Hourly Dispatching Utility-Scale Solar PV Power with Megawatt Multilevel Grid Inverter

Abstract

This study demonstrates a dispatching scheme of solar PV power utilizing two different types of energy storage components, namely, lithium-ion (Li-ion) battery and supercapacitors (SC). The cost optimization of the energy storage system, considering both cycling and calendar aging expenses, is assessed based on its usage of depth of discharge. It is found that the Li-ion battery is a better solution than the SC in terms of economic assessment for hourly dispatching PV power. Also, multilevel inverters, T-type and I-type neutral point clamped (NPC) inverters, are investigated due to their superior attributes: high efficiency, low total harmonic distortion, and reduced common-mode voltage. The power losses between the three-level T-type and I-type NPC inverters are compared, to identify the superior grid inverter topology for this application. The inverter loss analysis is conducted using the parameter values of the switching devices in the MATLAB/SIMULINK environment, and the T-type NPC inverter was found to exhibit better performance than the I-type NPC inverter for megawatt-scale grid connected PV arrays. Furthermore, an LCL filter has been designed for higher efficiency and better harmonic attenuation to interface the inverter with the utility grid.