SCIENCE & EDUCATION

Article file: SE-BMSTU...o059.pdf (1724.72Kb)

1 Bauman Moscow State Technical University, Moscow, Russia

 The paper dwells on stabilization of rotor on active magnetic bearings (AMBs) when developing a mathematical model of the axial rotor pump in ventricle assist device (VAD) and considers vibrations of hard titanium rotor with magnetic inserts.
The urgency of research follows from the increasing number of patients suffering from heart failure. A global aspect in the VAD design is that there is a need to stabilize the rotor and control its movement.
Magnetic bearings, which allow us to provide stabilization of a predetermined position through magnetic forces, solve the problem of contactless suspension of rotor and the problem of its control as well. Therefore, the paper studies the problems of rotor positioning. The essence of work is to find the solution for the rotor control with precision of 0.2 mm at a rotational speed of 5000 to 12000 rev / min. The control problem is solved using a linear-quadratic optimization taking into account the influence of external forces acting on the rotor in the blood stream.
Active magnetic bearings are limited in power, voltage and current control resources. So it is desirable to control resource consumption and minimize it. On the other hand, the bearing must hold the rotor, which is under the influence of disturbing forces, with a given accuracy. Experience shows that a method of linear-quadratic (LQ) optimization is one of the most suitable in this sense for the magnetic suspension, so the paper uses it for magnetic suspension control.
The study showed that the LQ-control provides the most rapid stabilization - at least 1 second. For this problem were selected the gains k_sA,B = 10⁵ N·m^-1, k_iA,B = 10 N·A^-1 that could be realized in practice.
It was found that LQ-control system stabilizes the system in the best way. Displacements of the centers of the rotor sections A and B are about 10-7 m, which is within the error. The LQR-method optimizes work on several criteria. In this case, these criteria were the center displacements of rotor bearings and the control currents. As the regulatory maximum values were chosen: max i _{x,y_A,B} = 0.03 A for control currents, max x _bA,B = max y _bA,B = 0.2 mm for displacements. The values of control currents were within 0.3 - 12 mA, depending on the rotor speed. The study suggests further implementation in practice.

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