Development of a low – voltage hybrid ac/dc distribution Microgrid.

Abstract

Micro grids are small-scale power grids that can operate independently or collaboratively with other small power grids. Hybrid micro grids integrate two or more independent ac and dc micro grids. In Uganda, the power systems face a lot of power quality issues like voltage sag or swell, voltage unbalance, power factor, harmonics and voltage fluctuations. In this study, we will be focusing on the AC distribution network whose power quality is majorly hindered by harmonics that lead to power losses and how a hybrid AC/DC micro grid will reduce the harmonics and hence power losses incurred due to those harmonics. These harmonics have been increasing steadily over the recent years due to increased power demand in the system. The harmonics are caused by electric equipment with non-linear loads drawing in current in abrupt short pulses like PCs, copies, fluorescent lights, transformers, elevators among others. This project therefore proposes a hybrid AC / DC micro-grid consisting of an AC grid and a DC grid. The proposed micro grid consists of DC and AC buses that have different types of loads distributed over the voltage levels of AC (415V and 240V) and DC. The DC grid is being supplied by a solar PV system, a Battery Energy Saving System and AC power from the ac grid converted to dc to supplement the dc supply. This hybrid micro grid is being implemented in a housing estate where the houses / homes use both the AC and DC for their power needs. The lighting, TVs, copies and printers and PCs would use the DC and the rest will be catered to by the Ac grid. Micro grids can help reduce dependence on fossil fuels and increase the overall efficiency of the power grid by reducing the power quality issue of harmonics. A complete model of this micro grid is simulated using Matlab/Simulink. The proposed model is used to study the effect of harmonics on the hybrid and how much of them are reduced and how power losses are also reduced. Simulation of measurements related to power quality variables such as current and voltage total harmonic distortion were calculated including capability to compute power line losses. The results obtained in the analysis of the two scenarios were discussed and the total harmonic distortion and the power losses obtained from the simulation were less than those in the case study. However, their main challenge remains the initial cost of setting up the system but is cost efficient in the long run because it would reduce the power losses incurred due to harmonics significantly hence less money lost.