Week 6 Fuel cell powered vehicle model

Aim:

To model a fuel cell powered electric vehicle.

Theory:

Construction and Working of Fuel Cell :

A fuel cell is composed of an anode, cathode, and an electrolyte membrane. A typical fuel cell works by passing hydrogen through the anode of a fuel cell and oxygen through the cathode. At the anode site, a catalyst splits the hydrogen molecules into electrons and protons. The protons pass through the porous electrolyte membrane, while the electrons are forced through a circuit, generating an electric current and excess heat. At the cathode, the protons, electrons, and oxygen combine to produce water molecules. As there are no moving parts, fuel cells operate silently and with extremely high reliability.

The electricity generated in the fuel cell of a hydrogen engine can take two routes, depending on the demands of the specific driving situation. It either flows to the electric motor and powers the FCEV directly or it charges a battery, which stores the energy until it’s needed for the engine. This battery, known as a traction battery, is significantly smaller and therefore lighter than the battery of a fully electric car, as it’s being constantly recharged by the fuel cell.

The electric motor converts the car’s kinetic energy back into electrical energy and feeds it into the back-up battery.

There is one crucial difference between hydrogen fuel cell cars and other electric vehicles – hydrogen cars produce the electricity themselves. So, unlike in fully electric or plug-in hybrid vehicles, the vehicle doesn’t get its power from a built-in battery that can be charged from an external power source. Instead, hydrogen cars effectively have their own efficient power plant onboard: the fuel cell.

Pros:

• No engine noise while starting and driving. The experience is same as driving the electric vehicle.
• Another advantage is the quick charging time. The hydrogen tanks of fuel cell cars, on the other hand, are full and ready to go again in less than five minutes.
• For the time being, hydrogen cars still have a longer range than purely electric cars. A full hydrogen tank will last around 300 miles (approx. 480 kilometers).
• The range of fuel cell vehicles is not dependent on the outside temperature. In other words, it does not deteriorate in cold weather.

Cons:

• The biggest shortcoming of the Hydrogen fuel cell car is the huge shortage of refueling stations. A hydrogen engine is refueled at special fuel pumps, which in the future will probably find their way into ordinary service stations.

Fuel Cell Model in Simulink:

The above diagram shows the full model of Fuel Cell Electric Vehicle. The signal builder is used to give the signal for fuel flow rate. The signal is derived from UDDC drive cycle and then converted into current signal which is used for 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 20 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 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.

Results:

Results Explained:

The simulation is done for 100 seconds.

The reason why the fuel flow rate is constant for the first 20 seconds because the speed for UDDC drive cycle is 0 for first 20 seconds. As the speed increases after 20 seconds we can see the variation of fuel flow rate. The constant fuel flow rate is about 50 lpm.

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 126A. The flow rate is automatically set in order to maintain the nominal fuel utilization. Observe the DC bus voltage and DC bus current(Scope2) which is very well regulated by the converter. The convertor maintains the contant voltage of about 100 volts and constant current of about 60 amps

At t = 10 s, there is no change in fuel flow rate but it changes after 20 seconds as the vehicle moves in forward direction. As we can see in the graph that there is a high ripple around 38th second because of a sudden decrease in vehicle velocity.