Design And Research Of 6.6kW Single Stage Three Phase PFC DC-DC On Board Charger

Under the call of environmental protection and energy conservation,electric vehicles have developed rapidly in recent years,in the meantime their related industries have also been highly valued by the market and consumers.In order to respond to the demand for long endurance capacity and fast charging of electric vehicles,it is of great significance to develop a high-power on-board charger with low input current total harmonic distortion,high power factor and high efficiency.In this paper,a 6.6kW full digital control on-board charger is taken as the main research content to explore the feasibil:ity of a new single-stage three-phase power topology in high-power applications.Firstly,the existing power factor correction topology and isolation voltage regulation topology schemes are fully investigated,then pointing out the natural advantages of single-stage topology.A new single-stage three-phase converter topology with three transformers series-parallel structure is proposed.In the second chapter,under careful analysis of the original proposed topology,the corresponding equivalent working topology is proposed.On the basis of this,the working mechanisms of the circuit at various moments are expounded.The power factor correction performance of proposed circuit is analyzed with the influence of input-to-output factor-M’;Respectively,the realization conditions of zero-voltage-on of the phase-shifted full-bridge four lags switches are analyzed;The characteristics of automatic power equalization and output automatic current sharing of the three transformers series-parallel structure are analyzed;The mechanism of the duty cycle loss in the phase-shifted full-bridge circuit and the problem of transformer secondary voltage oscillation are studied,then corresponding solutions are carried out.According to the operating indexes of the circuit,the design method and result of the key parameters of the main circuit are given.The simulation and experimental results also verify the effectiveness of the design based on PSIM platform.The key design points of PFC inductor and transformers are elaborated,and the general design methods are given;For the inherent problem of high-coupling,dynamic difference and difficult-closed loop for the bus-bar voltage and output voltage,an effective control strategy of frequency pulse width control with phase shift hysteresis control is proposed;Finally,the prototype was completed and the corresponding experimental tests were completed,and some key circuit wave forms were analyzed in detail;The completed prototype was tested at rated input line voltage(380Vac@50Hz)and rated output voltage,the highest efficiency of it is 96%,and its full load efficiency is higher than 93%;Under full load conditions,the prototype’s power factor is greater than 98%,and its THD is less than 3.5%;The experimental results verify the validity of the design parameters in this paper,and also showing the excellent performance of proposed topology.