Abstract: An Input-Series-Output-Parallel (ISOP) arrangement of converter modules is a common solution for realizing power converters with relatively high input voltages. ISOP systems allow for high voltage (HV) power processing using low voltage (LV) Wide Band Gap (WBG) devices, leading to a low cost, reliable, and modular solution. The main challenge with ISOP systems is ensuring equal voltage sharing across the series connected modules for safe and stable converter operation. This is even more challenging for three-port based ISOP modular systems due to additional coupling between input ports. In this paper, the authors propose a hybrid feedforward-feedback control approach for voltage balancing in ISOP Triple Active Bridge Series Resonant converter (TABSRC) modules. The proposed ISOP modules serve as a rectified AC to DC, |AC|-DC, stage in a single-stage unfolding based Solid-State Transformer (SST). Analysis and simulations are provided to illustrate the control approach, followed by hardware results demonstrating stable operation of two TABSRC modules in ISOP configuration.