375 15th INTERNATIONAL CONFERENCE ON MICRO/NANOTECHNOLOGIES AND ELECTRON DEVICES EDM 2014 978-1-4799-4668-6/14/$31.00 ©2014 IEEE Abstract – In this study the novel transformerless AC-voltage converters with reduced number of switches are considered. The paper presents mathematical models, control and energy characteristics, and optimal control regions of the converters. The properties of the novel transformerless AC-voltage converters and converters described in [1,2] are compared according to such criteria as voltage control range, quality of the consumed and generated power, and total power rating of the reactive components. Computer simulation of the novel converters was implemented. The results of this research can be used to choose the converter for a specific application. Index Terms – transformerless AC-voltage converter, pulse- width control. I. INTRODUCTION T HE APPLICATION field of AC-voltage converters is very wide. They are used for control and stabilization of supply voltage, as compensators of voltage asymmetry or distortion, as soft starters of induction or synchronous motors etc. Linear voltage converters, based on autotransformers or multisectional windings transformers, are bulky, have low response time and their automatization is difficult. Switch mode voltage converters such as series voltage injection converters (with phase or pulse-width control) [3] – [5] and tap changing converters have many advantages in comparison with linear voltage converters [6] – [8]. However they also require a transformer, that has a significant effect on size, weight and price of the converter. The most popular industrial voltage converters are SCR- based converters because of low price, compact size and high reliability. However, they have many well-known disadvantages [9]. First of all, SCR-based converters are not capable to boost voltage. Another problem is that SCR- based converters have poor quality of output voltage and input current, which is very important nowadays due to the increasing stress of switch mode devices on supply systems [10]. In addition, the response time of SCR-based converters is limited by supply voltage frequency, which is not enough in some applications. Transformerless AC-voltage converters based on fully controlled bidirectional switches [11] – [16] are becoming more and more popular nowadays due to compact size, high quality of consumed and generated power, high response time etc. Much attention is paid to topologies which were derived from well-known DC-DC converters [11,13]. Many new converters were also introduced [14] – [16]. In this paper the novel transformerless AC-voltage converters and the converters described in [1,2] are considered. Each power circuit includes only two transistors, which results in a low price of the converter and a simple control system. II. PROBLEM DEFINITION The purpose of this study is to analyze and compare properties of the novel transformerless AC-voltage converters and converters described in [1,2]. It is necessary to build mathematical and computer models of novel converters, to obtain their control and energy characteristics (and some necessary characteristics for converters described in [1,2]), and to define optimal control regions of the considered converters. III. THEORY Power circuits of the considered AC-voltage converters are depicted in Fig.1, where circuits Fig.1a, b are the novel circuits. Each converter includes two three-phase bidirectional switches (S1, S2), which operate in such a way that when one switch is ON the other one is OFF. The output voltage is controlled by a pulse-width control technique at high frequency. A special feature of the considered converters is that there are two possible connection types of supply source (with inductances L 1 for circuits a, b, c) and load: in one connection it is necessary to have access to all 6 connectors of source while in the other connection – to all 6 connectors of load. It is important to note, that converters Fig.1a, b are universal as their properties are equal in both connection types. Properties of converters Fig.1b, c depend on the connection type, so an analysis of the converter Fig.1b has been done for both cases, which are indexed as “dir” for direct connection (Fig.1b) and “rev” for reverse connection. In reverse connection the converter Fig.1c is a well-known boost AC-voltage converter [13], so this connection is not considered in this study. To obtain energy and control characteristics of the considered voltage converters the direct methods of analysis (ADE) [17] were used. An analysis was done for a resistant- inductive load. Mathematical models of converters were built in the form of a differential equation system with discontinuities parameters Three-Phase Transformerless AC-Voltage Converters with Reduced Number of Switches Roman L. Gorbunov 1 , Graduate Student Member, IEEE, Gennadiy S. Zinoviev 2 , Member, IEEE 1 National Research Tomsk Polytechnic University, Tomsk, Russia 2 Novosibirsk State Technical University, Novosibirsk, Russia