Two-Stage Coordinated Control Strategy of AC/DC Hybrid Power System Based on Steady-State Security Region

Abstract

The large-scale shift of power flow after DC blocking will seriously affect the secure operation of the system. Furthermore, after DC blocking, the system uses different control objectives in different operation stages. Therefore, a two-stage coordinated control of AC/DC hybrid power system based on steady-state security region (SSR) is proposed. Firstly, after DC blocking, the system needs to quickly restore secure operation with minimum cost. Therefore, the security correction guidance vector and the security distance sensitivity of the different control variables to it are obtained based on the linear fitting of the boundary surfaces of the SSR. The control cost of different control variables is characterized by the expansion and contraction of the SSR. According to the sensitivity of each control variable to the guidance vector and their actual adjustment ability, they are sorted and substituted into the security correction model to minimize the total adjustment cost during the process. Secondly, system will frequently be in a critical security state and not able to meet the needs of long-term secure and economic operation after security correction. Therefore, the security and economics of the system after security correction are comprehensively evaluated with the system generation cost, voltage deviation, and security margin under normal operating conditions and N-1 contingency conditions of heavy load lines. By calculating the security distance sensitivity of each control variable to the transmission limit of the crucial section, the sensitive generators and DCs that have significant effects on the transmission power of the crucial section are determined. Then the projections of security sub-region of high-sensibility control variables to optimization dispatch target, generation cost, voltage deviation, and the crucial section are depicted under different security margin, providing richer and more accurate operation information and strategic guidance for optimization dispatch. The calculation and analysis of the transformed IEEE 39-node system and the simplified actual power grid verify the correctness and effectiveness of the proposed coordinated control strategy.