Method for Monitoring the Operation of a Frequency Converter, and Frequency Converter

Abstract

A method for monitoring the operation of a frequency converter (1), which is designed to drive an electric motor (2), wherein the method comprises the following steps: generating phase voltages (u1, u2, u3) for corresponding phase sections (2.1, 2.2, 2.3) of the electric motor (2), ascertaining a voltage rotating field, measuring occurring phase currents (i1, i2, i3), ascertaining a current rotating field depending on the measured phase currents (i1, i2, i3), calculating a phase difference between the voltage rotating field and the current rotating field and/or calculating a frequency difference between the frequency of the voltage rotating field and the frequency of the current rotating field, and determining a fault state when the phase difference exceeds a phase difference threshold value and/or when the frequency difference exceeds a frequency difference threshold value. pa (FIG. 2)

Claims

1-10. (canceled)

11. A method for monitoring operation of a frequency converter designed to drive an electric motor, the method comprising the steps of: generating phase voltages for corresponding phase sections of the electric motor based on setpoint values for the phase voltages; determining a voltage rotating field; measuring occurring phase currents; determining a current rotating field depending on the measured phase currents; calculating a phase difference between the voltage rotating field and the current rotating field and/or calculating a frequency difference between a frequency of the voltage rotating field and a frequency of the current rotating field; and determining a fault state when the phase difference exceeds a phase difference threshold value and/or when the frequency difference exceeds a frequency difference threshold value.

12. The method according to claim 11, wherein the voltage rotating field is determined depending on the setpoint values for the phase voltages.

13. The method according to claim 11, wherein the phase voltages for the corresponding phase sections of the electric motor are generated by way of pulse width modulation with varying duty cycles, and the voltage rotating field is determined depending on the duty cycles of the pulse width modulation.

14. The method according to claim 11, wherein after the fault state has been determined, fault handling is carried out.

15. The method according to claim 14, wherein the fault handling is carried out by suppressing the generation of phase voltages.

16. The method according to claim 11, wherein after the fault state has been determined, a safe torque off function is carried out.

17. The method according to claim 11, wherein the frequency converter comprises: a control unit; a power unit; and at least one safety unit, wherein the control unit, the power unit and the at least one safety unit are coupled to one another for data exchange via a communication channel, wherein the setpoint values for the phase voltages are transmitted from the control unit via the communication channel to the power unit, wherein measurement values relating to the measured phase currents are transmitted from the power unit via the communication channel to the control unit, and wherein the at least one safety unit evaluates the respective setpoint values for the phase voltages transmitted via the communication channel and the measurement values relating to the measured phase currents transmitted via the communication channel in order to determine the fault state.

18. A frequency converter, comprising: a control unit; a power unit; and at least one safety unit, wherein the frequency converter is operatively configured to: generate phase voltages for corresponding phase sections of the electric motor based on setpoint values for the phase voltages; determine a voltage rotating field; measure occurring phase currents; determine a current rotating field depending on the measured phase currents; calculate a phase difference between the voltage rotating field and the current rotating field and/or calculate a frequency difference between a frequency of the voltage rotating field and the frequency of the current rotating field; and determine a fault state when the phase difference exceeds a phase difference threshold value and/or when the frequency difference exceeds a frequency difference threshold value, and wherein the control unit, the power unit and the at least one safety unit are coupled to one another for purposes of data exchange via a communication channel, wherein the setpoint values for the phase voltages are transmitted from the control unit via the communication channel to the power unit, wherein measurement values relating to measured phase currents are transmitted from the power unit via the communication channel to the control unit, and wherein the at least one safety unit is designed to evaluate the respective setpoint values for the phase voltages transmitted via the communication channel and the measurement values relating to the measured phase currents transmitted via the communication channel in order to determine the fault state.

19. The frequency converter according to claim 18, wherein the control unit is configured to regulate the phase currents.

20. The frequency converter according to claim 19, wherein the control unit is configured to use the phase voltages as manipulated variables for regulation of the phase currents.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 highly schematically shows a drive system with a frequency converter and an electric motor driven by means of the frequency converter; and

[0038] FIG. 2 is a schematic block diagram of an internal structure of the frequency converter shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 highly schematically shows a drive system with a frequency converter 1 and an electric motor 2 driven by means of the frequency converter 1.

[0040] The frequency converter 1 is designed to generate three phase voltages u1, u2, u3 for corresponding phase sections 2.1, 2.2, 2.3 or between corresponding phase sections 2.1, 2.2, 2.3 of the electric motor 2 and to measure occurring phase currents i1, i2 and i3. Reference should also be made in this respect to the relevant technical literature.

[0041] FIG. 2 shows a schematic block diagram of an internal structure of the frequency converter 1 shown in FIG. 1.

[0042] With reference to FIG. 2, the frequency converter 1 has a control unit 3, for example in the form of a microcontroller.

[0043] The frequency converter 1 also comprises a power unit 4. The power unit 4 comprises a conventional inverter 8 for generating the phase voltages u1, u2 and u 3. The power unit 4 also comprises conventional current sensors 9, for example in the form of shunt resistors. The phase currents i1, i2 and i3 are measured by means of the current sensors 9. The power unit 4 also comprises a control device 10, which controls all essential functions of the power unit 4. The power unit 4 also comprises a safe torque off (STO) circuit 11, by means of which an STO state can be brought about. The inverter 8 is connected to the control device 10 via optocouplers 12 and 13. The current sensors 9 are connected to the control device 10 by means of an optional signal amplifier 14.

[0044] The frequency converter 1 also comprises a first safety unit 5 and a second safety unit 6.

[0045] The control unit 3, the power unit 4 (DC-isolated by an optocoupler 15), the first safety unit 5 and the second safety unit 6 are coupled to one another for the purpose of data exchange via a communication channel 7. A point-to-point data link between the two safety units 5 and 6 is optionally provided.

[0046] A respective setpoint value for the phase voltages u1, u2, u3 is transmitted from the control unit 3 via the communication channel 7 to the power unit 4. Measurement values relating to the measured phase currents i1, i2, i3 are transmitted from the power unit 4 via the communication channel 7 to the control unit 3.

[0047] The safety units 5, 6 are each designed to evaluate, independently of one another, the setpoint value or values for the phase voltages u1, u2, u3 transmitted via the communication channel 7 and the measurement values relating to the measured phase currents i1, i2, i3 transmitted via the communication channel 7 in order to determine a fault state.

[0048] For this purpose, the safety units 5, 6 each ascertain a voltage rotating field depending on the phase voltages u1, u2, u3 generated or to be generated. The safety units 5, 6 also each ascertain a current rotating field depending on the measured phase currents i1, i2 , i3 and each calculate a phase difference between the voltage rotating field and the current rotating field and/or calculate a frequency difference between the frequency of the voltage rotating field and the frequency of the current rotating field. The safety units 5, 6 each determine a fault state when the phase difference exceeds a phase difference threshold value and/or when the frequency difference exceeds a frequency difference threshold value.

[0049] If a fault state has been determined in at least one of the safety units 5, 6, they carry out fault handling independently of one another by virtue of the safe torque off (STO) circuit 11 being signaled to bring about an STO state by way of suitable driving of the inverter 8.

[0050] The safety units 5, 6 can be arranged on a safety printed circuit board 16. The control unit 3 can accordingly be arranged on a control printed circuit board 17. The power unit 4 can finally be arranged on a power printed circuit board 18.