A Flexible, Cost-Effective Battery Management Systems (BMS) Manufacturing Test Platform

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"The NI PXI platform coupled with the LabVIEW development environment delivered the ideal tools to quickly design and build a BMS test platform that is flexible enough to test multiple customer products, and accurate enough to meet or exceed BMS testing requirements."

- Grant Gothing, Turnkey Systems Manager, Bloomy

The Challenge:
Provide a flexible, cost-effective production test system for several designs of battery balancing, monitoring, and management system (BMS) printed circuit board assemblies. BMS test system requirements include simulating a pack of advanced chemistry batteries, performing high accuracy voltage and current measurements, and communicating with the BMS under test via serial and/or CAN.

The Solution:
Developing a BMS Manufacturing Test System based on NI PXI modular instruments, NI LabVIEW and TestStand development software, and Bloomy’s Battery Simulator 1200 and UTS Software Suite, to simulate battery packs, and provide the flexibility and accuracy needed to test multiple BMSs.

Author(s):
Grant Gothing, Turnkey Systems Manager - Bloomy

Rapid advancements of battery systems extending the range of electric vehicles, increasing the availability of power from renewable sources, and proliferating mobile as well as stationary applications for aircraft, marine, telecom, recreation, and many others; present new challenges for battery system testing.  New products require design validation and production-level test systems with short lead times, high accuracy, repeatability, reliability, and operator safety. One such challenge discussed here involves production testing of BMSs for lithium-ion and other advanced chemistry battery packs.

The BMS handles all of the monitoring, control, and safety circuitry of battery packs and control systems.  This includes accurately monitoring cell charges, balancing voltages between cells to maintain a constant voltage across packs, managing charging and discharging, and protecting the system from over-voltage, under-voltage, over-current, and over-temperature conditions. In addition, BMSs monitor cell temperatures, handle system power saving (by entering sleep modes to reduce current draw), monitor the state of charge and state of health, and communicate with external controllers to provide system feedback.  While there are several types of battery management boards, including individual pack balancing and monitoring boards, and system control boards, we refer to them all as BMSs in this application note.

BMS Features and Test Requirements

Because the BMS is so important to the safety, performance, and longevity of advanced batteries it is critical that each manufactured board performs to strict specifications. Cell voltages must be monitored to millivolt accuracy, alarms and safety interlocks must occur properly, and the BMS must draw current from individual cells to balance voltages across the entire pack. Functional test of these processes requires a highly accurate, flexible, and robust test system capable of simulating packs of cells, applying system voltages, measuring cell and pack-level voltages, currents, and temperatures, and communicating with the BMS.

BMS Test System Hardware Design

By starting with the UTS functional test platform, Bloomy produced a flexible, high-accuracy base system capable of testing multiple models of BMS printed circuit board assemblies utilizing a standard mass-interconnect fixture receiver and interchangeable fixtures. The system is centered upon Bloomy’s Battery Simulator 1200, which is used to simulate a substack of 12 cells per unit with individually programmable 0-5V levels per cell, and the ability to sink and source current. Several Battery Simulator 1200s may be combined in series, or an optional high-voltage power supply may be used to simulate the overall pack voltage.

 A high-accuracy PXI-4071 7.5 digit digital multimeter is multiplexed to measure voltages within the required millivolt specifications. A PXI-6221 multifunction data acquisition module provides analog outputs, TTL digital inputs/outputs, and high-speed analog input measurements. The PXI-6515 Industrial DIO module reads switches and actuates fixture relays.  Fixed low-voltage and programmable high-voltage and high-current power supplies are used to provide additional system power as required by testing specifications. A USB connection on the fixtures allows flexible addition of other BMS-specific communications and peripheral hardware. All hardware is housed in a standard desk-height 19” rack. The test rack provides a system capable of making any measurement and supplying any source required by a BMS circuit board. The system layout is shown in Figure 1.

Figure 1.  Base Platform System Layout

A standard fixture receiver permits several different BMS designs to be tested using the same base hardware. Each fixture type is electronically keyed, guaranteeing that the correct test sequence will run for the attached fixture. Interchangeable fixtures greatly reduces system cost and lead times by sharing key instruments among multiple BMS models and board types.  Once the base system is deployed, new fixtures and their associated test software are designed and built very quickly. Figure 2 shows the base system.

Figure 2.  BMS Manufacturing Test System

Series Cell Simulation Using the Battery Simulator 1200

To simulate a stack of 24 advanced battery cells, the individual cells of two Battery Simulator 1200 units are connected in series.  The cell levels are individually programmed from 0 to 5V, for a combined substack voltage of up to 60V, and each cell can source and sink current in order to test a wide range of BMS functions. During cell voltage testing, the software polls the BMS for its reported cell voltages which are compared to the Battery Simulator 1200’s readback voltages to determine the accuracy of the BMS’s cell monitors.  For tests measuring each cell’s balancing current, the +/- 4mA accuracy of the Battery Simulator 1200’s current readback eliminates the need for external shunt or hall-effect current sensor.  Moreover, the Battery Simulator 1200’s ability to simulate an out-of-balance condition in order to exercise and test the BMS’s cell balancing function in real time is an essential capability of the test system. The Battery Simulator 1200 is ideally suited for BMS testing because it provides safe and repeatable simulation of advanced battery cells regardless of the battery’s chemistry. Unlike real batteries, the Battery Simulator 1200's characteristics don’t change with each charge/discharge cycle, and it is safe and easy to simulate a fault condition. Unlike conventional power supplies, the Battery Simulator 1200’s cells can both sink and source current, and are isolated to 1000V, allowing you to connect several units in series in order to simulate a high-voltage pack if needed.

Figure 3:  24 Series Cell Connections using two Battery Simulator 1200s

BMS Test System Software Design

The test software consists of Bloomy’s UTS Software Suite, which is developed using NI LabVIEW and TestStand.  All test parameters are contained in a configuration file to allow the customer to update, tighten, or loosen test specifications without making software changes.  In addition, all instrument and channel names and addresses are stored in a separate configuration file allowing hardware or wiring changes to be made without affecting the underlying software.  The operator interface is designed for a manufacturing environment, and requires minimal operator interaction.  During standard operation the test technician simply opens the safety lid of the fixture, scans the barcode serial number of the BMS under test, then closes the fixture, and the test starts.  When testing is finished, the test result is shown, test data is logged to file, and any failed tests are highlighted for the technician.

The UTS Software Suite contains debugging and diagnostic modes which provide engineers more manual control over the system.  The debug mode allows test engineers to run smaller subsets of the main test to narrow down the possible causes of a failure.  The diagnostics control screen provides access to all aspects of the system pertaining to the attached fixture.  This allows the engineer to manually read all system voltages and currents, control all power supplies, actuate relays, and communicate with the BMS.

Figure 4. The UTS Software Suite’s operator interface with test sequence and BMS under test shown

An Accurate and Flexible BMS Test Solution

The BMS Manufacturing Test System is used for end-of-line manufacturing test of BMS master and modules, autoloading of BMS firmware, calibration of cell- and pack-level voltages, currents, and temperature monitors; as well as engineering prototype and return material authorization (RMA) testing. The Battery Simulator 1200 facilitates safe, fast, and repeatable simulation of advanced battery cells for comprehensive BMS functional testing. The overall system is flexible to accommodate many different BMS models and designs including different advanced battery chemistries; accurate to perform precision voltage, current, and temperature measurements; reliable, robust and easy to use by test operators in a typical electronics manufacturing environment. The system is a commercial, off-the-shelf solution that expedites time to market and eliminates risk.

About Bloomy

Bloomy provides products, platforms, and turnkey systems for automated test, data acquisition, and control, serving manufacturers in aerospace, batteries, electric vehicles, energy, and industrial electronics. Our BMS test products include the Battery Simulator 1200, the BMS Hardware-In-the-Loop (HIL) Test System, the BMS Validation System, as well as the BMS Manufacturing Test System. We are a 22-year NI Platinum Alliance Partner awarded “Outstanding Technical Resources” by NI.

For more information on this case study, contact:

Peter Blume
Bloomy 
839 Marshall Phelps Road
Windsor, CT 06095
Phone: (860) 607-2045
E-mail: Info@bloomy.com

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