Boost topolgy has some drawbacks in my case. The Bus voltage must be 40-50V greater than 540VDC bus
Yes, three separate DC/DC isolators is of course an option. But you need relative large DC bus capacitors if you don't want to design the DC/DC converters for double peak power.
What do you mean by double peak power?
The PFC is supplying 100 Hz pulsating power to the DC bus, peak power is double the average power. If the DC/DC is sinking constant 1700 W from the DC bus, you get about 70 V ripple with 660 µF capacitors. This can work if the DC/DC achieves respective voltage regulation.
Comments about the schemativ in post #8:
1. There should be no filter capacitor after the rectifier. The pfc circuit must use the unfiltered rectified voltage.
2. For a buck pfc, there is a relationship between power factor and output voltage.
When the input voltage rises from zero, the buck pfc can't increase the input current until the input voltage is higher than the output voltage.
I think the current waveform (and power factor) will be bad for a 400VAC input and 350VDC output buck pfc.
I think the output voltage should be much lower to get an acceptable power factor for a 2000W buck pfc.
If I had the possibility to achieve better efficincy for the PFC-Buck stage for 48VDC output voltage, it would be possible to use semiconductors with 100V breakdown voltage and much more important it would be possible to go beyond 400-500kHZ switching frequencies for the cascading phase shift converter.
I don't understand this. Why would 100V breakdown be enough for a 48V output buck pfc?
I think the semiconductors must withstand almost the same voltage as for a boost pfc.
The input of the PFC-Buck is 540VDC. And the regulated PFC Buck converter output is 48VDC. The difference stays on the PFC-Buck inductor, the more energy you store on the buck inductor the more effective is the power factor correction.
Sorry, that's not right. The inductor has 0 V at start up, so all of the rectified bus must be on the semiconductor.
If the inductor does carry all of that voltage, as you suggest, the change in voltage across the inductor during charge or discharge has to be limited to less than 48V. Not a good limitation if you want efficiency or PFC or both.
Back in post #7, FvM wrote "There are examples in literature like the swiss rectifier which can be seen as a current bus complement of the vienna rectifier. "
I suggest you look up the Swiss rectifier - a quick look at an IEEE paper shows that it takes the rectified three phase and performs power factor correction sufficiently high to have good harmonic content.
Lower PFC output voltage corresponds to higher output current, higher semiconductor losses etc. The effect doesn't seem to be considered in your calculations. Higher buck voltage rates than 4:1 are generally undesirable.
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