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High-frequency (HF) sinusoidal pulsating signal injection is an effective technique to achieve encoderless control for permanent magnet synchronous motor (PMSM) drive systems, particularly for low-speed regions. Classical methods usually use coherent demodulation to extract the rotor position from the HF current envelope. However, its design requires specific low-pass filters (LPFs), which limits the bandwidth of the subsequent rotor speed estimation, hence severely restricts the overall control performance. In this work, a novel fast time-domain demodulator is proposed, which eliminates the underlying LPF and significantly improves demodulation speed and accuracy of the ac-modulated signal. The proposed solution is verified via experimental data at a lab-constructed test bench. Results confirm that the proposal achieves good control performances at low-speed ranges.
Zhang et al. (Wed,) studied this question.