ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

the dire need for more efficiency in EVs, especially in emerging markets such as India where EVs were too overpowered, overpriced and ‘over- battery-ed’ for buyers to feasibly make good returns on them. “So we quickly moved forward on the demonstrator to obtain real- world results showing that an eDTS motor could achieve double-digit improvements [across a vehicle’s full range of operating speeds], rather than the 2-3% gains most researchers are aiming for, and without relying solely on simulated or test bed data.” Motors with eDTS technology are designed quite differently from conventional PMSMs. The latter feature numerous uniformly shaped and routed stator windings, along with a speed- torque curve that is initially flat at the top and runs asymptotically towards its top speed. They have only one ‘sweet spot’ of peak efficiency across their performance range, a spot they fall short of across most other speed points. Also, they need to draw extra current for field weakening as they approach their highest speeds, lest the back-EMF cuts off their ability to continue accelerating at their input voltage. In an eDTS motor, multiple reconfigurable windings allow the electric motor to provide high torque at low speeds without drawing high current from the batteries, and high speeds at low torque levels without using deep field weakening. Among the sets of windings, connected variably in series and parallel, a device called a switch matrix is used to switch between them, all the while telling the inverter which ‘motor’ is receiving the power. “We’ve had some questions about the ‘redundant windings’, but no windings are redundant in eDTS,” Hudson points out. “We have current flowing through all the copper at all times.” Based on the operating needs, the control system determines (in real time) where the system should be on the adaptive shift map. The control system then configures the switch matrix, which enables the various modes. The ECU can switch electronically and dynamically between these, much as a conventional IC powertrain uses mechanical gears to switch to different speed-torque curves suited for different road conditions. “As a result, each mode will have different characteristics, including torque profile, speed range and constant power range,” Hudson says. “It’s always an optimal or near-optimal motor, no matter how your weight or the road changes. The control software navigates between windings to find the highest efficiency, and keeps the phase currents as low as possible in each operating condition to minimise iron and copper losses.” Development and testing Hudson notes that the core technology is established in Dr Shirazee’s original patent and is now in the eDTS motor prototypes. The company is now focused on the motor control algorithms to optimise switching and power efficiency. After that, road testing will be carried out to observe how EVs feel and handle when running on eDTS motors, particularly to minimise any changes in vehicle response when switching between motor modes. “When the opportunity came to join ePropelled as director of EV strategy earlier this year, I leapt at the chance to become part of their big push,” Hudson says. “Nick’s confident about the difference that Nabeel’s tech can make in the EV space, and in being able to make agile and accurate strategic decisions using what I’ve learned over the years.” Hudson anticipates that testing and application validation of the eDTS technology will take up most of ePropelled’s focus for the next several years. Key EV markets will initially include light-duty automotive OEMs in South Asia, where programmes aimed at creating compressed natural gas infrastructure have failed to bear fruit, and electrification – mostly via battery-swapping infrastructure – is now being promoted, as well as marine and aircraft customers. “It will take some work, as our initial eDTS prototypes have generally been 70-80 kW units, and the target market in South Asia is mainly 10 kW vehicles,” he notes. “And once we’re satisfied with the software and approach to scalability, we’ll focus on certifications for all the automotive, aviation and other standards that end-users expect. “Also, marine might be an unexpected area to look into, but it’s very interesting. There are huge sections of the maritime industry that are rapidly moving towards electrification, but are doing so with very crude, inefficient and expensive powertrain technologies, especially compared with road vehicles. “An eDTS outboard motor could work brilliantly, because speedboats have very similar torque-switching requirements to cars. You need high torque at low speeds to pull your propeller, but once you’re planing, you can cut the torque because your drag force has dropped dramatically.” In addition to future advances in solid-electrolyte batteries, Hudson anticipates that improvements across a huge range of technologies such as additive manufacturing, composites and even bearing concepts stand to go a long way towards reducing the drag, weight and frictional losses that are holding EVs back from their full potential. “There are many technological challenges in the EV space, but I do feel most of them are being faced head-on,” he says. Winter 2021 | E-Mobility Engineering 19 InConversation | David Hudson