Sensorless control technique is regarded as the enabler of the reliability improvements for interior permanent magnet synchronous motor (IPMSM) drives. However, the conventional estimation schemes by using the phase-locked loop (PLL) and the frequency-locked loop (FLL) may experience undesired accuracy under acceleration and deceleration cases (ADCs). To address this, a speed estimation scheme by combining a closed-loop active flux observer (CLAFO) with a tracking differentiator-based frequency-locked loop (TD-FLL) was proposed in this paper. Starting from a brief introduction of the conventional PLL and FLL performance analysis based on ADCs, a detailed analysis is provided. Accordingly, an estimation scheme based on the TD-FLL is elaborated. Considering the performance of the proposed TD-FLL scheme is adversely affected by various disturbances, a CLAFO is carefully designed to improve the disturbance immunity of the proposed TD-FLL scheme. Extensive experimental tests are conducted to verify the effectiveness of the proposed TD-FLL scheme under different test cases.