Multi-harmonic oscillation and stability analysis of double-input buck/buck-boost inverter

In this study, multi-harmonic oscillation behaviour and stability problem in double-input buck/buck–boost inverter are investigated both theoretically and experimentally. First, the observer-pattern model is obtained by the local orthogonal and autonomous transformation in order to eliminate the time-variance effect from both fundamental component and the ‘hidden’ second-harmonic in the double-input cascade system. Based on the proposed model, bifurcation analysis method is employed to reveal the underlying mechanism of the multi-harmonic oscillation behaviour and identify the dominant harmonics. It is shown that the occurrence of Hopf bifurcation results in the double-adding harmonic oscillation, and the interaction between the double-adding harmonic components and the ‘hidden’ second harmonic component is also responsible for the multi-harmonic oscillation behaviour. Meanwhile, the occurrence of the multi-harmonic oscillations leads to the decrease of the system efficiency. For stability enhancement, the harmonic-stability sensitivity is presented to evaluate the influence of the key circuit parameters on the system stability quantitatively. In addition, the stability boundaries of the double-input inverter for these key parameters are provided to guide the system optimal design. Finally, the effectiveness of the above analysis is verified by those experimental results.