FEV and the Art of EV Testing

The engineering group has expanded its global footprint into EV testing and development to keep pace with changing technologies and customer demand.

The enormous new 350-kn battery-shaking rig installed at FEV’s new eDLP complex in Germany. (FEV)

Before the impending flood of electric vehicles (EV) expected for the 2025 timeframe enters the market, every one of them – and their subsystems – must be fully tested, validated and calibrated. Companies specializing in engineering, design and testing services are making significant investments to meet industry demand in this already-booming field. One of them, the Aachen, Germany-based FEV Group, has expanded its global footprint into the electrification-testing realm in a big way.

A Porsche Taycan EV undergoing full-vehicle dynamometer testing at FEV. The company’s global test facilities and processes are going through significant upgrades to adapt to the new high-speed electric machines that operate at 25,000 rpm and the increased voltage and current levels of new EV battery systems. (FEV)

Famous for its powertrain-development competency, FEV recently added a 12,000-m2 (~130,000 ft2) facility dedicated to testing batteries, electric drives and related components. Dubbed eDLP, the complex is among the largest test facilities in FEV’s global network and claims to be the largest independent battery test facility in the world. With a solar-panel array integrated into its full roof area, the new complex near the village of Sandersdorf-Brehna brims with resources for the comprehensive testing of cells, modules, and complete high-voltage batteries.

Climatic chambers? The eDLP has 54 of them, with an electrical output of 30,000 kW. Abuse testing? The complex has its own “fire hall” for them, with associated workshops covering short-circuit tests, simulation of internal cell failures, and acceleration and impact tests for packs and complete vehicles in the event of a crash under extreme situations. And this battery-test facility would not be complete without a monstrous 350-kN shaker rig that enables combined mechanical and electrical tests in ambient conditions ranging from -40 to 100°C.

Modularity is a hallmark of FEV’s design-engineering concepts as shown in a general-purpose inverter (motor controller) developed with a replaceable power stack. (FEV)

“The eDLP is indeed unique,” noted Harsha Nanjundaswamy, the director of e-mobility for FEV North America, whose own new development center in Auburn Hills, Mich., is busy with EV optimization, calibration, performance improvement and range testing. Auburn Hills is where FEV conducted testing for the new Lucid Air, following the SAE J1634  standard [Battery Electric Vehicle Energy Consumption and Range Test Procedure].

But all of FEV’s global facilities can be accessed from customers located anywhere. “An EV customer in North America can access our test facilities in China, India or Germany,” Nanjundaswamy said. “All locations have capability and capacity to meet most of the local and global market needs for electrification. Ours is a structure of shared resources and a global pool of talent.” Globally FEV has about 1,500 employees working on electrified propulsion development.

Optimizing components and systems

FEV North America has six high-speed electric motor test rigs at its Auburn Hills facility that are configurable to test wide variety of e-motor development. Testing tasks include Performance (full torque); Efficiency Mapping; Thermal Evaluation with varying coolant temperatures; Reduced Voltage Evaluation (simulate various battery SOCs); NVH Assessment; Motor Characteristic Measurements, and Inverter Control Algorithm Evaluation. (FEV)
E-Mobility director Harsha Nanjundaswamy said measurement-chain accuracy is a bar that is continuously being raised in EV testing. (FEV)

As their EV portfolios and launch plans grow, each OEM is looking for unique design combinations – recipes – that define their selling propositions that will deliver an edge over competitors’ products. A key criteria they’re bringing to FEV is energy efficiency. “Most testing that is focused on design optimization, product validation and calibration primarily looks at efficiency improvements, robustness, and energy optimization across the vehicle,” Nanjundaswamy said.

Beyond the propulsion system the testing spans the component-to-vehicle levels and includes HVAC and other ancillaries. While the engineering solutions provided are project-dependent, typically they begin with simulations to define the targets, including vehicle range, systems efficiency, power losses and NVH improvements.

“From the vehicle-level specifications, requirements and targets that are defined, we dive down into the component level. Batteries, for example, have efficiencies from charge to discharge. We look at losses, energy use for the thermal management, and C-rate [a measure of the rate at which a battery is discharged relative to its maximum capacity],” he explained. Same for electric machines, electric drive systems, charge units, HVAC systems. Then the software and controls are methodically calibrated to ensure that the hardware is capable of achieving the targets at a component level.

A growing OEM priority for EV vehicle and systems testing and optimization is improving the efficiencies of traction motors – how to make them more compact with less iron-and-copper losses [the two main areas of energy losses in electric motors]. “Ninety percent of the energy stored in the battery is used by the traction motor for propulsion,” Nanjundaswamy said. “The more we can make the motor efficient, the more energy can be saved and the more range delivered by the vehicle. Power electronics also have a huge influence on overall efficiency.”

With decades of its own design-engineering expertise, FEV approaches much of its EV testing as an engineering-solutions development. “We look at inverter technology – what kinds of power-switching devices are used, what type of software, and how the motor controls are done,” he said. “We study the harmonics, performance, overload capacity, efficiency, and overall behavior of the electric drive system.”

The second greatest area of OEM focus is thermal management, and a driver of FEV’s climatic-test investments for EVs. The more batteries, chargers, electric drives, and wiring can be designed to be less sensitive to temperature variation, the less energy losses and the more robust and efficient the system. “It means better vehicle performance from cold to hot weather and helps mitigate any impact of temperature on overall range,” Nanjundaswamy noted.

On batteries, the industry’s focus is on reducing weight and increasing specific energy. “It’s more on the design side,” he said, with much emphasis on cold start, hot start, high C-rate, impact on thermal management and energy recovery and efficiencies. “If there is a bottom-plate cooling methodology on a pack and it may be less efficient to achieve higher current discharges from a cell because of cell temperature issues, we take that type of design and we can modify, optimize and improve it with alternative cooling methods such as intercellular or direct cooling,” he said. FEV then prototypes it and returns it to the customer as “a compact, high-specific-energy, very high-C-rate-capable battery. That’s the type of deliverable we provide.”

Fast-paced changes

The 2020s begin an extremely dynamic time for the mobility industry, with many emerging propulsion and energy-storage technologies and strategies. Test facilities and processes are going through significant upgrades and changes, he said, to adapt to the new high-speed electric machines that operate at 25,000 rpm, and the increased voltage and current levels of new EV battery systems.

“The new silicon-carbide technology that is used in power-switching devices has improved efficiencies quite a bit. But once the efficiency increases, the losses are reduced,” he explained. That means the way speed, torque, current and voltage are measured needs to be highly accurate in order to calculate exact efficiency.

“We have paid a lot of attention to measurement-chain accuracy as well involving equipment and method of data collection,” Nanjundaswamy said. “Our testing processes have changed so that even minute losses can be determined, so we can improve the component behavior. At the vehicle level, even a small-kilowatt-hour variation can have a huge impact on the number of miles [of range] that you determine.”

The rapid pace of change in electric vehicle technology is challenging the testing community, particularly as related to accurately characterizing the components and systems. “Compared with five years ago, e-motor technology and Design for Manufacturability have improved so much,” he observed. “The EV leaders’ key motor designs have changed significantly from their earlier designs – Tesla, for example, has moved from an induction machine to a permanent-magnet machine and from low-speed to extremely high-speed e-motors. The highest efficiencies of those are 93 to 95 percent and above – levels typically unheard of until recently.

“It clearly shows,” he continued, “that the electric motor is not a simple device; it’s very complex and has many areas that can be design-optimized to meet certain specifications. The more powerful, higher-speed motors, new power-electronics methods, new integrated traction drives and new battery chemistries will change the way we test – along with the changing user experience for the end customer,” Nanjundaswamy said.

“In the future we may not test an electric drive by itself – we may instead be testing the entire powertrain system, including the battery, as a single piece. A lot more integration is going to happen because it offers a lot to gain,” he said.