Distributed Reactive Power Optimization Computing in Multi-area Power Systems Using Ward Equivalent

This paper presents a new decomposition and coordination algorithm based on Ward equivalent to solve distributed reactive-power optimization problem in multi-area power system. At first, multi-area interconnected power system is partitioned into master and slaver areas, boundary buses are defined as different bus types respectively corresponding to different areas, and hence the transfer method of phase angles from master area to slaver areas is determined. Secondly the initial value of equivalent injection power is obtained according to power-flow calculation at basic operating state. Then computational efficiency of the equivalent admittance matrix of external network due to change of transformer ratios is highly enhanced during optimization process by means of the inverse matrix modification lemma, and also the equivalent accuracy of external network is improved greatly. Moreover a kind of external coordination strategy which is suitable for reactive-power optimization calculation is introduced and better coordination effects with less coordination communications are obtained. Finally testing results on 538-bus practical systems is used to validate the correctness and effectiveness of the proposed algorithm in comparison with the centralized optimization method.