Power-voltage coordinated control in hybrid AC/DC medium voltage distribution networks based on VSC

Abstract

There are limited spaces for the fast increasing, highly concentrated loads in urban distribution networks. Voltage control is another challenge with integration of large number of distributed generation (DG) due to limited flexible control methods. This paper proposed to convert some AC lines to DC ones, and interconnected them with voltage source converter (VSC), so that node voltages can be adjusted through power control of VSC, based on which DG can be further accommodated. Different structures of VSC and its ability of power control were analyzed. Two operation states were divided, which are normal state and risk state, based on node voltage in distribution networks. Two optimal models were developed for each state in order to optimize active and reactive power of VSC. Losses were minimized in the normal state, while voltage deviations were minimized in the risk state. The efficiency and flexibility of the proposed method are verified in case study. The penetration of DG was increased based on power control of VSC, which optimized voltage profile. Node voltages can also be kept stable when a sudden change of DG output happens. The influences of normal state range on optimal results were analyzed.