Effect of PID Controller on Direct Current Motor Speed Control Performance under Varying Load Torque Disturbance

Abstract

The MATLAB/Simulink model of DC motor speed control with varying load torque disturbance has been studied. Simulation was initially conducted without a controller considering unit step input and the transient response time domain performance characteristics of the uncompensated system were found to be remarkable but the desired speed was not tracked. The response speed was found to reach 1.649 rad/sec, which was well above the reference speed (1.0 rad/sec) by 64.9%. The introduction of load torque at 4 seconds further increased the magnitude of the motor speed response from 1.649 rad/sec to 3.008 rad/sec, which is 82.4% increment. With 300 rad/sec reference speed, simulation was conducted without PID controller and the resulting response was 494.6 rad/sec which was 64.9% increment. Thereafter, a load torque from 0 to 10 Nm is introduced at 4 seconds into the DC motor control loop and the response showed that the magnitude of the response motor is increased to 508.2 rad/sec, whicj is undesirable. A Proportional integral derivative (PID) controller plus pre-filter was introduced to DC motor speed control loop to compensate for the performance of the system. The step response showed that with the PID plus pre-filter circuit, the desired motor speed was tracked with remarkable time domain performance characteristics. With the introduction of unit load torque at 4 seconds, the step response of the PID controlled DC motor speed changed and tracked the desired speed with just 1% (0.01) deviation. Simulations were further performed with PID controller by setting the reference speed at 300 rad/sec without and with load torque varied from 0 to 10 Nm introduced into the control loop. The response was the same as the desired motor speed but increased to 300.1 rad/sec which is just 0.03% increment from the desired speed. Generally, the simulation tests conducted showed that the designed real PID controller plus pre-filter actually provided better speed response performance for DC motor control by offering precise tracking and robustness under varying load torque disturbance.