Modelling of converter systems paralleled via interphase transformers in cyclic cascade topology and optimization of PWM carrier shifts

High power converters can be constructed by paralleling N interleaved converters via Interphase Transformers (ITRs) to produce multilevel output voltages while minimizing circulating currents among converters. With the ITRs connected in cyclical cascade topology, the ITR voltage stress is highly dependent on number of parallel converters and phase shifts between Pulse Width Modulation (PWM) triangular carriers. To analyse the ITR system performance a model of cross-coupling produced by ITRs is needed to establish links between the converter voltages and ITR voltages and cross currents circulating among converters. The main goal of this paper is to give a comprehensive overview of a model of the system based on the ITR cyclical cascade topology which can be used for estimation of its performance. Based on this model, opportunities for minimisation of the ITR voltages and core losses, via optimization of the converter PWM carrier shifts, are identified and discussed. Application of the theoretical results is illustrated in an example case with N=5 converters.