Optimal control and DC fault ride-through of transmission level, MMC-based, isolated DC/DC converter

摘要

This paper investigates an optimum control strategy for an isolated dual-active-bridge DC/DC converter based on MMC (Modular Multilevel Converter) technology. The control goal is to achieve minimal current magnitude for given power transfer and to provide fast control for full positive and negative power range. The control strategy is derived in the rotating dq frame. The optimal operation is achieved using outer control loops that maintain and balance magnitude of both modulation indices to 0.95. The inner current control loops are used on both bridges in order to limit current magnitude under faults. The controller facilitates normal operation of DC/DC converter under DC faults. The validity of the converter controller is verified using a 1GW, 500kV/640kV test converter on a detailed PSCAD model for both normal and fault conditions.