Modified Backward/Forward Sweep Load Flow Methods for Islanded Microgrids

Abstract

The rise in electricity demand over the years till this day has led to the inadequacy of conventional power generation systems in meeting the needs of consumers. Complete overhauling of traditional power systems will be costly and unsustainable and has therefore led to other means of augmenting the current power systems. The advent of distributed generation (DG) as a mean of power generation has been crucial in helping to satisfy the increased electricity demand thereby leading to increased electricity penetration. The flexibility provided by DGs is such that they can operate either grid-connected or islanded as a microgrid with the added advantage of making electricity realizable in remote locations. However, DGs have added more complexity to the existing distribution systems. As a result, current power flow methods such as Gauss-Seidel, Newton Raphson and fast decoupled which naturally cannot cater for the added complexities that come with the addition of DGs have however been modified to work efficiently in AC microgids. On the other hand, the backward/forward sweep (BFS) which is one of the most efficient power flow methods for distribution networks has not been well-adapted yet to microgrids. Hence, a novel modification on BFS load flow algorithm is proposed to solve power flow for islanded droop-controlled AC microgrids. The proposed method has been formulated such that the system frequency is one of the system's unknown variables which is typical for an islanded network justifying further the absence of a slack bus. As a result, new equations have been systematically developed and incorporated with the conventional BFS method. In this work, two Modified BFS algorithms have been proposed for radial and meshed microgrids. The proposed methods are validated using the 33-bus test system and the results obtained are compared with simulation results from PSCAD/EMTDC. The proposed methods are accurate, simple and easy to implement thus serving as a useful tool for microgrid analysis and planning.

Date of Award	May 2017
Original language	American English