Week 6 Fuel cell powered vehicle model
AIM: To prepare a Simulink model of a fuel cell electric vehicle
THEORY:
Fuel cell electric vehicle (FCEV) is a type of electric vehicle which uses a fuel cell, instead of a battery, or in combination with a battery or supercapacitor, to power its on-board electric motor. Fuel cells in vehicles generate electricity to power the motor, generally using oxygen from the air and compressed hydrogen. Most fuel cell vehicles are classified as zero-emissions vehicles that emit only water and heat. A fuel cell needs three main components to create the chemical reaction: an anode, cathode, and an electrolyte. First, hydrogen fuel is channeled to the anode via flow fields. Hydrogen atoms become ionized (stripped of electrons) and now carry only a positive charge. Then, oxygen enters the fuel cell at the cathode, where it combines with electrons returning from the electrical circuit and the ionized hydrogen atoms. Next, after the oxygen atom picks up the electrons, it then travels through the electrolyte to combine with the hydrogen ion. The combination of oxygen and ionized hydrogen serve as the basis for the chemical reaction.
A boost converter (step-up converter) is a DC-to-DC power converter that steps up voltage (while stepping down current) from its input (supply) to its output (load).
working of fuel cell:
Basic description of how a fuel cell works and describes basic components.
a GIF animation of internal working of fuel cell stack for better visualization of how electron transfer happens and how electricity is generated
GENERAL LAYOUT OF FUEL CELL VEHICLE:
the technical viewpoint of the layout:
SIMULINK MODEL:
Simulink module explanation:
The ramp input is replaced with a current builder block and UDDS datasheet is being given as an input for the following simulation, the simulation is done for 150 seconds.
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(liters per minute) in order to observe the variation in the stack voltage. That will affect the stack efficiency, fuel consumption, and air consumption.
Fuel cell voltage, current, DC/DC converter voltage, and DC/DC converter current signals are available on the Scope2. Fuel flow rate, Hydrogen and oxygen utilization, fuel and air consumption, and efficiency are available on the Scope1.
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. Observe the DC bus voltage (Scope2) which 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.
There are 2 output results Scope 1 and Scope 2, from scope 1 we can analyze the data of rate of fuel consumption, stack consumption, stack efficiency, and utilization of oxygen and fuel(hydrogen).
In Scope 2 we can observe the voltage and current and output from both DC-DC boost convertor.
UUDS DRIVE CYCLE INPUT
OUTPUT
simulation for 150 seconds for better visualization:
simulation for the whole drive cycle:
RESULTS:
At the first 20 seconds of the curve, it is rather unaffected as the first 20 seconds input has 0 speed and we can see small repels, and later we can see sudden changes in the speed i.e increase in the current demand due to sudden brake or sudden acceleration.
The flow rate is automatically set in order to maintain the nominal fuel utilization.
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%.
At t = 10 s, the vehicle is in stationary position till t=20 secs and when the vehicle starts moving forward and the fuel flow rate is increased within a small timespan and is done by the hydrogen utilization. This causes an increase of the Nernst voltage so the fuel cell current will decrease. Therefore the stack consumption and the efficiency will decrease (Scope1).
In electrochemistry, the Nernst equation is an equation that relates the reduction potential of an electrochemical reaction (half-cell or full cell reaction) to the standard electrode potential, temperature, and activities (often approximated by concentrations) of the chemical species undergoing reduction and oxidation.
from scope2 we can see that the DC bus voltage and DC bus current maintains 100 volts and 60 amperes respectively, the ripples in the DC-DC convertor occurs due to the sudden decrease in vehicle voltage, and these ripples are quickly adjusted to maintain the specified requirement.