RU2242646C2 - Magnetic bearing - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: magnetic bearing has electromagnet which engages the rotor and means for control of windings of the electromagnets provided with output circuits. Each circuit is additionally provided with a throttle which is connected to the diagonal of the bridge made of a pulse current controller and capacitor connected in series between the diode of the bottom arm of the bridge and power source. Each winding of the electromagnet is connected in parallel to the capacitor.

EFFECT: expanded functional capabilities.

2 dwg

Description

The proposed magnetic bearing relates to mechanical engineering and is an electromechanical device designed to be used as contactless rotor bearings when creating various machines, for example, power gyroscopes, gas pumping units, turbo expanders, electric spindles, turbomolecular pumps and large units operating in extreme conditions at high speeds of rotation rotor and in extremely clean environments.

Currently, magnetic bearings (MP) are successfully used in the above machines and there is the prospect of expanding their use in new projects of domestic and foreign machines.

An analysis of the state of the art, taking into account existing domestic experience in the development of electromagnetic bearings for gas compressors [1], shows that the operation of machines with magnetic bearings is adversely affected by various forms of rotor vibrations at their own frequency, which, as a rule, are in the operating range of rotational speeds cars or close to it. When working in the resonance region, the amplitude of the rotor oscillations in the magnetic field increases, which can lead to disruption of the machine’s performance.

To reduce the influence of these rotor vibrations, one of the known methods can be used, which consists in improving the damping properties of the magnetic field, which is associated with the need to increase the control power and dynamic stiffness of the magnetic field [2].

According to the principle of operation, magnetic bearings are a system for automatically controlling the position of a ferromagnetic body (rotor) using an electromagnet that performs the function of an executive body of the system. The current in the electromagnet winding is controlled by the control equipment according to the signal of the rotor position. Regulation is carried out so that there is a gap between the rotor and the electromagnet. In the general case, in order to stabilize the position of the rotor in each of the directions of freedom of movement of the rotor, the MP system should contain its own electromagnet with the corresponding output stage of the control equipment.

Known MPs have output stages of control equipment operating in a pulsed mode and made according to a single-cycle voltage converter in the form of an "incomplete bridge" [3], which is shown in Fig. 1. Transistors Q1 and Q2 operate in a pulsed mode. The winding of the electromagnet L1 is included in the diagonal of the "bridge". With open transistors, the current in the winding of the electromagnet increases, and with closed transistors, the current closes through diodes D1, D2 and the power supply V1. If the transistor Q1 is closed, and Q2 is open, then the current is closed through the diode D1. In this mode, the average value of the voltage on the winding of the electromagnet U1 is proportional to the voltage of the power supply V1, the value of which is selected depending on the parameters of the elements of the output stage and the voltage level of the backup power supply, and the duty cycle of the S1 of the transistor Q1, which can be adjusted usually by analog or digital methods, those.

U1 = S1V1

In the known MP [4], adopted as a prototype, with the above-described output stage circuit, the average voltage on the electromagnet winding cannot be more than the voltage of the power supply source. The ripple of the supply voltage of the electromagnet winding, occurring at a high switching frequency of transistors, is the main source of radio noise created by the cable connecting the winding to the output stage. These factors do not allow the well-known MP to achieve improved damping properties by increasing the control power, because the magnitude of the voltage across the winding is limited by the voltage of the power source. The dynamic stiffness of the MP is limited by the existing level of radio interference.

Thus, the use of the known MP is limited in machines that require a reduction in the existing level of rotor vibrations when passing critical rotational speeds and / or in the operating mode, which narrows the scope of the MP.

The present invention solves the problem of creating a magnetic field characterized by improved damping properties, which allow to reduce rotor vibrations to the maximum permissible level of functioning of the components and assemblies that make up the machines.

The technical result achieved by the present invention, which consists in improving the damping properties of the magnetic field, is based on the modernization of the output stage of the control equipment of the magnetic field by supplementing its functions with the ability to increase the average voltage on the winding of the electromagnet higher than the voltage of the power supply, and to filter the voltage on the winding, reducing the effect of high-frequency ripples.

The problem is solved in such a way that in comparison with the known MP, including one or more electromagnets with control equipment, the output stages of which, according to the number of electromagnets, regulating the current in the electromagnet windings, contain transistors Q1, Q2 and diodes D1, D2 connected according to the "incomplete" circuit bridge "and installed respectively in opposite shoulders, and the electromagnet winding is included in the diagonal of the" bridge ", it is new that each output stage is equipped with an additional inductor L2 included in the diagonal of the" bridge "instead the windings of the electromagnet L1, and a capacitor C connected in series between the diode D1 of the lower arm of the "bridge" and the power source, and the winding of the electromagnet L1 is connected in parallel with the capacitor C.

Indeed, the inclusion of an additional inductor and capacitor in the output stage of the MP control equipment allows the fullest use of the properties of the inductive energy storage and the energy advantages of the pulse control method to increase the voltage on the electromagnet winding higher than the voltage of the power supply. In addition, the capacitor acts as an element that smooths out the voltage ripples on the electromagnet winding, which occur at a high frequency corresponding to the switching frequency of power transistors. This allows you to reduce the overall level of radio interference in the control system and, accordingly, increase the dynamic stiffness of the MP.

Thus, additional elements included in the output stage of the control equipment of the proposed MP, allow to increase the control power by increasing the voltage on the winding of the electromagnet without changing the voltage value of the power source and to improve the damping properties of the MP.

Based on the foregoing, it can be concluded that the essential features presented in the formula of the invention are sufficient to obtain the desired technical result.

Figure 2 presents a diagram of the output stage of the control equipment of the proposed MP, which is one of the options for controlling the movement of the rotor in one of the directions of free movement. The complete rotor MP system contains such a number of electromagnets and, accordingly, output stages in the control equipment, which is necessary to limit the movement of the rotor in the required directions. Each electromagnet has a winding 1, the current in which regulates the output stage, containing transistors 2, 3, operating in a pulsed mode, and diodes 4, 5, interconnected according to the "incomplete bridge" circuit and mounted respectively in opposite arms of the "bridge". The inductor 6, which serves as an energy storage device, is included in the diagonal of the "bridge". A capacitor 7, transforming the energy stored by the inductor, and smoothing high-frequency oscillations, is connected in series between the diode 4 of the lower arm of the "bridge" and the power source. The winding of the electromagnet 1 is connected in parallel with the capacitor 7.

With open transistors 2, 3, the current in the inductor 6 increases and energy accumulates. When the transistor 2 is closed and the transistor 3 is open, the inductor current closes through the diode 4 and the capacitor 7 connected in parallel with the electromagnet winding 1. The energy stored in the inductor is transformed into a capacitor 7, and the voltage on it can exceed the voltage of the power source V2. In this mode, the average value of the voltage on the winding of the electromagnet U2 is connected with the duty cycle of the S2 switch on of the transistor 2 and the power supply voltage V2 by the ratio

If transistors 2, 3 are closed, then the inductor current closes through diodes 4, 5, in parallel connected capacitor 7 with winding 1 to the power source V2.

The voltage ripple on the electromagnet winding at a high frequency corresponding to the switching frequency of the transistors in this circuit is reduced in accordance with the transmission coefficient of the L2C filter compared to the ripple level equal to the supply voltage in the known MP.

Thus, the proposed MT allows to reduce the level of rotor vibrations by improving the damping properties in the MT due to the use of output stages in the control equipment, which have the ability to increase the control voltage on the electromagnet winding higher than the supply voltage and, accordingly, the control power, as well as a low level of high-frequency pulsations, which makes it possible to increase the dynamic stiffness of the MP.

The possibility of implementing the proposed MP and achieving the required technical result is practically confirmed in the Scientific Research Institute of VNIIEM on an experimental sample of MP designed for use in gas pumping units.

Sources of information

1. Proceedings of NPP VNIIEM. Questions of Electromechanics, Volume 100, 2001, p.275-282.

2. Proceedings of NPP VNIIEM. Magnetic suspension of rotors of electric machines and mechanisms, Volume 89, 1989, p.41-44.

3. Sources of secondary power. / Edited by Yu.I. Konev. - M.: Radio and Communications, 1990, p.93.

4. The control system of magnetic bearings. Operation manual TAIK. 656447.018 RE - Documentation NPP VNIIEM (prototype).

Claims (1)

A magnetic bearing, including at least one electromagnet interacting with the rotor, to create a gap between the rotor and the electromagnet, controls for the windings of electromagnets with output stages in the number of electromagnets, each of which contains transistors and diodes connected according to an incomplete bridge circuit and installed respectively in opposite the shoulders of the bridge, characterized in that each output stage is equipped with a choke included in the diagonal of the bridge, and a capacitor connected in series between Odom lower bridge arm and the power supply, a coil of each electromagnet connected in parallel with the capacitor.

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