SU1372540A1 - Method of quasicontinuous power control - Google Patents

Abstract

The invention relates to electrical engineering and can be used in installations with significant inertia of the technological process. The purpose of the invention is to reduce asymmetry. The control of the power consumed by the load I is carried out by sequentially connecting the phases 2-4 of the load to the inputs 8-1I for connecting the supply network with a frequency reduced compared to the frequency of the voltage in the network. Cyclic alternation of connected load phases is performed in the order of their indices with a frequency equal to the frequency of connecting the load phases to the network. 5 il. g

Description

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The invention relates to electrical engineering and can be used to control the power consumed by installations with significant process inertia, for example resistance furnaces.

The purpose of the invention is to reduce asymmetry.

Fig. 1 shows one of the possible schemes for the power section of the device, allowing the proposed method to be implemented; Fig. 2 is a control circuit of the device of Fig. 1; Figures 3–5 are voltage diagrams, but they are lower.

The device (figure 1) contains a three-phase, star-connected load I with phases 2-4, keys 5--7, made on triacs. Switches 5-7 are included between inputs 8-10 for connecting phases A, B, C of the power supply network and one of the terminals 2-4, the other terminals of which are connected to input 1I for connecting the neutral conductor.

The device control circuit (FIG. 2) contains bus 11 control number codes, permanent storage devices (ROM) 12-14, multiplexers 15-17, ring counters 18-20, analog switches 21-29, shift registers 30-32, zero indicators (NI) 33 35, T-triggers 36-38, elements AND 39-41, elements 42-44 of delay, single-oscillators 45-47, formers 48-50 pulses of control of triacs, conclusions 51-53, signals from which: are supplied to the control electrodes of the keys 5- /, respectively.

The device according to the proposed .v method works by following the image (tm.

At the first stage of adjustment (Fig. 3) for an interval; above regulation t, - tj, control pulses are applied to turn on, for example, key 5. Key 5 is turned on for the time T c, connecting phase 2 to phase voltage of the CDR network.

In a subsequent adjustment step, the 12 - t l drives the control signals to the next key. Thus, in the case of direct alternation of load phase indices, control signals are supplied to key 6. Key 6 is turned on, connecting phase 3 to the phase voltage and the supply network. Then the control signals are supplied to CL1 1h 4, connecting phase 4 for the time Tg to phase voltage, Yes

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The next sequence of operation of the simistors is repeated.

At the second stage of regulation (Fig. 4), LMpuls of control is applied to switch on key 5 for time T, and KjijiiMa 6 for time T ,,. As a result, phase 2 of the load is connected to the power supply CHD for a time

1 rll 1

T

and phase 3 is for voltage 11

 lia postpitage (its network for the time of the next adjustment interval serves control pulses for switching on key 6 for time Tp, and key 7 for time Tg. As a result, load phases 3 and 4 are connected to the supply mains of the network for Tp and T .

 in the subsequent adjustment interval, control pulses are applied to turn on the triac 7 for time Tp, and triac 5 for the time Tg. As a result, phases 4 and 2 of the load are connected to the phases of the mains supply, respectively, for the time Tp and Tg. Further the sequence of work of triacs continues.

At the third stage of regulation (Fig. 5), in the first adjustment interval, control pulses are applied to turn on keys 5 and 6 for time Tp, and switch 7 for time T. As a result, phases 2 and 3 of the load are connected to the supply mains phases for time T- and phase 4 - for time T. In the second repetition interval, control pulses are applied to turn on keys 6 and 7 for time T., and key 5 for the time Tg.

0 As a result, phases 2 and 3 of the load remain connected to the network for the time Tg and Tp, respectively, and phase 4 is connected to the network for the time T. In the subsequent repetition interval

control pulses are supplied to turn on keys 5 and 7 for time Tp, and key 6 for time Tg. As a result, phases 3 and 4 of the load remain connected to the network for time T and T, respectively, and phase 2 is connected to the network for time T. Further, the sequence of operation of the keys 5-7 is repeated.

Similarly, the control of a three-phase load connected to the interphase voltage of the supply network is carried out.

The control circuit of the device (Fig.2) works as follows.

313

When the voltage A, B, C of NI 33-35 is applied to the terminals 8-11, cifflx-pulses are generated at the time of the passage through zero of the phase voltage Tsdo Ueo, respectively. The frequency of these pulses is equal to twice the frequency of the supply voltage. The pulses are fed to the inputs of the corresponding T-flip-flops 36-38, at which point there appear pulses with a network frequency. These pulses are applied to the inputs of the ring meters 18-20, which control the address inputs of the respective multiplexers 15-17. The inputs of the multiplexers 15-17 are supplied with the bit information embedded in the ROM 12-14. The selection of the number of the ROM slot with the code recorded for the multiplexer in it is determined by the digital code set on the address inputs of the ROM (on the control signal code bus 11). Information from the ROM is read at the moment the pulse arrives from the output of the corresponding T-flip-flop at the input Rip sampling ROM. The information contained in the ROM determines the triac control algorithm.

Let the enabled state of key 1 correspond to the enabled state of keys 5-7

0-1 / 3 1 / 3-2 / 3 2 / 3-1

at the output of multiplexers 5-6. The key management algorithm provided by the ROM can be represented in parallel with a parallel-digit digital code, for example, 11 ... 10..00. And with an increase in the control signal at the outputs of the ROM 12-14 signals Log. 1 appear sequentially in proportion to the adjustment signal. The most obvious thing can be shown by the example of power control of the load (see table).

Claims (1)

Invention Formula A method of quasi-continuous power control, consumed by a three-phase load, by changing the number of phases of the load and the integer number of periods for which the phases of the load are connected to the terminals for connecting the mains phases for a given adjustment period multiple to the integer number of mains supply periods that, in order to reduce asymmetry, cyclical alternation of connected load phases is carried out in order of following their indices with a frequency equal to the connection frequency. 1..10..00 0000 0000 111 11..JO..OO 0000 111 11111 I .. 10. .00 ( + WITH -with Irj "Vj WITH  ъ and ) t5fc