JP2000262092A - Starter for ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a starter for starting a plurality of AC motors, that stop and start repeatedly using fewer starting inverters than in a conventional case, without impairing the service life of the AC motors. SOLUTION: A starter for AC motors includes an inverter 210, AC electromagnetic contactors 311,..., 3n1, and 3n2 for connecting each AC motor 411, 421 to 4n1 selectively to the inverter 210 or a commercial power supply, and a controller 500. The controller 500 stores the number of past full-voltage input starting of each AC motor 411, 421 to 4n1. When the plurality of AC motors 411, 421 to 4n1 are started at the same time, the AC motor 4 with the largest number of past full-voltage startings is given priority in inverter start, so that the other motors are subjected to full-voltage start.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a starting device for an AC motor, and more particularly to an AC motor starting device that uses a small number of starting inverters to start each AC motor without impairing the life thereof.

[0002]

2. Description of the Related Art A small-capacity induction motor or the like is usually started by so-called direct start, in which the entire voltage of a commercial power supply is directly applied to a motor winding. However, in a use environment in which starting and stopping are repeated frequently, the winding temperature rises due to a large current at the time of direct-on start, and if such a temperature rise is repeated frequently, the life of the AC motor is shortened. On the other hand, according to the inverter starting in which the starting current is limited via the inverter, it is possible to prevent a short life.

[0003] VVVF is used for starting the inverter of an AC motor.
Such an inverter is provided in parallel with the commercial power supply, and after the AC motor has reached a steady rotation, the operation is switched from the inverter to the commercial power supply. Therefore, the inverter is idle after the start is completed. Note that synchronous switching is desirable for smooth switching to commercial power.

FIG. 3 is a block diagram showing a configuration of a conventional AC motor starting device.

The power line L has no-fuse circuit breakers 111, 121,.
.., 2n1, AC electromagnetic contactors 311 and 32
AC motors 411, 421, 1,.
.., 4n1 are connected. , 4n1 between the power supply line L and each of the AC motors 411, 421,..., 4n1, the non-fuse breakers 111, 121,. , 3n1 are connected in parallel with no-fuse circuit breakers 112, 122,..., 1n2 and AC electromagnetic contactors 312, 322,.

In the above configuration, at the time of starting, the AC electromagnetic contactors 311, 321,..., 3n1 are turned on, and the inverter 211,221,.

When the predetermined start-up operation time is over, the AC electromagnetic contactors 311, 321,..., 3n1 are opened, and the AC electromagnetic contactors 312, 322,. You.

[0008]

However, in the above-described conventional inverter type AC motor starting device, each of the AC motors 411, 421,..., 4n1 is provided with one inverter 211, 221,. Therefore, there has been a problem that the size of the apparatus is increased and the equipment cost for the apparatus is increased.

In view of the above circumstances, the present invention is directed to a plurality of AC motors that repeatedly start and stop frequently, and can be started by using a smaller number of starting inverters than in the prior art without impairing the life of each motor. It is intended to provide an electric motor starting device.

[0010]

To achieve the above object, according to the present invention, in order to control the starting of a plurality of AC motors, one inverter and each AC motor are connected to a commercial power supply. Alternatively, an AC motor starting device including an AC electromagnetic contactor selectively connected to an inverter, and a control device, wherein the control device stores the past number of times of direct on-line start and the number of times of inverter start for each AC motor. On the other hand, when a plurality of AC motors are started simultaneously, a direct start or an inverter start is selected so as to average the number of times of direct start in the plurality of AC motors.

According to a second aspect of the present invention, in the AC motor starting device according to the first aspect, the control device inverter-starts the AC motor having the largest number of past direct start operations among the AC motors simultaneously started, It is characterized by directly starting the other.

According to a third aspect of the present invention, in the AC motor starting device according to the first aspect, when the number of times of direct-on start of the plurality of AC motors is the same as the maximum number of AC motors among the AC motors started simultaneously, It is characterized in that an AC motor with the least number of times of starting the inverter in the past is started by the inverter, and the others are directly started.

According to a fourth aspect of the present invention, in the AC motor starting device according to the third aspect, the control device is configured such that, among the simultaneous starting AC motors, a plurality of AC motors have the same number of direct-on start times and the least number of inverter start times. When the number is the same, the AC motor selected according to the facility management number of the AC motor is started by the inverter, and the other AC motors are directly started.

According to a fifth aspect of the present invention, in the AC motor starting device according to the first aspect, the control device also stores the execution order of the past direct start and the start of the inverter together, and In this method, the AC motor having the largest number of consecutive start-up operations is started by the inverter, and the other is started by direct operation.

[0015] In a plurality of AC motors that repeatedly start and stop frequently, there are generally more opportunities to start the AC motors alone than to start them simultaneously. On the other hand, the inverter is idle after the start is completed as described above. Therefore, there is a possibility that one inverter can be shared by a plurality of AC motors by sequentially providing services to the AC motors that are started individually one after another at different times. The starting device of the present invention focuses on this possibility and arranges one inverter for a plurality of AC motors.

[0016] However, the chance of starting a plurality of AC motors simultaneously is not zero. When that becomes reality,
If one inverter is shared by a plurality of AC motors, some AC motors cannot receive the inverter start service.

In such a situation, the present invention is based on the fact that the influence of the direct-on start is not remarkable unless it frequently overlaps. Select Start or Direct Start. By doing so, it is possible to prevent the number of times of direct start of only a specific AC motor from being increased and the life thereof to be impaired. When an arbitrary AC motor is started independently, it is natural that the inverter is always started if the inverter is empty and available.

[0018]

FIG. 1 is a circuit diagram showing an embodiment of an AC motor starting device according to the present invention, and FIG. 2 is a time chart showing the operation-stop state of each AC motor along a time axis.

As shown in FIG. 1, in this embodiment,
One inverter 210 is connected to the power supply line L via the no-fuse breaker 110,
., 3n1.
, 4n1 are connected through the AC motors 411, 421,..., 4n1. In addition, each AC motor 411, 421,
, 4n1 and the power supply line L are connected in parallel with the inverter 210, respectively.
21, ..., 1n1, AC electromagnetic contactors 312,322,
.., 3n2 are connected. Further, the inverter 21
0, and AC electromagnetic contactors 311, 321,.
3n1, and AC electromagnetic contactors 312, 322, ..., 3
The opening and closing of n2 is controlled by the control device 500.

The control device 500 has a storage device (not shown) therein, and each of the AC motors 411, 421,.
, The number of times of the inverter start and the number of direct-on start are stored, and the inverter start or the direct-on start is selected so that those numbers are averaged in each AC motor.

Next, the operation of the above-described AC motor starting device will be described with reference to FIG.

In the time chart of FIG.
1 and M4 are started and stopped at the same time, and then the AC motors M2 and M3 are started and stopped independently, respectively.
Further, an operation pattern in which AC motors M1 and M4 are started simultaneously and stopped simultaneously is shown.

In this pattern, control device 500 determines that the number of past inverter starts and the number of direct start starts are averaged in each AC motor. When the AC motors M1 and M4 are first started, for example, the AC motor M1 is started by the inverter, the AC motor M4 is started by the direct drive, and the AC motors M2 and M3 are both started by the inverter. In this case, the storage device in the control device 500 stores the number of times of direct start and the number of times of start of the inverter.

Next, when the AC motors M1 and M4 are started again at the same time, the AC motor M1 is started directly and the AC motor M4 is started by the inverter as determined by the control device 500 as described above. As a result, in the AC motors M1 and M4, the number of times of starting the inverter and the number of times of direct starting are respectively 1
It increases each time and averaging is realized.

As described above, according to the present embodiment, the inverter start or the direct start is selected so that the number of times of direct start of each AC motor is averaged. As the number of AC motors increases, the life of the AC motors can be prevented from being impaired. In addition, since a plurality of AC motors are started by a single inverter, the AC motor starting device can be made compact, thereby reducing equipment costs.

<Other Embodiments> In the above embodiment, when starting a plurality of AC motors at the same time, control device 500 determines whether the number of direct ON starts in the plurality of AC motors is to be equalized. Alternatively, the control is performed so as to select the inverter start. In this case, the operation may be performed based on the following criteria.

First, as a criterion for averaging the number of times of direct-on start of each AC motor, an AC motor having the largest number of past on-line start-ups among a plurality of AC motors simultaneously started is inverter-started. Start the other directly.

As a second criterion, in the case where two or more AC motors are started simultaneously, if the number of times of direct-on start of the plurality of AC motors to be started is the largest and the same, the past number of inverter starts is the least. The AC motor is started by the inverter and the others are directly started. This criterion is necessary to prevent the control device 500 from being unable to make a determination.

As a third criterion, when a plurality of AC motors to be started have the same number of direct startups and the same number of inverter startups as the minimum, the selection is made, for example, according to the magnitude of the equipment management number of the AC motor. The AC motor starts the inverter. The facility management number referred to here may be other data as long as the AC motor for starting the inverter can be specified. Such a final rule is provided in consideration of a case where the priority order cannot be determined even if the number of inverter start-ups is considered together with the number of past direct-onset start-ups.

As a fourth criterion, when control device 500 also stores the execution order of past direct start and inverter start, and simultaneously starts a plurality of AC motors, the number of successive consecutive start operations is the largest. Is started by the inverter, and the others are started by direct entry. This is a criterion based on the fact that if the direct-on start is continuously performed in a short time, the life is adversely affected. However, a criterion in which the time interval between each start is considered is also possible. It should be noted that it is desirable to prepare a criterion similar to the second and third criterion for a case where the number of times is the same as the largest number among a plurality of AC motors.

[0031]

As described above, according to the AC motor starting apparatus of the present invention, a plurality of AC motors are started by one inverter, so that the AC motor starting apparatus becomes compact, thereby reducing equipment costs. can do.

Further, according to the starting rule incorporated in the AC motor starting device, the chances of starting the inverter for each AC motor are averaged, so that only a specific AC motor is increased in the number of times of direct ON and its life is shortened. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an AC motor starting device according to the present invention.

FIG. 2 is a time chart showing a running / stopping state of each AC motor along a time axis when the AC motor starting device shown in FIG. 1 is used.

FIG. 3 is a configuration diagram illustrating an example of a conventional AC motor starting device.

[Explanation of symbols]

L: power supply lines 110, 111, ..., 1n1: no-fuse breaker 210 ... inverters 311, 312, ..., 3n1, 3n2: AC electromagnetic contactors 411, 421, ..., 4n1: AC motor 500 :Control device

Claims (5)

[Claims] An AC motor includes an inverter, an AC electromagnetic contactor for selectively connecting each AC motor to a commercial power supply or an inverter, and a control device for controlling starting of the plurality of AC motors. An AC motor starting device, wherein the control device stores the past number of times of direct-on start and the number of times of inverter start for each AC motor, and when starting a plurality of AC motors simultaneously, the direct-on start in the plurality of AC motors An AC motor starting device, wherein direct start or inverter start is selected so as to average the number of times. 2. The AC motor starting device according to claim 1, wherein, among the AC motors that are started simultaneously, the control device starts the AC motor having the largest number of times of direct on-line starting in the inverter, and directly starts the other AC motors. An AC motor starting device for starting. 3. The AC motor starting device according to claim 1, wherein the control device is configured such that, when the number of times of direct start of the plurality of AC motors is the same as the maximum number of the AC motors among the AC motors started simultaneously, the control device controls the past inverter. An AC motor starting device, wherein the AC motor having the least number of starts is started by an inverter, and the others are directly started. 4. The AC motor starting device according to claim 3, wherein the control device has the same number of direct start operations and the minimum number of inverter start operations of the plurality of AC motors among the simultaneous starting AC motors. An AC motor starting device characterized in that an AC motor selected according to a facility management number of the AC motor is started by an inverter, and the others are directly started. 5. The AC motor starting device according to claim 1, wherein the control device also stores a past execution order of the direct on-line start and the inverter start, together with the latest consecutive one of the simultaneous start AC motors. An AC motor starting device characterized in that an AC motor having the largest number of times of direct start is started by an inverter, and the others are started by direct input.