[JAC291] Control Simulation of Switching Number of Poles in a 6-Phase Induction Machine

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Overview

Control Simulation of Switching Number of Poles in a 6-Phase Induction Machine
Multiphase design may be used in drive motors to increase high power density, enhance redundancy during operation and reduce torque ripple. In a cage inductance motor, the number of poles is determined by the rotating magnetic field generated by the stator side. A wide range of motors with good characteristics can be built by switching the number of poles at both the low and high-speed sides. For practical use, we want to minimize the change in torque when switching the number of poles.
To accurately evaluate the behavior of switching the number of poles during a simulation, the motor model to be controlled must also be highly accurate. The JMAG-RT model is a high-accuracy behavior model created by FEA-based calculations that can express motor characteristics that account for magnetic saturation and slip dependency.
In this document, the behavior of a 6-phase induction motor during the switching of the number of poles is evaluated by simulation.

Control Circuit

The control circuit is shown in Fig. 1.
A controller and inverter are arranged for both the 4-pole and 8-pole drive. Use only the 8-pole drive for the time between 0 to 4 sec. For each current command value between 4 and 6 sec, decrease the values for the 8-pole drive and increase the values for the 4-pole drive. After 6 sec and beyond, use only the 4-pole drive.
The switching pattern is shown in Fig. 2. The linear and exponential switching patterns are evaluated here.

Fig. 1. Control circuit
Fig. 2. Switching pattern

Coil Current Waveform (Steady State)

The coil waveforms in the steady state for both the 8-pole drive and 4-pole drive are shown in Fig. 3 and Fig. 4.
In an 8-pole drive, the phase difference is off by 120 deg, similar to a 3-phase sine wave, and in a 4-pole drive, the phase difference is off by 60 deg, similar to a 6-phase sine wave.

Fig. 3. Coil current waveform (8-pole drive)
Fig. 4. Coil current waveform (4-pole drive)

Current Waveform on the Controller Side

The current command value and current waveform for a linear switching pattern is shown in Fig. 5 and the current command value and current waveform for an exponential switching pattern is shown in Fig. 6.
It can be seen that, the current waveform follows the current command value in each switching pattern.

Fig. 5. Current command value and current waveform (Switching pattern: linear)
Fig. 6. Current command value and current waveform (Switching pattern: exponential)

Torque Waveform

Fig. 7. Torque waveform
The torque waveform is shown in Fig. 7.
There is a large fluctuation when the number of poles are switched and you can see that the fluctuation is smaller when the switching pattern is linear. However, for practical use, it is necessary to design a system that can further reduce this fluctuation.

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