海上风电柔直并网系统多时间尺度协同惯量支撑策略OA

[Objective]Modular multilevel converter based high-voltage direct current(MMC-HVDC)technology serves as the optimal technical solution for power transmission of large-scale far-offshore wind farms.The grid integration of large-scale offshore wind power via MMC-HVDC leads to insufficient inertia and damping deficiency in onshore AC power grids.To solve the above problems,this paper proposes a multi-time-scale coordinated inertia support strategy.[Methods]This paper quantitatively investigates the transient power support capability of sub-module capacitors in MMC-HVDC systems,and proposes a decoupling control-based capacitor energy regulation grid-forming control strategy.By dynamically adjusting the number of inserted sub-modules in each phase,the proposed strategy eliminates the coupling between sub-module capacitor voltage and DC bus voltage.While maintaining DC voltage stability,the operating range and energy utilization potential of sub-module capacitors are significantly expanded.On this basis,a frequency deadband link is introduced,and a multi-time-scale coordinated inertia support strategy with DC voltage as the intermediate medium is designed.The proposed strategy realizes hierarchical and orderly frequency support,which preferentially utilizes capacitor energy under small disturbances and adopts coordinated wind turbine participation under large disturbances.[Results]Simulation results based on PSCAD/EMTDC verify that the system achieves inferior support performance under sudden load increase conditions compared with sudden load decrease conditions.Under identical load variation amplitudes,the maximum frequency deviation of the onshore power grid is reduced by 33.3%and 20.0%under sudden load decrease and sudden load increase scenarios,respectively.The core reason for this performance difference is the quantity limitation of bridge arm sub-modules,which results in a lower energy release margin than the energy absorption margin of sub-module capacitors.[Conclusions]The proposed control strategy effectively integrates and optimizes the utilization of inertia support resources of MMC-HVDC systems and offshore wind farms.The adoption of the frequency deadband link enables coordinated inertia support from multiple support subjects.The proposed strategy not only ensures system frequency stability,but also isolates offshore wind farms from the impact of small disturbances,thereby improving the frequency dynamic performance of offshore wind power MMC-HVDC integrated grid systems.