12vDC to 400V DC Boost converter for inverter application

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manojvalan

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12v to 400v

Hi Friends,

I am designing a transformerless inverter(800VA) for home application.I want to convert 12v DC /70A to 400VDC using a boost converter. I have some doubt to choose an inductor.To calculate a inductor value (L ≥ Vout x (1-D)/(ΔI x Fs) ) what will be my peak to peak inductor curent value.Is it 70A + ripple current.in this case what could be the size of a inductor.Please share your view.

Thanks in Advanced
 

dc-dc converter 400v

for a boost converter, the inductor size must be >= Vin*D*Ts/( il'), where il' = allowable inductor peak to peak ripple current.

this small signal current ripple will ride on the average current you are going to draw at the output. so, the peak output current = avg(output current) + il'/2.
 

dc dc converter 400v

It's surely no good idea to use a single inductor boost converter for this. Just consider that switching losses are roughly proportional to the switched power, which would be 70A*400V = 28kW. Also you need a switch transistor with 400 V capacity instead of 24 V for a transformer push-pull converter.
 

two stage boost converter

you will be operating at very high duty cycle. not a good idea. best is you use an invert operating at 12 v and then use a transformer.

hock
 

push pull boost converter

Hi Friends,

Thanks for your reply.Idea behind transformerless is to make a compact inverter :idea:

Code: 
 FvM: I...,. switched power, which would be 70A*400V = 28kW. Also you need a switch transistor with 400 V capacity instead of 24 V for a transformer push-pull converter

incase I go for a push-pull converter what will be my switching transistors maximum power(Is this also same as 28KW) .

Code: 
 hock: you will be operating at very high duty cycle. not a good idea. best is you use an invert operating at 12 v and then use a transformer
yes ,To convert 12v to 400v dc i need to have 0.9 Also please explain me about the invert operating at 12 v.
 

400v dc

Assuming ideal operation, switched power should be 24V*70A for a transformer push-pull converter. The transistor voltage rating should be higher because of leak inductance generated overvoltage. Generally, as a forward converter, it can be most likely build compacter than a boost converter, cause the magnetics hasn't to store energy.
 

12vdc to 400vdc

Hi manojvalan

To get 400V DC from 12V DC we need 97% duty cycle.Practically it is impossible.you should use highfrequency tranformer to boost up 12V DC to 400V DC.See below graph
 

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    manojvalan

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12v boost converter

The graph actually proves nothing. It's an empirical result from a specific application. 97% duty cycle in boost or flyback circuits is possible in general and even meaningful in some cases. 12:400 is a typical voltage ratio observed e.g. with a standard electric ignition system in a car.

But you're right anyway, in a practical sense, regarding the said application.
 

400v step up converter

Hi FVM

I saw your previous answer about boost converter duty ratio limitation.You told that you observed boost up of 12V DC to 400V DC with a standard electric ignition system in a car.

Let me know,are you not using high frequency transformer for that?let me know which type of boost topology are u using?

Practically 97% is not possible with simple boost converter,which is not using high frequency transformer.parastic elements of mosfet or igbt switches,inductor,boost diode..... etc limits the duty ratio near to 80%.

Thanks & Regards
Srinivas
 

boost converter duty cycle

I simply referred to standard ignition coil operation. It isn't a boost converter, cause the output voltage isn't rectified. However, I have designed small power boost converters with similar step-up voltage ratios.

Please consider my statement at the begin of this thread, why the high step-up ratio isn't maningful for power conversion. It's feasible generally, but with poor efficiency due to switching losses.

The shown graph doesn't state any operation conditions. It may be an empirical measurement under certain conditions, of course. But it's meaningless without revealing them.
 

converter and inverter

is better to do more to 2 stage elevation. i worked on hibrid dc dc converter since 100 vdc to 400 vdc, get this is complicated. regards.
 

12v dc booster

Hi Friends,

Yes, very well we can achieve 12:400v conververtion with multilevel boosting. But still i have a doubt that such a tansformerless design is advisible?? though we can get high gain and less loss(no transformer ) but we don't have any isolation.
 

12vdc to 400 vdc

A transformer solution can be expected to give highest efficiency, as previously said. Without the need for isolation, you are able to design a transformer with much lower leakage inductance.
 

Re: 12vDC to 400V DC Boost converter for inverter applicatio

hi,
Generally for such a high voltage conversion isolation is a must. Many topologies using high frequency transformer with reduced turns ratio are presented.
or else try for isolated boost converters!!!!!
 

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