PX4-Autopilot/src/modules/mc_att_control/RateControl/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
	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
	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);
}