DC Motor Speed Modeling in Labview

DC Motor Modelling

A common actuator in control systems is the DC motor. It directly provides rotary motion and, coupled with wheels or drums and cables, can provide transitional motion. The electric circuit of the armature and the free body diagram of the rotor are shown in the following figure:

For this example, we will assume the following values for the physical parameters.

• moment of inertia of the rotor (J) = 0.01 kg.m^2/s^2
• damping ratio of the mechanical system (b) = 0.1 Nms
• electromotive force constant (K=Ke=Kt) = 0.01 Nm/Amp
• electric resistance (R) = 1 ohm 
• electric inductance (L) = 0.5 H
•  input (V): Source Voltage

The motor torque, T, is related to the armature current, i, by a constant factor Kt. The back emf, e, is related to the rotational velocity by the following equations:


In SI units (which we will use), Kt (armature constant) is equal to Ke (motor constant).



Next, we will start to modelling with Newton's law and Kirchoff's law. These laws applied to the motor system give the following equations:






Modelling the DC motor in LabviewThe above derived equations we can model easily in labview.The Integrator can found in Control Design& Simulation Tool kit as shown in figure.

 
The multiply, Division blocks can found in mathematics tool kit as shown

Signal summing block as shown in below

The Final Model is as shown in figure:

Open loop response:To find the open loop response of the model, we have to connect the diagram as shown in fig:we have to use Control & Simulation loop

Source is Step signal to find out open loop response 

To  check the out we need a waveform chart.

The overall open loop system as shown in figure:

The response of the system in open loop condition as shown in Fig: 

Tuning of PID controller Parameters:  In Labview GUI interface is beautiful and very easy. We can tune the parameters on line in continuous run mode .

The PID parameters found as follows:
Kp = 81.632Ki = 79.58Kd = 4.08

Happy wiring