Power Electronics Converters for Microgrids with Smart Grid Functionality: Digital Implementation of Proportional Resonant Controllers
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- Institutt for elkraftteknikk 
The fast evolving technology has resulted in an extensive use of power electronics. The desire of making a grid network more intelligent can be fulfilled by these power electronics device. Based on the controller design and implementation, smartness feature can be improved. Real time communication requirement between the units in a grid can be removed by droop control.The objective of this thesis is to do a thorough theoretical and practical study of Proportional Resonant controllers based on the journals available in the research field and then implement it in a digital setup, in order to realize its advantages over conventional Proportional Integral controllers.All simulations were performed using the simulation software MATLAB Simulink. Additionally, another tool called OPAL-RT was used to interface discretized MATLAB Simulink models to the laboratory setup.A preliminary test of Proportional Resonant controllers was done in continuous domain during Autumn 2013. It dealt with droop control for islanded operation mode (inductive output impedance) at different load conditions. The purpose of this preliminary project is to verify if the Proportional Resonant controllers can be implemented as voltage controllers for a single as well as multiple micrgrids in standalone operation mode. During this test, the current controllers were considered ideal.However, in order to investigate the effect of current controller in the overall system which includes the cascaded outer voltage controller, a Proportional Resonant current controller has been implemented in this study.In order to prove that the established controllers are feasible, laboratory tests were conducted, thus requiring discretization of the established controllers.A review of different discretization methods was conducted. The most suitable one for the Proportional Resonant controllers is analyzed further and used to discretize the controllers. Thereafter, they are tested in both MATLAB Simulink and laboratory environment via a prototype setup.Simulation results show that the established Proportional Resonant controllers work as intended. The laboratory tests which use the discretized controllers prove that the proposed controllers work, with comparable results as the simulations predicted.The controller behaviour was not optimal in terms of the settling time issue but the most relevant task of reference tracking has been achieved.