Hey @cvabc

this library has started as a reaction to very expensive and somewhat difficult to understand hardware+software combinations for running the BLDC motors such as ODrvive, Trinamic and similar.

If you take for example ODrive, it has two mode of operation, either BLDC motor (high power) or gimbal motor.
When you are using the gimbal motor mode, it does not use the current control loop. When I saw that, I told myself, if I can make the rest of the functionalities relatively implemented well, we could have the same level of control for the gimbal motors as the ODrive for much lower price and with customisable code 😃
This is the first reason why I did not initially implement the current control loop.
The second reason is because the boards providing the measurement of the phase current are still somehow rare and I did not have any of them on my hands to try out and implement. Recently I have came across the aliexpress board with the DRV8302/8301 chip which is perfect for this purpose. Aliexpress link

The last reason is maybe the most important one regarding your question.
Field Oriented Control algorithms usually have current control loop for two reasons:

tracking of rotor magnetic field orientation
torque control

Tracking of rotor magnetic field orientation

FOC was first developed as the powerful control method for the AC motors and there it is not enough to measure the rotor position to know the magnetic field orientation of the rotor generated by the induced currents. You need to measure the currents of the stator and check the influence of the rotor field on them. Basically without the currents you will not know good enough how to set the right angle of your stator field.
The good thing about BLDC motors is that they have permanent magnets in the rotor and their rotor field is not influenced by the stator currents (for smaller motors). Therefore it is enough to measure the position of the rotor to know the field orientation, no need to measure the current.

Torque control

The electric motor torque T is a value proportional to the current I

T = K*I

therefore in order to control the torque applied by the motor you need to measure the current. But since the current measurement is very often unavailable for smaller motors I decided to go for a simpler solution.

If you take the example of a DC motor, it has the same proportional relation in between current I and the torque T but in most cases you don't measure the current of the DC motor but build the position and velocity control of the DC motor without using the current loop, without using the torque control. So since DC motor doesn't really need the torque control (current measurement) then the BLDC motor doesn't as well.

Unless you really need precise torque control
Or you need to limit torque and current

Therefore in this library in this stage, you can do a generalised torque control using voltage (here is a quick explanation how it works: voltage torque control), velocity and position control.

The current control loop is very high in my priorities and it will be implemented in next release of the library.

Let me know what do you think!
Did you have something more specific in mind with your questions?

No current sensing? #6

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