How to vary switching frequency on run-time

Javier Vara

Hello,

I am using the HVMTR development kit running a low inductance motor. The controlboard used is F28069MISO.

I am running the lab2c with some modifications to read from the CAN bus some parameters to modify in run-time things like speed and acceleration. I have had no problem at all to get that with speed o acceleration but when I tried to do the same thing with the PWM switching frequency things started to get tricky and I have not been able to solve it properly. I know that there are lots of parameters that depend on it and that is why I tried running again the USER_setParams, HAL_setParams and CTRL_setParams right after reading the new switching frequency but it does not work well. In the best of the cases I managed to once it reads the new frequency run again the whole identification process with the new switching frequency (pretty much the same thing as if it started from the beginning of the program again) but obviously that is undesirable and I have not been able to get around that.

Is there any better way to do it? or at least one that works fine?

Thanks in advance

Javier

over 8 years ago

0 Yichao Zhang over 8 years ago

Intellectual 495 points

changing pwm frequency also changes ADC sampling frequency. why do you need to change that?

0 Javier Vara over 8 years ago in reply to Yichao Zhang

Expert 1575 points

we would like to test the perform of an inverter at different switching frequencies without having to compile and download the program every time we change the frequency

0 Yichao Zhang over 8 years ago in reply to Javier Vara

Intellectual 495 points

Hi,

the pwm frequency is originally defined in macro. But in the code ,actually pwmperiod is used. in the function USER_setparams(),

pUserParams->pwmPeriod_usec = USER_PWM_PERIOD_usec;

It affects the pwm switching frequency.

you need to replace the macro USER_PWM_PERIOD_usec by a variable. Everytime you want to change the frequency, you restart the whole code and edit the variable.

Yichao

0 ChrisClearman over 8 years ago in reply to Yichao Zhang

TI__Guru** 118000 points

just be aware that by changing the PWM frequency you are also changing the effective frequencies for the CTRL, EST, current, speed, and trajectory portions.

0 Javier Vara over 8 years ago in reply to Yichao Zhang

Expert 1575 points

Hi,

Thanks for the answer it works. Sorry for taking so long to answer but I was having some problems with the procedure because I was using lab 2c and every time I changed the frequency I had to restart the whole cycle and therefore re-estimate the motor parameters. I was busy trying to get around this and I forgot to answer.

Thanks!

Javi

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How to vary switching frequency on run-time