pid_p.h

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 * @details
 * This file defines the @ref control_system::pid::PID_P class, which
 * implements a proportional-integral-derivative (PID) controller with
 * configurable derivative filtering and feed-forward control.
 *
 * The controller provides configurable proportional, integral, and
 * derivative gains. The integral contribution and total controller
 * output can be limited independently.
 *
 * The derivative term can optionally be filtered using a first-order
 * low-pass filter. A feed-forward term can also be added to the
 * controller output.
 *
 * The class provides access to the individual proportional, integral,
 * and derivative contributions as well as the final controller output.
 *
 * @tparam T Numeric data type used for the controller calculations.
 *
 * @author Abhinay Kumar
 * @version 1.0.0
 * @date 2026-08-11
 *
 * @copyright
 * Copyright (c) 2026 Abhinay Kumar
 */
 
#ifndef CONTROL_SYSTEM_PID_PID_P_H
#define CONTROL_SYSTEM_PID_PID_P_H
 
#include "filters.h"
#include "../utility/utility.h"
 
namespace control_system
{
 
    namespace pid
    {
        /**
         * @namespace pid
         * @brief Contains proportional-integral-derivative controller implementations.
         */


         *     I_max,
         *     u_max
         * );
         *
         * double output = controller.update(reference, measurement);
         * @endcode
         */
        template <typename T>
        class PID_P
        {
        public:
             *
             * @details
             * Constructs the controller with its parameters and internal
             * state initialized to their default values.
             */
            PID_P();


             * @param[in] Ki_ Integral gain.
             * @param[in] Kd_ Derivative gain.
             * @param[in] I_max_ Maximum allowed integral contribution.
             * @param[in] u_max_ Maximum allowed controller output.
             * @param[in] d_filter_ Enables or disables derivative filtering.
             * @param[in] fc_ Cutoff frequency of the derivative filter in Hz.
             *
             * @details
             * Initializes the controller parameters and optionally
             * configures the derivative low-pass filter.
             */
            void init(T dt_, T Kp_, T Ki_, T Kd_, T I_max_, T u_max_, bool d_filter_ = false, T fc_ = 10.0);


             * @param[in] Ki_ Integral gain.
             * @param[in] Kd_ Derivative gain.
             * @param[in] I_max_ Maximum allowed integral contribution.
             * @param[in] u_max_ Maximum allowed controller output.
             * @param[in] d_filter_ Enables or disables derivative filtering.
             * @param[in] fc_ Cutoff frequency of the derivative filter in Hz.
             *
             * @details
             * Updates the PID gains, sampling time, output limits, and
             * derivative filter configuration.
             */
            void set_param(T dt_, T Kp_, T Ki_, T Kd_, T I_max_, T u_max_, bool d_filter_ = false, T fc_ = 10.0);


             * @param[in] u_ff_ Feed-forward control input.
             *
             * @return PID controller output.
             *
             * @details
             * Calculates the proportional, integral, derivative, and
             * feed-forward contributions and combines them to produce
             * the controller output.
             *
             * The integral contribution and final controller output are
             * subject to their configured limits.
             */
            T update(T x_0, T x, T u_ff_ = 0.0);


             * derivative, controller output, feed-forward value, and
             * startup state.
             */
            void reset();

             * @brief Merges an external controller output into the PID state.
             *
             * @param[in] u_k_1_ Previous or externally provided controller
             * output.
             *
             * @details
             * Updates the internal controller state using the specified
             * previous controller output.
             */
            void merge(T u_k_1_);

             * @brief Sets the controller sampling time.
             *
             * @param[in] dt_ Sampling time in seconds.
             */
            void set_dt(T dt_);

            /**
             * @brief Sets the proportional gain.
             *
             * @param[in] Kp_ Proportional gain.
             */
            void set_Kp(T Kp_);


            void set_Ki(T Ki_);


             */
            void set_Kd(T Kd_);


             * @param[in] I_max_ Maximum allowed integral contribution.
             */
            void set_I_max(T I_max_);


             *
             * @param[in] u_max_ Maximum allowed controller output.
             */
            void set_u_max(T u_max_);

             * @brief Enables or disables derivative filtering.
             *
             * @param[in] d_filter_ Derivative filter enable state.
             */
            void set_d_filter(bool d_filter_);

            /**
             * @brief Sets the derivative filter cutoff frequency.
             *
             * @param[in] fc_ Cutoff frequency in Hz.
             */
            void set_fc(T fc_);


            void set_ff(T u_ff_);

            T get_dt();

            T get_Kp();

            T get_Ki();

            T get_Kd();

            T get_I_max();

            T get_u_max();

            bool get_d_filter();

            T get_fc();

            T get_ff();

            T get_P();

            T get_I();

            T get_D();

            T get_u();

            T get_e_k_1();
 
        private:
            LPF_1<T> lpf;

            T dt = 0.0;

            T Kp = 0.0;

            T Ki = 0.0;

            T Kd = 0.0;

            T I_max = 0.0;

            T u_max = 0.0;

            bool d_filter = false;

            T fc = 0.0;

            T e_k_1 = 0.0;

            T P = 0.0;

            T I = 0.0;

            T D = 0.0;

            T u = 0.0;

            T u_ff = 0.0;

            bool start = true;
        };
 
#include "../../src/pid/pid_p.tpp"
    }
}
 
#endif