The article describes how to convert space vectors written in a stationary multiphase system, consisting of a number of phases where n > 3, to the stationary alfa beta orthogonal coordinate system. The transformation of vectors from a stationary n-phase system to the stationary alfa beta orthogonal coordinate system is defined The inverse transformation of a vector written in the orthogonal coordinate system to a stationary n-phase system is also defined. The application of the extended Clarke transformation allows control calculations to be performed in both stationary alfa beta or rotating dq orthogonal coordinate systems. This gives the possibility of performing different control strategies. It has a practical application for drive systems with five-phase, six-phase or dual three-phase motors.

Abstract. The paper presents vector control structures for n-phase AC motors derived from generalized Clarke transformation. In contrast to known works, where authors operate on generalized formulas of the Clarke transformation, in this work, only a number of actually used phases, of mostly industrial purposes, are considered (n = 5, 6, 2£3). This allows to perform control calculations in stationary orthogonal coordinates aβ or rotating dq. There are implementations of different control strategies: ROC (rotor-oriented control) or FOC (field-oriented control). Next, the paper presents the novel concept of a voltage modulator designed for multi-phase drive systems. Operation of the modulator is based on the extended Clarke transformation for multiphase systems. A mathematical model of the multiphase voltage modulator, operating in open-loop and closed-loop current control has been presented. Some selected oscillograms of voltage and current waveform, which illustrate properties of proposed control structures have been presented. Why multiphase drive systems?In the last years, more and more often there appear works devoted to multiphase drives. Most of them refer to drives with induction motors, but published there are also descriptions of drives with permanent, magnet-synchronous motors. Many works refer to drives with 5-phase, but also with 6-phase motors, and dual 3-phase motors. A work on drives with multiphase motors justifies the advantages of such motors, compared to 3-phase motors:• With the same nominal values of power and supply voltage, the nominal values of phase currents for an n-phase motor are reduced, as compared to a 3-phase one.• In transistor power converters, components of a smaller permissible collector current can be applied. This problem is important in high-power drives used in traction, metallurgy, mining transport, high-power pump drives, fans, and compressors [11,12].• In n-phase systems, the angle between the phases of the motor is smaller. When using direct torque control method, it is possible to accurately determine the position of the rotor.• In n-phase motors, there is a decrease in the amplitude of fluctuations of the torque, and an increase in their frequency (for a specified angular velocity of the rotor) [13].• By increasing the number of phases, the drive offers a greater robustness. It is possible to work with a damaged single phase in the motor or branch in the inverter [14].

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