A Comprehensive Multi-Level Control System for Micro-Grids Operating in Islanded Mode

Abstract

This thesis presents a new control architecture tailored for single-phase Microgrids (MGs) operating in the islanded mode. The main feature of the proposed control architecture is its capability to improve the transient performance of the MG components, to have autonomous operation, to compensate for harmonics, and to offer a tight regulation of the voltage across the load. The presented control architecture includes a converter-level controller as well as a supervisory-level controller. The proposed converter-level controller is able to significantly improve the transient performance. The converter-level control includes new power estimator, which can accurately estimate the active and reactive power values very fast. Thus, the transient performance is significantly improved. In addition, the converter-level controller includes a new harmonic compensation system in order to deal with harmonics. The harmonic compensation system includes a hybrid load observer. The hybrid load observer is able to estimate both the harmonics component and the linear components of the load. Thus, the hybrid load observer allows the harmonic compensation system to detect, estimate, and compensate for various load harmonics and disturbances caused by nonlinear loads in MGs (e.g. synchronous and asynchronous harmonics, and DC components). The proposed harmonic compensation system can substantially increase the reliability of MGs in the islanded mode of operation where nonlinear/linear loads produce asynchronous/synchronous harmonics. The other main contribution of this thesis is a novel supervisory-level controller for power converters in MGs. The proposed supervisory-level control scheme further enhances the reliability and transient performance of MGs by providing predictive features to control systems. This predictive feature is produced by a new dynamic controller block, which sets the parameters for the grid-side controller and the ones for the source-side controller. The supervisory-level controller effectively harmonizes the source-side controller and the load-side controller in order to improve the transient performance and stability of MGs. The converter-level controller along with the supervisory-controller provide a very reliable solution for MGs in order to deal with nonlinear loads and perform precise power flow control. Mathematical analysis, simulation and experimental results verify the feasibility of the proposed control techniques and demonstrate their superior performance.