pid-controller.h

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#ifndef PID_CONTROLLER_H
#define PID_CONTROLLER_H

/**********************************************************************/
/*
 * Copyright (c) 2017, Jetro AS
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONRIBUTORS ``AS IS'' AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the EVE platform.
 */

/**
 * \file
 * \brief Abstract PID-controller implementation
 *
 * \author SE, Jetro AS
 */ /******************************************************************/

/**
 * \defgroup pid PID controller
 * \ingroup util
 * \{
 */

/**********************************************************************
 * PUBLIC TYPES
 **********************************************************************/

/**********************************************************************/
/** \brief PID controller instance data.
 */
struct pid_controller_t
{
  float ProportionalCoeff; //!< Coefficient for proportional part of controller. Equal to K from standard formula.
  float IntegralCoeff;     //!< Coefficient for integral part of controller. Equal to K/Ti from standard formula.
  float DifferentialCoeff; //!< Coefficient for differential part of controller. Equal to K*Td from standard formula.
  float IntegralValue;     //!< Variable holding current integral value
  float PreviousErrorDiff; //!< ErrorDiff on the previous iteration for differential part calculation
  float MinIntegral;       //!< Minimal allowed integrated part value
  float MaxIntegral;       //!< Maximal allowed integrated part value
};

/**********************************************************************
 *  PUBLIC FUNCTONS
 **********************************************************************/

/**********************************************************************/
/**
 * \brief Initialize PID controller data.
 * Function gets standard coefficients from PID formula:
 *   f(n) = K * ( Error(n) + SUM(Error(0) * dt(0)...Error(n) * dt(n)) / Ti + Td * Error(n) / dt(n))
 *
 * \param  Pid          Pointer to PID controller data
 * \param  K            K coefficient from standard PID formula.
 * \param  Ti           Ti coefficient from standard PID formula.
 * \param  Td           Td coefficient from standard PID formula.
 * \param  MinIntegral  Minimal allowed integrated part value.
 * \param  MaxIntegral  Maximal allowed integrated part value.
 */
void PidInit(struct pid_controller_t* Pid, float K, float Ti, float Td,
             float MinIntegral, float MaxIntegral);

/**********************************************************************/
/**
 * \brief Reset PID controller.
 *
 * @param  Pid   Pointer to PID controller data
 */
inline void PidReset(struct pid_controller_t* Pid)
{
  Pid->IntegralValue = 0.;
  Pid->PreviousErrorDiff = 0.;
}

/**********************************************************************/
/**
 * \brief Calculate PID function
 *
 * \param  Pid       Pointer to PID controller data
 * \param  Error     Desired value minus current value
 * \param  ErrorDiff Error for differencial part.
 *                   For classic PID it should be set equal to Error.
 *                   To avoid peak output on sharp desired value change, tis can be set to (-) current value.
 * \param  TimeDelta Time between this and previous Error calculation/measurement.
 * \return           Calculated PID value
 */
float PidFunc(struct pid_controller_t* Pid,
              float Error, float ErrorDiff, float TimeDelta);

/** @} pid */

#endif // PID_CONTROLLER_H