Multiport power converters are needed in a wide range of applications including battery management systems, data center power delivery, and renewable energy systems. These systems comprise numerous distributed and modular power conversion cells with sophisticated and bidirectional power flow. This paper systematically investigates the architecture, modeling and control of multiport power converters with a large number of ports, and explores the theoretical foundation of an emerging 'Power FPGA' concept - Flexible, Programmable, Granular and Adaptive power electronics - that will enable a wide range of exciting applications. We classified multiport power converters into two major categories, and developed a software tool based on Newton-Raphson method to rapidly identify the control strategy. We analyzed the applicability and limitations of this control framework, and simulated a 100-port energy converter with programmable power flow. A four-port programmable energy converter is built and tested to experimentally validate the proposed modeling and control strategy.