High voltage direct current (DC) transmission systems in restructured electricity markets

The proposed algorithm provides the solution for hybrid high voltage alternative current (AC)/direct current (DC) transmission systems in restructured power systems. The proposed algorithm solves the security-constrained unit commitment (SCUC) problem with a detailed representation of DC transmission system with current source converters (CSCs) and voltage source converters (VSCs). The SCUC problem is decomposed into a master problem for solving the unit commitment (UC) problem and hourly transmission security check subproblems that evaluate branch flows and bus voltages in hybrid transmission systems. The solution of the transmission security check subproblem is based on a linear programming (LP) formulation that minimizes AC bus mismatches subject to AC/DC transmission constraints. The nonlinear AC/DC equations are linearized and the Newton-Raphson method is utilized to solve the linearized network in the base case and contingencies. The final SCUC solution prescribes an economic and secure operation and control strategy for AC/DC transmission systems. The solution coordinates DC power transfers for enhancing the economics and the security of AC transmission systems. This study also presents a hybrid model for AC/DC transmission expansion planning in restructured power systems. The Benders decomposition method is utilized to decompose the mixed-integer planning problem into a master planning problem with integer investment decision variables and subproblems which check the feasibly of master planning schedules and the optimal market operation subproblem over the planning horizon. The Monte Carlo simulation method would consider random outages of generating units and AC/DC transmission lines as well as load forecast errors. The numerical examples provided throughout the chapters signify the effectiveness of the proposed models and algorithms in the optimization of power system planning and operation.