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Diffstat (limited to 'src/lib/external_lgpl/tecs/tecs.cpp')
| -rw-r--r-- | src/lib/external_lgpl/tecs/tecs.cpp | 542 |
1 files changed, 542 insertions, 0 deletions
diff --git a/src/lib/external_lgpl/tecs/tecs.cpp b/src/lib/external_lgpl/tecs/tecs.cpp new file mode 100644 index 000000000..1d5c85699 --- /dev/null +++ b/src/lib/external_lgpl/tecs/tecs.cpp @@ -0,0 +1,542 @@ +// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*- + +#include "tecs.h" +#include <ecl/ecl.h> + +using namespace math; + +#ifndef CONSTANTS_ONE_G +#define CONSTANTS_ONE_G GRAVITY +#endif + +/** + * @file tecs.cpp + * + * @author Paul Riseborough + * + * Written by Paul Riseborough 2013 to provide: + * - Combined control of speed and height using throttle to control + * total energy and pitch angle to control exchange of energy between + * potential and kinetic. + * Selectable speed or height priority modes when calculating pitch angle + * - Fallback mode when no airspeed measurement is available that + * sets throttle based on height rate demand and switches pitch angle control to + * height priority + * - Underspeed protection that demands maximum throttle and switches pitch angle control + * to speed priority mode + * - Relative ease of tuning through use of intuitive time constant, integrator and damping gains and the use + * of easy to measure aircraft performance data + * + */ + +void TECS::update_50hz(float baro_altitude, float airspeed, const math::Dcm &rotMat, const math::Vector3 &accel_body, const math::Vector3 &accel_earth) +{ + // Implement third order complementary filter for height and height rate + // estimted height rate = _integ2_state + // estimated height = _integ3_state + // Reference Paper : + // Optimising the Gains of the Baro-Inertial Vertical Channel + // Widnall W.S, Sinha P.K, + // AIAA Journal of Guidance and Control, 78-1307R + + // Calculate time in seconds since last update + uint64_t now = ecl_absolute_time(); + float DT = max((now - _update_50hz_last_usec), 0ULL) * 1.0e-6f; + + // printf("dt: %10.6f baro alt: %6.2f eas: %6.2f R(0,0): %6.2f, R(1,1): %6.2f\naccel body: %6.2f %6.2f %6.2f\naccel earth: %6.2f %6.2f %6.2f\n", + // DT, baro_altitude, airspeed, rotMat(0, 0), rotMat(1, 1), accel_body(0), accel_body(1), accel_body(2), + // accel_earth(0), accel_earth(1), accel_earth(2)); + + if (DT > 1.0f) { + _integ3_state = baro_altitude; + _integ2_state = 0.0f; + _integ1_state = 0.0f; + DT = 0.02f; // when first starting TECS, use a + // small time constant + } + + _update_50hz_last_usec = now; + _EAS = airspeed; + + // Get height acceleration + float hgt_ddot_mea = -(accel_earth(2) + CONSTANTS_ONE_G); + // Perform filter calculation using backwards Euler integration + // Coefficients selected to place all three filter poles at omega + float omega2 = _hgtCompFiltOmega * _hgtCompFiltOmega; + float hgt_err = baro_altitude - _integ3_state; + float integ1_input = hgt_err * omega2 * _hgtCompFiltOmega; + _integ1_state = _integ1_state + integ1_input * DT; + float integ2_input = _integ1_state + hgt_ddot_mea + hgt_err * omega2 * 3.0f; + _integ2_state = _integ2_state + integ2_input * DT; + float integ3_input = _integ2_state + hgt_err * _hgtCompFiltOmega * 3.0f; + + // If more than 1 second has elapsed since last update then reset the integrator state + // to the measured height + if (DT > 1.0f) { + _integ3_state = baro_altitude; + + } else { + _integ3_state = _integ3_state + integ3_input * DT; + } + + // Update and average speed rate of change + // Only required if airspeed is being measured and controlled + float temp = 0; + + if (isfinite(airspeed) && airspeed_sensor_enabled()) { + // Get DCM + // Calculate speed rate of change + // XXX check + temp = rotMat(2, 0) * CONSTANTS_ONE_G + accel_body(0); + // take 5 point moving average + //_vel_dot = _vdot_filter.apply(temp); + // XXX resolve this properly + _vel_dot = 0.9f * _vel_dot + 0.1f * temp; + + } else { + _vel_dot = 0.0f; + } + +} + +void TECS::_update_speed(float airspeed_demand, float indicated_airspeed, + float indicated_airspeed_min, float indicated_airspeed_max, float EAS2TAS) +{ + // Calculate time in seconds since last update + uint64_t now = ecl_absolute_time(); + float DT = max((now - _update_speed_last_usec), 0ULL) * 1.0e-6f; + _update_speed_last_usec = now; + + // Convert equivalent airspeeds to true airspeeds + + _EAS_dem = airspeed_demand; + _TAS_dem = _EAS_dem * EAS2TAS; + _TASmax = indicated_airspeed_max * EAS2TAS; + _TASmin = indicated_airspeed_min * EAS2TAS; + + // Reset states of time since last update is too large + if (DT > 1.0f) { + _integ5_state = (_EAS * EAS2TAS); + _integ4_state = 0.0f; + DT = 0.1f; // when first starting TECS, use a + // small time constant + } + + // Get airspeed or default to halfway between min and max if + // airspeed is not being used and set speed rate to zero + if (!isfinite(indicated_airspeed) || !airspeed_sensor_enabled()) { + // If no airspeed available use average of min and max + _EAS = 0.5f * (indicated_airspeed_min + indicated_airspeed_max); + + } else { + _EAS = indicated_airspeed; + } + + // Implement a second order complementary filter to obtain a + // smoothed airspeed estimate + // airspeed estimate is held in _integ5_state + float aspdErr = (_EAS * EAS2TAS) - _integ5_state; + float integ4_input = aspdErr * _spdCompFiltOmega * _spdCompFiltOmega; + + // Prevent state from winding up + if (_integ5_state < 3.1f) { + integ4_input = max(integ4_input , 0.0f); + } + + _integ4_state = _integ4_state + integ4_input * DT; + float integ5_input = _integ4_state + _vel_dot + aspdErr * _spdCompFiltOmega * 1.4142f; + _integ5_state = _integ5_state + integ5_input * DT; + // limit the airspeed to a minimum of 3 m/s + _integ5_state = max(_integ5_state, 3.0f); + +} + +void TECS::_update_speed_demand(void) +{ + // Set the airspeed demand to the minimum value if an underspeed condition exists + // or a bad descent condition exists + // This will minimise the rate of descent resulting from an engine failure, + // enable the maximum climb rate to be achieved and prevent continued full power descent + // into the ground due to an unachievable airspeed value + if ((_badDescent) || (_underspeed)) { + _TAS_dem = _TASmin; + } + + // Constrain speed demand + _TAS_dem = constrain(_TAS_dem, _TASmin, _TASmax); + + // calculate velocity rate limits based on physical performance limits + // provision to use a different rate limit if bad descent or underspeed condition exists + // Use 50% of maximum energy rate to allow margin for total energy contgroller + float velRateMax; + float velRateMin; + + if ((_badDescent) || (_underspeed)) { + velRateMax = 0.5f * _STEdot_max / _integ5_state; + velRateMin = 0.5f * _STEdot_min / _integ5_state; + + } else { + velRateMax = 0.5f * _STEdot_max / _integ5_state; + velRateMin = 0.5f * _STEdot_min / _integ5_state; + } + + // Apply rate limit + if ((_TAS_dem - _TAS_dem_adj) > (velRateMax * 0.1f)) { + _TAS_dem_adj = _TAS_dem_adj + velRateMax * 0.1f; + _TAS_rate_dem = velRateMax; + + } else if ((_TAS_dem - _TAS_dem_adj) < (velRateMin * 0.1f)) { + _TAS_dem_adj = _TAS_dem_adj + velRateMin * 0.1f; + _TAS_rate_dem = velRateMin; + + } else { + _TAS_dem_adj = _TAS_dem; + _TAS_rate_dem = (_TAS_dem - _TAS_dem_last) / 0.1f; + } + + // Constrain speed demand again to protect against bad values on initialisation. + _TAS_dem_adj = constrain(_TAS_dem_adj, _TASmin, _TASmax); + _TAS_dem_last = _TAS_dem; +} + +void TECS::_update_height_demand(float demand) +{ + // Apply 2 point moving average to demanded height + // This is required because height demand is only updated at 5Hz + _hgt_dem = 0.5f * (demand + _hgt_dem_in_old); + _hgt_dem_in_old = _hgt_dem; + + // printf("hgt_dem: %6.2f hgt_dem_last: %6.2f max_climb_rate: %6.2f\n", _hgt_dem, _hgt_dem_prev, + // _maxClimbRate); + + // Limit height rate of change + if ((_hgt_dem - _hgt_dem_prev) > (_maxClimbRate * 0.1f)) { + _hgt_dem = _hgt_dem_prev + _maxClimbRate * 0.1f; + + } else if ((_hgt_dem - _hgt_dem_prev) < (-_maxSinkRate * 0.1f)) { + _hgt_dem = _hgt_dem_prev - _maxSinkRate * 0.1f; + } + + _hgt_dem_prev = _hgt_dem; + + // Apply first order lag to height demand + _hgt_dem_adj = 0.05f * _hgt_dem + 0.95f * _hgt_dem_adj_last; + _hgt_rate_dem = (_hgt_dem_adj - _hgt_dem_adj_last) / 0.1f; + _hgt_dem_adj_last = _hgt_dem_adj; + + // printf("hgt_dem: %6.2f hgt_dem_adj: %6.2f hgt_dem_last: %6.2f hgt_rate_dem: %6.2f\n", _hgt_dem, _hgt_dem_adj, _hgt_dem_adj_last, + // _hgt_rate_dem); +} + +void TECS::_detect_underspeed(void) +{ + if (((_integ5_state < _TASmin * 0.9f) && (_throttle_dem >= _THRmaxf * 0.95f)) || ((_integ3_state < _hgt_dem_adj) && _underspeed)) { + _underspeed = true; + + } else { + _underspeed = false; + } +} + +void TECS::_update_energies(void) +{ + // Calculate specific energy demands + _SPE_dem = _hgt_dem_adj * CONSTANTS_ONE_G; + _SKE_dem = 0.5f * _TAS_dem_adj * _TAS_dem_adj; + + // Calculate specific energy rate demands + _SPEdot_dem = _hgt_rate_dem * CONSTANTS_ONE_G; + _SKEdot_dem = _integ5_state * _TAS_rate_dem; + + // Calculate specific energy + _SPE_est = _integ3_state * CONSTANTS_ONE_G; + _SKE_est = 0.5f * _integ5_state * _integ5_state; + + // Calculate specific energy rate + _SPEdot = _integ2_state * CONSTANTS_ONE_G; + _SKEdot = _integ5_state * _vel_dot; +} + +void TECS::_update_throttle(float throttle_cruise, const math::Dcm &rotMat) +{ + // Calculate total energy values + _STE_error = _SPE_dem - _SPE_est + _SKE_dem - _SKE_est; + float STEdot_dem = constrain((_SPEdot_dem + _SKEdot_dem), _STEdot_min, _STEdot_max); + float STEdot_error = STEdot_dem - _SPEdot - _SKEdot; + + // Apply 0.5 second first order filter to STEdot_error + // This is required to remove accelerometer noise from the measurement + STEdot_error = 0.2f * STEdot_error + 0.8f * _STEdotErrLast; + _STEdotErrLast = STEdot_error; + + // Calculate throttle demand + // If underspeed condition is set, then demand full throttle + if (_underspeed) { + _throttle_dem_unc = 1.0f; + + } else { + // Calculate gain scaler from specific energy error to throttle + float K_STE2Thr = 1 / (_timeConst * (_STEdot_max - _STEdot_min)); + + // Calculate feed-forward throttle + float ff_throttle = 0; + float nomThr = throttle_cruise; + // Use the demanded rate of change of total energy as the feed-forward demand, but add + // additional component which scales with (1/cos(bank angle) - 1) to compensate for induced + // drag increase during turns. + float cosPhi = sqrtf((rotMat(0, 1) * rotMat(0, 1)) + (rotMat(1, 1) * rotMat(1, 1))); + STEdot_dem = STEdot_dem + _rollComp * (1.0f / constrain(cosPhi * cosPhi , 0.1f, 1.0f) - 1.0f); + + if (STEdot_dem >= 0) { + ff_throttle = nomThr + STEdot_dem / _STEdot_max * (1.0f - nomThr); + + } else { + ff_throttle = nomThr - STEdot_dem / _STEdot_min * nomThr; + } + + // Calculate PD + FF throttle + _throttle_dem = (_STE_error + STEdot_error * _thrDamp) * K_STE2Thr + ff_throttle; + + // Rate limit PD + FF throttle + // Calculate the throttle increment from the specified slew time + if (fabsf(_throttle_slewrate) > 0.01f) { + float thrRateIncr = _DT * (_THRmaxf - _THRminf) * _throttle_slewrate; + + _throttle_dem = constrain(_throttle_dem, + _last_throttle_dem - thrRateIncr, + _last_throttle_dem + thrRateIncr); + _last_throttle_dem = _throttle_dem; + } + + + // Calculate integrator state upper and lower limits + // Set to a value thqat will allow 0.1 (10%) throttle saturation to allow for noise on the demand + float integ_max = (_THRmaxf - _throttle_dem + 0.1f); + float integ_min = (_THRminf - _throttle_dem - 0.1f); + + // Calculate integrator state, constraining state + // Set integrator to a max throttle value dduring climbout + _integ6_state = _integ6_state + (_STE_error * _integGain) * _DT * K_STE2Thr; + + if (_climbOutDem) { + _integ6_state = integ_max; + + } else { + _integ6_state = constrain(_integ6_state, integ_min, integ_max); + } + + // Sum the components. + // Only use feed-forward component if airspeed is not being used + if (airspeed_sensor_enabled()) { + _throttle_dem = _throttle_dem + _integ6_state; + + } else { + _throttle_dem = ff_throttle; + } + } + + // Constrain throttle demand + _throttle_dem = constrain(_throttle_dem, _THRminf, _THRmaxf); +} + +void TECS::_detect_bad_descent(void) +{ + // Detect a demanded airspeed too high for the aircraft to achieve. This will be + // evident by the the following conditions: + // 1) Underspeed protection not active + // 2) Specific total energy error > 200 (greater than ~20m height error) + // 3) Specific total energy reducing + // 4) throttle demand > 90% + // If these four conditions exist simultaneously, then the protection + // mode will be activated. + // Once active, the following condition are required to stay in the mode + // 1) Underspeed protection not active + // 2) Specific total energy error > 0 + // This mode will produce an undulating speed and height response as it cuts in and out but will prevent the aircraft from descending into the ground if an unachievable speed demand is set + float STEdot = _SPEdot + _SKEdot; + + if ((!_underspeed && (_STE_error > 200.0f) && (STEdot < 0.0f) && (_throttle_dem >= _THRmaxf * 0.9f)) || (_badDescent && !_underspeed && (_STE_error > 0.0f))) { + _badDescent = true; + + } else { + _badDescent = false; + } +} + +void TECS::_update_pitch(void) +{ + // Calculate Speed/Height Control Weighting + // This is used to determine how the pitch control prioritises speed and height control + // A weighting of 1 provides equal priority (this is the normal mode of operation) + // A SKE_weighting of 0 provides 100% priority to height control. This is used when no airspeed measurement is available + // A SKE_weighting of 2 provides 100% priority to speed control. This is used when an underspeed condition is detected + // or during takeoff/climbout where a minimum pitch angle is set to ensure height is gained. In this instance, if airspeed + // rises above the demanded value, the pitch angle will be increased by the TECS controller. + float SKE_weighting = constrain(_spdWeight, 0.0f, 2.0f); + + if ((_underspeed || _climbOutDem) && airspeed_sensor_enabled()) { + SKE_weighting = 2.0f; + + } else if (!airspeed_sensor_enabled()) { + SKE_weighting = 0.0f; + } + + float SPE_weighting = 2.0f - SKE_weighting; + + // Calculate Specific Energy Balance demand, and error + float SEB_dem = _SPE_dem * SPE_weighting - _SKE_dem * SKE_weighting; + float SEBdot_dem = _SPEdot_dem * SPE_weighting - _SKEdot_dem * SKE_weighting; + float SEB_error = SEB_dem - (_SPE_est * SPE_weighting - _SKE_est * SKE_weighting); + float SEBdot_error = SEBdot_dem - (_SPEdot * SPE_weighting - _SKEdot * SKE_weighting); + + // Calculate integrator state, constraining input if pitch limits are exceeded + float integ7_input = SEB_error * _integGain; + + if (_pitch_dem_unc > _PITCHmaxf) { + integ7_input = min(integ7_input, _PITCHmaxf - _pitch_dem_unc); + + } else if (_pitch_dem_unc < _PITCHminf) { + integ7_input = max(integ7_input, _PITCHminf - _pitch_dem_unc); + } + + _integ7_state = _integ7_state + integ7_input * _DT; + + // Apply max and min values for integrator state that will allow for no more than + // 5deg of saturation. This allows for some pitch variation due to gusts before the + // integrator is clipped. Otherwise the effectiveness of the integrator will be reduced in turbulence + // During climbout/takeoff, bias the demanded pitch angle so that zero speed error produces a pitch angle + // demand equal to the minimum value (which is )set by the mission plan during this mode). Otherwise the + // integrator has to catch up before the nose can be raised to reduce speed during climbout. + float gainInv = (_integ5_state * _timeConst * CONSTANTS_ONE_G); + float temp = SEB_error + SEBdot_error * _ptchDamp + SEBdot_dem * _timeConst; + if (_climbOutDem) + { + temp += _PITCHminf * gainInv; + } + _integ7_state = constrain(_integ7_state, (gainInv * (_PITCHminf - 0.0783f)) - temp, (gainInv * (_PITCHmaxf + 0.0783f)) - temp); + + + // Calculate pitch demand from specific energy balance signals + _pitch_dem_unc = (temp + _integ7_state) / gainInv; + + // Constrain pitch demand + _pitch_dem = constrain(_pitch_dem_unc, _PITCHminf, _PITCHmaxf); + + // Rate limit the pitch demand to comply with specified vertical + // acceleration limit + float ptchRateIncr = _DT * _vertAccLim / _integ5_state; + + if ((_pitch_dem - _last_pitch_dem) > ptchRateIncr) { + _pitch_dem = _last_pitch_dem + ptchRateIncr; + + } else if ((_pitch_dem - _last_pitch_dem) < -ptchRateIncr) { + _pitch_dem = _last_pitch_dem - ptchRateIncr; + } + + _last_pitch_dem = _pitch_dem; +} + +void TECS::_initialise_states(float pitch, float throttle_cruise, float baro_altitude, float ptchMinCO_rad) +{ + // Initialise states and variables if DT > 1 second or in climbout + if (_DT > 1.0f) { + _integ6_state = 0.0f; + _integ7_state = 0.0f; + _last_throttle_dem = throttle_cruise; + _last_pitch_dem = pitch; + _hgt_dem_adj_last = baro_altitude; + _hgt_dem_adj = _hgt_dem_adj_last; + _hgt_dem_prev = _hgt_dem_adj_last; + _hgt_dem_in_old = _hgt_dem_adj_last; + _TAS_dem_last = _TAS_dem; + _TAS_dem_adj = _TAS_dem; + _underspeed = false; + _badDescent = false; + _DT = 0.1f; // when first starting TECS, use a + // small time constant + + } else if (_climbOutDem) { + _PITCHminf = ptchMinCO_rad; + _THRminf = _THRmaxf - 0.01f; + _hgt_dem_adj_last = baro_altitude; + _hgt_dem_adj = _hgt_dem_adj_last; + _hgt_dem_prev = _hgt_dem_adj_last; + _TAS_dem_last = _TAS_dem; + _TAS_dem_adj = _TAS_dem; + _underspeed = false; + _badDescent = false; + } +} + +void TECS::_update_STE_rate_lim(void) +{ + // Calculate Specific Total Energy Rate Limits + // This is a tivial calculation at the moment but will get bigger once we start adding altitude effects + _STEdot_max = _maxClimbRate * CONSTANTS_ONE_G; + _STEdot_min = - _minSinkRate * CONSTANTS_ONE_G; +} + +void TECS::update_pitch_throttle(const math::Dcm &rotMat, float pitch, float baro_altitude, float hgt_dem, float EAS_dem, float indicated_airspeed, float EAS2TAS, bool climbOutDem, float ptchMinCO, + float throttle_min, float throttle_max, float throttle_cruise, + float pitch_limit_min, float pitch_limit_max) +{ + // Calculate time in seconds since last update + uint64_t now = ecl_absolute_time(); + _DT = max((now - _update_pitch_throttle_last_usec), 0ULL) * 1.0e-6f; + _update_pitch_throttle_last_usec = now; + + // printf("tecs in: dt:%10.6f pitch: %6.2f baro_alt: %6.2f alt sp: %6.2f\neas sp: %6.2f eas: %6.2f, eas2tas: %6.2f\n %s pitch min C0: %6.2f thr min: %6.2f, thr max: %6.2f thr cruis: %6.2f pt min: %6.2f, pt max: %6.2f\n", + // _DT, pitch, baro_altitude, hgt_dem, EAS_dem, indicated_airspeed, EAS2TAS, (climbOutDem) ? "climb" : "level", ptchMinCO, throttle_min, throttle_max, throttle_cruise, pitch_limit_min, pitch_limit_max); + + // Update the speed estimate using a 2nd order complementary filter + _update_speed(EAS_dem, indicated_airspeed, _indicated_airspeed_min, _indicated_airspeed_max, EAS2TAS); + + // Convert inputs + _THRmaxf = throttle_max; + _THRminf = throttle_min; + _PITCHmaxf = pitch_limit_max; + _PITCHminf = pitch_limit_min; + _climbOutDem = climbOutDem; + + // initialise selected states and variables if DT > 1 second or in climbout + _initialise_states(pitch, throttle_cruise, baro_altitude, ptchMinCO); + + // Calculate Specific Total Energy Rate Limits + _update_STE_rate_lim(); + + // Calculate the speed demand + _update_speed_demand(); + + // Calculate the height demand + _update_height_demand(hgt_dem); + + // Detect underspeed condition + _detect_underspeed(); + + // Calculate specific energy quantitiues + _update_energies(); + + // Calculate throttle demand + _update_throttle(throttle_cruise, rotMat); + + // Detect bad descent due to demanded airspeed being too high + _detect_bad_descent(); + + // Calculate pitch demand + _update_pitch(); + +// // Write internal variables to the log_tuning structure. This +// // structure will be logged in dataflash at 10Hz + // log_tuning.hgt_dem = _hgt_dem_adj; + // log_tuning.hgt = _integ3_state; + // log_tuning.dhgt_dem = _hgt_rate_dem; + // log_tuning.dhgt = _integ2_state; + // log_tuning.spd_dem = _TAS_dem_adj; + // log_tuning.spd = _integ5_state; + // log_tuning.dspd = _vel_dot; + // log_tuning.ithr = _integ6_state; + // log_tuning.iptch = _integ7_state; + // log_tuning.thr = _throttle_dem; + // log_tuning.ptch = _pitch_dem; + // log_tuning.dspd_dem = _TAS_rate_dem; +} |