Coupled optimization of electricity and natural gas systems using augmented Lagrangian and an alternating minimization method

• Coupled optimization of the electricity and gas systems.
• Decomposition of the overall problem based on the Augmented Lagrangian method.
• An alternating minimization method is used for coordinating the two interdependent systems.
• Lagrange multipliers are updated using the subgradient method.
• The method is evaluated on the Greek power and gas systems.

A coupled optimization of the electricity and gas systems is presented in this paper. The electricity problem involves a unit commitment with co-optimization of energy and reserves under a power pool, considering all system operational and unit technical constraints. The gas problem involves a medium-scale highly non-convex and non-linear problem structure, which is modeled as a Mixed Integer Non-Linear Programming model. The decomposition of the overall problem is based on the Augmented Lagrangian method. An iterative process is implemented, coordinating the two interdependent systems using an alternating minimization method, in which the Lagrange multipliers are updated using the subgradient method. The gas problem is solved in two phases in order to avoid numerical instabilities; first, the direction of flow is defined, and then the gas flow is derived in the second phase. The solution algorithm is evaluated using the Greek power and gas system, comprising thirteen gas-fired units and fifty-three gas network nodes. The test results indicate the strong interdependence of the two systems, and demonstrate the efficiency of the presented algorithm in coordinating them.