## 1 Introduction
In a further part of this article, a review and preliminary analysis of multi-pulse rectifiers used in TRU and ATRU units is presented [3,4]. Based on the above, it can be concluded that the problem of multi-pulse rectifiers is very important in the area of the ever-increasing trend of the electrified aircraft. The concept of a more electric aircraft has been known for a long time, but only with the development of power electronic devices, components and systems based on advanced semiconductor technology, has it been implemented to modern aviation in the field of advanced power systems. Systems of this type use variable frequency sources as well as high voltage direct current (HVDC) architecture and alternating current HVAC (High Voltage Alternating Current). In turn, the implementation of the trend of a more electric aircraft contributed, among others, to increase the efficiency of the entire aircraft in terms of increasing its reliability, flexibility and economy. Technological solutions in line with the MEA/AEA concept are constantly evaluated and have enormous potential in terms of weight, quality and operating costs. Review and Analysis of Multi-Pulse Rectifiers Used in the TRU and ATRU Units in the Field of the PES System in Accordance with the MEA Concept  
Currently, in technologically advanced aviation (military, civilian), and increasingly in designed on-board autonomous power systems, one can observe a dynamic trend in the development of power electronic multi-pulse rectifiers in the PES system, particularly on aircrafts compatible with the concept of the electrified aircraft. Multi-pulse rectifiers (6-, 12- and 18-, 24-impulse), determined for the needs of, among others, aviation issues as so-called transformer-rectifier devices TRU, are a key component of the power electronic system of contemporary military aircrafts (F-22 Raptor and F-35), as well as civilian ones (A-380 and A-350 XWB, B-787), and play a key role in the implementation of the trend of a more electric aircraft. When performing a preliminary analysis of rectifiers used by TRU and ATRU units, it should be noted that aviation systems converting AC to DC current (AC to DC) used in aviation are obliged to provide \"rectified\" voltage in two different ranges in the electricity network of more electric aircraft (MEA). They consist of multiphase generators and rectifier circuits. Rectifiers of this type are power electronics systems designed to convert AC voltages into DC (unidirectional) voltages. Usually they are powered by single or three-phase sinusoidal voltages. With reference to the time waveform of the unidirectional output voltage, determined by the rectified voltage whose value depends on the type of rectifier (voltage drops), the properties of the applied filter and the load affecting its efficiency consist of appropriate sine voltage sections supplying the rectifier. DC voltages received from rectifier circuits always contain higher harmonics, which negatively affect the operation of drive systems of electric engines. The systems responsible for converting AC voltage to DC are usually non-linear systems that convert electrical energy and cause distorted currents and voltages in the electrical network of the aircraft. In general, AC distribution systems require a longer processing time than DC systems. It should be noted that the conversion sequence is short (or even non-existent) if the AC sources and loads are connected to the AC mains, and the DC sources and loads are connected to the DC network. In such cases, processing equipment is unnecessary and there are no associated costs. In turn, higher harmonics of substation load current cause additional voltage drops in the substation power supply network and the resultant voltage is always deformed. Hence, there is a need to minimize the harmonic content in the power supply in ATRU systems.