Does the motor efficiency change with the varying frequency using VFD? If so, is the variation is significant or not? If the change is significant, is it possible to calculate or estimate the efficiency change of the motor itself?
Hi!
From the article:Article Electric Motor Efficiency Under Variable Frequencies and Loads
the answers appear to be:1. On the average, there is no apparent difference;
2. For an individual motor, differences as large as 18% were observed;
3. Relative motor efficiencies can be higher or lower with a VFD;
4. There appears to be more variation in performance between motors as the relative loads and relative rpms decrease;
5. At 100% relative rpm, there was no more than a ± 5% difference in motor efficiency.
Dear Constantin,
Thank you very much for your reply. I have already found the paper you mentioned but I wonder if there is a more detailed study or not. For instance, which motor is differentiated 18%? Is this differentiation occurred due to its capacity (motor power) or anything else?
Frequency variation using VFD will have almost no impact on the efficiency of motor due to the fact that the VFD will maintain constant V/f ratio (flux dist. will remain the same 4.44 N × f × Φpk). However, other means of frequency deviation (irrespective of the supply voltage) will have impact on the efficiency of the motors.
Dear colleagues, everything is not so simple. Asynchronous electric drive. and I understand it is about him - a nonlinear structure and vector control "does not correct" this. If by efficiency we understand the magnitude of the stator currents at a constant moment or the magnitude of the slip, then in the first approximation we can say the following. If the load is small - up to 10% of the nominal. then the efficiency will be the same in the frequency range -10% - 130% of the nominal frequency. If the load is significant - more than 80% of the nominal - then the efficiency will be in the acceptable range - (up to 80% of the nominal at frequencies of 75-100%) and sharply decrease at frequencies below 30% of them above 110% of the nominal frequency. This is also determined by the type of engine - its power and rotor resistance and control method. .
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