SU1753575A1 - Ac electric motor drive - Google Patents

Abstract

Usage: in various industrial units. Essence: the device contains an asynchronous short-circuited electric motor 1, two transformers 4 and 8, two batteries of capacitors 5 and 9, connected in triangles, a three-phase switch 7 and a direct frequency converter 10. Speed control is possible from zero to the nominal value in three subranges, on each of which the algorithm of operation of the circuit elements is changed. 1 il.

Description

The invention relates to electrical engineering and may find application in various industrial units.

The aim of the invention is to improve the energy performance while expanding the range of speed control.

The electric drive circuit is shown in the drawing.

The drive contains a three-phase asynchronous, short-circuited motor 1. The stator windings 2 of which are connected to the star are connected to the first terminals of the primary windings 3 of the three-phase transformer 4, three capacitors 5 connected in a triangle, and the tops of which are connected to the second conclusions of the primary windings 3. The secondary windings 6 of the transformer 4, included in the star, are connected by leads to the inputs of a three-phase switch 7, the outputs of which are interconnected.

The drive also contains an additional three-phase transformer 8 and three capacitors 9, as well as a direct frequency converter 10 with natural commutation. Additional capacitors 9 are connected in a triangle pattern, with the tops of which are connected the leads of the secondary windings 11 of an additional transformer 8 connected in a star. The first terminals of the primary windings 12 of the transformer 8 are connected to the leads of the stator windings 2 of the electric motor 1, and the second terminals of the primary windings 12 are connected to the buses 13, 14 and 15 of the power supply through the direct frequency converter 10.

The device works as follows.

The entire range of smooth speed control conventionally consists of three

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subranges, on each of which the regulation is carried out due to different algorithms of operation of circuit elements.

In the lower sub-band, the regulation is performed by the frequency method, i.e. due to the operation of the keys of the converter 10 in the mode of the actual direct frequency converter. In this sub-band, the speed of the electric motor is regulated from zero to one third of the nominal value. In this case, the three-phase switch 7 is in a closed state, which causes the transformer 4 to be switched to short-circuit mode. In this subrange, due to the relatively low pg, the output voltage of converter 10, the presence of transformers and capacitors does not adversely affect the efficiency of the device. However, these same elements filter the higher harmonics of the output voltage of the converter 10, which improves the energy characteristics of the electric drive.

On the average subrange, the converter 10 operates in the thyristor voltage regulator mode supplied to the stationary windings 2 of the electric motor through the primary windings 12 of the transformer 8. In this case, the three-phase switch is in a closed state, which corresponds to the following:

shorted state of secondary windings b of transformer 4;

almost zero voltage drop in the primary windings 3 of the transformer 4, which is in short-circuit mode;

connecting capacitors 5 to the terminals of the stator windings of the electric motor and, as a consequence, maintaining the current continuity mode in them even at intervals of the simultaneous disconnected state of all the keys of the converter 10.

Finally, in the upper subrange, rate control by changing

the duty cycle of switching on the three-phase switch 7 when the primary windings 12 of the transformer 8 are constantly connected to the power supply buses,

Thus, in the device, the speed of the asynchronous motor is regulated from zero to the nominal value and the energy characteristics are improved, thus achieving the goal.

Claims (1)

AC drive motor comprising an asynchronous three-phase short-circuited electric motor, stator the windings of which are connected to the star are connected by terminals respectively to the first terminals of the primary windings of a three-phase transformer, three capacitors connected in a triangle circuit with the second capacitors connected to the vertices the terminals of the mentioned primary windings, and the secondary windings of a three-phase transformer connected in a star are connected to the inputs of a three-phase switch, the outputs of which are connected between characterized in that, in order to improve the energy performance when expanding the rotational frequency control range, an additional three-phase transformer and three capacitors are introduced into it, as well as a direct frequency converter with natural commutation, with additional capacitors connected according to a triangle, with the vertices The secondary windings of the auxiliary transformer connected in a star are connected, the first primary leads of the specified transformer are connected to the stator windings of the electric motor, and the second primary leads are connected to a direct frequency converter that has leads to connect to the power supply buses. / J #