Distributed energy sources (DES) remain the characteristics of intermittent and randomness. How to supply the longest sustainable power to the customers in nanogrid becomes a crucial issue. Therefore, distributed energy source unit (DESU) is necessary in nanogrid. A novel circuit form consisted of resonant push-pull circuit cascaded single-phase inverter with high step-up ratio and efficiency applied for DESU is proposed in this paper. Each DESU could transfer input voltage 24 V from battery-packs to AC 220 Vrms. Whilst, in order to supply enough power to the customers, expansion for DESUs is necessary. But inconvenient control, different charge and discharge levels would lead the battery to remain different aging level. Namely, the initial SoC values and capacities of the battery-packs among DESUs are different. And state-of-charge (SoC) of each DESU cannot be balanced. Therefore, a novel droop-based distributed state of charge balancing control using for expansion is put forward to eliminate the error of SoC of each DESU with different sizes. And SoC of each unit could be balanced by utilizing the proposed method in condition that each DESU has different initial SoC, different battery-pack capacity. Experiment results verify the correctness of the proposed cascaded unit and expansion method.