Hover-in-place Drones Powered Through High-Voltage Tether

Article By : Maurizio Di Paolo Emilio

To enable a thinner and lighter tether, power must be delivered from the host ship to the drone at very high voltage and low current. This allows greater mobility and heavier aircraft payloads, which leads to improved communications and surveillance.

Dragonfly Pictures (DPI) has developed a new class of drones, the tethered hover-in-place drone. This new vertical take-off drone is weatherproof and can stay in the air for long periods of time. The drone uses a flexible cable as a permanent physical link to provide power and communications as well as mechanical support. Unlike battery-operated multi-rotor drones that require a battery change every 20 minutes or a fast recharge, tethered drones receive power through an electrical cable connected to a base station. This allows them to remain operational for more than 400 hours at up to 500 feet above sea level – thanks to the continuous flow of energy through the tether. The tethered military/industrial-grade UMAR (Unmanned Multirotor Aerial Relay) drone is designed to track maritime and land-based platforms such as ships, boats, trucks, and other vehicles, in addition to the classic use as a base station for naval communications.

Tethered Drones

The increased demand for remote communications and intelligence, surveillance, and reconnaissance (ISR) has driven interest in drones; however, earlier generations of drones have encountered technical difficulties and limitations, especially in flight control. Fixed-wing drones that travel at high speed for logistics applications are not equipped for onboard surveillance and communication. Untethered drones experience stabilization problems in adverse conditions such as strong wind and heavy rain. To overcome these difficulties, Dragonfly has developed a new class of drones, the tethered hover-in-place drone. Compared to classic drones, these offer vertical take-off and landing capabilities. No runway, launch, or recovery equipment is required. They also offer good performance in turbulent weather, rain, snow, dust, and heat and are optimized for saltwater marine environments. The tether eliminates the dangers of electronic interference and therefore makes the system autonomous from GPS and radiofrequency. DPI’s tethered drones are currently qualified for use by the U.S. Navy in marine/maritime environments for intelligence, surveillance, reconnaissance (ISR), communications, and video applications. Drones typically provide up to a few hundred meters of operational altitude, with the limiting factor being the ability of the drone to support the weight of the tether. Tethers can be made of aramid or other lightweight synthetic materials to provide strength, with copper or plated copper for energy conduction and optical fiber for data and communications. The system can be ground-based or vehicle-based. Tethered drones, which hover hundreds of feet above a ship, overcome the challenge of ship communication systems that are limited by the curvature of the earth and can only communicate in line of sight with the horizon. Tethered Unmanned Aerial Systems (UAS) can provide continuous communications Beyond Line of Sight (BLOS). The tether provides continuous power and command/control to the UAS, thus greatly increasing the duration of the mission. Connected UAS systems reduce operator workload and mission planning, allowing the host ship and the off-board resource to communicate longer. “UMAR can host a variety of sensors including cameras, radar, and weather data can be collected at altitude for an extended duration. DPI has tested its tethered UAS systems on various vessels from 45 ft US Coast Guard vessels, US Navy ships, and US Army ground platforms,” said Joe Pawelczyk, vice president of operations at DPI.
UMAR (Unmanned Multirotor Aerial Relay) [source: DragonFly]

Power Challenges

The design challenges for the tethered architecture are mainly directed to the power supply system. Power must be delivered from the host ship to the multi-rotor drone at very high voltage and low current to allow the use of thinner and lighter hardware resources, which in turn allows greater mobility of the drone and higher air payloads. The weight, dimensions, and electrical properties of the tether have a direct impact on the performance of tethered drones. The power delivery network (PDN), in turn, has a direct impact on the tether design. To enable a thinner and lighter tether, power must be delivered from the host ship to the drone at very high voltage and low current. This allows greater mobility and heavier aircraft payloads, which leads to improved communications and surveillance. The power levels are of the order of 8 to 10kW; under these conditions, UMAR drones are extremely powerful and robust and can maintain persistent stationary positioning in turbulent conditions affecting the positioning of the host ship. Inside the multi-rotor drone, the high voltage conversion must be done with the smallest footprint possible and with a form factor that reduces space and thermal effects. To meet these aggressive power challenges, DPI employs low-profile Vicor high voltage BCM VIA modules within its UMAR to enable high efficiency (98%) conversion with only 2% loss and heat from 800V to 50V. To power the eight independent drone rotors, DPI uses eight Vicor high-voltage BCM4414 fixed ratio DC-DC converters. These modules have intrinsically low EMI with few high-frequency harmonics. Integrated EMI filtering within the Vicor BCMs helps minimize EMI noise by adding less size and weight than conventional DC-DC converters. “Using Vicor power modules, we have been able to lower the weight of all the components onboard the drone to increase altitude and airspeed while carrying the required mission payload,” said Pawelczyk.
Eight Vicor HV BCMs power the eight independent UMAR DPI rotors [source: Vicor]
The UMAR could be a useful tool to communicate with unmanned surface ships during defense and commercial operations. The UMAR could also be a back-up for telecommunications as a backhaul method for mobile communications at sea. Its potential applications include a base station for communications in offshore oil and gas and renewable energy operations. For longer distances, multiple daisy-chained drones can be used. This article was first published on EE Times Europe

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