A Novel Three-Phase to Nine-Phase Transformation using a Special Transformer Connection

Abstract: Multiphase i.e. more than three phase electric power supply for electric drive system is the main focus of research in the last decade. Since the three-phase supply is available from the grid, there is a need to develop a static phase transformation system to obtain a multiphase supply. As, the variable speed multiphase drive system considered in the literature are mostly of five, seven, nine, eleven, twelve, and fifteen phases and such multiphase drive systems are invariably supplied from power electronic converters, thus overall system constitutes of complex control circuit and moreover the line current drawn from three phase supply have appreciable amount of harmonics due to power electronics elements in the circuit. In contrast, this paper proposes technique to obtain nine-phase output from three- phase supply system using special transformer connections. Thus, with the proposed technique, a pure nine-phase sine- wave voltage/current is obtained, which can be used in multiphase drive systems.

Keywords: Multiphase, nine phase, transformer, turn ratio.