This paper proposes a fully decentralized control approach, based on AC bus signaling, to integrate the operation of voltage- and current-controlled converters that exist in an isolated low-voltage microgrid, so they may be fully steered under grid-feeding, grid-supporting, and grid-forming control principles. The proposed strategy, devised by classic and modified droop-based controllers, allows control of the microgrid active power relating to the system frequency, while regulating the reactive power related to the voltage, dispensing any need for communication infrastructures. Beyond ensuring proper microgrid power balance at all times, the control strategy prioritizes energy extraction from non-dispatchable sources (i.e., photovoltaic-based systems), whereas it uses dispatchable sources (i.e., battery-based systems) to share active and reactive power proportionally to their capabilities. As a consequence of the proper and novel management of battery-based converters, battery overvoltage and overcurrent are avoided, supporting a prolonged lifespan. Simulation results considering an autonomous microgrid operating under several scenarios are presented, to demonstrate the capabilities of the proposed control scheme on steering the different topologies of converters.

This paper presents the implementation of a single-controllable microgrid in the engineering school of the Federal University of Minas Gerais using commercial devices. Such a microgrid exchanges controllable active and reactive power terms with the upstream grid, proportionally shares active/reactive power among the battery-based DERs and endows the microgrid with the capability of operating in both grid-connected and islanded modes. The energy storage system is composed of three different battery technologies: lead-acid, lithium-ion and sodium–nickel, which are coordinately controlled according to their inherent features. A usable average energy control is proposed to avoid mismatches between the batteries’ states of charge. The single-controllable microgrid performs the following services: self-consumption, energy time shift, peak-shaving and reactive power support to the upstream grid. The coordinated secondary control and the operating modes of the microgrid were validated by means of full-scale experimental results using commercial devices. The lithium-ion battery showed the best performance in terms of round-trip efficiency, 93% over 85% (lead-acid) and 81% (sodium–nickel). The results demonstrated the microgrid’s capability of delivering ancillary services at the connection with the upstream grid, and proportionally exploiting the dispersed battery banks. In addition, the challenges of practical implementation were analyzed.

Voltage regulation in low-voltage (LV) distribution grids is essential to increase the penetration of photovoltaic (PV) rooftop units. Hence, PV inverters are commonly embedded with volt-var (VV) and volt-watt (VW) control functions to support the grid voltage regulation within the grid codes. Such an approach usually increases the LV grid hosting capacity (HC) by 1.5 to 2 times at the cost of energy curtail. Thus, the use of decentralized battery energy storage systems (BESS) near to nodes sensible to overvoltage become appealing, as it stores energy without creating current circulation within the grid. However, there are still gaps in sizing of decentralized BESSs and in quantifying their improvement in terms of HC. Thus, this paper contributes with a comprehensive study that evaluates the HC of a generic LV grid comprised of PV units with embedded VV and VW control functions, and proposes a methodology to guide the sizing of small decentralized BESS used to increase the grid HC. Using OpenDSS software, the VV and VW control functions are evaluated and compared with a base scenario where PV units operate at a unity power factor. The active power curtailment is used to size decentralized BESS to absorb excess energy, avoiding PV active power derating. Results show that BESS units, sized at about 5-10% of the PV power capacity, can reduce revenue impacts and increase HC by over 30% in LV grids.