Alpha beta gamma filter for cascaded PID motor position control

Abstract

PID controller is normally used in position control e.g. motor position control. However, in real application, a motor is non-linear due to factors like friction and power saturation. Therefore, in this paper, cascaded PID controller is proposed to reduce these nonlinearities. The cascaded PID controller was used because of the fast response and better disturbance rejection. The error from the motor position is fed into the first PID, and the output from the PID controller is used as velocity reference for the second PID. With these characteristics of a cascaded control, the nonlinearity in a motor can be reduced. Implementation of PID controller is done in a digital form and usually, the derivative elements are subject to noise from sampling time error and quantization error. To solve this problem, the alpha beta gamma filter is used to estimate the velocity of the motor. Experiment was conducted using a microcontroller to show the effectiveness of cascaded control in reducing nonlinearity of a motor, and the alpha beta gamma filter was implemented to reduce sampling time and quantization error. Results show an overdamped system with no steady state error was produced.