Congestion pricing in electricity markets: Infeasibility, sub-optimality and degeneracy

Infeasible, sub-optimal and/or degenerate solutions of the economic dispatch problem cause undesirable effects on the ex-ante and ex-post market price calculations. To determine market prices, this paper explores a scheme that relies on a dual formulation of the economic dispatch problem, stated in terms of prices, i.e. prices become variables. With such a dual perspective, direct control of the prices is achieved, e.g. minimizing the side payments needed to comply with a revenue sufficiency guarantee to market participants. The proposed method combines a primal formulation to find the dispatch (MW), and a dual formulation to determine Locational (nodal) Marginal Prices (LMPs) into a single primal-dual model. Having both, dispatch levels (MW) and nodal prices ($/MWh), as variables, opens possibilities not explored before, e.g. constraints and objective functions that combine both, MW and prices. Computational experiments demonstrate the benefits of the alternative proposal.