Fuel Cell for Standalone Application Using FPGA Based Controller

Abstract

Recently, increase in energy consumption, uncertainty of crude oil price and universal environment changes has enforced researchers to focus more on new and renewable energy sources. Different renewable sources are available e.g. photovoltaic and wind energy; however each source has some limitations or other. One of the potential sources that can provide renewable energy is fuel cell which is better compared to other possible renewable sources of energy in certain terms. Solid oxide fuel cell (SOFC) is a more effective, environmental friendly renewable energy source. This paper focuses on standalone fuel cell power system (FCPS) using SOFC which can be used as a backup power source for household and commercial units. This backup power source will be efficient and will provide clean energy at an affordable per unit cost. Standalone fuel cell power system mainly comprises a fuel cell module, DC-DC converter and DC-AC inverter. This paper focuses on modeling, control of DC-DC converter and DC-AC inverter. Exhaustive simulation is conducted to validate our concepts and FPGA based experimental results confirm the same. Dynamic model of SOFC is developed to obtain output voltage, efficiency, various losses and power density of the fuel cell stack. This model contains the mathematical modeling and electrical features of the fuel cell system. It also describes the different types of possible losses i.e. i) Activation voltage loss, ii) Concentration voltage loss, and iii) Ohmic voltage loss. Detailed loss modeling facilitates accurate calculation of output voltage that ultimately drives further stages in a power supply scenario. Furthermore, it includes the calculation of the partial pressure of hydrogen, oxygen and water. In this investigation the output voltage of fuel cell is fed to a DC-DC converter to step up the output voltage. This converter steps up the output voltage that is a necessity as fuel cell normally provides a low output voltage at a reasonably high current. We first store energy in an inductor and that additional energy is then delivered at intervals through MOSFET acting as a switch regulated by PWM (Pulse width modulation) to a capacitor. The prototype of single phase fuel cell power system with Hysteresis Current Control (HCC) technique is developed. FPGA (Field Programmable Gate Array) implementation of HCC is done using NI -CompactRIO-9014. The HCC provides accurate pulse width modulation signal to drive the DC/AC inverter. This output wave form from the inverter indicates that the voltages are almost sinusoidal of frequency 50 Hz that is desirable for a specific load. Thus a fuel cell based standalone system is developed and its performance is evaluated.