In modern aircraft power systems, active power converters are promising replacements for transformer rectifier units concerning efficiency and weight. To assess the benefits of active power converters, converter design and optimization should be carefully done under the operation requirements of aircraft applications: electromagnetic interference (EMI) standards, power quality standards, etc. Moreover, certain applications may have strict limits on other converter specifications: weight, size, converter loss, etc. This paper presents the methodology for performance optimization of different active power converters (active front-ends, isolated DC/DC converters and three-phase isolated converters) for aircraft applications. Key methods for power converter component (e.g. inductors, semiconductor devices, etc.) performance optimization and loss calculation are introduced along with the converter optimization procedure. Targeting at achieving extreme converter efficiency, a 3 kW interleaved Vienna rectifier (active front-end) with over 99% efficiency was designed and constructed based on the proposed methodology. Moreover, a 1.2 kW three-phase isolated AC/DC converter aiming at achieving both high power density and converter efficiency was constructed and tested. This converter achieved 22 W/inch3 power density and 97.1% full load efficiency. The models involved in the design were validated and the design estimations were verified experimentally by the three prototypes.