PARAMETER IDENTIFICATION FOR INDUCTION MACHINES

Abstract

A method and a control apparatus for determining parameters for controlling an electric drive having an electric machine improve the start-up of the electric drive by applying a current indicator as a signal at three-phase winding connections of the electric machine, and measuring a d-component and a q-component of the stator voltage and of the stator current at the winding connections. In a first measurement step, a rotating current indicator is applied to the three-phase winding connections and the electric machine is oriented such that an exciter current in the q-axis assumes a minimum. In a second measurement step, when the rotor of the electric machine is stationary, a field winding of the electrical machine is short-circuited and a current indicator in form of a binary noise signal is applied to the winding connections. A stator impedance is then determined as a first control parameter.

Claims

1.-8. (canceled)

9. A method for determining control parameters for a vector control controlling an electric drive having an electric machine, comprising: in a first measurement step, applying a rotating current indicator to the three-phase winding connections and orienting the electric machine such that an exciter current in a q-axis assumes a minimum; in a second measurement step, when a rotor of the electric machine is stationary, short-circuiting a field winding of the electric machine and applying to the three-phase winding connections a current indicator in form of a binary noise signal; measuring at three-phase winding connections a d-component and a q-component of a stator voltage and of a stator current; determining from the measured d-component and the q-component of the stator voltage and of the stator current as a first control parameter a stator impedance; generating the binary noise signal using a pseudo-random number sequence produced with a feedback shift register having a shift clock, with different predeterminable frequency spectra being generated with a plurality of shift clocks.

10. The method of claim 9, wherein the stator impedance is frequency-dependent and determined using a Fast Fourier Transformation.

11. The method of claim 9, further comprising calculating a frequency response of the real part and the imaginary part of the stator impedance.

12. The method of claim 9, further comprising measuring a field current of the short-circuited field winding, and determining from the field current and the d-component of the stator current as a second control parameter a ratio of the field current to the stator current.

13. The method of claim 12, wherein at least one of the first and second control parameters are stored for use in the vector control.

14. A control apparatus for an electric drive for carrying out a vector control as set forth in claim 9, wherein the control apparatus is configured to determine and store at least one control parameter for the vector control in a start-up phase, and to use the at least one stored control parameter for the vector control after completion of the start-up phase.

15. An electric drive, comprising a frequency converter having a control apparatus as set forth in claim 14; an electric machine; and a voltage measuring apparatus and a current measuring apparatus arranged in an electrical connection between the frequency converter and the electric machine.

Description

[0017] The invention is described and explained in more detail hereinafter with reference to the exemplary embodiments shown in the figures, in which:

[0018] FIG. 1 shows an electric drive,

[0019] FIG. 2 shows a flow chart, and

[0020] FIG. 3 shows the frequency response of a stator impedance.

[0021] FIG. 1 shows an electric drive 1 with an electric machine 2 which is supplied with electrical energy via a frequency converter 5. The frequency converter 5 has a control apparatus 4. This control apparatus 4 has a measuring apparatus 3 for carrying out the proposed method. This measuring apparatus 3 does not necessarily have to be part of the frequency converter 5 or part of the control apparatus 4. However, it is advisable to use the frequency converter 5 as a voltage source for the electric drive 1, the voltage of which is predetermined by the measuring apparatus 3. The winding connections U, V, W are the connection terminals of the electric machine 2. These are connected to the stator winding of the electric machine 2. The stator current is measured at the winding connections U, V, W by means of the current measuring apparatuses 6 and the voltage between the winding connections is measured by means of a voltage measuring apparatus 8. It is sufficient to determine only two of the three voltages or currents as the third voltage or the third current can be mathematically determined from the other two.

[0022] In order to determine the control parameters, the signals of the current measuring apparatuses 6 and the voltage measuring apparatus 8 are transmitted to the measuring apparatus 3.

[0023] Furthermore, the electric machine 2 also has a field winding 7 in the rotor, also referred to as a rotor winding. The field winding 7 is short circuited by means of a further current measuring apparatus 9. The current measured in this case can also be transmitted to the measuring apparatus 3. From the signal of the further current measuring apparatus 9, the exciter current can be determined, with which the orientation of the d- and q-axis can take place.

[0024] FIG. 2 shows a flow chart of the parameter determination. In a first measurement step 11, the electric machine is oriented. This means that the position of the d-axis and the q-axis offset by 90° is determined. For this purpose, a rotating current indicator is fed into the electric machine 2, the q-axis being detected at a minimum of the exciter current.

[0025] After detection has been successfully completed, the method changes to the second measurement step 12. In this case, the stator currents and the stator voltages are measured and the stator impedance Zd is determined therefrom as the first control parameter. These measurements can be carried out over a frequency range, so that the stator impedance results as a frequency response, i.e. as a function of different values of the frequency.

[0026] If this second measurement step is also completed, the control apparatus can carry out the vector control with the help of this data and control the electric machine 2 precisely in an open-loop manner and control it steadily in a closed-loop manner.

[0027] FIG. 3 shows a typical measurement result of the stator impedance, divided into a real and an imaginary part. The left ordinate indicates the numerical values for the real part, the right ordinate for the imaginary part. From these measuring points, the frequency response of the stator impedance can be determined using interpolation methods which are already known.

[0028] In summary, the invention relates to a method for determining parameters for controlling an electric drive, the electric drive having at least one electric machine. In order to improve the start-up of the electric drive, it is proposed that a current indicator is applied to three-phase winding connections of the electric machine as a signal, wherein in each case a d-component and a q-component of the stator voltage and the stator current is measured at the winding connections, wherein in a first measurement step, a rotating current indicator is applied to the three-phase winding connections and the electric machine is oriented such that an exciter current in the q-axis assumes a minimum, wherein in a second measurement step, when the rotor of the electric machine is stationary, a field winding of the electric machine is short circuited and a current indicator in the form of a binary noise signal is applied to the winding connections, wherein a stator impedance is determined from the measured values as a first control parameter. The invention also relates to a control apparatus for an electric drive, the control apparatus being configured to carry out such a method.