With the rapid development of voltage source converter-based high-voltage direct current (HVdc) transmission, it is an irresistible trend that HVdc grid will come into being. High-voltage and high-power dc/dc converters will serve as dc transformers in HVdc grid to interconnect dc lines with different voltage ratings. This article proposes a monopolar symmetrical dc/dc converter which is composed of cascaded half-bridge submodules and series-connected insulated-gate bipolar transistors. This hybrid topology features low capital costs, high efficiency, small footprint, and bidirectional power transfer capability. Operation principle, parameter design, and the control strategies of this topology are introduced. A 480-MW, ±500 kV/±160 kV monopolar symmetrical dc/dc converter is simulated to verify its performance and evaluate the efficiency. In addition, a downscaled prototype rated at 2.4 kW, ±300 V/±100 V has been built and tested. Experimental results further validate the effectiveness of the proposed dc/dc converter.

中文翻译：

---

用于 HVDC 互连的单极对称混合级联 DC/DC 转换器

随着基于电压源换流器的高压直流（HVdc）输电技术的快速发展，HVdc电网将成为不可阻挡的趋势。高压和大功率 DC/DC 转换器将用作高压直流电网中的直流变压器，以互连具有不同额定电压的直流线路。本文提出了一种由级联半桥子模块和串联绝缘栅双极晶体管组成的单极对称 DC/DC 转换器。这种混合拓扑具有低资本成本、高效率、小尺寸和双向电力传输能力。介绍了该拓扑的工作原理、参数设计和控制策略。对 480 MW、±500 kV/±160 kV 单极对称 DC/DC 转换器进行仿真，以验证其性能并评估效率。此外，还构建并测试了一个额定功率为 2.4 kW、±300 V/±100 V 的缩小原型。实验结果进一步验证了所提出的 DC/DC 转换器的有效性。