Modeling and controllers design for three-leg and four-leg grid-forming converters: A benchmark

We approach the modeling and a control strategy for three-phase three-leg three-wire and four-leg four-wire grid-forming converter under unbalanced conditions in an au-tonomous distribution network. In most cases, the analysis of three-phase AC power systems becomes simplified when the system is in three-leg three-wire configuration and perfectly balanced. However, one of the biggest challenges of grid-forming converter is to guarantee the quality in the energy supply, highlighting the voltage unbalanced caused by unbalanced load. Therefore, this paper aims at analyzing operation of three-leg three-wire and four-leg four-wire grid-forming converters under unbalanced conditions. The control scheme is a cascaded control with two loops referenced in the synchronous reference frame: (i) An inner current loop and (ii) an outer voltage loop. Simulations and experimental results are provided to verify the performance of the proposed control strategy.