Comparing to traditional onboard chargers,integrated onboard charger system (IOCS) takes obvious merits in terms of cost and power density. In this paper,an IOCS based on a six-phase permanent magnet motor drive is designed,and model predictive current control (MPCC) methods are studied for the IOCS under the grid-connection modes. At first,the topology of the IOCS is analyzed and the mathematical model is established. Following this,the implementation of traditional MPCC is also introduced. Then,a MPCC based on duty cycle optimization (DCO-MPCC) is proposed to overcome the disadvantages of the traditional MPCC including high computation burden and bad steady-state performance. On the one hand,the computation burden is alleviated by reducing the number of the alternative voltage vectors. On the other hand,a duty cycle optimization technique is proposed to enhance the steady-state performance. Finally,the effectiveness and superiority of the proposed control strategy are verified using experiments. The experimental results indicate that the proposed control strategy can significantly enhance the steady-state performance of the system and reduce the computation burden. The total harmonic distortion (THD) of grid current is reduced by 6.18% and 5.92% under charging and vehicle to grid (V2G) operations,respectively. Meanwhile,the execution time of the proposed strategy is decreased by 17.54 μs.