The most common two challenges in high-voltage direct current (HVDC) multi-terminal transmission are the DC fault isolation and the DC voltage stepping up/down. Additionally, interconnecting voltage source converter (VSC)- and line commutated converter (LCC)-based HVDC network topologies has been challenging. This study introduces a new DC–DC converter topology concept connecting both LCC- and VSC-based HVDC networks with bidirectional power flow without operation stoppage. The proposed topology is formed of two front-to-front connected bridges with an AC-link formed of a capacitor and an inductor (which can be replaced by a transformer for voltage step-up/step-down). The LCC-HVDC network bridge is formed of insulated gate commutated thyristors while the VSC-HVDC network bridge is formed of insulated gate bipolar transistors. Therefore, ON/OFF switching of both bridges and bi-directional power flow are possible. Moreover, the reactive power transfer is nullified at rated active power exchange between the proposed converter bridges. The proposed concept's detailed analysis and control equations are introduced. Different operation scenarios are simulated in addition to scaled-down experimentation to test the applicability of power transfer scenarios without operation stoppage in normal operation.

中文翻译：

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DC-DC转换器概念允许基于HVDC系统的线路换向转换器和电压源转换器进行连接

高压直流（HVDC）多端子传输中最常见的两个挑战是DC故障隔离和DC电压升/降。此外，互连基于电压源转换器（VSC）和基于线换向转换器（LCC）的HVDC网络拓扑也具有挑战性。本研究介绍了一种新的DC-DC转换器拓扑概念，该概念将基于LCC和VSC的HVDC网络与双向功率流连接在一起，而不会发生操作停止。所提出的拓扑结构由两个前后连接的电桥构成，交流电桥由电容器和电感器构成（可以用变压器代替以进行升压/降压）。LCC-HVDC网络桥由绝缘栅换向晶闸管构成，而VSC-HVDC网络桥由绝缘栅双极晶体管构成。因此，可以对两个电桥进行ON / OFF切换和双向潮流。此外，在所建议的转换器电桥之间的额定有功功率交换时，无功功率传输被取消。介绍了提出的概念的详细分析和控制方程。除了按比例缩小的实验以外，还模拟了不同的操作方案，以测试功率传输方案的适用性，而该操作在正常操作中不会停止。