| Arc welding inverters are more and more widely used in our country. Arc welding inverters have many good qualities, such as small volume, lightness, high efficiency and rapid dynamic response. Conventional arc welding inverters consist of diode rectifier and capacitance filter , the AC power of net transfer by rectifier, capacitance is charged to peak of input AC voltage could keep output DC voltage stably. It would result in harmonic pollution of the power network with input current has serious distortion and contains heavy harmonic current. Thesis analyze the circuit of rectifier. Then give the Power Factor(PF) formula of arc welding inverters. Author imitate the electric circuit point out the key factor lead to the decrease of PF of arc welding inverters.Much criterion have established along with restraining the harmonic of electrical equipment in many country. Arc welding inverters work with more than sixteen A current, it require a under ten percent current distortion. The power factor correction is applied into arc welding inverters to reduce the harmonic current and advance PF. The capability of arc welding inverters has improved with the development of power electronics and autocontrol technology. After referring to plenty of the PFC circuits and point out their characteristics, then the single-phase active power factor correction(APFC) technique choose Boost circuit as arc welding inverters PFC in this paper. The PFC circuit of Boost make use of pulse wide modulate technique to provide aptitude power factor with load variety.Boost inverter has three control modes, they are peak current control,current resort control and average current control. Pointing out their characteristics author decide average current control for PFC. Under this control mode , instantaneous input current is average current of high frequency .The error is low with the peak inductance current and average current, it make average current follow input AC voltage .We would reduce current harmonic with control.The basic circuit of Boost PFC have much problems such as Diode rectifier exhaust,current distortion while it g et to zero,MOSEFT dredge exhaust and boost diode reverse renew exhaust and so on. In this paper ,using soft switch technique increase an assistance switch tube, a diode, a resonance inductor and a resonance capacity, can attain the result of the soft switch. Make the main switch tube break through under the condition of zero electric voltage; the main diode breaks under the condition of zero electric current. Lowered the equipment's exhausts about the switch machine piece and raised the ability of electric circuit's electro magnetism. Make Boost ZVT-PWM inverter as arc welding inverters PFC application.In this paper , the control rules of the average current control APFC circuit's main components are discussed in details and the equations of the current and the voltage passing through the main components are obtained .Base on sinusoidal pulse wide modulate ,under stability instance , could keep input current go with input AC voltage when boost inductance is high enough and power switch modulate occupancy by sinusoidal orderliness .Design switch frequency forty KHz for Boost ZVT-PWM PFC system .We could make lower power inverter volume,lightness,get rapid control and reduce current distortion .Author research on arc welding inverters front power factor corrector ,the load of front which is inverter circuit and arc load has effect on front power factor corrector .But it is difficulty to account for precise . Take into account the welding process of non-load ,author design a inductance load as front power factor corrector load. Power factor corrector with inductance load is designed .Referring to reference ,thesis design the power switch parameter,boost inductance and capacitance filter ,the PFC circuit improve the PF of arc welding inverters. Making use of the Multisim to imitate the PFC system, get the imitate forms to optimize circuit parameter .The control system of single phase PFC is very pivotal, in order to stabilize output voltage when the input current being in phase with input voltage, this article give the transfer functions of the current and voltage for system correction based on the analysis of the average APFC circuit . This PFC device chooses UC3855A to control the electric circuit . We apply two loop idea with current loop and voltage loop in the whole control system . APFC control system construct from voltage feedback,current forward feedback and voltage forward feedback . Voltage feedback control the output voltage to be a constant value ; voltage forward feedback is used to achieve that the input current is be inphase with the input voltage ;current forward feedback is used to keep the form of input current follow input voltage form .With the particular design of PFC control system ,under this control mode ,we can realize high power factor intent . At last, the author build Boost ZVT-PWM PFC actual circuit, some experimental results are given out at last. From which we can see single phase input current are inphase with input voltage, and they are relative standard sine-wave, the power factor is 1, the THD of the current is less than 10%, all of this has meet the international harmonic criterion . |
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