Multi-secondary transformer: A modeling technique for simulation

Pulse Step Modulation based High voltage power supply has played significant role in fusion research. Multi-Secondary transformers are invariably used for generation of tens of kV range outputs with fast (μS order) transient response. In this scheme, large numbers of isolated voltage sources are connected in series to generate the output. Isolated voltage sources can be achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (~40) on single core is the preferred solution due to its space and cost consideration. For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software. While many simulation softwares provide transformer models with limited number (3-6) of secondary windings, they still fail to predict the actual observed results from a manufactured unit. This paper discusses the difficulties in modelling, step by step with representative schemes of multi-secondary transformer, advantages/disadvantages of each scheme with simulation results. Finally, a model using flux coupled cores as basic building block is proposed, this model is able to simulate actual transformers very close to its observed parameters in test and actual usage.