WAVE Inductive Charging Purpose-Built for Large EVs
In-road wireless charging attracts transit buses and other medium- and heavy-duty vehicle applications.
The largest all-electric transit bus fleet in the U.S. serves as a vivid example of commercial vehicles ditching diesel fill-ups. “WAVE’s wireless charging solution is purpose-built for medium- and heavy-duty vehicles, and we remain laser-focused on that sector,” said Michael Masquelier, chief technology officer for Salt Lake City, Utah-based WAVE (Wireless Advanced Vehicle Electrification).
Southern California’s Antelope Valley Transit Authority (AVTA) opted to transition from diesel-fueled to battery-electric buses in 2014. Today, 48 of the current 54 BYD-built buses are equipped with WAVE’s patented wireless charging system. Each BYD bus has two asynchronous three-phase motors. The 40-ft buses are 150 kW; the articulated 60-ft buses are 180 kW.
“Depending on the season, our cost of fuel – electric in this case – is anywhere from 50 percent to 70 percent less than our diesel fleet was. And we avoid about 2,700 metric tons of CO2 emissions for every million miles driven, with 21,600 metric tons avoided since we started the project,” said Esteban Rodriguez, AVTA’s director of Operations and Maintenance.
Wireless charging centers
Within a 100 sq. mi. (260 sq. km) area, AVTA has 12 wireless charging centers, each providing 250 kW. “AVTA uses scheduling software Optibus to optimize and extend the range of a bus by adding en-route charging at designated layovers to get a minimum of 10 minutes to a maximum of 20 minutes via WAVE’s inductive charging,” Rodriguez said.
Buses are charged overnight to provide a 100% state of charge at the start of a day’s route. “A handful of buses that are not equipped with the WAVE charging equipment are scheduled to come to the depot for a midday charge because of the miles required on those routes,” Rodriguez said.
At a scheduled wireless charging stop, an AVTA bus – fitted with an undercarriage-mounted power receiver – is parked on top of a ground-embedded transmitter packaged within a ruggedized pad. “WAVE uses a single-pad design that not only allows for a very sizable alignment window, but it also helps deliver power transfer efficiency equal to or better than some conductive chargers,” Masquelier explained.
WAVE’s charging system typically reaches its maximum power in a few seconds. “The pace at which full power is reached is controlled by the vehicle’s battery management system, which varies based on a number of factors, including the size of the battery pack and the pack’s state of charge,” Masquelier noted. The charging activity occurs within a 5- to 8-in. (127- to 203-mm) air gap between the vehicle and the roadway. “We use a process called magnetic resonant inductive power transfer,” he said.
Purpose-built for large EVs
To enable the inductive charging process, the all-electric buses are fitted with a communications antenna, a system interface controller, a user display and an undercarriage-mounted power receiver that’s positioned rearward of the front axle. The wireless charging loop is completed via the in-ground charging pads, each with an underground connection to an above-ground box that contains the primary power electronics. An adjacent above-ground box contains the primary power supply with a cooling unit.
Seasonal weather changes are not considered problematic for wireless charging. “With no moving parts, the ruggedized system requires little maintenance. And being free of moving parts, connectors or cables means there is nothing to break or freeze,” Masquelier said. WAVE’s wireless charging system substantially differs from legacy plug-in and overhead charging systems.
At the power levels required to add meaningful driving range to medium- and heavy-duty EVs, the cables, cooling requirements, mechanical and manual-driven operations required by legacy conductive charging solutions present adoption challenges, according to Masquelier. For instance, to scale up for a large-vehicle electrification application, many low-power plug-in chargers, or several DC fast chargers, are needed to achieve range and duty-cycle requirements. That’s largely attributed to medium- and heavy-duty trucks and buses using up to 10 times more power than light-duty passenger EVs.
“WAVE’s wireless charging technology, purpose-built for large EVs, simplifies medium- and heavy-duty vehicle electrification by delivering higher power more quickly and in a more compact, space-saving configuration while requiring less labor and maintenance than legacy charging solutions,” Masquelier said.
In early 2022, the first WAVE 125-kW wireless charging systems were installed at the Port of Los Angeles’ West Basin Container Terminal to power battery-electric yard tractors. “This California Energy Commission (CEC) grant-funded project calls for a total of 12 charging stations and 10 vehicles,” Masquelier noted. Another CEC grant provided for the installation of a 380-kW charger to support a Hyster battery-electric top loader.
In late 2021, WAVE demonstrated a 500-kW wireless extreme-fast-charging system for a Cummins-supplied battery-electric Class 8 truck as part of a project partially funded by the U.S. Department of Energy. “This test marked a milestone achievement by successfully charging the vehicle in 15 minutes,” Masquelier said.