Week 6 Fuel cell powered vehicle model

AIM:- To make a MATLAB model of fuel cell-powered electric vehicle.

Fuel Cell Electric Vehicle:-

               FCEVs use a propulsion system like that of electric vehicles, where energy stored as hydrogen is converted to electricity by the fuel cell. Unlike conventional internal combustion engine vehicles, they produce no harmful tailpipe emissions.

These are few examples of fuel cell-powered vehicles launched in recent year

• 2008 - Honda FCX Clarity
• 2015 - Toyota Mirai
• 2016 - Riversimple Rasa
• 2016 - Honda Clarity Fuel Cell
• 2018 - Hyundai Nexo

Fuel Cell Working:- 

               The most common type of fuel cell for vehicle applications is the polymer electrolyte membrane (PEM) fuel cell. In a PEM fuel cell, an electrolyte membrane is sandwiched between a positive electrode (cathode) and a negative electrode (anode). Hydrogen is introduced to the anode, and oxygen (from air) is introduced to the cathode. The hydrogen molecules break apart into protons and electrons due to an electrochemical reaction in the fuel cell catalyst. Protons then travel through the membrane to the cathode.

               The electrons are forced to travel through an external circuit to perform work (providing power to the electric car) then recombine with the protons on the cathode side, where the protons, electrons, and oxygen molecules combine to form water. 

               Below is the working animation of the cell.

SIMULINK Model:-

Description of Model:-

              Above is the Proton Exchange Membrane (PEM) Fuel Cell Stack model feeding an average value 100Vdc by DC/DC converter to the RL circuit with 6kW load.  For the EV application study, we can use this arrangement of RL load circuit to make an electric vehicle model that is powered by the fuel cell. We are assuming vehicle equivalent to resistance value in ohm. This model has a feedback system, which controls the fuel flow rate.

             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 according to the drive cycle values with a maximum of 90 lpm(litre per minute) in order to observe the variation in the stack voltage. That will affect the stack efficiency, fuel consumption, and air consumption.

Blocks Used in Model:-

1) Signal Builder:-

             In the default Matlab model, a ramp signal is given as load reference. The ramp signal block act as the flow rate reference. If you need the model to power an EV, defined flow rate data can be given as input. It can depend on the drive cycle for a vehicle.

             So while designing the EV model, I have changed the fuel flow rate according to the drive cycle made in excel file. The data is in litres per minute (lpm) which is for 100 secs.

              As discussed earlier that for 10 sec the fuel flow is regulated by the regulator, whatever the fuel flow is given initially trough data for 10 sec will not affect the fuel consumption at the start for 10 secs. Whatever the effect of the drive cycle is used will be shown after the 10-sec values. So in this case, the output effect will be for rest 90 sec which will depend on the drive cycle.

               The output of signal builder block is the input for the fuel stack. But it passes through the flow rate selector.

2) Flow rate Selector:-

                
              This is the inside view of the flow rate selector subsystem. It is implemented by a simple Simulink block. Here the clock gives current simulation time as an output. Here basically the time span of 10 sec is getting compare to satisfy the condition of the regulated flow of hydrogen for 10 seconds. After comparing the signal it goes to the switch.

3) Switch:-

              The Switch block is controlled by an external physical signal. If the external physical signal is greater than the value specified in the Threshold parameter, then the switch is closed, otherwise, the switch is open.

The condition is given as below-

4) Saturation block:-

             The Saturation block produces an output signal that is the value of the input signal bounded to the upper and lower saturation values.

             The default value given in the block is 85 in the default model which is the upper limit value for the signal. The maximum speed value attained during the cycle can be given as the upper limit given.

             In this model, the value is changed to 90.

5) Fuel Cell Stack:-

             The Fuell Cell Stack implements a generic model parameterized to represent the most popular types of fuel cell stack 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 the Model details level in the block dialog box.

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

V-I Characteristics:-

6) DC/DC Converter & Series RLC Branch:-

               DC/DC converter voltage in subsystems is loaded with 100dvc Boost. A DC/DC boost converter is used to increase the voltage produced by the fuel cell and supply it to the vehicle represented by the series RLC branch to the right. The voltage and current are measured using DC voltage and current measurement blocks.

Inside DC/DC Converter-

             The Average-Value DC-DC Converter block represents a controlled average-value DC-DC converter. You can program the block as a buck converter, boost converter, or buck-boost converter by providing the duty cycle. The diagram shows the equivalent circuit for the block with a duty cycle as input.  

             Here RL branch is used as a load of 6kW. RL load can be considered as equivalent to the load, which the vehicle requires.

7) Flow rate Regulator:-

                 The flow rate regulator takes Input as feedback to compare and regulates the flow rate. Here in this case it is used following the expressions:

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

Inside view-

Parameters-

OUTPUT:- 

                Fuel Cell Used: PEMFC- 6KW – 45 Vdc (PEMFC - Proton Exchange Membrane Fuel Cell ). 

                The below output graph shows the output for a 6kW load. The simulation is run for 100 seconds.

1) Scope 1 Output:

                The fuel cell stack parameters like fuel & air consumption, fuel flow rate, Hydrogen & Oxygen utilization, and stack efficiency are studied in this scope.

                From the above graph, we can observe the fuel flow rate as per signal builder data in liter per minute (lpm). For the first 10 seconds, the fuel flow rate is according to the regulated flow. But after that, for the remaining 90 seconds, the fuel flow rate is increasing and decreases according to the drive cycle. 

                The oxygen utilization is constant throughout the cycle for the whole 100 seconds which is 60%. The hydrogen utilization is 99.56% for the first 10 seconds as discussed earlier. It decreases with acceleration and increases while decelerating. The utilization is constant for constant speed i.e constant flow rate.

                Also from the stack consumption graph, we can see that up to 10 secs the oxygen and hydrogen consumption more and gradually increases, and after 10 seconds hydrogen and oxygen consumption decreases and remains constant.

                From the stack efficiency plot, we can observe that the efficiency is decreasing for an increase in fuel consumption i.e. with an increase in the speed of the vehicle. It remains constant for further constant fuel flow rate & increases while decelerating.

2) Scope 2 Output:-

                At the start, for the first 10 seconds, voltage drops suddenly for sudden required increased fuel flow rate and after 10 seconds it tries to become steady. It increases and decreases according to the fuel flow rate. The highest voltage after 10 seconds is 55 volts and it decreases while decelerating. For acceleration & deceleration, the current requirement is more which can be seen from the graph. 

                For DC bus voltage there is a small overshoot after the first 10 seconds and there is a negligible overshoot in DC bus current also. This means the only change in voltage and current can be seen at the transient state of the system. Otherwise, there is no change in the DC Bus Voltage, as the DC/DC Converter of 100Vdc is taken into consideration.

Drive Cycle Data Used in Model in litre per minute (lpm):-

https://drive.google.com/file/d/1HwmDiX6e1ezIyos73q8xWsOMGpueSKmz/view?usp=sharing