*

ODrive-fw-v0.5.6/Firmware/MotorControl/sensorless_estimator.cpp

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+
+#include "odrive_main.h"
+
+void SensorlessEstimator::reset() {
+    pll_pos_ = 0.0f;
+    vel_estimate_ = 0.0f;
+    V_alpha_beta_memory_[0] = 0.0f;
+    V_alpha_beta_memory_[1] = 0.0f;
+    flux_state_[0] = 0.0f;
+    flux_state_[1] = 0.0f;
+}
+
+bool SensorlessEstimator::update() {
+    // Algorithm based on paper: Sensorless Control of Surface-Mount Permanent-Magnet Synchronous Motors Based on a Nonlinear Observer
+    // http://cas.ensmp.fr/~praly/Telechargement/Journaux/2010-IEEE_TPEL-Lee-Hong-Nam-Ortega-Praly-Astolfi.pdf
+    // In particular, equation 8 (and by extension eqn 4 and 6).
+
+    // The V_alpha_beta applied immedietly prior to the current measurement associated with this cycle
+    // is the one computed two cycles ago. To get the correct measurement, it was stored twice:
+    // once by final_v_alpha/final_v_beta in the current control reporting, and once by V_alpha_beta_memory.
+
+    // PLL
+    // TODO: the PLL part has some code duplication with the encoder PLL
+    // Pll gains as a function of bandwidth
+    float pll_kp = 2.0f * config_.pll_bandwidth;
+    // Critically damped
+    float pll_ki = 0.25f * (pll_kp * pll_kp);
+
+    // Check that we don't get problems with discrete time approximation
+    if (!(current_meas_period * pll_kp < 1.0f)) {
+        error_ |= ERROR_UNSTABLE_GAIN;
+        axis_->error_ |= Axis::ERROR_SENSORLESS_ESTIMATOR_FAILED;
+        reset(); // Reset state for when the next valid current measurement comes in.
+        return false;
+    }
+
+    // TODO: we read values here which are modified by a higher priority interrupt.
+    // This is not thread-safe.    
+    auto current_meas = axis_->motor_.current_meas_;
+    if (!axis_->motor_.is_armed_) {
+        // While the motor is disarmed the current is not measurable so we
+        // assume that it's zero.
+        current_meas = {0.0f, 0.0f};
+    }
+    if (!current_meas.has_value()) {
+        error_ |= ERROR_UNKNOWN_CURRENT_MEASUREMENT;
+        axis_->error_ |= Axis::ERROR_SENSORLESS_ESTIMATOR_FAILED;
+        reset(); // Reset state for when the next valid current measurement comes in.
+        return false;
+    }
+
+    // Clarke transform
+    float I_alpha_beta[2] = {
+        current_meas->phA,
+        one_by_sqrt3 * (current_meas->phB - current_meas->phC)};
+
+    // alpha-beta vector operations
+    float eta[2];
+    for (int i = 0; i <= 1; ++i) {
+        // y is the total flux-driving voltage (see paper eqn 4)
+        float y = -axis_->motor_.config_.phase_resistance * I_alpha_beta[i] + V_alpha_beta_memory_[i];
+        // flux dynamics (prediction)
+        float x_dot = y;
+        // integrate prediction to current timestep
+        flux_state_[i] += x_dot * current_meas_period;
+
+        // eta is the estimated permanent magnet flux (see paper eqn 6)
+        eta[i] = flux_state_[i] - axis_->motor_.config_.phase_inductance * I_alpha_beta[i];
+    }
+
+    // Non-linear observer (see paper eqn 8):
+    float pm_flux_sqr = config_.pm_flux_linkage * config_.pm_flux_linkage;
+    float est_pm_flux_sqr = eta[0] * eta[0] + eta[1] * eta[1];
+    float bandwidth_factor = 1.0f / pm_flux_sqr;
+    float eta_factor = 0.5f * (config_.observer_gain * bandwidth_factor) * (pm_flux_sqr - est_pm_flux_sqr);
+
+    // alpha-beta vector operations
+    for (int i = 0; i <= 1; ++i) {
+        // add observer action to flux estimate dynamics
+        float x_dot = eta_factor * eta[i];
+        // convert action to discrete-time
+        flux_state_[i] += x_dot * current_meas_period;
+        // update new eta
+        eta[i] = flux_state_[i] - axis_->motor_.config_.phase_inductance * I_alpha_beta[i];
+    }
+
+    // Flux state estimation done, store V_alpha_beta for next timestep
+    V_alpha_beta_memory_[0] = axis_->motor_.current_control_.final_v_alpha_;
+    V_alpha_beta_memory_[1] = axis_->motor_.current_control_.final_v_beta_;
+
+    float phase_vel = phase_vel_.previous().value_or(0.0f);
+
+    // predict PLL phase with velocity
+    pll_pos_ = wrap_pm_pi(pll_pos_ + current_meas_period * phase_vel);
+    // update PLL phase with observer permanent magnet phase
+    float phase = fast_atan2(eta[1], eta[0]);
+    float delta_phase = wrap_pm_pi(phase - pll_pos_);
+    pll_pos_ = wrap_pm_pi(pll_pos_ + current_meas_period * pll_kp * delta_phase);
+    // update PLL velocity
+    phase_vel += current_meas_period * pll_ki * delta_phase;
+
+    // set outputs
+    phase_ = phase;
+    phase_vel_ = phase_vel;
+    vel_estimate_ = phase_vel / (std::max((float)axis_->motor_.config_.pole_pairs, 1.0f) * 2.0f * M_PI);
+
+    return true;
+};