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The electric-spring (ES) technology is recently integrated into a solid-state transformer (SST) to support the power grid at the distribution voltage level and provide an 800-V dc grid for large-scale electric vehicle (EV) charging infrastructure. The ES-enabled SST (ES-SST) studied here consists of a diode-clamped converter (DCC) and several dual active bridges (DABs). The failure of one DAB could pose a big challenge to the balance of the dc-link capacitors and threatens the operation of the whole system. Existing voltage-balancing methods are not suitable for the faulty ES-SST due to the highly uneven distribution of the capacitor output power. In this article, a fault-tolerant control method is proposed to keep the capacitor voltages balanced under the DAB failure and maintain the operation of the system. The proposed control features a modulation algorithm to maximize the balancing capability of the DCC, the insertion of a zero-sequence voltage offset in the ac voltages, and the deliberate generation of reactive power. A numerical tool is also developed to predict the operability of the faulty system and design the controller. Simulation and experiments are conducted to verify the proposed control.
Yuan et al. (Thu,) studied this question.