DMC has delivered numerous Battery Pack Exerciser+Monitor Systems to our clients, spanning the 1UP, 4UP, an 6UP variations. The test control software application was developed using National Instruments LabVIEW and is delivered to clients as an open platform.
Details on specific features of the Environmental Exerciser Test Stands are given below:
Cost Savings of 4-Up and 6-Up Multiplexing:
Given the relatively long test durations that are inherent in endurance (environmental) monitoring tests being performed, having a cost effective means to simultaneously execute many tests becomes critical to achieve the desired testing throughput. By sharing core instrumentation and hardware components, the 4-Up and 6-Up designs provid this desired bandwidth while minimizing associated hardware costs. A connection multiplexing schema (for both low power and high power signal lines) is used to allow for the ability to connect this set of shared instrumentation to as many as six separate DUTs. The ability to scan from one DUT to the next in order to provide the required semi-continuous monitoring of all battery packs allows test coverage of all DUTs.
Hardware Abstraction Layer:
While the hardware designs are naturally slightly different between the 1-Up, 4-Up, and 6-Up system configurations, the same general testing processes are shared. This is accomplished through a hardware abstraction layer within the software, making it possible to run the same high level program functions on both system configurations while still accounting for and cleanly managing the different underlying hardware layouts. This approach greatly expedites the user setup experience (e.g. general system configuration parameters, test sequence editing/execution framework, data acquisition settings and analysis/grading criteria). Likewise, having a single implementation of these shared functionalities makes the software very concise, maintainable, and expandable moving forward by avoiding redundant functionalities in the codebase.
High Power Cycling:
The Exerciser test systems include high power (500 A) contactors that connect the battery pack's high voltage terminals to a battery cycler system. The test stands are designed to integrate with Aerovironment's line of Power Cycling and Test Systems (PCTS). This provides the capability to perform charging and discharging cycles (up to 900 VDC, 1000 A, 250 kW) as an integrated part of the overall functional or endurance testing sequence. The test stands can control the Aerovironment cyclers using either an RS232 serial interface or CAN interface, and can utilize one or both of the available output channels (A side/B side) on the cycler unit in either an independent or parallel configuration. The built-in safety interlocks of the Aerovironment cyclers are directly integrated into the hardwired safety interlocks of the Exerciser test stand for consolidated safety handling.
The Exerciser test systems monitor all CAN traffic that is broadcast by the battery pack(s) being tested. This CAN traffic is parsed into distinct channels and scaled to engineering units via a configurable CAN database that is loaded into the test control application. All CAN-reported data is evaluated against any user-specified grading/abort limits for the given channel, and is logged continuously to disk as a function of time.
Manual Mode Operation:
The Exerciser software package supports a "manual mode" of operation, providing the ability to use “soft front panel” interfaces for direct, on-demand control of measurement instruments, power supplies and battery cycler equipment, communication bus/interface devices, and system relays. This mode of operation provides a high degree of flexibility, and is useful for detailed ad-hoc measurements and investigations that fall outside the bounds of the pre-defined test procedures. In this mode, the operator can perform any measurement or operation that the test stand hardware is physically capable of through keystrokes and mouse clicks, making the system a massively powerful tool for product engineers in Research and Development scenarios.
Automated Test Sequence Engine Operation:
The primary operating mode of the Exerciser software package is an automated Test Sequence Engine. This mode provides a powerful and flexible interface designed to support current testing requirements and to adapt to future/evolving test requirements without actual program source code modifications.
In this mode of operation, the user is able to configure a variety of test step types, enter appropriate setup parameters for each of these test steps, organize these test steps into a test sequence, save this sequence to file, and then execute the desired test sequence. All test sequence data is stored within XML file format. Test sequences can be run individually, or called as subsequences by higher level test sequences to enable a hierarchical organization of testing operations.
Once the prescribed automated test sequence has been configured, the operator is able to initiate the full test sequence with a single click. The list of test steps to run is displayed in an intuitive tree structure. The Sequence Engine application executes each defined test step one after another as defined by the sequence structure. Real time data for the current test/steps is displayed while it is running.
Below are some of the types of test steps available within the Exerciser Sequence Engine:
- For Loop
- While Loop
- If Statement
- Pause Test
- Abort Test
- Call Subsequence
- Wait (for Time or Condition)
- Display Message to Operator
- Execute Math / Calculation Script
- Set Variable Expression
- Set Variable Value
- Set Variable to Waveform Profile
- Process Data (Grade Data Value, Log Data to File, etc.)
- Configure Grading Criteria
- Activate Cycler
- Deactivate Cycler
- Transmit CAN Messages
- Stop Transmitting CAN Messages
- Configure DMM
- Set CAN Bus Connection
- Set DUT Power Connection
- Set Switched AC Connection
Test Data Storage using TDMS:
The Exerciser systems store test results and data logs using LabVIEW’s TDMS (Technical Data Management System) file format, a preferred way of storing channel and time based test data in LabVIEW.
This White Paper provides a thorough overview of the TDMS file format, file structure/operations, advantages, tools for working with TDMS files, etc.
At a high level, the TDMS format provides the following features and advantages:
- TDMS format is optimized for streaming many channels of data to disk simultaneously (supporting large volumes of data if needed).
- TDMS files are binary files, which results in significantly lower data file sizes on disk as compared to text based storage formats.
- Data can be accessed by a variety of viewer applications to view as plots/graphs or in tabular form.
- Data sets can be exported to csv format from viewer applications.
- Data stored in a TDMS file is far easier to extract for post processing with a LabVIEW application.
- Data can be loaded into Excel using an available (free) Excel TDMS plugin for convenient post processing using familiar Excel functions.