Stability analysis of input-series output-parallel connected buck rectifiers

AC voltages in the range of few kV have to be processed before being fed to traction motors. DC traction motors are normally designed for medium voltage and high current (1.2kV-1.5kV and 1200-1500A). Front-End Buck-Rectifiers are a viable solution for direct conversion of high ac voltage to low dc output voltage. However several buck-rectifier modules need to be connected in input-series output-parallel (ISOP) configuration, in order to achieve the input voltage and output current sharing. In the paper, stability of the input-series-output-parallel configuration for buck rectifier is analysed through small signal model. Common duty ratio scheme is implemented. The proposed scheme is capable of equal voltage sharing, irrespective of large variation in design parameters and retains stability for perturbations in load. The configuration is extremely simple for hardware implementation, as no extra controllers are required. The performance of the circuit is verified through simulation results.