Simulation for Battery Management System

Task
The battery management system (BMS) monitors the electric and thermic state of the batteries used in hybrid or electric vehicles. According to the drive's requirements and environment impacts, the BMS influences each battery and its cells to hand provide the energy needed and to maintain optimal operation conditions for good performance and long battery life.

Challenge
Batteries for electric vehicles have extremely high voltages and currents, so the BMS is safety-critical. To ensure safety during HIL simulation, the overall voltage might have to be scaled down. Electrical failure simulation is also needed to make sure the BMS reacts correctly in all circumstances. These are typical failure tests:

  • Broken wire
  • Short circuits
  • Loose contacts

 

Solution
The typical HIL simulation setup for battery management system tests comprises a processor board, HIL I/O boards for I/O interfaces, a board for CAN interfaces, and a failure insertion unit for testing electric failures. Restbus simulation is used for simulating unavailable cell stacks. dSPACE offers specialized hardware and software for testing a BMS, for example, the Battery Cell Voltage Emulation Board for simulating high-voltage batteries at cell level and the ASM Multi Cell Models. The test system can virtually represent the electrical and thermal properties of a battery down to cell level.
Other components are high-precision voltage sources from 0 to 6 V, which can take the load of the current flowing in cell balancing. Typical requirements for cell voltage simulation are a precision of about 2 mV and a current up to a few hundred mA. The voltage sources are galvanically isolated and can be switched in sequence to form cell modules. The voltage of the entire battery can be simulated this way. Failure simulations such as a break in the measurement cable or the cell connectors (galvanic disconnection of the cell stack) can be run. The voltage sources are connected to the processor board via an LVDS interface, with connection distances of up to 5 m with copper cabling and up to 100 m with optic cabling. All the cell voltages in a battery can be adjusted in less than 1 ms.