How to calculate accurate Sample time for PWM generator block & Current Controller (Here I am using Torque Controller with FOC Controller & 3 Phase IPMSM)

Hi,

I don't know how to calculate accurate sample time for PWM generator block & Current Controller.Here i am using FOC with TORQUE controller for three phase ipmsm.

for my project :speed - 9500 rpm , torque -1 Nm, Power - 1.1kw ,Fsw - 16000 Hz.

when i am increased sample time from 10e-5 to 10e-6 for current controller ,machine output's Torque result is without ripples and within limited bandwidth.

when i am increased sample time from 10e-6 to 10e-7 for current controller ,machine output's Torque result is without ripples and within limited bandwidth.and Most torque accurracy level is higher when i am using 10e-7 than 10e-6.

i don't know what is exact sample time for pwm generator and current controller.

I want to know exact sample time for PWM generartor and current controller.

how to choose exact sample time for all project(Please tell any common formula or method for choosing exact sample time for pwm generator and current controlller)

Notes:in my model,i used 50 samples 16000hz*50 samples = 800000 ,Ts=1/800000 = 1.2500e-05 .The torque is dropped after 1 sec for 1nmand 9500 rpm.

when samples are increased greater than 100 ,torque are stabilized.but,i don't know which sample time and samples are best to use for model.

Answer 1

[Mohamad Nazir]

The general rule is Nyquist's theorem which is a sampling frequency at least 10x the frequency of the signal you are trying to sample. For the PWM generator for example it is at least 10x the switching frequency (10x 16000hz).

As for the control loop bandwidth the same logic is applied, in case of current and torque controllers the control loop bandwidth should be at least 10x faster than the electrical time constant of the machine (L/R).