E-Mobility Engineering 019 | In conversation: Stephen Lambert l WAE EVR l Battery case materials focus l Quality control insight l Clipper Automotive Clipper Cab digest l Optimising battery chemistries insight l Powertrain testing focus

68 May/June 2023 | E-Mobility Engineering such as electrically assisted turbochargers in competition and high-performance hybrid powerplants spin faster still. “IC engine powertrains can be tested against water brakes or eddy current dynos, but given the regenerative capabilities of an EV powertrain, the only logical choice of dyno is a full electrical system.” That opens the way to energy savings, the expert adds, as the company operates test systems that integrate the battery simulator onto the same DC link as the dyno. “In this way, energy harvested by the dyno is used to power the battery simulator, so the only power required from the grid is for covering the electrical and mechanical losses,” he says. “Without this technology, test houses would require far more power to cover EV testing.” He says that has driven a bigmove away fromolder testing technologies towards systemswith lower inertia and consequently greater use of permanent magnet dynos. The company offers dynos and battery simulatorswith ratings of up to several megawatts, and systems that supportmachinery that spins at up to 120,000 rpm. Also, test data sampling rates tend to be much higher than in IC engine testing, engineers from the vehicle test and validation services provider point out. Tests such as power analysis require data to be measured at millions of samples per second. The engineering consultancy and services provider says measurements with such high sampling rates require highly accurate current and voltage sensors. Testing high-speed electrical machines also brings specific considerations to mechanical set-ups, requiring the use of balanced shafts and adapters, and requiring very high accuracy in alignment, for example. The vehicle test and validation services provider has EV powertrain testing facilities in the US, UK and Germany, with battery simulators that can deliver up to 1000 V, 1000 A sound quality engineering including jury testing and sound design, the expert says, with detailed work extending to complete wind noise analysis of the vehicle. For energy flow analysis, the service is centred on the use of a test cell dedicated to vehicle energy management. The cell features ambient temperature control from -10 to 45 oC, and houses a spindle direct drive dyno that can run AWD vehicles, and a rig that has been upgraded with a 300 kW EV supercharger to enable the efficiency of energy transfer from the grid to the battery to be calculated, for example. Here, the questions customers want answered are not so different from those that have long occupied IC powertrain developers, the expert says. They want to know how efficient their drivelines are, which component is generating the most losses, and what the effects of different control settings are on driveline efficiency. “Now, a typical issue would be degradation of e-motor control during cold starts to increase heat generation, and the effect that has on driving range,” he says. “There is a balance between the requests for pure development/validation of customers’ own systems and benchmarking.” Challenges drive change In terms of the unique challenges that EV powertrains present to testing organisations, the engineering consultancy and services provider cites the range of needs discussed above, along with more specific issues such as electromagnetic compatibility (EMC), mechanical resilience and high voltage safety. “Safety when dealing with HV systems is paramount, as they present a high level of risk,” its expert says. “When directly coupling to high-speed e-machines, driveline systems must be able to run at very high speeds.” Test systems therefore need to be modified to ensure safe and accurate testing, he continues. That might mean changes to start-up and shutdown procedures, and precautions against EMI using sensors or isolating HV systems. While heat rejection from EV systems is generally lower than from IC engines, testing is generally conducted across a wider climatic range. “We can test e-machines up to 30,000 rpm and EDUs to 4000 rpm wheel speed,” he says. “We have single and multi-axis rigs up to 4000 Nm and power ratings of 500 kW for single-axis, and 1 MW for multi-axis. Our facilities are designed to test a range of passenger vehicle systems, although we also test smaller, heavy-duty marine and aerospace systems.” In the case of the primary powerplant, the speed range ismuchwider in EVs, the variable-speed drives and controls systems provider says. Typical roadcar engine dynos are rated up to 8000 rpm, whilemotorsport equivalents go up to 16,000, but EVmotors almost universally spin at up to 20,000 rpm. Subsystems Focus | Powertrain testing Acoustics are an important element of EV powertrain testing, feeding into sound design to create cues that reflect driving conditions such as acceleration and braking, cues that would otherwise be absent (Courtesy of Siemens)