The fault current of the high-voltage and large-capacity flexible DC power grid has the characteristics of a fast rising rate, high peak value, and large influence area; therefore, fault current suppression equipment suitable for the flexible DC power grid has become a research hotspot. First, the fault mechanism and fault current calculation associated with the DC converter are analysed in this study; subsequently, a multiport superconducting fault-current-limiting circuit breaker (SFCLCB) suitable for a flexible DC power grid is designed. The circuit breaker adopts ground drainage to transfer the fault current. It only needs to be equipped with a single-way conduction power electronic switch group and the number of switches is not affected by the number of DC lines, considerably improving the cost effectiveness of the equipment. In addition, the workflow and current-limiting principle of SFCLCB are analysed, and the optimal matching method is determined with respect to the resistance of the superconducting current limiter and the power electronic devices of the main circuit breaker. Afterwards, the four-terminal flexible DC transmission simulation system is observed to exhibit high efficiency in suppressing the fault current and high cost effectiveness based on comparative simulations. Finally, its engineering applicability is verified by the digital physical and hybrid simulation platform.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
In order to fully study the working characteristics of large-scale power electronic devices in the field of renewable energy delivery, it is imperative to build digital and physical hybrid simulation platforms. A power interface algorithm based on damping impedance is proposed to improve the stability of DC power grid hybrid platforms. Firstly, according to the characteristics of the open-loop transfer function of the damping impedance method, the matching principle between damping impedance at the power interface and equivalent impedance of the physical simulation system is obtained. Secondly, the calculation method of the equivalent impedance of multi-type equipment on the physical side is proposed, and the impedance real-time matching under different working conditions is realized. In order to reduce the simulation error caused by interface delay, a DC voltage interface delay compensation method based on slope prediction is proposed, and a prediction compensation model is established. A digital and physical hybrid platform for a four-terminal flexible DC power grid with DC circuit breakers is built to verify the proposed interface algorithm. The simulation results show that the proposed interface algorithm can effectively compensate for the interface delay and ensure the stable operation of the platform under different conditions.
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