Optimal Power Flow (OPF)

Optimal power flow, OPF, combines the network equations of power flow with an optimization problem that searches for the best operating point according to a defined objective. In practice, it is used to minimize generation cost, losses, or emissions while still respecting all electrical and operational limits across the system.

Key Aspects of Optimal Power Flow:

• Optimization Objective: The objective can be economic, such as minimizing production cost, or technical, such as reducing losses or relieving overloads. The chosen objective determines how generation and controllable devices are adjusted.
• Network Constraints: OPF must satisfy the full set of electrical constraints, including bus power balance, generator active and reactive limits, transmission thermal ratings, transformer tap limits, and voltage bounds at each bus.
• AC vs. DC Formulations: AC OPF represents voltage magnitude, reactive power, and losses more accurately, but it is nonlinear and computationally heavier. DC OPF is faster and widely used in markets, but it neglects reactive effects and assumes simplified network behavior.
• Operational Role: System operators use OPF to support dispatch decisions, congestion management, and secure operation under changing load or renewable output. In market environments, OPF is also the basis for locational marginal pricing.
• Security Extensions: In security-constrained OPF, the solution must remain feasible not only in the base case but also after selected contingencies. This makes the problem more demanding, but much closer to real operational practice.