AC-AC converters as shown in Fig. are frequency converters. They produce an AC voltage in which both the frequency and voltage can be varied directly from the AC line voltage, ., from a 60- or 50-Hz source. There are two major classes of AC-AC, or so-called direct static frequency converters, as shown in Fig. . 1. Cycloconverters, which are constructed using naturally commutated thyristors. The commutation voltage is ensured by the supply voltage. These are so-called line commutated converters. 2. Matrix converters, which are constructed using full-controlled static devices, such as transistors or GTOs (gate turn-off thyristors). Cycloconverters In Figs | 3 AC-AC Conversion Sandor Halasz Introduction Budapest University of Technology and Economics Cycloconverters Matrix Converters Introduction AC-AC converters as shown in Fig. are frequency converters. They produce an AC voltage in which both the frequency and voltage can be varied directly from the AC line voltage . from a 60- or 50-Hz source. There are two major classes of AC-AC or so-called direct static frequency converters as shown in Fig. . 1. Cycloconverters which are constructed using naturally commutated thyristors. The commutation voltage is ensured by the supply voltage. These are so-called line commutated converters. 2. Matrix converters which are constructed using full-controlled static devices such as transistors or GTOs gate turn-off thyristors . Cycloconverters In Figs. and the two typical types of cycloconverters are presented. In the first case there are two three-phase midpoint controlled rectifiers connected back to back. The second case shows two three-phase bridge rectifier converters connected back to back. Both are used for three-phase to three-phase conversion. In Fig. the single-phase output voltage and current waves are presented for the FIGURE Classification of frequency converters. 2002 by CRC Press LLC R S T V 60 Hz FIGURE Cycloconverter scheme with three-phase midpoint controlled rectifier. R S T FIGURE Cycloconverter scheme with three-phase bridge controlled rectifier. bridge rectifier circuits. The output voltage Va and current ia have Va1 and ia1 fundamental components with 01 phase displacement and numerous harmonics. Because of the load inductance the current harmonics will be significantly lower than the voltage harmonics. The firing angles are aP and aN for the p and n converters respectively. In general the controls are designed so that only the thyristors of either the p or n converter is firing which produces a current in the desired direction. During this period the other
