JP2949502B2 - Inverter control circuit - Google Patents

Description

The present invention relates to an inverter control circuit for an inverter that supplies power to a motor that drives a turbo-molecular pump or the like using a magnetic bearing in a high-speed rotating unit.

<Conventional technology> Conventionally, in a system in which an induction motor is operated at a variable speed by a VVVF inverter, a short circuit of a motor winding or a mechanical lock occurs in a load connected to the motor and an overcurrent flows in the inverter. In such a case, an output control circuit is provided so that the output stop circuit is activated by detecting the overcurrent by the overcurrent detection circuit and the power supply to the motor is instantaneously stopped to protect the inverter circuit.

《Problems to be solved by the invention》 When a turbo-molecular pump equipped with a magnetic bearing is driven by such a system, when the turbo-molecular pump enters the atmosphere, the driving resistance increases and the rotation speed decreases instantaneously. As a result, an overcurrent occurs and the output of the inverter is stopped.

On the other hand, the rotor of the turbo-molecular pump usually falls off from the state supported by the magnetic bearing when it enters the atmosphere, and becomes a state supported only by the protective bearing. as a result,
The rotating portion of the rotor or the like is decelerated by friction or mechanical resistance of the protective bearing, and its rotation is reduced, and eventually stops.

As described above, after the inverter detects an overcurrent due to the entry into the atmosphere, only the power supply to the motor is stopped, and the regenerative braking which is one of the effects when the inverter is used is not performed at all. The rotation of the motor is only decelerated by the resistance to the protective bearing, so that the stopping time is prolonged, the load on the protective bearing is increased, and the protective bearing is significantly worn. In particular, when the wear is severe, the protective bearing may be destroyed before the rotation of the rotor stops spontaneously.

Therefore, the present invention has been made to solve such a drawback, and an object of the present invention is to stop the output by detecting an overcurrent in the inverter and to stop the rotation of the load. Another object of the present invention is to provide an inverter control circuit that enables regenerative braking.

<< Means for Solving the Problems >> In order to achieve the above object, the invention according to claim 1 controls an inverter that supplies power to an induction motor for driving a rotating shaft supported by a magnetic bearing, and An overcurrent detection circuit for detecting that a current supplied to the motor has exceeded a predetermined value, and an inverter for outputting a stop command signal for stopping power supply to the motor when the overcurrent detection circuit detects an overcurrent. A stop command circuit, wherein the power supply to the motor is stopped when the current supplied to the motor exceeds a predetermined value, wherein the overcurrent detection circuit detects overcurrent. When a predetermined time elapses after the inverter stops supplying power to the motor according to a stop command signal of the inverter stop command circuit, a restart command signal is issued. Comprising a starting circuit, and controlling so as to start the supply of the output of the regenerative braking by the restart command signal to said motor to said inverter.

According to a second aspect of the present invention, there is provided an overcurrent for controlling an inverter for supplying power to an induction motor for driving a rotating shaft supported by a magnetic bearing, and detecting that a current supplied to the motor exceeds a predetermined value. A detection circuit, and an inverter stop command circuit for outputting a stop command signal for stopping power supply to the motor when the overcurrent detection circuit detects an overcurrent. An inverter control circuit configured to stop supplying power to the motor when the value exceeds a value, wherein the overcurrent detection circuit detects an overcurrent, and the inverter is supplied to the motor by a stop command signal of the inverter stop command circuit. After the power supply is stopped, a restart circuit for issuing a restart command signal is provided. After the overcurrent detection circuit detects an overcurrent, While supplying regenerative braking output to the motor to perform regenerative braking,
When detecting an overcurrent during regenerative braking when a predetermined time has elapsed since the detection of the overcurrent, it is determined that a failure has occurred in the induction motor or a mechanical system connected thereto.

<< Operation >> According to the present invention configured as described above, when the overcurrent detection circuit detects that an overcurrent has flown into the induction motor connected to the inverter, the stop command signal from the inverter stop command circuit causes the overcurrent detection circuit to output the signal to the induction motor. When the power supply is stopped and a predetermined time has elapsed, the restart command signal generated by the restart circuit causes the output of the regenerative braking to the induction motor, that is, the rotation speed to be lower than the actual rotation speed of the motor. By starting the supply of the low-frequency output, the rotation of the motor can be quickly stopped. The motor current during regenerative braking has a normal value in the case of an instantaneous increase in motor load due to entry into the atmosphere, but in the case of an increase in motor load due to short-circuiting of the motor windings and mechanical locking of the motor, An overcurrent occurs.

<< Example >> Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an electrical configuration when the present invention is applied to a VVVF type inverter, and as shown in FIG.
After being rectified and smoothed by the capacitor 3, the commercial power supply 1 is converted from an output stage (inverter) 4 into an alternating current having a frequency indicated by the inverter control circuit 8 and output to the induction motor 5. . The induction motor 5 is connected to a rotating shaft of a turbo-molecular pump (not shown) supported by a magnetic bearing.

A current detection circuit 7 is connected to both ends of the resistor 6 connected to one of the output terminals of the AC / DC converter 2, and the current detection circuit 7 detects a voltage value that changes according to the load of the induction motor 5. The detection value is sent to the inverter control circuit 8 and the overcurrent detection circuit 9.

The overcurrent detection circuit 9 determines that the detected current is a predetermined value, that is, the input current value is the AC / DC converter 2 and the output stage 4.
Is sent to the inverter stop command circuit 10 when the allowable value is exceeded.

The inverter stop command circuit 10 sends a stop command signal to the inverter control circuit 8 and the timer circuit 11 when the overcurrent signal is input.

When the stop command signal is input, the timer circuit 11 starts a time counting operation, and sends a time-up signal to the restart command circuit 12 when a predetermined time has elapsed. The predetermined time set in the timer circuit 11 means that, in the turbo molecular pump driven by the induction motor 5, the load on the motor temporarily increases and an overcurrent flows as in the case of the entry into the atmosphere. This is the time required to return to the normal state.

When the time-up signal is input, the restart command circuit 12 sends a restart command signal to the inverter control circuit 8.

The inverter control circuit 8 controls the operation timing of each element of the output stage 4 in accordance with the current value detected by the current detection circuit 7 and, when a stop command signal is input, sends a signal from the output stage 4 to the induction motor 5. The output is stopped, and when a restart command signal is input, the output from the output stage 4 to the induction motor 5 is output for performing regenerative braking, that is, the output is restarted as a regenerative braking output having a lower frequency than during normal operation. .

Next, the operation of the main part of the embodiment will be systematically described with reference to the flowchart shown in FIG.

In the normal inverter output state, the induction motor 5 is driven at a predetermined frequency from the output stage 4, and during that time, it is determined whether or not the current value obtained from the current detection circuit 7 is an overcurrent. Monitor (step 20
1).

If an overcurrent is detected here (Step 201Y), the inverter stop command circuit 10 operates, sends a stop command signal to the inverter control circuit 8, and stops the output from the output stage 4 to the induction motor 5 (Step 202). ).

At the same time, the timer circuit 11 operates, and the state in which the output to the induction motor 5 is stopped is maintained until a predetermined time has elapsed (step 203).

When a predetermined time elapses, a restart command is sent from the restart command circuit 12 to the inverter control circuit 8 due to the time-up of the timer circuit 11, and the output from the output stage 4 to the induction motor 5 is restarted as an output for performing regenerative braking. (Step 20
Four). By this step 204, regenerative braking is activated and the rotation of the motor starts to decrease rapidly.

Next, the overcurrent detection circuit 9 checks again whether the current value obtained from the current detection circuit 7 is an overcurrent (step 205).

If an overcurrent is detected (step 205Y), the inverter stop command circuit 10 operates, sends a stop command signal to the inverter control circuit 8, stops output from the output stage 4 to the induction motor 5, and outputs a failure signal. Is output to the outside, and the process is terminated (step 206).

When the output of the inverter is restarted in this way, the detection of overcurrent again indicates a continuous increase in load, not a temporary increase in load such as entry into the atmosphere. Since it is considered that a failure has occurred in a mechanical system such as a rotating shaft connected to the motor, the output is stopped to protect the inverter.

If no overcurrent is detected (step 205N), the load is a temporary increase such as the entry into the atmosphere, and the regenerative braking can be continued.
Output to the induction motor 5 as an output for performing regenerative braking.
Is continued until it stops, an abnormal stop signal is output, and the process ends (step 207).

By performing the above processing, as shown in FIG. 3, in the magnetic bearing type turbo molecular pump connected to the induction motor 5, an excessive current temporarily flows due to the entry into the atmosphere, and the output of the inverter Even if the power is cut off, the output of the inverter is restarted after the load due to the entry into the atmosphere is restored, and the induction motor is braked by the regenerative operation. Compared to the conventional case where the inverter is simply stopped, the time is greatly reduced.

As a result, the load of the braking resistance on the protection bearing is reduced, the life of the protection bearing is extended, and the failure of the turbo-molecular pump to rotate frequently, which has conventionally occurred frequently due to the damage of the protection bearing, can be greatly reduced.

In the embodiment, the case where the turbo-molecular pump of the magnetic bearing type is connected to the induction motor has been described. However, when the inverter control circuit is applied to a driven machine having other magnetic bearings, the same effective braking can be achieved. The effect can be exerted.

In the embodiment, a predetermined time (step 203) after detecting an overcurrent during normal operation (step 201 in FIG. 2).
After the regenerative braking was started (step 204), the order of the steps was partially changed, and after detecting the variable current, the normal operation output was stopped (step 202) and the regenerative braking was started immediately (step 204). It is a matter of course that the invention according to claim 2 can be implemented even if an overcurrent during regenerative braking is detected a predetermined time after the current detection.

<< Effect of the Invention >> As described above, the inverter control circuit according to the present invention includes the restart command circuit, so that an overcurrent flows to the induction motor connected to the inverter, and the power supply to the motor is stopped. In this case, when a predetermined time elapses, regenerative braking output to the motor, that is, regenerative braking output at a lower frequency than during normal operation is performed, and the rotation of the motor can be stopped immediately. In addition, it is possible to prevent wear and destruction of the protective bearing for backing up the non-operation of the magnetic bearing due to entry into the atmosphere or the like, thereby increasing the durability of the bearing portion.

Also, if it is possible to detect that the current during regenerative braking is an overcurrent, it is possible to detect a failure of a mechanical system such as an induction motor or a rotating shaft connected to the motor. Can be determined, and necessary measures can be taken promptly.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electric configuration of an embodiment in which the present invention is applied to a case where a magnetic bearing type turbo molecular pump is driven, FIG. 2 is a flowchart showing an operation of the embodiment,
FIG. 3 is a braking characteristic diagram comparing the stop time between the embodiment and the conventional example. DESCRIPTION OF SYMBOLS 1 ... Commercial power supply 2 ... AC / DC converter 3 ... Capacitor 4 ... Output stage 5 ... Induction motor 6 ... Resistance 7 ... Current detection circuit 8 ... Inverter control circuit 9 ... Overcurrent detection circuit 10 ... ... Inverter stop command circuit 11 ... Timer circuit 12 ... Restart command circuit

Claims (2)

(57) [Claims] An overcurrent detecting circuit for controlling an inverter for supplying power to an induction motor for driving a rotating shaft supported by a magnetic bearing, and detecting that a current supplied to the motor exceeds a predetermined value. And an inverter stop command circuit that outputs a stop command signal for stopping power supply to the motor when the overcurrent detection circuit detects an overcurrent, so that the current supplied to the motor has a predetermined value. An inverter control circuit configured to stop the power supply to the motor when the power is exceeded, the overcurrent detection circuit detects an overcurrent, and the inverter controls the power to the motor by a stop command signal of the inverter stop command circuit. A restart circuit for issuing a restart command signal when a predetermined time has elapsed since the supply was stopped; An inverter control circuit for controlling supply of regenerative braking output to the motor to be started. 2. An overcurrent detection circuit for controlling an inverter for supplying power to an induction motor for driving a rotating shaft supported by a magnetic bearing, and detecting that a current supplied to the motor exceeds a predetermined value. And an inverter stop command circuit that outputs a stop command signal for stopping power supply to the motor when the overcurrent detection circuit detects an overcurrent, so that the current supplied to the motor has a predetermined value. An inverter control circuit configured to stop the power supply to the motor when the power is exceeded, the overcurrent detection circuit detects an overcurrent, and the inverter controls the power to the motor by a stop command signal of the inverter stop command circuit. A restart circuit for issuing a restart command signal after the supply is stopped, and after the overcurrent detection circuit detects an overcurrent, When the regenerative braking output is supplied to perform regenerative braking, and when an overcurrent during regenerative braking is detected when a predetermined time has elapsed since the overcurrent was detected, the induction motor or the An inverter control circuit characterized in that it is determined that a mechanical failure has occurred.