A multi-area Thevenin equivalent based multi-rate co-simulation for control design of practical LCC HVDC system

摘要

The line commutated converter (LCC) based HVDC transmission is often adopted to transmit the large capacity of renewable energy, however, it is threatened by several critical issues, such as, commutation failures (CFs). In order to reduce CFs and improve the recovery characteristics of the HVDC, improved control and protection strategies are always desirable. On the other hand, an accurate and efficient electromagnetic transient (EMT) simulation method is highly necessary to design the so-called control strategy, where the traditional transient stability and EMT models cannot meet the accuracy and efficiency requirements simultaneously. To resolve these issues, a Multi-Area Thevenin Equivalent (MATE) based multi-rate co-simulation method is proposed, where the accuracy is guaranteed by the proposed MATE based transmission line model (MATE-TLM) and the efficiency is significantly improved by adopting several accelerating techniques, such as, the MATE-TLM and multi-rate co-simulation scheme. Further, a novel improved control strategy based on the concept of virtual impedance is proposed to reduce CFs and to increase the recovery speed of DC system. Simulation results of a practical AC/DC grid by the improved control strategy have well validated the effectiveness of the proposed MATE based multirate co-simulation method.