# Three Level Flying Capacitor

## Main Question or Discussion Point

Hi All,

I would like to know what is the suitable capacitor value to be used in a three level flying capacitor(three-phase) with the input of voltage = 500V and resistance(load)=1K ohm while the inductance(load)=0.1H and also the switching frequency is 10KHz?

Can someone brief me on how to calculate the capacitor value? Sorry for the troubles,many thanks.

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meBigGuy
Gold Member
Sorry --- need more info --- Is this a tripler? Is it feeding 1K in series with 0.1H? What output ripple do you want to maintain.

The output ripple requirements, switching frequency, and load currents generally drive the capacitor size based on the basic relationship between capacitance, current, and voltage.

There are numerous tutorials on the considerations, starting with doublers. For example http://www.analog.com/static/imported-files/tutorials/ptmsect4.pdf [Broken]

Last edited by a moderator:
hereby i attached the waveform picture of npc inverter. here is the parameters that use for npc inveter.
__________________________________________________________________________________
DC Bus Voltage : 500 Vdc
AC Output : 250 V (line-line, rms), 60 Hz, 0.8 power factor (lagging)
Switching Frequency : 8 kHz
Capacitance : 2200 µF
Resistance : 1 Ω
Squirrel-cage Ind. M. : default
__________________________________________________________________________________

and here is the result that i get from simulation for npc inverter.
__________________________________________________________________________________
The following losses results are obtained from the PSIM simulation:
Diode Conduction Losses : 0236.54 W
Diode Switching Losses : 000.060 W
Diode Total Losses : 0236.60 W
Transistor Conduction Losses : 1868.69 W
Transistor Switching Losses : 0067.90 W
Transistor Total Losses : 1936.60 W
Total Losses per Module : 2173.20 W
Line to neutral voltage : 256 V
Line to line voltage : 499 V
Output current line A : 56.63 A
__________________________________________________________________________________

is it possible for me to get the exact waveform like 3 level npc 3 phase inverter, but using 3 level flying capacitor 3 phase inverter method? what would be the value for the capacitor and others? i also attached the schematic for 3 level flying capacitor 3 phase inverter. what should i put the value for all component?

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oh btw mr. meBigGuy, flying capacitor is for convert dc to ac, not stepping up voltage. :)

meBigGuy
Gold Member
I know nothing about them. Sorry

1 person
nah, it's okay bro. thank u for ur time! :)