الفهرس 
Smart grid
Rating-based control of DC microgridsOnly 14 pages are availabe for public view
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Abstract
Recently, the DC microgrid has grasped more attention due to its inherent advantages such as high reliability, increased efficiency and simple control. However, voltage regulation and proper current sharing are considered the major issues associated with the DC microgrid. Also, enhancing the closed-loop performance of the power converter of each DG represents the main challenge for the DC microgrids. Hence, a hierarchal control scheme is adopted to overcome these challenges. The primary loop is utilized to control the inner-loop of each DG and the droop method is adopted in this loop. The tertiary loop is used to account for the deviation in voltage occurred due to the droop characteristics and control the power flow in the grid-connected mode. Finally, an outer loop is used to adjust the droop characteristics and control the power sharing of each DG in the microgrid.
In this thesis a rating- based control strategy is presented in order to adjust the power shared by the committed DGs in the DC microgrid. The droop characteristic is adjusted based on the size of each DG and the power sharing is determined based on its rating.
A distributed cost-based control strategy is introduced in order to minimize the total generation cost. The power sharing is adjusted based on the cost function of each DG. The incremental cost method is utilized in a distributed scheme, and the optimal generation is reached when all DGs reach a consensus value of the incremental cost.
In order to enhance the closed-loop performance of the power converter, two control techniques are introduced. A finite-state-machine based controller is developed to control the inner-loop of the dc/dc boost converter of each DG. In this method, the converter can be in certain states based on the relative values of two consecutive samples of the output voltage and the reference voltage signal. The advantages of this method are the simplicity of control and that the controller operates in a voltage mode, thus no current sensors are required.
Moreover, an output voltage tracking performance recovery based controller is developed to improve the closed-loop performance of the power converter of each DG. In this method, disturbance observers are designed based on multivariable approach to account for model mismatches and uncertainties. The controller estimates and cancels the disturbances due to parameters and load variations. The advantages of this method are fast dynamic response and the elimination of steady state errors without the use of integrators.
The feasibility and the robustness of the proposed control schemes are investigated by means of simulation studies using PSCAD/EMTDC package.