Analysis of Fast-Scale Instability in Three-Level T-Type Single-Phase Inverter Feeding Diode-Bridge Rectifier With Inductive Load

In this article, the fast-scale instability in the three-level T-type single-phase inverter feeding diode-bridge rectifier with inductive load (3TSI-DR) is studied. Simulations suggest that such fast-scale instability on switching period scale can increase the harmonic content in the 3TSI-DR, which seriously affects its stable operation. To reveal the mechanism of this fast-scale instability, the state equation of the 3TSI-DR is derived, and state variables are solved based on quasi-static approximation principle. From state equation, the 3TSI-DR is periodic time-varying and piecewise smooth, belonging to Filippov system. Accordingly, the discrete-time mapping model of the 3TSI-DR is established, Filippov method is used for obtaining monodromy matrix, and Floquet theory is applied to explore instability mechanism. Theoretical results indicate that the fast-scale instability of the 3TSI-DR is caused by period-doubling bifurcation. Moreover, the Floquet multiplier sensitivities of different circuit parameters are calculated to identify key parameters; via comparing theoretical analyses with simulations, the unstable angle ranges of the fast-scale instability are given, and the stability boundaries in various parameter spaces are discussed. All these can provide design-oriented information for optimizing the 3TSI-DR to avoid instability due to period-doubling bifurcation. Finally, experimental results agreeing with simulations are presented to verify the correctness of theoretical analyses.