225 – Induced Voltage Analysis on Memory Motors Using Variable Magnets

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Application Note / Model Data


There are many kinds of variable flux motors, but the kind that makes a permanent magnet magnetization variable is called a memory motor.
The magnetic field for magnetizing and demagnetizing memory motor magnets is generated by the same three-phase coil current as in the drive system, so the magnetic force can be changed without adding any special devices.
In this document, the change in motor characteristics are checked as the memory motor variable magnet magnetization is changed using the three-phase coil current. One example of modeling a variable magnet is presented as well.

Changes in Variable Magnet Magnetization State and Induced Voltage

Fig. 1 shows the induced voltage when the variable magnets are fully magnetized, then demagnetized, and then magnetized again.
In Table 1, the induced voltage state for each interval in Fig. 1 is shown as well.
In interval (3) in Fig. 1, from demagnetizing the variable magnets, only the induced voltage due to the fixed flux magnets can be seen. The maximum change of induced voltage from this model is approximately 50 %.

Flux Line Changes Under No-load

Fig. 2 shows the flux lines at no-load when the variable magnets are magnetized and demagnetized.
The left is when magnetized and the right is when demagnetized. When the variable magnets are demagnetized, it can be seen that the magnetic flux from the magnets flowing in the stator is decreased.
Also, from the enlarged views of two variable magnets it can be seen that in the left view for the magnetization state several flux lines penetrate the variable magnets passing from one magnet core to the other and returning back again.
On the other hand in the right view for the demagnetization state, the flux lines do not penetrate the variable magnets, and it can be seen that the flux lines generated from the fixed magnetic force magnets flow around the variable magnets. This means that a stronger magnetic flux is generated from the fixed magnetic force magnets than from the variable magnets.

Variable Magnet Operating Points

The variable magnet operating points are shown in Fig. 3. While changing the input magnetization characteristics, it can be seen that the residual magnetic flux density Br changes when a magnetization/demagnetization current is applied.

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