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  • I am developing a FOC controller for a PMSM (in blue).
  • The outer loop (speed control, in orange) is made with a PI.
  • The inner loop (current control, in green) as well.

block diagram

Now I'm including the inverter (in yellow) between the current control and the plant. However, I'm not sure how to appropriately set the DC voltage level. If I'm not wrong, this value must be at least twice the voltage sent to the inverter from the current control.

Secondly, the voltage sent to the plant (either with or without the inverter) should be only in function of the motor parameters and speed. However, once I add the inverter, the DC voltage also plays a role in the voltage coming out from the current controller. Why does that happen?

Thanks in advance.

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  • \$\begingroup\$ Asking for papers (twice) means you probably don't exactly know what you want and this makes your "question" probably off-topic on this site. Given also that your description of your system would be better served by a diagram, I suggest you get to the crux of your misunderstanding in as helpful/readable a way as is possible. \$\endgroup\$
    – Andy aka
    Jul 4, 2019 at 11:36
  • \$\begingroup\$ Thanks for the comment. I hope I made myself clearer \$\endgroup\$
    – Alvaro
    Jul 4, 2019 at 14:17

1 Answer 1

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The influence of a DC voltage source is negligible for the control of the PMSM. For sure, considering that V_dc >= 2*V_phase. Indeed, if this condition is true, the DC voltage won't have any effect on the V_phase if the inverter is correctly modelled. There are two main factors to take into account when modelling the inverter:

  1. The input voltage to the inverter must be normalized using a gain = 1/V_dc
  2. There is a modulation factor that must be also applied in the gain. It may vary depending on the formulation used.

It is also important to understand well the Space Vector Pulse Width modulation. A very helpful post was this one

Finally be aware not to overmodulate the signal (when modulated voltage becomes higher than triangular signal of the inverter).

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