DE102013201241A1 - Method and device for determining the position of the rotor in a brushless DC motor - Google Patents

Abstract

The invention relates to a method for determining the position of the rotor (1) in a brushless direct current motor, which is determined by sensor technology and used by an electronic control unit (2) for the temporally offset control of electrical coils (1) assigned to the rotor (1) and arranged around it on the housing side 3) is signal-processed in order to generate a rotating field for the movement of the rotor (1), the position signal of a Hall sensor (4) being combined with the position signal of an incremental encoder (5) for calculating the position of the rotor (1) by the electronic control unit ( 2) is linked.

Description

Field of the invention

The invention relates to a method for determining the position of the rotor in a brushless DC motor, which is determined by sensor technology and signal processed by an electronic control unit for staggered control of the rotor associated with the housing side and arranged around this electrical coils to a rotating field for movement of the rotor to create. The invention further relates to a sensor device for carrying out this method as well as a brushless DC motor with such a device.

A brushless DC motor, which is also referred to as BLDC, BL, or EC motor, can be generally understood as a type of DC motor in which the usual mechanical commutator is replaced with brushes for current application by an electronic circuit. From the mechanical design of the motor brushless DC motors are identical to undamped synchronous motors, but have in combination with the electronic control unit further control options. Applications of such engines are in the range of small drives of fans and the like on compressors and other units in motor vehicles to actuators in the form of servomotors or drive systems for machine tools.

Usually, in brushless DC motors, the rotor is realized with a permanent magnet as a so-called permanently excited synchronous motor, but may also be a so-called reluctance motor. The fixed stator, in contrast, comprises the electric coils which are arranged around the stator and are actuated offset in time by the electronic control unit in order to produce a rotating field for the rotor which causes a torque on the permanently excited rotor. If the commutation of the brushless DC motor is independent of the position, speed and torque load of the rotor, in principle there is only a conventional synchronous motor. For brushless DC motors, the essential difference is the possibility to make the electronic commutation dependent on the rotor position, the rotor speed and the torque. This represents a form of direct feedback, whereby the frequency and, in particular, the systems of interest here, the amplitude as a function of the position and speed of the rotor are changed. The electronic commutation thus becomes a regulator, and the manner of generating the rotating field thus substantially determines the characteristics of the brushless DC motor.

In contrast to block commutation can be achieved by special control of the coils as a function of the rotor angle that the magnetic field rotates continuously. This reduces mechanical stress and noise and reduces power dissipation. For the correspondingly finer control of the coils, a more accurate measurement of the rotor position is necessary.

To detect the position of the rotor and the speed is primarily a sensor-controlled commutation is used. In this case, there are sensors - in particular Hall sensors - for detecting the magnetic flux of the rotor in the region of the stator. According to this position information, the windings are controlled by suitable power drivers of the control electronics, which generate a torque in the rotor. This sensor-controlled commutation works even at very low speeds or in the state. Usually, in this commutation in three or more phases not all phases are energized at the same time, but at least one phase is de-energized at any time.

State of the art

From the DE 101 36 482 A1 shows a commutating DC motor, which as a permanent magnet rotor or reluctance motor, a wound with a regulator winding stator, at least one Hall sensor for detecting the rotor position and a commutation electronics. The Hall sensor is influenced by the magnetic fields of at least one rotor-fixed permanent magnet and a stator fixed coil. The effective region of the Hall sensor is arranged outside of a leakage flux region of the coil, wherein the Hall sensor is electrically connected to the commutation electronics. As a result, a relatively simple implementation of the control of the coils in dependence on the angle of rotation of the rotor is possible.

A disadvantage of using Hall sensors to determine the position of the rotor, however, proves the fact that only very low resolutions are possible, which is sufficient only for block commutation. A more accurate resolution can be achieved by the use of resolvers, which are complex and prone to failure, since this is analog technology. When using incremental encoders without zero-point output, although a speed determination is possible, the position of the rotor can not be determined absolutely but only relative to the last position. Thus, the position of the sensor on the Engine are tuned, by means of a complex mechanical zero point adjustment.

Disclosure of the invention

It is therefore the object of the present invention with simple technical means to be able to accurately determine an absolute position of the rotor of a brushless DC motor.

The object is achieved on the basis of a method according to the preamble of claim 1 in conjunction with its characterizing features. The following dependent claims give advantageous developments of the invention. With regard to a sensor device, the object is achieved by claim 8. The claim 9 indicates a brushless DC motor with such a device.

The invention includes the procedural teaching that for determining the position of the rotor in a brushless DC motor, which is determined by sensor technology and processed by an electronic control unit to time-offset control of the rotor and the housing side arranged around this electrical coil signal, a rotating field to generate movement of the rotor, the position signal of a Hall sensor is linked to the position signal of an incremental encoder for calculating the position of the rotor by the electronic control unit.

The advantage of the solution according to the invention is, in particular, that the electrical position of the rotor can be absolutely and accurately determined by a low additional sensor-related expenditure. The electrical position is used for electrical commutation.

Preferably, the position of the rotor after the cold start of the DC motor is initially determined only by the Hall sensor before a link with the position signal of an incremental encoder is performed. This is sufficient to turn the rotor.

Preferably, when the next Hall bar segment of the Hall bar sensor is reached, the position of the rotor is calculated, namely from the absolute position of the last Hall segment boundary and the number of incremental steps determined by the incremental encoder since this limit has been exceeded. A Hall segment boundary is an angle at which the digital value for one of the Hall sensors of the Hall sensor changes. For example, with 3 Hall sensors that would be every 60 ° electrical.

Subsequently, when the next pole pair is reached, the position of the rotor can be calculated from the absolute position of the last pole pair limit and the number of incremental steps determined by the incremental encoder since this limit has been exceeded.

After a full mechanical revolution of the rotor can then be switched to the next following mode. Since all pole pairs are now passed through with all Hall segments, the position determination is now always carried out using the absolute value of the beginning of the first pole pair. This is always mechanically the same, eliminating the influence of inaccuracies or jitter of the other Hall segments or pole pair boundaries.

As further improvement measures and part of the invention, it is proposed that a determination or plausibility check (adaptation) of the incremental resolution can be carried out.

This means either that the incremental resolution is predefined or that the resolution is first determined by the signal processing.

According to the first alternative, the counted incremental value for a Hall segment or pole pair limit or for a full mechanical revolution deviates too much from the expected value according to the predefinition, this is recognized by the plausibility check and the appropriate appropriate compensation measure initiated. As a result, a more accurate position of the rotor can be determined faster than the subsequent second alternative.

According to the second alternative, the incremental resolution, on the other hand, is initially unknown, so the counted incremental value from one Hall segment or pole pair boundary or full mechanical revolution to the next one is initially only used to determine the incremental resolution, to save it and, if necessary, to check again in the sense of successively approximately the same values. If the incremental resolution is then known, the position of the rotor is calculated as described above. This method has the advantage over the first alternative that the incremental resolution need not be known or defined. This makes it possible to use different incremental sensors without the need to match that of the control algorithm.

In addition, a post-filtering of the position of the rotor is possible. In other words, if the counted incremental values are from one boundary to the next for one mechanical rotation can be stored, a pattern for the jitter of these limits can be determined. This in turn can be used to improve the position calculation for the calculation per Hall segment or per pole pair.

In the position calculation for the calculation per mechanical revolution of the rotor, there are no systematic errors that are due to mechanical irregularities, since all Inkermentalwerte here refer to the same Hall segment boundary. However, errors due to disturbances or mechanical play can occur, as can be seen from the fact that the incremental values counted per mechanical revolution are not exactly the same. Appropriate filtering, such as low-pass filtering, can improve the accuracy of the position calculation.

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. These show:

1 2 shows a schematic block diagram representation of a sensor device for determining the position of the rotor in a brushless DC motor,

2 a schematic representation of the detection ranges of a Hall sensor in combination with an incremental sensor for determining the position of the rotor,

3 a flowchart illustrating the individual method steps for determining the position of the rotor according to a preferred embodiment.

Detailed description of the drawings

According to 1 has a - not shown here - brushless DC motor for determining the position of a rotor 1 an electronic control unit 2 on which of the staggered control of the rotor 1 associated and arranged around this electric coil 3 serves. The spools 3 are for generating a rotating magnetic field for moving the rotor 1 intended.

The current position of the rotor 1 is inventively on the one hand with a Hall sensor 4 and secondly with an incremental encoder 5 determined. Both position signals are transmitted by the electronic control unit 2 for determining the position of the rotor 1 signal processing technology linked. This is ensured by a timer 6 for the time base, to calculate the speed immediately under certain circumstances. Although no timer is required for precise position determination. If necessary, the speed should and can be determined from the position immediately. This requires a time base.

The electronic control unit 2 gives as information for the position of the rotor 1 the electrical angle of the rotor 1 off and its speed.

In order for the motor to rotate only due to the Hall signals, it is necessary to resolve with the Hall sensors more accurately than to the pole pair. Usually three three-phase motors are used in each case electrically offset by 120 ° Hall sensors. This makes it possible to determine the position electrically by 60 ° and determine the direction of rotation.

The 2 illustrates the various distributed over the circumference of the rotor coil areas of the engine and detection ranges of the sensors. In this case, according to inner ring two motor pole pairs 8th available. The middle ring symbolizes the Hall segments 6 of the Hall sensor. Usually, a motor has three phases; normal brushless DC motors are built with one Hall encoder per phase, so here three Hall sensors. These are electrically offset by 120 ° each, resulting in a resolution of 60 °. The mechanical resolution is thus 30 ° for two pairs of poles here. An outer incremental sensor ring 7 has in this embodiment a total of 60 increments and thus a much higher resolution compared to the Hall segments 6 ,

With regard to the representation of the sequence of the individual process steps according to 3 the position of the rotor after the cold start of the DC motor is initially determined solely by the Hall sensor according to step I. Subsequently, after step II, a link with the position signal of the incremental encoder is performed by the position when reaching the next Hall segment of the Hall sensor of the rotor is calculated. The calculation is based on the absolute position of the last Hall segment limit and the number of incremental steps determined by the incremental encoder since this limit has been exceeded. Upon reaching the next pole pair identifying the position of the rotor after step III, which is determined by the Hall sensor, the position is calculated from the absolute position of the last pole pair limit and the number of incremental steps determined by the incremental encoder since this limit has been exceeded. After a full revolution of the rotor and passing through all pole pairs with all Hall segments, the further position of the rotor is performed after step IV using the absolute value of the beginning of the first pole pair.

From each of the states described above in steps II. To IV Transition to the state according to step I. possible. This always occurs when a plausibility check has detected an error, for example a failure of the incremental encoder.

An adaptation of the incremental resolution generated by the incremental sensor can be carried out after the full revolution of the rotor. It is also possible to perform a post-filtering of the calculated position of the rotor.

LIST OF REFERENCE NUMBERS

1

rotor

2

electronic control unit

3

electric coils

4

Hall sensor

5

incremental

6

Hall segments

7

Incremental sensor ring

8th

Motor pole pairs

α

angle of rotation

n

rotation speed

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10136482 A1 [0006]

Claims (9)

Method for determining the position of the rotor ( 1 ) in a brushless DC motor, which is determined by sensor technology and by an electronic control unit ( 2 ) for staggered control of the rotor ( 1 ) and arranged on the housing side around this electrical coils ( 3 ) is processed to a rotating field for movement of the rotor ( 1 ), characterized in that the position signal of a Hall sensor ( 4 ) with the position signal of an incremental encoder ( 5 ) for calculating the position of the rotor ( 1 ) by the electronic control unit ( 2 ) is linked. Method according to claim 1, characterized in that the position of the rotor ( 1 ) after starting the DC motor first from the Hall sensor ( 4 ) before a link to the position signal of an incremental encoder ( 5 ) is carried out. Method according to Claim 2, characterized in that when the next Hall segment of the Hall sensor ( 4 ) the position of the rotor ( 1 ) is calculated from the absolute position of the last Hall segment limit and the number of incremental encoders ( 5 ) determined incremental steps since exceeding this limit. A method according to claim 3, characterized in that upon reaching the next pole pair, the position of the rotor ( 1 ) is calculated from the absolute position of the last pole pair limit and the number of increments by the incremental encoder ( 5 ) determined incremental steps since exceeding this limit. Method according to one of the preceding claims, characterized in that after one full revolution of the rotor ( 1 ) and passing all pole pairs with all Hall segments, the further calculation of the position of the rotor ( 1 ) using the absolute value of the beginning of the first pole pair. Method according to one of the preceding claims, characterized in that a determination or adaptation of the incremental encoder ( 5 ) generated incremental resolution after a full revolution of the rotor ( 1 ) or a full penetration of a Hall segment or pole pair is performed. Method according to one of the preceding claims, characterized in that by the electronic control unit ( 2 ) a post-filtering of the calculated position of the rotor ( 1 ) is carried out. Sensor device for determining the position of the rotor ( 1 ) in a brushless DC motor comprising an electronic control unit ( 2 ) for staggered control of the rotor ( 1 ) and arranged on the housing side around this electrical coils ( 3 ) is processed by a rotating field for movement of the rotor ( 1 ), characterized in that the electronic control unit ( 2 ) the position signal of a Hall sensor ( 4 ) with the position signal of an incremental encoder () for calculating the position of the rotor ( 1 ) connected. Brushless DC motor with a sensor device for determining the position of the rotor ( 1 ) according to claim 8.

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