78 lines
2.9 KiB
C++
78 lines
2.9 KiB
C++
/*
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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The SlewLimiter filter provides an actuator slew rate limiter for
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PID controllers. It is used to reduce the P and D gains when the
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filter detects that the P+D components are pushing the actuator
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beyond the configured actuator rate limit. This can prevent
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oscillations that are caused by the output actuation rate going
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beyond the actuator maximum physical rate, which causes the
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actuation demand and achieved rate to get out of phase.
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this filter was originally written by Paul Riseborough for fixed
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wing use. It was adapted for wider use in AC_PID by Andrew Tridgell
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*/
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#include "SlewLimiter.h"
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SlewLimiter::SlewLimiter(const float &_slew_rate_max, const float &_slew_rate_tau) :
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slew_rate_max(_slew_rate_max),
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slew_rate_tau(_slew_rate_tau)
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{
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slew_filter.set_cutoff_frequency(10.0);
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slew_filter.reset(0.0);
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}
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/*
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apply filter to sample, returning multiplier between 0 and 1 to keep
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output within slew rate
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*/
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float SlewLimiter::modifier(float sample, float dt)
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{
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if (slew_rate_max <= 0) {
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return 1.0;
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}
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// calculate a low pass filtered slew rate
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const float slew_rate = slew_filter.apply((sample - last_sample) / dt, dt);
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last_sample = sample;
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// Rectify and apply a decaying envelope filter. The 10 in the
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// constrain limits the modifier to be between 0.1 and 1.0, so we
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// never drop PID gains below 10% of configured value
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// Do this separately for the positive and negative direction and use the smaller of
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// these to avoid single direction transients causing unwanted gain compression
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if (slew_rate > _max_pos_slew_rate) {
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_max_pos_slew_rate = fminf(slew_rate, 10.0f * slew_rate_max);
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} else {
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_max_pos_slew_rate *= (1.0f - fminf(dt, slew_rate_tau) / slew_rate_tau);
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}
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if (slew_rate < -_max_neg_slew_rate) {
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_max_neg_slew_rate = fminf(-slew_rate, 10.0f * slew_rate_max);
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} else {
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_max_neg_slew_rate *= (1.0f - fminf(dt, slew_rate_tau) / slew_rate_tau);
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}
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const float slew_rate_amplitude = fminf(_max_pos_slew_rate,_max_neg_slew_rate);
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// Calculate the gain adjustment
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float mod;
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if (slew_rate_amplitude > slew_rate_max) {
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mod = slew_rate_max / fmaxf(slew_rate_amplitude, slew_rate_max);
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} else {
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mod = 1.0f;
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}
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return mod;
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}
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