| In the normal motor theory. The only factor considered is fed by sinusoidal power supply ,when we are calculating loss .As the development of power electronics on a large scale, asynchronous motors fed by inverter are widely applied to production .inverter is used in order to control motor more conveniently and it is welcomed in the voltage and current provided by inverter is the ladder wave or the rectangular wave, which includes a great deal of harmonics. It brings the by-effect on the loss, torque and efficiency of motor . It is necessary to analysis the harmonics and calculate precisely loss so that we can take effective steps to weaken the by-effect. This paper introduced FULIAR method to turn the ladder or rectangle into the clusters of a series of sinusoidal supply. In the light of the change of notation difference and stator impedance and rotor impedance, a simple equal value circuit can be gained and the loss can be calculated. Finally , we designed a program to calculate the loss. Torque power factor and efficiency .It should be pointed that stator impedance and rotor impedance is influenced by collective response about the skin, But the reaction is opposite, we could neglect the response during the calculation .Thus ,not only the calculation is simplified ,but also the essence can be easily grasped. This paper mentions several ways of dealing with harmonic by computer program and the new method of harmonic control, At last part I will analysis the harmonic in symmetrical three-phase circuit and its effect on the measurement of Active Power . |
