A Modified Control Scheme for Power Management in an AC Microgrid with Integration of Multiple Nanogrids

This paper proposes a modified control scheme for a grid connected microgrid, which is contrived by integrating multiple nanogrids. In the considered system, each nanogrid consists of a generation unit from solar photovoltaic (PV) along with battery energy storage (BES) system and local loads. The nanogrid has the flexibility to operate in microgrid connected mode or islanded operating mode. Similarly, the microgrid can also be operated in grid connected mode or islanded mode. To achieve appropriate load sharing between different nanogrids considering local load demands and source power availability, a modified control scheme is developed. The proposed scheme compensates for the required reactive power, harmonics and unbalanced currents locally which are demanded by the local loads in nanogrids in order to improve the power quality in the microgrid. The smooth transition between the modes of operation of nanogrids and microgrid is achieved with the proposed modified control scheme. In addition, the proposed modified control scheme allows the microgrid and main grid to remain free from transients generated by load disturbances in nanogrid and disturbances in the microgrid respectively. Therefore, the effect of disturbances on voltage and frequency of the microgrid is reduced. A simple control scheme is developed to address the challenging issues for smooth operation of the microgrid such as active power sharing among the sources based on their ratings, power quality enhancement (compensation of harmonic components, unbalanced current and reactive power) and seamless transition between the modes of operation (during islanding from grid and re-synchronisation with grid). The performance of the proposed modified control scheme is verified in a real time simulator during variable loading conditions.