The bidirectional resonant DC transformer has all the desired features to drive the development of the DC power distribution networks of the future. This power-electronics converter provides galvanic isolation between DC buses, has desired open loop properties, and follows the system's power flow naturally, requiring only a power reversal algorithm to allow a bidirectional operation and smooth transitions. This paper proposes a solution to tackle the power reversal of the DCT with a dynamic algorithm, considering the system behaviour and the power converter characteristics. The proposed algorithm executes the power reversal in few switching periods and removes the DCT losses during no-load condition. Then, using low voltage prototype of DC transformer, experimental results along the paper demonstrate how this power reversal algorithm is applied under various operating conditions.INDEX TERMS LLC converter, DC transformer, DCT, resonant converter, power reversal, power transition.
In AC/DC power distributions networks, power converters are interfacing buses to ensure DC voltage regulation and power distribution. Active front ends are used between AC and DC buses and two typical control schemes that can be implemented are voltage regulation or power regulation. On the DC side, open‐loop operated DC transformers could be used between two DC buses to provide voltage adaptation, isolation and natural power flow. In this context, power flows and DC bus voltages in the power distribution network are dependent on the combined operation of the active front ends and the DC transformer. Mainly studied from a stability perspective, this interdependency between active front ends and DC transformers has lacked investigations in terms of dynamics. Fast dynamics is nevertheless important to operate optimally a network. In this paper, the assessment of the dynamic performance for distribution systems with DC transformers is performed for different mixes of voltage regulating and power regulating active front ends. The influence of DC line length and DC transformer power reversal method on the system is further investigated. A model of the system is proposed, validated experimentally and can be used to aid system level design and analysis of future DC systems.
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