A simplified position observer for zero-speed sensorless control of synchronous motors

This paper considers a sensorless control scheme based on pulsating high-frequency voltage injection applied to a linear permanent magnet synchronous motor (LPMSM). The injected signal is superimposed along the estimated d-axis and the mover position is obtained by minimizing the estimated q-axis current using a position observer. Three position observers, with different level of computational complexity, are considered. The first one utilizes a proportional-integral-derivative (PID) regulator, followed by the mechanical model of the LPMSM. The PID regulator output is the estimated torque and the mechanical system model is used to estimate speed and position. The second and third one employ a proportional-integral (PI) and proportional (P) regulator respectively to estimate the speed and an integrator to calculate the position. The use of the latter observer simplifies the commissioning procedure and reduces the computational burden without compromising performances. The comparison of the three schemes has been carried out with an extensive experimental study.