Novel Equivalent Circuit Model and Theoretical Analysis of Doubly Fed Machine

Doubly fed induction machine (DFIM) has been widely used in variable speed constant frequency electricity generation systems due to its small power converter capacity. Then another machine-brushless doubly fed machine (BDFM)-is widely concerned because of its similar characteristics but better reliability than DFIM. In fact, according to common features of DFIM and BDFM, these two machines can be collectively called doubly fed machine (DFM). Theoretical study on characteristics of these two machines has not formed concise, practical, and all-sided theoretical analysis system. Proceeding from basic theory of DFIM, this paper derived the physical model and established a novel synchronous-asynchronous series equivalent circuit model of DFIM at first. Based on the analysis method of DFIM, a novel equivalent circuit model of BDFM was established. These two models illustrated that the characteristic of DFM is the superposition of synchronous characteristic and asynchronous characteristic. Based on these circuit models, the characteristic under different operation mode was analyzed and corresponding analytical curves were drawn, which revealed the operation mechanism of DFM clearly. To verify the theoretical analysis of two novel equivalent circuit models, simulation models of DFIM and BDFM were established in Simulink and finite element analysis (FEA) software. Corresponding characteristic curves were drawn to compare with that obtained by circuit models. At last, combined with these characteristic curves, practical significance that circuit models and theoretical analysis bring to machine design and control theory was analyzed.