3.2.1. MCFC System

The fuel cell to be applied to the test bed is a 300 kW class MCFC system 'DFC300MA' model manufactured by 'POSCO Engineering' [28]. It is also a model that 'FuelCell Energy (FCE)' in the USA has developed as a basic model. Various development and experiments in several stages made the most optimized system at present. The fuel cell system consists of a stack module. EBOP (electric balance of plant) and MBOP (machinery balance of plant). The specification of the fuel cell system is shown in Table 1.


**Table 1.** Specification of the fuel cell system.

Figure 4 shows the peripheral equipment for the fuel cell system: Particularly, a fuel injection part for natural gas supply, a water injection part for making ultrapure water, a water discharge part and nitrogen/mixed gas injection part for stack protection. The Air injection part and the water discharge part are located on the upper side of MBOP within which two sets of exhaust fans are fitted.

**Figure 4.** Overall configuration for fuel cell system.

Figure 5 describes the concept of the electricity generation process. The system consists of three modes: A 'heat-up mode' for increasing the initial temperature of the fuel cell stack module, a 'ramp-up mode' for increasing the power output to the rated output, and an 'operating mode' for continuing the rated output.

**Figure 5.** Concept of the fuel cell power generation.

In the 'heat-up' mode of the fuel cell system, as shown in Figure 5, the Terminal Breaker (TB) is closed, and the fuel cell is operated by receiving electricity from the system. Since only the fuel cell consumes power, the Customer Critical Breaker (CCB) is opened. Respectively, it is designed to close the CCB to charge the ESS internal battery. In the 'ramp-up' mode (when the 'heat-up' is completed, and the fuel cell outputs power), the CCB is closed, and the EMS judges whether the ESS is on or off.
