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Measurement and analysis of electric power on board hybrid and electric vehicles at the Joint Research Center (Ispra - Italy)
"It was possible to meet all project requirements by ensuring the quality required to comply with international standards for electrical power measurement and analysis."
The challenge:
Realize a versatile, robust and compact datalogger able to measure the signals present on board the vehicle resulting from the accumulation, distribution and use of both DC and AC electric power, as well as from CAN bus control units, "raditional" sensors and GPS.
The solution:
Set up the new NI CompactRIO-9068 with specific hardware modules for the signals to be acquired, developing and integrating the software components (Windows, Real-Time and FPGA) for synchronous acquisition from the various data sources.
Application
It is widely believed that electric vehicles will be able to solve, or at least mitigate, the problems of automotive pollution only when new technologies will be available at affordable costs to all, ie when there will be batteries with higher accumulation densities, extremely light but safe vehicles, capillarity charging points, all at the cost to the consumer comparable to the now ultra centenarian traditional vehicles.
Meanwhile, the most widespread compromise is the hybridisation of internal combustion engines, with different solutions and architectures according to the level of complexity and costs that are set as a goal, with producers essentially divided between those who invent and those who inspire them.
Some of the most important considerations regard the energy balance of electric vehicles as well as hybrid components in the case of synergy with thermal engines, both with traction and with recharging on board (range extender), since an inefficient use of the accumulated electrical energy results in a greater global pollution, linked to the remote production of that energy.
The research center commissioned EURINS for a high-level integration system to measure all the parameters necessary for complete characterization on-board both on the road and in the test bench. These activities can not be carried out using traditional laboratory equipment, both because it would then be necessary to unify the data coming from the single specific instruments, and because in road tests it is necessary to be compact, robust and reliable, as well as quality equal or superior to the instrumentation reference.
Using the NI CompactRIO hardware platform, the NI Electrical Power Suite software library for LabVIEW and NI DIAdem, it was possible to meet all project requirements ensuring the quality required to comply with international standards for electrical power measurement and analysis.
With the same system it is also possible to measure the flows of electric energy during the recharging of the batteries on board the vehicle when it is connected to the public posts or to the boards for domestic use. In addition to voltages and currents in AC or DC depending on the products, it is particularly useful to acquire also the pilot signal which constitutes the communication protocol (handshake) between the management electronics in the vehicle and the one in the charging device.
A digital line changes its level according to discrete voltage steps (0, 3, 6, 9, 12 Volt) and becomes a variable duty-cycle square wave based on the start of charging, with a maximum or partial flow of energy, with the batteries almost charged or the cable disconnected.
Combining these measurements with all the other analogical and digital quantities, acquired in the various vehicle nodes where it is significant to evaluate the energy balance, is a feature of absolute innovation compared to traditional industrial or laboratory derivation instruments, with all data available at internal of a single file, and therefore synchronous on the same time base, ready for both a quality control on the field and for in-depth analysis and report generation, thanks to the use of NI DIAdem, and MATLAB.
• Datalogger on NI CompactRIO platform for data acquisition and storage combined with a Windows portable PC connected via ethernet where to configure the system, receive and analyze data
• 2 NI 9225 modules for a total of 6 simultaneous sampling differential channels (24 bit, 50 kS / s / ch, bandwidth 24.6 kHz) for voltage signals up to 300 V rms, possibility to measure much higher voltages by means of dividers voltage and voltage transformers thanks to the use of a 24-bit A / D converter
• 2 NI 9227 modules for a total of 8 simultaneous sampling differential channels (24 bit, 50 kS / s / ch, bandwidth 24.6 kHz) for current signals up to 5 A rms, possibility to measure much higher currents using transformers current through the use of a 24-bit A / D converter (ratios from "5: 5 A" to "1600: 5 A" with resolution from 0.3 μA rms to 96 μA rms)
• 6 voltage channels and 8 current channels for power lines allow simultaneous and synchronous measurement, ie timed at FPGA level, of voltages and currents (and therefore of power and its active, reactive, apparent components, as well as harmonics, transients and current consumption according to the standard EN 50160: 2007) simultaneously on the three most neutral phases in 2 nodes of the vehicle, typically upstream and downstream of a subsystem to evaluate its efficiency in the total energy balance, or in 6 (8) single-phase distributed nodes
• Current measurements use "split core" transformers or Hall effect amperometric clamps, so it is never necessary to interrupt the vehicle wiring
• Measurements and calculations fall within the IEC 61000-4-30: 2008 standard (Power frequency, Magnitude of the supply voltage, Flicker (IEC 61000-4-15), Supply voltage dips and swells, Voltage interruptions, Supply voltage unbalance, Voltage harmonics (IEC 61000-4-7), Mains signaling voltage on the supply voltage, Rapid voltage changes (RVC) (IEC 61000-4-30), Sag / Swell / Interruption at standard or custom levels (IEC 61000-4-30 ), Measurement of under-deviation and over-deviation parameters)
• Acquisitions can be resampled by synchronizing to a carrier frequency, for example in the case of power measurements during recharging from a fixed system, or using selectable sampling frequencies to digitize all the contents of interest and then make the analyzes both over time and in frequency
• 1 NI 9853 module with 2 high speed CAN ports and 4 NI USB-8473 modules (with 4 other high speed CAN ports available in the computer) for a total of 6 independent CAN lines that can be simultaneously managed to read and write messages (ID to 11) and 29 bit, baud rate up to 1 Mbps) according to the standards DBC, OBD, FMS, J1939 with the availability of an editor for creating customized messages to interpret unencoded flows
• 1 GPS receiver (NMEA standard) for continuous acquisition of geographic position, direction, absolute time and ground speed.
About the author:
Stefano Vianelli
EURINS