An Enhanced Sensorless Control Scheme for PMSM Drives Considering Self-inductance Asymmetry

Inductance asymmetry, which is brought by inherent asymmetric parameters, manufacture tolerance, winding fault, cables with unequal lengths, etc., of permanent-magnet synchronous machines (PMSMs) can cause current harmonics and inaccurate position estimation. This paper proposes an enhanced fundamental model based sensorless control strategy for PMSMs with asymmetric inductances. The proportional-integral-resonant current regulator is introduced to reduce the second-order harmonics of currents, but there are still negative sequence components in the estimated back-electromotive forces (EMFs), which can cause the position estimated error. Differing from conventional methods in which negative sequences are filtered out before the phase-locked loop (PLL) module, the proposed method directly applies the estimated back-EMF with negative sequences as the reference input of PLL. An improved PLL with a bi-quad filter is proposed to attenuate the arising second harmonic position error and heighten the steady-state accuracy. Then, this position error is used for asymmetric inductance identification and its result is utilized to update the observer model. Furthermore, the dynamic performance is improved by the output limitation on the bi-quad filter as well as the implementation of a fast-locking technique in the PLL. The effectiveness of the proposed scheme is verified by experimental results.