Flexible and curtailable resource activation in a distribution network using nodal sensitivities
Traditionally, the distribution system operator (DSO) relied on a fit-and-forget network design. However, there will be a greater need to integrate flexible and curtailable resources to cope with growing distributed generation (DG) installations and new consumer loads such as electric vehicles. Distribution network (DN) vulnerabilities, voltage and thermal limit violations, often require resource activation in the vicinity. Consumers located close to the end of the feeder in a radial DN witness more over-voltages (due to DG injection) and under-voltages (due to additional load). The per-unit change in active or reactive power of a consumer at the end of the feeder causes a greater marginal impact, referred to as nodal sensitivity. This will cause a higher activation of flexible resources close to the vulnerable nodes. A flat flexible activation priority will not be fair for such flexible owners. We propose a new mechanism to activate flexibility based on voltage sensitivity, which considers nodal sensitivities. The proposed activation design is motivated by inverter voltage control norms and has similarities with optimal power flow duals often utilized as locational marginal prices. These dual variables are active only when some network constraints are violated, and do not provide correction prior to such a violation. The proposed flexibility activation design, due to its drooping characteristics, actively contributes to avoiding such network issues from happening. The resource activation optimization formulation proposed is non-convex. Second-order cone relaxations are used to convexify the proposed resource activation optimization problem. We use numerical evaluations to show the proposed formulations can be used for activation of load flexibilities and can be used for valuing and planning flexible and curtailable resources.