The aircraft electrical system is composed as shown in Figure 1, including two parts: power supply system and electrical equipment.
The power supply system is a general term for the electrical energy generation, transformation, transmission and distribution parts of aerospace vehicles, including everything from the power supply to the input terminals of the electrical equipment. It is usually divided into two parts: the power supply system and the power transmission and distribution system. The power supply system is the part from the power supply to the power bus, and the power transmission and distribution system is the part from the power bus to the input end of the electrical equipment.
The aircraft power system is composed of main power supply, auxiliary power supply, emergency power supply, secondary power supply and ground power sockets. The main power source of modern aircraft is a power generation system directly or indirectly driven by aero engines. Usually, one engine drives one or two generators. On a multi-engine aircraft, the number of generators driven by each engine is the same. Aircraft generators are driven by aircraft engines, which are both reliable and economical, while aircraft main power sources composed of multiple generators are more reliable. When the main power supply is not working, the electrical energy required by the aircraft’s electrical equipment can be supplied by the auxiliary power supply or the airport power supply through the ground power socket on the aircraft. There are two types of auxiliary power supplies: aviation batteries and auxiliary power devices. Small aircraft mostly use aviation batteries, and large aircraft mostly use auxiliary power devices. The auxiliary power unit is composed of a small on-board engine, a generator, or a hydraulic pump or air compressor. When the main power supply is not working, the auxiliary power unit is started to work, so that the generator generates electricity or the hydraulic pump provides pressurized oil to the electrical equipment Power, oil or gas supply with hydraulic and pneumatic equipment. The engine is usually started by an electric motor. The auxiliary power unit can work both on the ground and in the air.
Once the main power supply fails during the flight, the emergency power supply will be used. Commonly used emergency power sources are aviation batteries and ram air turbine generators. When the main power supply is normal, the ram air turbine generator is stored in the aircraft body or wing, and is released after a failure. The oncoming air blows the turbine to drive the generator or emergency hydraulic pump. Due to the small capacity of the emergency battery and the ram air turbine generator, they can only supply power to the important electrical equipment on the aircraft to ensure the aircraft’s emergency return to the airport and landing.
When an aircraft conducts ground inspection or starts an aero engine at an airport, it is often powered by the airport ground power source. Generally, when ground power is supplied, the on-board power supply is not allowed to be connected to the aircraft power grid.
The secondary power supply is used to transform the electrical energy of the main power supply into another or multiple types of electrical energy to supply power to some electrical equipment on the aircraft. According to the power supply mode, the secondary power supply has two types: centralized power supply and decentralized power supply. Centralized secondary power supply refers to one or two secondary power supplies to supply power to the electrical equipment on the aircraft that uses this kind of electrical energy, one of which is the primary secondary power source and the other is the backup secondary power source. Distributed power supply means that each electrical equipment has its own required secondary power supply. Sometimes this secondary power supply is placed inside the equipment, which is called the internal power supply of the equipment or the internal power supply of the machine.
The purpose of this structure of aircraft power supply is to: ①Ensure continuous and reliable power supply to electrical equipment under various conditions;
② Ensure that high-quality power is provided to the electrical equipment when the main power supply is normal, and that the aircraft can land in an emergency and safely when the main power supply fails;
③Enable the aircraft to take off and land on its own without relying on the support of ground equipment, that is, to have self-sufficiency, which is particularly important for military aircraft. Some aircraft have a backup power supply to increase the power supply margin.
There are four control modes for the aircraft power distribution system: conventional, remote control, automatic and solid-state power distribution. The power distribution line of the conventional power distribution system is introduced into the power distribution center in the cockpit, which is used in small aircraft. The power distribution bus bar of the remote power distribution is close to the electrical equipment, and only the control line is introduced in the cockpit, and the pilot controls the electrical equipment through the contactor. Modern large and medium-sized aircraft use this power distribution method to reduce the weight of the power grid. In the automatic power distribution system, the computer transmits control information and status signals through a multi-channel data bus, and controls the electrical equipment through contactors or relays. This type of power distribution grid is light in weight, reliable in work, and highly automated. An automatic power distribution system that replaces contactors or relays with a solid-state power controller is called a solid-state power distribution system.
A schematic diagram of the layout of the power supply system on a dual-generation channel aircraft is shown in Figure 2.
Most spacecraft work for a long time and require a large power supply capacity. The weight of the power supply accounts for 15% of the weight of the entire spacecraft~
25%. Most spacecraft are unmanned, and their work completely relies on the power supply and power distribution system, so the spacecraft power supply system is required to have the characteristics of long life, high reliability, and maintenance-free.