Three-Port Multilevel Converter for Hourly Dispatching Solar PV Power with Battery Energy Storage System

This study investigates a dispatching scheme of megawatt-scale solar PV power for a one-hour dispatching period for an entire day utilizing an isolated multiport converter configuration and battery energy storage system. A multilevel triple active bridge (TAB) dc-dc converter has been proposed where a neutral-point-clamped (NPC) H-bridge is employed in the high-voltage side, and the conventional two-level full-bridge is configured in the low-voltage side across the high-frequency transformer. The power losses between the proposed TAB-NPC converter and conventional TAB converter are compared to identify the superior multiport converter topology for this application. The converter loss analysis is conducted using the parameter values of the switching devices in the MATLAB/SIMULINK environment, and the proposed TAB-NPC converter is found to exhibit better performance than the conventional TAB for megawatt-scale grid-connected PV arrays. Furthermore, the curve fitting and Particle Swarm Optimization techniques are implemented to seek the optimum value of depth of discharge for the battery energy storage system taking into account both the cycling and calendar expenses. A fuzzy inference system as a function of the battery state of charge is also developed to accurately estimate the grid reference power for each one-hour dispatching period, which helps to develop a cost-effective energy storage system for hourly dispatching PV power scheme.