pwm inverter filter inductor design

[sabu31]

Hi

I would like to know if the design method(Area product) used for designing boost inductor (dc choke) can be used for designing the filter inductor of a full bridge pwm converter which is working at 50Khz. thanks.

 

[goldsmith]

Hey gentleman!
Hi
No . because of its operation . if you wanna integrator coil to obtain ripple rejection , it's calculation is :
((5(vs-vo))/I)*(vo*t)/vs. but if you want to detect a message from an SPWM signal , you should use a LPF with normalized Impedance .
All the best
Goldsmith

 

[sabu31]

Hi

I have got inductor value as 15mH. But i wanted to know the methodolgy to calculate number of turns and airgap.Any reference regarding inductor design for PWM inverter would be helpful. thanks

 

[goldsmith]

Again hi
Switching power supply design by abraham I pressman . or switching powersupply cookbook by marty brown . are two terrific books for your aim.
Respect

 

[sabu31]

Hi
thanks for the books.I refered the books , but they are for designing filter inductors or transformers for smps (in which core loss is not a criterion) and ac inductor where the switching frequency is fundamental. I am confused which method is to be used for designing inductor for pwm inverter, as the swicthing frequency of inverter is 50Khz and fundamental is 50Hz.

 

[goldsmith]

Hey gentleman!
Hi
you cant design a filter for 50HZ because it will be expensive and big. but because your message is 50HZ and it is your lowest frequency, you can design a filter for 5KHZ lpf( then you will have 50hz at its out put. and about numbers of turns, i will send you a simple and incredible way for calculations of coils and inductors.
Respect
Goldsmith

 

[ravit245]

Hi goldsmith,
My requirement also similar to this.
plz send me the calculations of coils and inductors what u have mentioned.

Thanks
Ravi

 

[goldsmith]

Hi Ravi
How much are the values of maximum and minimum load ? can you predict them ? by the way , has your system any feedback ?
Best Wishes
Goldsmith

 

[ravit245]

Hi goldsmith,
My inverter output power rating is 300W,120 Vpk,5 Apk,30Hz pure sine wave.
presently our load is 10 ohm,8mH,which is variable.
Presently we dont have feedback,it includes in future planning.
I heard closed loop of inverter is somehow difficult ,please provide the good stuff for designing feedback for inverter.

 

[babatundeawe]

Hey gentleman!
Hi
you cant design a filter for 50HZ because it will be expensive and big. but because your message is 50HZ and it is your lowest frequency, you can design a filter for 5KHZ lpf( then you will have 50hz at its out put. and about numbers of turns, i will send you a simple and incredible way for calculations of coils and inductors.
Respect
Goldsmith

please can you explain further on this please

 

[goldsmith]

Hi Babatundeawe

please can you explain further on this please

Surely , but before that , do you know about average value of a square wave ? if yes what about PWM ? if no i should tell you about it .
Best Wishes
Goldsmith

 

[babatundeawe]

@goldsmith

please do explain. i will appreciate that.

thanks

 

[goldsmith]

Hi again
You need more explanations ? surely . Vave of an square wave is D.C*Vs . D.C is duty cycle . for a PWM D.C will be variable instead of message signal . a PWM has an spectrum . that can help you to understand more . but a simple way to understand is when D.C will have changes the average voltage will have change .
I hope you got the point . if you need more descriptions , as your question , more clearly , please . thus i can help you , more .
Best Wishes
Goldsmith

 

[babatundeawe]

if i can get what you mean. the output voltage of a pwm will be the dty cycle multiplied by the input voltage i.e.(dc*Vs) am i right.

but in the case of an spwm. is it still applicable because the dc will still be a variable. is my assumption rite

thanks

 

[goldsmith]

Hi again
The voltage before filtering is a PWM . but after filtering it will be an averaged signal . so if D.C have be variable the out put will vary too .
Best Wishes
Goldsmith

 

[dreamsys]

Please, I know how to analytically design and derive values for my low pass filter component at the output an SPWM inverter. But my problem is how to go about selecting the magnetic component to realize my design value. For example let say my calculate inductance value is 2.22mH,
1.how do I design the magnetic components (i.e Core, copper windings) in order to realize this values.
2. will the design of the inductor follows the same design procedure for a choke inductor at the output of a DC-DC converter.
Regards

 

[israel7732]

you may apply the iteration method. put the load and the capacitor then vary the inductor values until the wave becomes a pure sine. use an oscilloscope or get an inductance meter.

 

[dreamsys]

Thanks for your reply, the inductance value or calculation is not the issue, the problems is the magnetic design( i mean core selection). Should it be gapped like that of a choke filter design for DC-DC converter filter inductor, or ungapped like the core selected for a transformer or should the design follows common mode and EMI filter design procedure {because the function of common mode inductor and EMI filter is to pass certain signal while rejecting unwanted signals}. There are not many books that discuss how to design inverter output filter but a lot that discussed choke, common mode inductor, EMI filters etc.
regards/

 

[goldsmith]

you may apply the iteration method. put the load and the capacitor then vary the inductor values until the wave becomes a pure sine. use an oscilloscope or get an inductance meter.

Hi
Certainly that's not a good way .
Because i hope you know about response of a 2nd order LC filter ( LPF ) instead of different loads and resonant frequencies .
Furthermore , design of such a filter is so easy .

Best Wishes
Goldsmith

 

[dreamsys]

Hi
Certainly that's not a good way .
Because i hope you know about response of a 2nd order LC filter ( LPF ) instead of different loads and resonant frequencies .
Furthermore , design of such a filter is so easy .

Best Wishes
Goldsmith

Hi goldsmith, please check out the design I attached to this reply.

1. I used a constraint of total harmonic distortion of less than 3% of out put voltage and design for inductor that is non-saturate but thermally limited
Design parameters
a. PWM technique is SPWM
b. output voltage sinusoidal with THD<3% of output voltage
c. Output voltage RMS value =220V
d. Output power = 250Watts
e. Constraint condition for the inductor's inductive impedance is I(load)*2*PI*L <0.03*Vrms