inverter input and output

[Akshaydpal]

what will be the rms out put voltage of an inverter if the input is 240v DC?
how much input is required in DC to get a 240V AC rms output ?

 

[KlausST]

Hi,

How much water can you fill into a glass?

It depends:
* On your topology (half bridge, full bridge...)
* on output signal (waveform, single phase, three phase..)
* maybe on used filters
* output current
* input voltage stability
...

Klaus

 

[Akshaydpal]

pure sine wave inverter - full bridge - mosfets controlled by spwm signal 10Khz from Pic via mosfet driver . fliter used is LC filter
now what will be the output required in Dc to get 240v ac rms output? current will be around 5A output.

 

[FvM]

At least 240*√2, plus an add-on for transistor and filter voltage drops.

 

[KlausST]

Hi,

pure sine wave with full bridge.

I´m going back from the output:
* 240V RMS means +/-240V + sqrt(2) of peak voltage (abut 340V)
* the filter will have AC attenuation because of filter characteristic (even without load) --> therefore you need higher DC voltage
* the filter will reduce output voltage caused by: current x Filter_impedance (@ fundamental frequency) --> therefore you need higher DC voltage
* the Mosfet will reduce output voltage caused by I_mosfet x R_DS_ON --> therefore you need higher DC voltage
* Maybe you have wiring from DC supply to MOSFETs .. with impedance ... causing voltage drop --> therefore you need higher DC voltage
* Maybe your DC comes from rectified mains, then you will see a ripple on the DC path --> therefore you need higher DC voltage
* Maybe your DC comes from rectified mains, then expect that the mains voltage will vary (depending on your region) --> therefore you need higher DC voltage

* ...

We don´t have values for all the circuit.. therefore just an assumption:
Maybe go for 240V x 1.414 x 1.2 = about 400V (DC) then you have about 18% headroom for all the voltage drops.

Klaus

 

[abc_de]

very useful information1
I made 1 phase to 3 phase inverter for 3 phase motor but my inverter max output voltage was 170vac under no load condition VDC=325v
PWM switching at 10KHz
output voltage measured by analog meter
expected 220vac:thinker:

any idea
but commercial inverters gives 220vac
.

 

[FvM]

I made 1 phase to 3 phase inverter for 3 phase motor but my inverter max output voltage was 170vac under no load condition VDC=325v

Probably wrong modulation scheme. 3-phase inverters need to superimpose a common-mode system to phase voltages for full utilization of DC bus voltage. But even without it, you would achieve 199 Vrms with 325 Vdc.

 

[abc_de]

In my board i used scaler technique
Device is pic18f4431
Possible solution?

 

[KlausST]

Hi,

I made 1 phase to 3 phase inverter for 3 phase motor but my inverter max output voltage was 170vac under no load condition VDC=325v

With 3 phase inverters where the star point is not needed (motor application) you could optimize the output voltage when you modify the sine shape (referenced to star point)
If you do this correctely, then the phase to phase voltage is clean sine.

Klaus

 

[abc_de]

Please elaborate more
For inverter I Used spwm technique. By sine table

 

[Akshaydpal]

Please elaborate more

For inverter I Used spwm technique. By sine table

i used same method i.e sine table 10Khz Spwm using pic 16f877A @abc_de if your project is complete can you please share the circuit diagram i would like to know more about your project

 

[KlausST]

Hi,

https://www.infineon.com/dgdl/AP160...M.pdf?fileId=db3a304412b407950112b40a1bf20453

Klaus

 

[abc_de]

What problem you are facing in ur project?

 

[FvM]

Paragraph "3.4 SAPWM (Saddle PWM)" in the Infineon application note is describing the superimposed common mode system I mentioned in post #7. The explanation could be clearer...

 

[abc_de]

@fvm Any reference or calculation for third harmonic injection into fundamental wave

 

[FvM]

No reference, but a LibreOffice spreadsheet showing a possible generation algorithm (selecting the phase voltage with smallest absolute value, adding half of it to all phases. I'm using it in inverter PWM FPGA code.

 

[abc_de]

@fvm seems very useful document.
I will try this may be this will solve my problem

 

[abc_de]

Hello
I did some changes in sine look up table but out put voltage remain same 170vac for 3 phase inverter (phase shift 120, 240 degree)
But if do setup for 1 phase then output is 230vac expected ( phase shift 180 degree)
But what's wrong in 3 phase inverter output

 

[FvM]

We don't know why your inverter doesn't work as expected. Using suitable modulation scheme (said Saddle PWM, also flat-top modulation), you can achieve 230 Vrms phase-to-phase voltage with 325 Vdc bus voltage.