Fuel cell powered vehicle model
Aim: Modelling a fuel cell-powered electric vehicle.
Objective: Modelling of a fuel cell-powered car and to comment on the results obtained.
Theory:
Fuel cell electric vehicles (FCEVs) are powered by hydrogen. They are more efficient than conventional internal combustion engine vehicles and produce no tailpipe emissions—they only emit water vapour and warm air. FCEVs and the hydrogen infrastructure to fuel them are in the early stages of implementation. The U.S. Department of Energy leads research efforts to make hydrogen-powered vehicles an affordable, environmentally friendly, and safe transportation option.
What is a Fuel Cell Electric Vehicle:
FCEVs use a propulsion system similar to that of electric vehicles, where energy stored as hydrogen is converted to electricity by the fuel cell. Unlike conventional internal combustion engine vehicles, these vehicles produce no harmful tailpipe emissions. FCEVs are fueled with pure hydrogen gas stored in a tank on the vehicle. Similar to conventional internal combustion engine vehicles, they can fuel in less than 4 minutes and have a driving range over 300 miles. FCEVs are equipped with other advanced technologies to increase efficiency, such as regenerative braking systems, which capture the energy lost during braking and store it in a battery. Major automobile manufacturers are offering a limited but growing number of production FCEVs to the public in certain markets, in sync with what the developing infrastructure can support.
How does fuel cell work:
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.
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Key components:
| Battery (auxiliary): In an electric drive vehicle, the auxiliary battery provides electricity to start the car before the traction battery is engaged and also powers vehicle accessories. | Fuel cell stack: An assembly of individual membrane electrodes that use hydrogen and oxygen to produce electricity. | Power electronics controller (FCEV): This unit manages the flow of electrical energy delivered by the fuel cell and the traction battery, controlling the speed of the electric traction motor and the torque it produces. |
| Battery pack: This battery stores energy generated from regenerative braking and provides supplemental power to the electric traction motor. | Fuel filler: A nozzle from a fuel dispenser attaches to the receptacle on the vehicle to fill the tank. | Thermal system (cooling) - (FCEV): This system maintains a proper operating temperature range of the fuel cell, electric motor, power electronics, and other components. |
| DC/DC converter: This device converts higher-voltage DC power from the traction battery pack to the lower-voltage DC power needed to run vehicle accessories and recharge the auxiliary battery. | Fuel tank (hydrogen): Stores hydrogen gas on board the vehicle until it's needed by the fuel cell. | Transmission (electric): The transmission transfers mechanical power from the electric traction motor to drive the wheels. |
| Electric traction motor (FCEV): Using power from the fuel cell and the traction battery pack, this motor drives the vehicle's wheels. Some vehicles use motor generators that perform both the drive and regeneration functions. |
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 140 lpm in order to observe the variation in the stack voltage. That will affect the stack efficiency, fuel consumption and 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.
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 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 litres per minute (lpm) to 85 lpm during 3.5 s reducing by doing so the hydrogen utilization. This causes an increase of the Nernst voltage so the fuel cell current will decrease. Therefore the stack consumption and the efficiency will decrease (Scope1).
- we can see clrealy that for the first 10m secs, when the hydrogen supply(fuel flow rate) is constant, the curve rises and then is constant till 10 secs after this the limit is set to 140 lpm. The fuel flow rate follows the data entered from the signal builder.
- utilization curve shows the consumption of Oxygen(air) and hydrohen fuel.tOxygen supply is constant and hydrogen is maintained at 100 for the first 10 secs and then starts falling.
- while starting the vehicle, DC bus current rises and then remains constant. This explains that while starting the vehicle, the vehicle demands supply from the battery. During this period a large fluctuation can be seen in the amount of voltage of DC bus voltage as well.
- Also, current supply from fuel cell increases and then settles after the fuel flow rate is increased further after 10 secs. The Voltage also dips and then rises and then settles after 10 secs.
- The stack efficiency also falls over time.