Isolated DC Microgrids : a paradigm-shifting technology allowing the implementation of renewable energy sources

Details

Supervisors

De Jaeger, Emmanuel

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

The great majority of countries have their energy generation highly dependent on fossil fuel sources, which leads to tragic effects on climate change. The characteristics of this generation were central in the development of our energy grids, that are centralized in terms of generation and have long AC transmission architectures. This thesis discusses an alternative to that reality: Isolated DC Microgrids, a group of interconnected loads and energy sources within clearly defined electrical boundaries, with a DC transmission strategy and storage units guaranteeing the reliability of the whole system. While studying this alternative, we focused our attention on DC-DC converter, a group of devices that are responsible for adapting the voltage level of a given busbar, in order to comply with requirements within the microgrid. Given the wide range of DC-DC converters available in the market, we discussed the principle of operation and characteristics of the main ones, dividing them in two groups: non-isolated and isolated ones. A decision was made, mainly based on their efficiencies, to use Buck and Boost converters in our model. Having decided for them, we had to find a control approach to be used and we went for cascade control, where we have two controllers working in series with each other, one aiming at controlling the voltage level in the output capacitor and the other the current in the converter's inductance. After that, a mathematical strategy was developed in order to correctly set the control parameters of both controllers, where we would define two time constants, one for each controller, and, based on that and the characteristics of the converters, define the control parameters that would guarantee their first order response, with the time constants previously defined. Finally, a model of this Isolated DC Microgrid was developed on MATLAB/ Simulink, having two renewable energy sources, photovoltaic (PV) and wind, and using the control strategy defined to set the correct voltage levels at the load ends. These loads were grouped in what we called "houses", each having representations of very common residential loads, such as phones, computers, showers and even electrical vehicle (EV) chargers. With this model, we aimed at simulating a microgrid as close to the reality as possible and, as the results found were promising, we believe that a major argument in favour of this strategy was made.