Basic requirements for aircraft power supply systems

The basic requirements for aviation and aerospace power supply systems are the same, only some aspects are different. For example, aerospace power supply systems are generally maintenance-free, because it is difficult to maintain the power supply system in orbiting spacecraft.

The basic requirements for the power supply system are: reliability, equipment cost, maintainability, weight and power supply quality. If all the power supply systems that meet the above requirements are counted as 100 points, the share of each requirement is: 30 points for reliability, 24 points for equipment cost, 20 points for maintainability, 20 points for weight, and 6 points for power supply quality. This shows that reliability requirements are the most important. On the basis of these basic requirements, requirements for testing, security, safety, and airworthiness are also derived.

Reliability is a measure of success rate, usually expressed in mean time between failures (MTBF), measured in hours of operation. Sometimes it is also expressed by its inverse – the failure rate, which is the number of failures per thousand operating hours. Each power supply on an aircraft or spacecraft should be able to operate independently of any other power supply on board, the failure of one power supply should not render the other power supply incapacitated, and each power supply should be capable of starting and supplying power by itself. At the same time, the failure of the power supply should not cause the failure of the electrical equipment it is connected to, and the failure or combination of failures of any component of the electrical system should not lead to an unsafe state, and it will not expand the failure or cause serious accidents such as fire. High reliability comes from good design, careful manufacturing, thorough inspection, rational use, accurate installation and correct maintenance.

Equipment cost is an important factor that must be considered. Due to the extensive use of high-tech in the electrical system of aerospace vehicles, the cost of materials, devices, structures and tests is very expensive, so reducing equipment costs is an important prerequisite for the application of the equipment or components.

Maintainability is closely related to the tactical-technical performance of the aircraft. Due to the increasing complexity of airborne equipment, the failure rate has increased accordingly. Therefore, fault diagnosis and troubleshooting can be realized quickly and effectively, and the equipment can be restored to a good state, which can improve the attendance rate of civil aviation aircraft and improve the combat effectiveness of military aircraft. Modern aerospace electrical systems all have an internal automatic test (BIT) function, which performs initial self-test and operational self-test on the system or components, and finds and isolates faults at any time to improve maintainability.

Reducing the weight of aerospace electrical systems and devices will not only improve the performance of aerospace vehicles, but also contribute to their economics. When discussing weight, not only the weight of the equipment itself, but also its additional weight, such as the weight of the equipment mounting structure and derived weight in the cockpit or air-conditioning cabin, must be considered. Factors such as the increase in fuel weight caused by its internal consumption (loss) should be considered for generators or power converters. Careful design and manufacture can reduce the weight of the power generation system, so that the electrical, magnetic, insulating and mechanical properties of materials and components can be fully utilized. In addition to this, attention must also be paid to the influence of power quality on the weight of electrical equipment.

Power quality (Power Quality), strictly speaking, is mainly measured by indicators such as voltage, frequency and waveform. In a general sense, it refers to high-quality power supply, including voltage quality, current quality, power supply quality and power consumption quality. It can be defined as: the deviation of voltage, current or frequency that causes electrical equipment to fail or not work properly, and its content is the power supply system characteristics defined in relevant standards, including steady-state and transient characteristics, voltage, frequency and waveform characteristics.

Electromagnetic compatibility is the ability of a system and its components to perform their functions as specified in the general electromagnetic environment. It is necessary to prevent the interference signal in the power supply system from affecting the operation of the electrical equipment, and at the same time to suppress the interference generated by the electrical equipment from affecting the work of the power supply system.

The requirements for the power supply system are put forward under the harsh working conditions of aerospace vehicles. It can be seen that there is a big difference between the aerospace power supply system and the power supply system of the general industrial transportation sector, and the personnel engaged in the aerospace electrical business shoulder greater responsibilities.