165 – Creating IPM Motor Efficiency Maps

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Application Note / Model Data


Since an IPM motor uses rare-earth sintered permanent magnets with strong magnetic force, and can use reluctance torque generated from the difference between the d-axis inductance and q-axis inductance in addition to magnet torque due to a magnetic field and rotating magnetic field, it has a large operating region and is a highly efficient motor.
Since the efficiency varies with the rotation speed and load, it is useful to create an efficiency map for motor design and control design. Creating an efficiency map requires an enormous amount of computations and it takes time to organize the results. Although it is possible to estimate efficiency by calculating the torque, voltage, and current from motor voltage equations and torque equations, it is difficult to estimate iron loss this way. Also, taking into account the effects from nonlinear magnetization characteristics of the motor core is difficult. This makes it difficult to calculate efficiency accurately. In JMAG-Designer, an efficiency map can be easily created taking into account the influence from iron loss and nonlinear magnetization characteristics.
In this example, an efficiency map of an IPM motor is created and the loss ratios at each operating point are evaluated.

Efficiency Map

Fig. 1 shows the efficiency map.
From Fig. 1, the output torque and input torque efficiencies can be seen. It can be seen that in the high rotation speed half of the map that the efficiency is higher in the output torque area than in the input torque area.

Loss, Magnetic Flux, Power Factor Maps

Fig. 2 to Fig. 9 show the maps of loss, magnetic flux and power factor.

Loss Ratios at Each Operating Point

Fig. 10 shows pie charts that show loss ratios at low speed and high load, at low speed and medium load, at medium speed and medium load, and at high speed and low load.
Copper loss decreases with load. It can be seen that stator core losses increase with the rotation speed, especially eddy current loss. On the other hand, it can be seen that the loss of the rotor core is comparatively small.

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