JPS6118440B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an operation monitoring device for a group of electric motors, and in particular detects whether or not each electric motor is operating normally without using a rotation detector. The present invention relates to an operation monitoring device that can also monitor the operating state of a device.

Conventional methods for monitoring the operating status of a motor include a method of installing a tachometer to monitor the rotation speed, and a method of estimating the load status of the motor by detecting the motor current. There is an economical problem when using a large number of
Regarding the latter, there is a problem in detection accuracy when using a motor, such as a hysteresis motor, in which the motor current hardly changes depending on the load.

Therefore, the method shown in Japanese Patent Application No. 101767/1984 was devised. This method temporarily opens a switch connected in series to an operating motor and detects the voltage or frequency of the back electromotive force of the motor. Therefore, according to this method, it is possible to monitor the rotational speed of the motor without attaching a tachometer to the motor. This is nothing but using the motor itself as a tachometer while the switch is open, and is particularly effective for monitoring heavy inertial loads that do not cause problems even if the energization of the motor is stopped for a short time.

What is shown in FIG. 1 is an application of this motor monitoring device using back electromotive force to a drive system for a plurality of motors. In FIG. 1, 11 is a power supply device such as a thyristor inverter, 12-1 to 12-n are n electric motor groups, and individual switch groups 13-1 to 13 are connected in series to the power supply device 11, respectively. -n in parallel. 14 is an oscillator for setting the output frequency of the power supply device 11. 15
is a switching circuit that sequentially switches back electromotive voltages of n motors, and its switching control signal is cyclically given by an arithmetic circuit 16. Further, 17 is a switching circuit for giving opening/closing commands to the switch groups 13-1 to 13-n, and this switching control signal is also given by the arithmetic circuit 16. The signal selected by the switching circuit 15 according to the command from the arithmetic circuit 16 passes through the waveform shaping circuit 18 and is compared with the frequency signal of the power source obtained from the oscillator 14 by the comparison arithmetic circuit 19. When comparing voltages instead of frequencies, the signal from the oscillator 14 may be a signal corresponding to the power supply voltage. For example, if the frequency of the back electromotive force of the motors 12-1 to 12-n is _n1 to _no and the frequency of the power source is _s , the output of the comparison calculation circuit 19 is as follows.
The abnormal motor signal may be output under the condition of _nk (k=1 to n)<| _s − _p |. _p here
is the permissible slip frequency for an AC motor. In response to this abnormal signal, if the selection circuit 17 is controlled by the output signal of the arithmetic circuit 16 to keep the corresponding switch open, it is possible to simultaneously monitor the motor group and disconnect the abnormal motor. It also becomes possible to protect the electric motor.

In this type of monitoring device, it is important to monitor the operating state of the switch connected in series to the electric motor. For example, as shown in FIG. 1, the switching circuit 20 receives the operating states of the auxiliary contacts of the switch groups 13-1 to 13-n, and similarly to the switching circuits 15 and 17 described above, the switching circuit 20 receives the operational states of the auxiliary contacts of the switch groups 13-1 to 13-n.
If selective control is performed using the control signal, switch group 1
This means that the actual open/closed states of 3-1 to 13-n can be detected.

However, the system for monitoring the operating status of the switch group as shown in FIG. 1 has the following two drawbacks. One is the need for auxiliary contacts for the switch or a corresponding signal source, and the other is the need to install signal lines for each switch from those signal sources to the switching device 20. There were problems with the economy and reliability of the large number of operating devices.

The present invention has been made in view of the above points,
The basic idea is to monitor the operating state of the switch without using the auxiliary contacts of the switch and the signal lines connected to them.

Hereinafter, the present invention will be explained in detail using the drawings. FIG. 2 is a system diagram showing one embodiment of the present invention. In FIG. 2, the same parts as in FIG. 1 are designated by the same reference numerals, and since their operations are completely the same as in FIG. 1, their explanation will be omitted. Second
The feature of the configuration of the present invention shown in the figure is that the switching circuit 20 for the auxiliary contact signal of the switch in FIG. 15a
is controlled by the output signal of the arithmetic circuit 16 like the other switching circuits 15. However, the switching circuit 15a is configured so that its switching phase is shifted from that of the other switching circuits 15 or 17. That is, for example, when a certain switch 13-2 is open, the switching circuit 15 is switched to detect the signal corresponding to the switch 13-2, that is, the back electromotive voltage signal of the motor 12-2, using the output signal of the arithmetic circuit 17. However, the switching circuit 15
For example, a is configured to detect a back electromotive force signal of the electric motor 12-1. The output signal of the waveform shaping circuit 18a is compared with the output signal of the oscillator 14 by a comparison calculation circuit 19a.

The operation of the present invention in the above configuration will be explained below. The switching circuit 1 is activated by the control command from the arithmetic circuit 16.
The switches selected in step 7 are sequentially opened for a predetermined period of time, and the back electromotive force (or the frequency of the back electromotive force) of the motor corresponding to those switches is changed by the switching circuit 15 having the same switching characteristics as the switching circuit 17. Select the switch and
As described above, the rotation speeds of the motor groups 12-1 to 12-n are sequentially monitored. The switching circuit 15a is
For example, if the output signal of the arithmetic circuit 16 is used to control the switching phase to be delayed by one circuit from the switching phase of other switching circuits, the output signal of the switching circuit 17 can be used to control the switching phase immediately after finishing monitoring, that is, when the switch is in the closed state. The back electromotive force of the motor can be monitored. For example, the pattern for monitoring the back electromotive force of the motor with the switch open is 12 in the order of the motor number.
-1, 12-2, . . . 12-n, the pattern for monitoring the voltage in the closed state of the switch according to the present invention is in the form 12-n, 12-1, 12-2 . By performing such monitoring, it becomes possible to sequentially monitor the motor voltage when the switch is in a closed state, and it is possible to detect an abnormal state of the switch.

That is, the newly added switching circuit 15a, waveform shaping circuit 18a, and comparison calculation circuit 19a detect voltage even when no open signal is applied to the switch. That is, if the switch is normal, it is in the closed state, so the frequency signals detected by each circuit of the switching circuit 15a, the waveform shaping circuit 18a, and the comparison calculation circuit 19c are equal to the output frequency of the inverter device 11. It should be the same and should match the frequency signal from the oscillator 14 which determines the output frequency of the inverter. Conversely, if an abnormality occurs in the switch, but it is tripped and opened by a normally used overcurrent protection function (not shown), it will be detected by each circuit of the switching circuit 15a, the waveform shaping circuit 18a, and the comparison calculation circuit 19a. Since the frequency signal corresponds to the rotational speed of the motor, the comparison calculation circuit 19a detects the difference between the frequency signal and the frequency signal from the oscillator 14, so that it is possible to determine whether the switch is abnormal (tripping or opening failure). Of course, if the switch becomes abnormal just before the above detection operation, it cannot be detected because the motor rotation speed is almost synchronized with the power supply, but since detection is performed during cycling, when detection occurs one cycle later, the motor Due to the decrease in rotational speed, an abnormality in the switch is detected for the reason mentioned above.

By adding the new switching circuit 15a, waveform shaping circuit 18a, and comparison calculation circuit 19a in this way, it becomes possible to detect an abnormality in which the switch becomes open. This abnormal state is detected by comparing the output of the waveform shaping circuit 18a and the frequency signal obtained from the oscillator 14, as shown in FIG. This comparison may be performed based on the fact that if the switch is in a normally closed state, these two signals are the same signal (same frequency).

The above explanation was mainly about the method of monitoring the rotational speed of the motor and the opening/closing status of the switch using the frequency of the back electromotive force of the motor, but the method is exactly the same if this is not used as the frequency but as the magnitude of the voltage. It is clear that this configuration is possible, and therefore, the present invention is applicable to both AC motors and DC motors.

As explained above, according to the present invention, when detecting the rotation speed of a motor group using its back electromotive force,
To obtain an operation monitoring device for a motor group that can monitor the open/closed state of a switch group with a simple system without providing an auxiliary contact in the switch group or laying a large number of cables from the auxiliary contact. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing the configuration of a conventional motor group operation monitoring device, and FIG. 2 is a system diagram showing an embodiment of the motor group operation monitoring device according to the present invention. 11; Inverter device, 12-1 to 12-n;
Electric motor, 13-1 to 13-n; Switch, 14; Oscillator, 15, 15a, 17, 20; Switching circuit, 1
6; Arithmetic circuit, 18, 18a; Waveform shaping circuit, 1
9, 19a; Comparison calculation circuit.

Claims (1)

[Claims] 1. In an operation monitoring device for a group of electric motors connected in parallel to a common power source through switches, a switching circuit temporarily opens each of the switches in sequence, and a switching circuit for temporarily opening each of the switches, and the motors that are opened by each of the switches. a second switching circuit that sequentially detects the voltage or frequency of the switching circuit in synchronization with the switching circuit; and a voltage or frequency of the motor that performs switching operation with a certain phase difference from the switching circuit and that closes each of the switches. and a third switching circuit that sequentially detects the switching circuit, and the abnormality of each motor and each switch is monitored by the output signals of the second switching circuit and the third switching circuit. Driving monitoring device.