SU1554089A1 - Frequency converter - Google Patents

Abstract

The invention relates to a converter technique and can be used in a frequency-controlled electric drive. The aim of the invention is to improve the quality of the conversion by reducing the distortion of the input and output currents. The device contains thyristors 1-6 and reactor 7. Load 8 is connected to the middle point of the secondary winding of transformer 9. Pulse-phase control system 10 is connected through frequency switching unit 11 to pulse distributors 12 connected to form-forming amplifiers 13. Each output frequency corresponds to its pulse distributor. 5 il.

Description

t ± f

Vcm.UH li

but

SL SL

four

About 00

with

9u.t

The load 8 is connected to the midpoint of the secondary winding of the transformer 9. The system 10 of the pulse-phase control through the node 11 frequency switching is connected to the distribution

The invention relates to a converter technique and can be used in various sectors of the national economy, in particular in a frequency-controlled electric drive.

The purpose of the invention is to improve the quality of the conversion by reducing the distortion of the input and output currents.

FIG. 1 shows the device; in fig. 2,3 - diagrams of its operation at different output frequencies; in fig. 4.5 is an example of using a device for converting the number of phases with diagrams.

The converter (Fig. 1) contains thyristors 1-6 assembled according to a bridge circuit, a reactor 7 connected at the output of the bridge, and a load 8 connected between the middle point of the secondary winding of the matching transformer 9 and the point of connection of the thyristors of one of the bridge arms. The thyristors of the converter are controlled from a pulse-phase control system (SIFU) 10, the output of which is connected via a switching unit 11 to pulse distributors (RI) 12, made according to a scaling circuit, the outputs of which are connected to the inputs of the amplifiers of the drivers 13, and the outputs of the latter are connected with the control electrodes of the respective thyristors of the converter.

In the diagrams of FIG. 2.3 The following notation is accepted: Uc, fc - on

and

U,

n

network frequency and frequency; i FH - current, voltage and frequency in the load; adjustment angle;

i-M, the first harmonic of the load current; the numbers indicate the numbers of the gates conducting at the corresponding time intervals.

The converter (Fig. 4) contains three thyristor bridges 1-6 with reactors 7, a three-phase load 8, a four-winding transformer 9, SIFU 10, the output of which is through a switching node

bodies 12 pulses connected to the amplifier-formers 13. Each output frequency corresponds to its own pulse distributor. 5 il.

0

five

five

0

five

0

five

0

five

Frequency 11 is connected to the pulse distribution unit 12 (in the example, one RI), the outputs of which are connected to the inputs of the amplifier-shaper 13, and the outputs of the latter are connected to control electrodes of the corresponding thyristors.

FIG. 5: iHa, iHB, i Hc currents in a three-phase load; IH, the first harmonic of the load current; oi is the control angle; Uc, fc — mains voltage and frequency; Hz - current frequency in the load; the numbers denote the numbers of the valves conducting at the appropriate time intervals.

For all the diagrams (2,3,5), the switching of the tirlstors is neglected.

The device (Fig. 1) works as follows.

The thyristors 1-6 are turned on and their operation is performed in pairs, the numbers of simultaneously operating gates are indicated on the respective amplifier components. In the steady state, the current in the reactor 7 is continuous and fairly smooth. At the outlets of SIFU 10, in accordance with a predetermined angle of control about (voltage setting), there is a sequence of pulses (axis b in Fig. 2) displaced 180 electr. Relative to each other. network voltage (in Fig. 2 the angle of adjustment, its possible value is shown by a dotted line). If the switching node 11 (key) is in

eleven ,

position 3 (Extreme left position in Fig. 1), then on six outputs RI 12 (2) there appear sequences of pulses shown in Fig. 2 (C-and-3 axes) falling on the inputs of the shaping amplifiers 13. On the outputs of the latter. signals to control thyristor pairs 1-6, as shown in diagram 2 (axis and). At the same time in the load 8 current flows

the frequency of which is FH f s, and the swing-off from the sinusoid is much smaller than in the known transducer. In case key 11 is installed

then the weekend im1 1

in position - t 5

PULSE 10 pulses fall on RIs from 2m 10. At the RI outputs, pulse sequences appear, shown in FIG. 3 (PI-PK1). However, by combining the individual outputs RI 12 (shown by the dotted line between P1-P3, P2-P4, P6-P8, P7-P9 in Fig. 3), the sequences of pulses go to the inputs of the shaping amplifiers 13 (axes b-3 ), providing the current frequency Pu-5 fc

in load 8 (axis and fit 3).

Setting the key 11 to the following positions (, jr, etc.) ensures that frequencies are received in load 8 - f c, - fc, etc. Thus, each output frequency corresponds to its own RI, which makes it possible to increase the reliability of the converter, since one of the RIs can fail at other frequencies, which is possible in a number of cases.

The proposed converter can also be used to simultaneously convert the frequencies and the number of phases, for example, a single phase voltage to a three phase one. FIG. 4 shows a variant of the device for such a conversion with a frequency FH f c.

The device (Fig. 4) works as follows.

The output pulses of the SIFU 10 through the key 11 are fed to the input of the RI 12 s, the output pulses of which are distributed over the individual phases of the converter and the pairs of gates according to fig. 5, which provides a symmetrical, 120-degree shift of the first harmonics of the currents in the load 8 (axis and

k, l in fig. 5) with frequency - fc. AT

In general, the output frequency with a symmetric shift of the first harmonics of the current is expressed by: FH

1, f

with

where, 2,3 ... For example, for

0

five

0

five

0

five

0

five

0

five

Necessary to obtain frequency FH - fc

My output key 11 of FIG. 4 connecting the RI to 18 outputs (), for

frequency FH t-f required RI 54

output (), etc. Otherwise, the work of the phase number converter does not differ from the operation of the device according to Lig. one .

Claims (1)

Claim 1 g A frequency converter containing a single-phase thyristor bridge, between the DC terminals of which the reactor is turned on, and a control unit, including a PM-pulse-phase control system (SIFU), two frequency dividers with a frequency switching center, whose inputs are connected to the output, and the output through the driver-amplifiers to the control electrodes of the anode group thyristors, the input of the driver-amplifiers of the cathode group being connected to the output of a SIFU, characterized in that, in order to improve the quality of the conversion due to Endshen distortion input and output currents, it is equipped with a chain of two series-connected additional thyristors connected between the outputs of the direct current of the said bridge and the matching transformer, the secondary winding of which is made with a midpoint forming the first output terminal, and the ends of this winding are connected to the input terminals of the said single-phase bridge, and the second output terminal of the converter is formed by the connection point additional thyristors, moreover, n pulse distributors are introduced into the control unit, performed according to a ring scaler, where n is the number of possible output frequencies ate, each of which is configured 2t number of outputs, the inputs connected to the outlet valves IFSB node through said switching frequency, and outputs - a shaping amplifier inputs thyristors the converter, and the number - fr m, is equal to the given output frequency, where fc is the mains frequency. and U but Well and v 6 fa n PJ RF PS V pj n pi p $ I d e 3 11JIII IIL x 3 i / /. u / tA p.5 Lh u  Jy xx k ra if. Uri J- -O art  Jy ra if. Phi s U / l P gpf k -.- oo F tii 6/1 five 1 | TH1 AND U2i i and & ha 6ti  Uh Kfe B SHETs 9 + -zh with n.ranai and I and, & Well and / 77/3, b 13 / / vy / / LA ЈX / - in 3.6 H I 1,1 Fm.5 | / Lu