METHOD AND DEVICE FOR A FAILSAFE ROTATIONAL SPEED MONITORING PROCESS

Abstract

A method for fail-safe rotational speed monitoring of a sensorless three-phase drive, in which the three-phase drive is controlled in three phases with the phases U, V, W by drive electronics comprising an inverter, with the voltage signals at the three phases U, V, W being present as pulse width modulated signals, in which an output frequency of the inverter applied to the drive is determined and an actual rotational speed of the drive is determined therefrom, in which the actual rotational speed is compared with a predeterminable desired rotational speed and in which, if the actual rotational speed exceeds the desired rotational speed, the drive is switched off, the pulse width of the pulse width modulated signals being used to determine the output frequency of the inverter.

Claims

1. A method for fail-safe rotational speed monitoring of a sensorless three-phase drive, in which the three-phase drive is controlled in three phases with the phases U, V, W by drive electronics comprising an inverter, with the voltage signals at the three phases U, V, W being present as pulse width modulated signals, in which an output frequency of the inverter applied to the drive is determined and an actual rotational speed of the drive is determined therefrom, in which the actual rotational speed is compared with a predeterminable desired rotational speed and in which, if the actual rotational speed exceeds the desired rotational speed, the drive is switched off, exclusively the pulse width of the pulse width modulated signals being used to determine the output frequency of the inverter.

2. The method according to claim 1, wherein the pulse widths are used to determine a transformation angle.

3. The method according to claim 2, wherein the ratio from the transformed pulse widths in the stator-fixed coordinate system is used to determine a transformation angle.

4. The method according to claim 1, wherein a transformation angle difference is used to determine an output frequency.

5. The method according to claim 1, wherein the pulse widths are adjusted for a dead time compensation.

6. The method according to claim 1, wherein the output frequency is determined in two channels by means of a first microcontroller on the one hand and, depending on this, by means of a second microcontroller on the other.

7. The method according to claim 6, wherein the output frequencies determined by the two microcontrollers are exchanged and compared via cross-communication between the two microcontrollers.

8. The method according to claim 7, wherein the drive is switched off if the output frequencies are unequal.

9. A device for fail-safe rotational speed monitoring of a sensorless three-phase drive, in particular for carrying out the method according to claim 1, comprising drive electronics having an inverter by means of which the three-phase drive can be controlled in three phases with the phases U, V, W, a pulse width modulation generator by means of which voltage signals can be provided as pulse width modulated signals at the three phases, means to determine an output frequency of the inverter applied to the drive, a calculation unit to determine the actual rotational speed of the drive on the basis of the output frequency of the inverter, a comparison unit and a switch-off device, wherein the actual rotational speed can be compared with a predeterminable desired rotational speed using the comparison unit, wherein the comparison unit generates a corresponding signal in the event of the actual rotational speed exceeding the desired rotational speed and transmits it to the switch-off device by means of which the drive can be switched off, and means for detecting the pulse widths of the pulse width-modulated signals, wherein a determination of the output frequency of the inverter applied to the drive is exclusively possible on the basis of the pulse widths.

Description

DRAWINGS

[0049] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0050] Further features and advantages of the disclosure will become apparent from the following description on the basis of the drawing figures.

[0051] FIG. 1 shows a schematic circuit diagram of the device or method in accordance with the disclosure;

[0052] FIG. 2 shows an equivalent circuit diagram of an asynchronous drive and

[0053] FIG. 3 shows an equivalent circuit diagram of a synchronous drive.

[0054] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0055] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0056] FIG. 1 shows in a schematic circuit diagram the device 1 for fail-safe rotational speed monitoring of a sensorless three-phase drive 3 in accordance with the disclosure.

[0057] The three-phase drive 3 is controlled three-phase by drive electronics 2, namely with the motor phases U, V, W. The drive electronics 2 in turn is supplied by a three-phase supply line 4 with the phases L1, L2 and L3.

[0058] To control the three-phase drive 3, which is an electric motor in the form of an asynchronous motor, for example, the drive electronics 2 has a frequency converter 5, and the voltage signals at the three motor phases U, V, W are present as pulse width modulated signals.

[0059] In a manner known per se, the frequency converter 5 has a rectifier 6 and an inverter 7, which are interconnected by means of an intermediate circuit 8.

[0060] The device 1 according to the disclosure has two redundantly arranged microcontrollers 9 and 10, by means of which the inverter-side output frequency is determined in two channels. A first channel 11 and a second channel 12 are provided for this purpose, with the microcontroller 9 connected to the first channel 11 and the microcontroller 10 to the second channel 12. The two microcontrollers 9 and 10 are interconnected via cross communication 16.

[0061] During use as intended, the output frequency of the inverter 7 applied to the three-phase drive 3 is determined on the method side. The pulse width of the pulse width modulated signals is used to determine the output frequency.

[0062] The output frequencies determined by the two microcontrollers 9 and 10 are compared with each other via cross communication 16. In the event of an inequality, drive 3 is switched off immediately, for which purpose a switch-off device 18 is provided. This communicates with the drive 3 in accordance with arrow 19. Alternatively and also preferably, a communication connection between the switch-off device 19 and the frequency inverter 5 is provided in accordance with arrow 24. As soon as an unequal output frequency is detected, a signal is transmitted to the switch-off device 18 in accordance with arrow 17, which then ensures an immediate switch-off of the drive 3 either directly via the communication connection 19 or indirectly via the communication connection 24 by interposing the frequency inverter 5. The drive 3 is preferably switched off by actuating an appropriate switching device, for example by disconnecting the frequency converter 5 from the mains supply.

[0063] If the output frequencies determined redundantly by the microcontrollers 9 and 10 are the same, an actual rotational speed 20 of the drive 3 is determined on this basis. For this purpose, the device 1 according to the disclosure has a calculation unit 13 which is in communication connection with the microcontrollers 9 and 10 in accordance with arrows 14 and 15.

[0064] The actual rotational speed 20 determined by the calculation unit 13 is compared with a predeterminable desired rotational speed 21. For this purpose, the device according to the disclosure has a comparison device 22. If the actual rotational speed 20 exceeds the desired rotational speed 21, the drive 3 is switched off immediately, for which purpose the comparison device 20 is in communication connection with the switch-off device 18 in accordance with arrow 23.

[0065] The two microcontrollers 9 and 10 determine the output frequency on the basis of an angular difference as follows:

[00016]${\omega }_1=\frac{\mathrm{\Delta \phi }}{\Delta t}=\left({\phi }_{\left(k\right)}-{\phi }_{\left(k-1\right)}\right).Math.f_{CALC}$

where the rotor position, i.e. transformation angle φ, results as follows:

[00017]$\phi =\arctan \left(\frac{p_{\beta }}{p_{\alpha }}\right)$$\mathrm{where}\left[\begin{array}{c}{p}_{\alpha }\\ p_{\beta }\end{array}\right]=\left[\begin{array}{ccc}\frac{2}{3}& -\frac{1}{3}& -\frac{1}{3}\\ 0& \frac{1}{\sqrt{3}}& -\frac{1}{\sqrt{3}}\end{array}\right].Math.\left[\begin{array}{c}{p}_U-CN{T}_{\mathrm{TOTKOMP}U}\\ p_V-CN{T}_{\mathrm{TOTKOMP}V}\\ p_W-CN{T}_{\mathrm{TOTKOMP}W}\end{array}\right]$

where [0066] P.sub.U,V,W pulse width of the PWM signals for controlling the inverter valves [0067] φ rotor position (transformation angle) [0068] ω.sub.1 output electrical angular frequency

[00018]$\left[\frac{\mathrm{rad}}{s}\right]$ [0069] f.sub.CALC frequency of calculation.

[0070] As can be seen from the above illustration, the output frequency can be determined directly on the basis of the level of modulation of the PWM signals using the method according to the disclosure. Neither the output current nor the output voltage nor the intermediate circuit voltage need to be measured.

[0071] The schematic representation according to FIG. 1 is for explanation purposes only and is purely exemplary. In particular, it is possible to combine the calculation unit 13, the comparison device 22, the switch-off device 18 and the microcontrollers 9 and 10 to a common device. It can also be provided that the microcontrollers 9 and 10 each take over redundantly the functions of the calculation unit 13, the switch-off device 18 and/or the comparison device 22. Of disclosure-essential importance, however, is solely that a reliable determination of the rotational speed is effected solely on the basis of the control degree of the PWM signals, a two-channel determination being implemented which detects inequalities in cross-communication, wherein in the event of a detected inequality, the drive 3 is switched off immediately. In addition, drive 3 is switched off if the determined actual rotational speed is above a predeterminable desired rotational speed. Tolerance ranges, which must be defined in conformity with the standard, can be provided for the detection of inequalities and/or overspeeds.

[0072] FIG. 2 shows the equivalent circuit diagram of an asynchronous drive. For such a drive the actual rotational speed 21 results as follows:

[00019]$\omega =\frac{{\omega }_1}{p}.Math.\left(1-s\right)$$\mathrm{with}$$X_{1\sigma }={\omega }_1{L}_{1\sigma }\mathrm{and}{X}_{2\sigma }^{\prime }={\omega }_1{L}_{2\sigma }^{\prime }\mathrm{and}{X}_h={\omega }_1{L}_h$$\mathrm{where}$$Z_{1\mathrm{Re}}=\frac{u_{1\alpha }{i}_{1\alpha }+u_{1\beta }{i}_{1\beta }}{i_{1\alpha }^2+i_{1\beta }^2}$$Z_{1\mathrm{Im}}=\frac{u_{1\beta }{i}_{1\alpha }-u_{1\alpha }{i}_{1\beta }}{i_{1\alpha }^2+i_{1\beta }^2}$${\mathrm{and}\left(\frac{R_2^{\prime }}{s}\right)}^2+{\left(X_{2\sigma }^{\prime }+X_h\right)}^2=-X_h^2\frac{\left(X_{2\sigma }^{\prime }+X_h\right)}{Z_{1\mathrm{Im}}-\left(X_{1\sigma }+X_h\right)}$$Z_{1\mathrm{Re}}=R_1-\frac{\frac{R_2^{\prime }}{s}}{\left(X_{2\sigma }^{\prime }+X_h\right)}\left[Z_{1\mathrm{Im}}-\left(X_{1\sigma }+X_h\right)\right]$$s=\frac{R_2^{\prime }}{X_{2\sigma }^{\prime }+X_h}\frac{X_{1\sigma }+X_h-Z_{1\mathrm{Im}}}{Z_{1\mathrm{Re}}-R_1}$

where [0073] R.sub.1 stator resistance [0074] R.sub.2′ rotor resistance [0075] L.sub.1σ stator leakage inductance [0076] L.sub.2σ′ rotor leakage inductance [0077] L.sub.h main inductance [0078] s slippage.

[0079] FIG. 3 shows the equivalent circuit diagram of a synchronous drive. In this respect the following applies:

U.sub.2=U.sub.p+I.sub.1(R.sub.1+jX.sub.1)

U.sub.p=ω.Math.Ψ.sub.P

where the speed results as follows:

[00020]$\omega =\frac{{\omega }_1}{p}$

where [0080] Ψ.sub.P rotor flux [0081] R.sub.1 stator resistance [0082] L.sub.1d Stator inductance in d-direction [0083] L.sub.1d Stator inductance in q-direction.

[0084] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are inter-changeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.