Fuel cell vehicles: Reducing costs means having to use monitoring systems

Fuel cell vehicles: Reducing costs means having to use monitoring systems

Technology News |
By Christoph Hammerschmidt

In view of the enormous levels of fine particulate and nitrogen oxide pollution in urban areas, more and more hopes are being placed in electric mobility. The availability of mass-produced vehicles powered by alternative drive technologies could help to sustainably improve the quality of the air, as it would then be feasible to impose bans on cars with internal combustion engines for example. This in turn would give a boost to sales of electric vehicles.

Given an appropriate infrastructure, the fact that fuel cell vehicles are easier to refuel and have a greater range makes them superior to battery-powered electric cars. So it comes as no surprise that car manufacturers around the world are making a tremendous effort to promote the commercial use of fuel cell vehicles. The crucial aspect is to reduce the costs. These depend not just on the quantities produced, but even more so on the materials used.

Low-cost materials can cause problems

The heart of a fuel cell vehicle is the PEM fuel cell stack, in which hydrogen and oxygen are converted directly into water, producing electrical energy in the process. Here for example the costs can be reduced either by minimising the amount of platinum used as catalyst in the electrodes or replacing it altogether with alternative materials. It is a basic fact that the electrochemically active cell is susceptible to states occurring outside the operating range. For example: If a hydrogen pipe freezes in winter, cutting off the supply to one of the cells in the system, the intended reaction can no longer take place there. This gives rise to Irreversible corrosion mechanisms inside the cell affecting the carbon-containing components in particular. Consequence: Over the course of time the entire stack will sustain lasting damage and cease to function.

Such unwanted processes can only be avoided by monitoring the fuel cells. The characteristic quantities for fuel cell stack monitoring are the cell voltages. These provide detailed information on the condition of the stack at all times and so enable users to react promptly to critical operating states.

The advantages of individual cell monitoring

So-called Cell Voltage Monitoring (CVM) systems are thus an important component of the corresponding test benches employed in car manufacturers’ development departments. The standard procedure is to monitor the fuel cell stack as a complete system. This does however have certain disadvantages, as it does not permit the precise localisation of any faults occurring. Only with individual cell monitoring such as that provided by the MCM IntelliProbe system from SMART TESTSOLUTIONS is it possible to gain an in-depth insight into the situation inside the stack. Critical operating states are not just detected, they can also be accurately pinpointed.

An MCM IntelliProbe measurement system consists of up to 42 ten-channel
measurement modules, a link module and a bus termination tool.
It can also be extended to include the MCM Master
Module offering functions such as real-time local data processing.

A CVM system has to satisfy a whole host of requirements. Stationary test bench applications demand a high level of measurement accuracy in combination with a high scanning rate. This permits detailed examination of how the systems react to changes of state, for example changes in load. Certain designers also expect an extended measuring range to allow the simulation of critical operating states which cause the cell voltages to drop into the negative range. A further important aspect in the development of fuel cell vehicles is the investigation of how the systems are affected by ambient conditions such as temperature and moisture. The monitoring technology employed must therefore be capable of supplying perfect results even at temperatures down to as low as -40°C and the electronics must be protected against the ingress of moisture.

The particular challenges of on-board use

The demands made of the monitoring technology are even more exacting if a CVM system is to be used for mobile applications. The effort involved is however well worthwhile, as the installation of a CVM system in trial vehicles makes it possible to gather system findings under realistic conditions and to devise strategies for optimum operation. Another example: If an insufficient supply of fuel is detected in the system, operation could quickly be switched to electrolysis using the electrical energy available in the battery. In this case water is broken down into hydrogen and oxygen; the heat generated in the process melts any ice in the pipe, thus eliminating the cause of the hydrogen shortage and allowing the normal operating state to be resumed. Such an operating strategy would ensure reliable operation even in winter.

If operating strategies are linked to individual cell voltages, this logically means having to equip mass-produced vehicles with an appropriate monitoring system. Many car manufacturers are indeed thinking along these lines.

Despite its compact design, an MCM IntelliProbe
measurement module has an electric voltage of up
to 1,400 volts. Photo: SMART TESTSOLUTIONS


One of the basic prerequisites for integrating CVM systems into vehicles is an extremely compact design as the space available under the bonnet is generally at a premium. It is also advisable to accommodate the monitoring unit as closely as possible to the fuel cell stack to minimise measurement signal interference from external sources. The electronics can however only be installed at or on a fuel cell stack if the CVM system is capable of operating reliably in an extended temperature range up to 95°C. This is due to the fact that, for safety reasons, the fuel cell stacks are encapsulated in specially ventilated enclosures, which leads to elevated operating temperatures inside the stack housings. The system also has to be extremely robust and operate faultlessly even when subjected to vibration.

MCM IntelliProbe – the perfect solution for stationary and mobile use

The MCM IntelliProbe, the fourth generation of cell voltage monitoring systems from SMART TESTSOLUTIONS, satisfies all the requirements for both stationary and mobile applications. The system is of modular, compact design and features outstanding electric strength. It operates reliably even at high temperatures as well as being highly versatile. Measurements can be taken in the ranges from -1 to +5 V or from -3 to +3 V for example. This makes the MCM IntelliProbe system, which is already in use at numerous renowned car manufacturers working on fuel cell research and development around the world, an attractive technology for applications in other branches of industry as well, such as for battery cell quality control in lithium-ion battery pack manufacturing.

About the author: Dr. Markus Schuster is Business Development Manager New Energy Electronics at SMART TESTSOLUTIONS GmbH

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