SLAU958A January 2025 – March 2025 MSPM0G3507
In conventional SMO based rotor position estimators, the rotor flux angle is determined based on the arc tangent of estimated stationary co-ordinate BEMF values as in Equation 16:
With this method, the accuracy of the position and velocity estimations are affected due to the existence of noise and harmonic components. To eliminate this issue, the PLL model can be used for velocity and position estimations in the sensorless control structure of the PMSM. The estimated BEMF values can be used with a PLL model to converge motor angular velocity and compute the rotor position as shown in Figure 6-14.

Since and ; the error in angle between the actual rotor position and the estimated rotor angle can be computed as
The closed loop transfer function of above plant can be treated as second order transfer function including PI controller and an integrator for position estimator defined by Equation 19:
here the PI gains are defined by where is the damping factor of the response and is the natural frequency of the second order response.
As the feedforward term for estimated speed is added , the PI controller estimates only the error in speed thus Kp and Ki can be independent of speeds and can be fixed values unless noise or sudden disturbances in load are expected. By default the Kp and Ki values are defined in "angleTrackingPLL.c" under modules/algoLib/libraries/semiCloseLoopEstim/source.