SU1415369A1 - Method of controlling three-phase thyristor cyclic converter - Google Patents

Description

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HaoCpexeiuie is electrical engineering and can be used to control frequency converters for induction motor drives.

The purpose of the invention is to expand the frequency control range.

Nl FIG. 1 shows a diagram of the device implementing the method; in fig. 2, the frequency divider scheme in FIG. 3 - voltage diagrams.

A device for controlling a three-phase-three-phase thyristor cycloconverter 1 contains a synchronizer-former 2, the input of which is connected to the phases of the power source of the pi. Tani, and the outputs of which are connected to one of the inputs of the TteHTOB AND 3 - 8, the outputs of which 9–1A pulses connected to the appropriate} pulses are connected to the control electrodes of the cycloconverter thyristors 1, the thyristor state sensor 13 is connected to the output of the generator and the generator input 16 and the output of which is connected to the other inputs of the frequency management key input them: lementa 18 podk.pyuchennogo to the generator 16 input pulses specifying unit 19, connected to the output

the control input of the frequency divider 17.

Shaper-synchronizer 2 contains six formers 20 connected to the phases of the power source through the corresponding diodes 21, the sensor 15 of the state of the thyristors of the cyclocontroller 1 contains current transformers 22, the outputs of which through the rectifier 23, the G10th element 24 and the inverter Z3 , with the input of the generator 16 Pulses, containing a single-transistor; a transistor 26, a capacitor: 7 and a resistor 28 and 29. The frequency divider 17 contains the logical elements AND-NOT 30 - 32 and the binary-ten-Hbiii counter 33, ground: schchenny to output terminals through contacts 34 and 35 D e, the count input of counter 33 via an AND-PE 30 connected to the input terminal and the other input connected to the AND-NO elements 31 and 32 via the contacts Sb and 37 T1.I relay.

FIG. 3 shows a diagram of a three-phase voltage, a diagram 39 of a voltage on a capacitor 27, a generator 16 impulses1) Sov, a diagram 40 of control pulses, a diagram 41

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43 voltages at the output of the cycloconverter 1.

The operation of the device according to the proposed method is as follows.

The synchronization voltage in the form of pulses from the output of the synchralizer-former 2 is fed to the inputs of the AND 3 - 8 elements. Since the thyristors of the cycloconverter 1 are closed, then the output of the thyristor state sensor 15 has a signal that is fed to the input of the pulse generator 16. The capacitor 27 is charged in accordance with the voltage diagram 39 and, at a certain value of this voltage, the transistor 26 transforms at the bottom. At the output of the generator 16, an ampulse is produced (diagram 40), which is fed to the inputs of the AND 3-8 elements. pulses from the generator 16 and from the outputs of the synchronizer synchronizer 2 at the inputs of elements 3–8 last open and the signal is fed to the corresponding 9–14 controllers, which generate a voltage pulse, which is fed to the corresponding cycloconverter thyristors 1. Two thyristors are oppositely directed and are located in different phases. They open and allow current into the load. The voltage from the current transformers 22 of the thyristor state sensor 15 through the rectifier 23, the threshold element 24 is fed to the input of the inverter 25, at the output of which the signal takes a zero value. At this time, generator 16 does not generate a control signal. As soon as the thyristors of the cycloconverter 1 are closed, the output of the sensor 15 again generates a pulse, which is fed to the input of the generator 16 and the frequency divider 17 controlling the key element 18. Depending on the position of the key element 18, the generator 16 generates a control signal with a certain delay . In the case of a division factor, control pulses are generated with a delay of 5 / 6T t67 / 6T, and then a second impulse is formed for a time not longer than 1 / 3T (diagram 40) and then the whole process recurs. Thus, in phases of the load, the voltage is modulated, the main harmonic of which is south relative to the frequency314

those power sources 7 times (diagrams 41 - 3). The minimum turn-on time of the cyclo-converter is 1 / 4T, and the maximum turn-on time is 5 / 12T, respectively.

The minimum delay, which is 5 / 6T, is determined by the fact that with a further decrease in time, the current in the phases does not change its voltage, i.e. on load 38, the standing component passes through each other. The maximum delay is limited by the possibility of the appearance of a constant component of the current in the load, and accordingly, with the modulation of the lower frequency.

The minimum and maximum turn-on time of the cyclo-inverter is determined by the required magnitude of the effective voltage on the load, at which there is no overall modulation of the lower frequency.

To increase the frequency of the main harmonic of the voltage, the division factor of the frequency divider 17 is changed. For this purpose, for example, contacts 35 and 36 and the division ratio becomes 3. In this case

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the duration of the delay of the pulses is 5 / BT t: 4 / 3T, however, in comparison with the previous case, a pulse is added after 60 el, degrees, relative to the previous control pulse. The turn-on time of the cycloconverter thyristors increases accordingly and is not less than 5/12 T.

It is possible to further increase the turn-on time of the cyclo-converter to 7 / 6T by changing the division factor of the frequency divider of the fundamental harmonic of the modulating voltage. An increase in the on-time of more than 7 / BT causes a voltage ripple with the frequency of the power source and a failure to modulate the frequency of the frequency.

Thus, the proposed method provides frequency control at the output of the cycloconverter without changing the order of phase alternation on the load at a constant value of the time interval between voltage pulses, thus extending the frequency control range, increasing energy and electromechanical parameters load.

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Claims (1)

METHOD OF CONTROL OF THREE-PHASE THYRISTOR CYCLO-CONVERTER with counter-parallel connected thyristors in each phase, which consists in determining the moment of thyristor shutdown, in relation to which the main control pulses are formed with a time delay 5/6 p'T $ and (p + 1/3) T, where T is the period of the voltage of the power source; n — 1, 2, 3, In order to expand the regulation range, after switching on the thyristors, additional control pulses are generated and applied to thyristors having a positive anode voltage over time 1 / 4Τέί <7 / 6T, and after turning off the thyristors, the main control pulses are again formed.