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62 lines
2.4 KiB
62 lines
2.4 KiB
/* |
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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 the slew rate amplitude produced by the unmodified sample |
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// calculate a low pass filtered slew rate |
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float Pterm_slew_rate = slew_filter.apply((fabsf(sample - last_sample)/ dt), dt); |
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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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float alpha = 1.0 - constrain_float(dt/slew_rate_tau, 0.0, 1.0); |
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slew_amplitude = constrain_float(Pterm_slew_rate, alpha * slew_amplitude, 10 * slew_rate_max); |
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// Calculate the gain adjustment |
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float mod = slew_rate_max / fmaxf(slew_amplitude, slew_rate_max); |
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last_sample = mod * sample; |
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return mod; |
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}
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