| The on-board charger of new energy vehicles is directly connected to the power grid.Because the charger is a power electronic device,the power factor is low,which will cause harmonic pollution to the power grid.Generally,power factor correction(PFC)circuit is used to improve the power factor and reduce harmonic pollution.However,the current power factor correction circuit topology and its control strategy have some disadvantages,such as high input current ripple,large converter loss and large electromagnetic interference,which is not conducive to improving the power factor and the power density of the converter.Therefore,this paper will study the power factor correction circuit and its control strategy of vehicle charger.By selecting a better power factor correction circuit and control strategy,we can improve the power factor of vehicle charger,reduce harmonic pollution and ensure the power supply quality of power grid.Firstly,based on the understanding of the mechanism and harm of harmonic generation by vehicle charger,the PFC circuit structure and control strategy related to vehicle charger are analyzed.It is proposed that the vehicle charger adopts inductor interleaved parallel PFC(IP-PFC),which can not only improve the power factor and reduce the input current ripple,Moreover,it can reduce the voltage stress and conduction loss of the switch tube;The working principle and circuit characteristics of IP-PFC circuit are analyzed,the small signal model of the converter is established,and the compensation design of voltage / current closed-loop is carried out.It is concluded that the hard switch of this circuit has the problems of low switching frequency,high switching loss and high switching noise,which affects the power density of the converter;To solve these problems,a coupled inductors parallel PFC(CP-PFC)circuit based on inductive coupling is proposed,and the soft switching control technology is adopted.The commutation mode,circuit steady-state performance,selection of coupling coefficient and element loss of CP-PFC converter are analyzed in detail.It is concluded that CP-PFC converter can improve the switching frequency and reduce the switching loss and noise,It can also improve the utilization rate of the inductor core and solve the reverse recovery problem of the diode.Secondly,through the simulation analysis of the PFC Converters with the above two structures,it is verified that the CP-PFC converter can not only correct the power factor better,but also realize the soft switching technology and solve the reverse recovery problem of diodes;Under the wide input voltage range or wide load range of CP-PFC converter,there is a problem of large input current distortion.A duty cycle feedforward control strategy is proposed to improve the input current distortion,and the feasibility of this control strategy is verified by simulation;Finally,the hardware circuit and software program of CP-PFC converter are designed.Figure [79] table [10] reference [73]... |
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