Dynamic Reactive Droop Control Strategy for the MMC-HVDC system Integrating the Suburban Wind Farms into the Urban Power Grid

Over the past few years, wind power witnesses a continuous growing share in the conventional generation mix for its advantages in low-carbon and sustain. However, due to the randomness of wind energy, the integration of suburban wind farms into the urban power grid challenges the system operating safety. Due to the independent control ability of the active power and reactive power, modular multilevel converter based HVDC (MMC-HVDC) technology has become a good option for integrating the suburban wind farm into the urban power grid. Compared to the traditional AC transmission technology, MMC- HVDC could provide dynamic reactive power support to the urban power grid besides its excellent active power controllability, which could bring both control and stability benefit to the urban power grid. In this paper, a dynamic reactive power control scheme is proposed for the MMC-HVDC system integrating the suburban wind farm into the urban power grid. The proposed control provides different reactive power supports strategies for different operating conditions of the urban power grid. In addition, the proposed control could also realize fast and smoothly switch between different control scenarios of urban power grid dispatching instruction and emergency events so that providing effective reactive power support for the urban power grid. The small-signal model is also established in this paper for evaluating the stability of the dynamic droop coefficient. With the simulation results, the proposed control scheme is proved that this scheme can better support the voltage of the urban power grid.