why need to plus one
2 views (last 30 days)
Hi,I have a problem in code generation of ePWM module. I read the oficial routine of PMSM vector control, and see the TBPD in the ePWM configuration dialog is "target.PWM_Counter_Period+1". I don't know why need to plus one.
if you know, could you tell me why need to plus one. Thanks a lot.
Keyur Mistry on 12 Jan 2022
If you will check in the script file you will find the following equation for calculating PWM contrer: -
Target.PWM_Counter_Period = round(Target.CPU_frequency/Target.PWM_frequency/2)
Now let us say if CPU frequency is 200MHz and PWM frequency is 12kHz then PWM counter is 8333. The expacted sampling time is 8.333333e-5 sec but if we directly uses PWM counter value we will get sampling time as 8.333e-5 sec. Hence to match with expactation we add 1 to the counter value and the new sampling time will be 8.334e-5 sec.
So the reason of adding 1 is basically to keep the generated sampling time in processor always be equal or grater than the demanded sampling time.
If the ratio of CPU frequency and PWM frequency is an integer then you can remove + 1 to the counter value.
More Answers (1)
Walter Roberson on 16 Dec 2021
The range varies from 0 to PWM_counter_period. PWM outputs when PWM up-counter matches CMPA and PWM down-counter matches CMPB
That suggests to me that there are (PWM_counter_period plus 1) different states -- for example if PWM_counter_period is 3 then states 0, 1, 2, 3 would exist, which would be 4 different states.
However, this is not a topic I have ever examined before, and this is possibly not relevant.