# Why and how is PWM implemented in Field Oriented Control (FOC) ?

1. ## Why and how is PWM implemented in Field Oriented Control (FOC) ?

Hi everyone,

I am trying to understand and implement FOC algorithm in MATLAB for a PMSM. I understand we are converting the 3 phase stator currents into 2 time-invariant stator currents: (direct and quadrature currents or Id and Iq, respectively). But I do not unsderstand how PWM is applied here since PWM can only alternate between High and Low currents but I do not understand why this is required or how it will help in torque control since. I thought the PI controllers adjusted Id and Iq to be the same as the reference currents and then inverse Park transform and inverse Clarke transfroms would be applied to get 3 phase voltages. PWM shouldn't be used since we are feeding 3 phase voltages into the stator. So what is the function of PWM here ? What does it do ? Please your help would be really appreciated since I am struggling a lot with this. Thank you in advance.

Also could someone explain me how the PI controllers manage to convert currents into voltages to be fed into the inverse Park transform ?

Also why is SPWM employed ? what makes is that good ? (Could you also point me to a source (preferably academic) which explains SPWM ?

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2. ## Re: Why and how is PWM implemented in Field Oriented Control (FOC) ?

Hi,

But I do not unsderstand how PWM is applied here since PWM can only alternate between High and Low currents but I do not understand why this is required or how it will help in torque control since.
To say it with your wirds: PWM can alternate between high and low voltage, not current.
But current is different than voltage, since the motor winding is an inductance.
So the current slowly (relatively) increases and decreases...

With the right PWM modulation one can generate trapezoidal or sinusoidal current waveform to control a PMSM.

Klaus

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3. ## Re: Why and how is PWM implemented in Field Oriented Control (FOC) ?

respectfully - you appear to need a better understanding of the whole system - try talking to fellow engineers ...

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