Cascading dc-dc boost converters

[ee01akk]

Hi,
Does anyone know how you cascade boost converters together to step up from 12V to 340V d.c.? Can anyone explain why the d.c. equivalent of 240V r.m.s. is 340V d.c.? Do you use a special formula?
Thanks for any help you can provide.

 

[Aoxomox]

the mains power follows this function:

U(t) = Up * sin(w* t)

the rms value is the root mean square value of this time signal. this is a unit that discribes which DC voltage will dissipate the same power in a ohmic resistor as the AC voltage. (almost this).

Urms = 1/T integral (from 0 to T) [ U²(t) dt ]


When rectifying a DC voltage with a diode and a capacitor the diode will always conduct when the AC voltage is higher than the actual voltage over the capacity. So the capacitor will be loaded up to the maximum voltage available from the AC power. This is if you look at the first formula Up, the amplitude of the sine function.

when integrating a sine function and calculating Urms the functional connectiong is the squareroot of 2.

Up = Urms * squareroot(2).

just found this:
https://www.yokogawa.com/gmi/pdf/4sg_tm/Bulletin/Bull-DMMglossary-E.pdf


when cascading two or more DC-DC converters you must be carefull that both devices consume the same power from the primary. Otherwise the primary voltage of one converter can be much grater than the other one. It is very important to have a symmetric load distribution and may be an active compensation to reduce the stress of these converters.

Hope it helps

aOxOmOx

 

[Tornado]

Hi ee01akk, you have post in 2 different topics, that's hard to catch with
you, can you stay in one place so we will be able to help you? Thank you.

What is the output current and switching frequency?

Tornado

 

[sisc1525]

I think it's difficult to understand!

 

[ee01akk]

The output current of the boost converter is about 7A and the frequency is 25kHz.

 

[Tornado]

Here are some guidelines for a single stage:

Vin_min = 12.0V Vin_max = 12.0V Vin = 12.0V

Vout = 340.0V Iout = 7.0A f = 25.0kHz

L = 5.83µH Delta ILfor Vin_min = 79.5A

As you can see the currents are huge and you need very big
Mosfet(s) to do that, also the coil is huge too.

In to stage design my results are still very high

My opinion is you have to use a transformer.

 

[tgq]

obviously ee01akk tries to re-invent an inverter
cascading boost converters is a wrong idea for such a device, especially @ # 2 KVA output :?
use a transformer if you really have to build it yourself
my opinion is that its more expensive to build a 2 KVA inverter than to buy one