Advances in Power Electronics

Volume 2016, Article ID 4705709, 9 pages

http://dx.doi.org/10.1155/2016/4705709

## High-Voltage Converter for the Traction Application

^{1}Moscow Aviation Institute (National Research University), Volokolamskoe Shosse 4, A-80, GSP-3, Moscow 125993, Russia^{2}Joint-Stock Company “Transconverter”, Malaya Kaluzhskaya Street 15/17, Moscow 119071, Russia

Received 28 March 2016; Accepted 29 May 2016

Academic Editor: Pavol Bauer

Copyright © 2016 Sergey Volskiy et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

High-voltage converter employing IGCT switches ( V) for traction application is presented. Such a power traction drive operates with an unstable input voltage over 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.

#### 1. Introduction

Nowadays, most suburban trains in Russia have 2 head carriages, 5 or 6 motor carriages, and 3 or 4 auxiliary carriages [1]. Thus suburban train consists from 10 or 12 carriages. The traction driver is mounted at every second van of the train. It has nominal output power of 1200 kW at the unstable supply voltage ( V DC) in the contact network. Each traction drive supplies 4 brushed electric DC motors, which are connected in series. Used DC motors have a rated voltage of 750 V DC and nominal power of 250 kW.

Each traction drive contains contactor equipment and 18-item power circuit breakers and power starting resistors, which carry out start-up and regulation of the train speed. Numerous efforts to use semiconductor power traction drive instead of obsolete and unserviceable 18-item power circuit breakers with power starting resistors were not successful.

The difficulties of designing semiconductor power high-voltage converter for suburban trains in Russia are the following:(i)The wide range of input voltages (from 2000 V up to 4000 V DC) with possible short single impulses up to 5000 V DC and with duration up to 10 ms.(ii)The wide range of environment temperature (from minus 50°C up to plus 45°C) and presence of high humidity, frost, and hoarfrost.(iii)The absence of high-frequency high-voltage power semiconductor devices and capacitors and other elements, which are required to solve these problems.It is known that using the high-frequency principle of the electrical energy transformation is an effective and attractive mean for the power converters. It provides the advantage of reducing their weight, sizes, and cost. However, the use of high operating frequency for the power converters leads to the number of simultaneous problems. The important problem is related to the defence circuits of the power switches where the power losses are increasing in conformity with the frequency rise.

It should be noted that total losses in defence circuits for the converters of the Russian suburban trains are much higher because of the high supply voltage V DC [2–4]. Owing to this high-voltage level the power losses are increasing times in comparison with supply voltage 750 V DC or 1500 V DC.

Thus, the development of the defence circuits in such converter application is prime importance. Thereto, during the design process of defence circuits design, it is necessary to solve two conflicting problems. The first one is to provide normal operation for the semiconductor devices and could be solved by increasing of the components of the snubber circuit. The second problem is to minimize the losses in the protection circuit and should be solved by reducing the values of the parameters of the snubber circuit. The authors suggest a compromise solution of these problems.

Thus the described difficulties in designing a power traction drive require unusual approaches and decisions in designing high-voltage converter as a system, as well as in choosing power device and snubber circuits, control systems, and so forth. In this paper the authors are offered new power high-voltage high-frequency converter for traction drive employing IGCT switches ( V).

#### 2. The Power Circuit of the Proposed High-Voltage Converter

As noted, the required output power of the high-voltage converter is 1200 kW. However the maximum power of the traction drive, which is equal to the multiplication of the peak current after the input smoothing filter and maximum input voltage, must be not less than 1700 kW because of the wide range of voltages in the contact network (from 2000 V up to 4000 V DC). It is obvious that the design of highly reliable and relatively cheap traction drive for such power and high-voltage can be conducted only on the base of high-frequency power IGCT switches.

To get the high level of traction drive responsibility, it is necessary to specify very rigid requirements for the reliability of the power converter operation. Therefore it is thought to be reasonable to choose such principle of the work of the power circuit, which could provide the following:(i)The power semiconductor devices will have the best working conditions, particularly during transient processes.(ii)The control of the power high-voltage converter based on the rigid algorithm (independent from input voltage level, load value, etc.) must have a much higher fraction than control based on the flexible algorithm.After careful consideration of existing decisions and methods, a power Pulse Width Modulation (PWM) high-voltage converter was chosen [2, 4–8]. The open input of the converter makes the output characteristic rigid and, accordingly yields more simplifier control. The PWM technology for power high-voltage converter operating at constant frequency improves operation under no-load.

The first one is to provide normal operation for the semiconductor devices and could be solved by increasing of the components of defence circuits. The second problem is to minimize the losses in the protection circuit and should be solved by reducing the values of the parameters of defence circuits. The parameters of the defence circuits depend on choosing the power self-commutated devices. Therefore specific technical requirements and properties of the power semiconductor devices are considered [2, 6, 9–13]. Some of them are the following:(i)High current (rms, average, peak, and surge) and voltage (peak repetitive, surge, and DC-continuous).(ii)Low losses (conduction and switching).(iii)High reliability (low random failures, high power and temperature cycling, and high blocking stability).An important quality is improved robustness and low device coast.

By output current ( = 400 A) and supply voltage ( = 2000 V) properties parameters of power high-voltage semiconductor devices such as GTO (Gate Turn-off Thyristor), IGCT (Integrated Gate-Commutated Thyristor), ETO (Emitter Turn-off Thyristor), and IGBT (Insulated Gate Bipolar Transistor) are analyzed for Russian suburban train applicationand summarised in Table 1, where and are turn-off and turn-on energy switching losses over one period; is voltage saturation of semiconductor switch; is power consumption of control system.The best parameters of considered power semiconductor devices are in bold font. According to the above-described requirements IGCT devices are selected for traction high-voltage converter of suburban trains.