JP2600234B2 - Excitation method of superconducting winding - Google Patents

Description

The present invention relates to a method of exciting a superconducting winding, for example, a superconducting winding provided as a secondary winding of an induction motor, in a closed loop.

B. Summary of the Invention The exciting method of a superconducting winding according to the present invention is such that another winding is coupled to a closed superconducting winding, and a DC exciting current is applied to the other winding, and the exciting current is flowing. A method for exciting a superconducting winding in which the superconducting winding is shifted from a normal conducting state to a superconducting state during a period to capture magnetic flux, wherein a DC exciting current is supplied to the other winding while the superconducting winding is in a superconducting state. And superimposing an alternating current on the same exciting current while the exciting current is flowing, and by changing at least one of the amplitude and frequency of the alternating current, or while the exciting current is flowing. By changing at least one of the current and the magnetic flux of the superconducting winding, the superconducting winding is temporarily shifted from the superconducting state to the normal conducting state, and further shifted from the normal conducting state to the superconducting state to capture the magnetic flux. It is characterized by that.

C. Conventional technology The use of superconducting windings as permanent magnets in various types of equipment is being studied.

For example, the following document discloses that when a three-phase AC power is supplied to a so-called superconducting induction motor having a superconducting winding as a cage secondary winding, the motor finally operates as a synchronous motor.

`` THREE-PHASE INDUCTION MOTOR WIHT A SUPERCONDUCT
IVE CAGE WINDING '' H. Brechna et al .; IEEE TRANSACTIONS, VO
L.MAG15, NO.1, JANUARY 1979. FIG. 7 shows a schematic structure of a three-phase superconducting induction motor according to the above document. In the figure, a cage winding 1 of a rotor is made of a hollow composite conductor in which a superconductor and a stabilizing material (normal conductor) are combined in parallel, and a passage in a rotary shaft 2 is formed in the composite conductor.
A coolant (liquid helium) is supplied through 2a and the pipe 3 and is cooled to below the critical temperature. On the other hand, although the primary winding 4 of the stator is made of a normal conductor, a refrigerant passage is also provided in the primary winding 4 to absorb heat, and a refrigerant (liquid nitrogen) is supplied through a pipe 5. . The rotor and the stator are covered with a cover 6 and evacuated for heat insulation from the outside. 7 is a seal, and 8 is a bearing.

According to the above-mentioned literature, when three-phase power is supplied to a superconducting induction motor, it operates as a normal induction motor at the time of startup, and finally operates as a synchronous motor. (1) Since the slip value s is 1 in the stopped state, a voltage having the same frequency as the primary voltage is induced in the secondary winding 1, so that superconductivity is quenched by heat generated by high hysteresis loss and eddy current loss. You. Therefore, a small secondary current flows through the stabilizing material, a large starting torque is generated, and the rotor starts rotating.

(2) Thereafter, the speed of the rotor increases, and the slip decreases. Accordingly, since the frequency of the secondary voltage decreases, the heat loss continuously decreases to near the synchronous speed, and the secondary winding 1 is cooled toward the critical temperature.

(3) When the critical temperature is reached, the slip value s is not zero (for example, s <0.01), so that a low-frequency secondary current flows through the superconductor of the secondary winding 1, and It jumps to some high value limited by inductance.

(4) Due to the rapid increase of the secondary current, the rotor is accelerated, the secondary voltage is rapidly reduced, and the secondary current is reduced. Since the decrease in the secondary current causes the rotor to decelerate, the secondary voltage increases and the secondary current increases again. Thereafter, the oscillation of the secondary current and the acceleration / deceleration of the rotor continue as a transient state until the synchronous speed is reached.

(5) When the synchronous speed is reached, no voltage is induced in the secondary winding 1, and the current at that time flows semipermanently, and the secondary winding becomes a superconducting magnet. Thereafter, the superconducting induction motor operates as a synchronous motor. I do.

D. Problems to be Solved by the Invention As described above, the superconducting induction motor in which the secondary winding is a superconducting winding operates as an induction motor at the time of starting, so that the starting torque is high and the operation is easy. In addition, since the motor automatically operates as a synchronous motor near the synchronous speed, the loss is small, the speed does not depend on the load, and the output can be controlled by the load angle.
Furthermore, since the structure is the induction motor itself, it is robust and easy to maintain.

However, when the operation shifts from the induction motor to the synchronous motor, a transient state occurs and the secondary current, torque and speed oscillate, which is a major drawback, and the application field of this type of superconducting induction motor is limited. .

Therefore, it is considered that it is better to excite the secondary superconducting winding in a stationary state and to use the secondary superconducting winding as a permanent magnet in advance and to operate as a synchronous motor from the beginning, since there is no transient phenomenon and the field of application is widened.

However, there is no known method for exemplifying a stationary superconducting winding in a closed loop.

An object of the present invention is to provide a method of exciting a stationary superconducting winding in a closed loop state in view of the above-described related art.

E. Means for Solving the Problems The exciting method of the superconducting winding according to the present invention comprises the steps of: coupling another winding to a closed superconducting winding; supplying a DC exciting current to the other winding; In a method of exciting a superconducting winding, which captures magnetic flux by shifting the superconducting winding from a normal conducting state to a superconducting state while a current is flowing, the superconducting winding is in a superconducting state while the other windings are in the superconducting state. By passing a DC exciting current through the AC current, superimposing an AC current on the exciting current while the exciting current is flowing, and changing at least one of the amplitude and the frequency of the AC current, or By changing at least one of the current and the magnetic flux of the superconducting winding while flowing, the superconducting winding is temporarily shifted from the superconducting state to the normal conducting state, and further shifted from the normal conducting state to the superconducting state. Characterized in that the magnetic flux is captured.

In addition, as a method of shifting the superconducting winding from the superconducting state to the normal conducting state and further shifting from the normal conducting state to the superconducting state, at least one of the temperature, current, and magnetic field of the superconducting winding exceeds a critical value. And then change from that value to below the critical value. In particular, when the temperature is changed, it is easy to set the superconducting winding in a superconducting state in advance, superimpose an alternating current on a direct current exciting current flowing through another winding, and change the superposed alternating current. Further, among the methods of changing the superimposed AC current, the method of changing the carrier frequency by supplying the exciting current flowing through the other windings from the PWM-controlled inverter is simple.

In addition, as for the time when the superconducting winding shifts from the normal conducting state to the superconducting state, the period in which the exciting current is flowing through the other windings is at least three times the time constant of the superconducting winding in the normal conducting state. It is preferably time.

Further, when the superconducting winding is the secondary winding of the induction motor and the other winding is the primary winding, the value of the exciting current flowing through each phase of the primary winding is determined by calculating the value of the multi-phase balanced current. It is preferable to use the value at the time.

F. Operation In the above configuration, when a DC exciting current is applied to the other winding, a magnetic field is generated and acts on the closed superconducting winding. At this time, if the superconducting winding is in the normal conducting state, only the magnetic flux passes through the superconducting winding. When the state shifts from the normal conducting state to the superconducting state, the resistance becomes zero and a current flows through the superconducting winding so that the magnetic flux passing at that moment does not change thereafter. This is the trapping of the magnetic flux, and the superconducting winding is cooled to the superconducting state and the stationary superconducting winding becomes a superconducting magnet with the closed loop.

The superconducting winding has at least one of temperature, current and magnetic field.
If one exceeds the critical value, it will be in the normal conducting state, and if it exceeds the critical value, it will be in the superconducting state if it is below the critical value. Especially,
When the superconducting winding is put in the superconducting state in advance, and the AC current is superimposed on the exciting current of the other windings, the magnetic field contains an AC component, so that the superconducting winding generates heat and is quenched due to hysteresis loss and eddy current loss. It becomes conductive. This tendency becomes more pronounced as the amplitude of the superimposed alternating current increases and as the frequency increases. Therefore, when the amplitude of the superposed alternating current is reduced to zero or to a certain extent, the superconducting state is restored. When using a PWM-controlled inverter as the power supply, the excitation current from the inverter originally contains the harmonic current of the carrier frequency due to the PWM control.By using this AC component, the AC current is bothersome from the outside. There is no need to overlap. The amplitude of the AC component increases as the carrier frequency decreases, and decreases as the carrier frequency increases. Therefore, when the excitation current is supplied from the inverter of the PWM control, the superconducting winding enters the normal conducting state when the carrier frequency is lowered, and returns to the superconducting state when the carrier frequency is increased.

When an exciting current is applied to other windings, the magnetic flux passing through the superconducting winding in the normal conducting state increases exponentially according to the time constant, so when the magnetic flux increases, the superconducting winding is changed from the normal conducting state to the superconducting state. It is preferable in terms of efficiency to shift to. If the period during which the exciting current flows through the other windings is at least three times the time constant of the superconducting winding in the normal conducting state, the magnetic flux is sufficiently increased.

When the superconducting winding is the secondary winding of the induction motor and the other winding is the primary winding, the value of the exciting current flowing through each phase of the primary winding causes the magnetic flux captured by the secondary winding to change. Different in size and direction. Therefore, when the value of the exciting current of each phase is selected to be a value at a certain point in time of the multi-phase balanced current, the magnitude of the magnetic flux does not change and only the direction can be arbitrarily set.

G. Embodiment An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows an example of a control device in which a secondary superconducting winding of a three-phase superconducting induction motor 9 is previously excited by using an inverter 10 based on PWM control, and is operated as a synchronous motor from the beginning.

In FIG. 1, the primary winding of the superconducting induction motor 9 is made of a normal conductor, and the secondary winding is made of a superconductor. Cooling of the secondary winding is performed with a simple cooling device when using a normal temperature or high temperature superconductor, and a cooling device using a refrigerant such as liquid helium, liquid nitrogen is provided when using a low temperature superconductor,
In addition, the cooling of the primary winding and the heat insulation with the outside are performed as necessary.

The current control of the inverter 10 is performed by two hysteresis comparators 11 and 12. The difference between the a-phase current control command value and the actual current value is input to one hysteresis comparator 11, and the difference between the b-phase current control command value and the actual current value is input to the other hysteresis comparator 12. The deviation is entered. The ON / OFF outputs of both hysteresis comparators 11 and 12 are given to a gate circuit 13, and the inverter 10 is turned on and off so that a three-phase balanced current according to a command value is supplied from the inverter 10 to the primary winding in the form of a PWM current. Non-conduction is determined. The c phase is obtained by calculation. 14 is an a-phase current detector and 15 is a b-phase current detector.

The carrier frequency of the PWM control depends on the hysteresis width of the hysteresis comparators 11 and 12, and a narrower hysteresis width results in a higher carrier frequency and a wider hysteresis width results in a lower carrier frequency.

Both the hysteresis comparator 11 and 12 are those which can be varied by directing the hysteresis width, the command f _L and, both the hysteresis comparator by selecting a command f _H for the hysteresis width smaller that the hysteresis width and large by the switch SW ₃ I give it to 11,12.

Exciting current command device as a device that outputs a current command value
16 and an AC current command device 17, and a switch S determines which of the two devices 16, 17 obtains the current command value of each phase a, b.
Selection is made with W ₁ and SW ₂ .

The exciting current command device 16 has an exciting current command value I for the a-phase.
_oa and the b-phase excitation current command value I _ob are output. I _oa , I _ob
Is a constant value. In this embodiment, a, b, as an excitation current command value of c phase, 3-phase balanced currents i _a as FIG. 2, i _b, the value of a certain point P of the _{i c I oa, I ob,} I _{so that oc} can be selected arbitrarily
The configuration of the exciting current command device 16 is changed to any phase β and amplitude _Im
Is input, I _oa = I _m cosβ, I _ob = I _m cos (β−2π /
The configuration of 3) is performed to output the a-phase and b-phase excitation current command values I _oa and I _ob . The c-phase excitation current command value
I _oc does not necessarily need to be output. The reason for this is that I _m cos
This is because it is uniquely determined as (β + 2π / 3), and the gate circuit 13 performs a necessary logical operation.

 Here, the excitation will be described as follows.

In a three-phase motor, electric quantities f _a , f _b , f _{c of the} three axes _a , _b , _c
And the electrical quantities f _d and f _{q on} the _d and _{q 2} axes have the relationship of equation (1). Here, θ is the angle between the d axis and the q axis.

When the currents I _a , I _b , and I _c shown in Expression (2) are applied to the phases a, b, and c, the primary currents i _1q and i _1d of the q and d axes are expressed by Expression (3).

Further, if β = θ, equation (3) becomes equation (4).

On the other hand, the relationship between the primary currents i _1q , i _1d and the secondary magnetic fluxes λ _2q , λ _2d is expressed by equation (5).

Where M is the primary and secondary mutual inductance, L ₂ is the secondary self inductance, r ₂ is the secondary resistance, p is the operator, ω _b is the difference between the rotational angular velocity of the coordinate axis and the rotational angular velocity of the rotor. It is.

When the secondary magnetic fluxes λ _2d and λ _2q are obtained from (5) from the above equation, At the time of excitation, ω _b = 0 because of being stationary. ω _b = 0
When the conditions of Equation (4) and Equation (4) are put into Equations (6) and (7), λ _2d = 0 ... Equation (8) Now, if i _1q is changed stepwise, _Therefore , λ _2q = M · I _m {1-exp (−t / τ)} Equation (10) where t is time, and τ is a quadratic time constant (τ = L ₂ / r ₂ ). is there.

From the above results, the magnetic flux is generated which is represented by the formula only the q-axis (10), its size is M · I _m as the final value. When a time equal to or more than three times the time constant τ elapses after the application of the exciting current, the magnetic flux becomes 95% or more of the final value. No magnetic flux is generated on the d-axis. In other words, as shown in FIG. 2, when a current having a phase shifted by β is passed through each primary phase as a value of a three-phase equilibrium current at a certain point in time, the magnetic flux becomes a phase a as shown in FIG. It occurs in the direction also shifted by β from the axis. Therefore, the direction of the magnetic flux can be controlled in any direction by the phase β. β represents the initial position of the magnetic pole position.

The excitation current includes a harmonic current of the carrier frequency due to the PWM control, and the amplitude of the AC component decreases as the hysteresis width of the hysteresis comparators 11 and 12 increases as shown in FIG. The amplitude becomes large, and when the hysteresis width is narrowed, the carrier frequency increases and the amplitude becomes small.

Next, the AC current command device 17 will be described. In the case of speed control, the present device 17 includes a speed command input terminal 18, an encoder 19 for detecting speed, a detector 19 such as a resolver, and an amplifier for outputting a current value (i ^* _T) proportional to the speed deviation as a torque command. 20, a rotation angle detection circuit 21 for obtaining a rotation angle θ from the output of the detector 19, a rotation angle θ and a phase β at the time of excitation.
From the a-phase and b-phase AC waveforms cos (θ + β), cos (θ + β-
2π / 3) sine wave generator 22 and a-phase AC waveform
multiply cos (θ + β) by a torque command ｉi ^* _T ▼ to obtain an a-phase AC current command value ｉi ^* _a ▼ (= ▲ i ^* _T ▼ cos (θ +
β)) and a b-phase AC waveform cos (θ
+ Β-2π / 3) multiplied by a torque command ▲ i ^* _T ▼ to obtain a b-phase AC current command value ▲ i ^* _b ▼ (= ▲ i ^* _T ▼ cos (θ + β)
−2π / 3)). When the load angle control is performed, the load angle δ is input to the sine wave generator 22 as necessary, and cos (θ + β + δ) and cos (θ−2π / 3 + β
+ Δ).

 Next, the operation procedure will be described.

(1) Before starting operation, the secondary winding is brought into a superconducting state in advance. (Static) (2) keep the switches SW _1, SW _2, SW ₃ to the excitation (E) side. By the switches SW ₁ and SW ₂ , the exciting current command value becomes I _oa = I _m cos β I _ob = I _m cos (β−2π / 3), and the carrier frequency becomes low by the switch SW ₃ . Therefore, a DC exciting current and a large harmonic current due to a low carrier frequency flow through each phase of the primary winding. Therefore, a sufficiently large loss occurs in the secondary winding,
The superconductivity is quenched to the normal conducting state.

(3) When the exciting current flows through the primary winding, the magnetic flux becomes τ = L ₂
/ r slide into increased with a time constant of _2.

Therefore, the time constant sufficiently longer than the tau, when passed example 3τ above, to operate the switch SW ₃ (R) side, the carrier frequency is increased.

When the carrier frequency is increased, the magnitude of the harmonic current is reduced and the loss of the secondary winding is reduced, so that the secondary winding is restored to the superconducting state.

At the moment of the superconducting state, the magnetic flux is captured. Thereafter, even if the magnetic flux fluctuates, a current flows through the secondary winding so as to keep it constant.

(4) After capturing the magnetic flux, the switches SW ₁ and SW ₂ are set to the operation (R) side to operate as a synchronous motor. That is, by giving the speed command, the frequency of the three-phase output of the inverter 10 gradually increases, and the motor starts and rotates at a desired speed.

In the case where the torque control, instead of the torque command based on the speed command amplifier 20 outputs, providing a torque command to each of the multipliers 23 and 24 from the terminal 25 through the switch SW _4.

When performing position control, a position detector 26 is provided,
The deviation between the position command from terminal 27 and the detected position is
Amplify at 28, switch SW instead of speed command from terminal 18
The output of the amplifier 28 is set as a speed command by ₅ .

Control of the switches SW ₁ ~ switch SW _5, various operations may be performed by hardware or may be performed by software control.

Further, in the above embodiment, the hysteresis comparators 11, 1
2, the current of the inverter 10 of the PWM control is controlled. However, when the current is controlled by the triangular wave comparison method as shown in FIG. 5, the frequency command to the triangular wave generator 29 is set to f _L and f by the switch SW _3. Switch to _H. Switch SW when energized
₃ to generate a triangular wave having a frequency lower in the E side, causing the switch SW ₃ When the magnetic flux is large enough to generate a triangular wave of a frequency higher in the R-side. As shown in FIG. 6, the AC component in the current flowing through the primary winding increases when the triangular wave (carrier) frequency is low, and decreases when the carrier frequency is high. In FIG. 5, reference numerals 30 and 31 denote comparators without hysteresis. Further, the same members as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will not be repeated.

The method of operating the synchronous motor after the secondary winding has acquired the magnetic flux is not limited to the above-described embodiment, but stores the direction before the operation of the acquired magnetic flux, that is, the magnetic pole position, and sets the magnetic pole direction during operation. As usual, it can be detected by a rotary encoder or a resolver and operated as a normal brushless DC machine.

In each of the above-described embodiments, the quench and the return of the superconducting state are performed using the harmonic current depending on the carrier frequency originally included in the output of the inverter 10 by the PWM control, but the DC power supply and the AC power supply are separately used. The superposition of the alternating current may be turned on / off.

Instead of the superposition of the alternating current, the normal conduction and the superconductivity may be controlled by changing the magnetic field and the current density.

Further, the superconducting winding and the other windings connected thereto are not limited to the relationship between the secondary winding and the primary winding in the above-described superconducting induction motor, but may be arbitrary.

H. Effects of the Invention According to the present invention, any stationary superconducting winding that has been cooled and brought into the superconducting state in advance can be closed-loop excited to form a superconducting magnet. Therefore, particularly when the present invention is applied to a secondary superconducting winding of a superconducting induction motor, the secondary winding can be a superconducting magnet at rest,
Since the motor can be operated as a synchronous motor from the beginning, there is no transient phenomenon when switching from the operation of the induction motor to the operation of the synchronous motor as in the prior art, and the superconducting induction motor can be used in a wide field.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining selection of an exciting current value, FIG. 3 is a diagram for explaining a magnetic flux direction, and FIG. 4 is a diagram for explaining a hysteresis width and an AC component. FIG. 5 is a block diagram showing another embodiment, FIG. 6 is a diagram showing the relationship between the frequency of a triangular wave and an alternating current, and FIG. 7 is a sectional view showing a configuration example of a superconducting induction motor. . In the drawing, 9 is a superconducting induction motor, 10 is an inverter, 11
12 is a hysteresis comparator, 13 is a gate circuit, 14
15 is a current detector, 16 is an excitation current command device, 17 is an AC current command device, 19 is a speed detector, 21 is a rotation angle detection circuit, 22
Is a sine wave generator, 23 and 24 are multipliers, 26 is a position detector, 29
Is a triangular wave generator.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-91198 (JP, A) JP-A-63-249437 (JP, A) JP-A-64-25401 (JP, A)

Claims (7)

(57) [Claims] 1. A closed superconducting winding is coupled with another winding, a DC exciting current is passed through the other winding, and while the exciting current is flowing, the superconducting winding is brought out of a normal conducting state. In a method of exciting a superconducting winding that shifts to a superconducting state and captures a magnetic flux, a DC exciting current flows through the other winding in a state where the superconducting winding is in a superconducting state. By superimposing an alternating current on the excitation current and changing at least one of the amplitude and frequency of the exchange current, the superconducting winding temporarily transitions from the superconducting state to the normal conducting state, and further from the normal conducting state to the superconducting state. To
A method for exciting a superconducting winding characterized by capturing a magnetic flux. 2. The method according to claim 1, wherein an exciting current flowing through the other winding and an alternating current superimposed on the exciting current are supplied from a PWM-controlled inverter, and the carrier frequency of the inverter is changed. A method for exciting a superconducting winding, wherein the superimposed alternating current is changed. 3. The method according to claim 1, wherein a period during which the exciting current flows through the other winding is at least three times a time constant of the superconducting winding in a normal conducting state. A method for exciting the superconducting winding, wherein the superconducting winding is shifted from a normal conducting state to a superconducting state. 4. A superconducting winding according to claim 1, 2 or 3, wherein said superconducting winding is a secondary winding of an induction motor, and said other winding is a primary winding of said induction motor. A method of exciting a superconducting winding, wherein the value of the exciting current flowing through each phase of the primary winding is set to a value at a certain point in time of the multiphase balanced current. 5. A closed superconducting winding is coupled with another winding, a DC exciting current is passed through said other winding, and the superconducting winding is brought out of a normal conducting state while the exciting current is flowing. In a method of exciting a superconducting winding that shifts to a superconducting state and captures a magnetic flux, a DC exciting current flows through the other winding in a state where the superconducting winding is in a superconducting state. By changing at least one of the current and the magnetic flux of the superconducting winding, the superconducting winding is temporarily shifted from the superconducting state to the normal conducting state, and further shifted from the normal conducting state to the superconducting state to capture the magnetic flux. A method for exciting a superconducting winding, comprising: 6. The superconducting device according to claim 5, wherein when a time period during which the exciting current flows through the other winding is at least three times a time constant of the superconducting winding in a normal conduction state, A method for exciting a superconducting winding, wherein the winding is shifted from a normal conducting state to a superconducting state. 7. The superconducting winding according to claim 5, wherein the superconducting winding is a secondary winding of an induction motor, and the other winding is a primary winding of the induction motor. A method of exciting a superconducting winding, characterized in that the value of the exciting current flowing through each phase of the primary winding is a value at a certain point in time of the multi-phase balanced current.