SU68207A1 - Device for regulating the speed of an asynchronous motor - Google Patents

Description

Devices are known for controlling the speed of an asynchronous motor using a cascade connection of the latter with a single root converter. The present invention relates to such a device and consists in its specific implementation. The dryness of the invention is reduced to the use of a converter, the magnetic system of which, in order to provide a wide voltage regulation on the collector, is made with split poles. In order to increase the stability of the operation, the specified converter, in addition to the windings of independent excitation, is provided with windings of series excitation.

FIG. 1 shows a single line connection diagram of the device; in fig. 2 - diagram of the converter with split poles; in fig. 3 - distribution of magnetic induction in the air gap of the converter; in fig. 4 shows a current distribution pattern in the rotor of the main engine for one of its particular instances.

Converter K {, powered by a three-phase slip current / 2 from the slip rings of the main motor rotor (induction motor) AM feeds the converter / (2. The latter operates as a generator and supplies power to the network PZ,

proportional to the gliding AM motor.

The coil of the K.S series excitation is designed to increase the stability of the converter / C 1 operation when the load jolts the AM main motor shaft.

The series excitation winding F contributes to reducing the oscillation of current i with changes in engine load AM.

Due to the fact that a conventional converter does not allow wide adjustment of the voltage on the collector, in the proposed device, as already indicated above, a split-pole converter is used. FIG. 2, where the diagram of this converter is shown, the following notation is taken: a b - brushes on the core collector; N and 5 | - poles that create a magnetic flux Фь NZ and S2 - poles that create a magnetic flux P - the winding of the independent excitation of the poles NI and 5g, FZ - the winding of the independent excitation of the poles N and Sa; FZ - winding of the main current of the poles NI vi F - winding of the main current of the poles and Sz ,. F1 is the magnetic flux created by the poles and 5i; F2 - magnetic flux, generated by the poles L / 2 and S.

FIG. Figure 3 shows the magnetic induction distribution diagrams of c.

151

an air gap of a converter with split poles at different excitation currents in the windings of the machine.

Changing the direction of the current in the windings 2, and, consequently, the direction of the flow Φ, you can change the voltage at the collector between the brushes a and b. When the oppositely directed flows and 2 will be equal to each other, as shown in the lower diagram of FIG. 3, the voltage between the brushes a b of the machine will become zero. With a further decrease in the flux Φ, and an increase in the flux, as shown by the dotted line in the lower diagram of FIG. 3, the voltage between brushes a and b will change its direction to the opposite.

Under these conditions, the direction of the current i in FIG. 1 will be reversed (see dotted arrow), after which the / Ci converter will begin to rotate in the opposite direction; in this case, the phase alternation of the current / 2 in the rotor of the main engine is reversed and its rotor will begin to rotate at a speed higher than the synchronous one.

Before switching to the super-synchronous mode, the AM engine must go through a synchronous speed. At synchronous motor speed AM, the converter K rotor will be stationary. The pattern of current distribution in the rotor of the main engine AM for a random position of the stationary (fixed) converter / Cb when the positive brush touches the collector plate and the core section connected to one of the slip rings is shown in FIG. 4. The constant current i through a brush with a plus sign and a slip ring / flows into the right phase of the rotor and then, branching into two equal parts% r + H, is summed up in the brush with a minus sign and returns to the circuit.

The speed of the main motor AM can be adjusted by varying the magnitude of the DC excitation current flowing in the windings of the converter fi and 2. 152

Pa figs. 3, the upper diagram corresponds to the maximum voltage at the collector between brushes a and 6 and, therefore, the minimum speed of the main engine AM.

The bottom diagram of FIG. 3 (solid lines) gives a picture of the flow distribution at which the voltage on the collector between brushes a and 6 is equal to zero; in this case, the main engine AM rotates at a speed close to synchronous.

If we increase the flux Fg even more (see the dotted line in the lower diagram of Fig. 3) and, accordingly, decrease the flux Φ ,, the voltage between brushes a and b of the converter changes sign, and the current t also changes its direction. In this case, the direction of rotation of the converter is also reversed, and the main AM motor will rotate at a speed higher than the synchronous one.

The change in the fluxes Fx and F2 of the converter must be made in such a way that the sum of F1 and F is constant; in this case, the power factor of the converter Kz at different voltages between the brushes a and 6 will remain virtually unchanged.

Subject invention

1. A device for controlling the speed of an asynchronous motor to both sides of the synchronous speed using a single core converter supplied from the AC side of the secondary asynchronous motor and supplying, in turn, a DC-to-AC frequency converter, characterized in that As the specified DC / AC converter, a single core converter is used, the magnetic system of which, in order to provide a wide voltage regulation on the collector , made with split poles.

2. The form of the device independent excitation, with

pop 1, with the exception of the fact that the purpose of increasing the stability of the RADI converter is equipped with windings with successive poles, in addition to the thermal excitation.

FIG. one

plp | -