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Project MOSFET H-Bridge to generate single phase signal

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Kai Xiang

Sep 4, 2017
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Hi Harald,

Thank you so much for your guidance. I have corrected the C2 position.

???
The frequency response of an RC lowpass filter is determined by the values of R and C and does not fluctuate and settle.
For this, I am not sure how I can go about doing it and how can I check the frequency of my circuit?
I looked at the frequency through the voltage probe. I wanted to set the output of the circuit to be at 50Hz. I really hope you can help me out.

My revised circuit below:
upload_2017-9-23_15-17-24.png


Please correct me if I'm wrong. To design a three phase circuit, I will need 3 identical H-bridge circuits as attached above right? Based on my research, a three phase mosfet circuit will only have a total of 6 mosfets. Does that mean I remove the p-type mosfet when connecting the three H bridge circuits together?

Thank you so much.
Regards,
KX
 

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Harald Kapp

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Obviously the period of your sine wave is approx. 40 ms as shown on the oscilloscope display. 50 Hz is equivalent to 20 ms. You therefore need to speed up the modulating signal by a factor of approx. 2.

Does that mean I remove the p-type mosfet when connecting the three H bridge circuits together?
Definitely not.
This is what a three phase H-bridge looks like (you need to scroll down the page a bit for a picture. I#T won't hurt to read the full article, though.
 

Kai Xiang

Sep 4, 2017
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Hi Harald,

The sine wave is now at 50Hz. Thank you so much!.

Understood on the three phase H-bridge. I will make three identical circuit to form the three phase H-bridge.
My current circuit:
upload_2017-9-30_17-46-7.png

The next step I'm going to do is to add in a step-up transformer.
I tried adding in but was not able to get the step-up voltage.
Please help me. Thank you.
Regards,
KX

upload_2017-10-1_14-57-22.png
 

Harald Kapp

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You haven't understood the operation of an H-bridge. The load of the H-bridge is where R5 is in your circuit. You place the primary side of the transformer ibto the circuit instead of R5.
 

Kai Xiang

Sep 4, 2017
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Hi Harald,

I am rather confused.
I replaced R5 with the transformer, is this what u meant?

upload_2017-10-1_16-48-45.png

I tried increasing the number of secondary coil but the wave changed and voltage drop instead.
Please help.

Thank you.
Regards,
KX
 

Harald Kapp

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Your measurement setup makes no sense at all. The secondary of T2 is almost short circuited by C2.
C2 at 1mF is a very low impedance for a 50 Hz signal. Remove it or choose a much smaller value to get some filtering of the switching noise from teh H-bridge.
Connect the oscilloscope across the two ends of the secondary of T1 (parallel to C2). As it is, you try to measure the voltage between the secondary of T1 and GND. This makes no sense.
 

Kai Xiang

Sep 4, 2017
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Hi Harald,

I am sorry for my lack of knowledge, I am trying my best.
When I removed C2 and replaced it with the Transformer, the output is no longer a reasonable sine wave. So I added in the LC filter and the signal is back. Is it correct to do it like this?

upload_2017-10-4_16-33-51.png

I had problems stepping up the transformer output voltage to 220V.
I would really appreciate your guidance and advise and really thank you so much Harald for patience and kind assistance.
Regards,
KX
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Harald, may I ask if my circuit at post #27 is acceptable?

I'd say no.

From the sense that I can make of it (and it is both badly drawn and has insufficient information as to the signal sources) your mosfets will likely either run very hot, or fail.
 

Harald Kapp

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Kai,
I'm sorry but the history of this thread shows a profound lack of knowledge with respect to electronics. Dealing with high voltages (220 V) and possibly also high currents poses a high risk of electric shock. Following forum policy I will therefore close this thread to further comments.

For your own safety: please use a professionally made off-the-shelf inverter. Do not pursue this venue of building your own.
 
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