International Journal of Engineering Trends and Technology- Volume3Issue3- 2012 ISSN: 2231-5381 http://www.internationaljournalssrg.org Page 431 Control of a Three Phase Induction Motor using Single Phase Supply G. R. Sreehitha #1 , A. Krishna Teja *2 , Kondenti. P. Prasad Rao #3 Department of Electrical & Electronics Engineering, K L University, Andhra Pradesh, INDIA Abstract- In Industrial applications, two forms of electrical energy are used: Direct Current (DC) and Alternating Current (AC). Usually constant voltage, constant frequency Single-Phase or Three-Phase AC is readily available. However, for different applications different forms, magnitudes and/or frequencies are required. This paper proposes how the Three-Phase inductive load is run by a Single-Phase supply by using Cycloconverter and a Scott-T connected Transformer. The controlling of a Three- Phase Induction Motor is done by Frequency variable method. Single-Phase to Three-Phase for motors offered by using high in performance, low on maintenance and is used to reduce of breakdown of electrical equipment, our range is also suitable for saving energy and require low maintenance. Keywords- Cycloconverter, Scott-T Transformer, Single-Phase to Three-Phase conversion. I. INTRODUCTION A Scott-T Transformer[1] is a type of circuit used to derive two-phase electric power with 90 0 phase shift[2] from a three- phase source, or vice-versa. The Scott connection evenly distributes a balanced load between the phases of the source. The Scott three-phase transformer was invented by a Westinghouse engineer, C. F. Scott, in the late 1890’s t o bypass Thomas Edison’s more expensive rotary converter and thereby permit two-phase generator plants to drive Nikola Tesla’s three-phase motors[3]. Two-phase motors draw constant power the same as three- phase motors, so a balanced two-phase load is converted to a balanced three-phase load. However if the two-phase load is not balanced, the Scott-T transformer cannot fix this. Unbalanced current on the two-phase side causes unbalanced current on the three-phase side[1]. Frequency changers is an expanding field of power conversion technology. The increasing utilization of a.c motors in variable speed drives and the generation of electrical power from variable speed sources are examples of this field applications[4]. Cycloconverters are suitable for large a.c. machines because it has advantages: it has high efficiency owing to the simple construction of the main circuit, which consists, in its basic form, simply of an array of IGBT switches[5]. The application of a Cycloconverter is rather limited, because the control circuit is often very complex, and therefore expensive[6]. II. CYCLOCONVERTER This converter consists of back-to-back connection of two full-wave rectifier circuits. Fig. 1 shows the operating waveforms for this converter with a resistive-inductive load. The input voltage, V s is an AC voltage at a frequency, f i as shown in Fig. 1b. For easy understanding assume that all the Switches (IGBT) are fired at α=0° firing angle, i.e. Switches act like diodes. Note that the firing angles are named as α P for the positive converter and α N for the negative converter. Consider the operation of the Cycloconverter to get half of the input frequency at the output. For the first cycle of V s , the positive converter operates supplying current to the load. It rectifies the input voltage; therefore, the load sees two positive half cycles as seen in Fig. 1c. In the next cycle, the negative converter operates supplying current to the load in the reverse direction. Note that when one of the converters operates the other one is disabled, so that there is no current circulating between the two rectifiers. Fig.1a. Single Phase Cycloconverter with Sinusoidal Pulse Width Modulation (Converter Consists of Back-to-Back Connection of two full-wave rectifiers).
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International Journal of Engineering Trends and Technology- Volume3Issue3- 2012