SU1372541A1 - Frequency converter - Google Patents

Abstract

The invention relates to a converter technique and m. used in variable frequency drive AC. The goal is to increase efficiency. The device contains thyristor groups 1-6, 24, 25 to which cut-off diodes 7-12 are connected, connected to windings 20-22 of the smoothing reactor 19. The current in the outgoing phase of the motor 23 is maintained by the energy stored in the inductance x scattered reactor 19 and engine 23. In this case, the energy stored in the circuit is returned to the engine shaft. 3 il. with "e (L

Description

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This invention relates to a power converter technology and can be used in a variable frequency AC drive.

The purpose of the invention is to increase the efficiency.

Figure 1 presents the scheme of the frequency converter; 2 is a block diagram of a frequency converter control system; on fig.Z - time

Management process sweeps.

The device contains six main thyristor groups 1-6, three thyristors in each group; in groups 1,3, 5, the thyristors are connected by cathodes, in groups 2,4,6, the thyristors are connected by anodes. To the thyristor groups connected cut-off diodes 7-12 and switching capacitors 13-18, forming two groups connected by a triangle. In the output phases of the converter, a smoothing reactor 19 is connected, containing magnetically connected windings 20-22, connected respectively between cut-off diodes 7 and 8, 9 and 10, II and 12. A motor 23 is connected to the middle points of the windings of the reactor. Between the cut-off diodes 7-12 and the windings 20-22 drossel connected two (seventh and eighth) auxiliary thyristor groups 24 and 25, consisting of thyristors 26-31, Thyristors 26-28 have a common anode bar, and thyristors 29-31 have a common cathode bar, which are combined with each other Conclusions thyristor cathodes 26-28 are connected You respectively have cathodes 1m of cut-off diodes 7, 9, 11 and beginnings of windings 20-22 of a smoothing reactor 19, and outputs of diodes thyristors 29-31 are connected respectively with anodes of cut-off diodes 8, 10, 12 and ends of windings 20-22 of reactor 19. Converter it is powered by a three-phase network 32. In Fig. 1, thyristors 33-35 are shown involved in switching current

The control system (Fig. 2) contains a synchronization unit 36, a pulsed phase control unit 37, a pulse distributor 38 and a master oscillator 39. The outputs of the pulse distributor 38 with thyristors of 1-6 groups. The six channels of thyristor control pulse shaping 26-31 are implemented in the form of differentiating amplifiers 40-45, OR 46-51,

And 52-57 circuits, the inputs of which are connected to the outputs of the OR circuits and to the outputs of the block 58 of voltage sensors.

The converter works in the following way.

Consider the point in time when the potential of phase A of the supply network is most positive, the potential of phase B

most negative, the thyristors 33 and 34 are turned on and current flows along the circuit of phase A - thyristor 33 - cut-off diode 7 - winding 20 of smoothing reactor 19 - phase a and from the AC motor - winding 22 of smoothing reactor 19 - cut-off diode I2 - thyristor 34 - phase B of the mains. In this case, the switching capacitors are charged in such a way that their left plates become positive and the right ones become negative. For example, the capacitor 13 is charged along the circuit of phase A - thyristor 33 - capacitor 13 - cut-off diode 9 - winding 21 of smoothing throttle 19 - cut-off diode 10 - capacitor 18 - thyristor 34 - phase B

To switch the motor current from phase a to phase b, it is necessary to turn on thyristor 35. When turning on thyristor 35, thyristor 33 is applied a reverse voltage equal to the voltage on capacitor 13, along circuit 13 - 35 - 33 - 13. After switching off the thyristor 33, the switching voltage capacitor 13 is recharged around the circuit. Phase A - thyristor 35 - capacitor 13 - cutting diode 7 - winding 20 - motor phases a and c - winding 22 - cutting diode 12 - thyristor 34 - phase B. When the voltage on the capacitor 13 changes sign and will reach a value equal to the instantaneous linear value The electromotive voltage between phases A and B of the supply network, the cathode potential of the cutting diode 7 will become equal to the potential of the anode of the cutting diode 12 due to the emf inductances of the winding 20 of the smoothing throttle 19 and the output of the winding phase q of the motor 23. 31 and the phase current of the motor 23 closes along the phase a and from the motor circuit - thyristors 31 and 26 - the winding 20 of the smoothing reactor 19. At the same time, the current in phase b of the motor increases along the loop phase A of the mains supply - thyristor 36 - interrupting diode 9 - winding

21 smoothing throttle 19 phase Out of the engine 23 - winding 22, smoothing throttle 19 - cutting. diode 12 - thyristor 34 - phase B of the power supply network.

The current in the outgoing phase q of the motor 23 is maintained by the energy stored in the inductances of the scattering of the smoothing throttle 19 and the motor 23. Since the phase current Q, closing along the phase contour a and c is winding 22 - thyristors 31 and 26 - winding 20, is directed against the linear emf of the motor 23, then the energy stored in the circuit returns to the motor shaft, and after the phase Q drops to zero, the thyristors 26 and 31 are turned off. The operation of the control system is explained by the timescales of the signals shown in FIG. 3.

A three-phase voltage U, U, U coinciding in phase with the supply voltage is supplied to the input of the synchronization unit 36. At its output, six selector pulses d, F-Rf F., are formed, equal to a logical unit, provided that the corresponding half-wave phase EMF of the supply network is positive. In addition, the synchronization unit triggers the launching of sawtooth-shaped reference voltage generators in block 37 of a pulse-phase control, which converts the control voltage U | i into sequences of pulses u, and F, whose leading edges are shifted by an angle oi with respect to the beginning of the corresponding reference stresses. The master oscillator 39 generates six

selector pulses F, F,. F, and F,

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forming a six-phase voltage system with an amplitude equal to the logical unit, and a duration of 120 al. on the output frequency of the converter.

The pulses from the synchronization unit 36 of the system 37 of the pulse-phase control and the master oscillator 39 arrive at the distributor 38 pulses forming control pulses for the thyristors of groups 1-6 in accordance with the logical equation

R. , - - p, F 1 F, v) - “i ,; . j

where, b, c,

A, B ... - sequence

power network; , b, c.

a, b,., is the phase sequence at the converter output;

FJ - control signal on the thyristor, connecting the i-th phase of the mains with the j-th phase at the output of the converter, indices i, j are positive for thyristors 1, 3, and 5 groups and negative for thyristors of 2,4,6 groups; - a sequence of control pulses shifted by an angle with respect to the moment of the natural switching on of the thyristors connected to the i-th phase of the mains;

FJ - selector pulse

the i-th phase generated by the synchronization device 36;

FJ - selector pulse

j-th phase, formed with the master oscillator 39.

So, for example, the control pulses of the thyristor 33 from group 1, which connects the phase A of the mains with fa and a at the output of the converter, are calculated by the equation

U ,,, Fft (i P (d F d taxically for the thyristor 34 of group 6 - according to the equation

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Control voltages for thyristors 24 and 25 of the groups are formed from the signals F | g, Fl ,, FJ f ,, Fj, and F obtained at the output of differentiating amplifiers 40-45. The leading edge of the FJ signal coincides with the falling edge of the corresponding selector pulse F-, with the output generator of the master oscillator 39. The voltage sensor unit 58 generates six R, S, T, X, Y, Z signals equal to the logical one, then positive voltage at thyristor anodes, respectively 26, 27,28,29, 30,31. Logic circuits OR 46-51 and And 52-57 provide the formation of control voltages in accordance with the logical equation

, p- F. f. + p.p. f) i K f- + -C,

de j-a, b, c,

a, b, .. is the sequence of the output phases of the converter; P is a logical function

equal to one in the control voltage generation interval for the thyristor 24 of the group connected to the jth phase, respectively, the indices for the thyristors 25 of the group e-15 rut with minus; F R, S, T, X, Y, Z with, + b, + c, -a, -b, -c - a set of logical functions corresponding to 20 signals of voltage sensors on thyristors 26 - 31; F. - logical function

is equal to 1 at the time of forming the leading edge of the function F,. Thus, for example, the control voltage to thyristor 26 from group 24 is determined by equation 30

P.Q R F.Q - R-.

Similarly for thyristor 31 from py 25 - according to the equation

p 7 F + 7 - Fg-i. ,

Returning the energy stored in the switching circuit to the motor shaft increases the efficiency of the converter by 1-2%, preventing aosHHKHOBeF from overvoltages on the switching capacitors, especially during current overloads, which reduces the operating voltage of the capacitors and thus reduces the weight and size converter

Claims (1)

Invention Formula A frequency converter containing six main thyristor groups, a multi-winding smoothing reactor, switching capacitors, six cut-off diodes forming a three-phase bridge, a control system including a synchronization unit, a pulse-phase control unit, a master oscillator and a pulse distributor and implementing algorithm you 0 5 0 50 five five 0 control pulses according to the equation F F F F) 1 J characterized by the fact that, in order to carry out the K1Sch, the converter is equipped with seventh and eighth auxiliary thyristor groups, the windings of the smoothing reactor are connected between the cut-off diodes and are made, - common cathode bus, which are interconnected, the cathodes of the seventh group thyristors and the anodes of the eighth group thyristors are connected respectively with cathodes and anodes of the cutting diopes and beginnings and the ends of the windings of the smoothing reactor, the control system is equipped with voltage sensors on the thyristors of the seventh and eighth groups and a six-channel driver, each channel of which contains a differentiating amplifier and OR and AND logic circuits that implement the control algorithm in accordance with the equation R; F, FU F, F: ,,,, where, b, c, A, B, ..., - the sequence of the phases of the supply network; , b, c, a, b, .. ,, - sequence phases at the output of the converter; F; j control signal on the thyristor connecting the i-th input phase to the j-th output phase of the converter, the indices i, j are positive for the thyristors of the main groups connected by anodes to the input terminals and negative for the thyristors of the main groups connected by cathodes to the input terminals;  - a sequence of control pulses, with a torque of tii with respect to the moment of natural switching on, Fig. tsfov connected to the t-th phase of the mains; selector pulse of the i-th phase, generated by the synchronization unit; selector impulse of the j-th phase, formed by the master oscillator; R, S, T, X, Y, Z as j - | -a, + b, + c, -a, -b, -c, is the set of logical functions corresponding to the voltage sensor signals on the thyristors of the seventh and eighth auxiliary thyristor groups; logical function, equal to 1 at the time of formation of the leading edge of the function F; Oop uy.  n ppplppppg GP GP n n n n P ln V t ltl n n t IT n n t t t t fig.Z / V t n t IT t t t t