An FPGA based implementation of a flexible digital PID controller for a motion control system

Implementation of digital controllers in embedded environment suffers from the inherent problems associated with analog-digital signals interfacing in hard real-time, therefore, the control algorithms are invariantly subjected to approximations. This paper presents a novel technique for implementation of an efficient FPGA based digital Proportional-Integral-Derivative (PID) controller for the motion control of a permanent magnet DC motor. The implementation technique circumnavigates the problem of interfacing analog and digital systems in real-time. The controller is used in a speed control loop. The hardware implementation has been done on a Xilinx Spartan 3 FPGA chip. A novel technique has been adopted for the generation of the control input as a PWM signal for controlling the motor driver circuit and decoding the optical encoder data for using it for the speed feedback in the PID control loop. The VHDL algorithm for the proposed implementation has also been presented in this paper. A comparison of the experimental results with the Matlab^® based simulation shows the effectiveness of the proposed method.