Unmanned Systems Technology 016 | Hydromea Vertex AUV | Power management systems | Unmanned Space Vehicles | Continental CD-155 turbodiesel | Swift 020 UAV | ECUs | DSEI 2017 Show report

39 is waiting in a line or even driving along, allowing driverless cars to automatically return to base to recharge when the batteries are low, and to be replaced by a fully charged vehicle. That creates a constant supply of autonomous cars on the road without human intervention. There are many elements to electric wireless charging that need to come together, and car makers and equipment suppliers want to be able to provide a range of form factors, performances and implementations. These also need to work with infrastructure such as wireless charging points in the home and on the street, which have to link back into the electricity grid, and all of this has to work together seamlessly. Current wireless charging technology has a range of implementations. Most home systems use a 3 or 7.4 kW system, where a coil in the vehicle inductively couples at 85 kHz to a base pad on the floor of the garage with a vertical distance, or Z gap, of a few centimetres. The charging is then controlled through the vehicle’s electronics, and this gives the ability to transfer full power over a tolerance of ±75 mm in the driving direction and ±100 mm to the left and right with 90% efficiency. The link between the base pad and the car is typically 2.4 GHz wi-fi. Increasingly these designs use gallium nitride power devices, which have a 96% efficiency compared with 94% for the present wireless power devices that are based on a variant of CMOS. While that 2% difference doesn’t look much it can make a big difference in reducing the amount of heat generated and energy wasted. Although the wireless charging system is a complex mechanical and electrical design, it also requires a range of other technologies, such as safety detection to ensure that there are no metal objects on the plate, and that no people or animals can be harmed. The system design approach extends across the power conversion electronics, magnetics, control strategies, comms links and safety systems. There is growing interest in 11 and 22 kW systems for fast-charging points in the community to eliminate users’ anxiety that the battery will run down and leave them stranded. The higher the power, the faster the batteries can be safely charged. Backwards compatibility and interoperability between different types of car is essential. Infrastructure companies are looking for the ability of different cars with different Z gaps to drive over a single base pad and still be able to charge at 11 kW, and be backwards- compatible at 7, 11 or even 3.7 kW. The ancillary safety systems are key as well, particularly in detecting foreign metallic objects and shutting down to prevent a problem with the charging. The system then automatically restarts once the object is removed. There is also living object protection, which shuts the charging down if a human arm or animal is detected between the pad and charger. Techniques to ensure the vehicle is correctly positioned over the pad vary from a low-cost system for home charging or parking to a more comprehensive implementation to tell the driver or car to stop in the right position. For autonomous vehicles that charge by themselves, the system has to work with the ultrasonic, camera and radar sensors. All of this is a complex collection of technologies that is set to become even more complex in the future. Dynamic charging has been demonstrated at motorway speeds with a 100 m test track in Paris that can provide 20 kW of power to a vehicle moving at 100 kph. Power management systems | Focus Unmanned Systems Technology | October/November 2017 Smart chargers are giving developers access to much more data about the state and usage of the battery system (Courtesy of Lincad)