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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 85 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.
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 85 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).
This example shows operation of a Kinetic Energy Recovery System (KERS) on a Formula 1 car. The model permits the benefits to be explored. During braking, energy is stored in a lithium-ion battery and ultracapacitor combination. It is assumed that a maximum of 400KJ of energy is to be delivered in one lap at a maximum power of 60KW. Design parameters are the weight of the battery, ultracapacitor and motor-generator. If these parameters are all set to the very small value of 0.01kg, the lap time is 95.0 seconds, this corresponding to a car with no KERS. With default values set here, approximately 1/4 of a second is saved on the lap time when using any available electrical power when not braking. Applying KERS only to selected corners requires a larger ultracapacitor to show any significant benefit.
This model shows how Simscape™ Electrical™ and Simscape can be used to support system-level design. The KERS performance is a complex trade-off between the masses of the three main components (battery, ultracapacitor and motor-generator), plus the energy-management strategy. The KERS system adds mass which reduces acceleration due to the engine. The stored electrical energy from braking must more than compensate for this. Lithium-ion batteries have a very high energy per unit mass but a poor power per unit mass. Conversely an ultracapacitor has relatively low energy per unit mass, but a very high power per unit mass which suits this particular application.
Plot 1: The plot below shows the vehicle speed during a single lap. The driver knows the maximum speed the vehicle should be travelling at the corners on the track and applies the brakes to achieve that speed in the corner.
Plot 2: The plot below compares the two strategies for using the electrical drive during acceleration. One strategy uses the electrical powertrain during all corners, the other uses it only on selected corners. The difference is easiest to see on the plot of motor torque, where the selected corners strategy shows zero torque from the motor during a number of the corners in the lap (rapid deceleration and acceleration).
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