An FPGA Based Controller

Abstract

The main aim of this project is to design a productive utilization of digital PID control algorithms using Field Programmable Gate Array (FPGA) technology. The Proportional Integral, Derivative (PID) control method is the most common and effective feedback control technique that is used for realizing automatic control of many industrial processes. In process control industry it is called "Bread and Butter" in terms of economical profit.

In the proposed work we demonstrate one of the applications of hardware and software module development for realization of digital PID control algorithm in dynamical systems with fast response. We successfully implemented verified and analyzed the FPGA PID algorithm on the FPGA for a PMDC motor with high current and voltage ratings using Spartan - 3 FPGA which delivers an optimal balance of low risk, low cost, and low power for such applications.

Feedback module contains a proximity switch as a speed sensor to sense the speed of the PMDC, which is the measured variable (MV) for our application. The output of the sensor is in terms of RPM count. The output of the speed sensor is then given to the frequency to voltage (F/V) converter. The output the F/V converter is compared with the set-point (SP) for computing the error value. The error value (E) is then given to the Analog to Digital Converter (ADC) for converting the data into the digital format. For comparing the measured value with the set point value, an op-amp based comparator circuit is used.

The controller output is in terms of the voltage (manipulated variable, MV), which is given as an input to the chopper circuit. The output of the chopper circuit (controlling variable) is used to control the terminal voltage of the armature of the PMDC control the for the purpose of speed control. The MOSFET is used as a switch in the chopper circuit. The ON and OFF time of the MOSFET is dependent on the output of the controller. The other method widely used for controlling the speed of the motor is Pulse Width Modulation (PWM) method. In this method, the output of the PWM circuit is given to the armature which turn varies the terminal voltage depending on the duty cycle of the PWM output for the purpose of speed control. The work presented here is the modeling of the controller and the plant (PMDC motor) using MATLAB Simulink and System Generator tool by Xilinx and the final simulation results are presented here. Key words- Field Programmable Gate Arrays (FPGA), MOSFET, Proportional-Integral-Derivative (PID) controller, Pulse Width Modulation(PWM).