ABSTRACT
In general, there are several kinds of fuel cells such as PEMFCs, SOFCs, PAFCs, MCFCs, AFCs, DMFCs, ZAFCs, and PCFCs [1]. Among these fuel cells, PEMFC is suitable for fuel cell vehicles and distributed generators because it has high power density, solid electrolyte, a long cell and stack life, and low corrosion. Moreover, PEMFCs can easily operate at low temperatures (50–100°C), which enables them to have a faster startup time. However, in order to generate a reliable and efficient power response and to prevent membrane damage and oxygen depletion, a sophisticated control technique is crucial for the operation of fuel cell systems [2,3]. Several control approaches have been developed for PEM fuel cell systems [2–5] to achieve an optimal air supply, hydrogen flow rate, and pressure. The steady-state electrochemical model of PEMFCs has been developed in References 6, 7 and a new dynamic model has been introduced [8,9]. However, even though the temperature significantly affects the operation of fuel cell stack, a control strategy for temperature has mostly not been considered. In Reference 10, an optimal temperature control study has been conducted based upon the consideration that the humidity and temperature are limited in boundaries, instead of a detailed control analysis by checking Bode plots. There are many literature PEMFC studies regarding control approaches for PEMFCs [2–5], PEMFC modeling studies [6–9,11–14], and PEMFCs applications regarding power electronics, power systems, and auxiliary system control [12,15–21]. In References 2–22, because temperature has a slow dynamic compared with other parameters such as air, hydrogen flow, and pressure, the stack temperature is assumed to be constant so that a simplified control-oriented dynamic model was derived. However, in reality, the change of the fuel cell stack temperature dramatically affects the output current as well as the output power of the fuel cells system. Thus, this chapter is focused on the fuel cell temperature model based upon an electrical aspect to design a better 280accurate fuel cell temperature controller. In this study, the thermal equivalent circuit of PEMFC described in Chapter 6 is used to design a temperature controller, which makes it easier to develop a temperature control algorithm for PEMFC. With the PEMFC thermal equivalent circuit model, the fuel cell system can be viewed as one of electrical systems, and the design procedure of the controller is almost the same as the design for the conventional power converter’s controller explained in Reference 23. Therefore, the analysis of the fuel cell controller can be simply done by checking the phase margin and magnitude of the transfer function of Bode plots.
