Single phase SPWM Inverter

[sakthisudhursun]

Hello!!!.

Presently I am working in Single phase inverter for my mini project.

I am Using IRG4PH50UD IGBT from IRF and IR2111(Half bridge with fixed dead time) as driver.

The DC Bus to be operated is 460V.

Upto 150V of DC bus the Output voltage is coming close to theoretical value. But after that there is a huge difference of output voltage around 40V from theoretical value.

Presently I am using +15V power supply for IR2111. Gate resistance of 10 ohm.

What could be the fall in voltage when I operate at higher DC bus.

My switching frequency is 4kHz. SPWM is generated with the help of DSP F2812.

Please help me in debugging this.

 

[pradhan.rachit]

What is the voltage drop accross the Collector and Emitter of the IGBT that you are getting?
Also Vge(th) for your IGBT is 6V. Even though you are supplying your driver with 15V...Is the gate of your IGBT receiving above 6V?

 

[sakthisudhursun]

Thank you for your reply.

The drop across the device is typical:2V and max is 3.6V as per data sheet. while testing I didn't checked this but.

Surely my input voltage is greater than Vge(th) since between DSP i have connected one buffer and Optocoupler(TLP 250). Optocoupler output is 15V when measured for logic1.

Could you please provide some suggestion

 

[pradhan.rachit]

Possibly a problem in your DSP program?
Is your duty cycle varying sinusoidally ?

Also i think you should measure the forward voltage drop!

 

[sakthisudhursun]

DSP Program is correct since upto DC bus voltage of 150V output is coming correctly. only higher DC bus voltage problem exists.

Can you tell me how to measure forward voltage drop of switch.

Is more gate charge (current) for higher Vce required for IGBT?

Please provide suggestion.

- - - Updated - - -

DSP Program is correct since upto DC bus voltage of 150V output is coming correctly. only higher DC bus voltage problem exists.

Can you tell me how to measure forward voltage drop of switch.

Is more gate charge (current) for higher Vce required for IGBT?

Please provide suggestion.

 

[pradhan.rachit]

IGBT is a voltage controlled device with a very high input impedance. So the gate current is not a crucial element.

For checking the forward voltage drop, Adjust the DC Bus to the 400V. Adjust the multimeter at around 200V DC (Whatever is your measurement scale) and place the two probes between Collector and Emitter of the IGBTs.

What configuration of the inverter are you using for DC-AC conversion?

 

[sakthisudhursun]

I am using single phase full bridge unipolar SPWM.

Also I measured the voltage between collector and emitter it gave me 0.5 of DC bus voltage not the drop across it.

Then what about gate voltage? I have initially used +15V for supplying gate. today I changed to +18V around 10V output is increased. But still the output voltage difference (between theoretical & practical) at 400V is 26V which is intolerable.

Could you provide suggestion?

 

[pradhan.rachit]

Measuring the voltage between the Collector and Emitter is going to give you the voltage drop across the IGBT.
By saying 0.5 of DC Bus, do you mean half of DC Bus? Or do you mean 0.5V?

Make sure you don't increase the gate voltage more thane 20V since it will exceed the maximum rating on the datasheet.

 

[sakthisudhursun]

I mean to say half of DC bus.

Yes I am not increasing beyond 18V

 

[pradhan.rachit]

If Vce is half of the DC bus then the IGBT is not turning on!!
When the gate is at logic level 1, there should be minimum voltage drop on the IGBT which is not in your case!
Is it the same case with all of them?

 

[sakthisudhursun]

I have conncected the output from single phase SPWM inverter to a single phase transformer of 1:1 turns ratio.

And the secondary voltage I am getting more than primary voltage (i.e) I am getting a boost.

How could it is possible, since due to lekage inductance of transformer the secondary voltage should be less than primary voltage.
can any one through some light on this issue