ecl_yaw_controller.cpp

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/**
 * @file ecl_yaw_controller.cpp
 * Implementation of a simple orthogonal coordinated turn yaw PID controller.
 *
 * Authors and acknowledgements in header.
 */

#include "ecl_yaw_controller.h"
#include <float.h>
#include <geo/geo.h>
#include <mathlib/mathlib.h>

float ECL_YawController::control_attitude(const struct ECL_ControlData &ctl_data)
{
    switch (_coordinated_method) {
    case COORD_METHOD_OPEN:
        return control_attitude_impl_openloop(ctl_data);

    case COORD_METHOD_CLOSEACC:
        return control_attitude_impl_accclosedloop(ctl_data);

    default:
        static ecl_abstime last_print = 0;

        if (ecl_elapsed_time(&last_print) > 5e6) {
            ECL_WARN("invalid param setting FW_YCO_METHOD");
            last_print = ecl_absolute_time();
        }
    }

    return _rate_setpoint;
}

float ECL_YawController::control_attitude_impl_openloop(const struct ECL_ControlData &ctl_data)
{
    /* Do not calculate control signal with bad inputs */
    if (!(ISFINITE(ctl_data.roll) &&
          ISFINITE(ctl_data.pitch) &&
          ISFINITE(ctl_data.roll_rate_setpoint) &&
          ISFINITE(ctl_data.pitch_rate_setpoint))) {
        return _rate_setpoint;
    }

    float constrained_roll;
    bool inverted = false;

    /* roll is used as feedforward term and inverted flight needs to be considered */
    if (fabsf(ctl_data.roll) < math::radians(90.0f)) {
        /* not inverted, but numerically still potentially close to infinity */
        constrained_roll = math::constrain(ctl_data.roll, math::radians(-80.0f), math::radians(80.0f));

    } else {
        inverted = true;

        // inverted flight, constrain on the two extremes of -pi..+pi to avoid infinity
        //note: the ranges are extended by 10 deg here to avoid numeric resolution effects
        if (ctl_data.roll > 0.0f) {
            /* right hemisphere */
            constrained_roll = math::constrain(ctl_data.roll, math::radians(100.0f), math::radians(180.0f));

        } else {
            /* left hemisphere */
            constrained_roll = math::constrain(ctl_data.roll, math::radians(-180.0f), math::radians(-100.0f));
        }
    }

    constrained_roll = math::constrain(constrained_roll, -fabsf(ctl_data.roll_setpoint), fabsf(ctl_data.roll_setpoint));


    if (!inverted) {
        /* Calculate desired yaw rate from coordinated turn constraint / (no side forces) */
        _rate_setpoint = tanf(constrained_roll) * cosf(ctl_data.pitch) * CONSTANTS_ONE_G / (ctl_data.airspeed <
                 ctl_data.airspeed_min ? ctl_data.airspeed_min : ctl_data.airspeed);
    }

    if (!ISFINITE(_rate_setpoint)) {
        ECL_WARN("yaw rate sepoint not finite");
        _rate_setpoint = 0.0f;
    }

    return _rate_setpoint;
}

float ECL_YawController::control_bodyrate(const struct ECL_ControlData &ctl_data)
{
    /* Do not calculate control signal with bad inputs */
    if (!(ISFINITE(ctl_data.roll) && ISFINITE(ctl_data.pitch) && ISFINITE(ctl_data.body_y_rate) &&
          ISFINITE(ctl_data.body_z_rate) && ISFINITE(ctl_data.pitch_rate_setpoint) &&
          ISFINITE(ctl_data.airspeed_min) && ISFINITE(ctl_data.airspeed_max) &&
          ISFINITE(ctl_data.scaler))) {
        return math::constrain(_last_output, -1.0f, 1.0f);
    }

    /* get the usual dt estimate */
    uint64_t dt_micros = ecl_elapsed_time(&_last_run);
    _last_run = ecl_absolute_time();
    float dt = (float)dt_micros * 1e-6f;

    /* lock integral for long intervals */
    bool lock_integrator = ctl_data.lock_integrator;

    if (dt_micros > 500000) {
        lock_integrator = true;
    }

    /* input conditioning */
    float airspeed = ctl_data.airspeed;

    if (!ISFINITE(airspeed)) {
        /* airspeed is NaN, +- INF or not available, pick center of band */
        airspeed = 0.5f * (ctl_data.airspeed_min + ctl_data.airspeed_max);

    } else if (airspeed < ctl_data.airspeed_min) {
        airspeed = ctl_data.airspeed_min;
    }

    /* Close the acceleration loop if _coordinated_method wants this: change body_rate setpoint */
    if (_coordinated_method == COORD_METHOD_CLOSEACC) {
        // XXX lateral acceleration needs to go into integrator with a gain
        //_bodyrate_setpoint -= (ctl_data.acc_body_y / (airspeed * cosf(ctl_data.pitch)));
    }

    /* Calculate body angular rate error */
    _rate_error = _bodyrate_setpoint - ctl_data.body_z_rate; // body angular rate error

    if (!lock_integrator && _k_i > 0.0f && airspeed > 0.5f * ctl_data.airspeed_min) {

        float id = _rate_error * dt;

        /*
         * anti-windup: do not allow integrator to increase if actuator is at limit
         */
        if (_last_output < -1.0f) {
            /* only allow motion to center: increase value */
            id = math::max(id, 0.0f);

        } else if (_last_output > 1.0f) {
            /* only allow motion to center: decrease value */
            id = math::min(id, 0.0f);
        }

        /* add and constrain */
        _integrator = math::constrain(_integrator + id * _k_i, -_integrator_max, _integrator_max);
    }

    /* Apply PI rate controller and store non-limited output */
    _last_output = (_bodyrate_setpoint * _k_ff + _rate_error * _k_p + _integrator) * ctl_data.scaler *
               ctl_data.scaler;  //scaler is proportional to 1/airspeed


    return math::constrain(_last_output, -1.0f, 1.0f);
}

float ECL_YawController::control_attitude_impl_accclosedloop(const struct ECL_ControlData &ctl_data)
{
    (void)ctl_data; // unused

    /* dont set a rate setpoint */
    return 0.0f;
}

float ECL_YawController::control_euler_rate(const struct ECL_ControlData &ctl_data)
{
    /* Transform setpoint to body angular rates (jacobian) */
    _bodyrate_setpoint = -sinf(ctl_data.roll) * ctl_data.pitch_rate_setpoint +
                 cosf(ctl_data.roll) * cosf(ctl_data.pitch) * _rate_setpoint;

    set_bodyrate_setpoint(_bodyrate_setpoint);

    return control_bodyrate(ctl_data);

}