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Automating dynamometer testing – a winning solution

04 January 2012

Mark McDonnell describes how his company sought to automate the testing and characterisation of an integrated motor and inverter destined for an in-wheel electric vehicle drive system. The award-winning test rig, based on NI LabVIEW software and NI CompactDAQ integrated hardware, dramatically reduced both product testing time-scale and cost

The Protean Drive (PD) system is the most advanced in-wheel electric drive system for hybrid and battery-electric vehicles (BEVs) in the world. Farnham based cleantech company, Protean Electric developed the novel traction unit, which offers many advantages over existing hybrid vehicle platforms.

In particular, the integrated motor and inverter in the PD system provides the high power and torque density required by full-size saloons and SUVs without compromising vehicle performance or cost. It also enables full regenerative braking in normal driving to recapture large amounts of kinetic energy that is subsequently fed back into the battery.

The system is packaged in-wheel, which saves huge amounts of space in the vehicle for passengers and batteries, and eliminates all external transmission components. It also provides advanced vehicle dynamics through the independent torque control of each wheel.

The cost and time challenge
Developing the drive system required a great deal of careful testing and characterising to cover every performance aspect of the integrated motor and inverter package. Characterisation is performed on in-house dynamometers and involves the interaction of a number of different systems for control and data acquisition. Both the Protean Drive system and the dynamometers are separately controlled via controller area networks (CAN), and during testing a large amount of data is collected from a wide variety of inputs, including multiple CAN channels, temperatures, pressures, voltages, currents and digital inputs.

The aim was to automate this testing to help reduce the time that the engineers needed to spend performing characterisation work. Manually testing every aspect of both driving and regenerative braking performance across the complete speed and load range using a variety of third-party products would take up to two weeks of full-time work by an engineer. This would then be followed by up to a week spent processing and compiling all of the logged data from the various sources. Each new product has to be characterised on a large number of samples to ensure repeatability and to get a good average of the performance. Altogether, this would amount to several months of costly engineering time.

Meeting the challenge
The solution was to use the integrated hardware and software offered by National Instruments to reduce both time and costs through automation. LabVIEW was an obvious choice because of its widespread use in the industry and the large range of compatible hardware, which is either available directly from National Instruments or offered by third-party manufacturers.

LabVIEW was used to create a fully automated control program capable of independently controlling both the PD system and the dynamometer via CAN, as well as providing integrated fault monitoring and data logging. It proved easy to integrate with the company’s existing third-party CAN hardware through the use of readily available LabVIEW drivers, which reduced development time dramatically.

The LabVIEW control program allows the user to create predefined test cycles in spreadsheet format that can be loaded and run when required. This includes options for looping or conditional execution of certain sections of the cycle based on any of the available inputs. Using the LabVIEW PID and Fuzzy Logic Toolkit, Protean was able to automate the setting of torque, speed, temperature, or any other measured variable.

In order to achieve full automation, an error handling system was included that could monitor for many types of faults and shut the equipment down safely in the event of any failure. This allowed the equipment to be left running completely unattended, leaving the engineers free to do other things.

Data logging was added through the use of an NI CompactDAQ system and a selection of available C Series modules. The modular nature of NI CompactDAQ and the wide range of configuration options available enabled the test team to connect all of the temperature, voltage and digital inputs to just one piece of equipment.

The tight software and hardware integration between LabVIEW and the NI CompactDAQ system was used to log all the different types of data through a single program, making it much easier to manage. The LabVIEW program collects the data and automatically processes and organises it while the test is running, removing the need for manual processing at the end.

Using the LabVIEW Report Generation Toolkit, the system delivers completed reports in a standard Windows format that are ready to present to managers and customers alike.

The benefits
The automated, integrated system created using LabVIEW software and NI CompactDAQ hardware revolutionised the product testing. Testing that used to require up to three weeks can now be completed in just 12 hours, completely unmanned and automated; this has literally saved months of engineers’ time. Protean is also able to run standard automotive industry drive cycles with rapid transient changes in speed and torque that could never have been controlled manually.

In addition to this, the data that is being collected is much more detailed than before. It is also much more accurate and repeatable because every test is now performed exactly the same way instead of being open to operator influence.

With the recent purchase of additional NI CompactDAQ hardware, Prorean is now in the process of expanding the same system to all of its test rigs as well as the end-of-line production testing. The NI Developer Suite enables the software package to be deployed through the included code distribution tools, meaning that expansion is simply a case of installing the control software and plugging in a CompactDAQ module.

Mark McDonnell is with Protean Electric

Protean's test system was Industry Winner of National Instruments' Graphical System Design Achievement Awards 2011

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