DMC built upon its previous Battery Test Platform design experience to produce a completely automated test system specifically designed for Battery Management System (BMS) validation, verification, environmental, and Hardware in the loop (HWIL/HIL) testing. Numerous new features and functionalities were implemented in this second generation version of DMC's BMS Test Stand to meet the customer's latest testing requirements.
To fully evaluate a BMS, the first challenge is to simulate all input signals that the device sees within an actual battery pack system. By directly generating (and thus having complete control over) all such signals, the BMS can be subjected to any possible combination of inputs that it could potentially encounter in real world operation. The operation and response of the BMS is measured and monitored to verify that all its functions (reporting diagnostic information, controlling high power contactors, identifying potential safety issues, etc.) are performed properly for each combination of inputs.
DMC provided the customer with a comprehensive hardware and software platform for testing their BMS . The system was tailored to meet the customer's unique testing requirements, but was also developed with the flexibility to accommodate multiple BMS designs as a key objective.
A combination of high performance off the shelf hardware components (selected with complete vendor independence to meet design specifications at the lowest cost to the customer) and custom subsystem components designed in-house by DMC were integrated to build the system. A fully featured testing application was developed in LabVIEW using DMC's "Test Executive" architecture that has proven highly effective in previous battery test and measurement projects
Details on specific subsystems and features of the BMS Test Stand are given below:
Cell Voltage Simulation
The BMS Test Stand simulates up to 108 battery cells (expandable to 216 cells with an optional secondary chassis), all of which are joined in series to create a full battery stack voltage of up to 750 V. With each simulated cell capable of outputting 0-7 V with 12 bit resolution (2 mV) and rapid voltage output response times, battery packs of varying chemistries can be effectively simulated. More information on the cell simulator design and specifications are available in this description of DMC's first generation BMS Test Stand
Voltage and Current Measurement on All Simulated Cells
High precision measurements of the current draw on any battery cell or the exact voltage differential between any two cells can be performed, providing information that is very important in evaluating the operating characteristics of a BMS. DMC designed a custom low-cost multiplexing solution
consisting of over 600 DC relays (1000 V) to make it possible to perform these measurements on the high number of simulated cell channels using a single high precision PXI digital multi-meter.
Direct Manual Operation for Flexibility and Control
The BMS Test Stand software includes an intuitive user interface that allows operators to directly control all instruments, simulated outputs, and connections from the test stand to the BMS. This feature allows complete flexibility to subject the BMS to any imaginable combination of inputs and evaluate its response.
Fully Automated Testing for Speed and Consistency
To fulfill the customer's requirement to perform a well defined set of testing procedures on the BMS, DMC integrated a suite of fully automated testing procedures into the test software. A configuration interface allows the operator to set up a list of tests they wish to perform, the order in which those tests should be completed, and to enter whatever grading limit and setup parameters are appropriate for each given test procedure. Once configured, a full functional evaluation of the BMS can be initiated with a single click. No further user interaction is required, and all PASS/FAIL results of the testing will be both displayed in real time on-screen and logged to file.
Battery packs for electric vehicles (including the BMS itself) are subjected to a wide range of environmental conditions during real world operation, and thus extended duration environmental testing requirements are common. The configuration interface allows evaluation or monitoring procedures to be sequenced and iterated to accommodate this style of longer term testing. The BMS operation can thereby be monitored while the BMS itself is exposed to demanding conditions within an environmental chamber.
Resistive Temperature Sensor Simulation
The BMS Test Stand simulates 50 separate variable resistance temperature sensors
to allow evaluation of all thermal monitoring functions of the BMS. Each sensor has 4 bits of resolution, meaning a total of 24 different resistance can be applied to each of the 50 simulated sensors. A modular architecture of swappable daughter cards containing different resistance values gives the flexibility to evaluate multiple BMS designs (which may each be built to interface with different thermistors). Optionally, the same hardware could be used to simulate 25 temperature sensors with 8 bit resolution if a larger range of resistance settings are required.
CAN Unified Diagnostic Services
DMC leveraged NI's Automotive Diagnostic Command Set API
to rapidly implement CAN communication with the BMS under test using the UDS (Unified Diagnostic Services) protocol. This poll and response based protocol, defined by ISO 15765-3
, is commonly used as a standardized method of reporting of diagnostic information in automotive applications.
CAN Traffic Logging
In addition to monitoring and evaluating whatever CAN data is of interest for each automated testing procedure, the testing software also performs real-time logging of all CAN messaging traffic on two separate CAN buses simultaneously whenever testing is in progress. Directly logging all CAN data transactions to disk provides the customer with a low-level record of the BMS state during all segments of testing and is a valuable reference when performing detailed analyses of failure points.
Battery Pack Contactors
Full battery packs include multiple high power contactors that connect/disconnect the battery stack from the vehicle's propulsion system. An important responsibility of the BMS is to handle opening and closing these contactors during vehicle operation, as well as to disconnect them whenever the BMS identifies a safety fault. The BMS Test Stand includes a battery pack contactor module that contains the same physical high power contactors that are used in the battery pack. Integrating these contactors into the simulated cell stack in the same configuration as in a full battery pack provides a more complete simulation of the BMS's "natural environment", which in turn allows more comprehensive functional testing to be performed.
System State Display
A secondary monitor display near the top of the test stand provides a graphical representation of the state of all subsystems, connections, CAN traffic, measurements, and instruments. This display is updated in real time during automated testing to provide visual feedback on the test stand activity.