Sensorless Control Strategy of Nine-phase PMSM Based on Piecewise Combination of Open-loop and Sliding Mode Observer

To overcome the inaccurate measurement of rotor position in low-speed range of nine-phase permanent magnet synchronous motor by sliding mode observer, current and frequency (IF) open-loop starting strategy is adopted. In the high-speed range, the rotor position is measured by sliding mode observer. The chattering problem of sliding mode observer is improved by using sinusoidal saturation function and phase locked loop (PLL). The smooth switching from IF open-loop control to sensorless vector control based on sliding mode observer is realized by adopting an improved switching strategy based on double d-q spaces. The feasibility of the proposed compound control strategy is confirmed by experimental results.