Independent Per-Phase Power Control in Four-Leg Virtual Synchronous Generators

Distribution grids are facing a great transformation in recent years with the advent of smart grid technologies. Particularly, more and more controllable devices, based on power electronics, are being deployed in this part of the power system. These interfacing devices are in charge of the active power management of many resources ranging from renewable energy sources to energy storage systems. For this reason, it has to be considered that power electronics may provide valuable ancillary services for improving the operation of distribution networks. With this regard, it is important to stress that low-voltage distribution systems and microgrids are by nature unbalanced due to single-phase loads. Consequently, the flexibility requirements and control capacities of converters interfacing distributed resources have to be greater with respect to those of balanced systems. This work proposes independent power control for each phase of a three-phase, four-wire virtual synchronous generator specially suited for these unbalanced environments. The technical feasibility of the control approach has been successfully validated through several Control Hardware-in-the-Loop tests analyzing both steady-state and transient responses as well as the performance on a microgrid scenario. In this last scenario, the performance of the proposal has been also compared to a virtual synchronous generator based on symmetric components decomposition.