In modern Electrical Power Distribution System (EPDS), power electronics devices are gaining more prominence. Three-phase ac/dc converters provide a fully-controlled interface between the onboard ac and dc electrical equipment. In the context of utility ac electrical power systems, impedance-based stability analysis under Synchronous Reference Frame (SRF), or dq impedance has been established as a powerful tool to evaluate stability and optimize control design. However, precise measurement of the dq impedance is challenging in practice especially for high-capacity or high ac fundamental frequency systems. In this paper, a hardware-in-the-loop (HiL) platform is proposed for measuring dq impedance. An aircraft ac EPDS bus is built with a grid forming (GFM) converter and an active front end (AFE) converter to verify the proposed scheme. A comparison is made between the HiL measurement results, the experimental results and the analytical model, validating that dq-impedance measurement with the proposed setup provides a precise and efficient solution that obviates the need for complete hardware experiments.