| Input-series and output-parallel (ISOP) full-bridge (FB) converter, including several FB converter modules, which input sides are in series and output sides are in parallel, can reduce the voltage stress of all switches, so it is very suited for the high input voltage and high power dc-dc conversions. In order to make the ISOP-FB converter work normally, we should ensure the voltage sharing of the input divided capacitors and current sharing of the output current of each module. This paper derives the voltage conversion characteristics of the ISOP-FB converter, and analyzes the reasons for the un-sharing voltage and un-sharing current. After that, a control strategy with three closed-loops is proposed, which has input voltage sharing loop, output voltage loop, and output current loop. The output signal of input voltage sharing loop revises the given value of current inner loops, so that the output current of the module with higher input voltage will increase, and in the meanwhile, the output current of the module with lower input voltage will decrease, and as the result, the input voltages and output currents of the modules will be balanced respectively. At the same time, the modules are interleave controlled, with the ripple cancel effect, the sum of the output currents of the modules has reduced ripple, so the output filter capacitor can be reduced. The small-signal model of the ISOP-FB converter with the proposed control strategy is established, and the compensation network is designed in details in this paper. The effectiveness of the proposed control strategy is verified by the simulation results. A 3kW prototype is designed and built in our lab, and the experimental results verified the effectiveness of the proposed control strategy. |
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