# Applying full state feedback on DC motor with torque load

I tried to apply full state feedback on DC motor (with no load) and it works fine in the simulation on Simulink

But the question is if I have a load applied on the motor (let’s say constant load or any thing else) the system in this case has two inputs voltage and torque load (Tl).

I can control only one input (voltage) and I have no control on the other input (Tl), So in this case what can I do in order to be able to perform full state feedback ?

• First of all, you need to have the mathematical model with or without load. Mar 24, 2020 at 6:02

Based on the following state space model of a DC motor:
The speed is controlled by acting on the armature voltage and the load torque is included in the system as a disturbance:

This model is based on Pole Placement Method: https://www.youtube.com/watch?v=FXSpHy8LvmY.
The K and Kr matrices are build using only the second column of B which is corresponding to the armature voltage.
ex.: K=place(A,B(:,2),poles)

• Yup - this is the way we do it Jun 5, 2022 at 19:01

One possibility: since you are saying that you know what this load is a priori, you can just add a time dependent function into your dynamics, something like $$P(t)$$ where $$P$$ represents the load. You will then have a time dependent system, which you can still control.

If the load is uncertain, you can add noise to the system dynamics and try experimenting with Kalman Filters and LQG controllers.

You need to think about how the load is going to affect your system. Then you need to add it to your model, as you said you have already the mathematical model of it. And probably you will notice that the load is going to act as a disturbance of the system. Thus, if you consider the Torque (not the load) as a state you will easily find the state-space equation. An example of a state-space mathematical model of the motor is stated here

http://ctms.engin.umich.edu/CTMS/index.php?example=MotorSpeed&section=SystemModeling

However, I would recommend you to read https://robotics.stackexchange.com/a/10054 since I think that you are a little confused about how the motor works. Good luck!