Testing: Life choices
Simulation tools combined with data drawn from the road are being used to predict the effects on electric vehicle batteries of real-world scenarios
James Scoltock in Focus.
- Published in Focus.
Anticipating the life of electric vehicle batteries is key to the technology’s success
Bringing electric vehicles to the market is helping OEMs to reduce their carbon emissions, and dependence on the combustion engine. But, while the durability of a gasoline or diesel powertrain has been proven over more than 100 years of development, an electric vehicle’s battery pack is comparatively unknown.
OEMs and Tier One suppliers are using CAE tools to accelerate the testing process, and extrapolate how long a battery can survive in everyday driving scenarios.
But it’s a challenging task for engineers because there are so many variables, including driving pattern, climate conditions, and component faults. Jeff Kessen, technical vice-president of A123 Systems, says: “To find out if a battery can last 10 years or more you have to accelerate the testing. We typically test individual cells. Those tests characterise the performance at many different power levels and many different temperatures. Then we use that broad data from the cell level to calculate the effects of a particular application, and project the life of the entire battery.”
The starting points for most battery tests are commonly used drive-cycle tests such as the NEDC. It gives a standard driving pattern that battery firms can use as a baseline, before complex scenarios are added.
But Kessen says: “One of the biggest variables in battery simulation is the influence the driver has. One particular customer gave us a series of different driver profiles, characterising different driving styles, and they gave us different combinations of how often the person would recharge the battery.
“Using those models after 10 years, the worst case had the battery retaining about 76% of its capacity, while the best case was 93%.”
The unknown variants of how drivers will use electric vehicles make it difficult to predict how long batteries will last. A123 Systems is tackling this problem by feeding into the simulations data from real-world sources.
Kessen says: “We have been in series production for three years with hybrid buses and we have 100 million miles of service accumulated over the fleet. So we’re starting to have enough real-world experience of different climates and different driving styles. Now we can take that and see the correlation with the predictions made in simulation some years ago.”
Proving the life of electric vehicles’ batteries will help to boost market acceptance
