There are a large number of equipment in modern aviation and spacecraft. The equipment that operates on hydraulic energy is called hydraulic equipment, the equipment that operates on pneumatic energy is called pneumatic equipment, and the equipment that operates on electrical energy is called electrical equipment.
- Aircraft electrical equipment
According to their functions, the electrical equipment on the aircraft can be divided into: ①The control equipment of the engine and the aircraft. For example, engine starting, fuel injection, ignition equipment; engine thrust or speed control equipment; aircraft instrumentation, flight control, navigation, communication and fuel supply equipment; landing gear retractable and door opening and closing equipment, etc. ②Equipment required for life and work of personnel on board. Such as cabin environment control system, lighting and heating equipment, oxygen equipment, safety and life-saving equipment, etc. ③The equipment needed to complete the flight mission. This is related to the type and purpose of the aircraft. For example, military aircraft have fire control equipment, bomb targeting equipment, and lighting reconnaissance equipment; civil aircraft have cabin lighting equipment and kitchen equipment.
The electrical equipment on the aircraft can be divided into: ① DC electrical equipment, such as DC motors. ② AC power equipment, such as asynchronous motors. AC power equipment can be divided into equipment that has nothing to do with or has little to do with frequency, and equipment that requires stable power frequency. Some equipment (such as electric gyroscopes and some electric instruments) require a three-phase alternating current with a very stable frequency and a sinusoidal waveform. AC power equipment can also be divided into single-phase AC power equipment and three-phase AC power equipment according to the number of AC voltage phases. ③ AC and DC dual-purpose equipment. Some electrical equipment (such as incandescent lamps) can work when powered by a DC power supply or an AC power supply, and there is no strict requirement on the frequency of the power supply.
According to the impact on the power supply after the electrical equipment is connected to the power supply, the electrical equipment is divided into the following categories: ① Electrical equipment with linear characteristics. For example, heating equipment and incandescent lighting, etc., its characteristics comply with Ohm’s law, and resistance or impedance does not change due to voltage or current. When the incandescent lamp is energized, because the filament resistance is small, there is a large current that is connected, but this current lasts for a short time. ② Motor load. When the motor load is directly connected to the grid, there is a large starting current. When the grid voltage drops suddenly, and when the speed regulating motor is braking, the running motor will become a generator, and its energy may also be fed back to the grid. ③Constant power characteristic load. There are special switching power supplies in modern electronic or instrument equipment, and their output voltage stability is very high, so the output power is basically unchanged. If the power loss is constant, the input power is constant, which makes this type of electrical equipment have constant power properties for the power supply, which will have a greater impact on system characteristics. ④ Equipment that generates harmonic currents. The widespread application of power electronic devices has brought pollution to the power supply, because the power electronic devices in the power electronic devices are non-linear devices, which distorts the current waveform of the AC power supply, resulting in distortion of the voltage waveform; increasing the current pulsation of the DC power supply, resulting in voltage The pulsation increases, so it must be taken seriously. ⑤Equipment with current and power impact. The switching on and off of the electrical equipment or the sudden change of the internal power consumption of the electrical equipment will cause the change of the power supply voltage (commonly called the transient surge voltage), or cause a voltage spike with a duration of several microseconds. The spikes and surges of the power supply voltage in turn affect the work of various electrical equipment on the power grid.
Electric equipment can be divided into three categories according to its importance: key equipment, important equipment and general equipment. Key equipment such as flight control systems and cockpit displays, important equipment such as anti-icing and de-icing equipment, environmental control systems and electronic equipment used to complete flight tasks, and general equipment such as kitchen heating and entertainment equipment. Electrical equipment has different requirements for the power quality of the aircraft power supply system. There are clear requirements for the magnitude of DC voltage ripple, AC frequency stability, waveform distortion, and three-phase voltage symmetry. The purpose is to make the equipment have predetermined performance. But this requirement cannot be too high.
Conversely, the power supply also has certain requirements for electrical equipment. For example, the selection of the power supply voltage of electrical equipment should meet the standard requirements, and it is not advisable to propose special voltage requirements, so as not to complicate the power supply equipment. Generally speaking, when the power consumption of AC power equipment is greater than 500V·A, three-phase power supply should be used.
In short, the electrical equipment on the aircraft requires the supply of a certain type and quality of electrical energy, but the type and quality of electrical energy should be limited to a certain degree to meet the standardization requirements. There are many types of electrical equipment, which in turn will change the power quality of the power supply and thus change the operating characteristics of the equipment. Therefore, it is very important to understand the characteristics of power supplies and electrical equipment and their mutual influence.
- Spacecraft electrical equipment
There are many classifications of spacecraft loads, and the main classification methods are as follows.
According to the different energy sources, the load can be divided into: direct bus load and indirect bus load. Most electrical loads generally obtain electrical energy directly from the bus, and some electrical loads obtain high-efficiency and high-power energy directly from the power generation device, and some loads reduce the impact on the bus, such as some pulse loads, directly from the power generation device. Energy storage devices obtain energy. The indirect bus load means that the bus is transformed by the secondary electric energy and then supplied to the user’s load.
According to different flight missions and safety, the load can be divided into: flight critical load, mission critical load and general load. Flight critical load generally refers to the load necessary for the spacecraft to maintain attitude and communication; mission critical load generally refers to the load of the spacecraft to complete a specific task; general load generally refers to the auxiliary electrical load of the spacecraft.
According to the different characteristics of the load itself, the load can be divided into: resistive load, capacitive load, inductive load, resistive-capacitive inductive load, pulse load, frequency load, etc.
According to the purpose of the load, the load can be divided into: command load, telemetry load and power load, etc. The command load is generally a relay package, etc.; the telemetry load is generally a resistive-capacitive load for the spacecraft to provide telemetry; the power load is generally a load that completes the function of the spacecraft.