IPOS three-state boost converter and its volt-second balance method based output voltage sharing control strategy for bipolar DC bus applications

The bipolar DC bus configuration has been widely used in DC nano-grids due to its flexibility and stability. Input-parallel-output-series (IPOS) converters are utilized in bipolar DC bus and RES applications due to their simple structure. However, there is a big challenge with this structure. To ensure system safety and stability, the two output voltages of an IPOS converter need to be balanced. On this basis, an IPOS three-state boost converter with a balanced output voltage is proposed in this paper. At the same time, output voltage balance can be obtained by adjusting the duration of the three-state converter based on the volt-second balance method. In the proposed strategy, a switch series diode is added to the IPOS Boost converter topology, and the voltage across the main inductor can be changed through one degree of freedom, where the corresponding output voltage is regulated due to a change in inductor voltage. In addition, under different dead time conditions, adjusting the gate drive of the switch can be used to achieve voltage balance. Moreover, a comprehensive analysis and relative calculations are provided. Finally, a 20–200 V prototype is built to verify the analysis.