SU1288853A1 - Frequency converter with direct coupling - Google Patents

Abstract

The invention relates to a converter technique thereof. b. used for frequency control of an ac motor. The goal is to improve the quality of the output current over a wide range of frequency variations. The device contains tr-p 1, to the secondary winding of which anodic and cathode thyristor groups 2-19 are connected. The three-phase thyristor bridge 27-32 is connected to the thyristors 2-19 and the three-phase diode bridge 21-26. The capacitors 33,34 are connected to the outputs of the diode bridge 21-26 and the neutral load 20, the windings of which are included in the star and connected to the thyristors 2-19. When changing the polarity of the voltage of any phase, the thyristor groups are switched by the mains voltage through the common mains neutral and the loads and one of the capacitors. Resonance effects between the load windings and the capacitors are eliminated due to the use of a diode switch as the cut-off valves. 2 Il. (L

Description

The invention relates to electrical engineering, namely to converter equipment, and can be used for frequency control of an AC motor,

The purpose of the invention is to improve the quality of the output current in a wide range of variation of its frequency.

Fig, I presents the scheme of the proposed device; in fig. 2 - forms of voltages in the phases of the load (a thin line when using a known frequency converter with direct coupling, a thick line when using the proposed

my transducer). I

The device includes a transformer 1, the secondary winding of which is connected to the star A, B, C - phases of the secondary winding of the transformer connected to the output of the transformer anodic and cathodic groups of thyristors 2-7 for forming phase A of the load, anodic and cathodic groups of 8 13 to form a load phase B, anode and cathode groups 14-19 to form load phase C, load 20 connected to a star and connected to the outputs of the thyristor groups, a three-phase diode bridge 21-26 connected to the outputs of the thyristor groups 2-19 three phase An aristocratic bridge 27–32, the anodic and cathode groups of which are connected respectively with the cathodic and anode groups of the diode bridge, two capacitors 33 and 34, one terminals of which are connected to the outputs of the diode bridge 21-26 and the inputs of the thyristor bridge 27–32, the second terminals are connected to the neutrals of the load and the secondary winding of the transformer 1, the control system of the converter 35, performed according to the standard scheme, but not containing a current sensor and devices for forming a pause when the polarity of the current of each phase changes: with separate control left-

Research institute

Transformer 1 is used to power the converter, thyristor groups 2-19 are used to form the voltage in load phases 20, diode bridge 21-26 is used to charge capacitors 33 and 34, thyristor bridge 27 to 32 is intended for: discharge of capacitors

33 and 34 through load phases 20, control system 35 is necessary to control thyristor viII of the thyristor groups and thyristor bridge.

The device works as follows.

At the initial moment of time, thyristors 2 and 14 open, the current generated by the voltage of phase A of the transformer flows through the load phases A and C, forming positive voltage half-periods, simultaneously charging the capacitor 33 with diodes 21 and 25 to the load neutral, then opening thyristor 9, the current flows through the load phase B, forming a negative half-period of the voltage, at the same time charging the capacitor 34 through the diode 26 to the neutral of the load.

After some time, the voltage in phase A of the transformer begins to fall off, the capacitor 33 through the opened thyristors 27 and 31 is discharged through phases A and C, maintaining the voltage on them.

I

Then the thyristor 1I opens,

the current flows through phase B, it forms a negative half-cycle in phase B of the load. At the same time, dose capacitor 34 is charged through diode 26 and thyristor 32 is locked, etc.

When the polarity of the voltage changes under active-inductive load, for example, in phase C, from positive to negative, the device works as follows.

The voltage on the secondary winding of the transformer is reversed, the current flows through the neutrals of the transformer and the load, capacitor 34, diode 22, and locking thyristor of the anode group of phase C of the load. The energy stored in phase C of the load, through diode 22, charges the capacitor 34, which is then discharged through the other phases of the load.

On the thyristor 27, the pulses are fed simultaneously with the pulses of thyristors 2, 4, 6, duration. Adequate for its opening to the beginning of the decline of the positive voltage half-periods in the phases of the transformer. Similarly, the thyristor 29 is supplied with control pulses synchronously with the thyristor 8, 10, 12,

on thyristor 31 - synchronously with thyristors 14, 16, 18, on thyristor 28 - synchronously with thyristors 15, 17, 19, on thyristor 30 - synchronously with thyristors 3, 5, 7, on thyristor 32 - synchronously with thyristors 9, 11, 13,

When changing the polarity of the voltage of any phase, the thyristor groups of the converter are switched by the mains voltage through the common neutral of the network and the loads and one of the capacitors. The reactive energy stored in the load inductance through the diode bridge charges the capacitor, which is discharged through the other phase of the load using a thyristor bridge.

Thus, the thyristor groups of the converter do not go into the inverter mode, therefore, there is no need to use devices for joint or separate control.

The resonance between the load windings and the capacitors is eliminated due to the use of a diode on-thyristor switch as cut-off valves.

Using the present invention, when smoothing the voltage shape, will allow a smoother shape of the stator current and, consequently, magnetizing forces, which will reduce the radial beats of the rotor. This will expand the control range in the low-frequency region. Switching the thyristor groups through the load neutral and the transformer, a capacitor and a diode with the transfer of energy stored in the load inductances into the capacitance and its subsequent transfer back to the load will significantly simplify the control system, since at any values of cos load

switching of the thyristor groups is performed when the polarity of the supply voltage is changed, which will eliminate the pause when the polarity of the current of each phase changes and thereby greatly simplify the control system. The formation of the output voltage curve can be performed both under rectangular and sinusoidal control voltage,

Claims (1)

Invention Formula Direct coupled frequency converter containing three anode and three cathode thyristor groups assembled according to three-phase zero circuits, a three-phase diode bridge connected to the outputs of the thyristor groups, three-phase thyristor the bridge, the anodic and cathodic groups of which are connected respectively to the cathodic and anodic groups of the diode bridge, the thyristor control system of the converter, which is (fp y and so that, with the improvement of the quality of the output current in a wide range of variation of its frequency, two capacitors are inserted into it, one of which is attached to the outputs of the diode bridge, the latter are combined to form a output for connecting to the zero points of the load and the supply network, and the AC outputs of the three-phase thyristor the bridge is connected to the outputs of the thyristor converter groups. FIG ..