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Registered Member #295
Joined: Tue Mar 07 2006, 06:59PM
Location:
Posts: 23
Prologue: while i have been a long-time member of 4hv (i think i've seen three generations of forums go by) but for the last year my automotive hobbies (crashing and rebuilding high-HP cars) and the workforce has consumed my every resource. only recently did i stumble across a set of 1000V 6300A (pulsed 10ms) E-puck SCRs i scammed off IRF , and now i have this urge to use them,you know how it goes. anyway, enough about me.
My actual question: i'm not sure how a diagonal half bridge is constructed using SCRs. I am not aiming to be able to control pulse lengths like most who build IGBT based H-bridges. i would however like to be able to recover some energy and hopefully in doing so reduce the fall-time of the pulse. all i'm looking for is a quick MSpaint sketch. i seem to recall that an H-bridge with 2 switches replaced with 2 diodes was supposed to describe a diagonal half-bridge, but looking @ it i cant see how it would function. and yes, i have googled and searched the archives, but bridge topology information is really hard to come by.
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Are you referring to the (in)famous SCR V-switch? I don't really know how a scr halfbridge would work, in particular, how can we switch off the current allowing the energy recovery. Without a system that turns off the current the SCR-s will turn off only when the bank is discharged at 0V (really -2 * Vdiode drop). After that, the residual current (that can be high up to 100-200A depending on L,C and R) will reload the capacitors, but it is no more than 10% of the original stored energy, and, most important, it turns off slowly.
Registered Member #295
Joined: Tue Mar 07 2006, 06:59PM
Location:
Posts: 23
i dont actually want to switch off the current in the coil, i realize the (unfortunate) limits of SCRs, i was instead just going to wait for the coil current to fall to zero (an underdampened coil would have a sinusoudial current). hopefully the SCRs are fast enough to turn off during the zero-crossing. now i just need a configuration that allows the reversed current to recharge the caps (with the correct polarity to avoid a catastrauphic failure).
so what does a simple diagonal half-bridge look like?
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
for the current to drop to zero, all the energy from the inductor is going to charge up the cap backward. I dont' see how a diagonal half bridge would work using SCRs.
Registered Member #295
Joined: Tue Mar 07 2006, 06:59PM
Location:
Posts: 23
Perhapes i can't see past my own logic, but for the energy stored in the coil to "re"-charge the capacitors backwards there needs to be a reversal of voltage, meaning the voltage will decrease, pass, zero, and THEN increase in magnitude with the opposite polarity. and if the voltage drops to zero, then the current must also (out of phase obviously as we talking inductors) drop to zero before increase in the opposite direction. what am i missing?, i cant be the only one with this logic.
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Applying an SCR based diagonal bridge to simple coilguns
, and now i have this urge to use them,you know how it goes. anyway, enough about me.
