Decoupling Control of 5 Degrees of Freedom Bearingless Induction Motors Using ®-th Order Inverse System Method

A 5-degrees-of-freedom bearingless induction motor is a multi-variable, nonlinear and strong-coupled system. In order to achieve rotor suspension and operation steadily, it is necessary to realize dynamic decoupling control among torque and suspension forces. In the paper, a method based on a-th order inverse system theory is used to study dynamic decoupling control. Firstly, the working principles of a 3-degrees-of-freedom magnetic bearing and a 2-degrees-of-freedom bearingless induction motor are analyzed, the radial-axial force equations of 3-degrees-of-freedom magnetic bearing, the electromagnetic torque equation and radial force equations of the 2-degrees-of-freedom bearingless induction motor are given, and then the state equations of the 5-degrees-of-freedom bearingless induction motor are set up. Secondly, the feasibility of decoupling control based on dynamic inverse theory is discussed in detail, and the state feedback linearization method is used to decouple and linearize the system. Finally, linear control system techniques are applied to these linearization subsystems to synthesize and simulate. The simulation results have shown that this kind of control strategy can realize dynamic decoupling control among torque and suspension forces of the 5-degrees-of-freedom bearingless induction motor, and that the control system has good dynamic and static performance.