The term “Smart Grid” refers to this connection. Since production is now decentralized, the new system improves electricity quality, which is the primary driver of institutions’ expanded study on the idea. To increase the flexibility and dependability of the power system, smart grids (SG) connect small power production units, mostly from renewable sources, and employ sophisticated control technology. Figure 1 shows a typical microgrid system with energy storage. As a sole energy storage technology is unlikely to deliver these essentials effectively and economically, it is vital to couple multifarious energy storage technologies, creating a hybrid energy storage system (HESS) hybrid energy storage system. For example, BESS and ultracapacitor/supercapacitor (SC) technology can be coupled to build HESS. The BESSs have high specific energy, low specific power, low self-discharge, low cycle life, long charge times, higher cost per watt, and relatively lower cost per watt-hour. On the other hand, the SC storage systems have high specific power, low specific energy, high cycle life, very high self-discharge, short charge times, lower cost per watt, and higher cost per watt-hour [24], [25]. The HESS makes use of complementary properties of BESS and UC and provides large energy supply, high power, and fast dynamic response at the same time economically and effectively [26]–[29]. Nevertheless, to optimize the lifetime of both BESS and UC, it is vital to ensure that both operate within their operational constraints. BESS must operate within its state-of-charge (SOC) and current bounds and UC within its voltage and current bounds. At the same time the UC should respond to rapid high current signals in order to maximize the lifespan of the BESS [30]. There-fore, in order to maximize the profit it is crucial for a RS provider to optimize both capacity and operation of HESS.
HESSs are a useful combination that can provide the described power profile by integrating an energy source which mainly stores energy and another one which mainly transfers power.