Security constrained OPF model for AC/DC grids with unbalanced DC systems

The role of HVDC in power transmission systems continues to grow. The number of HVDC installations worldwide is increasing, and first, multi-terminal and meshed HVDC grids are being built. Large meshed HVDC grids with many terminals are expected to be operational in the near future. Bipolar HVDC grids can be operated in an asymmetrical configuration with converter stations connected between single poles. This paper presents a reliability assessment model for unbalanced AC/DC grids. The DC grid is modeled using a multi-conductor representation. A security-constrained optimal power flow model is developed allowing the representation of single-pole contingencies and single-line conductor outages. The model is implemented in the Julia/JuMP framework as an extension of the open-source package PowerModelsACDC.jl. The model is applied to a 67-bus test case considering several N-1 contingencies. Results show that unbalanced operation of HVDC grids in contingency situations can decrease operational costs by higher utilization of HVDC grid flexibility.