Classification of hydrogen hybrid systems for UAVs
1.The principle of hydrogen hybrid power system
The UAV hydrogen hybrid system usually uses hydrogen as the main energy source, combined with other energy sources (such as batteries), and converts the chemical energy of hydrogen into electrical or mechanical energy through chemical reactions to power the flight of the drone.
Hydrogen can undergo an electrochemical reaction in a fuel cell to produce electrical energy, which directly drives the motor to operate; It can also be burned to produce high-temperature and high-pressure gases to drive turbines or piston engines to work, and at the same time recover waste heat for other systems to improve energy efficiency.
The battery assists the system by providing additional power during start-up, acceleration, high loads, etc., or when the fuel cell output is insufficient, and can recover braking energy for storage.
2.Classification of hydrogen hybrid power systems
(1) Hydrogen fuel cell-battery hybrid system
Proton exchange membrane fuel cell (PEMFC) is the main power generation device, which has the advantages of high energy conversion efficiency, zero emission and low noise. Batteries (e.g. lithium batteries) are used as auxiliary power sources, and the two are connected to the drone's electric drive system via a power converter.
During flight, the fuel cell provides a stable base power, and the lithium battery provides additional power when the instantaneous power demand is high, and the energy is recovered and stored under low fuel cell efficiency conditions (such as low loads), optimizing the efficiency and performance of the entire system.
At present, most of the hydrogen hybrid drones use hydrogen fuel cell-battery hybrid systems.
(2) Hydrogen internal combustion engine-battery hybrid system
The hydrogen internal combustion engine is used as the power source, and the power generated by the combustion of hydrogen in the cylinder is used to drive the drone to fly. Hydrogen internal combustion engines have the characteristics of mature technology and high power density, but their emission and thermal efficiency are lower than those of hydrogen fuel cells.
In this system, the battery is mainly used to improve the starting performance of the internal combustion engine, achieve fast power adjustment and recover braking energy, reduce energy waste, and reduce the fuel consumption and emissions of the hydrogen internal combustion engine under some working conditions, and improve the overall economy and environmental protection.
Because the hydrogen internal combustion engine-battery hybrid system needs to burn hydrogen in the cylinder to generate power, it is generally used in relatively large aircraft.
China's first self-developed general aviation aircraft powered by hydrogen internal combustion engine is equipped with a 2.0L zero-emission supercharged direct injection hydrogen internal combustion engine, using high-pressure gaseous hydrogen storage, hydrogen storage weight of 4.5kg, hydrogen internal combustion engine maximum thermal efficiency of more than 43%, comprehensive thermal efficiency of more than 40%.
(3)Hydrogen fuel cell-solar-battery hybrid system
In addition to fuel cells and batteries, solar panels have also been introduced.
Solar panels convert solar energy into electricity during the day when there is enough light to replenish the drone's flight, or to recharge the battery.
The fuel cell is the main continuous energy supply device, and the battery plays a role in balancing power, storing energy, and ensuring the operation of the drone at night or when the light is insufficient.