JPH0935931A - Drive circuit for ac superconducting magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the size of a power supply by reducing required power- supply voltage and power-supply capacity in a drive circuit for an AC superconducting magnet. SOLUTION: A drive circuit for an AC superconducting magnet includes a primary circuit having an AC power supply 7, a phase advance capacitor 8 and a drive coil 9 which are serially connected, and a secondary circuit having a superconducting coil 11 and a phase advance capacitor 12 which are serially connected. The secondary circuit is a superocnducting circuit with little loss (through a resistor 13). The drive coil 9 and the superconducting coil 11 are closely located to constitute a superocnducting transformer. The capacitance C1, C2 of the phase advance capacitors 8, 12, respectively, and the inductance L1, L2 of the coils 9, 11, respectively, are so set that the primary circuit and the secondary circuit resonate. Thus, the current amplification factor and the voltage amplification factor of the superconducting transformer are greater than one, and the voltage and capacitance required for the AC power supply 7 are smaller than in a conventional circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an AC superconducting magnet.

[0002]

2. Description of the Related Art Conventionally, there is known a technique in which a superconducting coil is formed from a superconductor which transitions to a superconducting state at an extremely low temperature, and a large alternating current is supplied to the superconducting coil to generate a strong magnetic line of force. In general, a superconducting coil that generates magnetic field lines according to an alternating current in a superconducting state is called an alternating-current superconducting magnet.

2 and 3 show a schematic structure of a drive circuit for a conventional AC superconducting magnet. In addition, in these drawings, the same symbols are attached to common portions. In the drive circuit shown in FIG. 2, a high-voltage AC power supply 1, a shunt resistor 2, and a superconducting coil 3 are connected in series, and a phase advancing capacitor 4 is connected in parallel with the superconducting coil 3.
Is connected. The inductance L of the superconducting coil 3 and the capacitance C of the phase advancing capacitor 4 satisfy the resonance condition of ωL = 1 / (ωC), and the entire circuit is set to be an LC parallel resonance circuit. There is.

The circuit shown in FIG. 3 is a circuit in which a large capacity AC power source 5, a shunt resistor 6, a phase advancing capacitor 4 and a superconducting coil 3 are connected in series, and constitutes an LC series resonance circuit. ing. In addition, in FIG. 2 and FIG.
When driving the AC superconducting magnet, the superconducting coil 3
Is cooled to a cryogenic temperature by a coolant such as liquid helium and transitions to a superconducting state. In such a state, when an AC signal having a frequency matching the resonance frequency of each drive circuit is output from the power supplies 1 and 5, a large current flows in the superconducting coil 3 and a strong magnetic line of force is generated.

[0005]

By the way, the LC parallel resonance circuit shown in FIG. 2 requires a high-voltage power supply 1 although the power supply current may be small. In addition, the LC shown in FIG.
In the series resonance circuit, the power supply voltage may be small, but a large capacity power supply 5 is required. Such a feature is extremely exhibited when it is necessary to realize a large current drive like a drive circuit for a superconducting magnet for alternating current.

Conventionally, in the LC parallel resonance circuit, V = jωL
A power supply voltage of several kV represented by I is required, but several kV
Since there is no semiconductor device that withstands pressure and is linearly driven, we prepared for the loss using a separate transformer. Further, in the LC series resonance circuit, it is necessary to prepare a power source having the same capacity as the large current flowing through the magnet, and the loss in the output device of the power source becomes large, so that the power source tends to become extremely large. .

That is, in the conventional device, the required power supply voltage or power supply capacity is remarkably increased, which causes the power supply device to become huge. The present invention has been made in view of the above circumstances, and provides a drive circuit for an AC superconducting magnet capable of downsizing a power supply without significantly increasing the required power supply voltage and power capacity. The purpose is to do.

[0008]

In order to solve the above-mentioned problems, the present invention provides a primary side circuit in which an AC power source, a phase advancing capacitor and a driving coil are connected in series, a superconducting coil and an advancing coil. A secondary side circuit in which a phase capacitor is connected in series, the secondary side circuit is a low-loss superconducting circuit, and the driving coil and the superconducting coil are arranged in proximity to each other to form a superconducting transformer. However, the capacitance of each of the phase advancing capacitors and the inductance of each of the coils are set so that the primary side circuit and the secondary side circuit resonate.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a drive circuit for an AC superconducting magnet according to an embodiment of the present invention. The drive circuit shown in this figure is divided into a primary side circuit and a secondary side circuit. Has been done. Generally, if the voltage is boosted n times by a transformer, the current becomes 1
It is considered that the primary side circuit and the secondary side circuit resonate with each other and the loss (resistance) in the secondary side circuit is extremely small in this embodiment. By doing so, the voltage amplification factor and the current amplification factor are made greater than 1 at the same time.

In the primary side circuit of the drive circuit shown in FIG. 1, 7 is an AC power source of electromotive force E [V], 8 is a phase advancing capacitor of capacitance C1, 9 is a winding number n1 and inductance L1 [H]. Drive coil, 10 is resistance value R1
Resistance (loss in the primary side circuit), which are connected in series to form a primary side circuit. In the secondary side circuit, 11 is the number of turns n2 and the inductance L2.
[H] superconducting coil (AC superconducting magnet), 1
Reference numeral 2 denotes a phase advancing capacitor having a capacitance C2, and a resistor (loss in the secondary side circuit) 13 having a resistance value R2 is connected in series to form a secondary side circuit.

It is desirable to configure the circuit so that the resistance value R2 of the resistor 13 of the secondary circuit is as low as possible.
The inductance L1 is set so that L1 <L2. Further, the driving coil 9 of the primary side circuit
The superconducting coil 11 on the secondary side and the superconducting coil 11 on the secondary side are arranged close to each other so that mutual inductance M [H] is generated between them, and form a superconducting transformer. Further, the capacitances C1 and C2 and the reactances L1 and L2 are set so as to satisfy the following expression (1) so that the resonance frequency of the primary side circuit and the resonance frequency of the secondary side circuit are the same.

[Equation 1]

When a mesh circuit analysis is performed on the drive circuit having the above-mentioned configuration, the following equations (2) to (5) are obtained.

[Equation 2]

(Equation 3)

(Equation 4)

(Equation 5)

When the drive circuit shown in FIG. 1 completely resonates, that is, ωL1 = 1 / ωC1 and ωL2 = 1.
When / ωC2, Δ and I1 are given by the following (6),
It is expressed by equation (7).

(Equation 6)

(Equation 7)

Further, the following equation (8) representing the current amplification factor is derived based on the equations (6) and (7).

(Equation 8)

When the voltage applied to the driving coil 9 is VL1 and the voltage applied to the superconducting coil 11 is VL2, these are expressed by the following equations (9) and (10).

[Equation 9]

(Equation 10)

Further, the following equation (11) representing the voltage amplification factor is derived based on the above equations (9) and (10).

[Equation 11]

Here, the current flowing through the driving coil 9 is I
1 [A], the current flowing in the superconducting coil 11 is I2 [A]
Then, from the above equations (8) and (11), R2 →
In the limit of 0, I1 = 0, I2 = jE / (ωM),
VL1 = E, VL2 = −L2E / M, and in the limit of R2 → ∞, I1 = E / R1, I2 = 0, VL1 = jω
It can be seen that L1I1, VL2 = -jωMI1.

By the way, due to the characteristics of the superconducting coil 11, the resistance R2 on the secondary side of the drive circuit shown in FIG. 1 becomes extremely small. That is, the state is close to the limit of R2 → 0. In addition to this, in the drive circuit of FIG. 1, the capacitances C1 and C2 and the inductances L1 and L2 are set so that the resonance condition of the expression (1) is satisfied. Therefore, in the drive circuit of the present embodiment, the current amplification factor I2 / I1
Is greater than 1. Also, in general, M <(L1 ・ L2)
^Since it is ^1/2 and L1 <L2 in this embodiment, the voltage amplification factor VL2 / VL1 is also larger than 1. From the above, the voltage and capacity required for the AC power supply 7 are
It can be seen that the voltage and current required to drive the superconducting coil 11 in the past can be small compared with the voltage and current.

[0019]

EXAMPLE Next, an example in which the drive circuit according to the above embodiment is actually configured will be described. In the present embodiment, the alternating-current superconducting magnet (superconducting coil 11) has an inner diameter of 34
× 10 ⁻³ [m], outer shape 60 × 10 ⁻³ [m], length 90 ×
10 ⁻³ [m], wire diameter φ0.70 × 10 ⁻³ [m], and number of turns n2 = 980 [turns], and the driving coil 9 has a diameter of 64 × 10 ⁻³ [m] and length. 72 × 10
^-3 [m], wire diameter φ0.70 × 10 ^-3 [m], number of turns n1
= 98 times.

Other circuit constants are as follows. L1 = 0.29 × 10 ⁻³ [H], L2 = 12.
74 × 10 ⁻³ [H], M = 1.55 × 10 ⁻³ [H]
, R1 = 1.026 [Ω], R2 =
0.176 [Ω], C1 = 22.85 × 10
^-3 [F], C2 = 582.4 x 10 ^-6 [F], E
= 2.98 [V].

The results of measuring the current values I1 and I2 and the voltage values VL1 and VL2 applied to the coils of the primary side circuit and the secondary side circuit by actually configuring the drive circuit having the above-mentioned circuit constants are shown below. Show. I1 = 1.71 [A], I2 = 5.00 [A],
VL1 = 2.87 [V], VL2 = 23.6 [V]. From this result, the current amplification factor I2 / I1 = 2.92 and the voltage amplification factor VL2 / VL1 = 8.22 were obtained.

The calculated value of the current amplification factor is 3.23 and the calculated value of the voltage amplification factor is 8.21 in the drive circuit having the above-mentioned circuit constants. It is getting a little low. It is considered that this is because the occurrence of contact resistance due to the connection of the circuit elements in the secondary side circuit increased the resistance value R2. Therefore, if the circuit constant is set in consideration of the increase in the resistance value R2 due to the contact resistance, the desired amplification factor can be achieved.

[0023]

As described above, according to the present invention,
The driving coil of the primary side circuit and the superconducting coil of the secondary side circuit are arranged close to each other to form a superconducting transformer, and the capacitance of the phase advancing capacitor and the inductance of the coil of each circuit are the primary side circuit and the secondary side. It is set to resonate with the side circuit. Further, the secondary side circuit is a superconducting circuit, and its loss is extremely small. Therefore, the current amplification factor and the voltage amplification factor of the superconducting transformer are higher than 1, and the voltage and capacity required for the power supply are smaller than those of the conventional ones. Therefore, there is an effect that the power supply can be downsized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a drive circuit for an AC superconducting magnet according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of a drive circuit for a conventional AC superconducting magnet.

FIG. 3 is a circuit diagram showing an example of a drive circuit for a conventional AC superconducting magnet.

[Explanation of symbols]

7 ... AC power supply, 8, 12 ... Phase advancing capacitor, 9 ...
... drive coil, 10 ... resistance (loss in primary side circuit), 11 ... superconducting coil (superconducting magnet for AC), 13 ... resistance (loss in secondary side circuit).

Claims (1)

[Claims] 1. A primary side circuit including an AC power source, a phase advancing capacitor, and a driving coil connected in series, and a secondary side circuit including a superconducting coil and a phase advancing capacitor connected in series. The secondary side circuit is a low-loss superconducting circuit, the driving coil and the superconducting coil are arranged close to each other to form a superconducting transformer, and the capacitance of each phase advancing capacitor and the inductance of each coil are A drive circuit for an AC superconducting magnet, wherein the primary side circuit and the secondary side circuit are set to resonate.