Improved Initial Rotor Position Estimation for PMSM Drives Based on HF Pulsating Voltage Signal Injection

In a permanent magnet synchronous motor (PMSM) drive system, high-frequency (HF) pulsating voltage signal injection has demonstrated high accuracy to estimate the initial rotor position. However, a conventional signal demodulation method may face the problems of long convergence time and limited system stability, owing to the low-pass filter (LPF) used in signal demodulation process. Thus, a direct signal demodulation method is proposed, in which, the LPF is removed to improve system stability and dynamic property. A direct demodulation collection is generated to extract the position deviation signal from estimated q-axis HF current. Recursive discrete Fourier transform is employed to calculate the amplitude of estimated d-axis HF current, thus an amplitude normalized technique is implemented to reduce the effects of HF signal and PMSM. Meanwhile, the stability and dynamic property are compared between the conventional and proposed method, with the aid of D-partition technique and amplitude-frequency characteristics diagram. Furthermore, a novel magnetic polarity detection method is put forward based on the magnetic saturation, which has a high signal-to-noise ratio. Finally, the experimental results on three PMSM drive systems prove that the proposed method is practicable and effective.