Nonlinear Model Analysis and “Switching Model” of AC–DC Three-Degree-of-Freedom Hybrid Magnetic Bearing

The most widely studied linear models of the suspension forces in ac-dc three-degree-of-freedom hybrid magnetic bearings may not be practical for application to the precision control of bearings with larger air gaps for larger suspension forces. In addition, the simplified linear and the real nonlinear models in linear zone of current and displacements have not been compared before. In this study, the two most commonly used nonlinear models are analyzed comprehensively to address the lack of nonlinear model analysis in previous research and to seek the most appropriate model for both nonlinear and linear zones (full zone). The results show that no single model completely approximates the test results over the entire zone. A composite model, such as the “switching model,” is more accurate. To illustrate the applicability of the results to both nonlinear model analysis and the proposed “switching model,” nonlinear stiffness and performance test experiments were conducted. It is concluded that the model analysis and the proposed “switching model” can provide a control system with the most suitable mathematical models of the suspension force.