WO2008022788A1

WO2008022788A1 - Permanent magnet synchronous motor

Info

Publication number: WO2008022788A1
Application number: PCT/EP2007/007415
Authority: WO
Inventors: Manfred Dollinger; Wolfgang Benzing; Wilfried Fritsch
Original assignee: Abm Greiffenberger Antriebstechnik Gmbh
Priority date: 2006-08-23
Filing date: 2007-08-23
Publication date: 2008-02-28
Also published as: DE102006039499A1

Abstract

The invention relates to a permanent magnet synchronous motor (1), comprising a rotor (10) with several permanent magnets (20, 21), a stator (30) surrounding the rotor (10), with stator windings and a controller (5), which supply the stator windings with a current changing over time, wherein the controller (5) is designed to measure a counter voltage induced in the stator windings by the rotor(10), to determine the angular position (γ) of the rotor (10) based on the measured counter voltage and to operate the stator windings based on the determined angular position (γ) of the rotor (10). The rotor (10) is designed such that the counter voltage induced in the stator windings is an essentially sinusoidal curve.

Description

Permanent magnet Svnchronmotor

The present invention relates to a permanent magnet synchronous motor according to the preamble of claim 1, wherein a so-called. Sensorless control is provided.

Permanent magnet synchronous motors (PSM) are finding increasing use in recent times as compared to conventional stepping motors because they better meet the requirements for high reliability, high power density, high efficiency and smooth running. Whereas in conventional stepping motors the direction switching of the current for the stator windings takes place independently of the position of the rotor or the position of the permanent magnets provided on the rotor, the synchronous motor is indexed in synchronism with the rotor. Due to the orientation on the rotor magnetic field, therefore, the synchronous motor allows the use of higher torques and thus a higher dynamics. The speed ranges in which synchronous motors can be used are also significantly greater compared to stepper motors.

A classic permanent magnet synchronous motor consists of a metallic rotor supporting the permanent magnets and a stator housing the windings. Usually, the motor is designed as a three-phase motor, wherein the windings are connected to three phases in a star or delta.

In order to ensure that the synchronous motor is actually switched in synchronism with the rotor, a more complex electronic commutation of the phases is required compared with a stepper motor since the commutation must be adapted as exactly as possible to the rotor position. This procedure is usually referred to as field orientation (FOC or Field Oriented Control), because with the position of the rotor, the position of the magnetic field is detected and the appropriate energization of the stator winding can be adjusted. In the past, special position sensors were used primarily to detect the rotor position. In particular, in this case the use of so-called Hall sensors or resolvers is known.

However, since the number of components for the motor is increased by the use of additional sensors, solutions were sought to the rotor position on other To identify ways. In this case, a so-called. Sensorless rotor control was developed, which is based on the fact that the voltage induced by the rotor magnets in the stator windings, which is often referred to as electromotive force or back EMF or reverse voltage, used for detecting the position of the rotor. This procedure is therefore based on the fact that the permanent magnets rotating with the rotor induce a voltage in the stator windings whose shape or course gives information about the angular position of the rotor. Since in this procedure the rotor position can be detected exclusively by the voltage applied to the windings or the course of the winding current, it is possible to dispense with the use of separate sensors.

Fig. 9 shows the typical course of the reverse voltage in a conventional permanent magnet synchronous motor, as it is used today. The course of the countervoltage is reminiscent in a broader sense of a sinusoidal course, but in the areas of the maxima and minima areas or plateaus are present in which the counter-voltage is almost constant. This results in the problem that no clear differentiation is possible in these areas, which in turn means that the angular position of the rotor can only be determined with a limited accuracy. This ultimately has the consequence that an adaptation or synchronous control of the windings to the rotor position is only possible to a limited extent, which is why sensorless motors have so far been able to prevail only to a certain extent.

The present invention is based on the object to further develop known permanent magnet synchronous motors with a sensorless control such that a more precise control of the windings is made possible synchronously with the rotor position and accordingly the possible applications of such a motor can be extended.

The object is achieved by a permanent magnet synchronous motor having the features of claim 1. Advantageous developments of the invention are the subject of the dependent claims.

The present invention is based on the idea of further developing the motor so that a more accurate determination of the angular position of the rotor is made possible in the context of sensorless control. This is inventively achieved in that the rotor is designed in a special way, in particular such that the induced voltage in the stator windings now has a substantially sinusoidal course. According to the invention, the design of the rotor is thus particularly influenced in such a way that the countervoltage induced in the stator windings no longer has any horizontal plateaus in comparison with the voltage curve shown in FIG. Instead, a continuous sinusoidal course is sought, which ultimately makes it possible to determine its angular position with high accuracy in all positions of the rotor.

Therefore, according to the present invention, there is proposed a permanent magnet synchronous motor having a rotor supporting a plurality of permanent magnets, a stator having stator windings surrounding the rotor and a control circuit which supplies a time-varying current to the stator windings, the control circuit being configured to rotate one through the rotor To determine counter tension induced in the stator windings, to determine the angular position of the rotor based on the determined counter voltage and to control the stator windings in dependence on the determined angular position of the rotor, and wherein the rotor is designed such that the counter voltage induced in the stator windings substantially sinusoidal course has.

The manner of the embodiment of the rotor, by means of which this measure according to the invention is achieved, is in particular subject of the dependent claims. Thus, the goal of the substantially sinusoidal course of the counter-voltage is achieved in particular by virtue of the fact that the rotor has a relatively strong magnetic asymmetry (reluctance). This is achieved by several measures, which are explained in more detail below.

Thus, according to the invention, it may initially be provided that the permanent magnets of the rotor do not rest against its outer circumference, but instead are arranged inside the rotor. For this purpose, the rotor may have in its peripheral region axially extending recesses which serve to receive the permanent magnets. The recesses and thus the permanent magnets in this case preferably have a substantially rectangular cross-section, but it is particularly preferred that additional recesses are provided in the recesses on the longitudinal sides of the permanent magnets, which are for example. Semicircular and serve to reduce the magnetic leakage flux , The recesses may also serve to introduce adhesive or other potting dimensions to easily secure the magnets within the rotor. Another measure, which is crucial for the formation of the required reluctance of the rotor, is that in the outer peripheral region of the rotor located between the magnet recesses are provided. As a result, the asymmetrical impedance distribution of the rotor is further increased, which ultimately contributes to the formation of the desired sinusoidal voltage. Furthermore, the efficiency of the rotor can be improved by the measure, since not usable by the introduction of these recesses harmonic torques are avoided. This also leads to a reduction of the noise emission and to reduce the torque ripple within a single revolution of the rotor.

The rotor itself preferably consists of a plurality of axially successively arranged sheets, which consist in particular of a magnetic flux conducting material. These sheets can then each have the previously mentioned recesses for receiving the permanent magnets and the recesses in the peripheral region. On the front side, however, sheets can be used in which the recesses for the magnets have been dispensed with, so that ultimately each magnet is completely enclosed by the sheets.

An additional development may also consist in that the magnets extend in the axial direction only over a portion of the rotor. This makes it possible to adapt the magnetic and electrical properties of the rotor as needed to the geometry of the air gap between the rotor and the stator. Ultimately, this leads to the fact that the usable speed range of the engine is increased and an improved torque output can be achieved at high speeds.

The above-mentioned measures to improve the sensorless permanent magnet synchronous motor primarily concerned the design of the rotor. However, additional measures can be provided on the stator in order to promote the desired sinusoidal profile of the reverse voltage. In particular, it may initially be provided to distribute the stator windings to a multiplicity of stator slots. Ideally, this again provides a sinusoidal inductance distribution of the pole windings, which leads to a further improvement in the interaction between stator and rotor.

Another measure relates to the configuration of the stator windings. It is provided according to a particularly preferred embodiment, these in the form of To realize floor windings, in which case the windings are each connected in parallel in four groups. This multiple-parallel circuit allows a higher current load, which in particular leads to advantages at low operating voltages of the motor.

Ultimately, therefore, an overall concept for a sensorless motor is proposed, which has significant advantages in terms of its operating characteristics compared to previously realized engines.

The invention will be explained in more detail with reference to the accompanying drawings. Show it:

1 schematically shows the structure of a permanent

Synchronous motor;

FIG. 2 shows the side view of a permanent magnet rotor used in the motor according to the invention; FIG.

3 is a sectional view of the rotor according to the section I-I in Fig. 2.

Fig. 4 is the view II-II of the rotor in Fig. 2;

Fig. 5 is a sectional view in the axial direction of the rotor according to a first

Exemplary embodiment;

6 is a sectional view of the rotor in the axial direction according to a second exemplary embodiment;

FIGS. 7a to 7c show different possibilities for configuring the stator windings;

8a shows the angle-dependent inductance of the rotor;

FIG. 8b shows the course of the countervoltage which results in the motor according to the invention and FIG

9 shows the course of the reverse voltage in an engine according to the prior

Technology. O

The block diagram of a permanent magnet synchronous motor according to the invention, generally indicated by the reference numeral 1, corresponds to the classical structure of such a motor type. Core element of the engine 1 is first a permanent magnet rotor 10 which is rotatably disposed within a stator 30. The stator 30 supports the stator windings which are distributed on a plurality of stator slots and provide a rotating magnetic field by supplying respective currents. This in turn cooperates with the magnet arranged inside the permanent magnet motor 10 in such a way that rotation of the rotor 10 takes place.

The control of the stator windings is carried out by a control circuit or a current regulator 5, which, taking into account in the supplied external signals, which specify, for example, a target speed U _so u for the engine 1 or a desired torque, a subordinate three-phase bridge 6, which according to the information of the current controller 5 provides a time-varying stator current. Here, three stator windings are supplied with sinusoidal currents, which are offset by 120 ° each phase. Through the use of sinusoidal currents for the stator windings while the torque ripple can be avoided during engine operation, resulting in a quieter rotor. On the other hand, the control of the

Stator windings take place as synchronously as possible to the rotor position, which is ensured by the current regulator 5.

In contrast to solutions in which separate sensors are provided for determining the rotor position, a sensorless operation is provided here. This means that no additional sensors are used as components to determine the rotor position. Instead, the angular position γ of the rotor 10 is determined from the counter-voltage induced in the stator windings, which is caused by the rotating magnetic field of the permanent magnet rotor 10. By evaluating this induced back voltage (Back EMF) so can the

Control circuit 5 determine the angular position γ of the rotor 10 and make a corresponding control of the stator windings.

The peculiarity of the motor 1 according to the invention consists in the fact that the counter-voltage induced by the rotor 10 has an approximately sinusoidal profile, which is brought about by special measures on the rotor 10 and the stator 30. These will be explained in more detail below, with first the design of the rotor discussed in more detail and then the stator is explained. Fig. 2 shows first a side view of the rotor 10, which is arranged rotatably within the stator 30 by means of an unspecified axis 7. The rotor 10 consists of a package of plates 11 arranged one behind the other in the axial direction, the configuration of which can be seen in the illustration in FIG. Each plate 11 has a circular shape with a passage opening I Ia for carrying the rotor axis. 7

The basic design of a rotor through such a laminated core is already well known. However, a first special feature consists in the fact that the permanent magnets 20 and 21 are not arranged on the outside of the rotor 10 but instead are accommodated in this. For this purpose, the sheets 11 located in the peripheral region recesses 13, 14, which are provided for receiving the magnets 20, 21. The recesses 13, 14 and thus also the magnets 20, 21 have a substantially rectangular cross section, whereby the use of conventional, cuboid bar magnets for the permanent magnets 20, 21 is made possible. This initially contributes to a more cost-effective production of the rotor 10.

Furthermore, however, a particular advantage of this embodiment is that the arrangement of the magnets 20, 21 below the surface of the

Rotor 10, the formation of a magnetic leakage flux, which could adversely affect the engine operation is reduced. This also contributes to the fact that the recesses 13, 14 for receiving the magnets 20, 21 each have at their two ends additional recesses 13a, 14a, which are preferably formed semicircular as shown. Other shapes for these recesses 13a, 14a, which also reduce the formation of the magnetic stray flux, would be possible. In addition, these recesses 13 a, 14 a also provide a simple way of attaching the magnets 20, 21, since in them an adhesive or other potting compounds can be introduced to safely store the magnets 20, 21 within the rotor 10. Another feature of this

Recesses 13a, 14a may also be to use these optionally to form a starting cage for the engine 1. It should also be noted that instead of the illustrated four permanent magnets, the number of these can also be varied.

In order to additionally secure the magnets 20, 21 in the axial direction, the two end plates 12, as shown in FIG. 4, are also configured without these recesses 13, 14. Accordingly, the magnets 20, 21 are enclosed on all sides by the sheets 11 and 12, respectively, so that they are securely held within the rotor 10. Another special feature of the rotor 10 according to the invention consists in recesses 15, which are arranged in the outer peripheral region of the individual sheets 11, in particular in the region between two adjacent magnets 20, 21. These recesses 15 cause a separation between individual pole pieces 16 of the rotor 10 and have the consequence in that the rotor 10 has a strong magnetic asymmetry between the transverse inductance L _q and the longitudinal inductance L _d . This magnetic asymmetry or reluctance of the rotor ultimately allows accurate rotor position determination without the use of special sensors. This can be seen from the illustration in FIG. 8 a, which shows the angular dependence of

Inductance of the rotor 10 shows. It can be seen that this has a sinusoidal shape, which then ultimately also contributes to the generation of the desired essentially sinusoidal countervoltage. Furthermore, it can be seen from the illustration in FIG. 8a that there are small differences in the successive maximum and minimum values, which is due to hysteresis effects and opens up the possibility of unambiguously distinguishing between the north and south poles of the rotor 10. Accordingly, in particular at the speed 0 and at low speeds, this pronounced curve shape of the inductance curve supplies a signal which can be evaluated unambiguously for the rotor position detection.

It should be noted that the pole shoes 16 formed by the recesses 15 have approximately a circular segment shape, although the center of the respective circular shape does not necessarily coincide with the center of the rotor 10. Instead, the pole shoes 16 have a slightly greater curvature, which further contributes to the expression of the strong magnetic asymmetry.

The permanent magnets 20, 21 may extend over the entire axial length of the rotor 10 as shown in FIG. Alternatively, however, it would also be conceivable, as shown in FIG. 6, for the magnets 20, 21 to extend only over a central subregion. This special design has to

Result that the inductance in the d-direction is further increased, which is advantageous if the motor with an additional field-forming stator current to be fed. Due to the larger inductance in the d-direction, a correspondingly greater voltage drop results, which compensates for the generator-generated voltage by the magnets 20, 21. This in turn means that the motor can be operated at a higher speed without having to increase the power converter output voltage. There is accordingly the possibility of increasing the speed of the motor beyond its rated speed, ie the engine power remains up to a value dependent on the design of the motor constant for a given rated power.

The previous measures, which contribute to the formation of the sinusoidal counter-voltage as possible, limited to the rotor 10. Subsequently measures will now be explained on the stator 30, which also pursue the purpose of supporting the sinusoidal interaction and thus an improved sensorless control.

A first measure consists in a distribution of the stator winding on a plurality of grooves or pole teeth, resulting in an approximately sinusoidal field profile of the magnetic field formed by the stator windings. In this case, it is possible to connect the winding in series or in two groups in parallel, as can be seen in the illustrations in FIGS. 7a and 7b. Both figures show schematically the course of the three stator windings in the stator slots 32 formed between the teeth 31. FIG. 7a shows a series connection, whereas the windings in the scheme according to FIG. 7b are connected in parallel in two groups.

In the motor according to the invention, it is now possible to connect the windings in series or in two groups in parallel. Moreover, a particularly preferred variant shown in FIG. 7c is to switch the windings in four groups in parallel. The resulting winding scheme has the consequence that the number of turns per groove multiplied. This in turn means that the windings can also be designed precisely for very small voltages-for example, during battery operation.

Advantageously, the arrangement of the windings is further carried out in floors, with the result that results over conventional arrangements in two floors, a smaller average winding length by shorter end connections. This reduces the copper requirement for the entire stator windings, which in turn contributes to a cost-effective implementation of the motor according to the invention.

The winding strands are preferably connected in a triangular circuit. This arrangement is problematic in itself, since it led to relatively high losses so far. However, according to the present invention, since the basic field is designed to be as sinusoidal as possible, no third harmonic occurs in the voltage, with the result that additional losses, which could be caused by additional circulating currents, are avoided. The rated power of the engine does not have to be reduced accordingly, with the result that the efficiency of the engine is significantly greater than in a conventional motor in which circular currents can form.

Ultimately, therefore, the entire configuration of the motor in the manner according to the invention leads to the fact that-as shown in FIG. 8b-the countervoltage induced in the stator windings by the rotating rotor has an approximately sinusoidal profile. This allows compared to the course of the counter-tension according to the prior art of Fig. 9 at each speed and position of the rotor much more precise determination of the rotor angle position and, accordingly, a more accurate and effective control of the motor.

By the present invention, therefore, an overall concept for a permanent magnet synchronous motor is provided, which can be used in many ways due to its excellent properties and its optimized efficiency. The measures provided in this case can be realized inexpensively, which represents a further advantage of the invention.

Claims

claims

1. permanent magnet synchronous motor (1), comprising

A rotor (10) carrying a plurality of permanent magnets (20, 21),

• a rotor (10) surrounding the stator (30) with stator windings, as well

A control circuit (5) which supplies a time-variable current to the stator windings, wherein the control circuit (5) is designed to determine a countervoltage induced in the stator windings by the rotor (10) based on the determined back voltage the angular position (γ) of the rotor (10) and to control the stator windings as a function of the determined angular position (γ) of the rotor (10), characterized in that the rotor (10) is designed such that the countervoltage induced in the stator windings is substantially sinusoidal History has.

2. permanent magnet synchronous motor according to claim 1, characterized in that the permanent magnets (20, 21) within the rotor (10) are arranged.

3. permanent magnet synchronous motor according to claim 2, characterized in that the rotor (10) in the peripheral region in the axial direction extending recesses (13, 14), in which the permanent magnets (20, 21) are arranged.

4. permanent magnet synchronous motor according to claim 3, characterized in that the permanent magnets (20, 21) have a substantially rectangular cross section and are cuboidal.

5. permanent magnet synchronous motor according to claim 4, characterized in that the recesses (13, 14) for receiving the permanent magnets (20, 21) on the longitudinal sides of the permanent magnets (20, 21) recesses (I Ia, 12a).

6. permanent magnet synchronous motor according to claim 5, characterized in that the recesses (13a, 14a) are semicircular.

7. permanent magnet synchronous motor according to one of the preceding claims, characterized in that the rotor (10) in the outer peripheral region between the magnets (20, 21) located recesses (15).

8. permanent magnet synchronous motor according to one of the preceding claims, characterized in that the permanent magnets (20, 21) seen in axial directions only over a portion of the rotor (10) extend.

9. permanent magnet synchronous motor according to one of the preceding claims, characterized in that the rotor (10) consists of a plurality of axially successively arranged sheets (11).

10. permanent magnet synchronous motor according to claim 9, characterized in that the sheets (11) consist of a magnetic flux-conducting material.

1 1. Permanent magnet synchronous motor according to one of the preceding claims, characterized in that the stator windings are distributed over a plurality of stator slots (32).

12. permanent magnet synchronous motor according to claim 11, characterized in that the stator windings are connected in parallel to four-groups.