The existing methods are difficult to meet the real-time calculation needs of large-scale power grid and quick response when performing reactive power optimization for the interconnected power grids

and also facing the problem of data collection throughout the whole network. To solve the problem

this paper uses the idea of decomposition-coordination algorithm and proposes a reactive power optimization method for multi-area voltage source converter based high voltage direct current(VSC-HVDC)interconnected power grid based on the Lagrangian dual relaxation theory. Firstly

according to branch power flow model

a centralized reactive power optimization model of multi-area VSC-HVDC interconnected power grids is established by using the second-order cone relaxation and rotated quadratic cone relaxation technology. Then

a reactive power optimization method is proposed based on decomposition-coordination algorithm for multi-area VSC-HVDC interconnected power grid based on the Lagrangian dual relaxation theory used in the centralized optimization model. The validity and correctness of proposed algorithm are verified by case study. Finally

the results from decomposition-coordination algorithm and alternating direction method of multipliers(ADMM)are compared

proving that the former one has an advantage on compution time.