Multi-area unit commitment for large-scale power systems

A large-scale multi-area unit commitment method is presented using a Lagrangian relaxation approach. The problem with a transmission network of several thousand buses and lines is equivalently modelled by a system with relatively few areas. Crucial tie-lines between areas are directly modelled, The network within an area is simplified from the application requirements. Based on a DC-flow model, the transmission constraints, as well as system demand and reserve requirements, are relaxed by attaching Lagrange multipliers to form a multiphase optimisation structure. A large-scale problem based on PG&E's power system with more than 2200 buses and 2500 lines is tested. Small cases are also tested for comparison. The numerical testing results show that the method is able to handle transmission constraints in large-scale unit commitment problems.