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Schematic and observation

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vanshajtaxali

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Hey
I am posting the schematic that i am implementing and also the observation on my oscilloscope and here are some points for better understanding
1) I am using STGW20NC60VD IGBT and the data sheet is attached also the diode I'm using for boot strapping and snubber are FR105 (datasheet attached as well)
2) The signal are the SPWM logic for a damping sinusoidal wave and whenever logic zero comes both low side are switched off to provide additional freewheeling path the bit rate of this PWM is 10khz
3) The value of inductor is not known(the biggest problem!!) but it gives a perfectly good sinusoidal wave at 10khz bit rate, i have attached the observations from my scope in a pdf
4) I am creating a SPWM text data file from c code consisting of 0,1 and-1 and then reading it via raspberry and hence controlling the GPIO .
5)I did not use the gate resistor because the outputs were just fine without them and have checked 100 times that there is no shoot through you can see it in the observation pdf as well...I have used no capacitor in parlell because when i did the current going back increased a lot
 

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  • Observations.pdf
    222.7 KB · Views: 48
  • 0900766b80db11b2.pdf
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  • 0900766b81298795.pdf
    192 KB · Views: 41

IMG_20160428_093451.jpg


I posted it along but i guess it didn't upload
 

you have no damping resistor going into your bootstrap caps...is your rail high-ish voltgae.....if so they are deffo needed.

- - - Updated - - -

and also if rail is high voltage, those bootstrap diodes must really be SiC ones.
 

and also if rail is high voltage, those bootstrap diodes must really be SiC ones
Don't think so. Bootstrap supply work well with fast rectifiers like US1M, even at 700 or 800 V bus voltage and surely over maximum IR21xx range.

It has of course disadvantages, have to decide if it's appropriate for a specific design.
 

oh well i agree US1M can do the job, but if i may say so, i believe your choice of damping resistor is more important, a little more critical, if you dont use a sic diode for bootstrappers.
 

I have to just use the supply to maximum 450V and presently im just operating it on 10-35V
 

could you please simplify the term i am not able to get you !:thinker:
 

I am now able to run the circuit up to 60V getting a good sinusoidal of 7.5A peak current but my power supply still read max 1.8A at this situation....couldn't understand why
 

Hi,

more details please:

I assume: power supply 60V DC and 1.8A DC. This gives 108W.
Load: 7.5A peak, sinusoidal = 5.3A RMS. But what voltage? And what load?

Klaus
 

Hey
Thanks for your reply and calculation are exactly correct but i am in a bit of a tight situation because i don't have the documentation for the load hence i could not give you the details...
but i think so i have figured the problem
If u see me observation carefully you will observe that 1st half of each high side cycle is kinda distorted actually what happening there is that i am getting a momentary shoot through and after the half when it becomes normal...so the problem is
1) Why i am getting shoot through only after connecting the load?? as before connecting the load dead times and all are just fine.
2) What should I do to solve the problem of this momentary shoot through??

I will try and post another observation pdf for you
 

I don't understand how you conclude there would be "shoot through" in your circuit, except for the current consumption being higher than expected?

One problem with your circuit is that the inductive load is feeding energy to the DC bus during part of the AC cycle. Your measurement shows that the bus voltage is raised.
 

Yupp you may be right and at this point i cannot deny your fact also let me make analysis again and tell you.... i overlooked it thanks for the hint
 

I am posting another set of observation (Observation2.pdf) where the current probe is set after the diode instead of placing it on the positive of battery just for the ease if you can conclude any thing from this.....i am confused at this point :-(
 

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  • Observation 2.pdf
    216.3 KB · Views: 45

hey FvM
Looks like you were right indeed i am getting inductive spikes at the beginning of every Pwm cycle...I removed the capacitor attached to the diode and tried to check the output and yupp i am getting spikes but it is only at the beginning of each High side PWM cycle....posting another pdf of observation please help me find a solution...
 

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  • Observation 3.pdf
    216.3 KB · Views: 33

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