Active Voltage Feedback Control for Hybrid Multiterminal HVDC System Adopting Improved Synchronverters

In this paper, we propose an idea to integrate more renewable energy into the existing China power grid and to provide remote islands with a reliable power supply. The idea is to expand the existing point-to-point line-commutated converter (LCC) HVDC transmission link into a hybrid multiterminal HVDC (hybrid MTDC) system, which contains LCC stations and voltage-source converter (VSC) stations. Accordingly, this paper proposes a novel control strategy for this system called active voltage feedback control, which does not need any high-speed communication system under various disturbances, such as wind speed variations, load fluctuations, faults, etc. This paper also adds secondary frequency regulation to the synchronverter, which is one way of combining the VSC converter with synchronous machine behavior. Then, this paper applies an approach to limit its current under fault conditions. Finally, the entire hybrid MTDC system is modeled in PSCAD/EMTDC. Simulation results show that the improved synchronverter is able to achieve secondary frequency control, and the presented active voltage feedback control works very well when exposed to various disturbances.