JPS61258699A - Controlling method for ac motor - Google Patents

Abstract

PURPOSE:To cooperate the speeds of a plurality of AC motors by using the frequency signal obtained by a special inverter as the frequency command signal of other inverter. CONSTITUTION:If the first inverter 37-1 operates a stall preventing function when the first AC motor 6-1 is driven by the first inverter 37-1, a frequency signal is varied. The frequency signal is produced from a signal terminal 36, and input to the frequency command signal terminal 33 of the second-n-th inverters 37-2-37-n. Thus, the first inverter 37-1 and the second-n-th inverters 37-2-37-n are controlled by the same frequency signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling a plurality of AC motors by using a plurality of inverter devices having a function of preventing stalling of the AC motors.

[Prior art]

Conventionally, there were those shown in FIGS. 3 and 4. FIG. 3 shows an inverter device, in which a power source (1) is connected to a converter (2). The capacitor (3) is connected to the output of the converter (2), a current detector is connected, and a load (7-1) is applied to the AC motor (6-1).

Further, a voltage detection signal (8) is taken out from both ends of the capacitor (3) and inputted to the overvoltage level detection circuit (1) together with the overvoltage level signal (9) from the overvoltage level setter (29).

Overvoltage signal (IC is the output of overvoltage level detection circuit (1Φ), PWM (Pulse Width Mod
lation) generation circuit (1).

In addition, the voltage detection signal (8) and the overvoltage stall prevention level signal from the overvoltage stall prevention level setting circuit (30) are input to the overvoltage stall detection circuit (14). With the output of the detection circuit α4),
Acceleration/deceleration circuit (input to 1Φ).

Also, from the output of the current detector (4), a current detection signal (1
'Q is taken out and sent to the overcurrent level detection circuit α9 together with the overcurrent level signal (1) from the overcurrent level setting circuit 01).
) is the output of the overcurrent level detection circuit (19) and is input to the PWM generation circuit (12).

In addition, the current detection signal α and the overcurrent stall prevention level signal C21) from the overcurrent stall prevention level setting circuit (3) are as follows:
The overcurrent stall detection circuit G22) outputs an overcurrent stall prevention signal 0) which is input to the acceleration/deceleration circuit 0.

Frequency setter (2 outputs become the frequency command signal (3), which is input to the acceleration/deceleration circuit (1@).
The output part of Φ is connected to the PWM generation circuit α2), and the PWM
The output part of the generating circuit α2) is connected to an inverter (5).

In addition, the power supply U), the first AC motor (6-1), the first load (7-1), and the frequency setter G! Let the part excluding 0 be the first inverter device (28, -1).

FIG. 4 is a block diagram showing a state in which a plurality of conventional inverter devices are connected and operated. Loads 7-1 to 7-n are connected to 6-1) to 6-n, respectively.

In addition, the first to nth inverter devices (28-1) to (28-
n) frequency command signal terminals (33) are electrically connected, and the frequency setter (25) of the first inverter device (28-1) controls the frequency command signal terminals (33) of the second to nth inverter devices (28-1).
-2) to (28-n) frequency command signals are determined.

Next, the operation of the inverter device will be explained with reference to FIG. 3, which describes a conventional control method.

An alternating current power source (1) is once converted to direct current by a converter (2), smoothed by a capacitor (3), and then converted to alternating current again by an inverter (5) to drive an alternating current motor (6).

Here, the frequency command signal (27) set by the frequency setter (2F5) is input to the acceleration/deceleration circuit (1), and outputs a frequency signal (2nd circuit α) with a certain time constant.
2) is a PWM signal G! so as to vary the output voltage and output frequency of the inverter (5). 4) to the inverter (5).

Next, the stall prevention function of this inverter device will be explained. First, the DC bus current detected by the current detection circuit (4) is sent as a current detection signal (17) to the overcurrent level detection circuit α9), which is an overcurrent level signal from the overcurrent level setting circuit (31). (Both 1$ and 1$ are input.) The overcurrent signal C is the PWM generation circuit α2 when the overcurrent level signal (current detection signal α7 compared to 1g1) is larger.
), and the PWM generating circuit (12) stops the output of the inverter (5) so as to protect the inverter (5). This operation is hereinafter referred to as overcurrent cutoff. On the other hand,
The current detection signal (17) is input to the overcurrent stall detection circuit C22) together with the overcurrent stall prevention level signal (21) from the overcurrent stall prevention level setting circuit (32).

The overcurrent stall detection circuit G22) outputs a current detection signal (17)
When becomes larger than the overcurrent stall prevention level signal (21), it is output to the acceleration/deceleration circuit 06), and the acceleration/deceleration circuit 0 works to lower the frequency signal (2), and the in...
The output frequency of the motor (5) is lowered to prevent the inverter from stopping due to overcurrent and the AC motor (6) from stalling. This operation is hereinafter referred to as the overcurrent stall prevention function. It goes without saying that the DC bus current level at which the overcurrent stall prevention function operates is set to a lower level than the DC bus current level at which the overcurrent cutoff operates.

Next, the stall prevention function of the inverter device using voltage will be explained. First, the DC bus voltage detected by the capacitor (3) becomes a voltage detection signal (8), which is sent to the overvoltage level detection circuit α together with the overcurrent level signal (9) from the overvoltage level setter (29). is input. The overvoltage signal (10) indicates that when the voltage detection signal (8) becomes larger than the overvoltage level signal (9), the PWM generation circuit (10)
The PWM generation circuit (1@) stops the output of the inverter (5) to protect the inverter (5).Hereinafter, this operation will be referred to as overvoltage cutoff.Also, the force-sensing pressure detection signal ( 8) is the overvoltage stall prevention level setting circuit (3
The overvoltage stall prevention level signal (13) from Φ is input to the overvoltage stall detection circuit (1). When it becomes large, acceleration/deceleration circuit α6
), the acceleration/deceleration circuit (1Φ) works to prevent the frequency signal C from dropping, keeps the output frequency of the inverter (5) constant, and prevents the inverter from stopping due to overvoltage and stalling the AC motor. .Hereinafter, this operation will be referred to as the overvoltage stall prevention function.

It goes without saying that the DC bus voltage level at which the overvoltage stall prevention function operates is lower than the DC bus voltage level at which the overvoltage cutoff operates.
t) corresponds to the output frequency and similarly the frequency signal 06
) also corresponds to the output frequency 〇Here, the frequency signal is assumed to change from O to Vl (V), the frequency command signal (27) is also changed from 0 to Vl (V), and the output frequency is 0 (v ), the lowest frequency is -
■It is assumed that the highest frequency occurs when M.

As shown in Fukiage, the inverter device is in operation 0. When a plurality of such inverter devices are used to control a plurality of AC motors as shown in FIG. 4, the first inverter device (28-1 ) frequency setter (25) of the second to nth inverter devices (28-2) to (28-
The frequency command signal terminals 03) of the first to nth inverter devices (28-1) to (28-n) are electrically connected to control the AC motor so that the frequency command signal (n) is also determined.

[Problem that the invention seeks to solve]

Since the conventional method of controlling an AC motor as described above is as described above, the first inverter device (28
Even if the stall prevention function operates in -1), different frequencies will be output to the second to n inverter devices (28-2) to (28-n), and the first AC motor (
There was a problem that the speeds of AC motor 6-1) and the other AC motors (6-2) to (6-n) were not linked.

This invention was made to solve this problem, and when the speed of a specific AC motor controlled by a specific inverter device changes, the speed of another AC motor controlled by another inverter device changes. It is also an object of the present invention to provide a method for controlling an AC motor, which allows the speed of a particular AC motor to be varied as well.

[Means for solving problems]

The AC motor control method according to the present invention uses a frequency signal obtained by a specific inverter device as a frequency command signal for another inverter device.

〔use〕

In this invention, a frequency signal obtained by a specific inverter device becomes a frequency command signal for other inverter devices, and the frequency signal obtained by the specific inverter device becomes a frequency command signal for the other inverter devices according to the speed change of the AC motor controlled by the specific inverter device. This means that the speed of the AC motor controlled by the motor also changes.

〔Example〕

1 and 2 show an embodiment of the present invention, FIG. 1 is a circuit diagram of an inverter device, and FIG. 2 is a block diagram showing a state in which a plurality of inverter devices are connected and operated. (1) to (35) are exactly the same as the above-mentioned subsidiary ones, and (3) is a frequency signal terminal.

In the figure, the power supply (1) is the first to nth inverter devices (
st -1) to (wing, -n) are connected to the input terminals (3), and the first to nth inverter devices (37-1) (37-n
) to the output terminals (34) of the
1) to (6-n) are connected, respectively, and loads 7-1 to 7-n are connected to these AC motors (6-1) to (6-n), respectively.

The frequency setter (25) includes a first inverter device (3
7-1) is electrically connected to the frequency command signal terminal (33). The frequency signal of the first inverter device (37-1) (the frequency setter terminal (3) which is the two output parts is connected to the frequency signal of the second to nth inverter devices (37-2
) to (37-n) frequency command signal terminals (33) are electrically connected.

In the method for controlling an AC motor according to the present invention, the first
The first AC motor (6-1) is driven by the inverter device (37-1), but when the stall prevention function operates in the first inverter device (37-1), the acceleration/deceleration circuit α is activated. The frequency signal C changes accordingly.

This frequency signal (2 is the frequency command signal (2) of the 2nd to n inverter devices (37-2) to (ay-n)
27) is input instead. Therefore, the first inverter device (37-1) and the second to nth inverter devices (37-1)
7-2) to (37-n) are the same frequency signals (26
), and as a result, the speeds of the second to nth AC motors (6-2) to (6-n) also change in response to changes in the speed of the first AC motor (6-1). become.

In the above embodiment, a case has been described in which the stall prevention function has both an overcurrent stall prevention function and an overvoltage stall prevention function, but it may be only one of them.

〔Effect of the invention〕

As explained above, this invention uses a frequency signal obtained by a specific inverter device as a frequency command signal for other inverter devices, so that the speed of the AC motor controlled by the specific inverter device and the speed of the AC motor controlled by the specific inverter device can be This has the effect that the speed of the AC motor controlled by the inverter device is linked.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of an inverter device showing an embodiment of the present invention, Fig. 2 is a block diagram showing a state in which a plurality of inverter devices are connected and operated, and Fig. 3 is a conventional inverter device that controls an AC motor. FIG. 4 is a block diagram showing a state in which a plurality of inverter devices are connected and operated. In the figure, G6) is an acceleration/deceleration circuit, G26) is a frequency signal, (2'D is a frequency command signal, (3) is a frequency command signal terminal, (3Φ is a frequency signal terminal, and (37) is an inverter device. In addition, the same symbols in each figure indicate corresponding parts.

Claims (4)

[Claims] (1) An AC device that uses a plurality of inverter devices having a stall prevention function to control a plurality of AC motors, in which a frequency signal of a specific inverter device is used as a frequency command signal for other inverter devices. How to control an electric motor. (2) The method for controlling an AC motor according to claim 1, wherein the stall prevention function is a function of lowering the output frequency when the current of the inverter device exceeds a certain value. (3) The method for controlling an AC motor according to claim 1, wherein the stall prevention function is a function that prevents the output frequency from decreasing when the voltage of the inverter device exceeds a certain voltage. (4) The stall prevention function is a function that lowers the output frequency when the current of the inverter device exceeds a certain level, and does not lower the output frequency when the voltage of the inverter device exceeds a certain level. A method for controlling an AC motor according to claim 1.