Disturbance Observer-Based Sliding Mode Observer With Enhanced Quadrature Phase-Locked Loop for SPMSM Sensorless Drive

The disturbance observer-based sliding-mode observer (DSMO) is featured by fast convergence and high estimation accuracy. However, when DSMO is applied in sensorless control of surface-mounted permanent magnet synchronous motors (SPMSMs), it is affected by the low-pass filter (LPF), causing a phase deviation in the estimated rotor position. This deviation causes the current phase to become misaligned with the actual flux linkage phase, generating harmonics, particularly at low speeds. To address this issue, a novel DSMO design based on an enhanced quadrature phase-locked loop (QPLL) is proposed. First, an enhanced QPLL incorporating feedforward compensation and normalization is applied to compensate for the phase deviation dynamically. Specifically, feedforward compensation eliminates the error caused by transient speed variations, while normalization mitigates the impact of speed and flux variations on rotor position estimation accuracy. Second, the softsign function with dynamically adjusted equivalent gains is designed to enhance the observer’s robustness at low speeds and effectively reduce chattering at high speeds. Additionally, a stricter uniform boundedness condition is provided to ensure that DSMO’s sliding surface converges to a smaller bound. Experimental results demonstrate that this scheme provides more accurate speed and rotor position for FOC and effectively improves the performance of sensorless control.