Founded in 2021, Bumblebee Power is a spin-out from the Wireless Power Lab at Imperial College London. At the heart of Bumblebee’s new charging platform for e-scooters is AirFuel Resonant, a high-frequency (MHz) resonant wireless charging technology that offers groundbreaking performance versus low-frequency (KHz) solutions. This innovation results in transmitter and receiver systems that are not only smaller, lighter, and easier to integrate but also more cost-effective. And of course, like with any other MHz wireless power system provides larger air gaps and therefore increased tolerance to misalignment.
The core technology can also be scaled to multi-kilowatt power levels, making Bumblebee uniquely poised to deliver high-frequency wireless charging into multiple markets.
The Challenge: Solve the two biggest problems for the shared e-scooter market: parking and charging
In the realm of shared e-scooter schemes, the two major hurdles are parking and charging. Dockless e-scooter schemes were once celebrated for their flexibility, leading to some of the fastest growing companies in history. However, in many cities, this flexibility has come to be seen as a drawback, with scooters being parked in inconvenient and even unsafe locations, causing disruption for pedestrians and adding to urban clutter.
As a response, city councils in the UK, for instance, increasingly require scooters to be left only within designated parking bays. Users cannot end the ride unless they comply. The current reliance on GPS technology is inadequate to verify whether a scooter has been left within a designated bay due to its inherent inaccuracy. This leads to a poor end-of-ride experience for users, who often must prove correct parking via a photograph.
On the other hand, battery recharging in hire schemes is usually done at a central depot. Manual battery swapping teams are sent out with vans full of batteries. This represents a substantial portion of the operational costs in micro-mobility share schemes, perhaps accounting for nearly 50%.
On the other hand, battery recharging in hire schemes is usually done either at a central depot or distributed re-charging stations. Manual battery swapping increases operational costs through having to buy additional batteries to cover for those on charge and the additional burden for the teams that do the swapping. This represents a substantial portion of the operational costs in micro-mobility share schemes, perhaps accounting for nearly 50%.
Addressing these challenges is crucial for creating a seamless and efficient micro-mobility experience in urban environments.
The Solution: e-scooter wireless charging platform
Bumblebee Power’s solution centers on a state-of-the-art 6.78 MHz wireless charging system using AirFuel Resonant technology. The transmitter (TX) is implemented through a ground pad, utilizing a push-pull class EF inverter, while the retrofitted receiver (RX) is mounted on the underside of the scooter, employing a voltage-doubler full-wave Class D rectifier. Notably, this system boasts a DC-DC efficiency surpassing 80% with a tolerance to misalignment of +/-15 cm in all directions. This adaptability is critical in real-world urban environments, where precise alignment during parking is not always feasible and where parking in either direction is desirable. Bumblebee’s current solution provides 100 W to the receiver with a ground clearance of ~8 cm.
The integration of Gallium Nitride (GaN) technology from GaN Systems, a wide bandgap semiconductor company, has been instrumental in overcoming the challenges in High-Frequency Inductive Power Transfer (HF-IPT). Driving the transmit coil and rectifying the induced high-frequency voltage without incurring significant switching losses has historically been a formidable challenge. The 650 V GaN transistors from GaN Systems are a crucial component of Bumblebee Power’s wireless charging platform due to their enhanced performance and efficiency at those frequencies.
The system is designed with modularity in mind. Even though the trial platform now hosts just 4 scooters, its adaptable framework can readily accommodate varying numbers of vehicles, providing scalability and versatility to suit diverse operational needs.
Safety is considered paramount with voltage, current, and temperature monitoring on both transmit and receive sides, enabling auto turn off in case of any faults. The system also features a Foreign Object Detection capability that promptly halts operation if a conductive object is detected within the air gap.
“The Bumblebee solution demonstrated remarkable reliability in real-world testing, eliminating the necessity for battery swapping and significantly enhancing the end-of-ride experience”
David Yates, CTO of Bumblebee Power
The Results: e-scooter wireless charging trial
Bumblebee Power’s solution demonstrated both reliability and safety in real-world testing scenarios, successfully completing a 3-months trial at a university campus. The trial was held at the University of Warwick, Coventry (UK), where the electric kick-scooters were made available exclusively to staff from the estates department for a 3-month time period.
Importantly, the magnetic resonance link allows for exact vehicle localization through received voltage checking, outperforming the capabilities of GPS. This is critical in urban settings where users are increasingly required to park the scooter precisely with designated bays. With a user focused approach, the system also incorporated LED indicators. When the scooter was parked correctly, the LEDs were illuminated green, allowing the user to simply walk away. However, if the LEDs flashed orange, it signaled that the scooter was misaligned and required a slight adjustment. State-of-charge was also indicated using the same LEDs. These features were particularly well received by the scheme operator, Voi, and the users.
Bumblebee Power’s solution includes remote monitoring and smart control functionalities, via a data dashboard and CCTV camera feed, allowing the operating team to conveniently manage their fleet of e-scooters remotely.
Looking ahead, Bumblebee Power is focused on further improvement and a wider roll-out. A custom battery charger has now also been integrated which enhances system efficiency and reduces weight. Additionally, an autotuning feature has been developed to adapt seamlessly to varying electromagnetic environments, automatically fine-tuning circuits in response to changes in ground metal presence. These forward-thinking enhancements underscore Bumblebee Power’s commitment to continuous improvement and meeting the evolving demands of urban mobility solutions.
Working Together to Create a Wire-Free World
As members of AirFuel Alliance, Bumblebee Power and GaN Systems are contributing to the micromobility charging standard which will be critical to delivering interoperable charging solutions for share schemes across global e-scooter products.
AirFuel Alliance® enables companies to provide cutting edge wireless charging and wireless power experiences for their customers. Members bring wireless power solutions to market today and champion innovation to advance wireless technologies tomorrow. They also receive access to the world’s leading wireless charging standards and development tools, and connect to a global community of companies working together to realize a vision of a world without wires.
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