Congestion Management in Distribution Networks With Asymmetric Block Offers

In current practice, the day-ahead market-clearing outcomes are not necessarily feasible for distribution networks, i.e., the network constraints might not be satisfied. Hence, the distribution system operator may consider an ex-post re-dispatch mechanism, exploiting potential flexibility of local distributed energy resources including demand response (DR) units. Many DR units have an inherent “rebound effect,” meaning a decrease in power demand (response) must be followed by an increase (rebound) or vice versa, due to their underlying physical properties. A naive re-dispatch mechanism relying on DR units with non-negligible rebound effect may fail, since those units may cause another congestion in the rebound period. We propose a mechanism, which models the rebound effect of DR units using asymmetric block offers-this way, those units offer their flexibility using two subsequent blocks (response and rebound), each one representing the load decrease/increase in a time period. We demonstrate that though linear approximations of optimal power flow (OPF) models as potential re-dispatch mechanisms are more computationally efficient, they can result in a different dispatch of the asymmetric blocks than an exact convex relaxation of an AC-OPF model, and therefore, must be used with caution.