Input-series systems are prevalent for applications with high input-voltage requirements. During the auxiliary power supply startup of submodules, the voltage oscillation problem caused by out-of-sync is less severe owing to the large submodule capacitance. However, it becomes significant for input-series system with small submodule capacitances, while rarely reported before. Therefore, one contribution of this digest is establishing a simulation model to evaluate the influence of parameters of passive components on the startup. Further, another contribution is proposing a two-stage startup scheme to avoid the voltage oscillation without increasing the values and sizes of passive components and experiments well validate it.
