Fuel Cell Vehicle (FCV) Power Train
Demonstration of a Fuel Cell Vehicle (FCV) power train using SimPowerSystems™ and SimDriveline™.
Olivier Tremblay, Souleman Njoya Motapon, Louis-A. Dessaint (Ecole de Technologie Superieure, Montreal).
Contents
Circuit Description
This example shows a multi-domain simulation of a FCV power train based on SimPowerSystems and SimDriveline. The FCV power train is of the series type, such as the one found in the Honda FCX Clarity [1]. This FCV is propelled by one electric motor powered by a fuel cell and a battery.
The FCV Electrical Subsystem is composed of four parts: The electrical motor, the battery, the fuel cell and the DC/DC converter.
- The electrical motor is a 288 Vdc, 100 kW interior Permanent Magnet Synchronous Machine (PMSM) with the associated drive (based on AC6 blocks of the SimPowerSystems Electric Drives library). This motor has 8 pole and the magnets are buried (salient rotor's type). A flux weakening vector control is used to achieve a maximum motor speed of 12 500 rpm.
- The battery is a 13.9 Ah, 288 Vdc, 25 kW Lithium-Ion battery.
- The fuel cell is a 400 cells, 288 Vdc, 100 kW Proton Exchange Membrane (PEM) fuel cell stack.
- The DC/DC converter (buck type) is current-regulated.
The FCV Vehicle Dynamics Subsystem models all the mechanical parts of the vehicle:
- The single reduction gear reduces the motor's speed to increase the torque.
- The differential splits the input torque into two equal torques.
- The tires dynamics represent the force applied to the ground.
- The vehicle dynamics represent the motion influence on the overall system.
- The viscous friction models all the losses of the mechanical system.
The Energy Management Subsystem (EMS) determines the reference signals for the electric motor drives, the fuel cell system and the DC/DC converter in order to distribute accurately the power from the two electrical sources. These signals are calculated using mainly the position of the accelerator, which is between -100% and 100%, and the measured FCV speed. Note that a negative accelerator position represents a positive brake position.
- The Battery management system maintains the State-Of-Charge (SOC) between 40 and 80%. Also, it prevents against voltage collapse by controlling the power required from the battery.
- The Power management system controls the reference power of the electrical motor by splitting the power demand as a function of the available power of the battery and the fuel cell. This power is controlled by the DC/DC converter current.
There are four main scopes in the model:
- The scope in the main system shows the accelerator position, the car speed, the drive torque and the power flow.
- The scope in the FCV Electrical Subsystem shows the results for the PMSM drive. You can observe the motor torque (electromagnetic and reference), the rotor speed, the mechanical power (electromagnetic and reference), the stator currents (magnitude, Iq and Id components), and the stator voltages (magnitude, Vq and Vd components).
- The scope in the FCV Electrical Subsystem/Electrical measurements shows the voltages and currents for the fuel cell, the battery and the DC/DC converter and the battery SOC.
- The scope in the Energy Management Subsystem/Power Management System shows the power references applied to the electrical components.
Demonstration
The demonstration shows different operating modes of the FCV over one complete cycle: accelerating, cruising, recharging the battery while accelerating and regenerative braking. Start the simulation. It should run for about one minute when you use the accelerator mode. You can see that the FCV speed starts from 0 km/h to about 90 km/h at 12 s, and finally decreases to 80 km/h at 16 s. This result is obtained by maintaining the accelerator pedal constant to 70% for the first 4 s, and to 25% for the next 4 s when the pedal is released, then to 85% when the pedal is pushed again for 4 s and finally sets to -70% (braking) until the end of the simulation. Open the scope “Car” in the main system. The following explains what happens when the FCV is moving:
- At t = 0 s, the FCV is stopped and the driver pushes the accelerator pedal to 70%. The battery provides the motor power till the fuel cell starts.
- At t = 0.7 s, the fuel cell begins to provide power but is not able to reach the reference power due to its large time constant. That's why the battery continues to provide the electrical power to the motor.
- At t = 4 s, the accelerator pedal is released to 25%. The fuel cell cannot decrease its power instantaneously; therefore the battery absorbs the fuel cell power in order to maintain the required torque.
- At t = 6 s, the fuel cell power is equal to the reference power. The battery is no more needed.
- At t = 8 s, the accelerator pedal is pushed to 85%. The battery helps the fuel cell by providing an extra power of 25 kW.
- At t = 8.05 s, the total power (fuel cell and battery) cannot reach the required power due to the fuel cell response time. Hence the measured drive torque is not equal to the reference.
- At t = 8.45 s, the measured torque reaches the reference. The fuel cell power increases so the battery power is progressively reduced to 6 kW.
- At t = 10.9 s, the battery SOC becomes lower than 40% (it was initialised to 40.32 % at the beginning of the simulation) therefore the battery needs to be recharged. The fuel cell shares its power between the battery and the motor. You can observe that the battery power becomes negative. It means that the battery receives some power from the fuel cell and recharges while the FCV is accelerating. At this moment, The required torque cannot be met anymore.
- At t = 12 s, the accelerator pedal is set to -70% (regenerative braking is simulated). The motor acts as a generator driven by the vehicle’s wheels. The kinetic energy of the FCV is transformed in electrical energy which is stored in the battery. For this pedal position, the required torque of -140 Nm cannot be reached because the battery can only absorb 25 kW of energy. The fuel cell power decreases according to it response time.
- At t = 15 s, the fuel cell power is about 2 kW (the minimum power).
Notes
1. The power system has been discretized with a 60 us time step.
2. In order to reduce the number of points stored in the scope memory, a decimation factor of 10 is used.
3. The PMSM drives (AC6 blocks) and the DC/DC converter (from the SimPowerSystems) uses the average value option of the detailed level. This option allows to use a larger simulation time step.
References
1. Honda FCX Clarity Press Kit, http://www.hondanews.com