JPS5842714B2 - Induction motor braking circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a braking circuit for an induction motor.

If a rotating induction motor is disconnected from the AC circuit and a DC voltage is applied to it, a DC current will flow, producing a fixed magnetic field in the stator, but since the rotor is rotating, At the same time that electric power is generated, the resulting current flows, and braking torque is applied to cause braking.

This principle is generally well known.

Furthermore, there are various conventional methods for applying a DC voltage.

One method is to apply a single-phase half-wave control voltage.

Even if a three-phase induction motor that is rotating at high speed is disconnected from the AC power source, the inertia of the motor itself and the load will cause
It takes a long time to completely stop.

Therefore, if a DC voltage is applied based on the above-mentioned principle, the motor will stop quickly, but depending on the load, instantaneous stopping may be required.

However, if the vehicle stops rapidly, the deceleration rate will be too high, and this can be a problem for some loads.

For example, if an electric motor that drives a conveyor has bottles on it, the bottle will fall over and break if it suddenly stops.

To avoid adding a negative acceleration rate when decelerating,
It is necessary to stop slowly.

However, the stopping time is required to be faster than when stopping the AC power by simply turning off the AC power source.

When the applied DC voltage is large, that is, the resulting DC current is large, the braking torque is large and the time required to stop is short.

Conversely, if the DC voltage is small, the braking torque will be small and it will take a long time to stop.

Considering that there are various loads on electric motors, it is desirable that the device be able to freely change the DC voltage and freely set the control torque.

Furthermore, let's consider what happens after the electric motor stops.

The DC voltage remains applied as before, and a large DC current is flowing through the stator windings of the motor, causing the windings to heat up.

Therefore, after the motor has stopped, it is necessary to remove the applied DC voltage as soon as possible.

It is desirable that the removal time can be set arbitrarily.

Even if it is removed, it is desirable to do it without an arc.

To summarize these points, the control device is required to be able to freely change the applied DC voltage so that the braking torque can be changed freely, and to be able to arbitrarily select the application time.

The present invention provides a braking circuit for an induction motor that can meet such requirements.

Hereinafter, the present invention will be described in detail with reference to the drawings.

In FIG. 1, three-phase AC voltage is applied to terminals R, S, and T.

M is a three-phase induction motor. 5 and 6 are electromagnetic contactors, and when the electromagnetic contactor 5 is turned on, the electric motor M rotates.

When the electromagnetic contactor 5 is disconnected and the electromagnetic contactor 6 is turned on, the electric motor M stops.

Reference numeral 7 designates a brake control circuit, which has a terminal 1°2.3, a thyristor 8, and a flywheel diode 9, the detailed configuration of which is shown in FIG.

5X is the excitation coil of the electromagnetic contactor 5, and 6X is the excitation coil of the electromagnetic contactor 6.

10 is a push button switch for stopping, 11 is a push button switch for running, 5a is an auxiliary contact of the electromagnetic contactor 5, which is a normally open contact, and 5b is a normally closed contact.

6b is an auxiliary contact of the electromagnetic contactor 6, which is a normally closed contact;
6a is its normally open contact.

15b is a normally closed contact of the electromagnetic relay 15 shown in FIG.

The operation will be explained with reference to the operation explanatory diagram in FIG.

Now, as shown in FIG. 2a, at time t.

When the push button switch 11 is pressed, voltage is applied to the excitation coil 5X, the electromagnetic contactor 5 operates, and at the same time the auxiliary contact 5a
is turned on, and the exciting coil 5X continues to be excited as shown in FIG.

As the electromagnetic contactor 5 operates, a three-phase alternating current voltage between terminals R, S, and T is applied to the motor M, which rotates as shown in FIG. 2g.

Next, as shown in FIG. 2C, when the stop pushbutton switch 10 is pressed at time t1, the circuit of the excitation coil 5X is cut off, and at the same time, voltage is applied to the excitation coil 6X, as shown in FIG. 2D. It is held by the contact 6a as shown in FIG.

Therefore, the contactor 5 is turned off and the electromagnetic contactor 6 is turned on.

Since the electromagnetic contactor 6 operates, the power terminal R2 connection point 54
from terminal 1, then thyristor 8, terminal 2, contactor 6,
Connection point 51° A closed circuit is formed from motor terminal U to w1, further to connection point 52, contactor 6, connection point 53, and power supply terminal T.

A voltage is applied to the thyristor 8, the ignition circuit of the circuit operates, and the thyristor 8 is ignited.

Then, a single-phase half-wave current begins to flow in this closed circuit, as shown in FIG. 2e.

When the firing phase of the thyristor 8 changes, the flowing current changes, and the braking torque of the electric motor M changes.

In addition to this closed circuit, from the connection point 51, the contactor 6, the terminal 2
, diode 9, terminal 3, contactor 6, connection point 52, a closed circuit is formed from motor terminal W to U, and by short-circuiting terminal ulW by diode 9, the motor M is disconnected as shown in Fig. 2f. Foil current flows.

Therefore, a direct current controlled by the thyristor 8 and the diode 9 flows through the electric motor M, and smooth braking is performed.

The electric motor M stops at time t3 as shown in FIG. 2g, and DC current continues to flow through the thyristor 8 and the electric motor M thereafter, but the current flowing through the thyristor 8 is cut off at time t4.

Thereafter, a flywheel current flows through the flywheel diode 9 and the motor M until time t.

At the set time t6, the electromagnetic relay 15 in the brake control circuit 7 is activated, the contact 15b is activated, and the exciting coil 6 is activated.
X is opened and the contactor 6 is in an open state.

As a result, the electric motor M is completely disconnected from the power source.
It is now ready for the next startup operation.

The above is a series of operations from startup to shutdown.

The brake control circuit 7, which is a feature of the present invention, will be explained in detail with reference to FIG.

In FIG. 3, 8 is a main thyristor, 9 is a flywheel diode, 12 is an amplifying rectifier circuit consisting of an auxiliary thyristor 19 and a diode 16°17 connected to the center tap, and 13 is a potentiometer that determines the braking torque. It is a control circuit, and includes a resistor 35, a variable resistor 32. Kociantha 28.
It consists of a unidirectional switching element 20.

21 and 22 are diodes, 23 is a Zener diode, and 34 is a resistor.

14 is a timer circuit, which includes an electromagnetic relay 15, diodes 18, 24, transistors 25, 26, Zener diode 27, capacitors 29, 30, 31, variable resistor 3
3 and resistors 36, 37, and 38.

In such a configuration, when the contactor 6 is turned on, a voltage is applied between the terminals 1 and 2;
If we consider a case where a voltage is applied in a positive direction to the terminal 2, a current flows from the terminal 2 to the resistor 35, the diode 21, the Zener diode 23, the diode 17, the resistor 34, and the terminal 1.

A voltage obtained by adding the voltage of the Zener diode 23 and the forward voltage of the diode 21 is applied to the series circuit of the variable resistor 32 and the capacitor 28.

This voltage charges the capacitor 28.

The speed of charging is changed by a variable resistor 32.

The charging voltage of the capacitor 28 is the same as that of the unidirectional switching element 2.
When a switching voltage of 0 is reached, it switches and
A current is passed from the gate of the auxiliary thyristor 19 to the cathode to ignite it.

When the auxiliary thyristor 19 fires, a current flows from the terminal 2 to the auxiliary thyristor 19, the diode 17, and the resistor 34, but the current is large and the voltage drop across the resistor 34 is large.

This voltage causes a current to flow to the gate of the thyristor 8, causing the thyristor 8 to fire.

That is, the thyristor 19 is an auxiliary thyristor for firing the thyristor 8.

When the thyristor 8 is ignited, a voltage is applied to the motor M, and the voltage between the terminals 2 and 1 becomes almost Ov.

Therefore, the operations of the amplifying rectifier circuit 12 and the phase control circuit 13 are stopped after the thyristor 8 is fired.

In the next cycle, when a positive voltage is applied to terminal 2 relative to terminal 1 again, the same operation is repeated.

The current flowing through the thyristor 8 is changed by a variable resistor 32.

The braking torque can be changed, and the time until stopping (time t2 to t3 in FIG. 2) can be freely selected.

The circuit described above is driven by the voltage applied to the thyristor 8, and therefore works normally no matter which of the three phases it is inserted into.

In other words, a major feature is that there is no need to consider phase relationships.

When the thyristor 8 is fired and direct current flows through the motor M, the motor M stops after a certain period of time.

Since voltage continues to be applied to thyristor 8 after that,
Amplifying rectifier circuit 12 and phase control circuit 13 operate, and current continues to flow through them.

If this state is left unattended, an excessive current will flow through the motor M and the windings will burn out.

Therefore, it is necessary to stop firing the thyristor 8 as soon as possible after the electric motor M stops.

Therefore, the circuit is a timer circuit 14. This circuit 14
is also driven by the voltage across the thyristor 8.

This timer circuit 14 is not influenced in any way by the operations of the amplifying rectifier circuit 12 and the phase control circuit 13, and is designed to operate at an accurate time.

While the amplifying rectifier circuit 12 and the phase control circuit 13 operate in a region where terminal 2 is positive with respect to terminal 1, the timer circuit 14 has a circuit configuration so that it operates with the opposite voltage. being done.

When the voltage of terminal 2 is negative with respect to terminal 1, a closed circuit of terminal 2 is established from terminal 1 through resistor 34, diode 18, resistor 36, diode 22, Zener diode 23, through connection point 55, and then through diode 16. A current flows through.

Therefore, the capacitor 29 is charged through the diode 24 by the voltage appearing on the diode 22 and the Zener diode 23.

This charging voltage becomes the DC power supply voltage of the timer circuit 14.

It is added to a series circuit of variable resistor 33 and capacitor 30, and capacitor 30 is charged according to its time constant.

When the charging voltage reaches the Zener voltage of Zener diode 27, current flows through resistor 38 to the base of transistor 25.

Transistor 25 is turned on and short-circuits capacitor 28.

Capacitor 28 is no longer charged and therefore thyristors 19 and 8 are no longer fired.

At the same time, current also flows through the resistor 37 to the base of the transistor 26, so it becomes conductive and the capacitor 31
is charged.

When this charging voltage reaches the operating voltage of the electromagnetic relay 15,
It operates and thus contacts 15b shown in FIG. 1 open.

Then, the excitation coil 6X is opened, and the contactor 6 is placed in an open state.

The current flowing through the thyristor 8 is cut off by the transistor 25 at time t4 in FIG. 2, and at time t5.
At this point, the current flowing through the flywheel diode 9 also attenuates to zero, and thereafter, at time t6, the electromagnetic relay 15 operates and the contactor 6 becomes open.

The time t2 to t4 can be changed freely by the variable resistor 33.

Knowing the time t3 at which the electric motor M stops, an appropriate time t4 is set using the variable resistor 33.

As described above, this timer circuit 14 is configured to operate using the reverse voltage of the thyristor 8 as a power source.

This allows such complex operations to be performed with a small number of parts.

Furthermore, since the timer circuit 14 is designed to operate with the reverse voltage of the thyristor 8, its operation will not be affected even if it is inserted into any of the three phases.

As explained above, this invention is based on Cyrisk's multi-phase half-wave current energization method that smoothly stops the motor.
The ignition circuit that controls the current and the timer circuit that cuts off the current at a predetermined time are driven by the voltage between the anode and power sword of the thyristor.

Note that although the embodiments have been described with respect to a three-phase induction motor, it goes without saying that the present invention can also be applied to a single-phase induction motor.

[Brief explanation of drawings]

Figure 1 is a main circuit configuration diagram showing one embodiment of the present invention.
The figure is an explanatory diagram of its operation, and FIG. 3 is a detailed circuit diagram showing an example of a brake control circuit that is a feature of the present invention. In the figure, 5 and 6 are electromagnetic contactors, 8 is a cyrisk, 9 is a flywheel diode, 10 is a stop push button switch, 11 is an operation push button switch, 12 is an amplified rectifier circuit, 13 is a phase control circuit, and 14 is a A timer circuit, 19 is an auxiliary sirisk, and M is an induction motor. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first switching means connected in series to each line connecting the AC power supply and the induction motor, and a second switching means connected to the first switching means of the first line of the respective lines. A main thyristor connected in parallel, a diode center tap rectifier circuit connected between one main electrode and gate of this main thyristor, an auxiliary thyristor connected in parallel to one diode of this diode center tap rectifier circuit, and one end. is connected to the second switching means, and the other end is connected between the first switching means of the second line of the respective lines and the induction motor via the third switching means. a foil diode, a means for connecting both ends of the first switching means of the second line via a fourth switching means; and an operation switch for driving the fourth switching means to open, a stop switch for driving the first switching means to open and driving the second, third and fourth switching means to close, and a stop switch for driving the second, third and fourth switching means to close. a phase control circuit capable of igniting the auxiliary thyristor and controlling its firing phase when the means is turned on; and a phase control circuit that is driven using the reverse voltage of the main thyristor as a power source and for a predetermined period of time after the second switching means is turned on. A braking circuit for an induction motor, comprising a timer circuit that stops the operation of the phase control circuit and opens the second, third, and fourth switching means when the time elapses.