JP3248963B2 - Speed controller for three-phase induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for hoisting, traversing and traveling various cranes, a drive device for various logistics machines,
Regarding a speed control device of a three-phase induction motor used for a drive device of a fan, a blower, and other various machines,
This enables stable speed control without causing resonance of the machine.

[0002]

2. Description of the Related Art As a speed control device for an industrial machine such as a crane using an induction motor as a drive device, there has conventionally been a phase control type primary voltage control device using a thyristor. This utilizes the fact that the torque of the induction motor is proportional to the square of the primary voltage, inserts a silisk into the primary circuit of the induction motor, controls the phase of this, thereby controlling the primary voltage of the induction motor, By changing the slip-torque characteristic,
The speed is controlled.

[0003]

This phase control type primary voltage control apparatus has a disadvantage that a complicated circuit is required for phase control, so that the apparatus becomes large and expensive. Also, during steady-state operation, the phase firing angle is fixed to a certain value, so it may resonate with the machine-specific frequency. Once the resonance starts, the firing angle will not change unless the command speed is changed. Since it does not change, there was a problem that the resonance expanded.

The present invention solves the above-mentioned problems in the prior art, and enables stable speed control of industrial machines using a three-phase induction motor as a driving device without generating resonance peculiar to the machines. It is an object of the present invention to provide a three-phase induction motor speed control device.

[0005]

SUMMARY OF THE INVENTION The present invention provides a thyristor inserted in at least two phases of a power supply line of a three-phase induction motor so as to be capable of conducting in both forward and reverse directions, and a command for the speed of the three-phase induction motor. Speed command means, a speed detection means for detecting the speed of the three-phase induction motor, a deviation detection means for obtaining a deviation between a command speed by the speed command means and a detection speed by the speed detection means, and the deviation detection means The thyristors are turned on by changing the ratio of the on-period and the off-period in a cycle longer than the cycle of the three-phase AC power supply for driving so as to reduce the speed deviation obtained by And switching control means for performing off-switching.

[0006]

According to the present invention, the average level of the applied voltage is changed by driving the thyristor by switching control (cycle control) and changing the period ratio between ON (energizing cycle) and OFF (stop cycle). Thus, speed control can be performed.

According to such control, since phase control is unnecessary, a complicated speed control device is not required, and a small and inexpensive configuration can be achieved.

Further, the phase is mutually 120 ° or 240 °.
Because the two phases that are shifted by two degrees are turned on at the same time, an imbalance occurs between the inrush current and the conduction time between the two phases. (Ie, the speed command value) is unbalanced. Then, the imbalance of the torque and the imbalance of the average level of the applied voltage causes an imbalance in the next energization cycle by the speed feedback, and this cycle is repeated. By this repetition, even if the command speed is constant, the on / off period ratio of the cycle control always slightly changes (that is, a random output). With such random control, even if there is a resonance frequency unique to the machine main body, a state in which the resonance point is kept at the resonance point does not hold, so that the occurrence of resonance can be prevented. However,
On average, the commanded constant speed can be maintained by the speed feedback.

[0009]

FIG. 1 shows an embodiment of the present invention. This is an application of the present invention to a hoisting and lowering device of a crane. In FIG. 1, each phase R.D.
S. At T, a reactor 12 for suppressing an inrush current and a surge is inserted. The reactor 12 can be replaced by a resistor. In addition, the two-phase R.D. In T, triacs F1 and F2 (for normal rotation) and R1 and R2 (for reverse rotation) are inserted. Triac F1, F2, R
1 and R2 switch the three-phase AC power supply 10 on and off in accordance with the variably controlled power supply cycle and stop cycle, and supply the three-phase AC power supply 10 to the driving three-phase induction motor 18. Brake 2
2 operates when the brake contactor 24a is opened to brake the three-phase induction motor 18. The power supply circuit (stabilized power supply) 26 is a three-phase AC power supply 10 (for example, 20
0V) is used to create a DC power supply of +12 V, +15 V, etc., necessary for the operation of the relay coil and each circuit.

Pulse generator 28 (speed detecting means)
Detects the speed of the three-phase induction motor 18 and outputs a pulse signal having a frequency corresponding to the detected speed. The F / V converter 30 converts the output pulse of the pulse generator 28 into a voltage according to the frequency. The direction detection circuit 32 detects the rotation direction (forward or reverse) of the three-phase induction motor 18 based on the output signal of the pulse generator 28. The polarity switching circuit 34 outputs a polarity signal based on the direction detection by the direction detection circuit 32. That is, in the case of forward rotation, +
The signal is output, and in the case of reverse rotation, a signal is output. When a tacho generator is used instead of the pulse generator 28, the F / V converter circuit 30, the direction detection circuit 3
2 and the polarity switching circuit 34 are unnecessary.

The controller 36 (speed command means) is for commanding the speed of the three-phase induction motor 18, and has a polarity (-for normal rotation, + for reverse rotation) and a voltage value according to the operation direction and operation amount. Output speed command signal with. The soft start / soft stop circuit 38 makes the rise and fall of the speed command signal gentle, and gives a soft start characteristic and a soft stop characteristic. However, if the soft start characteristic is effective, the inching operation is slowed down. Therefore, a signal obtained by differentiating the operation amount of the controller 36 is superimposed on the soft start characteristic to secure the inching operation.

The difference between the speed command signal and the speed detection signal is obtained at an addition point 44 (deviation detecting means). The relationship between the speed command value and the speed detection value during hoisting and hoisting changes as shown in FIGS. 2A and 2B, respectively. That is, in the case of acceleration and steady operation during hoisting, the detected value is lower than the command value, and in the case of deceleration, the command value is lower. In addition, in the case of acceleration during winding, the command value is larger, and in the case of steady operation and deceleration, the detected value is lower.

The deviation signal output from the addition point 44 is amplified by a speed control circuit (inverting amplifier) 40. The polarity of the output voltage of the speed control circuit 40 changes as follows depending on the operating conditions.

(1) At the time of hoisting (a) In the case of acceleration: | command value− |> | detection value + | (−voltage), which is inverted by the speed control circuit 40 and +
Output. (B) For steady operation: | command value- |> | detection value + |
, Which is inverted and becomes + output. (C) In the case of deceleration: | command value− | <| detection value + |, which is inverted and becomes −output.

(2) At the time of lowering (a) In the case of acceleration: | command value + |> | detection value− | (B) For steady operation: | command value + | <| detected value- |
, Which is inverted and becomes + output. (C) In the case of deceleration: | command value + | <| detection value− |, which is inverted and output as +.

By controlling the three-phase induction motor 18 with the output of the speed control circuit 40 which changes as described above, an operation according to the command is realized. That is, at the time of winding, FIG.
By driving the three-phase induction motor 18 in the positive direction as shown in FIG. 3A, an accelerated and steady operation state is obtained, and the three-phase induction motor 18 is driven in the negative direction as shown in FIG. As a result, a force for stopping the upward torque acts, and a deceleration state is obtained. Also, when unwinding,
By driving the induction motor 18 in the minus direction as shown in FIG. 3C, an accelerated state is obtained, and by driving the induction motor 18 in the plus direction as shown in FIG. A torque in the direction of applying a brake to the load to be applied acts, and a steady operation and a deceleration state are obtained.

An output signal of the speed control circuit 40 is input to a duty ratio variable circuit 46. The duty ratio variable circuit 46 changes the ratio between the energizing cycle and the stop cycle in one cycle of the switching control which is set in advance according to the magnitude of the input deviation signal, and outputs a pulse signal (“1” in the energizing cycle, (A pulse width modulation signal which becomes “0” in the cycle). That is, when the deviation signal is small, the energization cycle is shortened to lengthen the stop cycle, and when the deviation signal is large, the energization cycle is lengthened and the stop cycle is shortened. The duty ratio variable circuit 46 incorporates a circuit for setting the length of one cycle of the switching control (the number of waveforms of the three-phase AC power supply 10 (one waveform at half wavelength)). The length of one unit can be set variously, but if it is set long, the resolution of the duty variable becomes high, so that the resolution of the speed control becomes high. Conversely, if the setting is shorter, the response of the control is faster.

The ignition circuit 48 includes a duty ratio variable circuit 4
The photocoupler (not shown) is fired by the pulse signal output from 6. The output of the photocoupler becomes an electrically insulated output, and is input to the gates of the triacs F1, F2, R1, and R2 via the relay switches 14a and 16a, and ignites the output. Relay switch 14a,
The relay 16a is turned on and off by the relays 14 and 16. One of the relays 14, 16 selected by the forward / reverse closing logic 60 is excited.

The forward / reverse input logic 60 includes the controller 3
6 and the polarity switching circuit 34 and F /
Based on the direction and speed detection signals from the V converter 30, each operation of turning on, switching, and shutting off the forward rotation relay 14 and the reverse rotation relay 16 is performed so as to match the command of the controller 36. Even if the controller 36 is returned to the zero notch, the speed control according to the present invention is utilized until the speed of the induction motor 18 becomes close to zero speed (for example, 2% speed).

Thus, the forward / reverse input logic 60 operates as follows. That is, when the three-phase induction motor 18 is stopped and the controller 36 is at the zero notch, neither the forward-side closing signal nor the reverse-side closing signal is output. When the controller 36 is turned forward (or reversely), a forward-side closing signal (or reverse-side closing signal) is output, and the forward rotation relay 14 is turned on.
(Or the reverse rotation relay 16) is turned on, and the three-phase induction motor 18 is rotated forward (or reversely).

Even if the controller 36 has a zero notch,
Until the speed becomes close to zero speed, the zero speed signal is continuously output, so that the control is kept alive. That is,
The reverse torque is applied to the three-phase induction motor 18 so that the three-phase induction motor 18 is decelerated, and the control is stopped only when the speed becomes close to zero.

The brake operation circuit 66 is a speed at which the speed of the three-phase induction motor 18 applies a brake (for example, a 5% speed).
When it is lowered below and the controller 36 is at 0 notch, the brake operation relay 70 is cut off to turn off the relay 24, and the relay switch 24a is opened to operate the brake 22.

The forced firing circuit 74 stops the speed control according to the present invention when the controller 36 is set to the full notch, and fires the triac F1, F2 or R1, R2 over the entire waveform.

FIG. 4 shows the operation of the speed control device shown in FIG.
In FIG. 4, (a) shows a low speed and (b) shows a high speed.
Here, seven waveforms (one waveform = １ ／ cycle) of the AC power supply 10 are set as one cycle of the switching control, and the energization cycle is varied in units of one waveform. U phase is power supply R
The phase and the W phase are waveforms generated by the switching control of the power supply T phase. When the triacs F1 and F2 are fully turned on, the R and T phase waveforms become the U and W phase output waveforms as they are (all waveforms are shaded). The current of the W phase is delayed by 240 ° compared to the U phase.

The gate current (waveform corresponding to the output of the duty ratio variable circuit 46 and the firing circuit 48)
At every switching cycle starting at 180 ° or 180 °, it rises at the start of this switching cycle and is more than a predetermined amount α (for example, 0 ° <α <180) than the U-phase ON period.
°) Fall after a short time. This gate current is commonly supplied to the U-phase and W-phase triacs F1, F2 (R1, R2). Then, the triac is turned on when the gate current starts to flow, and turned off when the main current becomes zero after the gate current is cut off. Therefore, the U-phase and W-phase energization cycles are as shown by hatching in FIG. . That is,
Since the phase of the W phase is delayed by 240 ° from the phase of the U phase, if the phase is turned on at the same timing, imbalance occurs in the rush current. Also, the energization period is 60 degrees longer in the W phase than in the U phase, resulting in imbalance. Then, the imbalance of the rush current causes an imbalance in the torque, and the imbalance in the conduction time causes an imbalance in the average level of the applied voltage (that is, the speed command value). Then, the imbalance of the torque and the imbalance of the average level of the applied voltage causes delicate vibration (that is, speed fluctuation) to generate the next energization imbalance by speed feedback, and this cycle is repeated.

For example, in the case of a low speed in FIG. 4A, it is assumed that the triac F1 is fired so that the U phase is turned on for two waveforms (off for five waveforms) in the first switching cycle. At this time, the W-phase triac F2 has two waveforms +60.
Turn on for 5 minutes (5 waveforms-turn off for 60 degrees).

In the next switching cycle, the speed feedback is used to generate a slightly stronger torque.
The phase is turned on for three waveforms. At this time, the W phase has three waveforms +60
Turn on for ° min.

Further, in the next switching cycle, since the previous torque was too strong, the U-phase is turned on by two waveforms to generate a slightly weaker torque by the action of speed feedback. At this time, the W phase is turned on for two waveforms + 60 °. While repeating such ON and OFF states,
Control is performed to maintain the speed of the three-phase induction motor 18 at a constant low speed.

Next, the case of high speed in FIG. 4B will be described. At high speed, the ON period becomes longer to increase the output. First, in the first switching cycle, the triac F1 is fired so that the U phase turns on five of the seven waveforms. When the triac F2 is fired in the same state, the W phase is turned on by 5 waveforms + 60 °.

In the next switching cycle, the U-phase is turned on by six waveforms to generate a slightly stronger torque by the action of speed feedback. At this time, the W phase has 6 waveforms +
Turn on 60 °.

Further, in the next switching cycle, since the previous torque was too strong, the U-phase is turned on by three waveforms to generate a slightly weaker torque by the action of speed feedback. At this time, the W phase is turned on for three waveforms + 60 °. In order to keep the speed of the three-phase motor at a constant high speed while repeating such ON and OFF states,
Control is performed.

With the above operation, even if the command speed is constant, the ON / OFF period ratio of the cycle control always changes slightly (that is, a random output). With such random control, even if there is a resonance frequency unique to the machine main body, a state in which the resonance point is kept at the resonance point does not hold, so that the occurrence of resonance can be prevented.

Further, according to such an operation, a slight speed pulsation occurs due to the configuration of the minor loop by the speed feedback, but a constant speed as a whole (that is, an average) is obtained. Control is performed to keep.

Here, the duty ratio variable circuit 4 shown in FIG.
FIG. 5 shows a specific example of No. 6. Duty ratio variable circuit 46
(Switching pulse generation circuit) is an operational amplifier IC1
And a square wave oscillation circuit using the same. The output of the operational amplifier IC1 is integrated by the resistor VR1 + the resistor R5 and the capacitor C1 and input to the inverting input terminal of the operational amplifier IC1. A voltage obtained by dividing the output voltage by the resistors R3 and R2 is input to the non-inverting terminal of the operational amplifier IC1. The voltage is inverted each time the voltage and the integrated value cross each other, and a square wave signal having a constant period is output from the operational amplifier IC1. Is output. The duty ratio of the output square wave is variably controlled by changing the voltage level input to the non-inverting input terminal of the operational amplifier IC1 by the speed control signal IN1 input from the input terminal IN1 via the resistor R1. .

The cycle is set by the volume VR1. R4 is an output resistance. R6 is a pull-up resistor for stabilizing the output voltage. R1 is an input protection resistor. R7 is a pull-up resistor for suppressing input noise of the operational amplifier IC1. Z
D1 is the operational amplifier IC1 even if the input voltage is lower than the power supply voltage.
Is a Zener diode for lowering the power supply voltage of the IC 1 of the operational amplifier by about 1 to 3 V from a specified value so that an output with a duty ratio of 100% can be output.

FIG. 6 shows the operation of the speed control device of FIG. 1 when the duty ratio variable circuit 46 of FIG. 5 is used. In FIG. 6, (a) shows a low speed state, and (b) shows a high speed state. According to this, turning on the U-phase and the W-phase at the same timing causes an imbalance in the inrush current and the conduction time, and this imbalance causes a random operation of not only the duty ratio but also the cycle width and the ignition start timing. ing. This random operation acts so as not to cause resonance inherent to the machine. However, the commanded constant speed can be maintained on average by the speed feedback.

In the above embodiment, the thyristors are provided in two of the three phases, but they may be provided in all three phases.

[0038]

As described above, according to the present invention, the thyristor is driven by switching control (cycle control) to change the period ratio between ON (energizing cycle) and OFF (stop cycle). Speed control can be performed by changing the average level of the applied voltage. According to such control, since phase control is unnecessary, a complicated speed control device is unnecessary, and a small-sized and inexpensive configuration can be achieved.
Further, since two phases whose phases are shifted from each other by 120 ° or 240 ° are simultaneously turned on, an imbalance occurs in the rush current and the energizing time between the two phases, and the cycle control is turned on / off even when the command speed is constant. The period ratio always changes delicately, and by such random control, even if there is a resonance frequency unique to the machine main body, a state in which the resonance point remains in agreement does not hold, so that occurrence of resonance can be prevented. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a speed command value and a detected speed value in each driving situation.

FIG. 3 is a diagram showing a driving direction of an induction motor in each of the driving situations shown in FIG. 2;

FIG. 4 is a waveform chart showing the operation of the device of FIG.

FIG. 5 is a circuit diagram showing a specific example of a duty ratio variable circuit in FIG. 1;

6 is a waveform chart showing the operation of the device of FIG. 1 when the duty ratio variable circuit of FIG. 5 is used.

[Explanation of symbols]

Reference Signs List 10 three-phase AC power supply 18 three-phase induction motor 28 pulse generator (speed detection means) 36 controller (speed command means) 44 addition point (deviation detection means) 46, 48 variable duty ratio circuit, ignition circuit (switching control means) F1 , F2, R1, R2 Triac (thyristor) S. T Each phase power supply path

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 5/28-5/44 H02P 7/36-7/66 B66C 13/22

Claims (1)

(57) [Claims] 1. A thyristor inserted in at least two phases of a power supply line of a three-phase induction motor so as to be able to conduct in both forward and reverse directions, speed command means for commanding the speed of the three-phase induction motor, Speed detection means for detecting the speed of the phase induction motor; deviation detection means for obtaining a deviation between the command speed by the speed command means and the detection speed by the speed detection means; reducing the speed deviation obtained by the deviation detection means Switching control means for changing the ratio of the on-period and the off-period in each of the thyristors in a cycle longer than the cycle of the driving three-phase AC power supply, and simultaneously turning on and off the two phases at the same timing; A speed control device for a three-phase induction motor, comprising: