Hydrogen Fuel Cell-Powered Drones

New hydrogen power technology could mark a commercial breakthrough for drones, paving the way for mobile robot development with extended range and load capacity. Doosan Mobility Innovation (DMI) has announced it has successfully used hydrogen-powered drones to deliver humanitarian aid in remote locations. With two hours of flight time (longer than most battery-powered drones), the hydrogen drones transported masks and emergency supplies between the US Virgin Islands and delivered medical supplies to the top of Mount Hallasan, South Korea’s highest mountain, located on Jeju Island.

DMI has accumulated many years of knowledge in materials and systems related to phosphoric acid fuel cells (PAFCs) and proton-exchange membrane fuel cells (PEMFC), also known as polymer electrolyte membrane (PEM) fuel cells. PEMFCs generate electricity and operate on the opposite principle to electrolysis, which consumes electricity.  Thanks to this experience, Doosan is developing the PEMFC mobile power pack for drones.

In an interview with EE Times, Jiwon-Yeo, sales representative of Doosan Mobility Innovation, highlighted how the use of hydrogen-powered, long-distance drones is also allowing commercial monitoring of large areas such as Korea’s largest solar power plant in Solasido, Haenam. “When carrying out the same mission using a battery-powered drone, more than six battery replacements were required. Due to the high energy density of hydrogen fuel cell, which is 3~4 times higher than traditional batteries, the hydrogen fuel cell is a more efficient and effective energy source,” said Jiwon-Yeo.

The development of hydrogen power solutions encompasses a range of technologies from materials engineering to optimize the powertrain of the drone.  Being capable of flying for up to two hours on a single charge, these long-range fuel cell drones can cover even large sites in a single flight, rather than having to use multiple batteries and multiple launch points. Drones also offer advantages in personnel safety and accident prevention, as aerial scanning eliminates the need to climb over structures on site.

Figure 1: example of solar panel inspection (Source: Doosan Mobility Innovation)

The science of hydrogen fuel cell technology
Hydrogen is the lightest element on Earth. When it is combined with air (oxygen) in the atmosphere, water is formed, making hydrogen a pollution-free gas. The effort to reduce particulate matter, the dangers of nuclear power, and greenhouse gases worldwide is also increasing demands to use renewable energy. So hydrogen is emerging as the most promising alternative energy.

A fuel cell is a device that converts the chemical energy of a fuel into electricity and heat without using thermal cycles. Hydrogen (H2) fuel cells produce electricity and hot water from hydrogen and oxygen. The process is exactly the opposite of electrolysis: when splitting water (H2O) into H2 and O, it is necessary to supply current, the reversed process produces current and water. Reverse electrolysis takes place in the fuel cell: hydrogen comes from a tank, air from the surrounding environment.

The drone is powered by the electricity generated in the stack using hydrogen and oxygen, as visualized in figure 2. As Jiwon-Yeo pointed out, the stack consists of several cells made up of a polymer electrolyte membrane (PEM) and two electrodes, which generate ions and electrons through the hydrogen reaction and the oxygen reaction. The hydrogen is first compressed under high pressure before being used in the cell, thus ensuring a high supply period.  “DMI provides a complete hydrogen system in which filled hydrogen cylinders are shipped to customer sites. Users would just need to replace hydrogen cylinders, which takes about a minute,” said Jiwon-Yeo. She added, “Our tanks passed not only tests required to obtain hydrogen tank certification but also a variety of safety tests that are most similar to drone flights.”

Cells with a polymer membrane offer high conductivity and operate at temperatures between 70 and 100°C. They are mainly used for traction and small-scale generation/cogeneration (1 – 250 kW). Combustion cells offer high electrical efficiency, with values ranging from 40 to 60 percent, depending on the temperatures used. The modularity of the system makes it possible to increase the installed power. The cells can be arranged in series to form the “stack”, which can be assembled into modules to obtain the required power generators.

“One of the biggest challenges would be the lack of hydrogen infrastructure. We believe the increase of hydrogen fuel cell mobility such as drones would stimulate the market. With local partnerships, we have completed a hydrogen supply chain in Korea, China, and USA. We’re cooperating with local gas companies to charge our hydrogen cylinder, which is certified with DOT, TPED, and KGS mark,” said Jiwon-Yeo

Figure 2: How Power is Generated from Fuel Cells (Source: DMI)

 

Figure 3: Energy density comparison: hydrogen fuel cell vs. lithium power (Source: DMI)

Hydrogen Increases Flight Time of Drones
A 48V system handles the power management of a hydrogen cell-powered drone similar to tethered drones through the implementation of the power distribution network (PDN). In a power system design, the PDN is one of the most critical elements due to several factors that have a major impact on design choices. These factors are market-driven before being technology-driven. The optimization of the power supply in the PCB design is a system-wide issue. The PDN is designed to provide specific levels of voltage and current to the various loads within a system derived from a bulk power source(s). As system power demands rise, traditional PDNs are under tremendous pressure to deliver enough performance. PDNs based on a new standard such as 48V, is emerging in several applications.

The 2.6 kW DP30 power supply system used by DMI has two main groups that supply power to the drone rotors and controllers for the two stacks. Due to the wide range and variable output voltage of the DP30 power supply, from 40 to 74V, the output power units operate at 48V, 12A for the motors and at 12V, 8A for the control circuits and fans. The structure is supported by a Vicor PRM™ buck-boost regulators and a ZVS buck regulator.

“Wide range of Fuel Cell voltage and the hybrid connection to the conventional Li-Po battery is the key configuration of our power management system. By doing that, it allows the lithium batteries to automatically charge by Fuel Cell when needed, or discharge when Fuel Cells need additional power when the drone is operating. Thermal management is important to hydrogen fuel cell, and we have an inner cooling fan to regulate the heat,” said Jiwon-Yeo

DMI plans to diversify its product lines according to power capacity. Jiwon-Yeo pointed out that the company will soon be developing products with various capacities, ranging from the 1.5kW hydrogen fuel cell power pack that should be released next year to the 10kW power pack, and will be launching matching drones for each power pack.

The increased flight time, coupled with rapid refueling, opens a wide range of new business possibilities for companies using drones for offshore platform inspection, search and rescue operations, high-quality aerial photography, precision agriculture, deliveries and more.

Google, Amazon and Alibaba are experimenting with plans to launch a delivery service using drones. If fuel cell-powered drones are successful, optimists say they could create a low-carbon delivery system worldwide, curb air pollution and emissions, and replace road transport. The establishment of these aircraft will have to be subject to air traffic regulations that need to be revised and adapted to new mobility scenarios. Indeed, safety must be guaranteed before a myriad of vehicles crosses the skyscrapers of the megalopolises. The scenario in the 2015 film “Back to the Future” is not so far, then!