PM Electrical machine V/Hz characteristic

[AntonK]

Hi guys, i would like to give me your opinions about a problem i have. In our university laboratory we have designed and built a permanent magnet electrical machine and when we test it the Voltage/Frequency characteristic is not constant as we expected. You can find the graph on the link below. We thought that the rotor is vibrated due that some of the rotation frequencies coincides on rotor's eigenfrequencies, but i have strong doubts about that. What is your opinion?

 

[waross]

The V/Hz characteristics will be non linear at low levels of magnetic field strength due to hysteresis and will be non linear at high levels of magnetic field strength due to saturation.

Bill
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"Why not the best?"
Jimmy Carter

 

[AntonK]

Thank you waross for your answer.
One of three phases is linear and the other two are oscillated. Why this is happen?
Also i forgot to mention that we rotated the rotor using a drill, but we checked it four times with no changes.

 

[waross]

There is not enough information for an answer.
But, one phase good and two with issues suggests possible assembly issues.
Bad workmanship and turn to turn shorts.
Improper orientation of laminations.
Eddy currents due to shorted laminations.
Non uniform iron.
Uneven air gaps.
Please share some construction details.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AntonK]

The rotor consists of an aluminum 7075 shaft, iron m-235 which is placed in the center and 2 magnets NdFeB.
The shaft's length is 90mm and the length of the active core is 45.
Can you tell me what other construction details do you need?