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First of all, be careful about how you describe the converter. A full bridge can be phase shifted or PWM controlled, and both can be "hard switched." The phase shifted bridge however can usually be made ZVS over a limited line/load range. But they're all basically the same converter, just with slightly different control schemes.But supposing that this was done with 4 paralleled CCM boost PFC's.....into 4 paralleled plain full bridge converters...is there any reason why that wouldn't be a perfectly satisfactory solution?.....I mean, why is nobody on the web doing it like this?
It should be nowhere near the switching frequency, unless your parasitics are enormous for some reason. Like factor of five lower at least.The big killer for Phase shift full bridge with high voltage output is the high ringing that you get across the output diodes due to the high leakage inductance...this is a ring with a frequency near the switching frequency so is difficult to snub out....
A properly operating ZVS PSFB should have much less high frequency ringing than a hard switched FB, since it's hard switching that excites those sharp edges.you don't get this problem with plain full bridge and transformer interleave wound to reduce leakage inductance.
First of all, be careful about how you describe the converter. A full bridge can be phase shifted or PWM controlled, and both can be "hard switched."
Perhaps., let's see. For both, the waveform applied to the transformer primary should be exactly the same, so the primary current should be exactly the same. The only difference is the switching sequence of the FETs used to achieve the waveforms.thanks, I hear what you say, but do you agree that if the Phase shift full bridge is hard switched then it has much more switching loss than the plain full bridge?
If a PSFB is actually hard switched, then the diodes are never given time to conduct, period. Shoot through is possible, but only if you screw up badly.This is because in the PSFB, if it hard switches, we get horrendous effect of the higher fet switching ino the reverse recovering low-side anti-parallel diode, which gives an enormous shoot through current, and this doesn't happen with a hard switched plain full bridge smps, because the plain full bridge never has fets switching on into the reverse recovering diode because it doesn't have the primary circulating current seen in the PSFB?
Perhaps., let's see. For both, the waveform applied to the transformer primary should be exactly the same, so the primary current should be exactly the same.
SiC diodes have very high forward voltage, and since the current in the diodes is actually more with a PSFB than a plain full bridge, we wouldn't want to use sic diodes.the phase shift full bridge can be used for HV outputs, e.g. 400V just need good SiC diodes 1200V and snubbers...
Right, I forgot that the net magnetizing current is identical, but the primary/secondary currents are different, my mistake.Thanks, but I am sure you agree that the current waveform in a PSFB and a Plain Full Bridge are very different, and this is due to the freewheeling current, and the lower di/dt on the transitions with the PSFB
Note that the switching loss in the PWMFB depends on the voltage at each leg just prior to turn-on. Since the primary ringing in your PWMFB is very underdamped, this means that depending on the exact duty cycle, that voltage may be near either supply rail, and you may actually see ZVS if you're lucky, and your switching losses will be misleadingly low (or high, if the voltage happened to be at the opposite extreme). But it's not plausible to see that ZVS consistently, so you have to take your switching loss measurements with a grain of salt.The non-ZVS PSFB has switching power dissipation peaks which are 5 times higher than the plain full bridge.....this appears to confirm that the PSFB, when in non-ZVS behaviour, has far higher switching loss than the plain full bridge.
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