Week 6 Fuel cell powered vehicle model
Objective : To study about Fuel Cell Powered Electric Vehicle
Explanation
Fig.1.1. Simplified illustration of a working PEM fuel cell.
A fuel cell is a device that generates electricity through an electrochemical reaction, not combustion. In a fuel cell hydrogen and oxygen are combined to produce electricity, heat and water. Hydrogen fuel cells are very clean and versatile, producing zero emissions while being an extremely efficient, reliable and quiet source of power.
PEM (proton exchange membrane) fuel cells are a type of hydrogen fuel cell being widely commercialised across multiple applications and business sectors. They convert the chemical energy of hydrogen fuel directly into electricity via a solid conducting membrane sandwiched between two electrodes.
Fig.1.2.
During the vehicle design process, the vehicle manufacturer defines the power of the vehicle by the size of the electric motor(s) that receive electric power from the appropriately sized fuel cell and battery combination. Although automakers could design an FCEV with plug-in capabilities to charge the battery, most FCEVs today use the battery for recapturing braking energy, providing extra power during short acceleration events, and to smooth out the power delivered from the fuel cell with the option to idle or turn off the fuel cell during low power needs.
Lets study about Fuel cell model available in matlab,
Type, 'power_fuel_cell' in the command window in matlab to open the model of Fuel_cell arrangement. The ramp signal block act as the flow rate reference. If you need the model to power an EV, a defined flow rate data can be given as input. It can depend on the drive cycle for a vehicle. The drive cycle can be for a smaller duration of time (ex:100s) with one peak of acceleration and deceleration. The model is shown as per fig.1.3.,
Fig.1.3.
Use a signal builder block to give the data or add your own excel file data
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.
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.
The output shown in the signal builder block is as per fig.1.4.
Fig.1.4.
The default value given in the block is 85 which is the upper limit value for the ramp signal. The maximum speed value attained during the drive cycle can be given as the upper limit value here
Fig.1.5.
Open the fuel cell stack. You can change the PRESET model of the fuel cell from the drop-down menu. Keep the type of cell as PEM because it is the standard type of fuel cell used for EV vehicle. You can give any options from the drop-down menu. If you choose User-defined then, you must give a nominal voltage and current specification from a datasheet of fuel cell-powered EV. Otherwise keep a genuine range of power rating and work on the default values. But make sure your load (driving cycle) and the power rating of the fuel cell is compatible.
Fig.1.6.
Fig.1.7.
Fig.1.8.
Conclusion
Hence from the above plots we can conclude that :
1) With the Flow rate attain its peak value as the utilization of 02 remains constant and H2 utilization is reduced, with increased air consumption.
2) At t = 0 s, the DC/DC converter applies 100Vdc to the load RL,. The fuel utilization is set to nominal value of 99.56%
3) At t = 10 s, the vehicle is in stationary position untill few seconds and when vehicle starts moving forward 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 fuel cell current will decrease. Hence the stack consumption and efficiency will decrease (Fig.1.7).
4) In fig.1.8, there are ripple in DC-DC converter occurs due to the sudden decrease in vehicle voltage, and these ripples are quickly adjusted to maintain specific requirement.