Optimal voltage control strategy for grid-feeding power converters in AC microgrids

Predominant power generation by renewable energy sources poses an increasing challenge regarding the maintenance of a stable, reliable, but also affordable electricity supply. Power converters are the key system component to interface distributed generation systems to the electrical power grid and are increasingly required to provide grid supporting measures to an extent comparable to classical centralized power stations. Thus, improving the control performance of power converters in microgrids is becoming more significant. This work proposes an optimal voltage control strategy for a grid-feeding active-front-end power converter, which inherently regulates its bus voltage within a defined tolerance band while simultaneously keeping the provided reactive power at a specified optimal level. The focus is put on the proposed multi-loop control which incorporates a fast model predictive based current controller. Simulations and experiments on a power converter test bench are presented to validate the performance of the proposed voltage regulation scheme. The controller implementation is carried out for a three-level neutral-point-clamped voltage source inverter with an LCL output filter. Based on the results of the experimental validation, a simulation-based case study demonstrates its performance for multiple grid-tied power converters in an AC microgrid.