<p>The harsh underground environment during coal mining operations leads to fluctuations in the internal parameters and external loads of the permanent magnet semi-direct drive (PMSD) scraper conveyor system, imposing greater demands on the speed control of the permanent magnet synchronous motor (PMSM). To this end, this paper proposes an improved sliding mode controller (ISMC) for PMSM speed control in the semi-direct drive scraper conveyor. First, an improved sliding mode reaching law (ISMRL) is proposed, which introduces the power term of the sliding mode surface and the variable speed adjustment function into the constant-speed switching term and the exponential approaching term of the exponential approaching law (ESMRL), respectively, and replaces the traditional switching function with the hyperbolic tangent function. It is verified through theoretical analyses and examples that this method allows the system state to reach the sliding surface faster and more smoothly from any initial state. Furthermore, for the uncertain disturbance in the speed control of the PMSD system, an adaptive sliding mode disturbance observer (ASMDO) that does not depend on the disturbance boundary information is proposed based on a double-layer adaptive algorithm. It can change the observer input and achieve fast and accurate disturbance estimation, which is then compensated to the ISMC. Then rigorous theoretical analyses demonstrate the stability of the ISMC and ISMC+ ASMDO closed-loop control system. Finally, the results show that the proposed method improves the robustness, response speed and steady state performance of the PMSD speed control system.</p>