JPS5911276B2 - induction motor drive device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction motor drive device, and more particularly to an induction motor drive device suitable for rapidly accelerating and decelerating an induction motor using a semiconductor power conversion device.

2. Description of the Related Art A semiconductor power conversion device is known that supplies variable voltage, variable frequency alternating current power to an induction motor to perform variable speed operation of the induction motor.

FIG. 1 shows an example of a conventional induction motor drive device.

The AC power supplied to the power receiving terminal 1 is converted into DC by the rectifier 3, and is applied to the inverter 5 via the DC reactor 4. The inverter 5 converts DC power into AC power and drives the induction motor T. The speed command given to the speed command input terminal 16 is sent to an automatic voltage regulator (AVR) 11 via a command signal change rate limiter circuit 12 for suppressing the rapid speed change rate and suppressing the starting current of the motor.
as a voltage command, and as a frequency command to the voltage-to-frequency converter (V-F converter) 15, the DC braking application device IT
is given as a braking frequency command. The AVR II compares the voltage command with the terminal voltage of the induction motor 7 detected via the transformer 6, and calculates the deviation by using an automatic current regulator (ACR).
)10 as a current command. The ACRIO compares the current command and the current feedback signal detected via the current transformer 2, obtains the comparison result as a voltage signal, and supplies it to the automatic pulse phase shifter 9 as a command voltage. The automatic pulse phase shifter 9 generates a thyristor firing pulse with a phase corresponding to the command voltage, amplifies this pulse via a pulse amplifier 8, and uses it as a firing control signal for the thyristor constituting the rectifier 3. 3
The output voltage is controlled. On the other hand, the V-F converter 15
The frequency command given to 14 is converted into a pulse with a frequency corresponding to the command voltage, and this pulse
After being converted into pulses necessary to operate the inverter 5, the pulses are amplified by the pulse amplifier 13, used as firing pulses for the thyristors constituting the inverter 5, and used to control the output frequency of the inverter 5.

Further, the braking frequency command given to the DC control application device 17 is compared with the voltage of the DC braking application frequency setting command device 18 . When the voltage of the braking frequency command becomes lower than the voltage of the set frequency, the DC braking application device 17 issues a control signal for a predetermined period to stop the counting operation of the ring counter 14, and the inverter 5 is instructed to stop the counting operation of the ring counter 14. A firing pulse is continuously supplied only to the thyristor of the phase that was fired immediately before to stop the inverter operation, and DC power is applied to the induction motor 7 for a predetermined period of time to perform DC braking.
Note that during DC braking of the induction motor 7, the voltage detected via the transformer 6 becomes very small, so the output signal of AVRll (i.e., current command) becomes a very large value, but in this case, the It is controlled so that a built-in current limiter setting command device is operated and a current according to the command is supplied to the induction motor 7. FIG. 2 is a specific circuit diagram of a frequency comparison circuit included in the DC braking application device 17.

The potentiometer VRl sets the DC braking application frequency in terms of voltage. The set voltage of the potentiometer VRl and the braking frequency command voltage via the limiter circuit 12 are connected to the resistor R
1 and R2, and compared by an operational amplifier AMP1 provided with hysteresis characteristics by resistors R3 and R4. Note that the diode D1 clamps the negative output voltage of the output terminal 19 to zero volts. 3 and 4 are diagrams for explaining the DC braking operation of the induction motor 7. FIG.

Figure 3 shows a case where resistor R4 in Figure 2 is much larger than resistor R3 and the hysteresis characteristic can be ignored, and Figure 4 shows a case where resistor R4 is of the same size as R3 and hysteresis characteristic appears. This is the case. In Figure 3, a
shows the speed command from the limiter circuit 12 as a frequency F vs. time characteristic, and b shows the output terminal 1 of the DC braking application device 17.
9 shows a control signal B for applying braking and releasing the brake. If the frequency of the speed command is as shown in a, this speed command will match the frequency FDB set by potentiometer R1.
When the speed command becomes lower, the control signal shown in b becomes logic 61", and the inverter 5 is switched to the DC braking operation mode. Then, when the speed command rises again and becomes higher than FDB, the control signal becomes logic 0. , the inverter 5 is released from the DC braking mode and shifts to normal operation at a frequency according to the speed command.On the other hand, in the case of Fig. 4, when the inverter 5 enters the DC braking mode due to the hysteresis characteristic. The frequency FDB2 at which the DC braking is released is higher than the frequency FDB1.

By the way, from the point of view of motor speed control, Fig. 5 a
The speed command F and the broken line show the motor speed characteristics, and the braking control signal B characteristics are shown in Figure b. During starting acceleration, the motor cannot be started until the speed command reaches a considerably large value. Even after this, there was a problem in that the rotational speed V of the electric motor could not follow the speed command F, and the rapid acceleration operation of the electric motor could not be controlled. On the other hand, the motor rotation speed V
If the brake release set value FDB2 is lowered in order to improve followability, the set value FDB1 for applying direct current braking during deceleration will become lower, resulting in the problem that the motor cannot be braked quickly. This tendency becomes more pronounced as the width of the hysteresis characteristic of the comparison circuit of the DC braking application device 17 becomes larger, and the smaller the change rate set value of the limiter circuit 12, the slower the start of the engine starts under the speed command, and the followability becomes worse. Deteriorate. However, if the former type of hysteresis characteristic is not provided at all, there is a risk of causing a chattering phenomenon in which braking is repeatedly applied and released at the time of switching between braking application and release (especially when the slope of the speed command is small); If the rate of change setting value of the limiter circuit is increased, the starting current of the motor becomes large, causing problems such as heating of the windings. The present invention has been made in view of the above-mentioned problems, and is capable of causing the motor to follow a rapid start/acceleration command almost in accordance with the rate of change set value of the limiter circuit, and allows the motor to quickly follow a rapid start/acceleration command in response to a deceleration/stop command. The purpose of the present invention is to provide an induction motor drive device that can decelerate and stop at a speed of 100 seconds.

In order to achieve such an object, the present invention changes the braking application release characteristic to the speed command characteristic as shown in FIG.
During starting acceleration, the motor control is released from DC braking mode by increasing the speed command to a low frequency FDB2, and during deceleration and stopping, the motor control is transferred to DC braking mode by decreasing the speed command to a frequency FDBl, which is higher than frequency FDB2. This is what I did. FIG. 7 is a circuit diagram showing one embodiment of the present invention.

In the figure, the changeover switch 20 is the speed command input terminal 1.
The speed command signal from 6 is input to the limiter circuit 12 as it is, or the zero output is input to the limiter circuit 12. The switching is done by the output of the J-K flip-flop C3 in the DC brake application device 17. Determined by the state, the output of flip-flop IC3 becomes logic 11 (
(hereinafter abbreviated as "11"), the changeover switch 20 connects contacts a and c, and the output of IC3 becomes logic "O" (
(hereinafter abbreviated as "0"), the connection is between contacts b and c. The DC braking application frequency setting command device 18 includes a potentiometer R2 for setting the braking application frequency and a potentiometer R3 for setting the braking release frequency, and can independently set the frequency. DC brake application device 17
compares the braking frequency command signal from the limiter circuit 12 with the set value of the potentiometer VR2 by a comparator circuit composed of an operational amplifier AMP2, etc.
The braking frequency command is compared with the set value of the potentiometer R3 by a comparator circuit composed of 3, etc., and the outputs of both comparator circuits are inverted by logic inverter gates ICl and IC2, respectively, and the outputs are transferred to the clock input terminal C of flip-flop IC3. It is applied to the reset input terminal R, and the flip-flop IC
Braking is applied to the output terminal 19 from the NAND gate 1C4 which receives the Q output of 3 and the output of the inverter gate C2,
Obtain control signal for brake release. In addition, flip-flop I
For C3, when the R input is 601, the Q output becomes ``17'' regardless of the state of the C input, and when the R input is 11 and the C input changes from 61'' to 601, the Q output increases. 0", and once the Q output becomes 01, the J input terminal is set so that it maintains 607 no matter how the C input signal changes.
1'' is given, and 60'' is given to the K input terminal. FIG. 8 is a waveform diagram of each part for explaining the operation of this embodiment, in which a shows the speed command characteristic Fl6 given to the speed command input terminal 16, and b shows the output characteristic F of the changeover switch 20.
2O, c shows the output characteristic Fl2 of the limiter circuit 12, d shows the logic output of ICl, e shows the output of IC2, f&
The output of CIC3 is shown in g, and the output of IC4 is shown in g.

Note that FDBl is the braking application frequency set by potentiometer R2, and FDB2 is the braking application frequency set by potentiometer V.
Indicates the brake release frequency set by R3, FDB
l> Changed to FDB2. First, from time t1 to time T4, while the speed command signal rises to FDB2, AMP2
, AMP3 outputs are both at 111, the π input of IC3 becomes 600, its (output becomes 111), the a-c of the changeover switch 20 is short-circuited, and a speed command signal is given to the limiter circuit 12. At this time, the output of IC4 is No. 61, and the inverter remains in the DC braking mode.At time t1, the speed command signal is set to FDB2.
(In this case, since the speed change rate is small, the output signal of the limiter circuit 12 becomes the same as the speed command change rate), the AMP3 output signal is inverted from 61'' to 00'',
Since the C2 output remains "1" and the IC3 output remains "B" with no change, the output signal of IC4 changes from "1" to "0", and the inverter releases the DC braking mode and responds to the speed command. Starts and accelerates a motor with alternating current power of voltage and frequency. After that, the speed command increases, and at time T2, FDBL
When it reaches, AMP2 changes from “1” to “0” and C
The C signal of 3 also changes from 601 to 611, but the Q output of IC3 remains at 1'' and does not change.Next, the speed command changes from acceleration to constant speed to deceleration, but the slope of this deceleration pattern is steeper than the limiter value set by the limiter circuit 12, the limiter value of the speed change rate appears in the output of the limiter 12, and the motor is decelerated by this speed gradient.Then, at time T3 When the output signal of the limiter circuit 12 is decelerated to FDB1, the AMP2 output changes from ``0'' to ``17'', and the Q output of IC3 changes from ``11'' to 601. Due to this signal, the output of IC4 changes from ``0'' to ``17''. 11, the inverter enters the DC braking mode, and by switching the changeover switch 20, the output signal of the limiter circuit 12 becomes a zero speed command in steps. However, the output of the limiter circuit 12 decreases according to the limiter setting value, and when it reaches FDB2 at time T4, the AMP3 output changes from "0" to "1", and the R input of IC3 increases. 0
n, the Q output power changes from 01 to 61'', the changeover switch 20 is switched to connect between a and c, the speed command signal is again given to the limiter circuit 12, and at time t1
Return to previous state. Also, the Q output of IC3 is 61 as for the output of IC4. However, since the IC2 output power changes from 1" to 1", there is no change in the state and the inverter is still in the DC braking mode.In this way, even though the DC braking release frequency at the time of starting acceleration becomes a low value, On the other hand, the DC braking application frequency during deceleration and stop becomes a high value, and the electric motor
As shown in the figure, followability during starting acceleration is improved, and rapid deceleration and stop is possible during deceleration and stop.

Next, the portion from time T4 to T is for explaining the purpose of providing the changeover switch 20.
functions to prevent the inverter from getting stuck in the DC braking mode when the speed command signal decelerates and once becomes a frequency lower than FDBl, and then rises again before dropping to FDB2.

That is, once the speed command signal drops to a frequency lower than FDBl, by forcibly switching the changeover switch 20, even if the speed command increases thereafter, the output signal of the limiter circuit 12 will always be lowered to FDB. Then, each circuit of the DC braking application device 17 is returned to the same state as at the time of starting acceleration, and the changeover switch 20 is returned to its original state again to perform driving according to the speed command signal. As has been made clear above, according to the present invention, it is possible to improve the speed followability of the electric motor during startup and acceleration, and to achieve drive control that quickly stops the motor when it decelerates and stops.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional induction motor drive device.
Fig. 2 is a circuit diagram showing the DC braking application device in Fig. 1, Figs. 3 and 4 are waveform diagrams explaining the operation of the DC braking in Fig. 2, and Fig. 5 is a conventional speed command and motor speed. FIG. 6 is a diagram showing the relationship between the speed command and the motor speed in the present invention. FIG. This figure is a diagram explaining the operation of the DC braking in FIG. 7. Explanation of symbols, 12...Limiter circuit, 16...
... Speed command input terminal, 17 ... DC brake application device, 18 ... DC brake application frequency setting command device, 20 ... Changeover switch, VR2, R3.
...Potentiometer, AMP2, AMP3...
...Operation amplifier, ICl, IC2...Logic inverter gate, IC3...JK flip-flop, IC4...NAND gate.

Claims (1)

[Claims] 1. A power conversion device that supplies variable voltage variable frequency AC power to the induction motor, and a limiter that suppresses the rate of change to a predetermined value when the speed command for controlling the speed of the induction motor has a rate of change greater than a predetermined value. a control device that controls the output voltage and output frequency of the power conversion device according to the speed command signal passed through the limiter device; In an induction motor drive device comprising a DC brake application device including a reference signal generator for setting and canceling the DC braking mode of the conversion device, the DC brake application device has a reference signal generator that generates two types of reference signals having different values. It has a signal generator, and of the two types of reference signals generated, a reference signal value for canceling the DC braking mode of the power conversion device is lower than the other reference signal value for setting the DC braking mode. An induction motor drive device characterized in that: