why need to plus one

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yeyuan zhu 2021-12-16

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https://ww2.mathworks.cn/matlabcentral/answers/1611960-why-need-to-plus-one

评论： yeyuan zhu 2022-3-1

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.

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Walter Roberson 2021-12-16

ePWM -- appears to mean "enhanced Pulse Width Modulation"

PMSM -- appears to mean "permanent magnet synchronous motor"

TBPD -- I cannot find a meaning for.

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Answer 1

Keyur Mistry 2022-1-12

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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.

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yeyuan zhu 2022-3-1

thank you~

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Answer 2

Walter Roberson 2021-12-16

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I see at https://www.mathworks.com/help/mcb/ug/add-pwm-driver.html

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.

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yeyuan zhu 2021-12-16

编辑：yeyuan zhu 2021-12-16

I'm sorry that I typing TBPRD as TBPD and Thanks for the link about PWM. Oddly enough, I clicked on the link and found that the Timer Period configuration for the linked document had not plus 1 either.

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