The electronic protection unit of a high-voltage converter designed for operation with an input rated voltage of 3000 V DC is considered. It contains a high-voltage semiconductor power switch, in parallel to which a snubber resistor and a varistor are connected. The protection unit in question performs three functions. Firstly, it limits the input current of the converter during start, secondly, it provides protection against input overvoltage’s, and thirdly, it limits the input current in the abnormal overcurrent conditions of the converter. Taking into account the permissible operation of the high-voltage converter and the reliable operation of the power switch of the protection unit, all three functions impose contradictory requirements on the parameters of the snubber resistor. A study of a high-voltage converter with the considered protection unit has been carried out when limiting the input inrush current, at specified normalized input overvoltage’s and abnormal overloads. Taking into account the conducted research, a compromise solution was found and an algorithm for selecting the parameters of the snubber resistor and varistor of the high-voltage converter protection unit was proposed. This paper presents bench test results for the protection unit of a PSN110 Y1 high-voltage converter $(110 \mathrm{~kW})$. The unit was tested under a normalized $10 \mathrm{kV}, 2.5 \mathrm{~ms}$ overvoltage pulse. The findings are relevant for engineers designing protection systems for highvoltage converters in industrial and on-board applications.

In this article, the operating electromagnetic processes of a three-phase Grid-tie inverter are studied and the calculation of power circuit parameters is presented. Such a converter contains a three-phase bridge circuit, three output phase chokes and a control system using a pulse-width modulation. Mathematical models of the considered three-phase converter in abc- and dq0-coordinates are proposed. Taking into account the assumptions made and the first harmonic components of the output current and switching functions of power transistors, a relatively simple expression for calculating the amplitude of the output current ripple is obtained. An inequation for finding the minimum boundary value of the inductance of the output phase chokes is derived. Taking into account the topology of the power circuit of the Grid-tie inverter under consideration, an equation for calculating the minimum value of the input voltage DC at which the output current in form and phase coincides with the output voltage AC is defined. The obtained results are interesting for the developers of three-phase Grid-tie inverters, which can be used in renewable energy, in AC traction drives in the braking mode, in test-benches designed for testing AC power converters and electric machine generators, etc.

When designing test-benches SI150 NF4 and SI310 NF4, it was decided to use the twelfth-pulse rectifier to generate DC link voltage. Three well-known types of the twelfth-pulse rectifier are considered. Expressions for calculating the parameters of these types of rectifiers are obtained. For clarity, the parameters of each type of rectifier considered are normalized to the parameters of the twelfth-pulse rectifier with a balanced transformer. The analysis showed that the lowest current of the power diode has the twelfth-pulse rectifier with a balanced transformer. At the same time, power diodes have the lowest reverse voltage in the series twelfth-pulse rectifier. Expressions are obtained and the power of static losses in power diodes of three types of the twelfth-pulse rectifier are surveyed. For this purpose, a linear approximation of the volt-ampere characteristic of power diodes was used, taking into account the threshold voltage and the active resistance of the power diode in the open state. For the test-bench SI310 NF4, the junction temperatures of the power diodes used in the twelfth-pulse rectifier were additionally surveyed. For this purpose, it was developed a thermal model and it was obtained expressions for calculating the junction temperature of a power diode depending on the average output current of the rectifier. The results obtained show the advantages and disadvantages of various types of twelfth-pulse rectifier. This article has practical application, it allows developers of power converters to make the right choice of the type of twelfth-pulse rectifier, and then choose the type of power diode.

The single-phase DC-DC bridge converter of fast-charging station for electric vehicles is considered. The simplified equivalent circuit is proposed, and universal mathematical model is developed which is applicable both for PWM-control and for phase control of power transistors. The developed mathematical model was tested on unit TKP43. The experimental studies acknowledged that the developed mathematical model can be used both at PWM-control and at phase control of converter. The difference between experimental and calculated data is no more than 11%. This article is of interest to specialists who develop converters for fast-charging station for electric vehicles and others power sources.

The power converter for solar photovoltaic is considered, which contains one input choke, two transistors, two diodes and two output capacitors. The phase shift of the switching transistors of such a converter provides a doubling of the ripple frequency of the input choke current. This is due to the relatively small mass and cost of the converter. The use of a solar battery as a primary source of electricity and a three-level output DC/AC converter together with a rechargeable battery as a load determine the tasks of control this power converter. It is necessary that the control system is capable of both stabilizing the output voltage and limiting the output current, and working in the mode of searching for the peak power point of the solar battery. In order to create a control algorithm, a mathematical model of power converter for solar photovoltaic has been developed. The obtained mathematical model allowed to develop a control algorithm for the power converter concerned. A prototype of a power converter with a switching frequency of transistors equals 25 kHz and with an output power of 20 kW has been tested. The results obtained during the development of the control algorithm and testing of the prototype of the PC will be useful both for engineers developing converter equipment and for software engineers developing control for pulse converters.

High-voltage impulse converter is meant for a stability test of power converters to emergency states which occur at input overvoltage impulse. It is developed with the use of two switching units based at IGBT. The proposed converter forms an output overvoltage impulse with the required values both in amplitude and in duration of rise and fall. Analytical expressions which describe transient processes in the proposed electric circuit of the converter are determined. Computer simulation using MATLAB Simulink confirmed the accuracy of the analytical expressions obtained. A prototype sample of the proposed high-voltage impulse DC converter is developed. For example, the results of using the developed converter when testing the power converter of PSN235Y2 type are presented. The article is of interest for electrical engineering specialists who develop technological equipment for manufacture and testing the power converters both for railway transport and for industrial.

The article concentrates on the parallel operation of output the three-phase power inverters in MicroGrid. The MicroGrid for an electric train is considered that contains two output three-phase inverters with a total power 400 kVA. Analytic expressions for determination of a required phase and output voltage amplitude of the three-phase inverters are obtained. The problem related to current rushes appearance when the output three-phase inverter connected to the MicroGrid is shown. For solving this problem, the control algorithm of the output three-phase inverters with the use of two proposed control modes (PLL-mode and Droop-mode) was developed. It is shown that the combination of the developed PLL-mode and Droop-mode allows excluding the output current rushes and provides an equable output power division between the three-phase inverters at the level of 5%. This article is of interest for power electronics engineers who develop MicroGrid for stand-alone power supply systems with renewable electric power sources, and also for onboard power supply systems of aircrafts, watercrafts and electric trains with the use of several parallel operating output three-phase power inverters.

The article considers a laboratory setup for testing the stability of power converters to emergency conditions arising from an input overvoltage pulse up to 10 kV with duration of up to 12 ms as a result of switching processes. Such processes take place, for example, in the electrical circuits of DC electric locomotives. The laboratory setup has been designed using two power transistors and generates at its output an overvoltage pulse with the required duration of increasing to the specified amplitude and the required duration of decreasing to the specified voltage level. The setup electrical circuit diagram is given. Analytical expressions describing transients in the setup are defined, the accuracy of which is confirmed by computer simulation in the MATLAB Simulink environment. A mock-up sample of the proposed laboratory setup is described, and the results of its use in testing the PSN235 U2 auxiliary converter intended for the 3ES4K DC series electric freight locomotive are presented. The article is of interest to electrical engineers who are in charge for developing power electronic installations with an output pulse voltage of up to 10 kV for both railway rolling stock and industrial applications.

This paper discusses an important aspect of the grid-connected power converters control for electric trains. An analysis and synthesis of the second order Synchronous Reference Frame Phase Locked Loop (SRF-PLL) is considered. The problems of synchronization, stability, and noise immunity are studied using the discrete-time theory. This approach allows one to directly study the system implemented in software, skipping the usual application of the continuous-time model using the bilinear transform and Euler's approximation. The discrete-time SRF-PLL model with the first-order loop filter is considered. This article is of interest to engineers of converter control, which should be synchronized to the grid.

The paper discusses a control system of a threephase step-up converter which in addition to control functions performs phase current correction. Study of the control system operation is carried out and expressions for calculating the maximum permissible values of error amplifier factors are obtained. Influence of the error amplifier parameters on phase current quality is investigated. At a given value of power factor the dependence of total harmonic distortion as per IEC 61000-3-12:2004 on a combination of error amplifier parameters is obtained. The conditions under which the total harmonic distortion has a minimum value are found out. This article is of interest to power electronics engineers, who aim to develop threephase AC-to-DC converters with input phase currents of high quality.

This paper describes the issue of controlling three-phase power factor corrector (PFC) for unbalanced bipolar load and input asymmetrical three-phase voltage. The method of direct power control was chosen. By means of the suggested mathematical description, the compromise to provide satisfactory harmonic composition and to stabilize output voltage, when the difference of average bipolar voltages of output capacitors is min, was found. The prototype was presented. It has 400 V, 50 Hz input voltage and 50 kVA power. The paper is of great interest for those developers of three-phase PFCs who challenging to develop units with high efficiency factor and reliable control system.

The advanced aircraft electrical power generation with voltage ±270 V DC BUS is presented. The possible consumption capacities and power consumption on regional aircraft with electric traction on takeoff and on cruise flight segment are analyzed. A battery-generator electric supply system is proposed, in which electric engines provide a traction of the plane, battery with permanent magnet generator are electric energy source. Upon that the combustion engine that works in economically mode and rotates shaft of permanent magnet generator. A power circuit of active rectifier is presented. It generates a bipolar output voltage ±270 V DC, provides a sinusoidal waveform of phase current and keeps power factor close to unity. The appliance of Enhanced Phase-Locked Loop for control system is presented. The developed special analytical and numerical computational procedures and modification of Lyapunov function method allow to determine stability areas and reveal unintended latent attractors in respect to proposed battery-generating electrical supply system. This article is of interest to developers of electrical supply systems with bipolar voltage DC in particular with a level of 270 V DC BUS

This paper presents the development of the control system for the new three-phase power factor corrector with low power losses. The problem of designing of the control system of such type of converters is described. The mathematic model of the power scheme, block diagram and operation concept of the control system are presented. The prototype of 400 V input tree-phase voltage, 50 Hz, 670 VDC output voltage and 70 kW was designed and successfully tested. This paper was written to attract the three-phase power factor corrector developers who challenge to design converters with high power factor and reliable control system.

The power circuit of a new three-phase power corrector having reduced power losses is considered. The power circuit mathematical model and the control system operation principle are described. A specific feature of the single-loop control of the device active power with the input phase current synchronized with the input phase and with stabilizing the output DC voltage is shown. The results from computer simulation of the device prototype designed for the 400 V 50 Hz input three-phase voltage, for the 800 V DC output voltage and 70 kW output power are presented. The article is of interest for designers of three-phase power correctors with high efficiency and a reliable control system.

Three-phase AC/DC boost converters performing power factor correction are widely used at present. They ensure electromagnetic compatibility of the converter with the network and decrease the network load by making the phase currents proportional and co-phase with the phase voltages. Typically, a three-phase AC/DC boost converter contains input power reactors and a three-phase bridge rectifier. Better power factor value is achieved in such devices by applying three choppers based on bidirectional power switches or power transistor legs. However, a large number of controllable devices and components, the current states of which depend on their pre-switching state, is a factor that adds much difficulty to studying the electrical processes in the converter. A principle of reducing the number of equivalent circuits necessary for studying the electrical processes in the converters under consideration is described. The proposed principle follows from assumptions based on the target operating mode of an AC/DC boost converter. Three converters have been investigated by applying this principle of reducing the number of equivalent circuits with using the electric circuit theory (Kirchhoffs equations or the mesh-current method) techniques. Examples of applying the proposed approach for studying three-phase AC/DC boost converters (so-called Vienna rectifiers) are given. The proposed approach made it possible to decrease the number of analyzed equivalent circuits down to eight ones, and the conclusions drawn from an analysis of the obtained equivalent circuits were used to select the best configuration of a three-phase AC/DC boost converter. The obtained results are of interest for developers of three-phase power factor correction converters, uninterruptible power sources, frequency converters, and other AC/DC converters complying with more stringent requirements for the power factor, efficiency, and device prime cost.

High-voltage converter employing IGCT switches (VDC=2800 V) for traction application is presented. Such a power traction drive operates with an unstable input voltage over 2000⋯4000 V DC and with an output power up to 1200 kW. The original power circuit of the high-voltage converter is demonstrated. Development of the attractive approach to designing the low-loss snubber circuits of the high-frequency IGCT switches is proposed. It is established on the complex multilevel analysis of the transient phenomena and power losses. The essential characteristics of the critical parameters under transient modes and the relation between the snubber circuit parameters and the losses are discussed. Experimental results for the prototype demonstrate the properties of new power circuit. The test results confirm the proposed high-voltage converter performance capability as well as verifying the suitability of the conception for its use in the Russian suburban train power system and other high-voltage applications.