Research on Non-Linearity of H-Bridge Converter in Magnetic Suspension System Based on LRC Model

Abstract

The power amplifier, which regulates the excitation current, is the pivotal component of the magnetic suspension system. The control loop exhibits chaos and bifurcation phenomena due to the non-linear characteristics of the switching devices. This paper explores the non-linearity of the three-level H-bridge converter in the magnetic suspension system. First, the load coil's equivalent Inductance-Resistance-Capacitance (LRC) and Inductance-Resistance (LR) models are established, considering the current ringing effect induced by switching devices and the delay introduced by digital control. Then, Poincaré projection bifurcation diagrams of the excitation current are plotted using the proportional and integral bifurcation coefficients as dynamic variables, and the fast-transform analysis method is employed to determine the bifurcation points of the system. Finally, experimental comparisons are performed to analyse the chaotic motion trajectories of the excitation current under identical conditions in both the LRC and traditional LR models. The results indicate the compatibility of the LRC model-based analysis with the experimental data. Furthermore, the results reveal that although the time delay in the control system reduces the stability range of the static parameters, it does not alter the nature of the bifurcation or how the chaos is generated.