Operation of Microgrid with cascaded Current-Voltage Control of Voltage-sourced Converter based on H-infinity Repetitive Control Strategy

Abstract

The aim of this research is to identify some issues related to practical implementation of cascaded Current-Voltage Control of Voltage-sourced Converter (VSC), based on H-infinity Repetitive Control Strategy, through Simulations. Earlier research implemented the subject Control Strategy of VSC on a Laboratory scale System with a constant DC Voltage Source. This research replaces DC Voltage Source in Laboratory Setup with a 700 Volts DC Bus, with DC Voltage being controlled by Lead-Acid Battery based Battery Energy Storage System (BESS). DC Bus also includes a 40 kW Fuel Cell and 41 kW Photovoltaic (PV) System. The Control Strategy is tested for balanced Loads, unbalanced Loads and nonlinear Loads in Grid-connected and Islanded Modes. In Islanded Mode, the Voltage of DC Link can be controlled by BESS with smaller Discharge Power. In Grid-connected Mode, large Power Exchanges occur between Grid and DC Link at start up, due to slow response time of Repetitive Controllers, resulting in unacceptably large deviations of DC Link Voltage. To settle DC Link Voltage within reasonable time, BESS with Discharge Power equal to sum of Microgrid’s local Load and main Grid’s Demand is needed. Moreover, the DC Link Voltage has ripples at low frequency with unbalanced local Load in Grid-connected and Islanded Modes, despite presence of independently controlled Neutral Leg. All Simulations are carried out in MATLAB/Simulink Environment.