To address the issue of DC bus voltage fluctuation in a T-type three-level power conversion system when subjected to disturbance, an improved linear active disturbance rejection control (LADRC) method is proposed to enhance the control stability. This method improves the linear extended state observer (LESO) by first introducing a total disturbance differential state variable to enhance disturbance observation capability. Secondly, the observer is reduced to reduce both design complexity and phase lag, thereby improving disturbance estimation speed. Finally, a lag compensation loop is added on the total disturbance channel to attenuate noise amplification effects, achieving accurate and fast estimation of system total disturbances. Based on frequency domain analysis, it is found that the improved LADRC has better disturbance rejection performance than traditional LADRC. Multiple sets of experimental results demonstrate that compared with PI control and traditional LADRC, this strategy exhibits smaller overshoot and shorter transient time for DC bus voltage during active power transients, reactive power transients, and grid voltage drops. This validates the effectiveness of the proposed method and ensures normal and stable operation of the energy storage converter.