Modelling and simulation of variable speed pico hydel energy storage system for microgrid applications

The scheduling and dispatch of stochastic renewable energy sources can be difficult in a Microgrid (MG). Renewable energy sources can power the MG reliably if supported by energy storage systems, via hierarchical control of the MG. In this work, a sustainable energy storage system is modelled with the existing resources in an agricultural farm. The resource is a downscaled pumped hydro storage system called Pico Hydel Energy Storage System (PHESS). The PHESS is numerically modelled with the governing equations of various components in the system. The proposed configuration caters for the water demand of crops and the energy storage requirement in a renewable energy powered microgrid. A full scale power converter topology is employed for variable speed operation of the proposed energy storage system. The power absorbed from the microgrid and injected into the microgrid is controlled by adjusting the speed of PHESS. An adaptive perturb and observe algorithm is developed to control the storage system in the generating mode, thus enabling the maximum extraction of power at various discharge rates and hydraulic head. A relationship between the power and speed of the turbine is deduced through regression analysis to control the storage system in pumping mode. The proposed model of PHESS is optimized to accept power commands directly from the MG controller for various levels of controls in the MG thus ensuring plug and play feature. The results obtained from MATLAB/Simulink software justify the effectiveness of the control strategies in both modes of operation.