Common asynchronous electromotor is designed by constant frequency constant volt

Common asynchronous electromotor is designed by constant frequency constant voltage, get used to the requirement of frequency control completely impossibly. It is the transducer influence to electric machinery below

1, the problem of the efficiency of electromotor and temperature rise

No matter the transducer of the sort of form, all produce the harmonic voltage of different level and electricity in move, make electromotor moves below blame sine voltage, electric current. Refus data introduces, it is with the sine wave PWM that uses generally at present transducer exemple, its are low second harmonic is basically 0, those who remain is one times bigger than carrier wave frequency wave heft is right-and-left Gao Cixie: 2u 1 (U is compared for modulation) .

Gao Cixie wave can cause copper of bad news of electromotor stator copper, rotor (aluminous) of bad news, iron bad news and additional loss increase, most remarkable is rotor copper (aluminous) bad news. Because asynchronous electromotor rotates in order to receive the synchronous rotate speed of correspondence of place of frequency of close Yu Jibo, accordingly, voltage of Gao Cixie wave with bigger turn poor cut rotor guides hind, can produce very big rotor loss. Besides, the add copper waste time that because place of collect skin effect arises,still needs a consideration. These loss can make electromotor additional and calorific, loss of efficiency, output power is reduced, below the condition of blame sine power source that runs at transducer output like electromotor of asynchronous of will common three-phase, its temperature rise should increase 10%~20% commonly.

2, problem of electromotor insulation intensity

At present medium or small transducer, many it is the control means that uses PWM. His carrier wave frequency is about thousands of to ten conspicuous, this makes electromotor stator winding should bear very tall voltage rises rate, be equivalent to bringing to bear on to electromotor the concussion voltage with very big gradient, make of electromotor v/LIT all over the ground insulation bears relatively ordeal. Additional, the rectangular behead wave that generates by PWM transducer pounds voltage overlay to run voltage to go up in electromotor, can right to electromotor insulation constitutes menace, right insulation pounds next meetings to quicken ageing in high-pressured iteration.

3, harmonic electromagnetism noise and shake

When common asynchronous electromotor uses transducer power supply, can make by electromagnetism, mechanical, ventilated those who wait for what element place causes to shake to change with noise is more complex. The inherent space harmonic of the each time harmonic that contains in frequency conversion power source and electromotor electromagnetism part is interfered each other, form all sorts of electromagnetism to stimulate brace up force. When the inherent and oscillatory frequency of the frequency when electromagnetism force wave and electromotor airframe agrees or be close to, generation resonance phenomenon, increase noise thereby. Because range of electromotor job frequency is wide, rotate speed span is big, the frequency of all sorts of electromagnetism force wave keeps away from very hard of each component of electromotor inherent shake frequency.
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