A Current-transformer-based Auxiliary Power Supply Featuring Synchronous Power and Data Transfer for Modular Medium-Voltage Converter Systems

Demanding high isolation and scalability, the design of auxiliary power supplies (APSs) for the modular medium-voltage (MV) converter is quite challenging. Since the internally powered APS solutions suffer from the high step-down ratio and wide input voltage issues, this article applies a centralized powered current transformer (CT) based APS (CT-APS) for modular MV converters. Utilizing the single-turn structure CT as the isolation component, the highly isolated APS for all submodules (SMs) in the modular MV converter is constructed. Besides, the synchronous power and data transfer method using the amplitude-shift keying (ASK) is developed based on the common ac bus structure of the CT-APS. The proposed CT-APS with synchronous power and data transfer function is applied on a modular multilevel converter (MMC) prototype to fulfill its auxiliary power demand, meanwhile broadcasting the signals to all SMs for capacitor voltage balancing control and fault bypassing. Finally, simulation and experimental results verify the feasibility of the CT-APS featuring synchronous power and data transfer.