A new multifunctional converter based on a series compensator applied to AC microgrids

This paper proposes a new multifunctional converter based on a series voltage compensator applied to centralized AC microgrids. Besides the basic functionalities required for a centralized converter in microgrids, such as grid-supporting and grid-forming voltage support and smooth transition from operating modes, the proposed converter can change its connection topology from series to parallel and vice-versa, depending on the system's condition. Thus, it assumes all the basic defining features of series and shunt power converters. The devised control algorithm allows on-line change of converter operating modes either as voltage- or current-controlled sources. These flexible functionalities allow the converter to operate as: (i) a grid-forming converter providing voltage and frequency references for the entire microgrid, keeping the voltages at the point of common coupling (PCC) synchronized with the utility voltage; (ii) grid-feeding active power into the microgrid; and (iii) grid-supporting, performing ancillary services such as voltage regulation, voltage sag and swell compensation, along with active power filtering, reactive power, unbalance and harmonic compensation. The converter can be applied to both single-phase and three-phase three- or four-wire networks. The multifunctional control is implemented using a Texas Instruments TMS320F28335 digital signal processor, and then validated through a hardware-in-the-loop simulation developed in the Typhoon HIL 600 platform.