Slow-Scale Bifurcation in Three-Level T-Type Inverter With Passive Memristive Load

In this article, the slow-scale instability occurring in the three-level T-type inverter with a passive memristive (3LT(2)IPM) load is investigated. The average model of the 3LT(2)IPM, whose coefficient matrix is nonlinear periodic time-varying, is constructed, both harmonic balance method used to calculate the approximate solution of the average model and Floquet theory used to identify the circuit dynamic states are applied to explore the mechanism of the slow-scale instability emerging in the 3LT(2)IPM. Theoretical results indicate that the slow-scale instability of the 3LT(2)IPM is caused by Hopf bifurcation emerging in a region where the frequency is higher than line frequency but much lower than switching frequency. Also, the conditions of three theoretical parameters that make the theoretical analysis results as accurate as possible are presented. Different parameters impact on the stability boundary of the 3LT(2)IPM in various design parameter spaces are discussed, and the Floquet multiplier sensitivity is analyzed to identify key parameters for the stability of the 3LT(2)IPM, which are helpful to guide parameter adjustment of the 3LT(2)IPM to ensure its stable operation in practice. Finally, hardware experiment is established and experimental verification is provided. Physical experiments agree well with simulations, which together demonstrate the correctness of theoretical analysis.

Automated summary

This article investigates the slow-scale instability occurring in the three-level T-type inverter with a passive memristive load. The average model of the inverter is constructed and harmonic balance method and Floquet theory are applied to explore the mechanism of the instability. Theoretical results show that the instability is caused by Hopf bifurcation in a frequency range higher than the line frequency but much lower than the switching frequency. The parameters for accurate analysis and the impact of different parameters on the stability boundary are discussed.