DE1638600A1 - Procedure for operating an inverter - Google Patents

Description

Procedure for operating an inverter

The invention relates to.ein a method for operating a Inverter whose charging circuit is a parallel resonant circuit from the inductance of the consumer and a compensation capacitance with controlled valves, in particular thyristors, in a bridge circuit, each of which controls the valve diagonal bridge branches at the same time. The inverter is generally connected to the Output of a controllable converter connected. Such static frequency converters with thyristors are known well suited for inductive heating of electrically conductive material, especially for melting, annealing and Hardening of metal. The input line of the inverter New documents! Art. 7 § 1 para. 2 No. I Sau 3 of the amendment ^. v. 4.196

009844 / ΰ6Τ7 ^{Kln / Hü}

PLA 67/1452

..eriLhill t in; aLl ^ eraelnen a smoothing inductance, which is used to decouple the DC voltage source from the inverter.

In such an inverter feeding a parallel resonant circuit There may be * difficulties during commissioning because of the natural frequency and damping of the resonant circuit are not readily known. Z \ in the oscillation of the oscillating circuit namely need different physical conditions must be complied with at the same time. In a known arrangement Therefore, a special starting device is provided, which consists of a pre-flow device connected in parallel with the input of the converter for the smoothing reactor in the intermediate circuit and an oscillating device arranged in the load circuit. The gate current device contains a series circuit of a resistor it with a suitable switch, e.g. 3. a thyristor. Shortly before the inverter starts, the switch

switched on and the feeding DC voltage source supplies a bias current via the smoothing inductance of the DC circuit, which is determined by the size of the resistor. The _a starting device in the load circuit of the inverter contains a starting capacitor which receives a suitable charge from "an external voltage source" and is activated at the start via a suitable switch, e.g. a thyristor to which the parallel resonant _{circuit t is} switched. To start the parallel resonant circuit, the starting auxiliary capacitor is connected to the resonant circuit

- 2 -.: -. : A / Bg

0U984A / 06T7

BADORiGJMAL

£ PLA 67/1452

the inverter thyrietors supplies. Already with the first The thyristors of the assigned diagonal become half-oscillation der'Brückeschaltung ignited and take over the direct current flowing in the smoothing inductance. This launch device has the disadvantage that it represents a relatively large effort for the inverter.

The invention is based on the knowledge that essential additional facilities for the commissioning of said arrangement can be avoided if it is ensured that at the moment of starting the oscillation conditions for the parallel resonant circuit are met. To do this, the oscillating circuit must be during more energy is supplied to an oscillation than losses occurred in the previous oscillation. At the time of ignition of the thyristors responsible for the opposite current direction, the compensation capacitor must have a sufficient Charge and have the correct sign. In addition, the valves that go out are given a sufficient period of rest.

These conditions are met when according to the invention for Commissioning of the inverter the valves more diagonally Bridge branch at at least approximately Strom-Mull in the Capacitance can be ignited. To start up the inverter, you only need the current zero crossing to be recorded in the compensation capacitor. To this end

- 3 - '. ... Kin / Hü

0 0 9 8 LL / 06 1? _BA0

163860Ü

67/1452

the current can be measured directly or the current zero crossing can be recorded indirectly, for example from the Soheitelwert the tension can be derived. The invention is based on the consideration that the compensation capacitor in the Strömriüll passage currently has its highest charge and thus the ■ * Sufficient energy supply to the resonant circuit ensured is. When the current in the capacitor is zero, the thyristors of the other bridge diagonal ignited, the current jumps in the »Capacitor in the opposite direction to double the instantaneous value of the intermediate circuit current and then continues to oscillate in an approximately sinusoidal, angular manner. ·. "

After the beginning of the oscillation process, it is no problem possible to influence the control of the inverter in such a way that it works with the best possible power factor " the firing pulses for the thyristors towards · the zero crossing of the Moving the resonant circuit voltage, of which they are only one Maintain sufficient distance to prevent the inverter from tipping over to. avoid. Since in the practical operation of the inverter whose resonant circuit data and thus its operating frequency can change, a closed season control device can expediently for example, according to an earlier proposal (patent application S 108 879 VIIIb / 21d2-PLA 67/1166).

The operating method according to the invention can be based on a * Drawing explained in more detail; will. In Pig. 1 is the circuit of an inverter with a parallel resonant circuit illustrated. Fig. 2 shows a circuit with individual

\ -4-009844 / 0617 Kin / 3g

λ ■ - ■ -. ■ '■ - ■. ELA 67/1452

Components of the figure; T. In-Figure-3 are the current "and voltage of the resonant circuit as a function of the time t- in -a slide-."

gram shown. ^::] ■ - '. ^: - '■ -

FIG. 1 shows a known inverter with controlled valves 2 to 5, which can preferably be thyristors or a group of thyristors, the load circuit of which contains a parallel oscillating circuit made up of an inductance 9, for example the inductor of an induction melting furnace, and a capacitor 10. The inverter is; overfine: direct current intermediate circuit connected to a direct voltage source, which is shown as a rectifier and, for example, can be a controlled converter; DC circuit includes a smoothing 6, the inductance as large compared to the resonant $ ■ - can vreväen angeseiien-_-_ -. ', -: ■'_'-:

In Figure 2 is to explain the Anschwingvbrganges; 'a circuit ■. "". from / the Fig * 1 "d-arge.stel.l-tv which: the two; diagonally opposite valves 4 and 5, the smoothing throttle 6, the _; voltage source.7. and the parallel resonant circuit with the inductance 9 and the _: capacitor 1Ö- contains,; Λ7 ';' ^.: ..- .. "- ,. ■, '-. ■■ "" - ■ "- ^: "■:';'

According to FIG. 3, the arrangement according to FIG. 1 at time t _Q the valves 2 and 3 are given an ignition pulse. Then flows from the Gieichspannurig'squelie ^^ '. 7 over: "the choke 6 · and the thyristors 2 and 3 as well as in parallel over the inductance 9 and the capacitor 10 a steadily increasing current ± _z ,

. ■■ "- - ^: - - Child / 3g

ÖQ98U / 0617

which charges the capacitor 10 λ Mt increasing iaduiig of the capacitor 10, the current across the capacitor decreases. At the moment t. If the capacitor 10 has its maximum voltage, the current through the capacitor is zero and the entire intermediate circuit current i flows through the inductance 9. In this eye view, the thyristors 4 and 5 are ignited according to Pig »2 . The inductance 9 maintains its flowing current ir * which closes via the capacitor 10 as soon as the thyristors 2 and 2 go out. In addition, the current i flows in the choke ^. Via the thyristors 4 and 5, so that the current in the capacitor ViO to double the value of the load current i ^. starts up and the energy of the capacitor 10 swings around via the J> rossel * At time t "is the. Umschwingung terminated and the capacitor current i _n is zero, so that again the two other thyristors are fired 2 and 3 for the opposite ^{StromricLtung:} can. The firing of the thyristors in start-up operation thus takes place at the time of the maximum of the capacitor voltage

In order to achieve the highest possible amplitude of the first half oscillation, it is advisable to use the DC voltage for the ^; Select the starting process as high as possible. However, it can be withdrawn after just a few oscillations, making it impermissible

- ■■ '- ■■■ - ■ - ■ - ■ -. " ^J to prevent high intermediate current without oscillating circuit voltage.

A limitation control for the intermediate circuit current and the resonant circuit voltage can be used for this purpose. ^;

Es'i-ä't. 'According to this procedure, it is also possible to use a pre-flow device

ÖAD ORIGINAL

ELA 67/1452

to approach tung "The additional equipment in the load circuit of the known inverters are not required.

3 figures

5 claims

BATH

⁷ - 0098 4 4/0617

Claims (2)

The method ziim Ee-trleb a WechaelrichtÄra ,, deaaen .. Iiaatfenssia a Barallelsre & wiiigk-reia aua the inductance of the TerbraUfChÄra and a KompejisationsEcapacitor contains, with controlled; V / entÜen * in Brückenachaltüng ', van aind each of which controlled valves · s diagonal bridge branch "simultaneity, characterized gÄfcemizeieteet that for commissioning dea Wechaelrichters dte valves _(2; 3 or, ^ r- 5) tter diagonal Brüxslrenzweigie littleateita approximate: current zero in the capacitance (TQ) to be ignited * 2. Arrangement for the implementation of the method according to claim 1, " ^j characterized, that a S ^ trant— and- voltage: s: b: eegr« aizxin-gi provided iatv in Schwingkreia 3 ". Order; for the implementation of the procedure according to Anapruch: T. to operate a; a substitute judge, deaaen. Inputaleituiig; one Smoothing InduEtivity: contains, 'characterized by the fact that; one known Voratrom device for the- Glä tat (D) -vro rgeaehear iat «- -. " ORlQtHAL