A study of a solar PV and wind-based residential DC NanoGrid with dual energy storage system under islanded/ interconnected/grid-tied modes

Abstract

Progress in Direct Current (DC) power technologies has paved way for the emergence of DC Nano Grid (NG) as a new research area drawing international attention. This paper aims to design a simple and cohesive control algorithm for a solar PV and wind generator coupled low power residential DC NG with electrical and thermal energy storage systems. The envisaged NG control architecture extracts maximum power from solar PV, effects maximum active power transfer from wind generator with voltage regulation of the DC bus, draws/delivers balanced sinusoidal currents at Unity Power Factor (UPF) from/to the grid and monitors power scheduling to DC and thermal loads. The maximum solar PV power is extracted through incremental conductance algorithm and maximum wind power is tracked using a polynomial curve fit equation derived from the wind power curves without implementation of any speed/torque control loops. The maximum active power transfer from wind and UPF operation of the grid is achieved using a reference current generation method based on symmetrical components theory of equal current strategy with no complex transformations. A power factor of 0.99 with generation of balanced sinusoidal currents during both grid power import and export is achieved. Further, the operation of the proposed DC NG in all possible modes such as islanded/grid-tied/interconnected modes are monitored through a supervisory controller implemented in OPAL-4510 Real Time Digital Simulator (RTDS) under varying solar irradiation, wind velocity and load conditions, which projects the suitability of the system to be implemented in any geographical location (hilly terrain/rural/urban) either with limited availability of renewable sources or grid supply. The successful operation of the system is validated through experimentation on a 120 W scaled-down hardware prototype.