Yingguang Wang

Optimization of Damping Compensation for a Flexible Rotor System With Active Magnetic Bearing Considering Gyroscopic Effect

Active magnetic bearing (AMB) levitated rotating machineries are always required to operate above the rotor first bending critical speed to achieve a high power density. It is important to ensure safe rotor run-down through critical speeds. This paper presents an optimization of damping compensation for a flexible rotor to make maximal use of the limited electromagnetic force to retain flexible deformation. The design, rotor modal properties, and bending model test for an AMB test rig which typifies a 10-kW centrifugal compressor are described in detail. The optimal compensation phase angle with and without considering the gyroscopic effect is first derived from a theoretical model. The flexible deformations with the different control radius and phase are also analyzed. Then, the phase angle from flexible deformation to electromagnetic force in the existing control system is experimentally identified. A phase-shift filter is designed to compensate the corresponding phase difference around the bending frequency. The damping compensation experiments validate the proposed optimization approach.

Field Balancing of Magnetically Levitated Rotors without Trial Weights

Unbalance in magnetically levitated rotor (MLR) can cause undesirable synchronous vibrations and lead to the saturation of the magnetic actuator. Dynamic balancing is an important way to solve these problems. However, the traditional balancing methods, using rotor displacement to estimate a rotors unbalance, requiring several trial-runs, are neither precise nor efficient. This paper presents a new balancing method for an MLR without trial weights. In this method, the rotor is forced to rotate around its geometric axis. The coil currents of magnetic bearing, rather than rotor displacement, are employed to calculate the correction masses. This method provides two benefits when the MLRs rotation axis coincides with the geometric axis: one is that unbalanced centrifugal force/torque equals the synchronous magnetic force/torque, and the other is that the magnetic force is proportional to the control current. These make calculation of the correction masses by measuring coil current with only a single start-up precise. An unbalance compensation control (UCC) method, using a general band-pass filter (GPF) to make the MLR spin around its geometric axis is also discussed. Experimental results show that the novel balancing method can remove more than 92.7% of the rotor unbalance and a balancing accuracy of 0.024 g mm kg−1 is achieved.

Optimal phase compensation control and experimental study of flexible rotor supported by magnetic bearing

In order to pass through the bending critical speed of flexible rotor system supported by magnetic bearing, the phase changes from the rotors flexible deformation to magnetic force at bending critical frequency should be adjusted to increase its damping. In this paper, the optimal control phase of AMB controller is deduced from the theoretical model firstly. Then, the actual control phase is obtained using the method of dynamic analysis combined with model reference identification. Optimal phase to be compensated is determined finally. The experimental result shows that AMB controller added with a optimal phase compensator makes the rotors flexible deformation minimum nearby the bending frequency.

A FEM-based method dynamic analysis of a thrust magnetic bearing with permanent magnet bias

Active magnetic bearings (AMB) are well-known components for the suspension of mechanical objects. The hybrid thrust magnetic bearing (HTMB) with permanent magnet creating bias flux and subsidiary air gap in this paper is used to save energy, and two opposing electromagnetic poles allow control forces in two directions and take account of linearizing effects. The flux distribution is affected by the control voltage and the permanent magnets for the HTMB. Accurate analysis and efficient optimal design are essential to avoid costly trials. The dynamic performances of the HTMB with subsidiary air gap are analyzed. The flux distribution at different time in the HTMB is shown, and the time variation of the magnetic force, the displacement of the thrust plane, the speed of the thrust plane are given respectively in case the voltages are 15V, 20V, and 28V. The inductance of the thrust magnetic bearing is calculated for each position. The described method can simulate the dynamic behavior of the AMB with permanent magnets. It enables design optimization of sophisticated AMBs by extensive parameter studies.