METHOD AND APPARATUS FOR FAILSAFE MONITORING AN ELECTROMOTIVE DRIVE

• US 20110084642A1
• Filed: 10/27/2010
• Published: 04/14/2011
• Est. Priority Date: 10/10/2009
• Status: Active Grant

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: AMS, Mathias
• Granted Patent: US 8,310,196 B2
• Time in Patent Office: Days
• US Class Current: 318/490
• CPC Class Codes: H02H 7/0844 Fail safe control, e.g. by comparing control signal and controlled current, isolating motor on commutation error

Abstract

The invention relates to a method and to an apparatus for the failsafe monitoring of an electromotive drive (10) without additional sensors. The apparatus comprises a drive having a three-phase control of an electric motor, means (20) for detecting the current and voltage profiles of each of the three phases U(, V, W), as they are forwarded to the motor (10) by drive electronics (12), means (26) for determining the load speed (n_L) while using the detected current and voltage values, wherein the determination of the load speed (n_L) takes place by calculating an observer model with reference to the detected current, to the detected voltage, to the frequency f_FU preset by the control and to the characteristic data of the motor (10) and means (28) for generating a failsafe switch signal (30) for the motor (10) when the calculated load speed (n_L) does not correspond to a preset desired speed within the framework of preset tolerances. The load torque (M_L) can also be determined and monitored with reference to the observer model.

Claims

1. A method for failsafe monitoring of an electromagnetic drive (10) with a three-phase control comprising the steps:

1) detecting the current and voltage profiles, as they are provided to the motor (10) by drive electronics (12);

     2) determining the load speed (n_L) while using these values;

     3) failsafe switching off of the drive (10) when the calculated load speed (n_L) does not correspond to a preset desired speed within the framework of preset tolerances, characterized in that the step of determining the load speed (n_L) takes place by calculating an observer model with reference to the detected current (I_mess, I_eff), to the detected voltage (U_mess, U_eff), to the frequency (f_FU, f_sync) preset by the control and to the characteristic data of the motor (10).

2. A method in accordance with claim 1, characterized in that, in the case of the asynchronous motor, the load speed determination takes

3. A method in accordance with claim 1, characterized in that the load torque (M_L) is determined from the detected current (I_mess) and the characteristic data for the nominal torque (M_n) and for the nominal current (I_n) and a failsafe switching off takes place on exceeding a limit value.

4. A method in accordance with claim 1, characterized in that, in the case of the asynchronous motor, the load speed determination takes place with reference to the formula

n=n_syn(1−

s)

where n_syn is the synchronous speed and s is the slip.

5. A method in accordance with claim 4, characterized in that the slip is calculated from the effective values of current and voltage, the rotor resistance and the leakage inductance.

6. A method in accordance with claim 4, characterized in that the tilting torque (M_k) and the tilting slip (s_k) is calculated from the characteristic data and the load torque (M_L) is determined together with the slip (s) and a failsafe switching off takes place on exceeding a limit value.

7. A method in accordance with claim 1, characterized in that, in the case of the asynchronous motor, the load speed determination takes place with reference to the formula

8. A method in accordance with claim 1, characterized in that the calculation of the observer model takes place in a microprocessor (22, 24) and the detected current and voltage signals are adapted for a microprocessor evaluation.

9. A method in accordance with claim 1, characterized in that the voltages and currents of all three phases are detected and the third voltage and the third current respectively is determined from the respective voltages and currents in accordance with Σ

U=0 and Σ

I=0 respectively and a failsafe switching off takes place on deviations of a calculated value from the corresponding measured value.

10. A method in accordance with claim 1, characterized in that a motor or a generator operating mode is recognized via the phase angle between the current and the voltage.

11. A method in accordance with claim 1, characterized in that the direction of rotation is determined from the phase sequence of the three phases (U, V, W) and a failsafe switching off takes place on a deviation from a desired direction of rotation.

12. An apparatus for the failsafe monitoring of an electromotive drive (10) with a three-phase control of an electric motor, the apparatus comprising means (20) for detecting the current and voltage profiles of each of the three phases (U, V, W), as they are provided to the motor (10) by drive electronics (12), means (26) for determining the load speed (n_L) while using the detected current and voltage values (I_mess), (U_mess;

I_eff, U_eff), wherein the determination of the load speed (n_L) takes place by calculating an observer model with reference to the detected current, to the detected voltage, to the frequency (f_FU) preset by the control and to the characteristic data of the motor (10), and comprising means (28) for generating a failsafe switching signal (30) for the motor (10) when the calculated load speed (n_L) does not correspond to a preset desired speed within the framework of preset tolerances.

13. An apparatus in accordance with claim 12, characterized in that the means (22, 24) for calculating the observer model include a microprocessor (22, 24) and the apparatus has means (20) for adapting the detected current and voltage signals to the microprocessor evaluation.

14. An apparatus in accordance with claim 12, characterized in that means (38) for determining the load torque (M_L) are provided which determine the load torque (M_L) from the detected current (I_mess, I_eff) and from the detected voltage (U_mess, U_eff) and from the characteristic data and a failsafe switching off takes place on exceeding a limit value.

15. An apparatus in accordance with claim 12, characterized in that the means (20) for detecting the current and voltage profiles detect all three phases (U, V, W) and means (34) for consistency checking of the voltages and currents are provided with which the third voltage and the third current respectively can be calculated from two respective voltages and two respective currents in accordance with Σ

U=0 and Σ

I=0 respectively and a failsafe switching off takes place on deviations of a calculated value from the corresponding measured value.

16. An apparatus in accordance with claim 14, characterized in that the means (20) for detecting the current and voltage profiles detect all three phases (U, V, W) and means (34) for consistency checking of the voltages and currents are provided with which the third voltage and the third current respectively can be calculated from two respective voltages and two respective currents in accordance with Σ

U=0 and Σ

I=0 respectively and a failsafe switching off takes place on deviations of a calculated value from the corresponding measured value.

17. An apparatus in accordance with claim 12, characterized in that means (40) are provided for recognizing the operating mode to recognize whether a motor or a generator operating mode is present.

18. An apparatus in accordance with claim 14, characterized in that means (40) are provided for recognizing the operating mode to recognize whether a motor or a generator operating mode is present.

19. An apparatus in accordance with claim 12, characterized in that means (36) for determining the direction of rotation are provided which determine the direction of rotation from the phase sequence of the three phases (U, V, W) and a failsafe switching off takes place on a deviation from a desired direction of rotation.

20. An apparatus in accordance with claim 14, characterized in that means (36) for determining the direction of rotation are provided which determine the direction of rotation from the phase sequence of the three phases (U, V, W) and a failsafe switching off takes place on a deviation from a desired direction of rotation.

21. An apparatus in accordance with claim 12, characterized by a two-channel design, with in particular two redundant microprocessors (22 and 24) being provided which are preferably diverse and/or on which diverse algorithms run.

22. An apparatus in accordance with claim 14, characterized by a two-channel design, with in particular two redundant microprocessors (22 and 24) being provided which are preferably diverse and/or on which diverse algorithms run.