Case Study of Single-Controllable Microgrid: A Practical Implementation

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.