Maximum Asymmetrical Support in Parallel-Operated Grid-Interactive Smart Inverters

Parallel operation of grid-interactive inverters has been continuously gaining attraction, and their contribution to sustaining the host grid stability has become strongly demanded. This paper investigates and discusses the trends in the most recent interconnection grid codes. Grid codes call for simultaneous requirements for the low-voltage ride-through capabilities of parallel operation of grid-interactive inverters as well as their effective asymmetrical voltage support by advanced active/reactive bi-sequence power provision under unbalanced grid faults. Addressing these demands in an optimized way becomes very challenging. This paper thus proposes a new methodology to simultaneously achieve three main objectives: (1) coordination of the asymmetrical ride-through and voltage support capabilities of parallel-operated inverters, (2) maximizing the utilization of each unit and their collective contribution in boosting the positive-sequence voltage and reduction of the negative sequence voltage subject to the constraints from the inverters and the grid, and (3) minimizing the impact of the support on the active power injections. Simulation and experimental results illustrate the effectiveness of the proposed algorithm.