Three operating modes are presented for photovoltaic (PV) generation systems connected to DC microgrid, including the maximum power point tracking (MPPT) control mode, constant voltage mode and constant power mode. A variable step size perturbation and observation method is used to achieve maximum power tracking in the MPPT control mode. The constant voltage control is achieved by the PI control method in the constant voltage mode. The constant power control is achieved by the PI control method in the constant power mode. When the constant voltage or constant power can not be realized, the operating mode is switched to the MPPT control mode and the energy manager is notified. The DC bus voltage is stabilized by the energy storage device dispatch or the load dispatch. So that the PV generation system is a controllable source of limited to the energy manager and is contributed to the stable operation of the DC microgrid. The multimode and control methods are simulated, and the results show that the PV generation system can operate in multimode, and the control objectives and mode switching can be achieved. Therefore, the PV generation system is changed into a controllable source of limited.