METHOD FOR RAPID CLOSED-LOOP CONTROL OF THE AVERAGE VALUE OF A CONTROLLED VARIABLE, DATA CARRIER WITH PROGRAM AS WELL AS MOTOR CONTROL UNIT FOR EXECUTING THE METHOD AND DRIVE MOTOR WITH SUCH A MOTOR CONTROL UNIT

Abstract

A method is disclosed for closed-loop control of a controlled variable to a given reference variable, wherein the actual value and/or the measured actual value of the controlled variable is/are influenced by a fluctuating effect with a certain periodicity. The controlled variable is only readjusted if there is a control difference between the reference variable and an average value of the actual value of the controlled variable averaged over the period duration of the periodicity. Measurement values are determined within the period duration of each periodicity at concrete measurement time points in a certain controller cycle, these measurement values correlating with a respective actual value of the controlled variable or corresponding to the actual value of the controlled variable, and/or being adapted to determine therefrom the control difference between the reference variable and the average value of the actual value of the controlled variable. The control difference is determined at each concrete measurement time point and the controlled variable is selectively readjusted.

Claims

1. A method for closed-loop control of a controlled variable to a given reference variable (w), wherein an actual value and/or a measured actual value of the controlled variable is/are influenced by a fluctuating effect with a certain periodicity, the method comprising: readjusting the controlled variable only if there is a control difference between the reference variable (w) and an average value of the actual value of the controlled variable averaged over a period duration (T, T.sub.1, T.sub.2) of the periodicity; determining measurement values (M.sub.1 to M.sub.n, M.sub.1′ to M.sub.n′) within the period duration (T, T.sub.1, T.sub.2) of each periodicity at concrete measurement time points (t.sub.1 to t.sub.n, t.sub.1′ to t.sub.n′) in a certain controller cycle, these measurement values correlating with a respective actual value of the controlled variable or corresponding to the actual value of the controlled variable, and/or being adapted to determine therefrom the control difference between the reference variable (w) and the average value of the actual value of the controlled variable; and determining the control difference at each concrete measurement time point (t.sub.1 to t.sub.n, t.sub.1′ to t.sub.n′) and selectively readjusting the controlled variable.

2. The method according to claim 1, comprising: for determining the control difference, calculating a differential value between the measurement value at the current measurement time point and the respective measurement value of a preceding periodicity that was recorded n measurement time points earlier, the control difference being derived from this differential value.

3. The method according to claim 2, comprising: for determining the control difference, calculating the actual average value of the controlled variable from the measurement value at the current measurement time point as well as from an n−1 measurement values of the earlier n−1 measurement time points.

4. The method according to claim 3, comprising: choosing the controller cycle such that at least six measurement time points (M.sub.1 to M.sub.n, M.sub.1′ to M.sub.n′) lie within the period duration (T, T.sub.1, T.sub.2) of the periodicity.

5. The method according to claim 4, comprising: choosing the controller cycle such that at least twelve measurement time points (M.sub.1 to M.sub.n, M.sub.1′ to M.sub.n′) lie within the period duration (T, T.sub.1, T.sub.2) of the periodicity.

6. The method according to claim 5, comprising: determining the period duration (T, T.sub.1, T.sub.2) of the periodicity continuously by evaluating the measurement values (M.sub.1 to M.sub.n, M.sub.1′ to M.sub.n′).

7. The method according to claim 1, applied for closed-loop control of a drive motor, the controlled variable being speed of the drive motor.

8. The method according to claim 1, wherein the actual value of the controlled variable is influenced by a fluctuating load with a certain load period.

9. The method according to claim 1, wherein the measured actual value of the controlled variable is influenced by periodic measurement errors within a measurement period, due to pitch errors or inaccuracies in a material measure of a rotary encoder.

10. A machine-readable data carrier containing a computer readable program, wherein the data carrier is configured for a motor control unit of a drive motor, and wherein the computer readable program is a sequence of instructions, which, when executed by a processor, will cause the processor to execute a method according to claim 1.

11. A motor control unit for a drive motor, the motor control unit comprising: a processor configured to and adapted to execute a set of computer readable instructions for causing the processor to perform closed-loop control of a controlled variable to a given reference variable (w), wherein an actual value and/or a measured actual value of the controlled variable is/are influenced by a fluctuating effect with a certain periodicity, the processor being configured to execute steps of: readjust the controlled variable only if there is a control difference between the reference variable (w) and an average value of the actual value of the controlled variable averaged over a period duration (T, T.sub.1, T.sub.2) of the periodicity; determine measurement values (M.sub.1 to M.sub.n, M.sub.1′ to M.sub.n′) within the period duration (T, T.sub.1, T.sub.2) of each periodicity at concrete measurement time points (t.sub.1 to t.sub.n, t.sub.1′ to t.sub.n′) in a certain controller cycle, these measurement values correlating with a respective actual value of the controlled variable or corresponding to the actual value of the controlled variable, and/or being adapted to determine therefrom the control difference between the reference variable (w) and the average value of the actual value of the controlled variable; and determine the control difference at each concrete measurement time point (t.sub.1 to t.sub.n, t.sub.1′ to t.sub.n′) and selectively readjusting the controlled variable.

12. A motor control unit according to claim 11, in combination with a drive motor wherein the drive motor comprises: a rotor; and the motor control unit.

13. The motor control unit and drive motor combination according to claim 12, wherein the drive motor comprises: at least one sensor for detecting a position or location or speed of the rotor, wherein the motor control unit is configured to calculate the control difference on a basis of measurement values provided by the sensor.

14. The motor control unit and drive motor combination according to claim 13, wherein the drive motor (1) is an electric motor, the sensor being a Hall sensor whose signal is also configured for commutating the electric motor.

15. A drive motor comprising: a rotor; and a motor control unit configured to and adapted to execute closed-loop control of a controlled variable to a given reference variable (w), wherein an actual value and/or a measured actual value of the controlled variable is/are influenced by a fluctuating effect with a certain periodicity, the motor control unit being configured to: readjust the controlled variable only if there is a control difference between the reference variable (w) and an average value of the actual value of the controlled variable averaged over a period duration (T, T.sub.1, T.sub.2) of the periodicity; determine measurement values (M.sub.1 to M.sub.n, M.sub.1′ to M.sub.n′) within the period duration (T, T.sub.1, T.sub.2) of each periodicity at concrete measurement time points (t.sub.1 to t.sub.n, t.sub.1′ to t.sub.n′) in a certain controller cycle, these measurement values correlating with a respective actual value of the controlled variable or corresponding to the actual value of the controlled variable, and/or being adapted to determine therefrom the control difference between the reference variable (w) and the average value of the actual value of the controlled variable; and determine the control difference at each concrete measurement time point (t.sub.1 to t.sub.n, t.sub.1′ to t.sub.n′) and selectively readjusting the controlled variable; wherein the drive motor is an electric motor and the motor control unit is additionally configured to calculate the control difference on a basis of values which it generates, without making use of a sensor, on a basis of the parameters inductance and electromagnetic force by an algorithm for determining a position or location or speed of the rotor.

16. The method according to claim 7, wherein the actual value of the controlled variable is influenced by a fluctuating load with a certain load period.

17. The method according to claim 16, wherein the measured actual value of the controlled variable is influenced by periodic measurement errors within a measurement period, due to pitch errors or inaccuracies in a material measure of a rotary encoder.

Description

[0022] Embodiments of the present invention will be explained in more detail hereinafter on the basis of drawings, in which

[0023] FIG. 1 shows a schematic flowchart of a method according to the present invention used for closed-loop control of the speed of an electric motor, and

[0024] FIG. 2 shows the associated speed curve of the electric motor.

[0025] In the statements following hereinafter, like components will be identified by like reference numerals. If a figure comprises reference numerals, which are not dealt with in detail in the associated description of the figure, reference is made to preceding or subsequent descriptions of a figure.

[0026] FIG. 1 shows a schematic flowchart of a method according to the present invention used for closed-loop control of the speed of an electric motor 1 connected to a fluctuating load, e.g. a diaphragm pump or a piston pump, having a certain load period. However, the flowchart shown here is, alternatively, also suitable for use with a rotary encoder exhibiting pitch errors or inaccuracies in its material measure within a specific measurement period. In FIG. 2, which shows the actual speed curve of the electric motor over the time t, two complete successive period durations T.sub.1 and T.sub.2 are shown. It can easily be seen that the actual speed reaches a maximum at the beginning and at the end of each period duration. These are therefore periodically recurring load characteristics, which lead to correspondingly periodically recurring speed characteristics of the electric motor. In the case shown, the period duration does not change. The period duration T.sub.2 thus corresponds to the period duration T.sub.1. The method works optimally, if the load changes correlate with the angle of rotation of the drive and exhibit a single or multiple periodicity to the speed of the electric motor. At this point, however, reference is made to the fact that the method according to the present invention will also be suitable for use, if the position of the changes of load and/or the period duration change slowly in relation to the controller cycle and/or the sampling rate. Likewise, also the load change characteristics may change slowly in relation to the controller cycle and/or the sampling rate.

[0027] The electric motor 1, which is shown only schematically in FIG. 1, has, for the purpose of commutation, at least one Hall sensor whose sensor signal can be used to determine the rotor position or the rotor speed and, in the case of the method according to the present invention, can serve to determine an average value of the actual speed averaged over the period duration T of the load period. To this end, the sensor signal is fed to the speed determination unit 2, which also takes into account the period duration T for determining the average speed. In some systems, the motor control unit may operate with a fixedly predetermined period duration under certain circumstances. Normally, however, it will be necessary to continuously determine the period duration and transmit it to the speed determination unit 2. This can be done e.g. by the motor control unit itself, in particular by an appropriate evaluation of the sensor signal, or by an external evaluation unit.

[0028] In the case of the embodiment shown in FIG. 2, the controller cycle and/or the sampling rate, have been chosen such that a total of twelve measurement values (M.sub.1 to M.sub.12 within period duration T.sub.1; M.sub.1′ to M.sub.12′ within period duration T.sub.2) is determined for each load period at a total of twelve concrete points in time (t.sub.1 to t.sub.12 within period duration T.sub.1; t.sub.1′ to t.sub.12′ within period duration T.sub.2). At each concrete point in time, an average value for the speed of the electric motor can be calculated on the basis of the respective current measurement value and the eleven measurement values measured immediately before. As shown in FIG. 1, this average value can then be compared with the respective reference variable w, which corresponds to the target speed. The respective resultant control difference is fed to the actual controller 3 of the motor control unit. This controller, in turn, transmits respective default values to the inverter 4, which supplies the individual phases of the electric motor 1 with voltage.

[0029] Instead of calculating an average value of the motor speed at each measurement time point from the current measurement value and the eleven measurement values recorded immediately before, the control difference may alternatively also be determined, as indicated in FIG. 2, by calculating the difference between the current measurement value and the measurement value of the preceding load period that was recorded 12 measurement time points earlier. In this respect, FIG. 2 shows exemplarily the measurement values M.sub.3′ of the second load period T.sub.2 and M.sub.3 of the first load period T.sub.1. If the difference between the measurement value at the current measurement time point and the respective measurement value recorded 12 measurement time points earlier is equal to zero, it can be assumed, according to a simplified determination of the control difference, that no control difference exists.

LIST OF REFERENCE NUMERALS

[0030] 1 drive motor/electric motor [0031] 2 speed determination unit [0032] 3 controller [0033] 4 inverter [0034] T, T.sub.1, T.sub.2 period duration of the periodicity or load period and/or measurement period [0035] t.sub.1 to t.sub.n measurement time points during the first period duration [0036] t.sub.1′ to t.sub.n′ measurement time points during the second period duration [0037] M.sub.1 to M.sub.n measurement values during the first period duration [0038] M.sub.1′ to M.sub.n′ measurement values during the second period duration [0039] n number of measurement time points/measurement values [0040] w reference variable (target value of speed)