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Top1. Introduction
Nowadays it is an increasingly environmental problem the use of an energy system based on fossil fuels. Despite the efforts of governments and research teams, renewables energies have a number of associated problems such as dependence on environmental conditions, lifetime, high price, etc. In order to reduce these problems, the use of hybrid systems is presented as a technically feasible optimal solution. Recently, the use of hydrogen as an energy vector has been presented as a viable solution to improve the performance of hybrid system (García, Torreglosa, Fernández, & Jurado, 2013).
The proper energy management of hybrid systems requires the design of a control system and energy management strategy. For this reason, different works have been presented in order to make an optimal management, increasing system performance, providing a real alternative to current energy production. Most of these works are based on strategies whose sole propose is to keep the load as long as possible. The main target of these strategies is to ensure the power balance. This parameter is presented therefore as the only decision criteria to operate the system. These strategies base their efforts on maintaining the demand, ignoring technical or economic criteria associated with the proper operation of the equipment and its operating regimes. The use of fuel cell and electrolyzer is determined by the power balance, generating or absorbing energy based on the amount of excess/deficit energy. Strategies with grid connected configurations, use the grid as an active element of the system increasing security by having a solution in situations of excessive excess or defect energy (Ahmed, 2012), (Alkano, Kuiper, & Scherpen, 2015), (Mohammadi & Nafar, 2013), (Tesfahunegn, Ulleberg, Vie, & Undeland, 2011), (Giannakoudis, Papadopoulos, Seferlis, & Voutetakis, 2010). In isolated topologies, it will depend on the use of short-term energy storage elements. In most applications, batteries or supercapacitors operate in the first instance in situations of excess or defect energy, absorbing or supplying energy respectively. The use of fuel cells and electrolyzers is determined by the maximum or minimum predetermined operating margins for the above equipment (Sun, Lian, Wang, & Li, 2009), (Li, Jiao, & Wang, 2013), (Osman Haruni, Negnevitsky, Haque, & Gargoom, 2013), (Tégani, Aboubou, Ayad, Becherif, & Bahri, 2014), (Feroldi, Degliuomini, & Basualdo, 2013), (Mbarek, Belhadj, Le, & Tunis, 2009), (Bizon, Oproescu, & Raceanu, 2015).
In the same way, there are different works with strategies which objectives include some technical decision factors. The main target of these strategies is to reduce the degradation of the more critical equipment during the system operation. These elements are battery, electrolyzer and fuel cell. The solutions adopted in the literature are diverse and depend on the main goal to study. Strategies which choose to increase battery life, operate it with very low depths of discharge, a fixed load condition or a narrow range of SOC (Alkano et al., 2015), (Sacarisen & Parvereshi, n.d.), (Ipsakis et al., 2008). Other strategies are based on overcurrent control, improving the battery charge process (Kim et al., 2014). Strategies which choose to increase the electrolyzer lifetime are based on operate it with minimal power point. The use of this parameter will increase the performance but with low purity of products (Alkano et al., 2015), (Dash & Bajpai, 2015), (Uzunoglu, Onar, & Alam, 2009).
In order to reduce the degradation of the fuel cell versus dynamic conditions, it will operate in stable power (Brka, Kothapalli, & Al-Abdeli, 2015), (Dursun & Kilic, 2012).