Design and Simulation of a DC Microgrid for a Small Island in Belize

A microgrid based on direct current (DC) was designed and simulated for a small island in Belize. The energy generated in the microgrid will come from DC sources and the loads on the island will also be DC. Therefore, it was proposed to design a microgrid based on DC to reduce the amount of conversion losses between AC-DC. A microgrid based on DC will have no power factor losses, less corona discharges due to the absence of the skin effect and allow for a cheaper and simpler system. DC microgrids are already widespread in the telecoms industry for data centres, airplanes, submarines and remote locations. MATLAB/Simulink was used to design and simulate the individual components of the microgrid. Power electronic converters were designed and simulated for use with photovoltaic (PV) modules and maximum power point trackers (MPPT) in order to extract maximum power from the solar resource. The perturb and observe (P&O) algorithm was coded into the MATLAB environment for the MPPT. A bidirectional converter (BDC) was also designed to allow power to flow from/to the battery which was controlled by a PI controller. A traditional buck or boost converter could not be used for the bidirectional converter due to the presence of diodes in their designs. The charge controller successfully controlled the bidirectional converter allowing power to flow from/to the battery to achieve voltage stabilization. A lead-acid battery was found to be the most cost effective option for integration into the microgrid. The solar and wind resources for the island were modelled along with the predicted load profiles of the island. A financial analysis was conducted using the Hybrid Optimization Model for Electric Renewables (HOMER) software. It was found that a DC microgrid could meet the load requirements with 20% less generation than an AC microgrid due to the absence of losses in inverters reducing the costs. An AC microgrid with diesel only generation which is currently in use resulted in the highest overall costs, an AC hybrid microgrid resulted in a cheaper system than the diesel only system and a DC microgrid resulted in the lowest costs. A long term, medium term and short term analysis of the DC microgrid was conducted. A 100% renewable microgrid was found to generate excess electricity throughout a year because the system needs to be sized to meet the load on periods of low renewable energy generation. Batteries can be used to decrease the excess electricity but they eventually increase the cost of the system and create battery disposal problems. The medium and short term analysis verified the functionality of the charge controller on a good day and bad day for renewable energy generation. Both simulations shown that the voltage was stabilized and the bidirectional converter functioned correctly. The microgrid would require 15.7% island cover from PV panels and 10 containers for the batteries. Therefore, it was proposed to size the solar generation to meet the base load and diesel generators to meet the peak load with hydrogen storage.