JP3517846B2 - Magnetic bearing control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic bearing control device for supporting a high speed motor in a non-contact manner by a magnetic attraction force.

[0002]

2. Description of the Related Art When a motor is rotated at a high speed, a high output can be obtained even if it has the same physical structure. However, as the rotational speed increases, the rotational friction of the bearings that support the rotating body increases, which raises the temperature and vibrations.Therefore, in conventional rolling bearings and fluid bearings, the rotational speed must be further increased. Was difficult. Therefore, magnetic bearings have been developed that support in a non-contact manner by utilizing magnetic attraction. An example applied to a radial bearing will be described with reference to FIG. Reference numeral 1 is a rotary shaft, and an iron core portion made of a magnetic material is formed on the outer peripheral portion thereof. A stator 2 composed of an electromagnet in which a coil is wound around an iron core of a magnetic material fixed to a fixed side such as a frame via an air gap on the outer periphery thereof.
1, 22 are provided to face each other. Stator 21, 22
Can suck the rotating shafts 1 in opposite directions. A displacement detector 3 detects a radial displacement of the rotary shaft 1, and is fixed near the stator 21 or 22. Reference numerals 41 and 42 denote current amplifiers for amplifying and outputting a current according to an input signal and supplying an exciting current to each of the stators 21 and 22. A levitation controller 5 includes a PID compensation element and sends a command to the current amplifiers 41 and 42. 61
Is a comparator that compares the flying position command and the signal of the displacement detector 3 and sends a deviation signal to the flying controller 5. In this configuration, the command for the levitation position and the levitation position of the rotary shaft 1 detected by the displacement detector 3 are compared by the comparator 61, and if there is a difference, the levitation controller 5 sends a command to the current amplifier 41 or 42 to fix it. An exciting current is applied to the child 21 or 22. Then, the rotary shaft 1 is held so as to come to a predetermined position by the magnetic attraction force acting between the stator 21 or 22 and the rotary shaft 1. Stator 2 shown
A levitation system having the same structure is provided in a direction orthogonal to the direction in which the rotary shaft 1 and 22 are supported.
Constitutes a radial bearing of. 2 sets of this radial bearing,
The rotary shaft 1 can be completely supported in a non-contact manner by being provided in the vicinity of both ends of the shaft. If the rotor of the motor is integrally provided on the rotary shaft 1, high speed rotation can be achieved. In this way, a high-speed motor composed of two sets of radial magnetic bearings, one axial magnetic bearing and a rotor of a motor can be reached by a conventional bearing because when the stator of the motor is excited by a high frequency inverter, the friction of the supporting portion is small. High-speed rotation of the region that could not be done is possible.

[0003]

However, when a high speed motor having such a structure is excited by an inverter and rotated at a high speed, there are the following problems. When an exciting current is supplied to the stator winding of the motor to generate a rotating magnetic field, an axially symmetrical magnetic flux distribution is generated, and the magnetic flux distribution rotates in synchronization with the excitation. If the motor is an induction motor with 2 poles, 2
The two main magnetic fluxes are distributed symmetrically and rotate according to the excitation frequency. However, this magnetic flux is not necessarily axially symmetric because the stator core material has magnetic anisotropy and the magnetic resistance of the magnetic circuit becomes non-uniform depending on the rotational position due to the effects of machining and assembly. Is not. A high frequency inverter that drives a motor using switching elements is also considered to be one of the causes. Although the causal relationship between these is not well understood, the following problems will occur because the magnetic flux distribution is not axisymmetric. That is, when the rotational speed of the magnetic bearing type high-speed motor is increased, even if control is performed to support the rotating shaft 1 at the center of the bearing by non-contact supporting with the radial bearing, as shown in FIG. It shifts from the center to the periphery in the direction of the unbalanced pull, and the deviation increases with the rotation speed. If the levitation controller of the magnetic bearing has a complete integration function, the levitation position will not shift as shown in the figure, but the motor unbalance pull will gradually increase, so it will be held at the rotation center position against it. A large exciting current is supplied to the stator of the bearing. When the integral function is not perfect and the rotating shaft has eccentricity, the more eccentric the unbalanced pull becomes, the more the stator current increases. In any case, if the unbalanced pull becomes large to the point where the floating position of the rotating shaft or the exciting current of the stator exceeds the limit, normal floating control will not be performed and the rotating shaft will contact the fixed side. It causes trouble. Therefore, it is an object of the present invention to provide a magnetic bearing control device that avoids various problems caused by such radial unbalanced pulling of a motor unit.

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention relates to a rotary shaft having a rotor of a motor, a rotor of a magnetic bearing fixed to the rotary shaft, and the rotor and an air gap. And a displacement detector that detects the floating position of the rotor with respect to the stator, and a levitation control that receives a signal from the displacement detector and a levitation position command signal. And a magnetic bearing control device comprising two current amplifiers which supply an exciting current to the stator in response to a command from the levitation controller, in a magnetic bearing control device, the bearing support force is determined from the output currents of the displacement detector and the two current amplifiers. a calculator for calculating a to balance gap immediately before rotation-floating
A bearing force command device for outputting a bearing force command signal of the computing unit, a comparator for receiving the bearing force command device and the signal of the computing unit for comparison, and receiving a flying position command by receiving the signal of the comparator. A supporting force controller for sending to the levitation controller is added to control so that the supporting force of the rotating bearing is supported by the supporting force before the rotation.

[0005]

With the above-mentioned means, even if the motor is excited to increase the rotational speed and the unbalance pull in the radial direction of the motor becomes large, the supporting force controller works to move the levitation position to the opposite direction of the unbalance pull. Since the rotor is deviated in the direction, unbalance pull can be eliminated and it can be supported by the supporting force before rotation, and it can be stably supported without levitation position or exciting current being saturated. .

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a magnetic bearing control device according to the present invention, and FIG. 2 is a detailed diagram of a computing unit in FIG. In the figure, 8 indicates two current signals i ₁₁ and i ₂₁ detected by the current detectors 43 and 44 that detect the exciting current applied to the stators 21 and 22 by the current amplifiers 41 and 42, and the signal of the displacement detector 3. It is a calculator that receives the bearing force _Xf and calculates the bearing force of the bearing. Reference numeral 9 is a support force command device that holds and outputs the support force command signal f _{s 0} of the computing unit 8 in which the gaps before rotation and immediately after ascent are balanced. A comparator 62 receives the output signal f _f of the computing unit 8 and the output signal f _s of the supporting force command unit 9 and compares them. 7 receives the output signal of the comparator 62 and receives the comparator 6
1 is a bearing force controller that sends a signal to 1, and includes at least an integral compensation element. Since the time constant of the integral compensation element may be such that the bearing force control responds to the increase in the rotation speed,
It is set to be considerably larger than the time constant of the levitation controller 5.

FIG. 2 is a detailed diagram of the arithmetic unit 8. 811
Is the output signal X _f of the displacement detector 3 and the axis center position signal X _0.
Is a comparator for obtaining the air gap between the stator 21 and the rotary shaft 1 by taking the difference An adder 812 calculates the sum of the output signal X _f of the displacement detector 3 and the shaft center position signal X ₀ to obtain the air gap between the stator 22 and the rotary shaft 1. 821 is an amplifier for amplifying the signal of the current detector 43,
Reference numeral 822 is an amplifier that amplifies the signal of the current detector 44. 831 receives the output signal X ₀ −X _f of the comparator 811 and the output signal i ₁ of the amplifier 821 and i ₁ / (X ₀ −
X _f ) is a divider. 832 is an adder 81
2 output signal X ₀ + X _f and amplifier 822 output signal i ₂
It is a divider that receives and calculates i ₂ / (X ₀ + X _f ). 841 receives the output signal of the divider 831 (i ₁
/ (X ₀ −X _f )) ² multiplier 842 receives the output signal of the divider 832 (i ₂ / (X ₀ + X _f ))
It is a multiplier that calculates ² . Reference numeral 813 is a comparator that receives and compares the output signal of the multiplier 841 and the output signal of the multiplier 842, and 85 is an amplifier that receives the output signal of the comparator 813 and adjusts the signal level. That is, since the magnetic attraction force of the electromagnet is proportional to (current / air gap) ² the calculator 8 calculates the bearing force of the bearing from the difference between the attraction forces of the two electromagnets. Become.

The comparator 62 outputs a bearing force command signal f _{s0 of} the computing unit 8 in which the air gaps before rotation and immediately after ascent and a bearing force command signal f _f corresponding to the bearing force during rotation are output. Since a signal is received and compared, when the motor rotates at high speed and an unbalanced pull occurs, the comparator 62 outputs the deviation of the supporting force regardless of whether the rotation shaft is eccentric. Support force controller 7 which received this signal
Outputs the command signal X _s by working to reduce the deviation. This command signal X _s is input to the comparator 61 as a floating position command of the floating control system. Then, the levitation control system that receives this command shifts the levitation position in the direction opposite to the direction in which the unbalanced pull of the motor is operating, so that finally the levitation position that gives the same bearing force as before rotation. It deviates to. In this way, if the levitation position is displaced against the unbalanced pull generated in the motor, the unbalanced pull is proportional to (1 / air gap) ² in the same way as the magnetic attraction force. Can be reduced.

[0009]

As described above, according to the present invention, even when an unbalanced pull due to an unbalanced magnetic attraction force is generated when rotating by a drive motor, the flying position is biased in the opposite direction. Since the unbalanced pull is eliminated by arranging the stator, the current of the stator is not saturated, a stable supporting state can be obtained even at high speed rotation, and the practicality of the high speed motor can be enhanced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a detailed diagram of a computing unit of the present invention.

FIG. 3 is a block diagram showing a conventional magnetic bearing control device.

FIG. 4 is a vector diagram showing an unbalanced pull.

[Explanation of symbols]

1 rotation axis 21, 22 Stator 3 Displacement detector 41, 42 Current amplifier 43,44 Current detector 5 Levitation controller 61, 62, 811, 813 comparator 7 Support force controller 8 arithmetic unit 812 adder 821,822 amplifier 831, 832 divider 841,842 multipliers 85 amplifier 9 Support force commander

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F16C 32/04

Claims (2)

(57) [Claims] 1. A rotary shaft provided with a rotor of a motor, a rotor of a magnetic bearing fixed to the rotary shaft, and two magnetic bearings provided so as to face the rotor via an air gap. A stator, a displacement detector that detects a floating position of the rotor with respect to the stator, a levitation controller that receives a signal of the displacement detector and a levitation position command signal, and a susceptor that receives a command of the levitation controller. in the magnetic bearing control device consisting of two current amplifiers for supplying an excitation current to the stator, and a calculator for calculating the bearing capacity of the bearing from the output current of the displacement detector the two current amplifiers, after pre-rotation-floating of
A bearing force commander that outputs a bearing force command signal of the arithmetic unit in which the air gap is balanced, a comparator that receives and compares the bearing force command device and the output signal of the arithmetic unit, and an output signal of this comparator And a supporting force controller for sending a floating position command to the floating controller. 2. The magnetic bearing control device according to claim 1, wherein the time constant of the integral compensation element of the bearing force controller is larger than the time constant of the levitation controller.