MORE TESTS, MORE COMPLEX SYSTEMS, LESS TIME
The need for sustainable mobility today continues to power innovation in the automotive field. Foremost among the trends in this field has been the push for electrification across global sectors. In India, the government has begun creating charging infrastructure and policy frameworks so that by 2030 more than 30 % of vehicles are electric vehicles.
In parallel, major players in the country are currently making efforts to further the cause of hybrid vehicles as natural evolution of the electrification process. But how do we welcome this transition among testers? Battery electric powertrain technology and internal combustion engine (ICE) powertrain technology are fundamentally different, requiring completely different set of tests and test capabilities. Integrating these two technologies in a hybrid vehicle may lead to a dramatic rise in test time and costs. The key to success here lies in understanding the challenges that exist in integrating these two technologies and developing solutions based on the insights gained.
HOW A HYBRID POWERTRAIN EVOLVES
One of the main differences between existing and EV powertrain technology lies in how their components are tested. The ICE involves physical testing in terms of combustion mechanics, pressures, temperatures, fluids and power transfer. The electric powertrain, on the other hand, depends on electrical testing, with power electronics and switching frequencies, voltages and currents, and induction and back EMF (electromotive force) being important.
Combining these technologies to create a hybrid powertrain involves integration testing to ensure that the system responds appropriately in all driving conditions and scenarios. The resultant powertrain is more complex in nature than either of its original systems and thus presents more opportunities for failure (1).
HYBRID VEHICLE TESTING: TOOLS OF THE TRADE
Test engineers, hence, must look to devise extensive integration test coverage that can map new test requirements introduced by electric powertrain components and ensure the two technologies work together seamlessly to deliver on all hybrid design goals. Here are some of the test tools that have evolved to help them meet these goals:
HIGHER FIDELITY & MORE COMPLEX MODELLING
The motors and inverters within EVs tend to display non-linear behaviour over their operation range, a situation that current ICE hardware-in-the-loop (HIL) testing cannot handle. So, test system providers like National Instruments and others are developing Field Programmable Gate Arrays (FPGA)-based simulation tools to facilitate running models from specialised electrical modelling tools in the micro-second range loop rates necessary. Subaru has successfully implemented such a system and reduced test time to 1/20th of the estimated time for equivalent testing on a dyno.
Due to the ECU and inverter being coupled together, power level testing is often preferred and requires power levels up to 200 kW. This requires specialised channel-to-channel isolated measurement equipment and power supplies that can sink and source dynamic loads of that magnitude, such as with this end-of-line inverter test bench developed by National Instruments Alliance Partner Loccioni for the Magneti Marelli inverters used in the LaFerrari hybrid sports car.
BATTERY MODULE/ PACK VALIDATION
Plug-in hybrid battery packs must be characterised at the individual cell, at the module, and at the pack level, (2). Because the cells are arranged in series/ parallel configurations, taking the required measurements can be challenging.
The battery pack can be tested at the component level using a simulated pack to exercise its control algorithms and functions (such as with this BMS test solution by National Instruments Alliance Partner Bloomy) but also together with the actual pack at the sub-system level. These tests happen in thermal chambers and incorporate both aspects of characterisation and durability testing as battery pack performance can be judged based on charge/ discharge behaviour, the cycle time across its lifecycle and based on how long will the battery pack last under normal use in various climates.
Effectively managing this matrix of testers, the generated data, and ensuring traceability of the data and confidence in test data validity requires test automation, system management and data management tools specifically designed for such use cases.
A major problem with physical validation testing is the prohibitive expense and time consumption to ensure sufficient test coverage across all anticipated use cases and operational conditions. To address this problem, test engineers are looking to augment physical testing with HIL testing, when performing system integration testing – blurring the line between physical validation and validation based on simulation.
In system integration testing, various pieces of the system can be simulated depending on the component or behaviour to be validated. Having a flexible test environment and architecture that can support various combinations of simulated and real components can dramatically decrease test times, while at the same time giving extensive test coverage and more confidence in system-level performance and reliability, (3).
WHY DON’T AUTOMAKERS JUST MAKE ALL-ELECTRIC VEHICLES?
All evidence so far suggests that the electric powertrain is superior with its higher performance, greater response, lesser emissions, lower maintenance, greater flexibility and fewer failure points. With India importing over 200 mn tonne of crude oil annually, EV solutions would help reduce its dependence on crude oil over time. It’s just that an all-electric powertrain is still too expensive, primarily due to the battery pack, (4). Additionally, close to 300 mn citizens lack access to electricity, making an all-EV automotive ecosystem a non-viable option for the moment.
Another issue specific to India is the lack of lithium reserves for manufacturing lithium-ion batteries. This could lead to a substantial change in the country’s energy security priorities, with securing lithium supplies, a key raw material for EV batteries, becoming as important as buying oil and gas fields overseas. This, however, is an issue that can be circumvented, with the Society of Manufacturers of Electric Vehicles (SMEV) stating that lithium recycling will begin within the next decade. Over time, advances in battery chemistry technology and the availability of alternative architectures will also aid in alleviating battery concerns.
The use of hybrid vehicles, in the meantime, presents its own challenges due to an increase in vehicle complexity, with more components and hence more points of potential failure. Managing this integration, hence, will require advanced components and even more advanced software and control methodologies.
KEEPING PACE WITH INNOVATION
The push for hybrid vehicles is motivated both by governmental mandates on fuel efficiency and emission levels as well as intense competition among automakers to provide a compelling electrified offering in the same timeframe as their competitors. These factors motivate aggressive vehicle programme timelines that put pressure on test engineers to complete more tests, of more complex systems, in less time to ensure these hybrid vehicle designs are safe, reliable, and high-performing.
Fortunately, testing platform tools and technologies are advancing at a similar pace to the innovation happening in the general automotive industry. Automotive test groups must avail themselves of these advances to meet the increasing demands being placed on them by their organisations and vehicle programme teams.
NATE HOLMES is Principal Solutions Manager at National Instruments in Austin, Texas Area (United States of America)