Fraunhofer researchers using student e-racer to demonstrate novel sensor and battery management systems
|The e-racer from the team at Hochschule Esslingen University of Applied Sciences Click to enlarge.
Researchers at the Fraunhofer Institute for Integrated Circuits IIS are using an electric race car designed by electrical engineering students from the e-racing team at the Hochschule Esslingen University of Applied Sciences (E.Stall) as a platform to showcase novel solutions for electronic sensor and battery management systems.
The Fraunhofer team developed the entire electronic sensor system in close collaboration with Seuffer GmbH & Co.KG, an industry partner with whom the institute has been working for over 11 years. Seuffer GmbH & Co.KG is based in Calw-Hirsau in Baden-Württemberg, southern Germany, and sponsors the students of the E.Stall racing team.
The EVE race car is powered by two 60 kW electric motors, one for each rear wheel. The racer can reach a top speed of 140 km/h (87 mph); two lithium polymer batteries with a combined capacity of 8 kWh support a range of 22 km (13.7 miles).
Besides wheels, brakes, damper unit, batteries and electric motors, EVE is equipped with numerous sensors. These include braking pressure, crash, temperature and acceleration sensors as well as sensors that monitor the accelerator and brake pedals, speed, steering angle, wheel speed and power.
These last six functions could all be performed by HallinOne sensors developed by Fraunhofer IIS, 3D magnetic-field sensors that are already a standard feature in washing machines, where they are used to determine the position and orientation of the drum.
The integrated 3D Hall sensor technology HallinOne allows 3-axis magnetic field measurement with one sensor chip, enabling low-cost contactless position measuring systems. Conventional Hall sensors are only sensitive against magnetic fields perpendicular to the chip surface. The Fraunhofer Hall sensor, however, is able to measure also magnetic fields parallel to the chip surface.
For each of the three magnetic axes the sensor chip has a separate sensor. The digitalization of the measured values is integrated on the sensor chip and allows for connecting the chip directly to a computer or micro controller.
Two electronic sensors attached at the sides of the batteries use 3D magnetic-field sensor technology developed by Fraunhofer IIS to measure the magnetic field generated by the flow of electrical current and thus to determine the battery’s level of charge.
The contactless sensors measure both the current that flows from the battery to the engine and the current that flows back again when the vehicle brakes. The integrated sensor system is able to eliminate disturbances and foreign magnetic fields, thus enabling precise measurements.
The system is also able to measure other aspects of the battery such as its voltage and temperature. The data is collected and sent to the power control unit (PCU) and the battery management system (BMS), which controls the charging and discharging processes.
The BMS developed by Fraunhofer IIS determines the impedance spectrum of all battery cells and constantly tests whether the cells are functioning properly. This allows cells’ condition, current capacity and potential service life to be ascertained and running times to be predicted more accurately.
As individual battery cells age, they are able to store less and less energy. The challenge lies in optimizing cell utilization.
Until now, a battery system was able to provide only as much energy as was available in its weakest cell. The energy stored in other cells remained unused. Our BMS has an active cell balancing system that moves energy between stronger and weaker cells. This means that all cells share the load equally, allowing the maximum capacity of the battery as a whole to be utilized. EVE’s current BMS is a system developed in house by E.Stall, but our solution could take its place.— Dr.-Ing. Peter Spies, group manager at Fraunhofer IIS in Nuremberg
POLKA. EVE’s compact design is built on a tubular steel space frame housed within a carbon fiber body. Fraunhofer IIS in Erlangen has developed POLKA, a polarization camera that can detect stress cracks in the carbon fiber material at an early stage by measuring stresses within unpainted surfaces of the carbon structure.
Material stresses in the plastic cause changes in polarization. POLKA is able to collect all the polarization information for each pixel in a single shot at speeds of up to 250 frames per second. Using real-time color coding, the dedicated software translates the information collected about the intensity, angle and degree of polarization into a visual display that is accessible to the human eye.
EVE, which has already competed in the international Formula Student Electric (FSE) race in Italy, will appear at the Sensor + Test measurement fair in Nuremberg from 14 -16 May. This year EVE will be in the lineup for the Formula Student race in Italy, Spain and Czechia.