Week 6 Fuel cell powered vehicle model
Fuel cells are an alternative energy technology that generate electric energy through the reaction between hydrogen (or a hydrogen-rich fuel source) and oxygen. These devices are particularly interesting due to high efficiencies relative to traditional combustion engines and low emissions, producing only heat and water as waste products. The development of new component materials with increased performance and cost-effectiveness is a critical part of emerging fuel cell research.
Fuel cell components-
Fuel cell devices are often composed of multiple fuel cells connected in series to form a stack ,which increases the total amount of generated electricity. Each individual fuel cell contains three primary components: two electrodes (anode and cathode) and a conductive electrolyte. In the case of PEM fuel cells, each electrode is comprised of a porous, high-surface area material impregnated with an electrocatalyst, typically platinum or a platinum alloy. The electrolyte material is a polymeric membrane and serves as an ionic conductor.
Electrical generation in a fuel cell is driven by two primary chemical reactions. For fuel cells operating on pure H2, hydrogen gas is split into protons and electrons at the anode. The protons are conducted through the electrolyte membrane, and the electrons flow around the membrane, generating an electrical current. The charged ions (H+ and e-) combine with oxygen at the cathode, producing water and heat.
SIMULINK MODEL:
The nominal Fuel Cell Stack voltage is 45Vdc and the nominal power is 6kW. The converter is loaded by an RL element of 6kW with a time constant of 1 sec. During the first 10 secs, the utilization of the hydrogen is constant to the nominal value (Uf_H2 = 99.56%) using a fuel flow rate regulator. After 10 secs, the flow rate regulator is bypassed and the rate of fuel is increased to the maximum value of 85 lpm in order to observe the variation in the stack voltage. That will affect the stack efficiency, the fuel consumption and the air consumption.
on running the model
Analysis :
At t = 0 s, the DC/DC converter applies 100Vdc to the RL load (the initial current of the load is 0A). The fuel utilization is set to the nominal value of 99.56%. The current increases to the value of 133A. The flow rate is automatically set in order to maintain the nominal fuel utilization. DC bus voltage is very well regulated by the converter. The peak voltage of 122Vdc at the beginning of the simulation is caused by the transient state of the voltage regulator.
At t = 10 s, the fuel flow rate is increased from 50 liters per minute (lpm) to 85 lpm during 3.5 s reducing by doing so the hydrogen utilization. This causes an increasing of the Nernst voltage so the fuel cell current will decrease. Therefore the stack consumption and the efficiency will decrease. As we can see, after 10 s the flow rate increases, hence as the stack cannot fullfil the amount of fuel to increased flowrate, the stack consumption and utilization of oxygen and hydrogen is reduced, hence reducing the stack efficiency of the fuel cell.
Although, there is only a minor spike in the voltage profile(DC bus voltage), current profile almost remains constant, meaning the load draws the required current irrespective of decreased consumption fuel and air, hence reducing the stack efficiency.