High Performance Control of AC Drives with Matlab / Simulink Models

7.1 Preliminary Remarks

The term ‘multi-phase’ in this chapter refers to a phase number greater than three. Three-phase electrical power is readily available as the power is generated, transmitted, and distributed in three phases. This is the most optimal number of phases for generation and transmission, as the trade off exists between the complexity and power handling capability of the three-phase system. The variable speed electric drive is also developed for three-phase AC machines. However, a power electronic converter, most commonly a voltage source or current source inverter, is invariably used to supply such three-phase drives. The power electronic converters do not pose any limit on their number of legs. The number of output phases in an inverter is the same as their respective number of legs. Hence, adding an additional leg to an inverter increases the number of output phases. This degree of freedom lead to interest in developing variable speed electric drives with more than three phases. The first proposal of a variable speed five-phase induction motor drive is believed to have been made in 1969 [1]. The five-phase inverter used initially operated in the square wave mode; however, later the pulse width modulation (PWM) mode of operation was used. Six-phase drives have attracted much attention in the literature, after their advantages were revealed in 1983 [2]. The research on high phase order motor drives remained steady until the end of the 19th century. The multi-phase ...