Control and Stability Analysis of a Direct Current Microgrid based on Modular Multilevel Converter for Integrating Renewable Energy Resources

Abstract

To strike climate change, the integration of higher levels of renewable energy sources to electric power systems is needed. Direct Current (DC) Microgrids are an alternative for this integration in low and medium voltage levels. A microgrid consists of a set of renewable energy resources, energy storage systems and loads that are managed as a single controllable entity. Generally, a 2 levels voltage source converter is the responsible for interfacing the microgrid with the main grid. However, there is also the possibility of interfacing the DC microgrid through a Modular Multilevel Converter (MMC). In this converter topology, the energy stored in the converter is no longer dependent of the DC circuit voltage level. Therefore, the MMC's energy can be used as an additional degree of freedom for stabilizing the microgrid. Hence, the objective of this research project is to propose a control strategy for an MMC that interfaces a DC microgrid with renewable power generation and energy storage systems from a railway power system taking advantage of the extra degree of freedom corresponding to the energy stored in the MMC. Moreover, a rigorous stability analysis will be performed using mathematical tools. To evaluate the control system's performance, the behavior of the DC microgrid facing a steep disturbance corresponding to the braking energy recovery system will be investigated.