The load inertia in permanent magnet synchronous motor speed control system is always unknown in practice. When the nominal inertia which is used as an observer parameter mismatches the actual inertia of the system

the transfer function of the system based on the conventional extended state observer will have conjugate poles. As a result

overshoot and oscillations occur during speed control. To address this

an improved high-order extended state observer(HESO)was proposed. By additionally observing lumped disturbance differential term and actively adjusting the location of zero-poles

this observer maintains good dynamic control performance under inertia mismatch. Meanwhile

an adaptive switching logic based on speed tracking error was introduced. And HESO based on adaptive switching logic(AS-HESO)was further developed incorporating this adaptive switching logic

which enhances the system's disturbance rejection ability in steady state. The speed control strategy based on the proposed observer exhibits smaller overshoot

faster dynamic response speed and stronger robustness to variations in the moment of inertia. The feasibility and effectiveness of the strategy is verified on a laboratory permanent magnet synchronous motor drive system.