JPS59165989A - Speed controller of inducton motor - Google Patents

Abstract

PURPOSE:To shorten a rise time by providing an accelerating time constant changing circuit, thereby stepwisely accelerating of an induction motor. CONSTITUTION:When a speed setting voltage Vm is raised, a slip increases, and the current of an induction motor 3 increases. When this current exceeds the current limit value for deciding the switching point of the accelerating time constant of a current limit setter 13, a comparison discriminator 14 is operated to operate the contact output group of a sequence circuit 15. A slow starting circuit 12 outputs a speed command voltage V by the input from a speed setter 11 and the operation of the contact group of the circuit 15 while stepwisely changing the accelerating time constant to an inverter. In this manner, when an overcurrent is produced as shown, the acceleration is temporarily stopped for the prescribed time, and is again operated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a drive control device for an induction motor using a TRS inverter.

2. Description of the Related Art Some induction motors, which are generally used as drive devices for various machines, have their rotation controlled through an inverter.

Recently, in order to save energy, a slow start method has been adopted to reduce the capacity of the inverter.

This starting method increases the frequency (rotation speed) to the specified operating speed with a certain time constant, and the acceleration time constant allows acceleration to overcome the increase in load in the high frequency region near the maximum speed. It takes a long time to rise because the value is limited.

Also, depending on the machine, it is necessary to shorten the start-up time to reduce various losses during startup.

The present invention was obtained as a result of various efforts to eliminate the problems caused by the long rise time as described above.

That is, the present invention provides a device for fully controlling an induction motor using an inverter, in which the slow start circuit of a speed controller that controls the output of the inverter detects the entire current of the induction motor during acceleration and changes the acceleration time constant. A speed control device for an induction motor provided with a circuit is provided.

A schematic block diagram of a speed control device for an induction motor according to the present invention is shown in FIG. 1 and will be described.

The speed controller 1 inputs the electric power 1c from the control power source and the signal voltage vfi proportional to the load current, and outputs the speed command voltage 2 and the driving signal Y to the impark 2. The inverter 2 receives the input from the speed controller 1 and 1 mi of power from the main power supply, supplies the speed command voltage V (with the corresponding frequency and voltage power F to the induction motor 3, and is proportional to the load current of the induction motor 3. The induction motor 3 outputs a signal voltage vf.The induction motor 3 drives the load machine at a speed expressed by the following equation using the frequency and voltage power F from the inverter 2.

N = −−−−−−(1−S) N Number of rotations of induction motor (R, P, λ1) P Number of poles of induction motor S, slip of induction motor f, output frequency of inverter (H2) Speed setter A schematic block diagram of 1 is shown in FIG. In the figure, the speed setting circuit 11 is connected to the impark 2. The speed setting voltage Vm corresponding to the minimum speed determined by the specifications of the induction motor 3 and the speed setting voltage V corresponding to the steady operating speed
s and the speed setting voltage Vm (, V, s - Vm
) are supplied to the slow star 1 road section 12. The slow start circuit 12 receives input from the speed setting circuit 11.

The speed command voltage V is applied to the inverter 2 while changing the acceleration time constant step by step by the operation of the contact group of the sequence circuit 15.
Output. The limit current setting circuit 13 sets a limit current value that determines the switching point of the acceleration time constant. The comparison judgment circuit 14 receives a signal voltage V based on the current value from the limit current setting circuit 13.
Compare the signal voltage vf from S and inverter 2 and find v
When f > Vs K, the output relay 24 is turned on and a contact output is supplied to the sequence circuit 15 (see FIG. 4). The sequence circuit 15 performs a predetermined sequence operation and outputs the contact output to the slow start circuit 12 and the inverter 2. The DC power supply circuit 16 generates DC voltages required by each circuit and supplies them to each section.

Details of the slow start circuit 12 #IVi are as shown in FIG. In the figure, 17a to 17c are operational amplifiers,
18a to 18n are resistors. I with 19U diode
), 20 is a capacitor. 213' to 21e' are contacts corresponding to relays of the sequence circuit section.

Details of the sequence circuit 15 are as shown in FIG.

In the figure, 22a and 22b are push button switches, and 21
a-21g is a rele. 21x' and 21g' are contacts corresponding to the relays (23a to 23c are timers, and 23a' to 23c' are time-limiting contacts corresponding to the timers. 24 is the output relay of the comparison/judgment circuit 14).
(not shown).

A starting method in the speed control device for an induction motor having the above configuration will be explained with reference to each of the above figures and FIG. 5 showing the acceleration customization.

Speed command voltage value V corresponding to the operating speed of the unswitched induction motor
The setting is performed by the speed setting circuit 11 of the speed controller I. Next, when the starting push button switch 22b of the sequence circuit 15 is pressed, the relay 21a, timer 23a, and power contact 21a are activated.
′ makes this circuit self-maintaining. With this operation, the speed command voltage value Vm is output from the slow start circuit 12 and input to the inverter 2.

Since the shunted operation signal Y of the inverter 2 is input, the inverter 2 supplies the induction motor 3 with electric power Fm at a frequency and voltage corresponding to the speed command voltage value Vm. After starting at the lowest speed and time t1 elapses, the timer 23a times up and the time limit contact 23a' closes and the relays 21b, 21
c works, slow start circuit 12 (7) contact 21
b', 21c' are closed. The speed command voltage V of the slow start circuit 12 increases from the speed setting voltage Vm with an acceleration time constant of 3, and the inverter 2 supplies electric power Fa of the corresponding frequency and voltage to the induction motor 3 to increase the speed for a time ta.

At this time, the induction motor 3 tries to rotate at a speed corresponding to the frequency, but as the speed increases, the balance between the acceleration torque and the acceleration time constant is lost, the slippage increases, and the current of the induction motor 3 increases. When this current exceeds the limit current value and a corresponding signal voltage is input, the output link (not shown) of the comparison/judgment circuit 14 is activated and the contact 24 of the sequence circuit 15 is closed, causing the relay 21f and timer 23b to operate. This circuit has contact 2
4 is self-maintained.

At the same time as this operation, the relay 21c turns OFF, so the contact 21c' of the slow start circuit 12 opens and the speed command voltage V
stops m speed at speed command voltage value Va. Inverter 2
is fixed at the frequency corresponding to the speed command voltage value Va, so the induction motor 3 is accelerated by the Karo speed torque, the slippage is reduced, and the current is also reduced.

In this state, time t2 elapses at the push point - this time timer 23b
is timed up, the time limit contact 23b' closes, and the contact 21d' of the slow start circuit 12 closes.
The inverter 2 supplies electric power Fb of the corresponding frequency and voltage to the induction motor 3 to increase the speed for a time tb. In the same way as above, when the current of the rust conductive ωJ machine 3 exceeds the current limit value again and the corresponding signal voltage is input, the output relay (not shown) of the comparison/judgment circuit 14 is activated, and the contact 21d of the slow start circuit 12 is activated. ' is opened and the speed command voltage V stops accelerating at the speed command voltage value vb. When time t3 elapses in this state, the timer 23c times up, the time limit contact 23c' closes, and the slow start circuit 12 contact 21e' closes, and the speed command voltage V changes to the acceleration time constant I(1(
The inverter 2 increases the power Fs at the corresponding frequency and voltage.
is supplied to the induction motor 3 and the speed is increased for a time tc.

When the induction motor 3 is accelerated and reaches the set speed of the speed command voltage value VS, the start-up operation is completed.

Next, to stop the induction motor, press the stop push button switch 22a, turn off the relay 21a and timer 23a, open the contact 213' and time limit contact 23a', and close all relays 21b-21g, timers 23b, 23c. Turn it off.

Due to the above operation, the inverter 2 receives the contact 21 which is the operation signal.
Since a' opens, the operation is stopped and power supply to the induction motor 3 is stopped. On the other hand, since the contacts of the slow start circuit 12 (d) are opened, the charges stored in the capacitor 20K are discharged, and the speed command voltage V becomes 0, resulting in the state before starting.

Although the present invention can be practiced as described above, it is not limited to the examples.

Zero speed control can be carried out not only by an open-loose system as in the embodiment, but also by a closed-loop system with a feedback circuit.

- The switching point of the acceleration time constant is set according to the characteristics of the induction motor, the required rise time, etc.

According to the present invention, an acceleration time constant changing circuit which detects the current of the induction motor during acceleration and changes the speed time constant is provided in the slow start circuit of the speed controller that controls the output of the inverter as described above. As shown in the figure, when the conventional linear knife speed (B) is used, the start-up time takes Ln, and when the stepwise acceleration according to the present invention (A) is performed, the start-up time becomes [S, which reduces the start-up time by about 30%. can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the speed control device for an induction motor according to the present invention. FIG. 2 is a block diagram of the speed controller, and FIG. 3 is a slow start circuit diagram. FIG. 4 is a sequence circuit diagram. FIG. 5 is an acceleration characteristic diagram. 1: Speed controller 2 Inverter 3: Induction motor 11, speed setting circuit 12 Nislo-start circuit 13: Limiting current setting circuit 14 Comparison/judgment circuit 15
, sequence circuit 16゛: DC power supply circuit 17a~
17c, arithmetic multiplier 1] device 18a (8n: resistor 19:
Diode 2o, capacitor 21a - 21g: Relay 22a, 22b
: Push button switches 23a to 23c: Timer user Toray Engineering Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1) In a device that fully controls the induction motor through an inverter, an acceleration time constant changing circuit detects the current of the induction motor during acceleration and changes the acceleration time constant in the slow start circuit of the speed controller that fully controls the output of the inverter. 1. A speed side device for an induction motor, characterized by being provided with.