Study of a DC Microgrid Integrating Renewable Sources and Storage Elements
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Date
2023
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université de msila
Abstract
In recent decades, the depletion of fossil energy resources has become commonplace. This depletion results in an ever-increasing expense of energy. Furthermore, these fossil energy resources are frequently blamed for being the main cause of global warming. This challenge necessitates the search for a feasible substitute for these fossil energy resources. On the other hand, a growing interest in the development of new technologies for the exploitation of renewable energy sources due to their technology maturation and low cost. Therefore, utilizing renewable energy for electricity production has become a popular solution. One of these solutions is the Microgrid system concept, which is particularly compatible and beneficial to electricity generation as well as the integration of renewable sources and energy storage systems. Despite the benefits of the DC Microgrid system, constant power loads provide a stability challenge due to the incremental negative impedance of their loads. This negative incremental impedance (INI) decreases the damping factor of the DC Microgrid, resulting in an undamped oscillation in the output current and voltage. As a result of these undamped oscillations, the DC Microgrid becomes unstable. This thesis treats the study and implementation of a DC Microgrid supplying constant power load (CPL), in which a boost converter with a tightly regulated output voltage emulates the CPL. This thesis work proposes a robust nonsingular terminal sliding mode controller to stabilize the system by avoiding the INI characteristic and conserving energy availability. The robust non-singular terminal sliding mode controller is characterized by the avoidance of the singularity problem that occurs by the traditional terminal sliding mode controller.
Apart from the challenge of the DC MG supplying a CPL, the power sharing issue between the distributed power systems that comprise the DC MG is also addressed. Using a case study of two paralleled buck converters supplying a single resistive load, the power-sharing problem is addressed utilizing a primary control level (Droop control method). The primary control level has been carried out using PI controllers for current and voltage regulation, as well as the addition of a virtual resistive load to avoid current circulation. The suggested controllers are confirmed using simulations and an experimental setup
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Keywords
DC Microgrid, droop control, constant power loads, power sharing, incremental negative impedance, terminal sliding mode, Nonsingular terminal sliding mode controller, singularity problem, PI controller