RateControl.cpp

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/**
 * @file RateControl.cpp
 */

#include <RateControl.hpp>
#include <px4_platform_common/defines.h>

using namespace matrix;

void RateControl::setGains(const Vector3f &P, const Vector3f &I, const Vector3f &D)
{
    _gain_p = P;
    _gain_i = I;
    _gain_d = D;
}

void RateControl::setDTermCutoff(const float loop_rate, const float cutoff, const bool force)
{
    // only do expensive filter update if the cutoff changed
    if (force || fabsf(_lp_filters_d.get_cutoff_freq() - cutoff) > 0.01f) {
        _lp_filters_d.set_cutoff_frequency(loop_rate, cutoff);
        _lp_filters_d.reset(_rate_prev);
    }
}

void RateControl::setSaturationStatus(const MultirotorMixer::saturation_status &status)
{
    _mixer_saturation_positive[0] = status.flags.roll_pos;
    _mixer_saturation_positive[1] = status.flags.pitch_pos;
    _mixer_saturation_positive[2] = status.flags.yaw_pos;
    _mixer_saturation_negative[0] = status.flags.roll_neg;
    _mixer_saturation_negative[1] = status.flags.pitch_neg;
    _mixer_saturation_negative[2] = status.flags.yaw_neg;
}

Vector3f RateControl::update(const Vector3f &rate, const Vector3f &rate_sp, const float dt, const bool landed)
{
    // angular rates error
    Vector3f rate_error = rate_sp - rate;

    // prepare D-term based on low-pass filtered rates
    const Vector3f rate_filtered(_lp_filters_d.apply(rate));
    Vector3f rate_d;

    if (dt > FLT_EPSILON) {
        rate_d = (rate_filtered - _rate_prev_filtered) / dt;
    }

    // PID control with feed forward
    const Vector3f torque = _gain_p.emult(rate_error) + _rate_int - _gain_d.emult(rate_d) + _gain_ff.emult(rate_sp);

    _rate_prev = rate;
    _rate_prev_filtered = rate_filtered;

    // update integral only if we are not landed
    if (!landed) {
        updateIntegral(rate_error, dt);
    }

    return torque;
}

void RateControl::updateIntegral(Vector3f &rate_error, const float dt)
{
    for (int i = 0; i < 3; i++) {
        // prevent further positive control saturation
        if (_mixer_saturation_positive[i]) {
            rate_error(i) = math::min(rate_error(i), 0.f);
        }

        // prevent further negative control saturation
        if (_mixer_saturation_negative[i]) {
            rate_error(i) = math::max(rate_error(i), 0.f);
        }

        // I term factor: reduce the I gain with increasing rate error.
        // This counteracts a non-linear effect where the integral builds up quickly upon a large setpoint
        // change (noticeable in a bounce-back effect after a flip).
        // The formula leads to a gradual decrease w/o steps, while only affecting the cases where it should:
        // with the parameter set to 400 degrees, up to 100 deg rate error, i_factor is almost 1 (having no effect),
        // and up to 200 deg error leads to <25% reduction of I.
        float i_factor = rate_error(i) / math::radians(400.f);
        i_factor = math::max(0.0f, 1.f - i_factor * i_factor);

        // Perform the integration using a first order method
        float rate_i = _rate_int(i) + i_factor * _gain_i(i) * rate_error(i) * dt;

        // do not propagate the result if out of range or invalid
        if (PX4_ISFINITE(rate_i)) {
            _rate_int(i) = math::constrain(rate_i, -_lim_int(i), _lim_int(i));
        }
    }
}

void RateControl::getRateControlStatus(rate_ctrl_status_s &rate_ctrl_status)
{
    rate_ctrl_status.rollspeed_integ = _rate_int(0);
    rate_ctrl_status.pitchspeed_integ = _rate_int(1);
    rate_ctrl_status.yawspeed_integ = _rate_int(2);
}