Ac stability of high power factor multi-pulse rectifiers

This paper studies the ac stability of high power factor multi-pulse rectifiers, proposing a new stability criterion to assess this condition under constant power load dynamics. Specifically, based on the multivariable generalized Nyquist stability criterion developed by MacFarlane and Postlethwaite, this paper shows how the fundamental stability problem at such ac interface is reduced to a single-input single-output (SISO) case. It is shown that the ac stability is fully determined by the SISO return-ratio of the d-d channel-or the power transfer channel of the desired d-q frame alignment; that is, the stability is solely determined by the d-d channel input and output impedances. Correspondingly, it is shown that the q-q channel trajectory on the complex plane is such that it cannot encircle the critical point (-1+j0) and be the cause of instability. Furthermore, it is shown that the multi-pulse rectifier stability can be indistinctively determined at either ac or dc terminals, which has great significance from a practical point of view. Simulation and experimental results are used to verify the implications of the proposed stability criterion.