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Electric Vehicle Battery Test Challenges

Electric vehicles (EVs) are the future of the automotive industry, with manufacturers such as Tesla leading the way. But traditional automakers are vying for market share, too: Volkswagen (VW), the world’s largest car and truck maker, is investing $91B to build EVs, including one priced no more than the current base Golf model—truly a ‘car for the people’.

Developing new vehicles is time-consuming, but the right investment can offset this challenge. VW has spent over $1B since 2015 to transform its Zwickau factory into the first plant dedicated to manufacturing electric vehicles based on its modular electric drive matrix (MEB) platform.

While many of VW’s electric vehicles are based on MEB, it presents potential complications. Its EV powertrain and associated technologies are unfamiliar to designers used to generating torque from internal combustion rather than an all-electric drivetrain.

And batteries serve a key function, ultimately defining vehicle cost, range, and consequent commercial success. Practically, battery evaluation and test at cell, module, and pack levels is time-critical to new EV platforms. Manufacturers require entirely new solutions to get EVs through design validation tests, production (assembly line) tests and into the market ahead of the competition.

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Figure 1. The automotive industry is transitioning to electric vehicles, creating significant test infrastructure development challenges.

Battery system designers have the tough job of evaluating different cell chemistries and optimizing pack design for the often-conflicting requirements of energy capacity, size, weight, and cost to meet multiple, varying environmental and driving conditions. The battery management system (BMS) is integral to performance and safety, with complex algorithms required to manage battery charge and discharge, maintaining state-of-health for maximum performance and longevity.

There are several battery system evaluation and test methodology options. One involves simulation using cell manufacturers’ data along with BMS and drive-train models. Another applies dynamic loads on real vehicles in test labs to collect data over simulated driving cycles, with on-the-road tests providing final confirmation. Most methods combine options, spreading the work across globally distributed teams and supply partners. Battery subsystem test sequences can be lengthy and, with ever-tightening vehicle program schedules, it’s a challenge to manage the process, collecting and analyzing globally generated data at a central location.

To speed up the process, some manufacturers employ duplicate facilities or external agencies, perhaps using automation for ‘lights-out’ testing and delivering remotely accessible results. Oftentimes, though, test systems are vendor-dependent, with disparate data-reporting formats across the lab and agency ecosystem, again making the task of optimizing system performance harder. Another way to speed up the process is to test the BMS independently, earlier in the design cycle, using model-based capabilities to simulate or emulate the battery cells and systems surrounding the device under test. This results in faster iterations and reduces the overall cost of test, but also generates data that requires careful validation for extrapolation into the real world.

For efficiency and speed throughout the design cycle, it’s ideal to incorporate a platform-based approach with interoperable hardware and software using a standardized test system architecture. This way, customers can use the same system architecture through the design and test process: From early simulation and cell-level characterization; to BMS hardware-in-the-loop (HIL) testing; to pack-level system integration, characterization, and durability testing. Using a platform-based approach helps customers take reconfiguration and update ownership so that they can reuse test systems on different vehicle programs and for different stages of development and test—from early prototyping through end-of-line production testing.

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Figure 2. Battery Test System Elements.

Such a system is available from National Instruments, the global leader in automated test and measurement systems. Designed to test electric vehicle battery packs and modules in validation workflows, the system consists of measurement and control hardware for automated test execution, a ‘cycler’ to take the battery through a range of charge and discharge conditions, and application software for automated long-running battery tests. These features bundle together with intuitive software for system management, test monitoring, and data reporting and management.

The test hardware is based around the NI CompactRIO system, a high-performance embedded controller that features industrial I/O modules, extreme ruggedness, industry-standard certifications, integrated vision, motion, and industrial communication, and human-machine interface (HMI) capabilities. For battery testing, a base system configuration includes four CAN interfaces; 24 cell-voltage measurement channels; 24 cell-temperature measurement channels; eight Digital In and eight Digital Out channels with PWM support; and one RS232 and one RS485 channel. A DC power source is also included, programmable from 0-60 V with a 216 W rating. Because this system is built on standard NI products, customers can customize this system by adding additional I/O modules to this base system, resulting in a configuration that exactly matches their current requirements while accounting for anticipated system changes.

A full test system solution also includes the NI battery cycler, scalable to 1200 V and 1600 A for differing battery packs (for example, for passenger-car 400 V systems or commercial-vehicle powertrains at 800 V and higher). The cycler features fiber-optic interfaces for high speed, low interference control, and high voltage- and current-accuracy monitoring. All of NI’s battery-cycler hardware supports bidirectional power flow, with regeneration back to the grid for energy savings. NI’s hardware acquisition modules, lab PC, and NI software completes the solution, along with an environmental chamber provided by the customer or system integrator.

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Figure 3. NI Battery Test System

NI battery-test software incorporates a Windows-based configuration and test sequencing user interface, with the option of deploying specific test steps to a ‘headless’ real-time engine for increased reliability during long-duration steps. The system adapts to changing requirements, with a hardware abstraction layer for flexible configuration and a sequence editor for import/export and test-sequence configuration. Various plug-ins offer support: Expand measurement I/O to quickly implement interfaces for new NI devices; incorporate a test sequencer for real-time OS-based test-script execution; and integrate user interfaces to, and publish data from, the data management engine via a configurable data logger. A watchdog function covers process safety, moving the system to a predefined safe state if the system exceeds specified measurement limits. The system works seamlessly with NI SystemLink software for test monitoring and data management.

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Figure 4. NI SystemLink Software Combines Distributed Battery Test System Elements with Cloud-Based Data Management.

NI SystemLink software manages groups of networked test systems and features user-defined dashboards to set up test sequences and monitoring, with open APIs and graphical interfaces managing cloud-based data transmission, visualization, analysis, and report scheduling. Configurable alarms and notifications monitor system health and performance. The web-accessible application supports NI products such as LabVIEW and TestStand, along with third-party software and hardware, and is expandable though a plug-in architecture. It provides managed software deployments and configurations to improve test repeatability and reduce the risk of mismatched software versions among test system groups.

The NI battery system test solution provides a secure route to EV development and validation evaluation, with test time improvement, through a platform that is inherently scalable and reconfigurable. The availability of industry-leading tools to improve data aggregation and analysis means manufacturers can now get the ‘edge’ they need in the competitive world of EV development.

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Nitisha Dubey

A diligent writer, who has been working from last five years in the same field. She has covered lots of event and expo for travel & judiciary, now covering technology. Book reading, exploring different destinations and varieties of cuisine are some hobbies. Love to watch biographies and historical movies.

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