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

36 Unmanned aircraft Unmanned aircraft have several different techniques for power management depending on the size of the platform. Smaller UAVs have detachable battery packs that are replaced by the user. Fast chargers are used to charge a second battery pack safely and quickly while the UAV is in the air, allowing a fast switchover when needed. And increasingly, smart chargers with smart cables are being used with such platforms. Some platforms, such as high-altitude long-endurance systems, are using solar cells as the power source to charge the batteries, and this technology is being applied to other airborne systems. This of course adds the MPPT charging algorithms into the mix of power management to ensure that the maximum energy is captured from the solar cells. However, the increasing use of autonomous control algorithms means that wireless charging is becoming viable. This allows a UAV to return to a base plate that couples inductively to a plate on the bottom of the craft. The two plates have to be close together, so the design of the UAV has to account for that, and it requires additional onboard power controllers and comms links to manage the charging process safely. This increases the weight of the craft, reducing the flying time. However, using autonomous UAVs means that some can be charging while others are still performing their assigned tasks. This capability is being driven by new wireless charging standards such as AirFuel and Qi that are being adopted for consumer equipment such as smartphones and laptops. Controllers using these specifications are able to provide fast wireless charging for these smaller batteries, but while they are often not powerful enough for fast charging of UAV batteries, they are starting to be adopted by UAV designers. Wireless schemes for electric vehicles are also being developed. However, even unmanned aircraft with traditional engines need power management units that can handle amounts of power up to 250 W. The engines generate electrical power and provide multiple output rails, each of which is user-configurable for voltage. The power management unit is fully battery-backed (in case of engine failure) to keep the navigation and comms systems alive, and has dual battery support for redundancy, while the battery back-up can also be used to start the engine. Like any UAV subsystem, it has to be lightweight, which means using more efficient topologies for the electronics such as active rectification and polyphase switching to provide the required performance. Control strategies Within the design of the autonomous control system there are also power management issues. The increasing complexity of the electronics, with FPGAs and GPUs, brings with it multiple power rails that can be as low as 1 V and need to be controlled within ±1%, or 1 mV. The rails also need to be powered up in a specific order or the electronics will not work correctly. And there is the power management of sensors such as Lidar, radar and cameras distributed around the vehicle to be considered. The processing requirements of autonomous systems are driving the need for much more sophisticated power management architectures. The total current requirement is rivalling the computer server market, at 100-200 A. Five years ago in the automotive sector there wasn’t a processor drawing more than 3 A; now there are GPUs requiring 20 A, and developers are talking about 50 and 100 A. Dynamically managing the clock signals at around 2 GHz and the October/November 2017 | Unmanned Systems Technology Focus | Power management systems A power management pack with dual redundant batteries to start a 29 cc UAV motor and power the system electronics (Courtesy of Millswood Engineering)