Dynamoelectric machines for multiples of three phases with unbalanced fractional-slot windings

DETAILED DESCRIPTION This invention relates to dynamoelectric machines such as synchronous motors for operation from an AC power supply of six or more phases with fractional-slot windings that are slightly unbalanced but still achieve low torque harmonics.
Static power conversion equipment is used to convert three phase power from a power line to a higher number of phases for driving motors.
For example, adjustable frequency synchronous motors are being designed for six, twelve and twenty-four pulse inverter systems for three, six and 12 phase operation, respectively.
Even higher pulse numbers may be used in the future.
The use of pulse numbers of multiples of six is desirable to reduce harmonic torque levels and damper losses.
The design of such motors is complicated by the fact that a motor manufacturer has available certain existing stator punchings which fix the number of available slots.
The available punchings and coil designs are primarily designed for six pulse (three phase) operation and often are not readily adaptable to six or 12 phase machines.
A general purpose of this invention is to provide machines with windings for multiples of three phases in cores having slot designs for three phases and to do so without adversely affecting machine performance to any significant degree.
It is straightforward to take an existing machine design for three phase operation and to simply regroup the windings to provide six phase operation if the slot numbers happen to be correct for the higher number of phases.
For example, a six pole, 72 slot machine offers a variety of possibilities.
It can be connected without problems for six pulse, 12 pulse, or 24 pulse operation, that is either three, six or 12 phases, because the number of coil slots per phase per pole is in each instant an integer.
This is another way of saying that the winding for the number of slots used for three phases can be regrouped into two or four separate windings for six or 12 phases.
This permits both six phase and 12 phase balanced windings, with uniform spacing, easily