Improved Model and Experiment for AC-DC Three-Degree-of-Freedom Hybrid Magnetic Bearing

Compared with the most popular DC and other emerging AC magnetic bearings, the AC-DC three-degree-of-freedom hybrid magnetic bearing (AC-DC 3-DOF HMB) invented in our research has a lot of advantages in cost savings and consumption reducing. In this paper, to overcome the insufficiency and shortcomings of the previously established classic model, a new mathematical model for suspension force of AC-DC 3-DOF HMB is deduced again to get more accurate results. To illustrate the improvement in the new model, some validation experiments and contrast experiments are designed and implemented to prove their correctness and accuracy. In the validation experiments, the nonlinearity, linearity, electromagnetic cross-coupling and kinematic cross-coupling of suspension force model are validated, which prove the correctness of the improved mathematical model. In the contrast experiments, the encouraging results between the experimentally measured result and two calculated results (classic and improved model results) show that the improved model is closer to the test results. Moreover, system performance comparison results show the control system based on the new model has stronger anti-disturbance characteristics than that based on the classic model. Thus, the improved modeling results on suspension force of AC-DC 3-DOF HMB is more accurate than the traditional results, even if they share the same modeling method (equivalent magnetic circuit method). So only a change of coefficient could help to significantly improve the accuracy of the mathematical model, and also the improved model instance has important reference value for solving other kinds of hybrid magnetic bearings.