Universal Controller for Three-Phase Inverters in a Microgrid

A universal controller for three-phase inverters (called UC3) is proposed to operate converters of a microgrid (MG) in grid connected (GC) and islanded modes and ensure seamless transition between these modes without reconfiguration of the control structure. These are desirable features for the flexible MG applications. UC3 provides control over real and reactive powers while offering voltage and frequency support. It emulates an inertia behavior that is grid supporting and stabilizing. Additional features of the proposed controller are summarized as follows: 1) it can be used in inverters with different output filters and is robust against their changes and uncertainties as well as the grid parameters; 2) it integrates the synchronization, which offers agile and smooth responses without causing stability issues; and 3) its structure is well suited for digital implementations. UC3 is the extension of the original single-phase work to three-phase. This paper presents the following contributions: 1) development of UC3 equations in a 2-D stationary domain; 2) derivation of a new quasi-linear model for UC3 in a GC operation; 3) a comparative stability analysis of the UC3-operated GC inverters using the developed quasi-linear model and the conventional method; 4) initial development of a new mathematical framework for the modeling and stability analysis of UC3-operated islanded inverters; and 5) comparative simulation and experimental results.