Modular ISOP Flyback converter: Analysis of auto-balancing mechanism in steady state

DC-DC Modular converters have been proposed as a solution to reduce electrical stresses on semiconductors due to the capacity of sharing current or voltage among modules. This characteristic allows the increasing of the switching frequency, the use of low voltage/current semiconductors and the standardization and expansion of converters. This paper presents a steady-state analysis of an input-series-output-parallel (ISOP) modular Flyback converter operating in the discontinuous conduction mode (DCM). The analysis of the average input voltage and output current balance is presented, whose results depend on the magnetizing inductance and on the duty cycle of any number of modules. Once the equations are obtained, all the results are underpinned by a set of simulations undertaken for three modules. In order to evaluate the theoretical analysis, a prototype consisting of three Flyback modules in DCM operation, with a rated power of 600 W and conversion ratio from 600 V to 200 V, was built. The obtained waveforms show the independence of each module to the connection, leading to an equal division of the current and voltage stresses over the semiconductors. This characteristic, added to the modularity, high efficiency and high current gain, makes the converter an alternative to DC/DC systems where the output voltage must be lower than the input voltage.