Theoretical And Experimental Study Of Passive Electromagnetic Damper

The vibration caused by unbalance of the rotor system is especially strong at critical speed. The methods of reducing the vibration are interested by many -researches. In this thesis, a single disk rotor supported by two rolling bearings is used for studies, and a new method of reducing the vibration is proposed. The main works of this thesis are as follows:Based on the comparison of various control methods for vibration suppression, akind of passive electro-magnetic damper is presented. The structure of it is similar to thatof the active magnetic bearing. The damper works with DC so that sensor and closed loopcontrol are not needed. The air gap between rotor and stator is changed with rotating ofrotor. As a result, the electromagnetic field intensity is changed accordingly andfluctuating current in the damper coil is created. Damping force is mostly producedbecause of the phase difference between fluctuating current and displacement of rotor.The formulas of fluctuating current and damping coefficient are deduced theoretically,and the calculated results are consistent with the experimental results. The passiveelectromagnetic damper is applied to an experimental rotor and a very good vibrationsuppression result is achieved. Because of its simplicity and reliability it may be used inindustry. Finally, the wave equation of the electromagnetic field of this kind damper isderived from the Maxwell's equation. The magnetic flux density at the boundary isassumed to be harmonic, so the analytical result of the wave equation is solved. When therotor rotates, eddy currents flowing inside the conducting material field are caused. Thetangential force acting on the rotor because of the action between eddy currents andmagnetic field is produced. The tangential force causes a retardation torque, which leadsto the increase of power and heating effects.