Functional model and stability analysis of 18-pulse auto-transformer rectifier unit (ATRU)

Abstract

This work mainly focuses on designing and modeling of 18-pulse autotransformer rectifier unit. The dq rotating reference frame (Park's Transformation) is used to design the average model. Polynomial fits are required to build up from essential parameters like α, k v and k i that must be extracted from switching model or actual setup. The designed model is computationally efficient, time invariant and has the key advantage of reduced simulation time, less convergence errors and having no numerical instabilities. The designed average model provides a much more accurate representation of the system dynamics both in frequency as well as in time domain. For this purpose, 18-pulse delta type autotransformer rectifier unit (ATRU) is modeled and analyzed for small signal behavior in order to realize the overall system stability. Finally average model is validated with hardware setup of 2 kVA prototype and its results are found to be closely matching with those of switching and average model proving the accuracy and reliability of the proposed model. Hence using these average models can greatly reduce the time consumption by avoiding mathematical instabilities while maintaining efficiency up to the mark on the other side.