Cross-feedback output-current-sharing control for input-series-output- parallel modular DC-DC converters

The input-series-output-parallel (ISOP) connection, consisting of multiple modular dc/dc converters connected in series at the input and parallel at the output, is a good alternative to be used under high-voltage input applications with low-voltage-rating switches. A novel output-current-sharing scheme, consisting of one output-voltage loop and individual output-currents loops, is proposed in this paper. The output-voltage loop provides a common reference for all individual current loops in which the current feedback for an individual converter is not its own, but the sum of all the remaining output currents. The stability and operation principles of the proposed scheme are analyzed. A three-module ISOP system is taken as an example to show small-signal analysis and loop-gain design with the proposed scheme. Both excellent sharing of the input voltage and the load current can be achieved with the proposed scheme. Besides, the output-voltage-regulation loop design is simplified and the overall reliability can be enhanced due to the inherent fault-tolerant and hot-swapping feature of the scheme. The performance of the proposed control strategy is verified by experimental results of a 200-W ISOP system consisting of three two-transistor forward dc/dc modules.