Output Current-Differential Control Scheme for Input-Series-Output-Parallel-Connected Modular DC-DC Converters

This paper proposes an output current-differential (OCD) control scheme that has a master-slave structure. It can be applied in dc/dc converters to connect the input in series and the output in parallel. All of the control and sample circuits in the proposed control scheme are on the output side, which means that there is no further isolation in the control loops. The proposed control scheme, consisting of one output voltage regulator loop and individual load-current-sharing loops, will enable low-voltage converters to be used for high-voltage specifications. The master module regulates the output voltage through a common output voltage loop and provides current references to slave modules. The individual current-sharing loops residing in the slave modules regulate the current in each module equally. According to the power balance, input-voltage sharing is realized simultaneously. To prevent a situation in which system failure is caused by master module failure, a fault-tolerant automatic master-slave output current-differential (FOCD) control scheme is developed. The performance of the OCD and FOCD control schemes is validated on a 450-W prototype input-series-output-parallel system comprising three forward converters.