The Possibility of Enhanced Power Transfer in a Multi-Terminal Power System through Simultaneous AC–DC Power Transmission

The feasibility of power transfer enhancement, through simultaneous AC–DC power transmission in a two-terminal transmission network, has been proposed earlier by the authors, and the concept is well established. To meet the increase in demand for electricity, a new technique is proposed in this article to increase the use of existing transmission lines in addition to independent control of AC and DC power flow. This paper extends the concept to a three-terminal transmission network by considering a power tapping from the middle of the line. DC is also superimposed in the already existing three-terminal AC transmission system. In the proposed topology, a multi-terminal simultaneous AC–DC system is used, which is integrated with a zig-zag transformer and more than two voltage source converter (VSC) stations. Each terminal may represent an area of the power system. Anyone/two-terminal(s) may act as sending end, whereas the remaining two/one terminal(s) may act as receiving end. Power can flow in either direction through each segment of the transmission system. At sending end, VSC converts a part of AC to DC and injects it into the neutral of the zig-zag transformer. On receiving terminal, DC power is tapped from neutral of zig-zag transformer and fed to VSC for conversion back to AC. The concept is verified in the digital simulation software PSCAD/EMTDC.

Junction Temperature Consistency Analysis of MMC Submodule

<p> Although modular multilevel converter<span style="font-family: 宋体;">（</span><span style="font-family: 'Times New Roman';">MMC</span><span style="font-family: 宋体;">）</span><span style="font-family: 'Times New Roman';">is widely used in the field of DC power transmission due to its</span></p><p>excellent topology performance, the natural DC bias characteristics cause thermal imbalance of internal devices. Too high temperature at the junction of power devices is one of the major causes of damage. Therefore, it is necessary to investigate the factors that affect the device junction temperature. Combining with the thermal resistance model, the junction temperature under two typical modulation strategies <span style="font-family: 'Times New Roman';">is compared, </span>and the power loss and junction temperature are calculated.</p>