Enhanced Sequential High-Frequency Voltage Injection Method for Low-Speed Sensorless Control of IPMSM

This article proposes a sensorless control strategy for permanent magnet synchronous motors at low-speed that reduce the position estimation error caused by dead-time effect through a sequential positive-negative high-frequency voltage injection (SPN-HFVI) method. A signal demodulation technique addresses the limitations of traditional positive voltage injection in the ABC-phase. But dead-time effects induce fundamental and HF voltage disturbances, causing dc offset and sixth harmonic distortion in position estimation. To counter this, the proposed SPN-HFVI strategy further inject both positive and negative voltage pulses in ABC-phase. A filter-less signal processing method extracts position information from HF currents, eliminating the fundamental voltage disturbance. To further reduce the sixth harmonic, a composite quadrature-filtered phase-locked loop (PLL) is proposed, one of the PLL utilizes an iterative method to filter out sixth harmonic by constructing an objective function. By setting appropriate weights to adjust the position and speed signals of both PLLs, the proposed method optimally balances filtering capability and bandwidth, effectively suppressing the sixth harmonic during low-speed operation. Experimental results on an interior PMSM prototype, under both steady-state and dynamic conditions, verify the feasibility of the proposed strategy.