mirror of https://github.com/TheAlgorithms/C
79 lines
2.9 KiB
C
79 lines
2.9 KiB
C
/**
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* PID Controller
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*
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* The PID controller is a linear control algorithm that has three terms:
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* - Proportional: A simple scaling of the error value by a gain kP
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* - Integral: Integration of the error value over time, then multipled by gain kI
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* - Derivative: Rate of change of the error value over time, multiplied by gain kD
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*
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* Terms of the controller can be removed by setting their gain to 0, creating a PI (kD = 0)
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* or PD (kI = 0) controller. Depending on the control problem at hand, some terms may not
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* increase the performance of the system, or may have a negative effect.
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*
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* For a more mathematical expanation of the PID Controller, see https://en.wikipedia.org/wiki/PID_controller
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*
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* Limitations of this implementation:
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* - Since this implementation is just for demonstration, the pid_step function takes the
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* dt as a parameter, and it can be provided by the user in main(). This allows deterministic
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* experimentation with the algorithm, rather than using time(NULL) which would make the function
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* non-deterministic.
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*
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* Inputs: e(t) - Current error at time t. For example, how far a servo is off the desired angle
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* Output: u(t) - Controller output at time t.
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*/
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#include <stdio.h>
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struct pid {
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// Controller gains
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float kP;
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float kI;
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float kD;
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// State variables
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float lastError;
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float integral;
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};
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float pid_step(struct pid* controller, float dt, float error) {
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// Calculate p term
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float p = error * controller->kP;
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// Calculate i term
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controller->integral += error * dt * controller->kI;
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// Calculate d term, taking care to not divide by zero
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float d = dt == 0 ? 0 : ((error - controller->lastError) / dt) * controller->kD;
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controller->lastError = error;
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return p + controller->integral + d;
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}
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int main() {
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printf("PID Controller Example\n");
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struct pid controller = {
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.lastError = 0,
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.integral = 0
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};
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// Take the controller gains from the user
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printf("Please enter controller gains in format kP, kI, KD. For example, \"1.2 2.1 3.2\"\n> ");
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scanf("%f %f %f", &controller.kP, &controller.kI, &controller.kD);
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printf("Using kP: %f, kI: %f, kD: %f\n", controller.kP, controller.kI, controller.kD);
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// How often the pid_step algorithm expects to be called. In a real life scenario this would
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// be provided by calling time(NULL) - last_time, or by calling the function reliably at X Hz (using a timer or RTOS etc)
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// For demonstration of this algorithm though, it is defined below as 1 second, allowing easy testing of integral
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// and derivative terms.
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float time_step = 1;
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float error_value;
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while (1) {
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printf("Enter error value\n>");
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scanf("%f", &error_value);
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float output = pid_step(&controller, time_step, error_value);
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printf("Output: %f\n", output);
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}
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}
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