An efficient multi-objective fuzzy logic based successive LP method for optimal reactive power planning

Abstract This paper presents a new and efficient method to solve the Optimal Reactive Power Planning (ORPP) problem, simultaneously minimising transmission losses and improving voltage profile using Multi-objective Fuzzy logic based LP (MFLP) model in Successive Linear Programming (SLP) framework. The ORPP problem is concerned with optimally siting and sizing new capacitors at prospective sites in a planned grid with projected load demands such that, minimum number and quantum of new capacitors are allocated, the transmission losses are minimised and a satisfactory voltage profile is obtained. In this paper, all the prospective capacitor locations are ranked using Voltage Performance Index (VPI) based on sensitivity factors. From the top of the ranked list, a minimum number of locations are chosen for siting new capacitors. Reactive powers at these selected capacitor sites along with generator voltage magnitudes, reactive powers of existing switchable VAR sources and on-load tap changer (OLTC) settings of transformers are used as control variables in this method. In the MFLP framework, each of the objectives and each of the constraints are assigned a satisfaction parameter. The satisfaction parameter corresponding to any objective quantifies the degree of closeness of the current state of the objective to the optimum. The satisfaction parameter corresponding to a constraint describes the degree of enforcement of that constraint. By maximising the minimum of these satisfaction parameters, the objectives are optimised and the constraint enforcements are maximised. The MFLP based SLP method is found to be very effective while planning for systems which have severe under-voltage violations due to insufficient reactive powers, as the method is capable of selectively relaxing certain load voltage constraints, while simultaneously enforcing all other constraints strictly. The MFLP technique optimises all the objectives, i.e. minimises number and quantum of new capacitors, minimises transmission losses and maximises constraint enforcement of all violated constraints, while simultaneously imposing all other problem constraints strictly. This method uses compactly stored, factorised constant matrices in all MFLP steps, both for construction of the MFLP model as well as for the power flow solution. The method was tested on IEEE test systems and on a practical 191 bus electric utility system. The merits of the method, compared with SLP method using non-fuzzy approach, are brought out.