Unified stability criterion of bidirectional power flow cascade system

The stability issues of cascade system have been studied for many years. Some classic criterions in the form of Zo/Zi like Middlebrook criterion has been proposed and the validity have been proved in the case like voltage source with a current sink. But they meet the challenge in some application, especially in the case of current source with voltage sink. In this paper, the stability issues of a bidirectional energy storage system have been discussed. System level small signal models are established to derive the transfer function in each mode. A unified stability criterion is summarized after the discussion of different modes. It can be seen that the stability only depends on the terminal characteristics design.