In asynchronous partitioning mode

frequency limit control (FLC) plays an important supporting role in the frequency stability of the high proportion of renewable energy sending end power grid. To reasonably arrange the HVDC and unit operation plan of the sending-end power grid and ensure the frequency support function of the FLC

this paper proposes improvement measures from the perspective of the day-ahead dispatch of the asynchronous interconnection sending-end power grid. By analyzing the frequency support mechanism of the FLC

a frequency constraint for the sending end power grid was established

including system inertia constraint

maximum frequency deviation constraints

and primary frequency regulation backup constraints. Nonlinear features were eliminated through the segmented linearization method. Taking the minimum system operation cost as the goal

considering the renewable energy consumption of the sending end power grid and improving the peak shaving of the receiving end power grid

a day ahead dispatch model of asynchronous interconnection sending end power grid considering HVDC frequency support is constructed

and a case is analyzed based on the improved IEEE RTS 24 node system. The case results show that the proposed day-ahead dispatch model can effectively guarantee the system's frequency security while improving its operating economy.