ZVT for boost converter

[rakesh1987]

I have to design a boost converter with zvt for 4-stage interleaved boost converter for 700v dc output from 3ph supply of 415v,50hz, switching frequency 20khz

 

[prashan]

Can u give a detailed Description so that we can help... ZVT abbreviation??

 

[rakesh1987]

Can u give a detailed Description so that we can help... ZVT abbreviation??

Zero voltage transition

 

[mtwieg]

Four phases interleaved boost phases from a 3 phase AC feed? So are you talking about running four separate three-phase rectifiers in parallel and interleaving their switching? That sounds... absurd.

Also why would one care about ZVT if the converter is only operating at 20KHz?

 

[rakesh1987]

three phase ac is rectified and given to a 4 stage boost converter, for 4 stage boost only requires zvt actually the frequency is 80KHz, it is divided and given to each switch in boost. ZVT should be used since to reduce conduction losses as it is for 25KW power.

 

[mtwieg]

three phase ac is rectified and given to a 4 stage boost converter

Okay so you have a separate AC-DC converter (what kind, what output voltage does it give?). So the 4 phase boost converter is strictly a DC-DC converter, correct?

for 4 stage boost only requires zvt actually the frequency is 80KHz, it is divided and given to each switch in boost.

The 20KHz per phase is what matters, and that's pretty low for ZVT.

ZVT should be used since to reduce conduction losses as it is for 25KW power.

ZVT lowers switching losses, not conduction losses. Are you sure you're explaining this correctly?

Also what kind of FETs/IGBTs will you be using?

 

[rakesh1987]

i am using igbt, ya separate ac -dc converter output 700vdc how to design zvt?

 

[mtwieg]

i am using igbt, ya separate ac -dc converter output 700vdc how to design zvt?

You're still not being clear. You have a separate AC-DC converter that outputs 700V? Then what is the boost converter boosting to?

And for ZVT, only resonant converters can truly achieve ZVT. And that means you're not really talking about a boost converter at all, but some kind of heavy modification. Here's one paper that describes a relatively straightforward design: https://bbs.dianyuan.com/bbs/u/24/1102667932.pdf

Please note that in that paper they build an experimental prototype which operates at 300KHz. That's the kind of operating frequency at which techniques such as ZVT provide significant benefits. I doubt it's worthwhile at 20KHz, unless you are using truly enormous IGBTs with a great deal of output capacitance.

 

[rakesh1987]

iam using a three phase rectifier, input to rectifier is 3ph ,415v,50 hz, then output of this to a 4 stage interleaved boost converter , the gate pulse to each boost switch is from 80khz PWM generator dividing it and giving to each switch so each switch has a switching frequency of 20KHz, the output is a 25KW,700V load so whether i can use an ZVT circuit or not, is it not good to use the ZVT for 20KHz...

 

[mtwieg]

so whether i can use an ZVT circuit or not, is it not good to use the ZVT for 20KHz...

Whether it's a good idea or not isn't a simple matter. Soft switching topologies generally offer greatly reduced switching losses at the expense of often higher conduction losses, higher voltage stresses, and extra components. Thus they are more favorable in designs in which switching losses dominate overall losses, which is true of high frequency converters. For a low frequency converter, the added conduction and voltage stresses in soft switching may hurt more than the lack of switching losses helps. Finding out whether that's the case or now requires a lot of calculation and comparison.