Active / Reactive dispatch in market environment and nodal active / reactive price determination

Abstract

This paper describes a mathematical formulation for the active/reactive dispatch in electricity markets, addressing a number of technical and economic difficulties present in market models in force in several countries. Traditional market approaches are implemented considering a sequence of activities namely in terms of active power dispatch (via the pool centralized market and bilateral contracts) and ancillary services. However, these two problems are coupled in the sense that dispatching reactive power is not independent from active power scheduling of generators and so a particular reactive power output required by the ISO may be unfeasible in view of the active power dispatch. The proposed model admits that it is known the purely economic pool dispatch together with bilateral contracts and then it aims at dispatching reactive resources considering voltage and branch limit constraints and constraints reflecting the alternator capability curve. The search on the solution space uses an Sequential Linear Programming, SLP, approach and it is governed by the minimization of an objective function reflecting branch active losses, the cost of generator active power adjustment bids required to accommodate reactive power requirements or to eliminate branch congestion and also load active power adjustment bids. As a sub-result, this formulation also outputs nodal active and reactive marginal prices that can be useful to build tariff schemes. Finally, the paper includes a case study based on the IEEE 30 bus/41 branch system to illustrate the results obtained with this approach.