Fuel cell powered vehicle model

FUEL CELL for EV vehicle

A Proton Exchange Membrane Fuel cell stack having an average vale of 100v DC/DC convertor is used.

A 50kW with 635Vdc fuel cell stack is selected. The properties of the fuel cell are listed below

Working:

Signal builder block is provided to the fuel system. The fuel flow rate increases in accordance with the input after T= 10sec. The input feeded into the signal builder block is taken from UDDS cycle and modified as er required. (Changes in the UDDS cycle are done to get better understanding of the fuel cell and its how its charateristics vary with input)

The Switch allows the fuel to pass into the fuel cell after 10 sec. The Fuel cell acting as the power house of the system, supplies current into the RL load. The current and volatge is increased with the help of a DC/DC boost convertor. This is used because the volatge obtained from the fuel cell is very less.

In order to take the feedback from the system, a flow rate regulator is connected to the current end from the fuel cell. 

This particular fuel cell has 900 cells in order to give 625vDC supply. The same numbers of cells are feeded into the flow rate regulator block, as shown in the figure above.

The input signal in the singal builder block is modified as shown above. After 10 sec high acceleration is provided upto 120lpm. 

The upper limit is set as 130lpm.

Also the RL load connected with the fuel cell is modified.

the new values for R&L load in shown.

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 120 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.

RESULT: 

The scope 1 results are as followed

- The Fuel flow rate stablizes till 10sec. After that the fuel rate increases upto 120lpm which is set as the upper limit for the same. The plot of the fuel rate is similar to what was provided in the input signal

- At T=10 sec, there occurs a transient stage as fuel is supplied to the fuel cell. This brings in changes in the H2 consumtion, voltage and current supplied too. DUe to this there is a sudden drop in the H2 utilization.

As fuel is supplied the volatge increases and subequently due to battery charateristics the current reduces. 

it can also be seen that at T=10 sec, the consumtion of air and fuel has changed in plot 3.

- hence in the plot 4 it can be seen that due to these changes, the overall stack efficiency reduces from 70% to less than 20%.

In Scope 2-

The initial 2 plot are the voltage and current graph from the fuel cell.

the Voltage increases to a certain saturated value according to the load applied. as the load is a RL load, the increase in voltage is exponential in nature.

With the inherit characteristics of the cell, the current reduces exponential upto 5A. 

After the fuel is supplied at 10 sec, volatge of the fuel cell increases and correspondingly the change in current is observed .

In plot 3rd and 4th in scope 2, the change in in DC volatge and current to the load is very minimal. The transient experienced at the load end is very less due to presence of controller in DC/DC boost convertor. The rise in voltage is observed, and is bring back to the required constant volatge and constate current. The boost controller does not allow changes to occur at the load end.