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Products & Applications Convenient testing of power levels in electric vehicles

Nate Holmes *

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High-voltage tests on electric vehicles are expensive. But boxing equipment is not very practical and often heavy. A rack-mountable measuring device based on the PXI platform promises a remedy.

How to analyze power electronics in an electric vehicle ?
How to analyze power electronics in an electric vehicle ?
(Source: Public Domain / Pixabay)

Battery voltages are getting higher and higher in electric vehicles. More than 800 V is used to power the entire vehicle, from the motor to the mirrors. Therefore, powertrain and power electronics components must be thoroughly tested to verify their functionality and increase efficiency. Engineers take a lot of effort to implement new high-voltage tests into expensive and inflexible power instruments. The RM-26999 power measurement system is designed to allow test engineers to be agile and validation teams to meet the budget (Figure 1).

Test labs for power electronics and powertrains have various box devices for power analysis. These are heavy instruments designed and priced for any type of power measurement. Although the equipment is well suited for research, it is not worth purchasing for automated measurements or durability testing. The RM-26999 breaks this convention by meeting the most important requirements for power electronics testing.

It is an external rack-mountable signal conditioner that enables high-performance measurements on the PXI platform. The device safely processes high voltage input paths at ±2000 V and indirectly reads up to ±2000 A with Danisense current transducers. It connects to PXI Express devices with simultaneous multifunction I/O (SMIO) on the NI platform and integrates into a modular PXI test system. This enables durability testing and test cell applications for predicting how components will behave over time and under different weather conditions. For powertrain testing applications, it is possible to integrate and synchronize three-phase power measurements with other critical data, including vibration, temperature or CAN bus data.

Power, data and output signals over one cable

The power measurement system processes directly connected input voltage paths with ±2000 V. It is UL-61010-1 certified for peak voltages from outside the power supply network. The rack-mountable signal conditioner indirectly measures currents with Danisense current transducers. It is supplied with the necessary current via a cable. At the same time, data is transmitted via the cable and the output signals of the current sensors up to ±2000 A is recorded. With four voltage input channels and four transformer connections for current measurements, up to four power measurements can be made.

The system can be connected to multiple NI-SMIO modules and devices. DAQ devices can be selected independently of the power measurement system, providing different sample rates and resolutions. With the right SMIO device, up to 14 million samples per second per channel can be captured with up to 18-bit resolution. If more than four power channels are required, two RM-26999 power measurement systems can be connected to a 16-channel SMIO module. With more than eight power channels, additional SMIO modules can be synchronized via the PXI backplane and measurement applications can be scaled via channel expansion.

Figure 2: For complete power characterization, the performance of all powertrain and power electronics components in an electric vehicle must be analyzed.
Figure 2: For complete power characterization, the performance of all powertrain and power electronics components in an electric vehicle must be analyzed.
(Source: National Instruments)

Power analyzers must not only provide measurement functions, but also the knowledge and analysis of the acquired data. Version 19.0 of the LabVIEW Electrical Power Toolkit (EPT) enables three-phase measurements in LabVIEW along with other power analysis libraries that are especially needed for powertrain and power electronics testing. With LabVIEW EPT 19.0, you can measure three-phase power according to IEEE Standard 1459-2010, including transformations to/from reference frames, frequency-domain power analysis, and inverter and motor efficiency libraries.
Battery power can also be measured for energy and charge integration and active power. LabVIEW EPT preinstalls specific examples for the RM-26999. LabVIEW's open development environment allows developers to create custom algorithms, processing, and analysis to meet their specific needs. Test houses that do not develop in-house with LabVIEW can use the international NI network of alliance partners to help them develop custom IP for power measurement systems.

Electric vehicle batteries power more than the engine. Battery power is converted to three-phase alternating current fed back to the auxiliary battery, distributed to key subsystems, and powered by external chargers and the charging connector. High-performance measurements are no longer a niche. They are necessary to characterize components and subsystems in an electric vehicle. Given the increased demand for high-performance measurements, expensive boxing equipment for analyzing performance in a vacuum is no longer acceptable.

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This article was previously published in German on Elektronikpraxis.

* Nate Holmes is Principal Solutions Manager, Physical Test at National Instruments.