Hello all !
Thanks for your replies and sorry for taking so long (I had to fix something).
But now, here I am and I will monitor this topic every day
I will try to reply your questions as best as I can.
The PWM duty-cycle determines the average voltage the motor sees (e.g. a 50% duty-cycle ideally generates a voltage 50% of the supply voltage), it does not directly control current. The motor current is determined by this voltage and the motor load.
Alright, I get it. It is more understable now how it works
If you want to determine the exact relation between PWM and motor current you'll need to find/measure the parameters describing the motor physics.
What kind of parameters describing the motor physics will I need ?
I can get the datasheet and I can measure some parameters (I have the material)
However, dynamical systems are by nature dynamical, so the current is not described simply by a single value. Do you need the current value for any particular purposes?
What is the exact purpose of the motor?
It will be easier if we can describe current by a single value.
What do you think ? Can we imagine there is an formula that links PWM value, current motor and motor load ?
The motor allows to make turn a wheel thanks to a chain.
Let's me present all the parts :
- Battery provides current to the VFD
- Variable frequency drive that drives and provides current to the motor
- Motor
- Wheel
Currently, I have a mathematical formula. Thanks to it, I can determinate the velocity wheel according to the current provided by the battery (the input is the current and the output is the wheel velocity).
Let's me precise more my problem.
I would like to set a proportionnal command (K*errors)
My setpoint value is a velocity and I can measure the wheel velocity.
To reach this setpoint value in terms of velocity, I command the PWM value.
So for a particular PWM value, I can get the wheel velocity.
I would like to compare my mathematical formula to the reality. But the input of my formula is not PWM value but battery current. That's why I am looking for the link between PWM value and current.
Notice : From battery current, I can find motor current (because I know VDF efficiency)
When loaded, it more like V-Va-I*R. Successful speed controls have been made this way. Va=V(armature).
Where is this formula from ? What is 'R' here ?
The average current is essentially proportional to the load or torque as before.
I agree with that. I have read about it.
I hope my explanations help well to understand my problem. Feel free to ask more if it is necessary.