Microgrid Operation and Control

Abstract

The world is moving toward renewable energy resources as a result of rising energy demand and the decline of fossil fuels. This move led to the shift of interest from the centralized conventional electric grids to decentralized smart grids. Microgrid is the basic structural unit of smart grid, it can utilize both renewable and non-renewable types of distributed generator (DG) technology. As many renewable DG technologies and storage elements are based on DC power, while many loads and devices depend on AC power, the importance of inverter-based DG technology increased. The output of these inverters in an islanded microgrid must achieve a good current sharing between DG unites in microgrid, maintaining stability and synchronization between DGs, and keeping voltages and frequencies within specific range. These criteria can be achieved with various control strategies including centralized control, master slave control, current distribution control and droop control methods. Consequently, the control and operation of microgrid is a challenging task that requires overcoming the obstacles relates to the nonlinearities and disturbances in the power system. In this thesis work, two feed-back control strategies were developed and implemented in droop control to operate multiple DG units in a microgrid. The two control strategies are state feedback control and hyperbolic tangent exponential Sliding Mode Control (SMC). The developed state feedback control provided a powerful performance with respect power sharing accuracy in steady state conditions and regulating the voltage and current disturbance caused by other DG units within the same microgrid. The proposed hyperbolic tangent exponential SMC utilizes the exponential SMC method and hyperbolic tangent reaching mode to provide robust, accurate, reliable behavior against unmodeled dynamics, hard nonlinearities, and parametric uncertainties. Furthermore, an experimental set is built to imitate a microgrid operation in real life application.