Week 6 Fuel cell powered vehicle model

Fuel Cell powered Vehicle Model

Aim- To Simulate and model fuel cell-powered electric vehicle

Components – Fuel stack, Boost DC-DC Converter, Flow Rate Regulator, Flow Rate Selector, Drive Cycle Source

Circuit Diagram -

Theory-

• Fuel Stack

The fuel stack block represents the generic block diagram of hydrogen fuel cell which uses hydrogen and oxygen combine to form electricity.

Like any other battery’s the fuel cell also has two electrodes and a membrane in between. At the anode, the hydrogen molecules are split into positive and negative ions and negatively charged electrons.

At the cathode, the electrons and positively charged hydrogen ions combine with O₂ to form water as an outlet. The membrane used in the hydrogen cell is a PEM type membrane (Polymer Electrolyte Membrane). This allows positive ions from the anode to pass through the cathode and negative electrons to pass through the external ckt causing electrical current.

The model used in this circuit is a proton exchange membrane fuel cell of 6KW 45Vdc.

Chemical Reaction at Electrode

Anode Reaction –

2H₂ → 4H⁺ + 4e^-

Cathode Reaction –

O₂ + 4H⁺ + 4e^- → 2H₂o

Overall Reaction –

2H₂ + O₂ → 2H₂o + heat + electrical energy

The input of the fuel stack is connected to a fuel flow selector via a switch and a saturator. The positive and negative terminal of the fuel stack is connected to a DC-DC boost converter.

Parameters of Fuel Stack

Boost DC/DC converter

The dc/dc boost converter is used to step the voltage from the fuel stack. The boost converter ckt uses an IGBT device along with a PI speed controller which acts as a feedback to the IGBT device.

The positive and negative terminal from the fuel cell is connected to the input of the converter. In practice, the output terminal from the converter is connected to the motor driver. But in this ckt, we connect a voltmeter across and an ammeter in series with the converter to the scope.

Flow Rate Regulator

It regulates the flow of the fuel i.e. hydrogen into the fuel stack. The fuel regulator monitors the current flow by taking it as input. A mathematical equation is implemented along with a saturation block to estimate the fuel flow.

Parameters of Fuel Rate Regulator

Flow Rate Selector

The Flow rate selector decides the rate of fuel to be supplied depending upon the external parameters. This block consists of a compare to constant block with operator >= 10 which lets the signal start after 10sec. The signal is passed to the

edge detector where the block detects the change in signal state.

The signal then goes to sample and hold block where it holds the output when the S input signal becomes falls. Now the output from sample/hold and ramp from the drive cycle is added to give Ramp_Fr.

Results

Artemis urban drive cycle was used as a ramp signal.

The Simulation time was 993sec. We obtain 2 different sets of Results

Scope 1

From Scope 1 we see that there are a frequent increase and decrease in the fuel flow rate depending upon the stack consumption.

We observe that with the decrease in the utilization of the hydrogen the fuel flow rate increase. The stack consumption of fuel in LPM is about 50 and stack efficiency is 55%.

Scope 2

From Scope 2 we measure the voltage and current from the DC-DC boost converter. We see that at the start of the current increase at 130A the voltage being at 45V for about 20sec.

As the vehicle accelerate and deaccelerate the voltage fluctuates w.r.t the current. As the voltage increases the fuel flow rate increase. The DC bus voltage and current remain constant at 100V and 60A respectively.