In the traditional double closed-loop control strategy for VSC-HVDC transmission system that supply power to passive networks, the control structure is complex, the PI parameters are more difficult, the tuning is slow, and the response speed is slow. Rectifier-side direct power control based on model prediction and direct AC voltage control strategy on inverter side are proposed. Based on the discrete mathematical model of the converter, the system output under all switching function combinations is calculated by the ergodic method, and the switching function that minimizes the objective function is selected to act on the inverter. The utility model has the advantages of simple structure, no complicated PI parameter setting, fast dynamic response, high voltage quality electric energy to the passive network, good steady state performance and dynamic performance. The simulation results verify the feasibility and effectiveness of the proposed control strategy.
VSC-HVDC has been widely used at home and abroad, but there is no clear conclusion about the characteristics and calculation method of the short-circuit current contributed by VSC-HVDC during the AC Short-Circuit Fault near the converter station. The calculation methods in the field of short-circuit current engineering have not been unified, and the adaptability and error of different methods have not been analyzed in detail. Through electromagnetic transient simulation, this paper analyzes the transient characteristics of VSC-HVDC contribution short-circuit current, and combs the key influencing factors of VSC-HVDC contribution short-circuit current. Finally, taking a VSC-HVDC system in China as an example, the adaptability of the commonly used short-circuit current algorithm is analyzed. It is verified that the existing engineering algorithms have made great progress compared with the original. However, compared with the electromagnetic transient refined simulation, there is still a large error in the calculation results of individual nodes under some control modes / fixed values.
In order to ensure stable operation of DC, the dual DC feed grid structure needs to ensure a certain grid strength, but it is necessary to study how to evaluate the impact of critical section maintenance on the AC system. Firstly, the strength evaluation index of the receiving power grid is analyzed. Secondly, an index that characterizes the effects of two DC couplings is proposed. Finally, a critical section channel maintenance evaluation method for double ultra-high voltage DC feed grid is proposed. The effectiveness of the proposed method is verified by the HN Power Grid simulation.
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