# Dc motor position control

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Eleni.T le 29 Juin 2020
Commenté : Eleni.T le 10 Juil 2020
Hello. I am modelling a solar tracker in Simulink. I have 2 LDR sensors attaches on a pv panel, and they give a voltage output depending on the sun light each one receives. I want to write a function that will read the two voltages values and compute the difference and then command a DC motor(which rotate the panel) to rotate until that voltage difference becomes zero. My question is what should be the command to the motor? The motor simulink block I created has an input of voltage and outputs an angle. If I use a PID controller I have to specify the referenced desired angle but this is unknown. The desired angle is reached when the voltage difference of the sensors is zero. Whould it be correct if I use a PID controller to control the motor speed? And the output of the function will be the desired speed(to operate the motors) and 0 to stop the motors.
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### Réponse acceptée

Vasco Lenzi le 2 Juil 2020
Hi Eleni
I think the best approach would be to model the LDR sensors in Simulink as well. I believe you are using Simscape Multibody (from your previous questions) so you can place a "light source" approximating the sun and use the Transform Sensor to meaure angle and distance from this light source and then model their voltage behaviour. You can even move the light source using something akin the Point On Curve Constraint to mimick the day passing.
Then I would feed directly the the voltage difference of the sensors to the PID block. In the end the PID act on the DC motor and continue to act until the input to the PID block is 0. So I would simply use the voltage difference, but in order to model and tune it in Simulink with this approach you do need a model for the LDR sensors and the sun position.
Just my 2 cents, good luck.
Vasco
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Eleni.T le 10 Juil 2020
Thank you very much, i am gonna try this.

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