[FEATURE] Foc_current mode and Current feed forward

[Candas1]

At the moment in voltage mode, if information like phase_resistance, phase_inductance and KV_rating are provided, q and d currents are used as target and the q and d voltages are estimated.

The foc_current could benefit from that and use those values as feedforward for the q and d PI controllers.
The q and d voltage estimation could be made a separate function not to duplicate the code.

That would probably improve the dynamics of the foc current control.

[Candas1]

This estimation function can also be reused in angle mode and velocity mode

Now it looks like that:
Vq = phase_resistance * Iq + BEMF
Vd = - SPEED * L * Iq

It could be later updated for field weakening in this way:
Vq = phase_resistance * Iq + BEMF + SPEED * L * Id
Vd = phase_resistance * Id - SPEED * L * Iq

Later, for salient motors like IPMSM, it could be updated to handle Ld and Lq:
Vq = phase_resistance * Iq + BEMF + SPEED * Ld * Id
Vd = phase_resistance * Id - SPEED * Lq * Iq

[Candas1]

I think I am wrong about the feedforward:

Only those values are being added as feedforward term after the PI output:

• Vq += BEMF + SPEED * Ld * Id
• Vd -= SPEED * Lq * Iq
  That could be added before the PID output ramp limiting.

That technique is called decoupling.
Vesc seems to give different options.

• only BEMF decoupling : Vq += BEMF
• cross decoupling : Vq += SPEED * Ld * Id and Vd -= SPEED * Lq * Iq
• both : Vq += BEMF + SPEED * Ld * Id and Vd -= SPEED * Lq * Iq

phase_resistance * Iq and phase_resistance * Id might be already covered by the PI controller.

[Candas1]

So something like that could be done.
In move() function for voltage mode

• if phase_resistance is available, Vq = phase_resistance * Iq and Vd = phase_resistance * Id

In loopfoc() function for all modes:

• if phase_inductance is available Vq += SPEED * Ld * Id
• if KV_rating is available Vq += BEMF
• if phase_inductance is available Vd -= SPEED * Lq * Iq

[Candas1]

Nice video about the cross decoupling:
https://www.youtube.com/watch?v=bOr_EgJUakI

[Candas1]

Nice article, and the benefit we could expect: