Research On Intergrated OBC-LDC Multifunctional Three-port Converter For Electric Vehicles

Electric vehicles have becoming more and more popular for their high efficiency and low emission to cope with the world energy crisis.Due to the limited space of electric vehicles,on-board equipment is required to be smaller in size,lighter in weight,higher in power density and stability.Therefore,the integration of on-board converters has become a focus of modern power electronics.Firstly,the traditional topologies of on-board battery charger(OBC)and low-voltage DC converter(LDC)have been compared in this dissertation.After that,an on-board three-port converter with integrated OBC-LDC functions has been proposed.In this proposed topology,a multi-winding transformer has been used to realize magnetic coupling between three ports.According to the different characteristics of each port,a bidirectional full-bridge circuit is used in high-voltage battery port,a full-bridge series resonant circuit is used at DC bus port and a synchronous rectification is selected in low-voltage DC port.Three operating modes of the proposed converter have been analyzed in this dissertation: 1)OBC mode;2)LDC mode;3)OBC-LDC simultaneous mode.Specially in mode 3),a buck circuit needs to be added after the synchronous rectification to modulate the output in the low voltage side.In order to remove the input filter of the traditional two-stage topology,an embedded buck circuit is given,with which the converter volume can be reduced greatly.Control strategies for the three working modes of the proposed converter have been designed.Frequency modulation combined with DC bus voltage regulation is used in OBC mode.PWM control is used in LDC mode.Frequency modulation in full bridge series resonant circuit,followed by PWM control in buck converter,is applied in OBC-LDC simultaneous mode.Simulation results are given to verify these control strategies.Finally,according to the design specifications,multi-winding transformer,series resonant components,output filter and auxiliary circuit are designed.A 6.6 k W prototype has been established for verification.Comparing the experimental results with theoretical analysis,the feasibility of the proposed three-port converter has been proved.