Control of a Grid-tied Multiport Inverter for a Microgrid with Renewable Energy Sources

This paper presents modeling and control of a two-stage grid-tied inverter for integration of different energy sources to the utility grid. These energy sources, e.g., wind turbine generator (WTG), photovoltaic (PV) panel, and battery, have different voltage levels as well as the different power-voltage characteristics, which makes it challenging to be integrated with a single converter. The focus of this paper is to develop two-level controllers on the AC side so that it can work in both grid-connected mode and standalone mode. The model in the d-q rotation frame is first derived from differential equations, based on the model; a converter-level controller is developed to regulate the grid current with sinusoidal waveform. Then the system-level droop controllers are developed to achieve the power sharing among converters in the microgrid. The experimental results testify the effectiveness of developed controllers, the multiport inverter is not only capable of working in the standalone mode but can share the power with other inverters in the grid-connected mode.