SU1494192A1 - Ac electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used to control three-phase asynchronous electric motors for general industrial purposes. The aim of the invention is to improve the accuracy of rotational speed control and the expansion of the field of application by providing reverse without switching in power circuits. The electric drive contains a motor 1, a thyristor bridge 2, a choke 3, a synchronization unit 11 performed on two switches 5 and 6, a comparator 7, a controlled frequency divider 8, a distributor 9 pulses, a driver 10 pulses, a digital unit of frequency and direction of rotation, block 12 phase shifters with setpoint adjuster 13, control signal amplifier block 14. The operation of the electric drive is based on the fact that by switching the stator windings of the electric motor 1 according to a certain law, the rotor is rotated at a frequency less than its nominal value determined by one of the expressions F = 1 / 6M-1FH

F = 1 / 2FH

F = 1 / 6M + 1FH, where M = 1,2,3,4 ..., FH is the nominal frequency, and in the latter case, the phase rotation of the voltage supplying the motor voltage is reverse with respect to the first two, i.e. . engine reversing is performed. The drive also provides a fairly wide range of discrete values of rotational frequencies of the electric motor 1 and a smooth transition between them. 5 il.

Description

,

t

WITH

314

Mutatori 5 and 6, a comparator 7j of the control of frequency divider 8, pulse distributor 9, pulse shaper 10, digital frequency setting and frequency direction generator 11, phase offset unit 12 with setpoint adjuster 13, control signal amplifier block 14. The operation of the electric drive is based on the fact that by switching the stator windings of the electric motor 1 according to a certain law, the rotor rotates at a frequency less than its reference value determined by one) of

192

typewriter f 1

 g. f I f

6п-1 - «Т н

f

6p + 1

„, Where m 1, 2, 3, 4, ...,

/ g

I, is the rotating frequency, and in the latter case, the order of alternation of the phases of the voltage supplying the motor turns out to be inverse to

the first two, i.e. carried out

reverse engine The electric drive also provides a fairly wide range of discrete values, frequencies of rotation of electric motor 1 and smooth

transition between pim. 5 il.

The invention of electric motors belongs to electric motors} P1ke n can be used to control П1 three-phase asynchronous electric motors of general purpose.

The goal of Bretepi - noBMmeinie is accuracy of rotational speed control and expansion of the field of application by providing a reverse non-curving gear in power chains.

Fig, 1 shows the structural scheme of electric drive; in fig. 2-4 - diagrams., According to its description, its operation at pa3jni4H rx frequencies of rotation of the electric motor, in Figure 5 - diagrams of the reverse 1 mode.: A.

Electric drive, alternating current contains asynchronous 1 st three-phase electric motor 1, three-phase T1: bridge 2, choke 3, synchro-block 4, complete} b1 on two switches 5 and b, comparator 7, control A frequency finder 8, a pulse distributor 9, a shaper 10 pulses, a digital frequency setting unit 11 and a directional direction, a phase shifter 12 with a setting unit 13 istaiki and a unit 14: 151 control signal. Od1P1 Novades of the stator winding of the electrodes 1 T.ch of gel 1 are connected to the terminals of the 1P1 set network and the others are connected to (.1) the alternating currents of the three-phase bridge 2, between the permanent terminals; p111go current which key. choke 3. D) S switches S and 6 are pairwise about-b (din1pl n form block 4 ingra} P1zatsii, connectirovi with clamp nos. 1 pn (, / cklyucheii to the mains, 1) g (5 connected to khods1m complex (1p 7,

the output of which is connected to the counting input of the controlled frequency divider 8, the output connected to the 1 input to the distributor's input 9. pulses, the stubby () output of which is connected to the first six-channel information input of the Spectrum 10 pulse, the second two-channel information input of which is connected to the output a phase shifting unit 12, the information Hbtfi input of which is connected to the output of the second switch 6. The first and second outputs of the digital frequency setting device 11 and the direction of rotation are connected to the control input al corresponding to An adjustable frequency divider 8 and a pulse generator 10, the first, second and third six-channel outputs of which are connected respectively to the six-channel control inputs of switches 5 and 6 and the inputs of the block 14 of amplifiers of the control signaling circuit, the inputs of which are connected to the control circuits three-phase thyristors 2.

Each of the switches 5 and 6 consists of a set of six controllable keys that are combined on the output.

The pulse shaper 10 is assembled on logic elements and generates six-channel pulse sequences, 9 pulses coming from the distributor output, six-channel bottom sistem1 1 pulse sequences that control the operation of switches 5 and 6. Additionally, the driver 10 pulses from two channels

five

sequences of pulse signals from the output of phase shifter 12, forms the third six-sequence sequence of pulse signals to control the thyristors of the three-phase bridge 2. Depending on the change of the digital code at the control input of the pulse shaper 10, the pulse control algorithm of the switches 5 and 6 and three-phase bridge thyristors 2, as illustrated in the diagrams shown in Figures 2-5.

figure 2-5 marked: ab, cb,

ca, la, be, ac is a six-phase line voltage system, 1d, ig, ic currents in the stator windings of engine 1 without taking into account valve switching processes and with sufficiently large inductance of droplets 3-, i, is the first harmonic of the engine current, having frequency f, and 3 voltage on the windings of the motor and drossel i and / and - voltage on the outputs of the setpoint adjuster 13 of the control angles of and /) i T15-T20 are the control pulses of the corresponding thyristors.

The operation of the AC drive is based on the fact that by switching the stator windings of an induction motor 1 according to a certain law, the magnetic field of the stator is rotated, and the rotor of the induction motor 1 is rotated at a frequency less than its nominal value and determined by. one of the three games:

one

6t-1

  n

1 6in + 1

and

n

(one)

(2) (3)

where n 1, 2, 3, 4, ... is the number of inclusions for the period of the converted frequency of the same pairs of thyristors of opposite phases,

f is the nominal frequency corresponding to the mains frequency, and the phase sequence for law (3) is inverse to (1) and (2).

Drive operation for mode 1

f

6m-1

q presented in figure 2

with n 1 mode f

on fig.Z when ha 2, dl

press f

figure 4 and for re-figure 5 at. Electric drive, for example, when f

If

„, Works as follows.

The six-phase system of linear voltages of the mains supply is fed to the inputs of switches 5 and 6, each of which contains alternating switching keys, which are connected at the output and controlled by the output pulse signals of the first and second six-channel outputs of the driver 10 pulses. Thus, the voltage Uj, U at the output of the switches 5 and 6 are sinusoidal sections of linear voltages with a duration of 300 el. hail (figa, b), “with the initial shift of the sinusoids in each section of the operation of the switches 5 and 6 between them is equal to 120 e. hail due to the rigid connection of the same inputs of switches 5 and 6 with a six-phase system of linear voltages ab, cb, sa, la, be, ac. Comparing the output voltage of the switch 5 with the zero level set on the comparator 7, allows to obtain at the output of the comparator 7 a sequence of pulses U 7; shifted relative to each other by 300 el. network frequency hail (FIG. 2BX) arriving at the counting input of a controlled frequency divider 8, the division factor of which is

this case f

1 avny 1

45

50

55

using the code set on its control input. As a result, a sequence of pulsed signals UQ is formed at the output of a controlled frequency divider 8 (Fig. 2d), similar to the input sequence received at the input of the pulse distributor 9, which converts the original pulse sequence into a six-channel sequence of pulse signals and j. 1st and 3.4 duration of 300 e. hail

(fig.2zh). From the outputs of the distributor 9 pulses and g -, - and 94 pass into

this case (f t f „) without change through the driver 10

coi jiacho pulses to the installed code on its control input and push the control to the inputs of both switches 5 and 6,

The voltage U, formed at the output of the commator 6 (fig.2b) is the sweep voltage, is fed to the information input 1 of the phageosimetis block 12, where it is compared in each of the two channels with the corresponding reference setpoint voltage 11 and U ". As a result, at the outputs of the phase shifting unit 12 (Fig. 2e, e), sequences of pulse signals and, and are formed. - with the corresponding control angles o / and / 3, which are fed to the second information input of the imaging unit 10 pulses. In the pulse shaper 10, a joint logical processing of the signals from the outputs of the pulse distributor 9 and the phase shifter 12 is carried out, resulting in a six-channel sequence of pulse signals T15-T20 designed to control the thyristors V5-20 (ph 2). These pulses are passed through a block of 14 amplifiers designed to amplify and galvanically isolate the thyristor control pulses of a three-phase bridge 2.

At each cycle of operation, at the moment corresponding to the 1st angle o /, a pair of thyristors is connected, connecting the choke 3 to the two corresponding phases of the electric motor 1, ensuring the flow of current through the two stator windings, then at the instant corresponding to the angle, the third thyristor is turned on, providing in conjunction with the previously opened shunting of the throttle 3 and the termination of the stator windings of the engine 1. The current through the choke 3 as a result flows continuously. The shape of the currents in the stator windings for mode f

 - f (I preds 1 Avlena figure 2 (1D

ift ic) I flt: the dotted line shows the first harmonic of the current in one of the phases i 1, the frequency of which corresponds to 1/5 of the mains frequency. By changing the settings for setting the control angles o (and p, it is possible to regulate the amplitude of the first harmonic of the current in the windings of the gate 1.

The operation of the device in the regimes of regulation of the frequency (l: h1 according to the law f

ten

fj is different from that described.

41928

 one

6in-1

above, only by changing the frequency using the digital setting device 11 and the direction of rotation of the digital code at the control input of the frequency divider 8, an appropriate division factor is set. Thus, for example, in the diagrams of FIG. 3, the operation of the device when setting the division factor to 2 is represented, i.e. happening

2,

f l-f 11

Output control e0

five

0

0

five

In this case, the splitter 8 passes each second pulse from the input (Fig. 3g), the algorithm of operation of the pulse generator 10 does not change, the difference is only in the control pulses of the switches 5 and 6, i.e. in the duration of the sections of switched linear voltages equal to 300 + 360 660 el. network frequency hail. In other words, in the considered mode, at each clock cycle of the pulse distributor 9, the same thyristor pair of the three-phase bridge 2 turns on twice and the current form in the windings takes the form shown in Fig. 3 (iy), ig, ic). Subsequently, when regulated according to the law f fn, for example, m 3

case m J or f f If the duration of the sections of the commumer, for J

5 17

linear voltages at the output of switches 5 and 6 are 300+ + 360 + 360 1020 el. network frequency, and on each clock of the operation of the distributor 9 pulses the same thyristor pair is turned on three times, etc.

The mode of operation of the device for an hour. one . 5 tots r - y y reflect diagrams on

FIG. 4. As for the case of f-f-n

(Fig. 2) the division ratio of frequency divider 8 is equal to 1, the operation of the pulse distributor 9 remains the same, however, by changing the code at the control input of the pulse shaper 10, the algorithm for tracking the control pulses generated in it

thyristors 15-20 and - switches 5 and 6 (L, and ", and".,, and, 0 t, and f (n). The key elements of the switches 5 and 6 commute through

one with the frequency doubled in relation to the case of FIG. 2, the shape of the voltages of the outputs of the com (tators 5 and fe in FIG. 4 remains the same as in FIG. 2; however, the connection algorithm of the corresponding sections of the linear voltages of the input six - phase system. As a result, the frequency of the first harmonic current in the stator winding (i /, ig, i from Fig. 4) is equal to half the network frequency.

In order to reverse the engine 1, a device operating mode with variable speed control is used.

1 f

the law t .Jr t, in which the alternation of the phases of the current in switchable stator windings with the same structure of the power circuit is inverse to the previously described modes, which is explained in the diagrams of FIG. 5 for the case m 1, i.e.

f y fn

A characteristic difference in the operation of the device in FIG. 5 from the operation in FIG. 2 is the setting of the division factor of the divider 8 frequency to 2 and the change in the algorithm for following the control pulses U, and (O at the outputs of the driver 10 pulses, resulting in the duration of the switched linear sections It reaches 420 e hail frequency, and the shift between linear a1 voltage of two switches 5 and 6 on each of the sections is equal to 60 e hail.The sequence of control of HNmynbcoB control with and 0, .., and, o, G7 " T15-T20 from the formers 10 impulse outputs in (5) is set reverse. Later in the regulation of the law

f -7g n for example, for m 2,

OP1 + 1

f -r f c, the division factor of the 8 frequency divider is set to 3, the duration of the switching voltages in this case is 420 + 360 780 el. hail m 3, f 1

Dc, coefficient 1; the division rate is set to equal 4, the duration is from switching voltage parts 420 + 360 + 360 1140 pl. hail and so on. Algorithm 1) work, 1 driver 10 impulses s ggry specified law iz 94I92 10

however, the frequency remains the same.

All the modes discussed above provide a discrete change in the frequency of the main harmonic of the current in the motor windings according to the series j 1 J j 1 2 5 11 23 direct phase rotation and according to 1111 1

f „at

ten

15

0

five

0

five

0

five

0

five

with reverse phase rotation. The adjustment of the rotational speed of the motor 1 within each range of a discrete frequency range is carried out by changing the effective value of the stator current by means of phase adjustment of the angles / and ft of the thyristor control 15-20.

Since the operation of the device is associated with the intermittent shorting of thyristors by 15-20 throttles 3, under real conditions in transient modes this may be accompanied by undesirable voltage jumps on the elements of the power circuit. To eliminate these phenomena and increase reliability, choke 3 is bridged by RC-chain 21.

Thus, in the proposed electric drive, the process of controlling the rotation frequency of the asynchronous motor 1 using a three-phase bridge 2, shorted by a choke 3, using the single-channel method of generating control pulses, is simple and reliable Hbw and provides greater control accuracy and the possibility of reversing without additional switching power circuit, with minimal means provided a sufficiently wide range of discrete values of rotation frequency and a smooth transition between them.

Claims (1)

Invention Formula An AC electric drive containing an asynchronous three-phase electric motor, some of the output winding pins of which are connected to the terminals for connecting the power supply, and the other leads to the AC three-phase transistor bridges, between the DC terminals of which the choke, synchronization unit, The entrances to Toporo are connected to); -ll for switching the mains supply, the bias power unit with the setpoint patch, the controlled frequency divider, the control signal amplifiers, the outputs of which are connected to the control: the three-phase thyristor circuits, In order to increase the accuracy of rotational frequency control and expand the scope of application by providing reverse without switching to power circuits, a comparator, a pulse distributor, a pulse shaper, a digital frequency adjuster and a direction of rotation, and a C unit chronization formed on two komgutatorah with six inputs and one output each, switches the inputs are combined in pairs and form a block in B inputs 1hroniza- tion, the first switch output connected to an input of a comparator, the output ba h YY / / / YY five 0 koi.1P1) G (; connected to the counting input of control 1 (the r-1 frequency divider, the output of which is connected to the input of the distributor of pulses, the six-channel output of the coyur is connected to the first ip-formation-1P) 1 m input of the pulse shaper, the second Information 1H) Two-way input which} 1en:. phase shifting unit, information, the E11Pny input of which is connected to the second output of the second switch, nepiaiif, the second and third 1 natural-HbiC outputs of the pulse generator connects H, respectively to the six-KaH, -iibHi, iNni control inputs of the first (, 1 H i oporo switches and with the inputs of the control signal amplifiers, nepBi.ui and the second output of the digital frequency task and the rotation of the iBJiciuiH rotation are connected to a control; the inputs of the corresponding frequency divider and pulse generator are compatible with the inputs. esii "v." 4ivrs "Csb S S ... , oiojjrtoioi ggt:;:; :: ::. . .  0 o ct l l 7-  Si S3 sj, .L 1/194192 h ,, l ff / vW yc vff .-. rff . / A A A / X A / X / tA / T / t a) ,, h ° A h PG h ° A A 4 A V jn. four:  u w I- - eleven. ) Uei.tfikT.Vg. B u A i "tf f-fUt" 4, (te (r, 0). | Wj-tf "RtLUMi.,. hy.iža. r "-I VS -i D) 7- - rfS - T " G2v  “If it --rr-it - / - f vff .-. rff  / T / four: Y -f-f- - - - - fA - t: rx