CN115001348A

CN115001348A - Method for operating an electric machine, device for operating an electric machine, electric machine

Info

Publication number: CN115001348A
Application number: CN202210185491.6A
Authority: CN
Inventors: A·奥克斯; J·葛鲍尔; T·库恩
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-03-01
Filing date: 2022-02-28
Publication date: 2022-09-02
Also published as: DE102021201901A1

Abstract

The invention relates to a method for operating an electric machine (1), wherein the machine (1) has a rotatably mounted rotor (2) and at least one motor winding (5), wherein a target rotational speed (N _ Soll) is predefined for the rotor (2), and wherein the motor winding (5) is loaded with a motor current in such a way that an actual rotational speed (N _ Ist) of the rotor (2) corresponds to the target rotational speed (N _ Soll). Provision is made for a target hysteresis angle (Phi _ Schlepp _ Soll) to be predefined for a current vector (13) which describes the motor current with reference to a coordinate system fixed to the rotor, wherein the target hysteresis angle (Phi _ Schlepp _ Soll) has an angular value from an angular interval from 0 ° to 90 °, and wherein the current amplitude (I _ Abs) of the motor current is set such that the actual hysteresis angle (Phi _ Schlepp _ Ist) of the current vector (13) corresponds to the target hysteresis angle (Phi _ Schlepp _ Soll).

Description

Method for operating an electric machine, device for operating an electric machine, electric machine

Technical Field

The invention relates to a method for operating an electric machine, wherein the machine has a rotatably mounted rotor and at least one motor winding, wherein a target rotational speed is predefined for the rotor, and wherein the motor winding is loaded with a motor current in such a way that an actual rotational speed of the rotor corresponds to the target rotational speed.

The invention further relates to a device for operating an electric machine having a controller.

The invention further relates to an electric machine having such a device.

Background

Electrical machines usually have a rotatably mounted rotor and at least one energizable motor winding. The motor windings are, for example, stator windings fixed to the housing, which are distributed around the rotor. In operation of the electric machine, a target rotational speed is usually predefined for the rotor and the motor windings are loaded with a motor current in such a way that the actual rotational speed of the rotor corresponds to the target rotational speed. That is to say a speed regulation is performed. Such a process is known, for example, from the publication DE 102008036483 a 1. In previously known methods, a cascaded control system consisting of a field-oriented control and a superimposed rotational speed control is often used.

Disclosure of Invention

The method according to the invention having the features of claim 1 has the advantage that: by means of the method, high torque fluctuations can be controlled particularly stably, in particular at low rotational speeds. To this end, according to the invention, a target delay angle is predefined for a current vector, which describes the motor current with reference to a coordinate system fixed to the rotor, wherein the target delay angle has an angle value from an angle interval from 0 ° to 90 °, and wherein the current amplitude of the motor current is set such that the actual delay angle of the current vector corresponds to the target delay angle. That is to say, an angle value from an angle range from 0 ° to 90 ° is predefined as a target lag angle and the current amplitude is set or changed in such a way that the current vector has the target lag angle as the actual lag angle. Within the scope of the disclosure, a motor current is to be understood as the entirety of the sinusoidal phase currents flowing through the phases of the motor windings. Because the coordinate system is fixed to the rotor, the coordinate system rotates with the rotor. Such coordinate systems are also referred to as dq diagrams. The first coordinate axis of the coordinate system describes the field-forming current component of the motor current. The first coordinate axis is oriented parallel to the magnetic field generated by the magnet arrangement of the rotor. The second coordinate axis of the coordinate system describes the torque-forming current component of the motor current. The second coordinate axis is oriented perpendicular to the magnetic field. Within the scope of the disclosure, the lag angle is understood as the angle with which the current vector is located in the direction of rotation of the rotor in front of the first coordinate axis. In this regard, the lag angle corresponds to the difference resulting from the current angle of the motor current on the one hand and the rotational angle of the rotor on the other hand. According to the invention, the target lag angle has an angle value from an angle interval from 0 ° to 90 °. If the actual lag angle of the current vector corresponds to the predefined target lag angle, the current vector is therefore located in quadrant 1 of the coordinate system fixed to the rotor in the case of a positive direction of rotation of the rotor. If the actual lag angle of the current vector corresponds to the predefined target lag angle, the current vector, in the case of a negative direction of rotation of the rotor, is located in quadrant 4 of the coordinate system fixed to the rotor. This has the following advantages, namely: the electric machine itself remains stable to a certain extent at constant rotational speed in the presence of torque fluctuations. If the torque load of the electric machine changes, the current vector is set in quadrant 1 or quadrant 4 in such a way that a balance exists between the motor output torque and the load torque. The orientation of the current vector is thereby temporarily changed with a constant current amplitude. Since the current amplitude is set according to the invention such that the actual lag angle corresponds to the target lag angle, the current amplitude is adapted in order to adapt the actual lag angle back to the target lag angle. The rotational speed of the rotor and the frequency of the phase currents are always at least substantially constant. Preferably, the electric machine is a synchronous machine excited by permanent magnets. Preferably, the current amplitude is set by regulation.

According to a preferred embodiment, it is provided that the current amplitude of the motor current is increased if an actual delay angle exceeding the target delay angle is present and/or is reduced if an actual delay angle below the target delay angle is present. This method facilitates the adaptation of the actual lag angle to the predefined target lag angle during operation of the electric machine.

According to a preferred embodiment, it is provided that the target angle of retardation has an angle value from an angle range of 20 ° to 80 °. The closer the angle value is to 90 deg., the smaller the magnitude of the current required to achieve the target speed. In this regard, a target lag angle with a high angle value is advantageous in principle. However, the closer the angle value is to 90 °, the smaller the gap with which the electric machine can react to torque fluctuations by temporarily changing the actual lag angle in quadrant 1 or quadrant 4. In this regard, a target lag angle with an angle value from an angle interval of 20 ° to 80 ° represents an advantageous compromise. Preferably, the target retardation angle has an angle value from an angle interval of from 30 ° to 70 °, particularly preferably from an angle interval of from 55 ° to 65 °.

Preferably, the target retardation angle is predefined as a function of the load torque fluctuations. That is, the angular value that the target retardation angle has is selected according to the load torque fluctuation. The target hysteresis is preferably predefined as a function of the ascertained load torque ripple and/or as a function of the expected load torque ripple. For example, a target retardation angle with a large angle value is predefined when the ascertained or expected load torque fluctuations are small, and a target retardation angle with a small angle value is predefined when the ascertained or expected load torque fluctuations are high.

Preferably, the target retardation angle is predefined as a function of the target rotational speed. That is, the angle value of the target retardation angle is selected according to the target rotation speed. As a result, an exact adaptation of the target lag angle to different operating states of the electric machine can be achieved, as a result of which a particularly stable operation of the electric machine can be achieved.

According to an alternative embodiment, it is preferably provided that the target retardation angle is predefined independently of the target rotational speed. That is, the same target hysteresis angle is always specified for each target rotational speed. This method results in low expenditure on control technology.

According to a preferred embodiment, a threshold rotational speed is predefined, wherein the current amplitude of the motor current is set only given a target rotational speed which is lower than the threshold rotational speed such that the actual lag angle corresponds to the target lag angle. In other words, the setting according to the invention of the current amplitude is stopped (ausgesetzt) given a target rotational speed that exceeds the threshold rotational speed. Preferably, the predetermination of the target retardation angle is also stopped if a target rotational speed is predetermined which exceeds a threshold rotational speed. As mentioned above, the method according to the invention leads to a stable operation of the electric machine, in particular at low rotational speeds. However, alternative methods for operating the electric machine at higher rotational speeds may be advantageous. Preferably, the electric machine is operated with the aid of a cascaded control system having a field-oriented control with superimposed speed control, given a target speed exceeding a threshold speed.

Preferably, a rotational speed from a rotational speed interval of from 20 rpm to 200 rpm, particularly preferably from a rotational speed interval of from 40 rpm to 200 rpm, is predefined as the threshold rotational speed.

Preferably, the current amplitude is set by means of field-oriented regulation such that the actual lag angle corresponds to the target lag angle. Thereby, an accurate setting of the current amplitude is achieved. Preferably, a target current amplitude is predefined for this purpose as a function of the deviation of the actual lag angle from the target lag angle. Preferably, within the scope of the adjustment of the field orientation, 0 is then used as the target variable for the torque-forming current component, the target current amplitude is used as the target variable for the field-forming current component, and the target current angle of the motor current is used as the steering angle with reference to a coordinate system fixed to the stator. As explained above, the electric machine is preferably operated by means of a control system with a field-oriented controller given a target rotational speed exceeding a threshold rotational speed. In this respect, setting or adjusting the current amplitude by means of field-oriented adjustment is particularly advantageous, since already existing adjustment structures can be used.

The device according to the invention for operating an electric machine having a rotatably mounted rotor and at least one motor winding is characterized by the features of claim 10 by a control unit which is provided specifically for carrying out the method according to the invention in a defined use. If the controller is used in a defined manner, the method according to the invention is therefore carried out by or in the controller. The advantages already mentioned are thereby also obtained. Further preferred features and combinations of features emerge from the description and from the claims.

The electrical machine according to the invention has a rotatably mounted rotor and at least one motor winding and is characterized by the device according to the invention with the features of claim 11. The advantages already mentioned are thereby also obtained. Further preferred features and combinations of features emerge from the description and from the claims.

Drawings

The invention is explained in more detail below with the aid of the figures. Wherein:

figure 1 shows an electrical machine;

FIG. 2 shows a plurality of current vectors in a coordinate system fixed to the rotor, and

fig. 3 shows a method for operating an electric machine.

Detailed Description

Fig. 1 shows an electric machine 1 in a simplified illustration. The machine 1 is a pump motor 1 of a fluid pump, not shown in detail. In this regard, the machine 1 is designed for operating pump elements of a fluid pump. However, the teaching of the disclosure can in principle also be transferred to electrical machines having further fields of application.

The electric machine 1 has a rotor 2 which is rotatably mounted in a housing which is not shown. The machine 1 is here a permanent magnet excited synchronous machine 1. Accordingly, the rotor 2 has a permanent magnet arrangement 3 with at least one permanent magnet 4.

Furthermore, the machine 1 has motor windings 5. The motor winding 5 is designed as a stator winding 5 and has three phases U, V and W, which are distributed around the rotor 2 in such a way that the rotor 2 can be rotated by supplying the phases U, V and W with sinusoidal phase currents.

The electric machine 1 is assigned an electrical energy store 6. The phases U, V and W are electrically/electrically connectable to the electrical energy store 6 via power electronics 7 with a plurality of switching elements.

Furthermore, the electric machine 1 has a device 8 for operating the machine 1. The device 8 has a controller 9, which is designed to actuate or switch the switching elements of the power electronics 7.

Motor winding 5 is assigned a sensor device 10, which has at least one current sensor 20 and is designed to detect the actual phase current flowing through phases U, V and W. The sensor device 10 is connected to the controller 9 with regard to communication technology in order to provide the controller 9 with the detected actual phase currents.

The rotor 2 is assigned a rotation angle sensor 21. The rotation angle sensor 21 is configured to detect an actual rotation angle of the rotor 2. Here, the rotation angle sensor 21 is configured to detect the actual rotation angle Phi _ Rot _ mech _ Ist of the machine of the rotor 2. The rotation angle sensor 20 is connected to the controller 9 in terms of communication technology in order to provide the controller 9 with the detected actual rotation angle. The controller 9 is designed to determine the electrical actual rotational angle Phi _ Rot _ el _ Ist of the rotor 2 from the mechanical actual rotational angle Phi _ Rot _ mech _ Ist and the pole pair number of the rotor 2.

Fig. 2 shows a coordinate system fixed to the rotor, i.e. a coordinate system rotating together with the rotor 2. The coordinate system has a first axis 11 and a second axis 12. The first coordinate axis 11 is oriented parallel to the magnetic field generated by the permanent magnet means 3. The second coordinate axis 12 is oriented perpendicularly to the magnetic field generated by the permanent magnet means 3. Such coordinate systems are also referred to as dq-maps.

The first current vector 13 is shown in the coordinate system. The first current vector 13 describes a particular first motor current, i.e., a particular combination of phase currents flowing through phases U, V and W. Here, the length of the current vector 13 describes the current magnitude of the first motor current. The angle between the first coordinate axis 11 on the one hand and the first current vector 13 on the other hand is the lag angle of the first current vector 13. This lag angle corresponds to the difference between the angle of rotation of the rotor 2 on the one hand and the current angle of the first motor current on the other hand.

Furthermore, a second current vector 14 is shown in the coordinate system. The second current vector 14 describes a particular second motor current. As is apparent from fig. 2, the value of the first current vector 13 on the second axis 12 corresponds to the value of the second current vector 14 on the second axis 12. In this regard, when the motor winding 5 is loaded with the first motor current, the electric machine 1 generates the same motor output torque M1 as when the motor winding is loaded with the second motor current. However, the second current vector 14 differs from the first current vector 13 in its length and its lag angle.

An advantageous method for operating the machine 1 is explained in more detail below with reference to fig. 3.

In a first step S1, the controller 9 presets a target rotational speed N _ Soll for the rotor 2. The target rotational speed N _ Soll is a target variable because the motor current, which causes the rotor 2 to rotate at the target rotational speed N _ Soll, is set or is to be set by the method described in fig. 3.

In a second step S2, the controller 9 compares the target rotational speed N _ Soll with a predetermined threshold rotational speed. According to the exemplary embodiment illustrated in fig. 3, a rotational speed of 100 rpm is predefined as the threshold rotational speed.

If the comparison shows that the target rotational speed N _ Soll exceeds the threshold rotational speed, reference is made to a third step S3. In a third step S3, the controller 9 then operates the machine 1 by means of a cascaded control system with torque control, in particular field-oriented control, with superimposed speed control.

However, if the comparison yields that the target rotational speed N _ Soll is lower than the threshold rotational speed, then refer to the fourth step S4. In a fourth step S4, the controller 9 determines a target current angle Phi _ I _ el _ Soll for the motor current from the target rotational speed N _ Soll with reference to a coordinate system fixed to the stator. The controller 9 determines the current target current angle Phi _ I _ el _ Soll from the cumulative target rotational speed N _ Soll by means of the angle values. Accordingly, a target current angle Phi _ I _ el _ Soll with a continuous trend or "angle ramp function" is obtained.

In step S4, the target current angle Phi _ I _ el _ Soll is defined. For this purpose, a threshold angle difference, here 90 °, is specified, and the target current angle Phi _ I _ el _ Soll is defined such that the angle difference between the target current angle Phi _ I _ el _ Soll on the one hand and the actual rotational angle Phi _ Rot _ el _ Ist of the rotor 2 on the other hand is at most the threshold angle difference. That is to say, a target current angle Phi _ I _ el _ Soll is initially determined as a function of the target rotational speed N _ Soll, which target current angle deviates from the actual rotational angle Phi _ Rot _ el _ Ist by more than 90 °, so that the initially determined target current angle Phi _ I _ el _ Soll is reduced in such a way that the angle difference from the actual rotational angle Phi _ Rot _ el _ Ist is at most 90 °. In the case of a positive direction of rotation of the rotor 2, it is thereby avoided that the target current angle Phi _ I _ el _ Soll lies outside quadrant 1 of the dq diagram. Accordingly, in the case of a negative direction of rotation of the rotor 2, it is avoided that the target current angle Phi _ I _ el _ Soll lies outside quadrant 4 of the dq diagram. Thereby, a loss of synchronization of the motor 1 is avoided.

According to another exemplary embodiment, in step S1, a target rotational position is predefined for the rotor 2 instead of the target rotational speed N Soll. In this case, the target rotational position is then directly converted to the target current angle Phi _ I _ el _ Soll in step S4. Preferably, the target current angle Phi _ I _ el _ Soll is also defined in this case, as explained above.

In a fifth step S5, the controller 9 determines the actual retardation angle Phi _ Schlepp _ Ist. The controller 9 determines the actual lag angle Phi _ Schlepp _ Ist by forming the difference between the target current angle Phi _ I _ el _ Soll and the actual rotational angle Phi _ Rot _ el _ Ist of the rotor 2.

In a sixth step S6, the controller 9 presets a target lag angle Phi _ Schlepp _ Soll. The controller 9 specifies a target lag angle Phi _ Schlepp _ Soll with an angle value of 60 °. The target lag angle Phi _ Schlepp _ Soll is a target variable because the motor current, the current vector of which has the target lag angle Phi _ Schlepp _ Soll as the lag angle, is set or is to be set by the method shown in fig. 3.

In a seventh step S7, the controller 9 determines the difference between the target retardation angle Phi _ Schlepp _ Soll on the one hand and the actual retardation angle Phi _ Schlepp _ Ist on the other hand as the manipulated difference. In this regard, the controller 9 presets a target lag angle Phi _ Schlepp _ Soll as a reference variable.

In an eighth step S8, the controller 9 finds a target current amplitude I _ Abs _ Soll for the motor current from the difference found in step S7. The controller 9 thereby determines the target current amplitude I _ Abs _ Soll in such a way that a setting of the target current amplitude I _ Abs _ Soll is facilitated, so that the target lag angle Phi _ Schlepp _ Soll is set or adjusted to the actual lag angle Phi _ Schlepp _ Ist.

In a ninth step S9, the controller 9 actuates the power electronics 7 or the switching elements of the power electronics 7 in such a way that the stator-fixed actual current vector of the motor current (which is represented by the actual current amplitude I _ Abs _ Ist and the actual current angle Phi _ I _ el _ Ist) corresponds to the stator-fixed target current vector, which is represented by the target current amplitude I _ Abs _ Soll determined in step S8 and the target current angle Phi _ I _ el _ Soll determined in step S4.

For this purpose, in step S9, the controller 9 presets a target current magnitude I _ Abs _ Soll and a target current angle Phi _ I _ el _ Soll and adjusts the actual current magnitude I _ Abs _ Ist and the actual current angle Phi _ I _ el _ Ist by means of field-oriented regulation. The target current amplitude I _ Abs _ Soll is specified as a target variable for the field-forming current component. 0 is specified as a target variable for a current component for forming torque. Furthermore, a target current angle Phi _ I _ el _ Soll is specified as a steering angle.

According to another embodiment, voltage regulation is performed in step S9. In this case, the target voltage amplitude U _ Abs _ Soll is then found in step S8. In step S4, the target voltage angle Phi _ U _ el _ Soll is determined. In step S9, controller 9 then actuates power electronics 7 or the switching elements of power electronics 7 in such a way that the actual voltage vector fixed to the stator, which is represented by actual voltage amplitude U _ Abs _ Ist and actual voltage angle Phi _ U _ el _ Ist, corresponds to the target voltage vector fixed to the stator, which is represented by target voltage amplitude U _ Abs _ Soll and target voltage angle Phi _ U _ el _ Soll. That is to say, in step S9, the voltage characteristic variable is used as a basis for the regulation instead of the current characteristic variable.

In the following, various aspects of the method are explained in more detail again with reference to fig. 2. As mentioned above, the same motor output torque M1 is produced when the motor winding 5 is loaded with the first motor current, as when the motor winding 5 is loaded with the second motor current. In the following, it is assumed that the motor output torque M1 is sufficient to rotate the rotor 2 at a predefined target rotational speed N Soll. Furthermore, the lag angle of the first current vector 13 is assumed to be a predefined target lag angle Phi _ Schlepp _ Soll. Finally, it is assumed that the second current vector 14 describes the motor current currently flowing through the motor winding 5. The lag angle of the second current vector 14 therefore corresponds to the actual lag angle Phi _ Schlepp _ Ist.

Based on this, in step S7, the controller 9 determines the difference between the actual lag angle Phi _ Schlepp _ Ist and the target lag angle Phi _ Schlepp _ Soll. Since the actual lag angle Phi _ Schlepp _ Ist is smaller than the target lag angle Phi _ Schlepp _ Soll, the controller 9 determines in step S8 a target current amplitude I _ Abs _ Soll which is smaller than the current amplitude described by the second current vector 14, i.e. smaller than the current amplitude described by the first current vector 13.

Finally, the controller 9 sets the target current amplitude I _ Abs _ Soll as the actual current amplitude I _ Abs _ Ist in accordance with method step S9. Since machine 1 is stable in quadrant 1 of the rotor-fixed coordinate system in the case of a positive direction of rotation or in quadrant 4 of the rotor-fixed coordinate system in the case of a negative direction of rotation, the lag angle of first current vector 13 is also automatically set to the actual lag angle Phi _ Schlepp _ Ist by setting the current amplitude described by first current vector 13 as actual current amplitude I _ Abs _ Ist. The rotational speed of the rotor 2 and the frequency of the phase currents are at least substantially constant, since the target current angle Phi _ I _ el _ Soll changes at a constant angular speed with respect to a coordinate system fixed to the stator as a function of the target rotational speed N _ Soll.

Claims

1. Method for operating an electric machine, wherein a machine (1) has a rotatably mounted rotor (2) and at least one motor winding (5), wherein a target rotational speed (N _ Soll) is predefined for the rotor (2), and wherein the motor winding (5) is loaded with a motor current such that an actual rotational speed (N _ Ist) of the rotor (2) corresponds to the target rotational speed (N _ Soll),

characterized in that a target lag angle (Phi _ Schlepp _ Soll) is predefined for a current vector (13), which describes the motor current with reference to a coordinate system fixed to the rotor, wherein the target lag angle (Phi _ Schlepp _ Soll) has an angular value from an angular interval from 0 ° to 90 °, and wherein the current magnitude (I _ Abs) of the motor current is set such that the actual lag angle (Phi _ Schlepp _ Ist) of the current vector (13) corresponds to the target lag angle (Phi _ Schlepp _ Soll).

2. Method according to claim 1, characterized in that the current amplitude (I Abs) of the motor current is increased in case an actual lag angle (Phi _ Schlepp _ Ist) exceeding the target lag angle (Phi _ Schlepp _ Soll) is present and/or the current amplitude (I Abs) of the motor current is decreased in case an actual lag angle (Phi _ Schlepp _ Ist) below the target lag angle (Phi _ Schlepp _ Soll) is present.

3. Method according to any one of the preceding claims, characterized in that the target lag angle (Phi _ Schlepp _ Soll) has an angle value from an angle interval from 20 ° to 80 °, preferably an angle value from an angle interval from 30 ° to 70 °, particularly preferably an angle value from an angle interval from 55 ° to 65 °.

4. Method according to any one of the preceding claims, characterized in that the target hysteresis angle (Phi _ Schlepp _ Soll) is predefined as a function of load torque fluctuations.

5. Method according to any one of the preceding claims, characterized in that the target retardation angle (Phi _ Schlepp _ Soll) is predefined as a function of the target rotational speed (N _ Soll).

6. Method according to any one of claims 1 to 4, characterized in that the target lag angle (Phi _ Schlepp _ Soll) is predefined independently of the target rotational speed (N _ Soll).

7. Method according to one of the preceding claims, characterized in that a threshold rotational speed is predefined, wherein the current amplitude (I Abs) of the motor current is set only given a target rotational speed (N _ Soll) which is lower than the threshold rotational speed such that the actual lag angle (Phi _ Schlepp _ Ist) corresponds to the target lag angle (Phi _ Schlepp _ Soll).

8. Method according to claim 7, characterized in that a rotational speed from a rotational speed interval of 20 to 200 rpm, particularly preferably from a rotational speed interval of 40 to 200 rpm, is predefined as the threshold rotational speed.

9. Method according to any one of the preceding claims, characterized in that the current amplitude (I Abs) is set by means of field-oriented regulation such that the actual lag angle (Phi _ Schlepp _ Ist) corresponds to the target lag angle (Phi _ Schlepp _ Soll).

10. Device for operating an electrical machine, wherein the machine (1) has a rotatably mounted rotor (2) and at least one motor winding (5), characterized in that the device (8) has a control unit (9) which is provided to carry out the method according to one of the preceding claims in a defined use.

11. Electrical machine with a rotatably mounted rotor (2) and at least one motor winding (5), characterized by a device (8) according to the preceding claim.