In solid-state transformers (SSTs), as a promising conversion technology that integrates high-frequency galvanic isolation, a robust bidirectional power flow operation is essential, considering numerous SST real-world applications. Although an open-loop-operated resonant converter is suitable for the galvanic isolation stage in SSTs, a power reversal method (PRM) is required to diagnose the power direction transition and enable the current flow in the inverted direction by altering the modulation between two converter bridges, a process also known as active bridge switchover (ABS). In double-stage SSTs, in which the resonant conversion stage is combined with an active front-end (AFE) stage, the dynamic interactions of the two stages under power reversal are crucial for SST performance. Furthermore, to achieve a robust PRM in this special case, investigating the interactive behavior of the AFE closed-loop controller with the open-loop LLC converters in the detection and postdetection process is vital. Consequently, this article analyzes the operating principles of the LLC resonant converter in a two-stage SST under power flow reversal initially. Subsequently, a new PRM is proposed based on the unique interactive behavior of two stages in SST under power reversal. In this method, detection is based on monitoring the primary and secondary DC voltage slope rates of the LLC stages that exhibit opposite trends in the SST, and ABS is smoothly secured to avoid unwanted transients. This method does not rely on any additional or high-resolution sensors, while robust and fast switchover detection is achieved, which prevents false alarms caused by load and grid transients. The validity of the proposed method is established by experimental test results.