Voltage Control of Smart Grid by an Online Hierarchical Distributed method

In this paper, an online optimal coordinated solution for the voltage regulation of a distribution smart grids including an on-load tap changer (OLTC) and multiple distributed generators (DG) is presented. The proposed strategy sets reactive power points of distributed generators as well as tap position of the OLTC hierarchically. In the first stage, a distributed sub-gradient method in order to find the optimal reactive powers for the DGs is implemented to minimize the power losses subject to voltage limits. If the first stage could not regulate voltage profile inside acceptable limits, in the second stage tap position of the OLTC will change optimally. The proposed solution is verified by studying suddenly load change and DGs’ active power output. An IEEE 123-bus unbalanced test system is used for the verification of the proposed method. Fast response, responsibility to different suddenly changes in the operating condition, and reduction in the number of needed taps are the results of this study. Moreover, analogous steady state results in comparison with another centralized method i.e. interior point algorithm demonstrate the ability and efficiency of the proposed solution.