Robust Decentralized Tracking Voltage Control for Islanded Microgrids by Invariant Ellipsoids

This manuscript presents a robust tracking (servomechanism) controller for linear time-invariant (LTI) islanded (autonomous, isolated) microgrid voltage control. The studied microgrid (MG) consists of many distributed energy resources (DERs) units, each using a voltage-sourced converter (VSC) for the interface. The optimal tracker design uses the ellipsoidal approximation to the invariant sets. The MG system is decomposed into different subsystems (DERs). Each subsystem is affected by the rest of the system that is considered as a disturbance to be rejected by the controller. The proposed tracker (state feedback integral control) rejects bounded external disturbances by minimizing the invariant ellipsoids of the MG dynamics. A condition to design decentralized controllers is derived in the form of linear matrix inequalities. The proposed controller is characterized by rapid transient response, and zero error in the steady state. A robustness analysis of the control strategy (against load changes, load unbalances, etc.) is carried out. A MATLAB/SimPowerSystems (R2017b, MathWorks, Natick, MA, USA) simulation of the case study confirm the robustness of the proposed controller.

Modelling and analysis of grid-connected solar-PV system through current-mode controlled VSC

Recently, solar-PV energy becomes one of the most vital renewable resources of electrical energy as it is utilized in all life applications. In case of connecting the solar-PV system with the utility grid a voltage-sourced converter (VSC) is required to convert the extracted solar-PV array’s DC power into AC. There are many methods to dominate the active and reactive power produced from the VSC. In the following model we use the current mode control as it has some features such as highly output accuracy, protection against over current troubles, robustness against AC side voltage and load variations. As the produced power from the solar cells is intermittent, the point of maximum power has to be tracked using an MPPT technique. Also, in order to reduce the system harmonics a filter must be implemented in the model. In this paper, a complete model of 50KW grid-connected solar-PV system using current-mode controlled two-level three-phase VSC (grid imposed frequency VSC) is implemented. Also, the Incremental Conductance model to track the point of maximum available power (MPPT) and LCL filter has been provided into the system with total harmonic distortion (THD) analysis in PSCAD/EMTDC