What it is
Fuel cells are chemical reactors that transform hydrogen and oxygen to electric energy and heat. A single fuel cell produces its electricity at a voltage of less than one Volt. So, for practical applications fuel cells are connected or stacked in series to achieve high voltages. Generally, the gasses are supplied to the cells in a parallel arrangement.
A consequence of this setup is that the gas supply to the individual cells of a stack can differ while the current flowing through them is identical. This can result into large differences in cell voltages within one stack. When a cell produces current at a low voltage (compared to the other cells in the stack), this is a clear indication something is wrong in the operation of this cell.
Since the efficiency of a fuel cell is measured by the cell voltage, cells are always operated at the highest possible voltage. Consequently any deviation from this optimal situation, e.g., due to a failing component or control, will be translated to a lowering of cell voltages. Consequently, cell voltages indicate the correct and safe operation of a fuel cell stack.
The main problem, however, in measuring individual cell voltages is the presence of a common mode DC voltage that is different for every cell and changes in time. Of course solutions exist to cope with this, but they tend to be expensive.
CellSense is a cell voltage monitoring device that can measure voltages of individual cells providing a solution to both problems. As a consequence it is well suited for monitoring commercial stacks and integration in control systems.
The technology used in CellSense is protected by a patent.
Het grootste probleem bij het meten van individuele celspanningen is echter de aanwezigheid van een standaard DC-spanning die voor elke cel anders is en in de tijd verandert. Er bestaan oplossingen om hiermee om te gaan, maar die zijn vaak duur.
CellSense is een daarom monitoringstool voor celspanningen dat spanningen van individuele cellen kan meten en een oplossing biedt voor beide problemen. Als gevolg hiervan is het zeer geschikt voor het bewaken van commerciële baterijcelpaketten en integratie in besturingssystemen.
De technologie die wordt gebruikt in CellSense wordt beschermd door een patent.
How it works?
CellSense is built in a modular way. One component in this design is an analog to digital converter that converts the voltages of four adjacent cells to digital information. This is called a voltage scanning unit or VSU. Any number of VSUs are connected in parallel, one for every four cells in a stack. All these VSUs are powered over a common isolated power bus and they send and receive data over a common isolated data bus. The other component in the design is the main controller. Its task is to read the data generated by the VSUs, to treat this data and to generate messages for a higher level controller in the fuel cell installation.
There are several advantages in using multiple VSUs:
- Very modular design, very few unused channels
- High common mode voltage rejection
- Measurements are performed quasi simultaneously (within less than 0.5 msec)
- Very low component count to achieve low cost
- Great flexibility for PCB lay-out in case of custom design
As pointed out, any deviation from optimal operation results in cell voltages dropping low. This means that malfunctions or unsafe situations can be detected by a CVM making it an effective and valuable component in safety, risk and operability assessments.
Possible advantages of the CVM are:
- Safety device to comply with risk assessment
- Lower gas stoichiometry (lower λ)
- Higher availability, better quality of electric power
- Less chance of damage
- Increased life expectancy
- Fast diagnosis in case of damage
- A complete history of on-site stack’s life