The dissertation is devoted to the solution of the actual scientific and applied prob-
lem, which consists in the development of the theory and principles of construction of non-reversible bi-directional DC converters with transformer galvanic isolation, which are a type of two - stage DC/DC converters. In work carried out development and research of the such converters based on a relatively new and little researched concept - the concept of separated commutation. Converters with separated commutation (CSC) are built on the ba-sis of inhomogeneous inverter-rectifier units: the topology of the one stage is based on voltage-source-inverter (VSI, or voltage-fed, VF) topology, and the topology of the other stage is based on current-source-inverter (CSI, or current-fed, CF) topology; the stages are connected by a transformer. A special algorithm for synchronous control of the both stages switches - algorithm of separated commutation (ASC) - provides favorable conditions for switching: for the VF stage switches the turning-on is natural (zero voltage switching, ZVS) and the turning-off is forced with the help of capacitive snubbers; for the switches of CF stage the turning-off is natural (zero current switching, ZCS) and the turning-on is forced with the help of inductive snubber (its role can be played by the transformer's leakage inductance). Limiting switching losses allows to increase the conversion frequency. The non-reversibility of the converter with the CF stage while maintaining the property of bi-directionality is ensured by the presence in the CF stage the four-quadrant switch (switches). For CSC with a bridge circuit with 4-quadrant switches based on MOSFET in the CF stage, the advantages and disadvantages of synchronous and independent control of the composite switches are identified. For CSC with IGBTs in CF stage, the use of a number of schemes with 4-quadrant switches was analyzed, with along with the bridge scheme with 4-quadrant switches, A CSC with an asymmetric topology of the CF stage is proposed and investigated, in which the current of the secondary winding flows not through 4, but through 3 switches. . It is proposed to limit its value to a level that provides the relative total duration of switching intervals for a period of about 10%, which is equivalent to the relative value of the short-circuit voltage xs* of the transformer within 16%. For CSC transformers of rod design, a expression for xs* was found. the value of the specific capacitance of snubber capacitors (per 1 A of IGBT switching current) was determined to provide approximately twofold reduction of the IGBT's turning-off energy with snubber relative to turning-off energy without snubber. The expediency of using the proposed principles of construction of PRC as a compo-nent of battery energy storage systems for the amplifying point of the traction power supply system of the DC railway (catenary voltage 2 - 4 kV) was considered. A symmetrical topology with a 4-quadrant key is selected for the CF lstage, the nominal output current of the converter is 200 A, the CF switches have the class of 6.5 kV, frequency is 1000 Hz, the voltage of the VF stage is 600 V, the switches of this stage have class 1200 V, the switching losses for the switches of this stage are about 7% of static. Estimation of the mass of the transformer - about 1.3 tons, the battery - from 7.15 to 21.5 tons, which allows you to place them on board the train.
