Method for operating an electric drive system

Abstract

A method for operating an electric drive system (100), having the following steps: - determining whether instability can be detected during operation of the electrical drive system (100), - determining an associated vibrational frequency (f_i) when instability is detected, and - displaying the determined vibrational frequency (f_i).

Description

[0001] Method for operating an electric drive system

[0002] The invention is based on the object of providing a method for operating an electric drive system that enables the safest possible operation.

[0003] The method is used to operate an electric drive system and comprises the following steps: determining whether an instability occurs during operation of the electric drive system, determining an associated vibration frequency if an instability is detected, and displaying the determined vibration frequency.

[0004] In one embodiment, the determination of whether an instability occurs during operation of the electric drive system is based on the detection of a limit-stable oscillation of the electric drive system. For this purpose, suitable sensor signals, control deviations, manipulated variables, etc. can be suitably evaluated.

[0005] The following describes, by way of example only, a possible method by which it can be automatically determined whether instability occurs during operation of the electric drive system.

[0006] The method is used for automatic stability detection of a controller cascade of an electric drive system. The controller cascade typically comprises a number of cascaded controllers, for example, between 1 and 6. A control error of a respective controller is processed by the respective controller according to its control algorithm, and the processed control error is conventionally output by the respective controller as a controller manipulated variable. A reference variable for the subsequent controller in the controller cascade is determined as a function of the controller manipulated variable of the preceding controller in the controller cascade. A control error refers to the difference between the setpoint or reference variable and the actual value of the variable to be controlled. With regard to the basic structure of controller cascades, reference is also made to the relevant specialist literature.

[0007] The method comprises the steps of: a) determining an energy content of a respective control error, b) determining whether an amount of a respective controller manipulated variable exceeds an associated limit value or not, and c) generating a stability measure for the controller cascade depending on the energy contents of the respective control errors and / or depending on whether the respective controller manipulated variables exceed their associated limit values ​​or not.

[0008] The stability measure represents the stability of the individual control loops of the controller cascade or the stability of the entire controller cascade. The stability measure can, for example, be embodied as a numerical value with a predefined range of values. The range of values ​​can, for example, extend between 0 and 10, where 0 corresponds to maximum stability and 10 corresponds to maximum instability. The stability measure can also be designed as a stability traffic light, where, for example, green corresponds to high stability, yellow corresponds to incipient instability, and red corresponds to instability, etc.

[0009] The energy content of the respective control error can be determined using energy operators.

[0010] If the energy content of the respective control errors increases, the stability measure is generated or changed in such a way that it indicates an increasing instability of the controller cascade.

[0011] In the event that the magnitudes of the respective controller manipulated variables exceed their associated limit values, the stability measure is generated or changed in such a way that it indicates an increasing instability of the controller cascade.

[0012] Steps a) to c) can be repeated at a fixed time interval, for example every 100 ms.

[0013] The controllers of the controller cascade are, for example, selected from the set of controllers consisting of: position controllers, speed controllers and current controllers.

[0014] In one embodiment, the stability measure is generated further depending on predeterminable properties of the controller cascade.

[0015] In one embodiment, the oscillation frequency is determined by measuring time periods between two zero crossings of a measured variable of the electric drive system.

[0016] In one embodiment, the oscillation frequency is determined by measuring the time intervals between minima and maxima of a measured variable of the electric drive system. In one embodiment, the oscillation frequency is determined by transforming a measured variable of the electric drive system into the frequency domain and evaluating it in the frequency domain.

[0017] In one embodiment, the measured variable is a control difference of a controlled variable of the electric drive system, and / or the measured variable is a manipulated variable of a controller of the electric drive system.

[0018] In one embodiment, the controlled variable is a speed, and / or a position, and / or a torque, and / or a current.

[0019] In one embodiment, recommendations for establishing the stability of the electric drive system are issued depending on the determined vibration frequency.

[0020] In one embodiment, in a first frequency range it is recommended to reduce a gain of a position controller, in a second frequency range it is recommended to perform a setpoint adjustment by filtering or other vibration-damping methods, in a third frequency range it is recommended to reduce a gain of the position controller or a speed controller, and in a fourth frequency range it is recommended to use a filter in a setpoint path.

[0021] One challenge in commissioning electric drive systems lies in the parameterization and commissioning of the controllers. Drive systems often have natural frequencies whose exact frequencies are unknown to the commissioning engineer or the mechanical engineer. These natural frequencies limit the dynamics of controlled systems and often lead to suboptimal controller settings. In certain frequency ranges, it may be useful to dampen the natural frequencies, for example, using notch filters or other filter mechanisms. This requires precise knowledge of the natural frequency.

[0022] This natural frequency can be determined, for example, through acoustic measurements or by recording measured values. Another option is to determine the natural frequency using a test signal and a fast Fourier transformation. In all cases, intervention by the user or commissioning engineer is required.

[0023] The present invention solves this problem by determining the natural frequency within the control system when / as soon as an instability is detected. This frequency is then displayed to the user, making it easier for the user to parameterize the filters. According to the invention, the natural frequency can also be determined and displayed independently of whether an instability occurs.

[0024] The instability frequency is the frequency at which a drive system executes limit-stable oscillations. This frequency often corresponds to a natural frequency of the system. According to the invention, this frequency is determined in the drive system as soon as the drive system detects an instability.

[0025] The determination can be carried out in various ways:

[0026] Determination of the time between two zero crossings of, for example, the difference between target and actual speed, difference between target and actual position, difference between target and actual torque, difference between target and actual current.

[0027] Determine the time between a number of zero crossings and then divide by the number of zero crossings. Here, too, the signal differences from the previous point are used.

[0028] Like the first two points, but not zero crossings, but times from minima to minima or maxima to maxima are evaluated.

[0029] Record a time sequence and perform a Fourier transform of one of the above-mentioned signal differences.

[0030] Perform many discrete Fourier transforms and find a frequency at which the amplitude is maximum.

[0031] The frequency determined in one of these ways or another is displayed directly to the drive system user. This allows them, for example, to adjust the frequencies of their filters to restore the stability of the closed control loop or to optimize their control loop.

[0032] Based on the instability frequency, various measures can be derived depending on the detected frequency. These are displayed to the user if necessary:

[0033] Frequency range 1 , for example < 5 Hz: Reduction of the position controller gain.

[0034] Frequency range 2, for example 5 to 50 Hz: Setpoint adjustment by filtering or other oscillation-damping methods (oscillation compensation).

[0035] Frequency range 3, for example, 50 to 250 Hz: Reduction of the position or speed controller gain. Frequency range 4, for example, > 250 Hz: Application of a filter in a setpoint path (speed setpoint path, current setpoint path, torque setpoint path). Various filters are conceivable, such as notch filters, low-pass filters, etc.

[0036] Overall, this provides the end user with a simple and understandable interpretation of the reason for instability, which simplifies the commissioning of electric drive systems.

[0037] The invention is described in detail below with reference to the drawing.

[0038] Fig. 1 shows a schematic block diagram of a controller cascade of an electric drive system.

[0039] Fig. 1 shows a block diagram of a controller cascade of an electric drive system 100.

[0040] The controller cascade comprises a position controller 1 for controlling a position cp, a downstream speed controller 2 for controlling a speed cu, and a downstream current controller 3 for controlling a drive current i. The drive system 100 further conventionally comprises an electrical control system 4 and a mechanical control system 5. A differentiating element 6 is also provided. Furthermore, with regard to the basic structure, reference is also made to the relevant specialist literature.

[0041] The method for operating the electric drive system 100 comprises the steps of: determining whether an instability occurs during operation of the electric drive system 100, determining an associated oscillation frequency f_i when an instability is detected, and displaying the determined oscillation frequency f_i, for example on an associated display 13.

[0042] The determination of whether an instability occurs during operation of the electric drive system 100 is based on the determination of a limit-stable oscillation of the electric drive system 100.

[0043] The oscillation frequency is determined by measuring time periods Tn between two zero crossings of a measured variable 7, 8, 9 of the electric drive system 100. Additionally or alternatively, the oscillation frequency can be determined by measuring time periods between minima and maxima of the measured variable 7, 8, 9 of the electric drive system 100 and / or by transforming the measured variable 7, 8, 9 of the electric drive system 100 into the frequency domain and evaluating it in the frequency domain.

[0044] In the present case, the measured variable is a control difference 7, 8 or 9 of a controlled variable in the form of the current i, the speed w or the position q> of the electric drive system 100 and / or a manipulated variable of the controllers 1, 2 or 3 of the electric drive system 100.

[0045] Depending on the determined vibration frequency, recommendations for establishing the stability of the electric drive system 100 are automatically output on the display 13.

[0046] For example, in a first frequency range it is recommended to reduce a gain of the position controller 1, in a second frequency range it is recommended to perform a setpoint adjustment by filtering or other vibration-damping methods, in a third frequency range it is recommended to reduce a gain of the position controller 1 or the speed controller 2, and in a fourth frequency range it is recommended to use a filter in a setpoint path 10, 11 or 12, respectively.

Claims

Patent claims 1. A method for operating an electric drive system (100) comprising the steps of: determining whether an instability occurs during operation of the electric drive system (100), Determining an associated oscillation frequency (fj) when an instability is detected and displaying the determined oscillation frequency (fj).

2. Method according to claim 1, characterized in that the determination of whether an instability occurs during the operation of the electric drive system (100) is carried out based on the determination of a limit-stable oscillation of the electric drive system (100).

3. Method according to one of the preceding claims, characterized in that the oscillation frequency is determined by measuring time periods (Tn) between two zero crossings of a measured variable (7, 8, 9) of the electric drive system (100).

4. Method according to one of the preceding claims, characterized in that the oscillation frequency is determined by measuring time periods between minima and maxima of a measured variable (7, 8, 9) of the electric drive system (100).

5. Method according to one of the preceding claims, characterized in that the oscillation frequency is determined by transforming a measured variable (7, 8, 9) of the electric drive system (100) into the frequency domain and evaluating it in the frequency domain.

6. Method according to one of claims 3 to 5, characterized in that the measured variable is a control difference (7, 8, 9) of a controlled variable of the electric drive system (100), and / or the measured variable is a manipulated variable of a controller (1, 2, 3) of the electric drive system (100).

7. Method according to claim 6, characterized in that the controlled variable is a speed (w), and / or a position ( <p), und / oder ein Drehmoment, und / oder ein Strom (i) ist.

8. Method according to one of the preceding claims, characterized in that recommendations for establishing the stability of the electric drive system (100) are issued as a function of the determined oscillation frequency.

9. Method according to claim 8, characterized in that in a first frequency range it is recommended to reduce a gain of a position controller (1), in a second frequency range it is recommended to carry out a setpoint adjustment by filtering or other vibration-damping methods, in a third frequency range it is recommended to reduce a gain of the position controller (1) or of a speed controller (2), and in a fourth frequency range it is recommended to use a filter in a setpoint path (10, 11, 12).

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