The increasing integration of renewable energy sources and energy storage systems into the electrical grid demands the development of high-performance power conversion technologies. In this context, the design of efficient and reliable power conversion systems (PCS) is crucial for the integration of these energy sources. The use of optimization tools facilitates the selection of power conversion architectures and converter topologies that enhance overall efficiency and reliability while reducing development time. This paper presents an advanced optimization tool developed for designing the dc-ac PCS of HESS, which integrates a lithium-titanate-oxide (LTO) battery and an aqueous-organicredox-flow (AORF) battery for grid connection. Four conversion architectures are explored with different degrees of dc-dc and dc-ac module parallelization. A set of optimization problems is defined to obtain the Pareto front of solutions for each architecture, resulting in different trade-offs between the system's performance metrics.