Harmonic Analysis Of Induction Motor Fed By SPWM Inverter

Nowadays, as the best speed regulation in the AC speed regulating field,variable-frequency adjustable-speed is widely used in different kinds of fields, whichmake variable frequency motor widely used. But because of many power electronicdevice used, which make harmonic of the motor become complicated and theproblems of harmonic pollution more and more serious. In order to save energysources and restrain the effect of harmonic on the system, Researchers carried out alot of researches on harmonic problems. Because of the harmonic of outputwaveform of frequency converter is developed by rectifying circuit and invertercircuit. Many researchers of harmonic of rectifying circuit have been done. Lots ofgood filtering methods are adopted, which make the output voltage of rectifyingcircuit approximated as the sine wave. But the study of harmonic produced byinverter is opposite less. This paper takes a4500kW induction motor fed by SPWMinverter as the investigated subject and does the harmonic analysis to it.First, this thesis introduces the development and the application of variable-frequency adjustable-speed, then point out the significance and the domestic andinternational development present condition of the study of harmonic. At the sametime, it introduces the basic principle of SPWM control technology and thetheoretical foundation of the output voltage of inverter.And then, putting the Fourier series and Bessel function as the mathematicalbasis, the mathematical expression of the output voltage of single-phase two-levelSPWM inverter is derived. According to the mathematical expression of the outputvoltage of single-phase SPWM inverter, we derive the mathematical expression ofthe output voltage of three-phase SPWM inverter. And the facts, which effect thedistribution of harmonic spectrum of SPWM output voltage, are discussed in detail.In addition, this thesis establishs the field-circuit model of the induction motorfed by inverter.After simulating the model, the distribution map of harmonic spectrum of output voltage is got. And then the paper analyse the harmonic spectrumin detail.At last, this thesis discusses the harmonic influences to the magnetic potential,torque, loss, efficiency and motor isolation, which provide the theory basis for designof electric machine.