TMS320F28335: TMS320F28335 epwm

Debanjan chatterjee

Hello Sir,

I am using f28335 for some power electronics application. My epwm has a switching frequency of 100khz. So, .TBPRD has been set to 750, so the epwm interrupt will come at every 10 us. ( for 100khz switching frequency). Burt since my application requires greater computational effort , i want the interrupt to come at every 6th event ie after 60 us but want to keep TBPRD=750 ie keep switching frequency same.

Application detail: for some signal processing and control application, i have to compute something which takes 54 us. but the power electronics system has switching frequency of 100khz. So, i will compute a control duty cycle after every 60 us, which will be fed to the inverter(PES system) for 6 switching cycles and hence want the interrupt to come after 6 events.

Thanks.

over 8 years ago

0 Gautam Iyer over 8 years ago

Guru 192875 points

Hi Debo,

What about using a CPU_timer ISR with 60us timing?

Regards,
Gautam

0 Cody Watkins over 8 years ago

TI__Mastermind 42195 points

Debanjan,

have you considered doing some handshaking between these two parts of code? You could set a flag when the computation completes, and then wrap your ePWM ISR in an "if" statement that checks if your flag is set, otherwise it just returns to your application code.

I think this type of solution may be more robust in the case that the signal processing takes longer than expected.(one example where this might happen would be an interrupt that could preempt and delay your Signal processing code)

Regards,
Cody

0 Debanjan chatterjee over 8 years ago in reply to Gautam Iyer

Intellectual 325 points

Hello sir,
But my PWM interrupt comes after every 10 us and i need that interrupt to generate PWM pulses for 100Khz switching frequency. I need to complete the computation in 60 us and then update the duty cycle .I need the PWM interrupt to hold that duty cycle for 6 cycles before the next computation is finished. How can i do that ?

I was also looking into calling the PWM event after every 6 cycles, but saw that at max it can be delayed by 3 cycles.
Please help.

0 Debanjan chatterjee over 8 years ago in reply to Cody Watkins

Intellectual 325 points

Hello Sir,
The computation is in real time and I need to finish it to find the duty cycle for my converter. The computation takes more time than 10us which is the time taken to generate the epwm interrupt. Can you suggest a way in slight detail?

Regards

0 Gautam Iyer over 8 years ago in reply to Debanjan chatterjee

Guru 192875 points

This is what I meant:
ePWM timer = 10us
Cpu_timer = 60us

Once you computation is done in cpu_timer you raise a flag, the moment ePWM_timer detects this raise in flag -> updates the duty.

0 Debanjan chatterjee over 8 years ago in reply to Gautam Iyer

Intellectual 325 points

Hello Sir,
Thanks for the help. I will study that and come back if I face any problems. Thanks again.

Regards

0 Gautam Iyer over 8 years ago in reply to Debanjan chatterjee

Guru 192875 points

Cool! Keep us updated.

0 Debanjan chatterjee over 8 years ago in reply to Gautam Iyer

Intellectual 325 points

Hello Sir,
I have few other questions. I would like to apologize if they are too novice.

If I use the pwm interrupt for duty cycle generation, it generates interrupt every 10us (my fs=100khz). is there any way to generate the interrupt on every 6th event ie 60us? It can make my job a lot easier.

Also if the use the Cpu timer and its interrupt every 60 us as well as use an ewpm interrupt ( which comes at every 10us), wont there be any problem in the 6th cycle ( if the consider the clocks to be synchronized) when both the interrupts need to be evaluated?

regards

0 Debanjan chatterjee over 8 years ago in reply to Cody Watkins

Intellectual 325 points

Hello Sir,
Are you telling me to start my computation, initialising flag=0; then do the computation and make flag=1; then only if flag==1, enter epwm isr?

So, will the generated interrupt not be executed till the flag==1? Wont it create any problem for the epwm isr?

regards

0 Cody Watkins over 8 years ago in reply to Debanjan chatterjee

TI__Mastermind 42195 points

Debanjan,
Yes, my thought was to have an "if" statement that is inside your ISR checking if the flag is set. If the flag is set, execute the code to adjust your PWM and clear the flag... if the flag is not set, increment a counter and check if the flag should be set for the next iteration.

Regards,
Cody

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TMS320F28335: TMS320F28335 epwm