Determination of optimal reactive power generation schedule using line voltage drop equations and genetic algorithm

Abstract

The reactive power generation schedule in a power system determines the bus voltage profile. The available reactive power capabilities of the generators have to be optimally deployed so that bus voltages are kept within specified limits. While applying the standard power flow algorithms, the voltage and real power injection are set for a generator bus. After running the power flow analysis, or while running the power flow analysis, reactive power limit is checked and if violated the voltage setting is removed and the generator treated as a PQ bus. The final reactive power generation schedule is determined by such trial and error procedures. Further the reactive power from the slack or swing bus is left totally free to assume any value. The basic feature of the new approach in this paper tends to recognize the weak coupling between real power flow and voltage. This facilitates focusing on the voltage/reactive power problem keeping the real power flows fixed to values determined from a base case load flow analysis. The reactive power flow in each line will determine the voltage drop in each line and indirectly the bus voltage profile. The line reactive power flows and the bus reactive power injections are kept in focus by writing two sets of equations, viz., reactive power balance at every bus including the slack, and line voltage drop equations. Generator reactive power injections are kept as variables and the total set of equations constitute the equality constraints. The objective function is to minimize the total generated reactive power. Reactive power generation limits and/or bus voltage magnitude limits are specified as allowable range of values of these variables in an optimization procedure using Genetic Algorithm (GA).