Low-Harmonic Sensorless Control of PMSM Using a Multipulse Rectifier Front-End

This paper presents a robust sensorless control strategy for three-phase PMSM drives, integrating a 36-pulse rectifier and an enhanced sliding mode observer (SMO). The rectifier, realized through passive pulse-tripling circuits, significantly reduces input current total harmonic distortion (THD) and DC voltage ripple, thereby improving the signal quality delivered to the observer. These enhancements are critical for mitigating the high-frequency chattering commonly induced by ripple contamination in conventional 12-pulse systems. To further suppress chattering, a power-type hyperbolic tangent function replaces the conventional sign function in the SMO. By tuning the power exponent, the switching behavior achieves a desirable balance between smoothing and responsiveness. Simulation results demonstrate that the proposed method reduces THD to below 5% and markedly improves rotor position and speed estimation under load disturbances.