Planetary gear (PG) power-split hybrid powertrains have been used in producing hybrid and plug-in hybrid vehicles from the Toyota, General Motor, and Ford for years. Some of the most recent designs use clutches to enable multiple operating modes to improve launching performance and/or fuel economy. Adding clutches and multiple operating modes, however, also increases production cost and design complexity. To enable an exhaustive but fast search for optimal designs among a large number of hardware configurations, clutch locations, and mode selections, an automated modeling and screening process is developed in this paper. Combining this process with the power-weighted efficiency analysis for rapid sizing method (PEARS), an optimal and computationally efficient energy management strategy, the extremely large design space of configuration, component sizing, and control becomes feasible to search through. This methodology to identify optimal designs has yet to be reported in the literature. A case study to evaluate the proposed methodology uses the configuration adopted in the Toyota Hybrid Synergy (THS-II) system used in the Prius model year 2010 and the Hybrid Camry. Two designs are investigated to compare with the simulated Prius design: one uses all possible operating modes; and the other uses a suboptimal design that limits the number of clutches to three.