Simple Control System Design with XCOS - Scilab Tutorial

Figure2: Feedback System

As can be seen from the Figure [2], a feedback system can be defined as; we have a dynamic system which responses to a given input and we are controlling it by the output. This kind of systems are called also Closed-Loop Systems. If we do not feed the output back into input these systems are called Open-Loop Systems. We are now feeding the output back and "Controlling" the system in a way but the important thing is that we need to control the system in a way that the system obeys certain requirements. These requirements can be achieved with different controlling techniques but in this tutorial i will talk about "Classical Control Techniques" Proportional, Derivative, Integral which is called PID controller. A PID controller is;

Figure3: PID Controller Scheme

Setting Up The System and Simulation

We will assume DC-Motor which is represented with a simple transfer function and its input is voltage and output is RPM and we will control the output with a PID controller. The transfer function is;

Figure4: DC-Motor Transfer Function Representation

From the Xcos Palette Browser the transfer function can be found from Continuous time systems/ CLR. Other blocks we need for simulation can be found from Palette Browser and typing search; STEPFUNCTION, SUMf, CMSCOPE, CLOCK_c, PID, GAIN, respectively. They are;

Figure5: Blocks Needed

Open-Loop vs Closed-Loop

Now, check both systems;

Figure6: Open-Loop

Figure7: Closed-Loop

First set PID gains as;

Figure8: PID Gains

Responses of both Closed and Open Loop systems to a given step input are;

Figure9: Responses with PID = [1 1 1] Now by adjusting the PID gains we will try to converge to given input. After several trials, I have found the PID gains as;

Figure10: New PID Gains

With the PID gains given in Figure [10] our Closed Loop response changes as;

Figure11: Response with PID = [28 19 0.5] As we can see from the Figure [11], our control system works really good with small error we have converged to the given input. We can see the importance of the control system in this example. I hope this tutorial will be helpful for you guys. Thank you :)

Proof of Work

• [Xcos File] (https://drive.google.com/open?id=1o4kTgG7dlMon_icaeK1Nv4d1DphYjuEM)