1.3.1 Module description

Controller Functions for CMSIS-DSP MCHP Library (dsPIC33A)

A Proportional Integral Derivative (PID) controller is a generic feedback control loop mechanism widely used in industrial control systems. A PID controller is the most commonly used type of feedback controller.

This group of functions implements (PID) controllers for single-precision floating-point and Q31 fixed-point data types, supporting functionalities which operate on a single sample of data and each call to the function returns a single processed value. S points to an instance of the PID control data structure. in is the input sample value. The functions return the output value.

Algorithm:
   y[n] = y[n-1] + A0 * x[n] + A1 * x[n-1] + A2 * x[n-2]
   A0 = Kp + Ki + Kd
   A1 = (-Kp ) - (2 * Kd )
   A2 = Kd
where Kp is proportional constant, Ki is Integral constant and Kd is Derivative constant The PID controller calculates an "error" value as the difference between the measured output and the reference input. The controller attempts to minimize the error by adjusting the process control inputs. The proportional value determines the reaction to the current error, the integral value determines the reaction based on the sum of recent errors, and the derivative value determines the reaction based on the rate at which the error has been changing.
Instance Structure:

The Gains A0, A1, A2 and state variables for a PID controller are stored together in an instance data structure. A separate instance structure must be defined for each PID Controller. There are separate instance structure declarations for each of the 3 supported data types.

Reset Functions:

There is also an associated reset function for each data type which clears the state array.

Initialization Functions:
There is also an associated initialization function for each data type. The initialization function performs the following operations:

  • Initializes the Gains A0, A1, A2 from Kp,Ki, Kd gains.

  • Zeros out the values in the state buffer.

Instance structure cannot be placed into a const data section and it is recommended to use the initialization function.