Abstrakt
The subject of this paper is the control possibility of the multiphase
cage induction motors having number of phases greater than 3. These motors
have additional properties for speed control that distinguish them from
the standard 3 phase motors: operation at various sequences of supplying
voltages due to the inverter control and possible operation with few
open-circuited phases. For each supply sequence different no load speeds
at the same frequency can be obtained. This feature extends the motor
application for miscellaneous drive demands including vector or scalar
control. This depends mainly on the type of the stator winding for a given
number of phases, since the principle of motor operation is based on
co-operation of higher harmonics of magnetic field. Examples of operation
are presented for a 9-phase motor, though general approach has been
discussed. This motor was fed by a voltage source inverter at field
oriented control with forced currents. The mathematical model of the motor
was reduced to the form incorporating all most important physical features
and appropriate for the control law formulation. The operation was
illustrated for various supply sequences for “healthy” motor and for the
motor operating at one phase broken. The obtained results have shown that
parasitic influence of harmonic fields interaction has negligible
influence on motor operation with respect to the useful coupling for
properly designed stator winding.
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