FEATURE WIRELESS TECHNOLOGY
CREATING THE DRIVE: WIRELESS CHARGING FOR ELECTRIC VEHICLES
Electric vehicles (EVs) are on the rise and autonomous vehicles increasingly feature in discussions on the future automotive landscape as car makers develop vehicles that are safer, cleaner and more connected. Charging these vehicles needs to be more simple, more efficient and more user-friendly. Wireless electric vehicle charging (WEVC) appears to be an obvious solution. Here Dr. Edward Van Boheemen, senior staff engineer at Qualcomm CDMA Technologies considers the latest capabilities
W
ireless electric vehicle charging (WEVC) would appear to go hand-
in-hand with Electric vehicles (EVs). This could see fleets of autonomous vehicles simply charge themselves. WEVC allows driverless cars to automatically return to base to recharge their batteries. This could facilitate a constant supply of autonomous cars on the road without human intervention. Furthermore, WEVC lends itself to charging an EV on the move - known as dynamic electric vehicle charging (DEVC). DEVC could be used, for instance, in slow moving traffic such as a taxi rank, or at higher speeds on highways. Qualcomm Halo WEVC systems have been successfully integrated and tested on a number of different vehicle platforms including: Renault Fluence; Nissan Leaf; BMWi3; BMWi8 and Honda Accord. It is expected that production orders will be placed soon and WEVC systems will be on production vehicles in the next two to three years. Both automotive manufactures and
equipment suppliers want to be able to provide a range of form factors, performance and implementations. These also need to work with infrastructure, such as wireless charging points in the home and on the street linking back into the electricity grid; and all of this has to work together seamlessly. One of the central challenges to adoption is that current electric charging technology requires a range of implementations. Most home charging systems use a 3kW or 7.4kW system, where a coil in the vehicle inductively couples at 85kHz to a base pad on the floor of the garage (with a vertical or Z gap of a few centimetres). The charging is then controlled through the vehicle electronics and this gives the ability to transfer full power over a tolerance of ±75mm in the driving direction and ±100mm to the left and right with an end to end efficiency of over 90%. The link
16 SEPTEMBER 2017 | ELECTRONICS
the base pad may be buried under the road. Where WEVC comes into its own is its application to autonomous vehicles, enabling these vehicles to charge by themselves. The system does of course have to work with the existing sensors on the vehicle, including ultrasonic, camera and radar.
Beyond the technological and practical Figure 1:
Qualcomm Halo WEVC systems
between the base pad and the car is typically 2.4GHz or 5GHz WiFi. While this is a complex mechanical and
electrical design, it also requires a range of other technologies, such as safety detection. Ancillary systems cover safety, such as foreign object detection (FOD), living object protection (LOP) and positioning. An FOD system identifies any metallic objects between the base pad and vehicle pad. This is important as metal items, even small objects such as a paperclip, may heat up and could pose a burn risk during power transfer.
SAFETY FEATURES An LOP system identifies the presence of humans or animals close to the power transfer system, where magnetic field levels may exceed exposure regulations. Positioning is another vital technological
consideration. This helps align the vehicle over the base pad, which may not always be visible. The base pad could sit on top of the road surface, this is likely for instance for home charging in your garage. The base pad could also be buried, such as in a car park or along the roadside. It’s important to consider how the technology performs where there are large gaps between the base pad and the vehicle, for instance with vehicles with a high ground clearance, such as SUVs and also where
challenges, there are considerations for making WEVC as compelling a solution as possible for users. There is increasing interest in 11kW and 22kW systems for fast charging. The higher the power, the faster the batteries can be charged and adopting these systems would lead to a dramatic increase in convenience for drivers. Compatibility and interoperability between different types of car is also essential. Consider the landscape for mobile chargers, support of interoperability from the start was necessary this is something key in the ongoing work with the various standards bodies regarding WEVC. The ideal is to be able to drive a WEVC enabled vehicle and charge in any WEVC parking spot, regardless of the EV make or model. Infrastructure companies are therefore
exploring the possibility of different cars with varying Z gaps, anything from an SUV through to a roadster, driving over a single base pad and still being able to charge at 11kW and be backwards compatible at 7kW or even 3.7kW. There are also different types of grid connections to work with, and these differences must be invisible to drivers. For example, in the UK there is a 230V single phase, 13A supply for the 3.7kW system and a 32A supply for the 7.4kW system, while in Germany the 16A, 230V 3 phase supply allows for an 11kW system. All of this must be considered when looking to make WEVC widely practical and accepted.
Qualcomm Technologies
www.qualcomm.com T: +1 (858) 587-1121
/ ELECTRONICS
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