Body
Hi Sven,
As your circuit has two SCRs two more SCRs are needed for switching off the original two SCRs. The switch-off SCRs have to have the cathodes in common and the shorting capacitor between the anode of a main SCR and its switch-off SCR.
If using this scheme of not totally discharging the capacitors it must be ensured that the voltage from the ferro resonant transformer doesn't keep charging the capacitors to some destructive voltage. That is the output from the ferro resonant transformer must not work as a current source. Perhaps this isn't a problem. Else some controller or protection circuit is needed to prevent the voltage from increasing above the component ratings.
Regards
Ole
---In [email protected], <s.friedrich@...> wrote :
Hi Ole, a capacitor inverts the polarity in the AC circuit in my case not suitable for commutation. you could not cancel the inversion by switching 2 capacitors in the row and there parallel to the Scr anodes. I switch negative and positive with a parallel scr inverter is always switched positive. Greetings Sven
Von Samsung Mobile gesendet
-------- Ursprüngliche Nachricht --------
Von: "onielsen@... [EVGRAY]"
Datum:02.03.2018 22:03 (GMT+01:00)
An: [email protected]
Betreff: Re: Aw: Re: Re: Re: Re: AW: [EVGRAY] Re: "Impressive"!
Hi Sven,
"To get SCR easy to go to 0 current: parallel a second capacitor to SCR circuit that discharges parallel to SCR path as internal current goes to 0 SCR switches off "
This is class C switching here: https://www.electronicshub.org/scr-turn-off-methods/#Class_C_Commutation https://www.electronicshub.org/scr-turn-off-methods/#Class_C_Commutation
When SCR1 is turned on the capacitor C is charged through the resistor R. Then when SCR2 fires the positive side of the capacitor is brought to the cathode potential or close to that potential. The negative side of C is then at a negative voltage with regards to the cathode voltage. This makes the current through RL go through the capacitor until the capacitor is discharged and then charged in the reverse direction which shuts of SCR1. SCR2 is then conducting keeping the positive side of the capacitor at the cathode voltage while the negative side is charging to the positive Vdc voltage through RL. Next time SCR1 fires we are back at the beginning once again which shuts off SCR2 by bringing the positive side of C that was at the cathode voltage down to a negative voltage with regard to the cathode voltage.
"Hector has written that you can discharge such a thyristor quickly."
That is the capacitor or the inductor that is discharged quickly. This is done by consuming the stored energy quickly which is done by choosing the proper impedance. For a capacitor to discharge fast a low impedance is needed. I.e. this gives big current. For an inductor to 'discharge' or demagnetize quickly the impedance must be high giving big voltage.
"I can not imagine anything circuit-technically under this description where this capacitor should be inserted."
The capacitor goes between the two anodes to be able to short the opposite SCR with the discharge pulse of the capacitor bringing the anode of the SCR to shut off to a negative voltage. This reverse biases the SCR thus forcing it to break the current.
""In PLUG switching we need to tailor CHOKE (reactor) to get switching to SCR at Max capacitor Plug
The VARISTOR alike to TUNE was in the Max Voltage turn on phase
peak ,,,
The Idea is to trigger at the top of the sine peak, were not reflective to AC Radiant source .. (reread Transverter Basics) "
Maybe you can explain these sentences to me."
This says the SCRs are to be triggered at max voltage which is when the capacitors are charged to max voltage and charge. This is also when the current reaches zero and if the connection is kept (no diodes) the current reverses to discharge the capacitors. Instead this is when the energy stored in the capacitors can go to the load and thus when the SCRs are to be fired. They must be finished discharging the capacitors before the cycle repeats. Either they must be shut off which gives a flyback voltage because of the inductance or the energy has to be consumed. To consume the energy requires the impedance of the load to be low enough to discharge the capacitors before the nest cycle starts.
If the load is too small (too high impedance) for the power generated the SCRs won't turn off by themselves. Higher load is then to be added (less impedance) for a faster discharge.
Regards
Ole
---In [email protected], <s.friedrich@...> wrote :
Sorry this ist right sentence:
To get SCR easy to go to 0 current: parallel a second capacitor to SCR circuit that discharges parallel to SCR path as
internal current goes to 0 SCR switches off .
regards
Sven
Gesendet: Freitag, 02. März 2018 um 20:23 Uhr
Von: "'Sven Friedrich' s.friedrich@... [EVGRAY]" <[email protected]>
An: [email protected]
Betreff: Aw: Re: Re: Re: Re: AW: [EVGRAY] Re: "Impressive"!
Hi Ole,
a transistor or mosfet makes the control more complicated and vulnerable, or you have to invest more in hedging.
Hector has written that you can discharge such a thyristor quickly.
SCR easy to go to 0 current: parallel to second SCR circuit that discharges parallel to SCR path as
internal current goes to 0 SCR switches off "
I can not imagine anything circuit-technically under this description where this capacitor should be inserted.
This description I also noticed that he uses a choke reactor here. So a coil to additionally influence the triggering of the SCRs!?!
"In PLUG switching we need to tailor CHOKE (reactor) to get switching to SCR at Max capacitor Plug
The VARISTOR alike to TUNE was in the Max Voltage turn on phase
peak ,,,
The Idea is to trigger at the top of the sine peak, were not reflective to AC Radiant source .. (reread Transverter Basics) "
Maybe you can explain these sentences to me.
regards
Sven ...