Hi there ,
My single phase PWM Inverter does not result Pure sinusoidal, In order to make Sinusoidal Suggest me Filter design Calculation L= C=?



Thanks
Janardhan

 

There is a problem. Doing a passive filter for power applications (50-60 Hz) requires values that are difficult to achieve in practice. What is the frequency of the PWM? Some loads may actually be fine with a PWM signal.

 

Hi there ,
My single phase PWM Inverter does not result Pure sinusoidal, In order to make Sinusoidal Suggest me Filter design Calculation L= C=?
View attachment 197172
Thanks
JanardhanView attachment 197172View attachment 197172

What is the carrier frequency, and what is the fundamental frequency?
What is the voltage output and what is the max current output?

It will be hard to get a really really pure sine, but you can get close with reasonable effort assuming the PWM pattern is also reasonable.

Also it would be good to know why you need a pure sine, what is the application.

 

There is a problem. Doing a passive filter for power applications (50-60 Hz) requires values that are difficult to achieve in practice. What is the frequency of the PWM? Some loads may actually be fine with a PWM signal.

I did a trial design assuming 15 kHz carrier and 60 Hz reference sine wave, using a 3-pole Butterworth filter with the corner at 866 Hz. which required a 220 mH inductor. Checking Digi-Key shows that the part is obsolete and out of stock.

BTW -- before designing a filter you need an adequate specification which you conveniently omitted. Wassup?

One more thing. A passive filter designed for any particular impedance will have a 6dB insertion loss.

 

There is a problem. Doing a passive filter for power applications (50-60 Hz) requires values that are difficult to achieve in practice. What is the frequency of the PWM? Some loads may actually be fine with a PWM signal.

Thanks for the response The PWM frequency is 2400Hz, Fundamental Frequency =50Hz

 

What is the carrier frequency, and what is the fundamental frequency?
What is the voltage output and what is the max current output?

It will be hard to get a really really pure sine, but you can get close with reasonable effort assuming the PWM pattern is also reasonable.

Also it would be good to know why you need a pure sine, what is the application.

Dear
MrAl
Thank you .
PWM frequency 2400Hz, Fundamental 50Hz

As my application is to feed current to the grid , Grid does expect a pure sinusoidal current , However I am looking for a (LC) filter design for current to become sinusoidal .I think voltage need not be pure sinusoidal( Pls help I dont know )
I am trying to inject a current of 10Amps from the inverter to the grid by using closed loop DQ0 theory

Thanks in advance

 

I did a trial design assuming 15 kHz carrier and 60 Hz reference sine wave, using a 3-pole Butterworth filter with the corner at 866 Hz. which required a 220 mH inductor. Checking Digi-Key shows that the part is obsolete and out of stock.

BTW -- before designing a filter you need an adequate specification which you conveniently omitted. Wassup?

One more thing. A passive filter designed for any particular impedance will have a 6dB insertion loss.

I did a trial design assuming 15 kHz carrier and 60 Hz reference sine wave, using a 3-pole Butterworth filter with the corner at 866 Hz. which required a 220 mH inductor. Checking Digi-Key shows that the part is obsolete and out of stock.

BTW -- before designing a filter you need an adequate specification which you conveniently omitted. Wassup?

One more thing. A passive filter designed for any particular impedance will have a 6dB insertion loss.

Thank you for the reply

Dear Papabravo,

Sorry for the insufficient data provided ,
PWM frequency 2400Hz,
Fundamental 50Hz,
230V rms
This filter(to be used ) is expected between inverter output and grid so that Inverter do not inject harmonics

Give me any online Lc Filter Design Link (if any that could readily calculate L and C values by providing info like PWM freq, Fundamental Freq, corner Freq )

 

Dear
MrAl
Thank you .
PWM frequency 2400Hz, Fundamental 50Hz

As my application is to feed current to the grid , Grid does expect a pure sinusoidal current , However I am looking for a (LC) filter design for current to become sinusoidal .I think voltage need not be pure sinusoidal( Pls help I dont know )
I am trying to inject a current of 10Amps from the inverter to the grid by using closed loop DQ0 theory

Thanks in advance

Oh what is your nominal DC buss voltage and i assume you are using an H transistor bridge.

 

Oh what is your nominal DC buss voltage and i assume you are using an H transistor bridge.

I work it this way that My DC bus voltage not less than (RMS 230*1.414) near around 330(please correct me if it is not the way)
And Yes it is H bridge with unipolar SPWM

 

it's my understanding, but I could be wrong, AC injection is done similarly as paralleling like DC supplies. Search for "HP power supply Handbook".

You would use a current source topology with a voltage limit just slightly above, "the measured voltage".
So within 230 +-10%, your current source would drop out.

I don;t know EXACTLY how it might work.

With a master/slave DC supply, one is configured as a voltage source say 1 V below the voltage you want. the other is configured as a current source with a voltage limit of the desired voltage. These would be say two 12 v 10 A power supplies that you want to deliver 12 V at 20 A.

 

In no respect what is the form of input signal, if one filters out solely the first harmonic frequency, the output by definition will be sinusoidal. Thus, make a good filter and shall obtain a good sinus. How - most often the cheapest and technologic is Sallen-Key. However in heavy duty power configurations nothing more appropriate as simple LC tank is not invented yet.

 

I work it this way that My DC bus voltage not less than (RMS 230*1.414) near around 330(please correct me if it is not the way)
And Yes it is H bridge with unipolar SPWM

I am afraid that is not a good enough description.
For one thing, the DC bus voltage has to be HIGHER than 230*1.414*1.15 or else you may find unexpected times that the unit does not deliver power to the line.
The second thing is, in order to figure out what size an inductor would have to be (or other filter) we have to know the differential between the instantaneous line voltage and the instantaneous DC buss voltage.

If you filter the switching frequency then you automatically filter the higher harmonics with an even greater attenuation as long as the filter acts like a low pass.

 

I don't know details about my grid because it is very reliable. During the few times it has failed we cheer and have a party in the dark.

1) Do you have a circuit to detect grid failure then it automatically connects your inverter or do you do it manually yourself?
2) When you connect your inverter to the grid, how do you know if an electricity worker has disconnected it so he can work on it then you zap and kill him?
3) If the grid fails and your inverter is powering every home and business in your city then isn't it overloaded?
4) When your inverter is powering the grid and the normal grid power returns then isn't there an explosion?

 

I don't know details about my grid because it is very reliable. During the few times it has failed we cheer and have a party in the dark.

1) Do you have a circuit to detect grid failure then it automatically connects your inverter or do you do it manually yourself?
2) When you connect your inverter to the grid, how do you know if an electricity worker has disconnected it so he can work on it then you zap and kill him?
3) If the grid fails and your inverter is powering every home and business in your city then isn't it overloaded?
4) When your inverter is powering the grid and the normal grid power returns then isn't there an explosion?

Line tied applications do not tie in when the line goes down, they tie in when the line is active ONLY.
Any other times presents a danger to people working on the line.
There are various associated logistics for tie in and out.

Also, most AC converters have to have current limit. If they dont they fail quickly.

 

Hi there ,
My single phase PWM Inverter does not result Pure sinusoidal, In order to make Sinusoidal Suggest me Filter design Calculation L= C=?
View attachment 197172
Thanks
JanardhanView attachment 197172View attachment 197172

If you have not already, I strongly suggest you get in contact with whatever organization manages/owns the grid into which you wish to tie. I am inclined to believe that all grid managers have, as mine has, published detailed requirements for equipment that will tie into the grid. Failure to comply with those requirements/regulations can have serious repercussions.