LC Filter for three phase inverter

Marc Sugrue

Joined Jan 19, 2018
222
Hi Marc,
When I use the DC source instead of the rectifiers output the waves are clean from both the current and the voltage.Does this mean the problem is with the rectifier ?
I have not connected any control elements so far, all I was trying is to connect the rectifiers output to inverter and get clean waveform.
Hi Prithvi,
You need to look for the source for distortion under rectified AC conditions. To my mind its either your rectified voltage waveform has significant 500hz ripple which is passing through your converter and modulating on top of your 400hz or your reference sine driving the HBridge is corrupted on AC.
 

Thread Starter

Prithvi10

Joined Apr 1, 2019
31
Hi Prithvi,
You need to look for the source for distortion under rectified AC conditions. To my mind its either your rectified voltage waveform has significant 500hz ripple which is passing through your converter and modulating on top of your 400hz or your reference sine driving the HBridge is corrupted on AC.
Hi Marc,

I tried simulating the rectifier separately and found that the input ac current from the three phase source is getting disturbed when i connect the inverter to the rectifier. Could this have something to do with the problem i am facing?
i have attached the waveform of the ac input current to the rectifier with and without the inverter.

Thank you
 

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Marc Sugrue

Joined Jan 19, 2018
222
Hi Marc,

I tried simulating the rectifier separately and found that the input ac current from the three phase source is getting disturbed when i connect the inverter to the rectifier. Could this have something to do with the problem i am facing?
i have attached the waveform of the ac input current to the rectifier with and without the inverter.

Thank you
Hi Prithvi,
The inverter is a nonlinear load so to keep a sine current on the input you would need a power factor correction circuit or whats known as a preregulator. However, your current waveforms goes back to post #3 from WendallB, your input waveforms are identical. I'm not sure that would be sensible at your power levels as the losses and harmonics would be awful. I see you have opened a new thread on this subject but at present you need to roll back to rectifier and 3 phase resistive load and check your input currents are rectified sine wave, then add a LC filter to make it DC then look into power factor correction.
 

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Last edited:

sparky 1

Joined Nov 3, 2018
756
My understanding is first start off with a small scale low distortion reference wave at single phase.
The three phase correction uses plan "A" , plan "B" and plan "C" to ensure fail safe implementation resulting in reference match.
The first attempt to correct must not interfere with A,B or C. So that if A fails go to B go to C go to A and B ect
The link established will sync and reset smoothly.

A sample of the genset output is stepped down and compared to the reference.
Each of the phases are simultaneously adjusted. The PWM interacts with drive source.
For example a MEP831A is studied regarding filtering 3 phase.
As a DUT the 831 under load with various noise injected results in a compromised power source.
The power source is operating within it's power rating but is ragged and requires plan C.

On a job site I have seen long extension cords, compressor and power tools in this case the power rating had exceeded
the genset's ability to handle when the compressor turned off the collapse of the field sent a surge back to the power source.
This example is intended to show how the smaller events can introduce the need for keeping the magnetic component even.

Because the alternating Current is being examined an appropriate conversion using a coil is connected to channel A and the voltage on B each leg connected individually to simplify having all phases at once. Having three separate colors is easier to keep them straight.
The software looks promising.
 
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tsan

Joined Sep 6, 2014
138
Do you still use the circuit shown in psim.docx, where star point of load resistors and filter capacitors is grounded? Then you might have a circulating current path to supply side ground point, which mess up the intended operation. circulating_current_path.png
 

Thread Starter

Prithvi10

Joined Apr 1, 2019
31
Do you still use the circuit shown in psim.docx, where star point of load resistors and filter capacitors is grounded? Then you might have a circulating current path to supply side ground point, which mess up the intended operation. View attachment 208219
Hi,

Yes I use the same circuit. Oh ok, then I'll remove the ground from the filter , am I crct
Mr.Tsan ? and run the simulation and check the output.
 

Marc Sugrue

Joined Jan 19, 2018
222
Hi Marc,

I ll do as you told and comeback.

Thank you
No worries, best to move left to right on you schematic and get a better understanding at the same time of how it works. You can resolve the issues step by step once you understand whats happening. If your rectifiers don't work properly on AC then thats the first thing to fix. You have my sim to try and copy and you can build from there you'll get there. It'll take a bit longer but thats life. Biggest issues are caused by doing too much too quickly ;)
 

tsan

Joined Sep 6, 2014
138
Hi,

Yes I use the same circuit. Oh ok, then I'll remove the ground from the filter , am I crct
Mr.Tsan ? and run the simulation and check the output.
Or measure the current on the ground connection to see how much it is.
This is my Inverter output when I use DC source as an input.
But when i connect the inverter inputs to the rectifier output, then the waveform of the current is distorted
This indicates that modulation is ok so I started to think, that perhaps ground circuit is different on DC version and rectifier version.
 

Thread Starter

Prithvi10

Joined Apr 1, 2019
31
Hi All,

I thank everyone for spending your valuable time to reply to this thread. I got my issues solved. Thank you for the valuable info you all have given me. I appreciate the effort you all have put in resolving the issue. Thanks for being patient with me.

Thanks to
Mr. Wendel
Mr. Marc,
Mr. Tsan,
Mr. Sparky1

Stay safe. Bye.

Regards
Prithvi
 
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