3phase Inverter Harmonics

[aletsoup]

The attached image shows the switching pulses of one of the upper switches of three-phase inverter.

As you can see, there are four symmetrical pulses over one switching period. Let's suppose that the switching period is TPWM. Which is going to be the first band of harmonics?4*1/TPWM or just 1/TPWM?
Thank you for your time.

 

[goldsmith]

The attached image shows the switching pulses of one of the upper switches of three-phase inverter.

As you can see, there are four symmetrical pulses over one switching period. Let's suppose that the switching period is TPWM. Which is going to be the first band of harmonics?4*1/TPWM or just 1/TPWM?
Thank you for your time.

Hi aletsoup
Harmonics of a SPWM signal ! it is as :
Message signal ( sine wave ) ( LF component ) .
Then Fspwm 3 Fspwm 5Fspwm ...... ( odd harmonics ) . and each on of em deals with some damping harmonics which means the amplitude of the side bands are decreasing . are my explanations clear to you ?

For instance : 3fpwm-2fm ...3fpwm-fm.....(3Fpwm)...3fpwm+fm....3fpwm+2fm this sequence ( from left and right side , goes to the infinite ! (-+)


Best Wishes
Goldsmith

 

[aletsoup]

Thanks for the answer!
I agree with everything you said but i still have some doubts about the switching frequency of the pulses i posted. As you can see over 1 switching period (in this case 2e-4) there are 4 symmetrical pulses (the igbt switches 8 times). If this pattern continues for the whole period of the output reference voltage the harmonics of the generated by the VoltageSourceInverter will be at 5Khz (1/2e-4) or at 20kHz (4*1/2e-4) ?

I hope i am clear in what i am asking

 

[FvM]

As long the switching pattern isn't periodical with 4*fpwm (obviously it isn't), you get a fpwm fundamental component. You can use fourier series tables to calculate the harmonics.

 

[goldsmith]

Thanks for the answer!
I agree with everything you said but i still have some doubts about the switching frequency of the pulses i posted. As you can see over 1 switching period (in this case 2e-4) there are 4 symmetrical pulses (the igbt switches 8 times). If this pattern continues for the whole period of the output reference voltage the harmonics of the generated by the VoltageSourceInverter will be at 5Khz (1/2e-4) or at 20kHz (4*1/2e-4) ?

I hope i am clear in what i am asking

About this i'm totally agree with "FvM"
Is your query solved or perhaps further questions ?


Best Wishes
Goldsmith