Project 2

Run simulations, change the threshold, create plots and measure current and hydrogen consumption. Specify the outputs. How to run the model. 

Aim:  To design the complete working model of Hybrid Fuel cell Electric Vehicle with battery and Ultracapacitor and to analyze hydrogen consumed, current, Load sharing and state of charge of battery and ultracapacitor.

Simulink full model

Driver subsystem

in this driver system input is desired velocity and actual velocity. it is a pid controller. error signal is calculated by comparing desired and actual velocity. this error signal is fed to this proportional integral and derivative controller. To avoid the unwanted error due to integrator, the external reset is done whenever the actual velocity is zero. Proportional gain is given as 0.75, Integral gain as 0.03 and Differential gain as 0. The PID output is from -1 to 1. If the output is between 0 to 1 it is given as accelerator command and if the output is between -1 to 0 it is multiplied with -1 and is given as brake command. output of driver subsystem is accelerator and brake command.

Electric powertrain system

Input to the subsystem is accelerator and brake commands. This consists of controller, torque/power, tractive force, Energy management system, fuel cell system, H2 consumption and energy storage system. output is tractive force Hydrogen consumption, state of charge of ultracapacitor and state of charge of battery.

Controller

Input of system is accelerator and brake. accelerator is multiplied with maximum torque to provide positive torque request. and brake is multiplied with minimum torque to produce negative torque request. And the negative torque is requested if the any one of state of charge of ultracapacitor and battery is greater than 0.8. If the SOC of Battery and ultracapacitor is less than 0.8 then the negative torque request is 0 goes for regenerative braking. Both positive and negative torque request is added to get the total torque request.

Torque power system

Energy management system

Positive power system

Fuel cell backup system

Battery backup system

Negative power system

Fuel cell subsystem

• The input to the fuel cell subsystem is fuel cell power.
• The fuel cell system is 80kW system.
• The operating range for the fuel cell is 23kW to 55kW. It is derived from the polarization curve.
• The active area of fuel cell is 420cm^2.
• The operating range starts from current density of 0.24A/cm^2 and ends at 0.76A/cm^2.
• The average voltage of each cell is 0.6V.
• If 380 cells are used in series, then then total voltage is 380*0.6 = 228V.
• Lower limit of current = 420*0.24 = 100.8A
• Upper limit of current = 420*0.76 = 319A
• Lower power limit = 228*100.8 = 22.9kW
• Upper power limit = 228*319 = 72.7kW
• At 72.7kW, the efficiency is less.
• So, the upper power limit is taken as 55kW for high efficiency.
• The power is converted to kW and is given to the power control subsystem which gives the current from the fuel cell.
• According to this current, the optimum pressure is obtained from the lookup table.
• From this current, the current density is calculated.
• According to this current density and pressure, the cell voltage is obtained from the polarization curve (2-D lookup table).
• The stack voltage is calculated by multiplying number of cells connected in series.
• This is multiplied with current to calculate the fuel cell power.
• The auxiliary load is present in the vehicle such as 12V system which consumes the power which is taken as constant of 1.724 kW.
• And compressor used for cathode also consumes some power.
• By subtracting the auxiliary and compressor power from the fuel cell power, the net power is obtained which is then again fedback to power control subsystem to calculate current.

Power control subsystem

According to power demand, the current is obtained from the Power-Current curve. This is then added with the controller output. The controller is PID controller which process the error signal and gives current as output.

Compressor subsystem

static screw compressor map

• The compressor is used in cathode side to maintain the optimum pressure for the oxygen from air to enter in the fuel cell for the proper working and efficiency.
• The input to the subsystem is the ambient pressure and optimum pressure from the lookup table.
• From this pressure ratio and compressor speed, the airflow is obtained and is converted to kg/s from static compressor map and the eta adiabatic is obtained from the static adiabatic map.

Air and Hydrogen consumption system

• he input to this subsystem is current and other parameters inputs are air fuel ratio, number of cells, molar mass of oxygen, molar mass of hydrogen, hydrogen utilization factor and faraday constant.
• From current obtained from the fuel cell, oxygen and hydrogen consumption is obtained by using the formulas.

Oxygen consumption = ( I * AFR * n_cell * molar mass of O2)/( 4 * faraday constant)

Hydrogen consumption (kg/s) = (I * n_cell * molar mass of H2)/(2 * H2_utility factor * faraday constant)

Hydrogen Consumption subsystem

The input to the system is hydrogen consumption in kg/s. It is then integrated to get the total hydrogen consumption inn kg.

Energy storage system

The energy storage system consists of ultracapacitor and battery. The input of the subsystem is ultracapacitor power and battery power. The output is state of charge of Ultracapacitor and Battery power.

Ultracapacitor

Current and charge calculation

• In the charge and voltage calculation subsystem, the current, voltage, open circuit voltage and charge calculation subsystem is formed.
• The current calculation is done by using the formula,

I = ((SOC*V_max)-sqrt((SOC*V_max)^2-(4*R*P_uc*eff))/(2*R)

• The input to OCV subsystem is current. The Open circuit voltage is calculated by using formula,

OCV = integral(I/C)dt

• The charge can be calculated by using formula,

Q = C*V_max*n_cells

• The input to voltage subsystem is current and SOC. Voltage is calculated by using formula,

V = (SOC*V_max*n_cells)-(I*R)

• The input to the SOC calculation subsystem is current and charge. The SOC is calculated bu using formula,

SOC = integral((I*eff)/Q)dt

Battery model subsystem

Current

SOC

Vehicle dynamics

• The input to this subsystem tractive force which is converted to velocity and is given as output.
• The Opposing force is reduced from the input tractive force and acceleration is calculated by dividing with vehicle mass. F = m*a.

• The acceleration is then integrated to get the actual velocity of vehicle.
• But due to the integral windup the overshoot occurs.
• This occurs because initially the error between the actual and desired velocity is more. In order to overcome this error, the overshoot occurs.
• Then due to this overshoot, another fluctuation less than desired velocity to overcome the error due to overshoot.
• This windup can be overcome by using anti windup. This is obtained by using external reset.
• When the acceleration and velocity is not equal to zero, then external reset is set.
• When the acceleration and velocity is zero, then the external reset is reset.
• By considering the initial condition of vehicle which is zero, in order to reject the unwanted errors, the memory is used.

Output results