Three-phase four-wire grid-forming converter connected to microgrid with unbalanced nonlinear load

Abstract

A microgrid with neutral conductor, generally, is composed of inverters, grid-forming convertes, units of renewable energy sources and several three-phase and single-phase local linear and nonlinear loads (in condition of unbalanced loads). Thus, there can be a significant increase of the unbalance and distortion at the point of common connection (PCC), which imposes additional restrictions and considerations on the control of the inverters connected to the microgrid, because of the oscillating voltage at DC side. In this context, the present project aims to analyze a three-phase four-wire voltage source converter (VSC) connected or isolated from the microgrid (isolated or not from the utility), which is controlled as a grid-forming converter. Therefore, the main result of this project is to improve the modeling of the conversion system with a four-wire VSC with split capacitor. It is intended to use the VSC modeling and control system based on the digital models and controls developed in the UNIPD, using the Typhoon HIL 402 platform. Thereby, it becomes possible to analyze the oscillating voltages and currents at each DC capacitor of the VSC, which are generated by the unbalanced and distorted currents at the PCC. In addition, it is expected that the results arising from this project can contribute to the state of the art and development of the four-wire VSC with split capacitor, with consequences in the academic and industrial sectors. (AU)