Traction batteries are used as an energy source in electrical vehicles and are composed of a various number of battery cells connected in series and parallel and packed in modules. SEM AB are developing electronic systems for controlling the voltage of a battery pack. The goal is to integrate the system for use in trucks. The system uses a microcontroller to control several transistors to connect and disconnect battery cells from the pack. If the system experiences a short circuit, internally or externally, high current can occur through the cells. A short circuit protection circuit is used to measure the current and disconnect the cells if the current is exceeding the maximum value allowed.

To ensure that the electronic short-circuit protection system complies with the requirements set by the client, the systems functionality must be verified by performing measurements at two different fault types: external and internal short-circuit. The fuse that is used as a secondary protection will also be tested to verify its function. The measurements are performed with a test setup which includes prototype circuit boards. The boards are modified to allow manual triggering of the transistors and to allow for measurements at selected points. A pulse generator is connected to one of the cards to control chosen transistors manually and thus simulate a short-circuit when the transistors are turned on. Selected properties are measured with oscilloscope, multimeter and Rogowski coils. The data from the measurements are then processed in Matlab.

The results from the measurements show that the short-circuit protection system opens the circuit within 1 μs after the current measurement circuit detects a current which exceeds the threshold value of 62,5 A. Due to the design of the circuit board, the current measurement circuit does not measure all the current. This can lead to higher short circuit current than the current measured by the sensor. Also, the current through an individual current sensor cannot be measured with the available equipment. When tested, it takes 750 μs for the fuse to blow at 25 V and the current achieves a maximum value of approximately 2000 A. The high current can cause damage to sensitive components and battery cells due to excessive power dissipation. The digital signals that turn off the transistors during a short circuit are affected by some interference. This can cause misread signals and can reconnect the battery during a short circuit. The distortions can be caused by the design of the circuit board. For example, if high current carrying paths is placed close to the path of the signal the distortions may be caused by electromagnetic interference.