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3 phase inverter with SCR

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miso156:
Hello,

I would like to build a 3 phase inverter from old SCRs to control 12V car alternator running as a motor.
My expectation is to use typical 3 phase inverter:



With waveforms:



Are SCRs able to handle frequency from 30 to 100Hz and current about 50A?
If I connect more SCR parallel, can imbalance couse some problem, or do i need to put some serial resistance for every of them?
What is the typical way how to turn SCRs off?
Is possible to use some LC tank to force current to zero and turn the SCRs off?
Do I need to maintain V/f ratio? Means when the phases are swithed with lower frequcency I need to apply lower Voltage.
Can be lower voltage obtained by shorter pulses?

Thank you.

Ground_Loop:
How will you turn off the SCRs

miso156:

--- Quote from: Ground_Loop on February 06, 2020, 08:34:08 pm ---How will you turn off the SCRs

--- End quote ---

LC resonant circuit in series or in paralell to SCR will decrease the current under holding limit and turn it off. Or by adition SCR and discharging capacitor. See comution classes of SCR turning off.

jmelson:
How do you commutate those SCRs?  You can apply a gate pulse to turn them ON, but you can't turn them off until some combination of input waveform and output voltage/current
allows each SCRs current to pass through zero.  I can't see anything that would turn them off with a DC input.

Jon

james_s:
Is there a reason you want to build something with 1970s technology instead of just buying one of the many cheap and readily available brushless DC motor controllers that are available?

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