Linear Quadratic Optimal Control for a Cascaded Converters-Based Microgrid

There is a constant transformation of the electric grid due to an ongoing interest in the deployment of renewable energy resources and electric microgrid formation. This transformation, though advantageous in many ways, poses great challenges for the energy industry and there must be a constant improvement in modeling, simulation, analysis and control techniques in order to characterize and optimize the system design and operation. In this light, the scope of this thesis is focused on developing a linear model, analyzing the stability and designing an optimal linear quadratic regulator (LQR) for a microgrid system. The microgrid system used is inspired by an existing, operational grid-connected microgrid testbed at the National Center for Reliable Electric Power Transmission (NCREPT). Simulation results using Matlab/SimulinkTM show that the linearized model has the same dynamics and converges to the same steady state values as the actual model with minimal error. The simulation results also show that the system’s stability margin lessens as the input impedance to the microgrid increases; suggesting a weaker coupling. Finally, it is observed through simulation that the proposed LQR controller remarkably improves the voltage settling time and overshoot, henceforth ameliorating the ability to include larger renewable generation capacity