Electric & Hybrid Vehicle Technology - July 2021
Easy BMS testing (Chroma)
2021-07-20 03:58:05
For the verification of today’s advanced EV batteries, a battery cell simulator offers multiple algorithms for cell balancing and testing
With the rapid move to electrification, lithium-ion batteries are a key factor in this transformation. For the proper handling and ensuring safety of these batteries, a battery management system (BMS) is necessary. It monitors and manages the batteries in real time, by balancing a cell’s voltage and temperature to ensure safe and reliable battery pack operation.
The BMS comprises functionalities from basic, over and under voltage protections, to advanced balancing circuits for operating batteries within safe voltage range and protecting them from damage due to cell imbalance. In the past, to test BMS functions it required multiple power supplies in series or simulating the cell output voltage with a resistor divider. Today, with the advancement of battery technology and power, BMS functions and battery cell strings have increased. Therefore, the use of multiple power supplies in series requires more hardware space, is more costly, and the use of a resistor voltage divider cannot ensure the voltage accuracy nor effectively isolate the voltage from each battery cell string.
The 87001 Battery Cell Simulator created by Chroma for BMS testing has been developed to be suitable for R&D verification, manufacturing, and quality inspection. Its bidirectional power supply design simulates the behavior of a battery cell, which means the user can create different voltage variation scenarios to trigger an active or passive balancing circuit, and verify the balanced current state. This helps ensure the stable operation of the balancing circuit.
Its voltage source with a setting accuracy of ±1mV and measurement resolution of 100uV can verify the BMS voltage measuring capability very precisely and monitor overvoltage protection conditions to avoid thermal runaway.
In voltage balancing designs, the passive balancing current will be 200mA~500mA whereas active balancing current can reach up to 5A. To satisfy all requirements, Chroma offers four ranges of current setting (250uA, 500mA, 5A and 9A) and measurement. When configured in 250uA range, a high-precision ammeter with 10nA reading resolution built into each channel will accurately measure the current consumption of each cell in sleep and active mode. The feature includes a Super Mode where it can attain current up to 9A for 500ms as some testing requires an active balance circuit over 5A.
Another feature of the 87001 is the fast sampling mode, which enables a user to record the passive balance current condition during the MOSFET switch, to draw a current-time graph and make it easier to analyze. It also provides various communication interface options such as Ethernet, USB and CAN. Therefore, when using standalone units in a different application, the system integrator will have more options to facilitate communication.
Being able to connect multiple standalone units in series offers more flexibility in application testing. For instance, 30 standalone units connected in series can simulate 480 cells in a string connection. This easy expandability of cross-unit connection allows the R&D engineers to focus on the BMS function verification to ensure its design quality.
Currently, many designers choose to employ BMS Hardware-in-the- Loop (HIL) simulation testing at the design phase for correcting faults at a primitive level. Chroma’s 87001 features 1mS high-speed voltage level programming and a command update rate within 10mS, which makes it suitable to integrate into BMS HIL testing.
Chroma 87001 also benefits from an open platform allowing users to develop their own control software. In one case study, an electric bus manufacturer has developed its own software to integrate the 87001 into the production line to verify the voltage measurement accuracy, protection function and active/ passive balancing circuit function of the BMS to achieve production line automation.
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Easy BMS testing (Chroma)
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