This cycloconverter is a step down cycloconverter. It converts the incoming line frequency to a lower frequency by the use of SCRs. The two bridge type. Variable frequency mostly cycloconverter is used as it involves single stage conversion. Fig (1) Power Electronic Converters Cycloconverter is a power electronic circuit which converts fixed AC input to variable voltage, variable frequency output. It is said to be step down cycloconverter when the output frequency is less than. Cycloconverters • 1. 1 Abstract— A cycloconverter is a type of power controller in which an alternating voltage at supply frequency is converted to an alternating voltage at load frequency without any intermediate D.C. This paper describes the working principle and operation of single phase to single phase cycloconverter and some applications. Keywords— Static frequency changers (SFCs); Intergroup reactor (IGR) I. INTRODUCTION Cycloconverters are static frequency changers (SFCs) designed to produce adjustable voltage adjustable frequency AC power from a constant voltage constant frequency AC source without any intermediate DC link. ![]() The basics of these converters were proposed by Hazeltine in 1926, and the first cycloconverter was built in 1930s using mercury arc valves for converting standard 50Hz supply to single-phase Hz supply for use in ac traction system in Germany. However, the practical and commercial utilization of these schemes waited until the SCRs became available in the 1960s. With the development of large power SCRs and microprocessor- based control, the cycloconverter today is a matured practical converter for application in large-power low-speed variable- voltage variable-frequency (VVVF) ac drives in cement and steel rolling mills as well as in variable-speed constant- frequency (VSCF) systems in aircraft and naval ships. Basically, cycloconverters are of two types: i) Step-down cycloconverters: The output frequency fo is lower than the supply frequency fs. Ii) Step-up cycloconverters: The output frequency fo is more than the supply frequency fs. Symbol of cycloconverter II. PRINCIPLE OF OPERATION The basic principle of operation of a cycloconverter is explained with reference to an equivalent circuit shown in Fig. Each two-quadrant converter (phase-controlled) is represented as an alternating voltage source, which corresponds to the fundamental voltage component obtained at its output terminals. The diodes connected in series with each voltage source, show the unidirectional conduction of each converter, whose output voltage can be either positive or negative, being a two-quadrant one, but the direction of current is in the direction as shown in the circuit, as only thyristors − unidirectional switching devices, are used in the two converters. Normally, the ripple content in the output voltage is neglected. The control principle used in an ideal cyclo-converter is to continuously modulate the firing angles of the individual converters, so that each produces the same sinusoidal (ac) voltage at its output terminals. Thus, the voltages of the two generators (Fig. 2)have the same amplitude, frequency and phase, and the voltage of the cycloconverter is equal to the voltage of either of these generators. ![]() It is possible for the mean power to flow either ‘to’ or ‘from’ the output terminals, and the cycloconverter is inherently capable of operation with loads of any phase angle − inductive or capacitive. Because of the uni-directional current carrying property of the individual converters, it is inherent that the positive half cycle of load current must always be carried by the positive converter, and the negative half-cycle by the negative converter, regardless of the phase of the current with respect to the voltage. This means that each two quadrant converter operates both in its rectifying (converting) and in its inverting region during the period of its associated half-cycle of current. Equivalent circuit of cycloconverter Cycloconverters Vishal N. Popat Electronics & Communication Dept Institute Of Technology Nirma University Ahmedabad, India [email protected] • 2 Figure 3. Basic waveforms showing working of cycloconverter The output voltage and current waveforms, illustrating the operation of an ideal cycloconverter circuit with loads of various displacement angles, are shown in Fig.
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