Control Strategies for Multi-Terminal DC Transmission System with Special Parallel Topology

• Published in: 2020 4th International Conference on HVDC (HVDC) pp. 164 - 169
• Main Authors: Su, Yun, Li, Shaohua, Li, Binbin, Ma, Xiaoting, Yao, Dongxiao, Zhang, Wang
• Format: Conference Proceeding
• Language: English
• Published: IEEE 06.11.2020
• Subjects: Control systems; dc current balancing control; HVDC transmission; Inverters; Multi-terminal dc (MTDC); parallel converters; paralleling/de-paralleling of converters; Rectifiers; Switches; Topology; Voltage control
• DOI: 10.1109/HVDC50696.2020.9292876

With the development of high voltage direct current (HVDC) transmission technology, parallel converters have received increasing attentions. The multi-terminal dc (MTDC) system with parallel connection of converters is particularly advantageous when the transmission is built in stages or when it works under de-icing mode. The simplest MTDC topology with the parallel converters located in the same station is the subject of this paper. The characteristics of four-terminal HVDC system with parallel converters are analyzed. A new cooperation strategy is proposed which rectifiers control dc current, inverters control dc voltage and a per-unit dc current balancing control function applied to avoid an unambiguous operating dc voltage. This cooperation strategy not only simplifies the control system design for the 4-terminal HVDC transmission, retains the independence of the two 2-terminal HVDC systems to the utmost extent, but also any proportion power distribution among the two inverters is achieved. De-paralleling the second converter and paralleling the first converter are of special interest for parallel operation, the methods of doing this are also described. Finally, a case of 4-terminal HVDC system with the special topology validates the control strategies using PSCAD/EMTDC.