Fuel cell electric vehicles and storage system components

IN the previous article, I explained the fuel cell electric vehicle technology and architecture.

This week, I delve into the maintenance, service and repairs of this class of vehicles.

When working around high-pressure lines, components and systems, the technician should always refer to depressurisation and high-voltage disabling procedures in the service information before components removal.

Therefore, in addition to H2 system depressurisation, high-voltage components must be disabled, if necessary, before repairing the fuel cell (FC) system.

Before continuing with depressurisation of high-pressure components, the technician should do a thorough visual inspection of the vehicle to evaluate the operational condition of the components.

If there is damage to the FC system, the technician should — utilising service information — determine the proper procedure to rectify the operational issue with the vehicle.

Pinched lines, damaged tanks, leaking fittings or any FC pipe or tubing damage can have detrimental effects on the operation of the FC stack. With decreased electrical output, the system will operate in a reduced performance mode that could affect the high-voltage system operation. H2 must be stored in a class 4 high-pressure tank to ensure the highest level of safety.

2016 Audi h-tron concept

The tank must be able to withstand the high H2 pressure and collisions, while being light enough to ensure the vehicle range is not significantly affected.

H2 fuel tanks are constructed from a seamless, one-piece, permeation-resistant, cross-linked ultra-high molecular weight polymer liner overwrapped with multiple layers of carbon fibre/epoxy laminate and an external protective layer for impact resistance.

This design will ensure a lightweight H2 storage system.

The H2 storage tank system will also include a pressure regulator to reduce high pressure to low pressure (that is, 50 pounds per square inch to 100 pounds per square inch [0,3 megapascal to 0,7 megapascal]) before the gas is delivered to the FC stack, a manual or electric cut-off valve to shut off H2 after vehicle shutdown or collision, and (on some units) a manual shut-off valve.

2025 BMW 374 hp FCEV Powertrain

Keeping the tank light will increase the vehicle range while minimising safety ramifications.

In addition to ensuring a lightweight tank and high-pressure capability, the refuelling requirements can change the amount of H2 that can be introduced into the tanks.

Most refuelling stations have a 5 000 psi to 10 000 psi (34,5 megapascals to 68,9 megapascals) fuel nozzle that will provide H2 at different pressures.

Utilising the Society of Automotive Engineers (SAE) J2600 standard, the shape and capacity of the H2 nozzle is standardised across original equipment manufacturers (OEMs).

Toyota Mirai Fuel Cell Electric Vehicle

To reach the 10 000 psi (70 megapascal) pressure, the H2 fuel needs to be chilled so that the pressure can be increased enough to provide the fuel cell electric vehicle (FCEV) the proper amount of fuel to the vehicle tank.

Communication between the vehicle and the fuelling station allows the proper amount of fuel to be dispensed from the latter to the former.

SAE standard J2799 provides the standardisation for wireless interface between the vehicle and the station to control the amount of fuel dispersed.

After the H2 fuel is transferred from the storage tanks, the pressure and safety control hardware reduce the H2 gas pressure before it is received by the FC stack.

The H2 storage tank system utilises an integral H2 pressure control system.

Therefore, the H2 gas pressure will be reduced before exiting the tank.

Toyota Mirai Fuel Cell Electric Vehicle

In FC stack systems, an FC boost converter is used to increase the output voltage of the stack.

Because FC stacks are high-current, low-voltage devices, the voltage needs to be boosted to operate components on the high-voltage bus. Higher voltage means components will be smaller and can operate at higher horsepower, torque and rotation per minute (rpm).

Higher voltage also results in lower operating currents, reducing electrical current demands.

Toyota Mirai Fuel Cell Electric Vehicle

The voltage boosting system utilises inductors that are switched at higher frequency to produce the higher voltages.

The converter can use phases to provide enough power overlap, transferred to a capacitor filtering system to ensure a smooth output to all other high-voltage components on the direct current (DC) power bus.

The four-phase converter can use one or more phases and change frequency to produce the necessary power to satisfy what is needed for load currents.

Taurayi Raymond Sewera is ASE and AutoCate Association-certified World Class Master Technician with 39ASEs, ASE Advanced Level Specialist L1, L2, L3 and L4, AMI-Accredited Master Electric Vehicles and Master Automotive Manager, and ACDC-certified Master Hybrid and Electric Vehicles Technician. He is the founder and CEO of TauRay Automotive. He can be contacted on: +263772341193, +263772357296 or rtsewera@gmail.com