Optimal power allocation strategy for black start in VSC-MTDC systems considering dynamic impacts

Abstract

The ability of voltage source converters (VSCs) to restore blackout grid has been widely accepted based on their abilities in flexible and independent power control. However, the traditional literature only studied the case of a two-terminal hybrid system in which all required black start (BS) power is provided by a single healthy AC grid. Meanwhile, the dynamic changes at the sending end, including AC grid and converter, are not considered. In this paper, an optimal power allocation strategy is proposed to perform BS in the VSC-based multi-terminal direct current (VSC-MTDC) systems. The new strategy ensures that all the healthy AC grids can cooperate to transfer BS power together to the blackout grid. Thus, each grid only needs to provide a proportion of the required power. Furthermore, since the grids and converters in practical VSC-MTDC projects are generally limited to small sizes, the capacities together with main dynamic characteristics are also considered in the new strategy. By reasonably setting the optimization objective and constraints, the overall dynamic impacts can be significantly reduced, and the stability of AC grids and converters can be guaranteed. Finally, the comparison tests on a typical four-terminal system verify the feasibility and effectiveness of the proposed method.