Research On Combined Serial-Parallel And Serial-Serial Two-Transistor Forward Converters

The input-series combined converters with the voltage stress of the switches reduced are very suitable for high input voltage and high power applications. The input-series and ouput-parallel (ISOP) converters can be selected to reduce the current stress of switches for large output current applications, while the input-series and ouput-series (ISOS) converters can be choosed to reduce the voltage stress of switches for high output voltage applications. Input voltage and output current sharing among the modules should be ensured for the ISOP converters, meanwhile, input and output voltage sharing should be guaranteed for ISOS converters.The input voltages of ISOP converters can be shared naturally in voltage control mode and a novel control for ISOP two-transistor forward converter (TTFC) are proposed, based the analysis and result on the voltage unbalance in current control mode. All the functions of interleaving PWM, output voltage control and input voltages balance are achieved with only a single PWM IC and a voltage regulator without any extra synchronizing or voltage sharing control regulator. The novel control is extended to ISOP converters consists of several modules. The small-signal model of ISOP-TTFC with the proposed input voltage sharing control strategy is constructed and the system stability is also analyzed with Matlab. Furthermore, the relationship between input and output voltage sharing in ISOS converters is analyzed. Neither voltage nor current control mode can guarantee the voltage sharing. Besides, the compare of two ouput parallel and series methods and their applications are also given in this paper.The effectiveness of the proposed control strategy is verified by the simulation and experimental results in this paper.