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With rapid development of HVDC transmission system, the coupling relationship between the AC and DC power grid has become increasingly stronger. Especially, the problem of voltage instability is prominent in HVDC receiving-end system, the dynamic reactive power performance of the receiving-end power grid is inadequate. Therefore, the new-generation synchronous condenser (NGSC) as ‘a strong reactive power support device” is widely applied to high-capacity DC transmission system. However, there is a lack of coordination control strategy between the NGSCs and AC/DC power grid, so it is difficult to give full play to the reactive power supporting capacity of the NGSCs. In this paper, a coordinated multi-objective reactive control strategy between the NGSCs and the AC/DC power grid is proposed . In steady state, the initial reactive power optimization method of a NGSC is proposed. In transient state, a commutation failure suppression scheme of DC system based on the NGSCs and the DC control system is proposed. In transition process, the coordinated control strategy of the NGSCs with capacitance and reactance is studied. The research results provide theoretical basis for subsequent study on the safety and stability of AC/DC power grid.