JP2917405B2 - Commercial motor / inverter operation switching control method for motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a commercial operation of an electric motor in a system in which an AC motor is driven by a commercial power supply when operating at a rated frequency, and is driven by an inverter when the operation is not performed at the rated frequency. The present invention relates to a control method after inverter operation switching.

[Conventional technology]

Conventionally, in a system using a general-purpose inverter of this type, as a control method for switching the motor from commercial operation to inverter operation, a certain period of time is set after the commercial power is turned off, and after the motor stops, the inverter is switched to zero speed. A control method of accelerating from a power supply to a desired operating frequency or a control method of giving a timing command to switch to an inverter and switching from commercial operation to inverter operation by this timing command signal has been adopted.

[Problems to be solved by the invention]

However, in the control method of switching to the inverter after stopping the motor described above, not only the smooth switching operation cannot be performed, but also the time until the motor stops after the commercial power supply is cut off differs depending on the machine. There has been a problem that the time required for shifting to operation must be adjusted according to each machine.

In addition, the control method of switching from commercial operation to inverter operation by giving a timing command to switch to the inverter requires a dedicated circuit and a control terminal for that, and has a disadvantage that it is expensive.

In view of the above, an object of the present invention is to provide a commercial operation of a motor that can smoothly transition to inverter operation even if the motor is operated by a commercial power supply and switched to inverter operation without any special timing command when switching to inverter operation. -To provide a control method after the inverter operation is switched.

[Means for solving the problem]

In order to achieve the above object, the control method after switching the commercial operation / inverter operation of the electric motor according to the present invention includes: after shutting off the commercial power of the AC motor driven by the commercial power,
An inverter that is outputting an AC voltage having a frequency equal to the frequency of a commercial power supply while the motor is rotating only by inertia is connected to the motor, and is generated in the motor when switching from commercial operation to inverter operation. An inrush current larger than the protection level of the inverter is detected, and this detection signal is set to the inverter frequency equal to the frequency before the switching (commercial power supply frequency) based on a timing trigger signal after switching from commercial operation to inverter operation. And performing control to gradually increase the inverter output voltage from a low voltage, and that a motor current of the motor is lower than a protection level of the inverter and exceeds a required limit level set as a reference level with the motor current during commercial operation. In this case, gradually lower the inverter frequency and decide on a V / F (voltage / frequency) pattern. After that, when the motor current decreases to the limit level, control is performed to increase the inverter frequency and the output voltage toward the set frequency. Features.

[Action]

According to the control method after switching between the commercial operation and the inverter operation of the electric motor according to the present invention, when the inverter that is outputting the AC voltage is connected to the electric motor that is rotating only by the inertia after the commercial power is cut off, By using the generated inrush current as a trigger signal for timing after switching to inverter operation, there is no need for a dedicated circuit or control terminal,
A smooth transition to inverter operation can be achieved.

〔Example〕

Next, an embodiment of a control method after switching between commercial operation and inverter operation of an electric motor according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a system block diagram showing an embodiment of a system to which a control method after switching between commercial operation and inverter operation of an electric motor according to the present invention is applied. Accordingly, in FIG. 1, reference numeral 10 denotes a commercial power supply. The commercial power supply 10 is connected to one terminal of a switch (for example, an electromagnetic contactor or the like that can be manually operated) 14 and the input side of the inverter 12. Connected to.

The output side of the inverter 12 is connected to the other terminal of the switch 14, the input side of the motor 16 is connected to the commercial power supply 10 or the inverter 12 via the switch 14, and the output side of the motor 16 is connected to the load 18. Connected. Therefore, the motor 16 is
Electric power can be obtained from the commercial power supply 10 or the inverter 12 via 14 to drive the load 18. Switching between the commercial power supply 10 and the inverter 12 is performed by the switch 14, and when shifting to each switching, a slight pause is provided so that the motor residual voltage attenuates.

Next, in the system having the above configuration, the motor 16
With reference to FIG. 2, a description will be given of a control method after switching between commercial operation and inverter operation according to the present invention. FIG. 2 shows the current I of the motor 16 when the load 18 is light when the motor 16 is switched from commercial operation to inverter operation.
FIG. 4 is a time chart showing respective level states of a frequency f and an output voltage V of an inverter 12.

In FIG. 2, a period A indicates a period when the switch 14 is connected to the commercial power supply 10 and the electric motor 16 is operated by the commercial power supply 10. At this time, since the inverter 12 is separated from the electric motor 16 by the switching unit 14, either of the operation and the non-operation may be performed.

The period B is a halt period provided when the motor 16 is switched from the commercial operation to the inverter operation, and there is no problem if a relatively small motor is around 1 second. In the idle period B, the inverter 12 is set to operate in advance to output an AC voltage equal to the commercial power supply 10.

A period C shows a case where the switching unit 14 is connected to the inverter 12 side with respect to the motor 16 which is in the free-run state even after the commercial power supply 10 is cut off, that is, the motor 16 rotating by inertia.
Usually, in this case, as shown in FIG. 2, an inrush current flows instantaneously, and when the inrush current reaches the protection level of the inverter, the inverter 12 stops operating.

The period D is a suspension period before the start of the inverter operation control, and is provided for about 1 second similarly to the period B.

The period E is a period during which the control by the inverter 12 is started, and the inverter output voltage V is gradually increased from a low voltage while the inverter frequency f is kept equal to the frequency of the commercial power supply 10. When the load 18 is light and the electric motor 16 is rotating by inertia, the torque is not so necessary, so that the control after switching from the commercial operation to the inverter operation is completed in this period.

 From the period F, the safe operation by the inverter 12 is started.

In this manner, when the motor 16 operating at the rated frequency by the commercial power supply 10 is switched to the operation by the inverter 12, the operation can be smoothly shifted to the inverter operation.

The inrush current in the period C is a trip level for protecting the inverter 12 and is instantaneous.
Since the current is sufficiently small and the time is short in comparison with the current generated when the operation is shifted from the inverter operation to the commercial power supply 10, there is no problem at all for the system and the inverter 12.

Next, a case where the load 18 of the electric motor 16 is heavy will be described with reference to FIG. Here, FIG. 3 shows the load 18 when the motor 16 is switched from commercial operation to inverter operation.
FIG. 6 is a time chart showing the level states of the current I of the electric motor 16 and the frequency f and the output voltage V of the inverter 12 in the case where is heavy.

The period A to the period D correspond to the load 18 shown in FIG.
Is the same as in the case of light, and the detailed description is omitted for convenience of description.

Period E is a period in which the control by the inverter 12 is started, as in FIG.
Leave equal to the frequency of 10 and keep the inverter output voltage V
Is a period in which is gradually increased from a low voltage. In this case, since the load 18 is heavy, the motor current I continues to increase,
The required limit level is set lower than the protection level of the inverter and the motor current during the commercial operation is set as a reference level.

The period F is a period in which the motor current I has exceeded the limit level, so that the frequency f of the inverter 12 is reduced to increase the torque. At this time, the inverter output voltage V continues to increase.

In the period G, when the voltage becomes equal to the voltage corresponding to the inverter frequency f, that is, the voltage determined by the V / F (voltage / frequency) pattern, the increase of the inverter output voltage V stops, and the inverter frequency f thereafter increases. This is a period in which the corresponding inverter voltage V is output. As the torque is obtained by lowering the inverter frequency f, the motor current I decreases to the limit level.

The period H is a period in which the inverter frequency f accelerates toward the set frequency because the torque is obtained in the period G and the motor current I decreases to the limit level. At this time, the inverter output voltage V also increases. I do.

The period I is a period in which the control after the switching from the commercial operation to the inverter operation is completed and the normal inverter operation of the electric motor 16 is continued.

As described above, FIGS. 2 and 3 show the control method after switching from commercial operation to inverter operation when the load is light and when the load is heavy. According to the control method after the switching, the load condition is not given to the inverter 12, but the control method shown in FIG. 2 or FIG. 3 is automatically performed according to the motor current I.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and many design changes can be made without departing from the spirit of the present invention.

〔The invention's effect〕

As is apparent from the above-described embodiment, according to the control method of the present invention after switching between the commercial operation and the inverter operation of the motor, the inrush current generated at the time of switching from the commercial operation to the inverter operation is determined by the timing trigger signal after the switching. When the inverter frequency is equal to the frequency before the switching (commercial power supply frequency) and the inverter output voltage is gradually increased from a low voltage, and the motor current exceeds the limit level, Inverter frequency f
Is gradually reduced to become equal to the voltage determined by the V / F (voltage / frequency) pattern. Thereafter, a voltage corresponding to the inverter frequency is output. If the motor current decreases to the limit level, the set frequency is set. Therefore, it is set to perform control to increase the inverter frequency and voltage toward the inverter, so that switching to the inverter operation is performed without stopping the motor as in the related art, or without giving a switching command. It can be achieved smoothly. For this reason, according to the control method of the present invention, there is no need for a dedicated switching circuit or control terminal, and there is an effect that unnecessary switching time can be reduced and system cost can be reduced. That is, the present invention has an excellent advantage that the operation can be smoothly shifted to the inverter operation even when the operation is casually switched from the commercial operation to the inverter operation regardless of whether the load is light or heavy.

[Brief description of the drawings]

FIG. 1 is a system block diagram showing an embodiment of a system to which a control method after switching between commercial operation and inverter operation of a motor according to the present invention is applied, and FIG. 2 is a load when switching the motor from commercial operation to inverter operation. FIG. 3 is a time chart showing the motor current and the level of the inverter frequency and the output voltage when the motor is light, and FIG. 3 shows the motor current and the inverter frequency when the load when switching the motor from the commercial operation to the inverter operation is heavy. It is a time chart which shows each level state of output voltage. 10 Commercial power supply 12 Inverter 14 Switch 16 Electric motor 18 Load

Claims (1)

(57) [Claims] After an AC motor driven by a commercial power supply is turned off, the inverter that is outputting an AC voltage having a frequency equal to the frequency of the commercial power supply while the motor is rotating only by inertia. Connected to a motor, detects inrush current greater than the protection level of the inverter generated in the motor when switching from commercial operation to inverter operation, and uses this detection signal for timing after switching from commercial operation to inverter operation. Based on the trigger signal, control is performed such that the inverter frequency is equal to the frequency (commercial power supply frequency) before the switching and the inverter output voltage is gradually increased from a low voltage, and the motor current of the motor is higher than the protection level of the inverter. If the current exceeds the required limit level which is set as a reference level with the motor current during commercial operation as the reference level If the inverter frequency is gradually decreased and becomes equal to the voltage determined by the V / F (voltage / frequency) pattern, a voltage corresponding to the inverter frequency is output thereafter, and the motor current decreases to the limit level. If so, a control method for increasing the inverter frequency and the output voltage toward the set frequency is performed.