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This paper points out a phenomenon of power backflow in traditional phase-shift (TPS) control of isolated bidirectional full-bridge DC-DC converter (IBDC), and analyzes the effects which backflow power act on power circulating flow and current stress. On this basis, the paper proposes a novel extended-phase-shift (EPS) control of IBDC for power distribution in microgrid. Compared with TPS control, EPS control not only expands regulating range of transmission power and enhances regulating flexibility, but also reduces current stress and improves the system efficiency. The operation principle of EPS control and the operation modes of IBDC are analyzed in the paper. By establishing mathematical models of transmission power, backflow power, and current stress, the paper comparatively analyzes control performances of TPS and EPS control. At last, experimental results verify the excellent performance of EPS control and correctness of the theoretical analysis.