mirror of https://github.com/ArduPilot/ardupilot
144 lines
3.8 KiB
C++
144 lines
3.8 KiB
C++
/// @file PID.cpp
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/// @brief Generic PID algorithm
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#include <cmath>
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#include "PID.h"
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#include <AP_HAL/AP_HAL.h>
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#include <AP_Math/AP_Math.h>
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extern const AP_HAL::HAL& hal;
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const AP_Param::GroupInfo PID::var_info[] = {
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// @Param: P
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// @DisplayName: PID Proportional Gain
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// @Description: P Gain which produces an output value that is proportional to the current error value
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AP_GROUPINFO_FLAGS_DEFAULT_POINTER("P", 0, PID, _kp, default_kp),
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// @Param: I
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// @DisplayName: PID Integral Gain
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// @Description: I Gain which produces an output that is proportional to both the magnitude and the duration of the error
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AP_GROUPINFO_FLAGS_DEFAULT_POINTER("I", 1, PID, _ki, default_ki),
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// @Param: D
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// @DisplayName: PID Derivative Gain
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// @Description: D Gain which produces an output that is proportional to the rate of change of the error
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AP_GROUPINFO_FLAGS_DEFAULT_POINTER("D", 2, PID, _kd, default_kd),
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// @Param: IMAX
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// @DisplayName: PID Integral Maximum
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// @Description: The maximum/minimum value that the I term can output
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AP_GROUPINFO_FLAGS_DEFAULT_POINTER("IMAX", 3, PID, _imax, default_kimax),
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AP_GROUPEND
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};
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float PID::get_pid(float error, float scaler)
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{
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uint32_t tnow = AP_HAL::millis();
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uint32_t dt = tnow - _last_t;
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float output = 0;
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float delta_time;
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if (_last_t == 0 || dt > 1000) {
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dt = 0;
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// if this PID hasn't been used for a full second then zero
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// the intergator term. This prevents I buildup from a
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// previous fight mode from causing a massive return before
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// the integrator gets a chance to correct itself
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reset_I();
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}
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_last_t = tnow;
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delta_time = (float)dt * 0.001f;
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// Compute proportional component
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_pid_info.P = error * _kp;
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output += _pid_info.P;
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// Compute derivative component if time has elapsed
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if ((fabsf(_kd) > 0) && (dt > 0)) {
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float derivative;
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if (isnan(_last_derivative)) {
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// we've just done a reset, suppress the first derivative
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// term as we don't want a sudden change in input to cause
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// a large D output change
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derivative = 0;
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_last_derivative = 0;
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} else {
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derivative = (error - _last_error) / delta_time;
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}
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// discrete low pass filter, cuts out the
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// high frequency noise that can drive the controller crazy
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float RC = 1/(2*M_PI*_fCut);
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derivative = _last_derivative +
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((delta_time / (RC + delta_time)) *
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(derivative - _last_derivative));
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// update state
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_last_error = error;
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_last_derivative = derivative;
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// add in derivative component
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_pid_info.D = _kd * derivative;
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output += _pid_info.D;
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}
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// scale the P and D components
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output *= scaler;
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_pid_info.D *= scaler;
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_pid_info.P *= scaler;
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// Compute integral component if time has elapsed
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if ((fabsf(_ki) > 0) && (dt > 0)) {
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_integrator += (error * _ki) * scaler * delta_time;
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if (_integrator < -_imax) {
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_integrator = -_imax;
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} else if (_integrator > _imax) {
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_integrator = _imax;
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}
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_pid_info.I = _integrator;
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output += _integrator;
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}
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_pid_info.target = output;
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return output;
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}
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void
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PID::reset_I()
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{
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_integrator = 0;
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// we use NAN (Not A Number) to indicate that the last
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// derivative value is not valid
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_last_derivative = NAN;
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_pid_info.I = 0;
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}
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void PID::reset() {
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memset(&_pid_info, 0, sizeof(_pid_info));
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reset_I();
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}
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void
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PID::load_gains()
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{
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_kp.load();
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_ki.load();
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_kd.load();
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_imax.load();
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}
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void
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PID::save_gains()
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{
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_kp.save();
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_ki.save();
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_kd.save();
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_imax.save();
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}
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