Fuel Cell-electric Drive Functional Test

Background

Numerous fuel cells connected in series are combined in the fuel cell stack. In a so-called "cold combustion", electrical energy is generated in these cells from hydrogen and atmospheric oxygen. In order to control this process, the supply of hydrogen and atmospheric oxygen must be precisely regulated and the entire fuel cell stack must be kept within a defined temperature range.

The fuel cell-electric drive is usually a complete component of a vehicle provided by a supplier. In combination with the other components of the vehicle powertrain, the result is the overall vehicle performance and dynamics. The characteristics, functions and properties of the fuel cell-electric drive are verified on test benches up to production release with various tests. To do this, current, voltage and power, as well as other measured variables such as temperatures, flow rates, pressures and humidity, must be acquired at various points in the fuel cell stack and powertrain.

Challenge

The functional tests cover all operating functions such as cooling circuit, cooling control, heating, hydrogen paths (anode path), air paths (cathode path), high-voltage electrical paths, sensor technology and fuel cell control unit. High-precision measurement of a wide range of physical parameters is required for functional testing and validation of the fuel cell drive system. In addition to temperatures, volumetric flows, humidity and pressures, high-voltage measurements of currents and voltages in the high-voltage circuits are necessary. From these, the delivered energy, power and efficiency are calculated.

With validation, the system requirements such as performance parameters, reaction speed to load changes or service life are proven with tests and endurance runs.

to check correct operation in the various operating phases. For example, the characteristic curve of the power during the warm-up phase, for start-up, load changes, partial load and peak load as well as various other distinctive operating points.

Ultimately, the specified efficiency curves of the fuel cell-electric drive are demonstrated. The efficiency is the energy delivered in relation to the hydrogen consumed. It depends on the load point and the optimal supply of the different media: hydrogen, atmospheric oxygen, humidity and cooling. A non-optimal supply, for example of stack humidification, leads to a drop in stack voltage.