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 control an electric motor (2), wherein the method comprises the steps of: - generating phase voltages (u1, u2, u3) for corresponding phase lines (2.1, 2.2, 2.3) of the electric motor (2), - determining a voltage rotating field, - measuring the occurring phase currents (i1, i2, i3), - determining a current rotating field based 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 a frequency of the voltage rotating field and a frequency of the current rotating field, and - determining an error state when the phase difference exceeds a phase difference threshold value and / or when the frequency difference exceeds a frequency difference threshold value.

Description

Technical Field

[0001] The invention relates to a method for monitoring the operation of a frequency converter and a frequency converter. Summary of the invention

[0002] The object of the present invention is to provide a method for monitoring the operation of a frequency converter and a frequency converter which allow reliable and cost-effective monitoring of the operation.

[0003] The invention achieves this object by a method for monitoring the operation of a frequency converter according to claim 1 and a frequency converter according to claim 7 .

[0004] The method is used to monitor the operation of a frequency converter which is designed to control an electric motor. The electric motor may be a synchronous motor or an asynchronous motor, for example.

[0005] In this method, based on the associated rated values ​​of the phase voltages, a normal phase voltage is generated for the corresponding phase line or between the corresponding phase lines of the motor. For example, the amplitude and frequency of the phase voltage are generated based on the rated values ​​so that a desired rotational speed of the motor and / or a desired torque of the motor occurs. Typically, three phase voltages are generated for three corresponding phase lines. In this regard, reference should also be made to the relevant professional literature.

[0006] As a further method step, the voltage rotation field is determined. In particular, the voltage rotation field is calculated based on the rated values ​​of the phase voltages. In determining the voltage rotation field, reference should also be made to the relevant professional literature.

[0007] As a further method step, at least one phase current is measured, which flows in the phase line and occurs due to the phase voltage. In the case of a three-phase motor, it may be sufficient to measure two of the three phase currents, since the third phase current is derived computationally from the other two phase currents.

[0008] As a further method step, a current rotation field is calculated from the one or more measured phase currents. In this regard, reference should also be made to the relevant specialist literature.

[0009] As a further method step, a phase difference between the voltage rotating field and the current rotating field and / or a frequency difference between the frequency of the voltage rotating field and the frequency of the current rotating field is calculated.

[0010] Finally, an error state is determined if the phase difference or the value of the phase difference exceeds a phase difference threshold value and / or if the frequency difference or the value of the frequency difference exceeds a frequency difference threshold value.

[0011] The phase difference threshold and the frequency difference threshold can be absolute or relative values. The phase difference threshold and the frequency difference threshold can take into account possible slip. The phase difference threshold and the frequency difference threshold can be in the range between 1% and 10% for example with respect to the phase of the voltage rotating field or with respect to the frequency of the voltage rotating field.

[0012] The position of the rotor of an electric motor is typically determined in applications with a safety function using so-called safety encoder systems. With the aid of such encoder systems, it is possible to determine the rotational speed and the angular position of the rotor. However, encoder systems represent a space and cost factor. Therefore, it is common to forgo such encoder systems in cost-critical installations. However, this leads to limitations in terms of dynamics and accuracy, but this is acceptable in many applications.

[0013] Conventional synchronous or asynchronous motors are operated with a three-phase voltage rotating field, wherein the phase lines are denoted in the following figure by 2.1, 2.2, 2.3 (also conventionally referred to as U, V and W). Angular speed of the rotor Depends on the angular velocity of the rotating field of the feed voltage Or rotation frequency f. Through the voltage rotating field, phase currents i1, i2, i3 are generated in each of the three phase lines 2.1, 2.2, 2.3. For the angular velocity Applicable to .

[0014] In the case of synchronous motors, there is a strict ratio between the angular velocity of the rotating magnetic field or voltage rotating field and the angular velocity of the rotor. In the case of asynchronous motors, the angular velocity of the rotating magnetic field or voltage rotating field is always higher than the angular velocity of the rotor during motor operation. The difference is described by the slip (s) and is required so that the asynchronous motor can apply torque. In this case, the slip during motor operation is always between 0 and 1. When calculating the mechanical speed, the number of pole pairs (p) must still be taken into account.

[0015] Therefore, for synchronous motors:

[0016] .

[0017] In the ASM case, it is still necessary to supplement the slip.

[0018]

[0019] According to the invention, a safety encoder system is now dispensed with, in which the frequency of the current rotating field and the frequency of the voltage rotating field are used to monitor the operation of the frequency converter, for example to monitor the angular speed of an electric motor actuated by means of the frequency converter.

[0020] The voltage rotating field describes the behavior of the voltage in the electric motor. In order to obtain the current alignment of the current vector and the voltage vector describing the current rotating field or voltage rotating field, the current voltage values ​​or current values, respectively, are geometrically added.

[0021] ,in .

[0022] In addition to the amplitude information, the value It also contains angle information. To calculate the rotational speed, only the derivative of the angle can be determined. Instead of the voltage, the duty cycle can also be used to calculate the angular velocity in the voltage rotation field. The duty cycle and the voltage differ only in amplitude, which in turn has no influence on the angular velocity.

[0023] In this case, the property can be used that the current and the voltage (or the duty cycle) contain the rotating field frequency and with these two values ​​it is possible to determine the speed of the rotor while neglecting the slip.

[0024] It is therefore possible to construct a two-channel structure in order to monitor the angular speed of the rotor. In this case, the first channel forms a voltage rotating field and the second channel forms a current rotating field.

[0025] After the error state has been determined, the frequency converter can be shut down, for example, based on the functions STO, SS1, SLS, SMS and SDI.

[0026] The invention is a cost-effective solution for transmitter-free safety technology, in particular for the functions SS1, SLS, SMS, SDI and SMS. In addition, even in the case of asynchronous motors, without additional sensor devices in the power output stage, it is possible to detect the output frequency safely. Thus, the invention makes it possible to implement speed-dependent safety functions, in particular in the case of asynchronous motors, without additional feedback systems.

[0027] The output frequency, i.e. the rotational speed of the electric motor, can be monitored by independently evaluating the phase angles of the current rotating field and the voltage rotating field. The monitoring can be carried out on a communication channel between the control unit and the power unit, wherein the voltage rotating field or the associated voltage space vector is formed by the setpoint values ​​of the phase voltages from the control unit and the current rotating field or the associated current vector is formed by the measured values ​​of the phase currents from the power unit.

[0028] The two-channel capability required for safety reasons is achieved by monitoring two physical variables that are separate from one another, namely, on the one hand, the angle of the voltage rotating field or voltage vector and, on the other hand, the angle of the current rotating field or current vector.

[0029] There is the possibility that both monitoring units monitor the angle of the voltage and current vectors and initiate or maintain a safe state if the detected rotational speed is outside predefined limits.

[0030] For the detection of the rotation speed, a feedback system at the motor is not required, thereby saving costs in the system.

[0031] According to one embodiment, the voltage rotation field is determined according to the setpoint value of the phase voltage. In this regard, reference should also be made to the relevant professional literature.

[0032] According to one embodiment, the phase voltages for the corresponding phase lines of the electric motor are generated by means of pulse width modulation with a variable pulse duty factor, wherein the voltage rotating field is determined as a function of the pulse width modulation pulse duty factor. In this regard, reference should also be made to the relevant specialist literature.

[0033] According to one specific embodiment, after the error state has been determined, error processing is carried out, in particular the generation of phase voltages and thus also of a rotating field is prevented.

[0034] According to one specific embodiment, a safe torque off function is executed after the error state has been determined.

[0035] According to one embodiment, the frequency converter further comprises: a control unit, for example in the form of a microprocessor, a power unit and at least one safety unit, in particular exactly two safety units independent of each other. The power unit can conventionally include, for example, an inverter with power semiconductors or the like, which is configured to generate phase voltages. The control unit, the power unit and the at least one safety unit are coupled to each other via a communication channel for exchanging data. The corresponding rated values ​​of the phase voltages are transmitted from the control unit to the power unit via the communication channel, wherein the power unit then generates the phase voltages according to the one or more rated values. The measured values ​​of the measured phase currents are transmitted from the power unit to the control unit via the communication channel. At least one safety unit is configured to evaluate the one or more rated values ​​of the phase voltages transmitted via the communication channel and the measured values ​​of the measured phase currents transmitted via the communication channel for determining an error state.

[0036] The frequency converter according to the invention is designed to carry out the above-described method.

[0037] According to one embodiment, the frequency converter has: a control unit, for example in the form of a microprocessor, a power unit and at least one safety unit, in particular exactly two safety units that are independent of each other. The power unit can conventionally include, for example, an inverter with power semiconductors or the like, which is configured to generate phase voltages. The control unit, the power unit and the at least one safety unit are coupled to each other via a communication channel for exchanging data. The corresponding rated values ​​of the phase voltages are transmitted from the control unit to the power unit via the communication channel, wherein the power unit then generates the phase voltages according to the one or more rated values. The measured values ​​of the measured phase currents are transmitted from the power unit to the control unit via the communication channel. At least one safety unit is configured to evaluate the one or more rated values ​​of the phase voltages transmitted via the communication channel and the measured values ​​of the measured phase currents transmitted via the communication channel for determining an error state.

[0038] According to one specific embodiment, the control unit is designed to regulate the phase currents.

[0039] According to one specific embodiment, the control unit is designed to use the phase voltage as a manipulated variable for regulating the phase current. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be described in detail below with reference to the accompanying drawings. In this case:

[0041] Figure 1 A highly schematic illustration of a drive system with a frequency converter and an electric motor actuated by means of the frequency converter, and

[0042] Figure 2 Shown in Figure 1 A schematic block diagram of the internal structure of the inverter is shown in FIG. DETAILED DESCRIPTION

[0043] Figure 1 A drive system having a frequency converter 1 and an electric motor 2 controlled by means of the frequency converter 1 is shown highly schematically.

[0044] The frequency converter 1 is designed to generate three phase voltages u1, u2, u3 for or between corresponding phases 2.1, 2.2, 2.3 of the electric motor 2 and to measure the occurring phase currents i1, i2 and i3. In this respect, reference should also be made to the relevant technical literature.

[0045] Figure 2 Show Figure 1 A schematic block diagram of the internal structure of the frequency converter 1 is shown in FIG.

[0046] Reference Figure 2 The frequency converter 1 has a control unit 3, for example in the form of a microcontroller.

[0047] The frequency converter 1 further comprises a power unit 4. The power unit 4 comprises a conventional inverter 8 for generating phase voltages u1, u2 and u3. In addition, the power unit 4 comprises a conventional current sensor 9, for example in the form of a shunt resistor. With the aid of the current sensor 9, the phase currents i1, i2 and i3 are measured. The power unit 4 further comprises a control device 10, which controls all basic functions of the power unit 4. The power unit 4 further comprises a safe torque off (STO) circuit 11, with the aid 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 sensor 9 is connected to the control device 10 with the aid of an optional signal amplifier 14.

[0048] The frequency converter 1 also has a first safety unit 5 and a second safety unit 6 .

[0049] The control unit 3, the power unit 4 (galvanically isolated by the optocoupler 15), the first safety unit 5 and the second safety unit 6 are coupled to one another for exchanging data via a communication channel 7. Optionally, a point-to-point data connection between the two safety units 5 and 6 is provided.

[0050] The respective setpoint values ​​for the phase voltages u1, u2, u3 are transmitted from the control unit 3 to the power unit 4 via the communication channel 7. The measured values ​​for the measured phase currents i1, i2, i3 are transmitted from the power unit 4 to the control unit 3 via the communication channel 7.

[0051] Safety units 5 , 6 are each designed to independently evaluate one or more setpoint values ​​for phase voltages u1 , u2 , u3 transmitted via communication channel 7 and measured values ​​for measured phase currents i1 , i2 , i3 transmitted via communication channel 7 to determine an error state.

[0052] To this end, the safety units 5, 6 determine the voltage rotating field from the phase voltages u1, u2, u3 generated or to be generated. In addition, the safety units 5, 6 determine the current rotating field from the measured phase currents i1, i2, i3, and calculate the phase difference between the voltage rotating field and the current rotating field and / or the frequency difference between the frequency of the voltage rotating field and the frequency of the current rotating field. If the phase difference exceeds a phase difference threshold and / or if the frequency difference exceeds a frequency difference threshold, the safety units 5, 6 determine an error state, respectively.

[0053] If an error state is detected in at least one of the safety units 5 , 6 , they carry out error processing independently of one another by signaling a safe torque off (STO) circuit 11 that the STO state is brought about by suitable actuation of the inverter 8 .

[0054] The safety units 5 , 6 can be arranged on the safety circuit board 16 . Correspondingly, the control unit 3 can be arranged on the control circuit board 17 . Finally, the power unit 4 can be arranged on the power circuit board 18 .

Claims

1. A method for monitoring the operation of a frequency converter (1), the frequency converter being designed for controlling an electric motor (2), the method comprising the steps of: - based on the rated values ​​of the phase voltages (u1, u2, u3), generating phase voltages (u1, u2, u3) for corresponding phase lines (2.1, 2.2, 2.3) of the electric motor (2), - determine the voltage rotation field, - measurement of the occurring phase currents (i1, i2, i3), - Determine the current rotation field from the measured phase currents (i1, i2, i3), - calculating the phase difference between the voltage rotating field and the current rotating field, and - When the phase difference exceeds a phase difference threshold, an error state is determined.

2. The method according to claim 1, characterized in that - generating phase voltages (u1, u2, u3) for corresponding phase lines (2.1, 2.2, 2.3) of the electric motor (2) by means of pulse width modulation with a variable pulse duty factor, wherein the voltage rotating field is determined as a function of the pulse width modulation pulse duty factor.

3. The method according to any one of the preceding claims 1 to 2, characterized in that - After determining the error status, error handling is performed.

4. The method according to claim 3, characterized in that After the error state has been determined, the generation of the phase voltages (u1, u2, u3) is prevented.

5. The method according to any one of the preceding claims 1 to 2, characterized in that - After the error state is determined, the Safe Torque Off function is executed.

6. The method according to any one of the preceding claims 1 to 2, characterized in that - The frequency converter (1) has: - Control unit (3), - Power Unit (4), and - at least one safety unit (5, 6), - wherein the control unit (3), the power unit (4) and the at least one safety unit (5, 6) are coupled to one another via a communication channel (7) for exchanging data, - wherein the setpoint values ​​of the phase voltages (u1, u2, u3) are transmitted from the control unit (3) to the power unit (4) via the communication channel (7), - wherein measured values ​​regarding the measured phase currents (i1, i2, i3) are transmitted from the power unit (4) to the control unit (3) via the communication channel (7), and - wherein the at least one safety unit (5, 6) is designed to evaluate the respective setpoint values ​​of the phase voltages (u1, u2, u3) transmitted via the communication channel (7) and the measured values ​​of the measured phase currents (i1, i2, i3) transmitted via the communication channel (7) in order to determine an error state.

7. A frequency converter (1), characterized in that: The frequency converter (1) is designed to carry out the method according to any of the preceding claims.

8. The frequency converter (1) according to claim 7, characterized in that: - The frequency converter (1) has: - Control unit (3), - Power Unit (4), and - at least one safety unit (5, 6), - wherein the control unit (3), the power unit (4) and the at least one safety unit (5, 6) are coupled to one another via a communication channel (7) for exchanging data, - wherein the setpoint values ​​of the phase voltages (u1, u2, u3) are transmitted from the control unit (3) to the power unit (4) via the communication channel (7), - wherein measured values ​​regarding the measured phase currents (i1, i2, i3) are transmitted from the power unit (4) to the control unit (3) via the communication channel (7), and - wherein the at least one safety unit (5, 6) is designed to evaluate the respective setpoint values ​​of the phase voltages (u1, u2, u3) transmitted via the communication channel (7) and the measured values ​​of the measured phase currents (i1, i2, i3) transmitted via the communication channel (7) in order to determine an error state.

9. The frequency converter (1) according to claim 8, characterized in that: The control unit (3) is designed to regulate the phase currents (i1, i2, i3).

10. The frequency converter (1) according to claim 9, characterized in that: The control unit (3) is designed to use the phase voltages (u1, u2, u3) as manipulated variables for regulating the phase currents (i1, i2, i3).

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