JPH07101051B2 - Magnetic bearing control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method of controlling a magnetic bearing that allows a rotating body supported by a magnetic bearing to safely pass a critical speed.

[Prior Art] As a non-contact type bearing, a magnetic bearing that attracts and holds a rotating shaft by a magnetic force of an electromagnet is known. In the magnetic bearing, the position of the rotating shaft is detected by the position sensor, and when the rotating shaft is displaced from the center position, the electric current of the electromagnet is changed by the servo system based on the signal from the position sensor to return the rotating shaft to its original position. Have control.

Since magnetic bearings are non-contact and have little friction loss, turbines,
Among rotary machines such as pumps, compressors, expanders, centrifuges, motors, and generators, they are used as bearings for particularly high-speed rotary machines. Since magnetic bearings do not require lubricating oil or gas, they are used for special applications such as molecular pumps, rotary machines for nuclear power and cryogenic temperatures.

[Problems to be Solved by the Invention] Generally, in a high-speed rotating body supported by a spring element, how to pass a critical speed causing resonance is a big problem.

In the conventional magnetic bearing, a method of increasing the damping constant of the magnetic bearing in the vicinity of the number of revolutions of the critical speed to pass the critical speed is adopted. However, with this method, it is difficult to exceed the higher critical speed, and in order to exceed the third critical speed, the spring constant of the magnetic bearing is changed according to the rotational speed of the rotating body. , It was necessary to find a route B that can safely pass the dangerous speed indicated by the broken line.

Such tuning is a manual adjustment of the spring constant by trial and error, which takes a lot of time and effort. Furthermore, if the rotating body is different, different tuning must be performed, and it cannot be handled uniformly. Further, in the path B passing through the critical speed while increasing (or decreasing) the rotation speed of the rotating body, the rotating body has inertia, so that the rotating body becomes the critical speed for a reasonable time that may cause a problem. Since the speed is kept close to each other, whirling of the rotating body may cause contact between the rotating body and the bearing and damage the bearing.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method of controlling a magnetic bearing that allows a rotating body to safely and easily pass a critical speed.

[Means for Solving Problems] A method of controlling a magnetic bearing according to the present invention, in which a rotating body supported by a magnetic bearing is accelerated to rotate when passing a primary, secondary, or tertiary critical speed thereof. When the body approaches the primary critical velocity curve, the spring constant of the magnetic bearing is sharply reduced to pass the primary critical velocity curve, and then the spring constant of the magnetic bearing is sequentially increased to obtain the secondary critical velocity curve. When approaching, the spring constant is suddenly decreased to pass the secondary critical speed curve, and the spring constant is increased until the tertiary critical speed curve is approached. Then, the spring constant is rapidly decreased to pass the tertiary critical speed curve. It was made to let.

[Operation] The critical speed is determined by physical quantities such as the shape, size, specific gravity, elastic modulus, and Young's modulus of the rotating body, and has a certain value when the spring constant of the magnetic bearing has a certain value. There are usually some critical speeds such as first-order, second-order, third-order, etc. from low speed to high speed. FIG. 1 shows an example of a critical speed curve when both ends of the rotary shaft are supported by magnetic bearings.

By controlling the current flowing through the electromagnet of the magnetic bearing by the control system, the spring constant, damping constant, etc. of the magnetic bearing can be arbitrarily changed.

In the present invention, the spring constant K of the magnetic bearing is controlled with respect to the rotation speed N of the rotating body as shown in, for example, FIG. To follow.

That is, the vibration system of the rotating body is analyzed to find the optimum spring constant and damping constant, and at the time of start / stop, the spring constant and damping constant of the magnetic bearing are set to optimum values as the rotational speed of the rotating body increases and decreases with a computer. Control. Then, when the critical velocity curve of each of the first order, the second order, etc. is approached, the spring constant of the magnetic bearing is rapidly reduced (increases when stopped). Since the spring constant of the magnetic bearing can be changed instantaneously (on the order of μsec) by changing the current flowing through the electromagnet, the rotating body quickly crosses the critical speed curve without time for vibration to increase at the critical speed. . Since the speed at which the spring constant of the magnetic bearing can be varied and the speed at which the rotational speed of the rotating body can be varied are completely different, the rotational speed of the rotating body remains almost constant while the rotating body passes through the critical speed curve. Can be considered The number of rotations of the rotating body at the time of passing the dangerous speed may be controlled to be constant.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a principle configuration diagram of the magnetic bearing 1, in which four electromagnets 3 are installed on the outer circumference of the rotary shaft 2 in the vertical and horizontal directions. By controlling the current flowing through the coil of the electromagnet 3, the magnetic force with which the electromagnet 3 attracts the rotating shaft 2 can be changed. An eddy current type gap sensor 4 is provided on the outer circumference of the rotary shaft 2 to detect the displacement of the rotary shaft 2.

FIG. 3 shows a control system for controlling the current flowing through the magnetic bearing 1. The control system is the rotary shaft 2 and the gap sensor 4
PID (proportional, integral, derivative) control is performed with the displacement x of and as a control amount.

In the proportional control, the displacement signal x and the reference signal x ₀ (displacement when the rotary shaft 2 is located at the central axis of the magnetic bearing 1) are compared, and their deviation, that is, the magnetic bearing of the rotary shaft 2 is compared. The displacement Δx from the central axis of 1 is input to the amplifier 5, and the displacement Δx
Is output by the displacement feedback gain K (N). K (N) is the spring constant of the magnetic bearing 1, and K · Δx is the spring force ΔF repulsive to the displacement Δx.
The output of the amplifier 5 is further amplified by the power amplifier 6 and supplied as a drive current for the magnetic bearing 1.

The rotation shaft 2 is provided with a rotation speed sensor 7 that detects the rotation speed N, and the rotation speed N is input to the CPU 8 of the computer of the control system. The relationship between the rotational speed N and the spring constant K as shown in FIG. 2 is previously input to the CPU 8, and the displacement feedback gain K (N) is controlled based on the rotational speed N from the sensor 7.

That is, when the rotational speed reaches a predetermined rotational speed close to the primary, secondary, and tertiary critical speed curves, the gain K (N) is sharply reduced and the currents to all the electromagnets 3 of the magnetic bearing 1 are reduced. It drops rapidly and the rotating shaft 2 passes the critical speed.

Also, for the purpose of differentiating (integrating) control, the signal x from the gap sensor 4 is input to the differentiating (integrating) device 9, and further the coefficient device
The coefficient α (β) is multiplied by 10 and input to the power amplifier 6. The differential component gives the damping force of the magnetic bearing 1, and the coefficient α is the damping constant of the magnetic bearing 1. An optimum value of the damping constant α is obtained from the vibration characteristics of the rotating shaft system and input to the computer in advance, and the damping constant α is automatically adjusted to the optimum value by learning. Further, the integral component acts to enhance the static rigidity of the magnetic bearing 1.

In determining the route A on the critical velocity diagram of FIG. 1, the route where the spring constant K is too high is not passed. This is because a high spring constant K requires a large power supply for supplying a large current to the magnetic bearing 1. However, if the spring constant K is made too small, the spring of the magnetic bearing 1 becomes weak and the position control of the rotary shaft 2 becomes impossible. Therefore, the position must be controlled to a certain extent. In rated operation, the spring constant K is made as small as possible to reduce the energy required for control.

Although the magnetic bearing 1 of the above embodiment is a radial bearing that supports the radial load of the rotary shaft 2, it can be applied to a thrust bearing that supports the axial load of the rotary shaft 2. Also,
The present invention is not limited to the shaft-shaped one, but can be applied to a disc-shaped or spherical-shaped rotating body. In addition, in the above embodiment,
Although the first and second critical speed curves are passed one by one, the first and second critical speed curves may be passed at once by a sudden change in the spring constant. Further, the present invention can of course be applied to passage of higher critical speeds of the fourth order or higher.

[Effects of the Invention] The present invention has the following effects.

(1) Since the spring constant of the magnetic bearing, which can be changed in an extremely short time, is suddenly changed in the vicinity of the critical speed so as to pass the critical speed curve, it is necessary to start the rotating body.
It is possible to safely and reliably pass the dangerous speed when the vehicle is stopped.

(2) The critical speed curve can be obtained by calculation from physical quantities such as the shape of the rotor and the specific gravity, and since the spring constant of the magnetic bearing is controlled based on this critical speed curve, troublesome tuning is unnecessary. In addition, it is a general control method that can easily pass through even higher critical speeds and can be applied to any rotating body.

[Brief description of drawings]

FIGS. 1 and 2 show an example of spring constant control of a magnetic bearing according to the present invention. FIG. 1 is a critical velocity diagram, and FIG. 2 is a diagram showing spring constant characteristics with respect to rotational speed. FIG. 3 is a block diagram showing a control system for carrying out the method of the present invention, and FIG. 4 is a block diagram showing the principle structure of a magnetic bearing. In the figure, 1 is a magnetic bearing, 2 is a rotating shaft, 3 is an electromagnet, 4 is a gap sensor, 5 is an amplifier, 6 is a power amplifier, 7 is a rotation speed sensor, 8 is a CPU, 9 is a differentiator (integrator), 10 Is a coefficient unit.

Claims (1)

[Claims] 1. When increasing the speed of a rotating body supported by a magnetic bearing and passing its primary, secondary, and tertiary critical speeds, when the rotating body approaches the primary dangerous speed curve, The spring constant is rapidly decreased to pass the primary critical velocity curve, and then the spring constant of the magnetic bearing is sequentially increased. When the secondary critical velocity curve is approached, the spring constant is rapidly reduced to the secondary secondary A method of controlling a magnetic bearing, comprising: passing a critical velocity curve, increasing a spring constant until it approaches a tertiary dangerous velocity curve, and then rapidly decreasing it to pass a tertiary critical velocity curve.