|| Fuel cell powered vehicle model ||

A Simulink Model for an Electric vehicle using Fuel Cells:

In MATLAB Command window type "power_fuel_cell" keyword to open, the simulink model of fuel cell powered Vehicle.

Fig.1 Main Model

Let us, understand each of the Blocks in brief. To get a clear vision of the simulated result.

1. Ramp:

Generate constantly increasing or decreasing signal. The Ramp block generates a signal that starts at a specified time and value and changes by a specified rate. The block's Slope, Start time, and Initial output parameters determine the characteristics of the output signal. All must have the same dimensions after scalar expansion.

We are taking, the parameters as,

2. Flow Rate Regulator:

As, by the name itself it is clear that, Flow rate regulates the flowrate of our Input by taking output as a feedback. Here in this case it is following the expression as:

60000*8.3145*(273+T)*Nc*u(1)/(2*96485*(Pf*101325)*Uf_H2/100*x/100)

In this flow diagram, it is cleared that it is taking the input from feedback (denoted by current 1)and giving out the output(denoted by flowrate 1)

Again, it is following the parameters as :

3. Flow Rate Selector:

Again, as per the name, it selects the and proceed out the required output, For any Input. To understand this block more clearly. Lets, Unmask.

We get,

The circuit have a clock, which Output the current simulation time. A Compare to Constant block is setted up, which let the signal start after 10 sec. as it is using >10 operator. And pass it to the Edge Detector, Which detect the change of 10. Now the signal goes into Sample and Hold Block, Where the holds it and pass it according to the values, Here circuit have 2(Fr_reg_in) for input. Where, if it doesnot satisfies, then will go into 3(Fr_reg_out).

Again, the sample and hold block have an output to the Add Block, Where it is adding the values with Ramp 1 Output. Now, Add Block is taking that inputs and giving out to the Ramp_Fr.

4. Switch:

Combine multiple signals into single signal. The Switch block passes through the first input or the third input signal based on the value of the second input. The first and third inputs are data input. The second input is a control input. Specify the condition under which the block passes the first input by using the Criteria for passing first input and Threshold parameters.

Here, we are taking criteria for passing from first input as u2>Threshold.

5. Satutarion:

Limit input signal to the upper and lower saturation values. The Saturation block produces an output signal that is the value of the input signal bounded to the upper and lower saturation values. The upper and lower limits are specified by the parameters Upper limit and Lower limit.

In Our case, we are taking Upper Limit as '95' and Lower Limit as '0'.

6. Fuel Cell Stack:

The Fuel Cell Stack block implements a generic model parameterized to represent most popular types of fuel cell stacks fed with hydrogen and air. The block represents two versions of the stack model: a simplified model and a detailed model. You can switch between the two models by selecting the level in the mask under Model detail level in the block dialog box.

Here, we are taking Detailed model level. With a pre-defined model of a PEMFC- 6KW- 45Vdc. Lets see, the Parameters of the fuel cell stack.

As, the Nominal operating point is taken as (V, I)=(133.3, 45) And (P, I) = (5.9985, 133.3)

similarly, Maximum operating points (V, I)=(225, 37) And (P, I) = (8.325, 225)

7. DC/DC Boost Converter:

A DC/DC Boost Convert Boosts the Voltage by, Compromising Current.

OUTPUT SIMULATED RESULTS:

TAKING SIMULATION RUN TIME AS : 20 Sec.

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.

At t = 10 s, the fuel flow rate is increased from 50 liters per minute (lpm) to 95 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 (Scope1).

• Scope 1:

i. Flow Flow Rate(lpm):

From 0 to 10 sec. of the time, the flow rate starts increasing and reamins constant, until it reaches 50 lpm. After, 10 sec. of the time. The flow rate increases upto 95 lpm which is attrained in 3.5 sec. of the total time.

We are controlling the voltage and current required for the system by changing the flow rate of the Hydrgen and oxygen.

ii. Utilization(%):

As, the Flow rate is increased to 95 lpm, there can be seen a reduction in the utilization of Hydrogen ie, 100% to 42%. Whereas, Oxygen remains contant with a value of 60%.

iii. Stack Consumption (lpm):

We, can see in the plot that, upto 10 sec. the oxygen and hydrogen consumption gradually increases and remains constant upto 10 sec. . Again, after 10sec. the hydrogen and oxygen consumption decreases and remains contant.

iv. Stack Efficiency(%):

At time t= 0 due to transient state the efficiency first increases and then decreases and remains constant,With the contant stack consumption. Efficiency again, decreases and remains constant after 10 sec.

• Scope 2 :

i. Voltage & Current :

Both voltage and current changes its values due transient state. We can see, voltage gets down and remains contant, Whereas Currrent goes up gradually and remains contant. Upto 10 sec. of simulation. After, 10 sec. with the increase in flow rate voltage of the system increases and to compensate with that current value got decreased.

ii. Dc bus Voltage & Current :

The only change in voltage and Current can be seen at transient state of the system. Otherwise, there is no change in the DC Bus voltage, as DC/DC converter of 100Vdc is taken into consideration.