SU59736A1 - Control method of asynchronous motors - Google Patents

Description

For pumping oil from h-wells, a motor-pump of translational action can be used, the moving part of which is a short-circuited rotor carried by a running magnetic field with a variable direction.

The power supply of such a motor from the mains with a constant frequency is associated with the rupture of large currents with frequent switching of phases, high starting currents and high losses in the motor windings. These drawbacks are largely eliminated when the alternating frequency is powered, which creates a traveling magnetic field with a constant amplitude of induction in the gap, uniformly accelerated (during acceleration) and uniformly slowed (when braking).

This principle of reversing accelerated magnetic field can also be effectively used in other areas, such as forging hammers, pile driving equipment, etc.

The main obstacle to the use of such drives and motors of the reciprocating

Action is the lack of simple, economically viable and reliable variable frequency generators.

According to the invention, a very simple way to control asynchronous motors is proposed, without these disadvantages.

Asynchronous motors according to this method are powered from an alternating current source of variable frequency, made in the form of an asynchronous machine. The latter is rotated by a special motor with a rotational speed twice as large as the synchronous rotational speed of the machine. Due to this, the motor can rotate the shaft of the asynchronous machine near the synchronous speed B side of rotation of the stator field.

The reversal of the controlled engine in this case provides for periodic fluctuations in speed from synchronous, which can be generated by periodically switching the drive engine from switching to the network on dynamic deceleration mode and vice versa.

A device that provides the implementation of the proposed method control, shown in the drawing.

The unit consists of two machines: an asynchronous machine 1 (with a corresponding transformation ratio with a stationary rotor), a drive motor 2 (an induction motor or a shunt direct current motor), which is approximately twice as high as the revolutions of the asynchronous machine 1.

In this example, for the sake of brevity, only one circuit with a direct current motor is considered.

On the rotor rings of the asynchronous machine 1 of the converter unit, the stator winding of the working short-circuited motor 3 is turned on.

The asynchronous machine 1 of the conversion unit is approximately equal in power to the working asynchronous motor 3. The drive (accelerating) motor core 2 is connected to the network via set resistance 5 or closes on set resistance 4. During unit operation, periodic switching on the core to the network and turning off simultaneously closing the core to the resistance 4 is produced by one double-sided contactor 7. Knife switches 8, 9 and 10 are used to connect an asynchronous machine and a drive motor.

The principle of operation of the converter unit is as follows.

The three-phase winding of the stator of the asynchronous machine 1 is turned on to a fixed frequency network, as a result of which a magnetic field is generated in the inter-iron space of the machine, which rotates at a constant speed.

Consider the dependence of the value of e. d. and its frequencies on the rings of an open rotor on the speed of rotation of the latter (the rotor is rotated by the auxiliary engine 2).

With a fixed rotor at its ends, we obtain the maximum value of e, d. S. E, determined by the voltage to which the stator winding is turned on, and the transformation ratio of the machine.

The frequency on the rings of the rotor of the machine 1 will be equal to the frequency of the network /.

At a certain speed of the rotor below the speed of the rotating field on its rings, we obtain the values of e. d. f and frequency / ,, proportional to the slip S.

E E-S with a rotor speed equal to the speed of a rotating floor:

, Oh and /, Oh,

at any rotor speed higher than the speed of the rotating field, the slip will be negative, but the ratios E E-S n remain valid, i.e. the ratio remains:

- / const,

J s

THAT provides a constant flow in the working engine.

Thus, if the stator winding of the working motor 3 is turned on the rings of the oscillating rotor of the asynchronous machine 1, then a reversing traveling field is formed in it, the speed of which will vary in the same way as the sliding 5 of the asynchronous machine 1.

The shaft of the asynchronous machine 1 is rigidly connected to the shaft of the accelerating motor 2. The direction of rotation of the accelerating motor, 2 hours, coincide with the direction of rotation of the field of the asynchronous machine 1.

When the stator of the asynchronous machine 1 (switch 8 is disconnected) is turned on, the asynchronous machine 1 is turned on the rotor rings of that machine 1-stator of the working engine 3 as an engine to a certain idle speed. The closure of the knife switch 8 in the core of the booster motor 2 does not cause a significant current jolt, since the measles unfolds in the same direction as the asynchronous machine 1 rotates.

The rotor of the asynchronous machine 1 with the help of the accelerating motor 2 quickly reaches a speed exceeding the speed of the rotating field. Asynchronous machine 1 will now operate in an asynchronous generator mode.