wherein the magnetic pockets (3) are arranged in a ferromagnetic material and, viewed radially outwardly, a region of lower permeability adjoins the magnetic pockets (3).

5. Dynamo-electric permanent-magnet machine according to claim 3 or 4, wherein the rotor (2) is designed such that the radially outward displacement of the permanent magnets (4) is effected by a centrifugal force increasing with increasing rotor speed.

A dynamo-electric pernnan-excited machine according to claim 5, wherein said pernnan magnets (4) are biased inward in the radial direction by a spring.

7. Dynamo-electric permanent-magnet machine according to one of claims 2 to 6 with a signal input for an error signal and an actuator for active displacement of the permanent magnets (4) from the magnet pocket (3) out in the case of an applied error signal.

8. Dynamo-electric permanent-magnet machine according to one of the preceding claims, wherein the permanent magnets (4) are magnetized substantially tangentially to the circumferential direction of the rotor (2).

9. Dynamo-electric permanent-magnet machine according to one of the preceding claims, wherein the rotor (2) is designed as an internal rotor.

10. At least partially electrically powered vehicle with a dynamoelectric machine according to one of the preceding claims.