SU1735992A1 - Ac drive - Google Patents

Abstract

Usage: in electric drives of machine tools, automatic lines and other production mechanisms. The essence of the invention is to conduct four power thyristors in the AC drive circuit, which makes it possible to switch the stator windings of a three-phase asynchronous electric motor, which, when fed with a single-phase motor, is obtained from an ordinary single-speed electric motor; tripling the number of pairs of poles of the machine and thus it was possible to put it into regenerative braking mode with subsequent switching to dynamic braking, which ensures high braking efficiency of the electric drive. 2 Il. (L

Description

The invention relates to electrical drives with three-phase asynchronous motors, and can be used, for example, in machine tools, automatic lines and other production mechanisms.

An alternating current drive with a three-phase asynchronous electric motor is known in which the braking circuit is implemented using a contactor, three power diodes and an adjustable resistor. In this circuit, the stator windings and two power diodes form short-circuited circuits; from the network half of the period of the supply voltage through the third power diode and a resistor in one phase | the stator is half-wave

the current, and in the rest of the period when the third diode is locked, the currents of the same direction go through all three phase stator windings, thereby ensuring dynamic braking of the electric motor.

However, in this electric drive, the switching of the power circuits of the electric motor is carried out with the help of contact equipment and does not provide high braking efficiency.

The closest in technical essence to the present invention is an AC motor with contactless control, containing a three-phase asynchronous electric motor, the stator winding of which is connected according to the star circuit, three pairs

sj

oe cn co soe

opposite thyristors connected in parallel, some of the terminals of which are provided with clamps for connection to the phases of the power source, other terminals are connected to the corresponding phase terminals of the stator winding, as well as two shunt thyristors, the anodes of which are connected respectively to the two phase terminals of the stator winding and the cathodes to the third stator winding output

However, in the known electric drive, in the zone of high rotational frequencies, where the main absorption of the kinetic energy of the rotating masses of the electric drive occurs, the braking torque is low, so the braking efficiency is low. This disadvantage is especially noticeable for high-performance machine equipment with a short operating cycle, the reduction of which by reducing the auxiliary non-process-related operations gives a significant economic effect.

The purpose of the invention is to increase the braking efficiency of the drive.

This goal is achieved by the fact that in an electric drive with dynamic braking of an induction motor containing three pairs of parallel-connected thyristors, one of the terminals of which are provided with terminals for connecting to the phases of the power source, the other terminals are connected to the corresponding phase terminals of the stator winding, two shunt thyristors, whose anodes respectively connected to the two phase terminals of the stator winding, and the cathodes to the third phase terminal of the stator winding, as well as an adjustable resistor, are introduced the third and fourth shunt thyristors and the fourth pair of anti-parallel-connected thyristors, one pin of which is connected to zero star of the stator winding, and the other to one pin of adjustable resistor, the other pin of which is equipped with a clip for connecting to zero power source the third and fourth shunt thyristors are turned on opposite the first and second shunt thyrs, respectively.

Figure 1 presents the scheme of the electric drive AC; figure 2 - three-phase stator winding

,

7359924

for obvious proof as in the proposed electric drive for the implementation of regenerative braking. the arrangement of the number of pairs of poles of the machine occurs.

The stator winding 1 three-phase asynchronous electric motor connect15

20

thirty

Nena star pattern. Conclusions of each

The 10 phases of this winding are connected to the corresponding phase of the network through the power thyristors 2 and 3, and 5, 6 and 7, each pair of which is switched on in a counter-parallel circuit. In addition, the first and second phase windings of the stator are shunted by parallel-connected power thyristors 8 and 9, and the second and third phase windings of the stator are shunted by similarly turned on power thyristors 10 and 11. Between the zero point of the stator stars and the zero of the power source, two anti-parallel are connected power thyristor 12 and 13 and

25 in series with them adjustable resistor 1.

The AC drive works as follows.

When starting the motor on | The operation mode of the power thyristors 2-7 performs the role of a contactless starter. When the braking command is issued, the thyristors 2,3,6 and 7 are switched off and the thyristors 8-13 are turned on, and the thyristors 8,9,10 and 11 connect the phases

35 stator windings in parallel, and with the help of thyristors and 5) 12 and 13, these windings are connected to a single-phase network voltage. The number of poles in the machine triples, it goes over to the generator mode, having carried out intensive regenerative braking.

The tripling of the number of poles of a machine in this case is convincingly illustrated by the example of a three-phase single-layer winding (FIG. 2) with parameters: z 24,, q. 2,. On fig.2a, a bmmot is shown when it is switched on in a three-phase network, on fig.26 it is shown with symmetric connection to a single-phase network. From Fig.26 it is seen that the number of poles at single-phase current will be. In both cases, the number of slots per pole and phase remains the same, namely

55 for three phase current

24

 - ABOUT

2p-t 4-3

for single phase current

2, T.e.

2p

z

q, m single phase

then when eating

by current

2P-IL. Consequently, the symmetrical connection of a three-phase winding into a single-phase network makes it possible to obtain a 3-fold lower frequency of rotation of the field of the statoi 1 pa across n0.

In series with the stator windings it is necessary to include an additional resistance 14 to limit the current and the magnitude of the magnetic flux. This is due to the fact that although the number of grooves per pole and phase q remains in single-phase mode the same as in the three-phase, but the winding coefficient K. in single phase mode for

Ogl

electric motors of average power range is 0.5-0.57, and in three-phase - typically Kosw 0.96. It means at the same phase voltage- (and 4.44 fW К „.„)

in ofr ll

This would lead to a sharp increase in magnetic flux.

After completion of regenerative braking, i.e., after, the rotational speed decreases to approximately

1 -s- noi, when the main stock of kinetic energy of the rotating masses is already extinguished, a command is given to turn on the dynamic braking. The control can be carried out as a function of the rotational speed (for example, using an induction relay for controlling the speed of the RKS type mounted on the motor shaft) or as a function of time.

When applying the command for dynamic braking, thyristors 5, 9, 11 and 13 are disconnected, thyristors 4, 8, 10 and 12 remain switched on. Half of the period of a single-phase voltage supply, the current flows from the network through the thyristor b, one phase stator winding, thyristor 12 and resistor

 1. The second half of the period when the thyristors and 12 are locked for all

15 electric motor that when powered by a single-phase current from a conventional single-speed electric motor, the number of pole pairs of the machine was tripled and thus it was possible to put it into regenerative braking mode, with subsequent switching to dynamic braking, thereby ensuring high braking efficiency water.

Claims (1)

Invention Formula An alternating current drive 30 containing a three-phase asynchronous electric motor, the stator winding of which is connected according to a star circuit, three pairs of anti-parallel connected thyristors, one terminals of which are provided with clips for connecting to the phases of the power source, other terminals are connected to the corresponding phase terminals of the stator winding, two shunt thyristor, the anodes of which are connected respectively to the two phase pins of the stator winding, and the cathodes - to the third phase output of the stator winding, adjustable re a resistor, characterized in that, in order to increase the braking efficiency, the third and fourth shunt thyristors and the fourth pair are inserted into the anti-parallel connected thyristors, one output of which is connected 40 45  The star of the stator winding is zero to zero, and the other is to one output of an adjustable resistor, the other output of which is equipped with a clamp to connect to a zero power source, the third phase stator windings of grades 55 and the fourth shunt thyristor shunt thyristors 8 and 10 are ry included opposite to the first TOKVI of the same direction, caused by the second and shunting thyristor, not only by the inductance of the stat, respectively. 735992 torus, but also by the electromotive force induced by the rotor magnetic field, thus providing a sufficiently large dynamic braking torque in the low frequency range of rotation. Monitoring the duration of dynamic braking is usually performed as a function of time. 10 Thus, the introduction of four power thyristors into the AC drive circuit allows us to switch the three-phase asynchronous three-phase asynchronous stator windings. 15 electric motor, that when fed with a single-phase current from a conventional single-speed electric motor, the number of pole pairs of the machine tripled and thus it was possible to transfer it to the regenerative braking mode with subsequent switching to dynamic braking. thus ensuring high braking performance of the electric drive. Invention Formula An alternating current drive 30 containing a three-phase asynchronous electric motor, the stator winding of which is connected according to a star circuit, three pairs of anti-parallel connected thyristors, one terminals of which are provided with clips for connecting to the phases of the power source, other terminals are connected to the corresponding phase terminals of the stator winding, two shunt thyristor, the anodes of which are connected respectively to the two phase pins of the stator winding, and the cathodes - to the third phase output of the stator winding, adjustable re a resistor, characterized in that, in order to increase the braking efficiency, the third and fourth shunt thyristors and the fourth pair are inserted into the anti-parallel connected thyristors, one output of which is connected 40 45  To zero the star of the stator winding, and the other to one output of an adjustable resistor, the other output of which is equipped with a clamp to connect to zero the power source, three J c en u t- Nv. rs SZHZ v - | Ј1ШШ1Ј ШШШШ | ЈЛ / 11 "Me and s Yo r : dr r / one f 78 } S n. 1} and #i ± r - 3 AT -% (pv Ј | ЈЛ / 11 "Me and s l : dr r / 7Ш 14 ft #y; 2ff F uP VL -four-