OPTIMIZED DESIGN OF HYBRID ENERGY STORAGE SYSTEMS FOR ENHANCED PERFORMANCE IN DC MICROGRID APPLICATIONS

Abstract

Due to easy integration with renewable energy sources as well as proliferation of dc-compatible loads, 
dc micro grids are gaining popularity. Because of high penetration of renewable energy sources in dc 
micro grids, these micro grids are highly susceptible to fluctuations in power generation. This is 
harmful so long voltage stability is considered. To absorb these fluctuations within, a battery based 
energy storage system and hybrid energy storage system (HESS) consisting of battery and super 
capacitor (SC) are proposed. The contrasting characteristics of battery and super capacitors make 
them a perfect combination for HESS applications. The HESS is interfaced to dc micro grid using a 
double-input bidirectional converter. This bidirectional converter provides decoupled control of 
battery and super capacitor power. This thesis presents a converter modeling method for the double- 
input bidirectional converter. A controller was designed based on this for voltage regulation 
application for a dc micro grid. The operation of converter made it possible to use same controller for 
both HESS charging and discharging operation thus making it a unified controller. The designed 
controller was also able to reject disturbances from source side as well as load side while maintaining 
the voltage stability of dc micro grid. Operation of the converters and performance of designed 
controller in voltage stability were validated with simulation results for both battery alone storage 
system and hybrid energy storage systems.