Efficient method for the optimal economic operation problem in point-to-point VSC-HVDC connected AC grids based on Lagrange multipliers

This paper describes a method based on Lagrange multipliers for efficiently solving the economic dispatch in power systems including point-to-point VSC-HVDC links. The proposed formulation bases on linear models of the AC systems and HVDC links where power losses are properly considered through incremental transmission loss factors. This timely formulation preserves suitable outcome accuracy while showing a greater computational efficiency than what is achieved with classical, nonlinear OPF methods. Its main features are demonstrated using two compelling test cases: a system accommodating one point-to-point VSC-HVDC link and another comprising multi-infeed HVDC connected AC power grids. Results of this approach are compared with those calculated by the nonlinear interior point method. It is confirmed that both fundamentally different approaches are in good agreement since errors smaller than 0.5% were obtained for generation costs, whereas the computational time was reduced by more than 60% with the introduced method. To show the method applicability in realistic power systems, the 10-generator New England Test system incorporating a VSC-HVDC link is studied. The DC link effect on system operation is examined for a 24-hour period dispatch thus demonstrating its usefulness, unrivalled modelling versatility and numerical efficiency with respect to existing approaches.