SU1443114A1 - Device for frequency control of induction motor - Google Patents

Description

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The current of the diode bridge 7, which is shunted by the choke 8 and the thyristor 9. The cathodes of thyristors 6.17 are connected to the vertices of triangles made up of condensates 1, 20, 21, the anodes of tyrstors 17.9 - to the tips of a triangle composed of capacitors 22, 23 24. One third of the top of the first triangle is connected to the cathode of the thyristor 9, and one third of the top of the second triangle with the anode of the thyristor 6. Consistently commute the thyristors 6, 17, 9, provide

The invention relates to electrical engineering, as well as to converter technology, and can be used in a controlled asynchronous electric drive of various branches of the national economy.

The purpose of the invention is expansion; up the frequency control range of the controlled asynchronous motor by increasing the relative voltage on the controlled motor.

FIG. 1 is a schematic diagram of a device for frequency control of an induction motor; Figures 2 to 4 are vector diagrams of the voltages at the individual phases of the load and the windings of the transformers of this device associated with it.

A device for frequency control of an induction motor contains a three-phase power transformer 1 (FIG. 1) with primary 2 and secondary 3 windings. The primary winding 2 is connected to the three-phase supply network by the first (start) terminals, and the second leads (ends) are connected to the AC terminals of the first diode bridge 4, shunted at the DC output by series-connected choke 5 and the thyristor 6. Secondary winding 3 of transformer 1 is connected into a star (with its ends (outputs) connected to the outputs of the alternating current of the second diode washing 7, shunted at the output of the direct current, in series, connect.

..

The various circuits for connecting the stator winding I3 of an induction motor with windings of the trassformators 1, 10, thereby reflecting the level of the voltage applied to it. The proposed device allows a threefold decrease in the magnitude of the steady-state voltage at the AC input of each of the diode bridges 4, 15, 7, provides the same voltage waveform on the stator winding 13 and the continuity of the current in it. 2 Il.

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inductor 8 and thyristor 9. The device also contains a second one. a three-phase transformer IO with primary 1.1 and secondary 12 windings, the first terminals (beginnings) of the primary winding of this transformer are connected to the alternating current leads of the first di-i of one bridge 4, and its second outputs (ends) are connected to the first leads (beginnings) the stator winding 13 of an asynchronous motor with a squirrel-cage rotor 14. The secondary winding 12 of the transformer 10 is connected to a star (Ends), and its outputs (beginnings) are connected to the alternating-current terminals of the second diode bridge 7,

The AC terminals of the third diode bridge 15 are connected to the second outputs (ends) of the stator winding 13 of the induction motor. The DC outputs of the specified bridge are shunded by series-connected choke 16 and thyristor 17. Power transformer 1 is provided with an additional 4 primary winding 18 with second terminals (ends) for connection to the mains, and the first viewpoints (beginnings) of this The windings are connected to the AC terminals. the third diode bridge 15. The cathodes, thyristors 6 and 17 are connected to the corresponding vertices of the triangle of capacitors 19-21 of the first group, and the anodes of these thyristors - with the corresponding vertices of the triangle of capacitors 22-24 of the second group. Third the top of the triangle capacitors

19-21 connected to the cathode of the thyristor 9, and a third of the top of the triangle of capacitors 22-24 - with the anode of the thyristor 6.g

The device works as follows.

The initial state of the device corresponds to the simultaneously locked state of all the punching thyristors 10 6, 9 and 17. In this case, the phase and serially connected windings 18 and 2 of transformer 1, windings II of transformer 10 and stator winding 13 form a common connection with a triangle, vertices which is connected to the mains tires. The phases of these windings form a closed conducting circuit at any time interval. Therefore, the voltage at each phase of the stator winding 13 is determined by the summation of the voltages at the corresponding phase of the series-connected windings of the device transformers. 25

The position of the voltage vector at any phase of the stator winding 13 depends on which of the diode bridges is shorted open by the thyristor-ZOr open at this time interval.

The shorted state of one or another diode bridge corresponds to the common point of those clamps of the corresponding winding of transformers 1 or 10 that are connected to the AC input of this bridge. Therefore, a transition, for example, from a shorted state of bridge 15 to a shorted state of bridge 4 corresponds to the transition from the connection of the winding 18 of the transformer 1 to the connection to the network by the star of the same transformer 2. In this case, if in the first case 45 are combined to the zero point of the beginning of the winding 18, then in the second case the ends of the winding 2. This causes a change in the initial voltage phase 180 on the transformer 1 windings, which should be done by constructing the vector diagrams of these voltages ( 2-4).

For different time intervals, each of which corresponds to the open state of the thyristor at the output of one of the three-phase diode bridges, vector voltage diagrams are drawn for those phases of the windings of the transformers 1 and 10, which are included in

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or another closed loop with its stator phase winding. Vector diagrams correspond to the shortening of bridges 4, 7 and 15 (figure 1).

Further, the operation of the device is described on the basis of these vector diagrams. The open state of the thyristor 17 at the output of the diode bridge 15 leads to the shorting of this bridge; connection to a common zero point marked with asterisks clips of individual phases of the winding 3 of the power transformer 1; connecting to the common zero point of the second terminals of the individual phases of the stator winding 13 of the controlled asynchronous motor; the star connection of the primary winding 18 of the transformer 1, the phases of which are directly connected to the mains as the rays of this star; the star connection is phase-wisely connected windings 2, II and 13, each of the beams of which is formed by the series connection of the individual phases of these windings. In this case, those phases of windings 2 and 18, which are located on the same transformer rod, are connected to different linear wires of the power supply network and therefore enter different rays of the corresponding connections by the stars of the windings mentioned earlier. Direct connection of the phases of the primary winding 18 of the transformer 1 to the power supply network leads to the induction of the same EMF transformer at each phase of the winding 2, which almost completely coincides with the voltage of the corresponding winding phase 18.. In this case, the total voltage on each phase of the series connection of the transformer winding 1 1 with the stator winding 13 of the induction motor is determined by the sum of the electromotive force in the winding 2 and the phase voltage of the corresponding star beam formed by the series connection of the windings 2, 11 and 13 (Fig. 1 ). The magnitude of the voltage on each of the phases of the series connection of the windings 11 and 13 is equal to the magnitude of the phase voltage of the beam of the star of the primary winding J8 connected in this time interval to the supply network. Taking into account the peculiarities of the interconnection of the windings both among themselves and. with the mains supply wires, as well as with the ac inputs of the diode module modulators, the input line voltages on the diode bridges 4 and 7 do not exceed the line voltage of the mains supply. However, the voltage on each phase of the stator winding 13 is 1.75 times the large phase voltage of the star winding 2, since the voltage on each of the phases of the winding 11 coincides in direction with the EMF on the series-connected corresponding phase of the winding 2. This is due to The winding 11 is the secondary winding of the two-winding transformer 10, the primary winding 6 of which is directly connected to the third winding 4 of the three-winding transformer 1, the EMF at the terminals of each phase which Determines with EMF at the terminals of the same phase winding 2, a three-winding transformer 1.

The next time interval begins with the supply of a trigger pulse to the charging electrode of the thyristor 6. The subsequent unlocking of this thyristor causes the previously opened thyristor 17 to be closed by the reverse voltage of capacitors 19 and 24 and then recharged by these capacitors to a voltage of opposite polarity, shorting the diode bridge 4, connecting the common zero point of the ends of the individual phases of the secondary winding 2 of the main transformer 1j to the common zero point of the start of the individual phases of the winding 14 of the second transform the torus 10, star-connected secondary windings of a power transformer 1 2, wherein the phase okazyvayuts directly connected to the mains line wire as a DR-chi this star; a star connection of phase-wise windings 18, 11 and 13, each of the beams of which is formed by the series connection of the individual phases of these windings. As in the considered case, those phases of windings 2 and 18, which are located on the same rod. the transformer 1 is connected to different linear wires of the mains supply and enters the different rays of the respective connections with the stars of these windings.

The direct connection of the phases of the secondary winding 2 of the transformer 1 to the mains leads to

in each of the phases of the primary winding 18. of the same transformer} EMF, almost completely coinciding with the voltage of the corresponding phase of the winding 2.

The vector diagram (Fig. 3) for the individual phases of both the stator winding 13 and the winding 18 and winding II of transformers 1 and 10 connected in series with it corresponds to the considered open state of thyristor 6 only.

The transition from shorting diode 5 of bridge 15 to shorting of diode bridge 4 is accompanied by a 60 ° change in the initial phase of the EMF in those phases of windings 2 and 18 that are located on a common rod, which is due, as 0, to a change in 120 of the initial phase voltage of the network to which directly Only one of the windings 2 and 18 is connected directly, as well as an additional 180 ° change of this initial 5 phase due to the transition from the connection to the zero point of the initial outputs of the windings to the connection to the zero point of the ends of these windings. Thus, the transition from the previously considered case to i-0 in this case is accompanied by a 60 ° change in the initial voltage phase on the star's beam, where sequentially connected phases of the stator winding 13, winding None winding 2 (in the first case) or winding 18 (in second case), by an additional 60 ° change of the initial phase of the EMF on windings II and 2 (in the first case) or on windings 11 and 0 18 (in the second case).

As a result, the initial phase of the voltage on each of the phases of the stator winding 13 changes by 120 ° when passing from shorting the diode-bridge 16 to shorting the diode bridge 15. It is this view that compares the vector voltage diagrams (Fig. 2 and 3). It also follows from these diagrams that the voltages on each of the phases of the stator winding 13 in both cases are three times higher than the phase voltage on any of the beams of the star connection windings; The voltage values at the input gg of the de-shorted diode bridge, which coincide with the voltages of the series connection of windings I and 13, do not exceed the star voltage phase, i.e. three times less voltage

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on the winding 13 of the stator of the controlled motor.

The following time interval by applying a trigger pulse to the control electrode of the thyristor 9 at the output of the diode bridge 7 leads to: closing the previously opened thyristor 4 by the reverse voltage of the capacitors 21 and 23 and the subsequent reloading of the capacitor until the voltage of the opposite polarity; to shorting the diode bridge 7; shorting windings 3 and 12 of both transformers; The decrease is practically zero to the voltage on the windings 3 and 18 of transformer I and on the winding 1I of the two-winding transformer 10; connecting each phase of the winding 13 of the stator of the motor to the corresponding linear wires of the supply network, the reception of the winding 13 is connected by a triangle. The vector diagram of the voltages on the individual phases of the statorial winding for this case is shown in Fig. 4.

Comparison of vector diagrams shows that the transition from the shorted state of diode bridge 4 to the shorted state of diode bridge 7 leads to a further abrupt change in the initial phase of the voltage on the stator winding 13 by 120 ° while maintaining the same amplitude of this voltage.

The next time interval begins by applying a trigger pulse to the control electrode of the thyristor 17,. which leads to the closing of the previously opened thyristor 9 by the reverse voltage of the capacitors 20, 22 and the subsequent recharging of these capacitors to a voltage of opposite polarity. This also leads to shorting of the diode bridge 15, and the processes are repeated.

The transition from the vector diagram () to the vector diagram (Fig. 3) corresponds to the transition from the short-circuited state of the diode bridge 15 to the short-circuited state of the diode bridge 4; the transition from directly connecting the star of the winding with 18 ends to the mains supply to directly connecting the star with the star of the winding 2 of transformer 1; the change in the initial phase of the voltage on each of the auxiliary windings

transformers I and 10 at 60 °; a change in the 120 beginning / 1st phase voltage at the stator winding 13 of the controlled asynchronous motor, which is caused by a simultaneous transition from the connection to the supply voltage of the start of this winding to the connection of the ends.

The transition to the vector diagram (FIG. 3) corresponds to the transition to the short-circuited state of the diode bridge 7 and the resulting reduction to almost zero voltage drops on all windings of both transformers I and 10, the transition to connecting each phase of the stator winding 13 between the line wires of the mains which corresponds to the connection of the phases of the stator winding by a triangle, a jump-like change in the initial phase of the voltage on the stator winding 13 to 120

A further transition to the vector diagram (Fig. 2) corresponds to the transition to the short-circuited state of the diode bridge 15, to an abrupt change by 120 of the initial phase voltage on the stator winding 13 of the asynchronous motor.

From the vector diagrams (Figures 2 and 3) it also follows that the linear voltage at the AC input of the unzipped diode bridge in both cases does not equal the linear voltage of the mains, between them as a linear voltage on the stator winding 13 of the induction motor exceeds the mains voltage is 1.73 times, which corresponds to the equality of the phase voltage of this winding to the linear voltage of the mains supply.

It follows from the vector diagram (Fig. 2) that the phase voltage of the stator winding is also equal to the linear voltage of the supply network, and if the number of turns of the windings 18 and 23 of the transformer I and the numbers of turns of the windings 12 and 11 of the transformer 10 are equal, the input of the unzipped diode bridge 7 also does not exceed the linear voltage of the mains supply.

The proposed device allows reducing the steady-state voltage at the AC input of each of the diode bridges by three times, providing the same voltage waveform at the load — the stator winding of the controlled asynchronous motor — since in both cases it is formed by three mutually equal intervals the step-step jump cycle of the initial phase of the supply voltage of 120, provides a mode of continuous current in all windings of both transformers 1 and 10 and of the stator winding 13. In tate dostigaet- these changes with range extension variable speed.

Claims (1)

Invention Formula A device for frequency control of an asynchronous motor containing a three-phase power transformer, the first primary windings of which are intended to be connected to a three-phase mains supply, and the second high speed diodes of the first diode bridge, the secondary winding of the specified transformer connected to a star and free stars The terminals are connected to the AC power of the second diode bridge, the second three-phase transformer, the primary winding of which is connected to the first terminals of the first terminals second outputs of the primary winding of the first transformer, a third diode bridge with alternating current outputs for connecting to the second pins of the stator winding of an induction motor, each of the diode chokes on the DC output are shunted in series with a choke and a thyristor, two a triangle group, two triangle tops of the capacitors of the first group are connected to the cathodes of the thyristors of the second and third diode bridges, the anodes of the thyristors are connected The two triangle triangles of the capacitors of the second group are connected to the cathode and anode of the thyristors of the first and third diode bridges, distinguished by the fact that, in order to extend the frequency control range of the asynchronous motor, the power transformer is equipped with additional primary three-phase winding with the second outputs for connection to the buses of the three-phase mains, the first terminals of this winding are connected to the outputs of the alternating The current of the third diode bridge, wherein the primary winding of the second three-phase transformer is provided with second outputs for connecting to the first outputs of the stator winding of an induction motor, and the secondary winding of the second transformer is connected in star and the outputs. - connected to the terminals of the alternating current of the second diode bridge. FIG. four