JP2012231086A - Exciting power supply for superconducting magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily perform the work to adjust a current value flowing through a superconducting coil to a desired current value.SOLUTION: A voltage control circuit 25 controls a transistor 22 so that an output voltage value of the transistor 22 becomes +3 V as compared with a voltage value set by a reference voltage value setter 28. A diode line 24 steps down +3 V which is the output voltage value of the transistor 22 by 6 V. As a result, the output voltage value of an exciting power supply 5 is controlled to a value within a range of -3 V or more and +3 V or less.

Description

  The present invention relates to an excitation power supply that supplies current to a superconducting coil that constitutes a superconducting magnet.

  In the NMR magnet and MRI magnet, current circulates through a permanent current switch (see Patent Document 1) provided in the superconducting magnet. In this current circulation loop, the current (magnetic field) slightly decreases, but the current continues to flow almost permanently with little loss. Then, normally, after a year or more has passed, the work of returning the slightly decreased current value is performed.

  In this operation, the current is temporarily switched to the current supply from the excitation power source brought from the outside. Specifically, first, as shown in FIG. 1, the excitation power supply 5 is connected to the current circulation loop A by the power cables 4 a and 4 b respectively connected to both ends of the permanent current switch 3. Next, a current corresponding to the current flowing in the current circulation loop A is supplied from the excitation power source 5 to the superconducting coil 2. Here, since the current value flowing through the current circulation loop A cannot be directly measured, the operator estimates the current value flowing through the current circulation loop A and determines the current value supplied from the excitation power source 5 to the superconducting coil 2. It will be. The current supplied from the excitation power source 5 flows in this order through the loop B including the excitation power source 5, the power cable 4a, the permanent current switch 3, and the power cable 4b. The direction of the current flowing through the permanent current switch 3 in the loop B is opposite to the direction of the current flowing through the permanent current switch 3 in the current circulation loop A. Therefore, the current flowing through the permanent current switch 3 gradually decreases. Then, the current circulation loop A is opened by the permanent current switch 3 at the timing when the operator determines that the current flowing through the permanent current switch 3 has become almost zero. Then, the current supplied from the excitation power source 5 flows through the loop C including the excitation power source 5, the power cable 4a, the superconducting coil 2, and the power cable 4b in this order.

  Here, when the current circulation loop A is opened, if the current value flowing through the current circulation loop A matches the current value flowing through the loop B, no voltage is generated at both ends of the superconducting coil 2. . In this case, the current value flowing through the loop C is adjusted to a desired current value using the excitation power source 5. When the adjustment is completed, the current circulation loop A is closed by the permanent current switch 3. At this time, almost no current flows through the permanent current switch 3, but when the current supplied from the excitation power supply 5 is lowered, the current flows into the permanent current switch 3 and is supplied from the excitation power supply 5. When the current becomes zero, all the current flowing through the superconducting coil 2 circulates in the current circulation loop A via the permanent current switch 3. At this time, the excitation power source 5 is disconnected from the superconducting magnet 1 to complete the operation.

  On the other hand, when the current circulation loop A is opened, if the current value flowing through the current circulation loop A does not match the current value flowing through the loop B, a voltage is generated at both ends of the superconducting coil 2. . If the current value flowing through the loop B (the output current value of the excitation power source 5) is larger than the current value flowing through the current circulation loop A (the current value flowing through the superconducting coil 2), the needle of the voltmeter 9 becomes positive. If the output current value of the excitation power source 5 is smaller than the current value flowing through the superconducting coil 2, the needle of the voltmeter 9 swings negatively. When a voltage is generated at both ends of the superconducting coil 2, the magnetic field in the vicinity of the superconducting coil 2 changes, and there is a possibility that the superconducting state is lost. Therefore, the operator closes the current circulation loop A again with the permanent current switch 3 to avoid a voltage increase or decrease when the needle is likely to swing while looking at the voltmeter 9. Since the current circulation loop A is closed, the current supplied from the excitation power source 5 circulates in the loop B, and the current flowing through the superconducting coil 2 circulates in the current circulation loop A. Thereafter, the operator finely adjusts the output current value of the excitation power source 5 and opens the current circulation loop A again with the permanent current switch 3. This operation is repeated until no voltage is generated at both ends of the superconducting coil 2.

  Patent Document 2 discloses a superconducting magnet device in which an excitation power source includes a switch circuit corresponding to a permanent current switch. In Patent Document 2, the switch circuit is turned on when a power failure occurs to short-circuit the output side of the current control unit (superconducting coil input side), and at the time of power recovery, the switch circuit is turned off and the output side of the current control unit (super The short circuit on the input side of the conductive coil is released, and the output current in the current control unit at the time of power recovery is made to coincide with the current value flowing in the superconductive coil at the time of power recovery.

JP-A-8-69911 Japanese Patent No. 4414636

  By the way, an operator's skill is required to adjust the current value flowing through the superconducting coil to a desired current value using an excitation power source brought from outside. As described above, since the value of the current flowing through the current circulation loop cannot be directly measured, the superconducting coil and the permanent current switch are jointed by simple construction or there is some problem, and the current circulation loop flows. When the current value decays severely, it is difficult to predict the current value flowing through the current circulation loop, and this work becomes more difficult. In such a case, it is effective to measure the magnetic field in advance and determine the value of the current flowing through the superconducting coil.

  An object of the present invention is to provide an excitation power source for a superconducting magnet that can facilitate the operation of adjusting the current value flowing through the superconducting coil to a desired current value.

  The excitation power source for the superconducting magnet in the present invention is an excitation for supplying current to the superconducting coil by connecting to both ends of the switch means provided in a part of the current circulation loop of the superconducting coil constituting the superconducting magnet. The power supply further comprises voltage limiting means for limiting an output voltage value to the superconducting coil to a value within a predetermined range.

  According to the above configuration, the output voltage value from the exciting power supply to the superconducting coil is limited to a value within a predetermined range. Therefore, when the current circulation loop is opened while supplying current from the excitation power source to the superconducting coil, the voltage value generated at both ends of the superconducting coil becomes a value within a predetermined range. If the value within the predetermined range is a value that does not affect the superconducting state, even if a voltage is generated at both ends of the superconducting coil, the operator does not need to rush and close the current circulation loop. Thereby, when opening a current circulation loop, the burden accompanying the operation | work which makes the electric current value which flows through a superconducting coil, and the output electric current value of exciting power supply correspond can be reduced. Therefore, the operation of adjusting the current value flowing through the superconducting coil to a desired current value can be facilitated.

  In addition, the excitation power source for the superconducting magnet according to the present invention may further include current control means for controlling the output current value to the superconducting coil to be a set value. According to said structure, it controls so that the output current value from an exciting power supply to a superconducting coil becomes a set value. Therefore, if the current circulation loop is opened, the current value flowing through the superconducting coil finally settles to the set value. As a result, if the set value is set to a desired current value, the current value flowing through the superconducting coil is desired without adjusting the current value flowing through the superconducting coil after opening the current circulation loop to the desired current value. Current value. Therefore, the operation of adjusting the current value flowing through the superconducting coil to a desired current value can be further facilitated.

  Further, in the excitation power source for the superconducting magnet according to the present invention, the voltage limiting means applies the voltage to the superconducting coil when the voltage value generated at both ends of the superconducting coil is larger than a first threshold value which is a positive value. When the output voltage value is clamped to the first threshold value and the voltage value generated at both ends of the superconducting coil is smaller than the second threshold value which is a negative value, the output voltage value to the superconducting coil is By clamping to the second threshold value, the output voltage value to the superconducting coil is limited to a value within the predetermined range with the first threshold value as the upper limit value and the second threshold value as the lower limit value. Good. According to the above configuration, when the voltage value generated at both ends of the superconducting coil is larger than the first threshold value which is a positive value, the output voltage value to the superconducting coil is clamped to the first threshold value. In addition, when the voltage value generated at both ends of the superconducting coil is smaller than the second threshold value which is a negative value, the output voltage value to the superconducting coil is clamped to the second threshold value. As a result, the output voltage value from the excitation power source to the superconducting coil is limited to a value within a predetermined range in which the first threshold value is the upper limit value and the second threshold value is the lower limit value. Therefore, the range in which the output voltage value from the excitation power source to the superconducting coil is limited can be easily changed by changing at least one of the first threshold value and the second threshold value.

  In the excitation power source for the superconducting magnet according to the present invention, the limitation by the voltage limiting unit is enabled during a certain period before and after opening the current circulation loop, and the limitation by the voltage limiting unit is invalid at other times than the certain period. There may be further provided voltage limiting limiting means. According to said structure, generation | occurrence | production of the voltage by the quench which arose in the superconducting coil cannot be detected while the output voltage value from an exciting power supply to a superconducting coil is restrict | limited to the value within a predetermined range. Therefore, the period for limiting the output voltage value from the excitation power supply to the superconducting coil is limited to a certain period before and after opening the current circulation loop. Thereby, quenching of the superconducting coil can be detected while the output voltage value from the exciting power supply to the superconducting coil is not limited.

  In the exciting power supply for a superconducting magnet according to the present invention, the switch means may be a permanent current switch provided inside the superconducting magnet and including a superconducting material. According to the above configuration, when the permanent current switch is in a superconducting state together with the superconducting coil, the value of the current flowing through the permanent current switch cannot be directly measured. For this reason, it has become more difficult to match the value of the current flowing through the superconducting coil with the output current value of the exciting power supply when the current circulation loop is opened. However, since the output voltage value from the excitation power supply to the superconducting coil is limited to a value within a predetermined range, the voltage value generated at both ends of the superconducting coil when the current circulation loop is opened is set to a value within the predetermined range. Become. Therefore, it is possible to further reduce the burden associated with the work of matching the current value flowing through the superconducting coil with the output current value of the exciting power supply when the current circulation loop is opened.

  In the exciting power source for the superconducting magnet in the present invention, the switch means may be a mechanical relay or a semiconductor switch provided outside the superconducting magnet. According to the above configuration, during the supply of current from the excitation power supply to the superconducting coil, the current suddenly changes due to the trouble of the excitation power supply itself, or the superconducting coil is quenched, etc. If an abnormality occurs in any of the magnets, both ends of the output of the excitation power supply are short-circuited by closing the mechanical relay or semiconductor switch. As a result, a current flows through the mechanical relay or the semiconductor switch, and the excitation power source and the superconducting coil are substantially separated, so that the excitation power source and the superconducting magnet can be prevented from being damaged. Here, if the mechanical relay or the semiconductor switch is set to the B contact so that the mechanical relay or the semiconductor switch is automatically closed at the time of a power failure, the excitation power source or the superconducting magnet can be more reliably prevented from being damaged.

  Further, in the excitation power source for the superconducting magnet according to the present invention, the switch means is provided in the superconducting magnet and includes a permanent current switch including a superconducting material, and is provided outside the superconducting magnet and serves as the permanent current switch. A mechanical relay or a semiconductor switch connected in parallel, and when circulating current in the current circulation loop, the current circulation loop is closed by the permanent current switch, while the superconducting coil is connected from the excitation power source. When supplying a current to the circuit, the permanent current switch may be opened and the current circulation loop may be opened and closed by the mechanical relay or the semiconductor switch. According to the above configuration, when the current is circulated in the current circulation loop, the current continues to flow almost permanently without causing any loss by closing the current circulation loop with the permanent current switch. On the other hand, when a current is supplied from the exciting power source to the superconducting coil, the permanent current switch is opened and the current circulation loop is opened and closed with a mechanical relay or a semiconductor switch. If an abnormality occurs in either the excitation power supply or the superconducting magnet while the current is being supplied from the excitation power supply to the superconducting coil, the mechanical power supply or the semiconductor switch is closed to close the excitation power supply. Short-circuit both outputs. As a result, a current flows through the mechanical relay or the semiconductor switch, and the excitation power source and the superconducting coil are substantially separated, so that the excitation power source and the superconducting magnet can be prevented from being damaged. Here, if the mechanical relay or the semiconductor switch is set to the B contact so that the mechanical relay or the semiconductor switch is automatically closed at the time of a power failure, the excitation power source or the superconducting magnet can be more reliably prevented from being damaged.

  According to the exciting power source for the superconducting magnet of the present invention, the output voltage value from the exciting power source to the superconducting coil is limited to a value within a predetermined range, so that a current circulation loop is provided while supplying current from the exciting power source to the superconducting coil. When opened, the voltage value generated at both ends of the superconducting coil becomes a value within a predetermined range. This can reduce the burden associated with the work of matching the current value flowing through the superconducting coil with the output current value of the excitation power source when opening the current circulation loop, so that the current value flowing through the superconducting coil can be reduced to the desired current value. It is possible to facilitate the adjustment work.

It is a schematic diagram which shows a superconducting magnet and an excitation power supply. It is a figure which shows the electrical structure of an exciting power supply. It is a figure which shows the output characteristic of an excitation power supply. It is a figure which shows the electrical structure of an exciting power supply. It is a schematic diagram which shows a superconducting magnet and an excitation power supply. It is a figure which shows the electrical structure of an exciting power supply. It is a figure which shows the structure of a current-voltage control circuit. It is a figure which shows the output characteristic of an excitation power supply. It is a schematic diagram which shows a superconducting magnet and an excitation power supply.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
(Configuration of superconducting magnet)
An excitation power source (excitation power source) 5 for a superconducting magnet according to this embodiment is used for a superconducting magnet 1 as shown in FIG. The superconducting magnet 1 has a superconducting coil 2 and a permanent current switch 3 as shown in FIG.

  The superconducting coil 2 is formed by winding a superconducting wire. In superconducting magnet 1 in the superconducting state, circulating current IL circulates in current circulation loop A including superconducting coil 2 and permanent current switch 3.

  The permanent current switch 3 is provided in a part of the current circulation loop A inside the superconducting magnet 1. Therefore, in the current circulation loop A, the circulating current IL circulates via the permanent current switch 3. The permanent current switch 3 has a superconducting wire 3a, which is a superconducting material, and a heater 3b. When the superconducting wire 3a is heated by the heater 3b and exceeds the critical temperature (Tc), it becomes normal conducting and functions as a resistance. On the other hand, the resistance of the superconducting wire 3a is substantially zero when the heater 3b is not energized. Therefore, if the state where the resistance of the superconducting wire 3a is almost zero is closed and the state where the superconducting wire 3a functions as a resistance is opened, the permanent current switch 3 can be closed when the heater 3b is not energized. The current circulation loop A is opened by closing the current circulation loop A and opening it when the heater 3b is energized.

  The permanent current switch 3 includes a superconducting wire 3a and a coil. When the superconducting wire 3a is excited by the coil and exceeds a critical magnetic field (H2c), the permanent current switch 3 becomes normal conducting and functions as a resistor. Also good.

  In a superconducting state where the circulating current IL circulates in the current circulation loop A, the joint portions 2a and 2b between the permanent current switch 3 and the superconducting coil 2 become superconducting joints. Therefore, the circulating current IL circulates through the current circulating loop A with almost no loss.

(Excitation power source configuration)
The excitation power source 5 is a power source for supplying current to the superconducting coil 2 from the outside, and is connected to both ends of the permanent current switch 3 by power cables 4 a and 4 b respectively connected to both ends of the permanent current switch 3.

  As shown in FIG. 1, the excitation power source 5 includes a heater circuit 6 and a voltmeter 9.

  The heater circuit 6 is connected to the heater 3b by a conducting wire 8, and when the button 6a is pressed, a current flows through the heater 3b. When the heater 3b is energized, the superconducting wire 3a heated by the heater 3b functions as a resistance, so that the permanent current switch 3 opens the current circulation loop A. On the other hand, if the heater 3b is not energized, the resistance of the superconducting wire 3a becomes zero, so that the permanent current switch 3 closes the current circulation loop A.

  The voltmeter 9 measures a voltage value generated at both ends of the superconducting coil 2.

  Further, as shown in FIG. 2, the excitation power source 5 includes a power source 21, a transistor 22, a transistor 23, a diode array 24, a voltage control circuit 25, a current control circuit 26, and a shunt resistor (current detector). 27 and a reference voltage value setting unit 28.

  The power source 21 is a switching regulator and is connected to an AC power source 31. The power source 21 converts AC power output from the AC power source 31 into predetermined DC power. The power source 21 includes a transformer that steps down the voltage from the AC power source 31 to a predetermined voltage value, a transistor circuit that supplies a DC current that is rectified and smoothed from the AC power of the transformer to the superconducting coil 2, and the like. May be.

  The two transistors 22 and 23 are connected to the power source 21 in series. The transistors 22 and 23 are usually composed of a plurality of transistors. In addition, although the general bipolar transistor is used for the transistors 22 and 23, each power element, such as a field effect transistor (FET), IGBT, or MOSFET, may be used.

  The voltage control circuit 25 is connected to the transistor 22. The voltage control circuit 25 receives the reference voltage value from the reference voltage value setter 28 and the output voltage value of the transistor 22. In the present embodiment, the reference voltage value of the reference voltage value setter 28 is + 3V, but is not limited to this. The voltage control circuit 25 controls the transistor 22 so that the output voltage value of the transistor 22 becomes the reference voltage value (+3 V). As a result, the output voltage value of the transistor 22 is + 3V. Since the specific configuration of the voltage control circuit 25 is known, its description is omitted.

  The diode array 24 is composed of a plurality of diodes directly connected. The diode array 24 is provided in parallel with the transistor 23. The forward voltage of each diode is about 0.6V. In the present embodiment, the diode array 24 is composed of 10 diodes directly connected. Therefore, a voltage drop of 6V occurs in the current flowing through the diode array 24. Therefore, the output voltage value of the excitation power supply 5 when a current flows through the diode array 24 is −3 V, which is a voltage value that is 6 V lower than the output voltage value (+3 V) of the transistor 22.

  The shunt resistor (current detector) 27 detects the value of current flowing through the superconducting coil 2 (more precisely, the output current value of the excitation power source 5). In addition, as a current detector, you may use the non-contact-type current detector which detects the magnetic field which generate | occur | produces with an electric current with a Hall element instead of a shunt resistance.

  The current control circuit 26 is connected to the transistor 23, and the current value detected by the shunt resistor 27 is input as a detection value, and the current value of a current value setter (not shown) is input as a set value. In the present embodiment, the set value is 100 A, but is not limited to this. The current control circuit 26 controls the transistor 23 based on the detection value detected by the shunt resistor 27 so that the output current value of the excitation power supply 5 becomes the set value (100 A). That is, the current control circuit 26 controls the output current value from the excitation power supply 5 to the superconducting coil 2 to be the set value (100 A). Since the specific configuration of the current control circuit 26 is known, its description is omitted.

  In the above configuration, when the current value detected by the shunt resistor 27 is smaller than the set value (100 A), the current control circuit 26 turns on the transistor 23 as a switch in order to increase the current value. As a result, the resistance value of the transistor 23 becomes substantially zero, and a current flows through the transistor 23. Then, the output voltage value of the excitation power supply 5 becomes +3 V which is the output voltage value of the transistor 22. Since the voltage control circuit 25 controls the transistor 22 so that the output voltage value of the transistor 22 becomes the reference voltage value (+ 3V), the output voltage value of the excitation power source 5 when the current flows through the transistor 23 is + 3V. It will never be bigger. Therefore, when the output current value of the excitation power supply 5 is smaller than the set value (100 A), the output voltage value of the excitation power supply 5 is + 3V. As described above, the transistor 22, the reference voltage value setting unit 28, and the voltage control circuit 25 restrict the output voltage value from the excitation power source 5 to the superconducting coil 2 from becoming larger than + 3V.

  When the current value detected by the shunt resistor 27 is larger than the set value (100 A), the current control circuit 26 turns off the transistor 23 as a switch in order to decrease the current value. As a result, the resistance value of the transistor 23 becomes larger than the resistance value of the diode string 24, and a current flows through the diode string 24. Then, the output voltage value of the excitation power supply 5 becomes −3V, which is the output voltage value of the transistor 22 + 3V dropped by 6V by the diode array 24. Since the voltage control circuit 25 controls the transistor 22 so that the output voltage value of the transistor 22 becomes the reference voltage value (+3 V), the output voltage value of the excitation power source 5 when the current flows through the diode array 24 is It will never be smaller than -3V. Therefore, when the output current value of the excitation power supply 5 is larger than the set value (100 A), the output voltage value of the excitation power supply 5 is −3V. As described above, the transistor 22, the reference voltage value setter 28, the voltage control circuit 25, and the diode array 24 are limited so that the output voltage value from the exciting power source 5 to the superconducting coil 2 does not become smaller than -3V. Yes.

  When the current value detected by the shunt resistor 27 is the set value (100 A), the current control circuit 26 sets the transistor 23 as a switch between ON and OFF in order to maintain the current value at the set value. To the state. As a result, the resistance value of the transistor 23 changes and a current flows through the transistor 23. At this time, since the possible value of the resistance value of the transistor 23 is not less than zero and not more than the resistance value of the diode array 24, the output voltage value of the excitation power supply 5 does not become larger than + 3V and does not become smaller than −3V. Therefore, when the output current value of the excitation power supply 5 is the set value (100 A), the output voltage value of the excitation power supply 5 is a value in the range of −3V to + 3V. Thus, the transistor 22, the reference voltage value setter 28, the voltage control circuit 25, and the diode array 24 set the output voltage value from the excitation power source 5 to the superconducting coil 2 to a value within a range of −3V to + 3V. Restricted.

  With the above configuration, the output characteristics of the excitation power supply 5 are as shown in FIG. Specifically, when the output current value of the excitation power source 5 is smaller than 100A, the output voltage value of the excitation power source 5 becomes constant at + 3V, and when the output current value of the excitation power source 5 is larger than 100A, the excitation power source The output voltage value of 5 is constant at -3V. Thus, the excitation power supply 5 has a constant voltage characteristic. In addition, when the output voltage value of the excitation power supply 5 is a value in the range of −3 V or more and +3 V or less, the output current value of the excitation power supply 5 is constant at 100A. Thus, the excitation power supply 5 has a constant current characteristic. That is, the excitation power source 5 is a constant voltage constant current power source.

(Excitation power supply operation)
Next, the operation of the excitation power supply 5 will be described.

  In superconducting magnet 1, as shown in FIG. 1, circulating current IL circulates in current circulation loop A including superconducting coil 2 and permanent current switch 3 by closing permanent current switch 3. If the circulating current IL circulating in the current circulation loop A is attenuated to the extent that it becomes a problem for continuous use after long-term use (several years), or if it is demagnetized by moving the superconducting magnet 1, etc., bring it from the outside. The current is switched to the current supply from the excitation power source 5.

  First, as shown in FIG. 1, the excitation power source 5 is connected to both ends of the permanent current switch 3 with the power cables 4 a and 4 b. Then, a current is supplied from the excitation power source 5 to the superconducting coil 2. The current supplied from the excitation power source 5 flows in this order through the loop B including the excitation power source 5, the power cable 4a, the permanent current switch 3, and the power cable 4b.

  Thereafter, the button 6 a is pressed to pass a current from the heater circuit 6. When the superconducting wire 3a heated by the heater 3b becomes normal conducting, the permanent current switch 3 opens the current circulation loop A. Then, the current supplied from the excitation power source 5 flows through the loop C including the excitation power source 5, the power cable 4a, the superconducting coil 2, and the power cable 4b in this order.

  Here, consider a case where the circulating current IL is reduced from 100A to 90A and the circulating current IL is adjusted to 100A. Note that the circulating current IL cannot be directly measured. The set value of the output current in the excitation power supply 5 is 100A.

  When the current circulation loop A is opened, a voltage is generated at both ends of the superconducting coil 2. At this time, the voltage value transiently generated at both ends of the superconducting coil 2 and the output voltage value of the excitation power supply 5 are each +3 V due to the constant voltage characteristics of the excitation power supply 5. Further, due to the constant current characteristics of the superconducting coil 2, the value of the current flowing through the superconducting coil 2 and the output current value of the excitation power source 5 are each 90A. As a result, as shown in FIG. 3, the output of the excitation power supply 5 is balanced at a point where the voltage value is + 3V and the current value is 90A.

  Thereafter, when the inductance of the superconducting coil 2 is L, the current is I, and the time is t, the voltage at both ends of the superconducting coil 2 is +3 V. Therefore, from the relationship of dI / dt = 3 / L. The value of current flowing through the coil 2 increases and reaches 100A. In FIG. 3, the change is indicated by an arrow c.

  Thereafter, the voltage at both ends of the superconducting coil 2 decreases and finally settles to 0V. In accordance with this, the output voltage value of the excitation power supply 5 decreases with the constant current characteristic of the excitation power supply 5 while the output current value of the excitation power supply 5 remains constant at the set value (100A). In FIG. 3, the change is indicated by an arrow d. Here, if the resistance values of the power cables 4a and 4b are taken into consideration, the resistance value of the superconducting coil 2 is 0Ω, and the resistance values of the power cables 4a and 4b are about 0.01Ω. Finally, the voltage value is about +1 V and the current value is balanced at the point b of 100A.

  As described above, the current value flowing through the superconducting coil 2 settles to the set value. Thereafter, as shown in FIG. 1, the current circulation loop A is closed by turning on the permanent current switch 3. At this time, almost no current flows through the permanent current switch 3, but when the current supplied from the excitation power supply 5 is lowered, the current flows into the permanent current switch 3 and is supplied from the excitation power supply 5. When the current becomes zero, all the current flowing through the superconducting coil 2 circulates in the current circulation loop A via the permanent current switch 3. At this time, the excitation power source 5 is disconnected from the superconducting magnet 1 to complete the operation.

  Next, consider a case where the circulating current IL is 110A. The set value of current in the excitation power supply 5 is 100A.

  When the current circulation loop A is opened, a voltage is generated at both ends of the superconducting coil 2. At this time, the voltage value transiently generated at both ends of the superconducting coil 2 and the output voltage value of the excitation power supply 5 are −3 V, respectively, due to the constant voltage characteristics of the excitation power supply 5. Further, due to the constant current characteristics of the superconducting coil 2, the value of the current flowing through the superconducting coil 2 and the output current value of the excitation power supply 5 are each 110A. As a result, as shown in FIG. 3, the output of the excitation power supply 5 is balanced at the point a 'where the voltage value is -3V and the current value is 110A.

  Thereafter, the value of the current flowing through the superconducting coil 2 decreases at a slope of dI / dt = −3 / L and reaches 100A. In FIG. 3, the change is indicated by an arrow c '.

  Thereafter, the voltage at both ends of the superconducting coil 2 decreases and finally settles to 0V. In accordance with this, the output voltage value of the excitation power supply 5 increases due to the constant current characteristics of the excitation power supply 5 while the output current value of the excitation power supply 5 remains constant at the set value (100A). In FIG. 3, the change is indicated by an arrow d '. Here, if the resistance values of the power cables 4a and 4b are taken into consideration, the resistance value of the superconducting coil 2 is 0Ω, and the resistance values of the power cables 4a and 4b are about 0.01Ω. Finally, the voltage value is about +1 V and the current value is balanced at the point b of 100A.

  As described above, the current value flowing through the superconducting coil 2 settles to the set value. Thereafter, as shown in FIG. 1, the current circulation loop A is closed by turning on the permanent current switch 3. Then, when all the current flowing through the superconducting coil 2 circulates in the current circulation loop A via the permanent current switch 3, the excitation power source 5 is disconnected from the superconducting magnet 1 to complete the operation.

  Thus, the output voltage value from the exciting power supply 5 to the superconducting coil 2 is limited to a value within the range of −3V to + 3V. Therefore, when the current circulation loop A is opened while supplying current from the excitation power source 5 to the superconducting coil 2, the voltage value generated at both ends of the superconducting coil 2 becomes a value within the range of −3V to + 3V. If the value in the range of -3V or more and + 3V or less is a value that does not affect the superconducting state, even if a voltage is generated at both ends of the superconducting coil 2, the operator rushes and closes the current circulation loop A. There is no need. As a result, when the current circulation loop A is opened, the burden associated with the work of matching the current value flowing through the superconducting coil 2 with the output current value of the excitation power source 5 can be reduced. Therefore, the operation of adjusting the current value flowing through the superconducting coil 2 to a desired current value can be facilitated.

  Further, the output current value from the excitation power source 5 to the superconducting coil 2 is controlled to be a set value (100 A). Therefore, if the current circulation loop A is opened, the current value flowing through the superconducting coil 2 finally settles to the set value. As a result, if the set value is set to a desired current value, the current flowing through the superconducting coil 2 does not have to be adjusted to the desired current value after the current circulation loop A is opened. The value is the desired current value. Therefore, the operation of adjusting the current value flowing through the superconducting coil 2 to a desired current value can be further facilitated.

  If the permanent current switch 3 is in a superconducting state together with the superconducting coil 2, the value of the current flowing through the permanent current switch 3 cannot be directly measured. For this reason, when the current circulation loop A is opened, it is more difficult to match the current value flowing through the superconducting coil 2 with the output current value of the excitation power source 5. However, since the output voltage value from the excitation power source 5 to the superconducting coil 2 is limited to a value within the range of −3V to + 3V, it occurs at both ends of the superconducting coil 2 when the current circulation loop A is opened. The voltage value is in the range of −3V to + 3V. Therefore, it is possible to further reduce the burden associated with the work of matching the current value flowing through the superconducting coil 2 and the output current value of the excitation power source 5 when the current circulation loop A is opened.

(Modification of excitation power supply)
The excitation power supply 5 may be configured as follows. That is, the excitation power source 5 includes a power source 21, a transistor 23, a transistor 29, a voltage control circuit 30, a current control circuit 26, a shunt resistor (current detector) 27, a reference voltage, as shown in FIG. And a value setting unit 28.

  The power source 21 is a switching regulator having a voltage control terminal 21 a and is connected to an AC power source 31. The reference voltage value (+ 3V) from the reference voltage value setter 28 is input to the voltage control terminal 21a. Thereby, the output voltage value of the power supply 21 is + 3V.

  The two transistors 23 and 29 are connected to the power supply 21 in parallel. The transistors 23 and 29 are usually composed of a plurality of transistors. In addition, although the general bipolar transistor is used for the transistors 23 and 29, each power element, such as a field effect transistor (FET), IGBT, or MOSFET, may be used.

  The voltage control circuit 30 is connected to the transistor 29. The voltage control circuit 30 receives the reference voltage value (+3 V) from the reference voltage value setting unit 28 and the output voltage value of the excitation power supply 5. The voltage control circuit 30 controls the transistor 29 so that a voltage drop of 6V occurs in the current flowing through the transistor 29. Therefore, the output voltage value of the excitation power supply 5 when a current flows through the transistor 29 is −3 V, which is a voltage value that is 6 V lower than the output voltage value (+3 V) of the power supply 21. Since the specific configuration of the voltage control circuit 30 is known, its description is omitted.

  The shunt resistor (current detector) 27 detects the value of current flowing through the superconducting coil 2 (more precisely, the output current value of the excitation power source 5). In addition, as a current detector, you may use the non-contact-type current detector which detects the magnetic field which generate | occur | produces with an electric current with a Hall element instead of a shunt resistance.

  The current control circuit 26 is connected to the transistor 23, and the current value detected by the shunt resistor 27 is input as a detection value, and the current value (100 A) of a current value setter (not shown) is input as a setting value. The The current control circuit 26 controls the transistor 23 based on the detection value detected by the shunt resistor 27 so that the output current value of the excitation power supply 5 becomes the set value (100 A). That is, the current control circuit 26 controls the output current value from the excitation power supply 5 to the superconducting coil 2 to be the set value (100 A).

  In the above configuration, when the current value detected by the shunt resistor 27 is smaller than the set value (100 A), the current control circuit 26 turns on the transistor 23 as a switch in order to increase the current value. As a result, the resistance value of the transistor 23 becomes substantially zero, and a current flows through the transistor 23. Then, the output voltage value of the excitation power supply 5 becomes +3 V which is the output voltage value of the power supply 21. Since the output voltage value of the power supply 21 is the reference voltage value (+ 3V), the output voltage value of the excitation power supply 5 when a current flows through the transistor 23 does not become larger than + 3V. Therefore, when the output current value of the excitation power supply 5 is smaller than the set value (100 A), the output voltage value of the excitation power supply 5 is + 3V. Thus, the power supply 21 and the reference voltage value setting unit 28 restrict the output voltage value from the excitation power supply 5 to the superconducting coil 2 so as not to be larger than + 3V.

  When the current value detected by the shunt resistor 27 is larger than the set value (100 A), the current control circuit 26 turns off the transistor 23 as a switch in order to decrease the current value. As a result, the resistance value of the transistor 23 becomes larger than the resistance value of the transistor 29, and a current flows through the transistor 29. Then, the output voltage value of the excitation power supply 5 becomes −3V, which is the output voltage value of the power supply 21 + 3V dropped by 6V by the transistor 29. Since the output voltage value of the power source 21 is the reference voltage value (+3 V) and the voltage control circuit 30 controls the transistor 29 so that a voltage drop of 6 V occurs in the current flowing through the transistor 29, the transistor 29 The output voltage value of the excitation power supply 5 when the current flows through the current does not become smaller than -3V. Therefore, when the output current value of the excitation power supply 5 is larger than the set value (100 A), the output voltage value of the excitation power supply 5 is −3V. As described above, the power supply 21, the reference voltage value setter 28, the transistor 29, and the voltage control circuit 30 limit the output voltage value from the excitation power supply 5 to the superconducting coil 2 so as not to be smaller than -3V. .

  When the current value detected by the shunt resistor 27 is the set value (100 A), the current control circuit 26 sets the transistor 23 as a switch between ON and OFF in order to maintain the current value at the set value. To the state. As a result, the resistance value of the transistor 23 changes and a current flows through the transistor 23. At this time, since the possible value of the resistance value of the transistor 23 is not less than zero and not more than the resistance value of the transistor 29, the output voltage value of the excitation power source 5 is not larger than + 3V and not smaller than −3V. Therefore, when the output current value of the excitation power supply 5 is the set value (100 A), the output voltage value of the excitation power supply 5 is a value in the range of −3V to + 3V. As described above, the power supply 21, the reference voltage value setter 28, the transistor 29, and the voltage control circuit 30 limit the output voltage value from the excitation power supply 5 to the superconducting coil 2 to a value within a range of −3V to + 3V. doing.

  With the above configuration, the output characteristics of the excitation power supply 5 are as shown in FIG. That is, the excitation power source 5 is a constant voltage constant current power source.

(effect)
As described above, according to the excitation power source 5 for the superconducting magnet according to the present embodiment, the output voltage value from the excitation power source 5 to the superconducting coil 2 is limited to a value within a range of −3V to + 3V. . Therefore, when the current circulation loop A is opened while supplying current from the excitation power source 5 to the superconducting coil 2, the voltage value generated at both ends of the superconducting coil 2 becomes a value within the range of −3V to + 3V. If the value in the range of -3V or more and + 3V or less is a value that does not affect the superconducting state, even if a voltage is generated at both ends of the superconducting coil 2, the operator rushes and closes the current circulation loop A. There is no need. As a result, when the current circulation loop A is opened, the burden associated with the work of matching the current value flowing through the superconducting coil 2 with the output current value of the excitation power source 5 can be reduced. Therefore, the operation of adjusting the current value flowing through the superconducting coil 2 to a desired current value can be facilitated.

  Further, the output current value from the excitation power source 5 to the superconducting coil 2 is controlled to be a set value (100 A). Therefore, if the current circulation loop A is opened, the current value flowing through the superconducting coil 2 finally settles to the set value. As a result, if the set value is set to a desired current value, the current flowing through the superconducting coil 2 does not have to be adjusted to the desired current value after the current circulation loop A is opened. The value is the desired current value. Therefore, the operation of adjusting the current value flowing through the superconducting coil 2 to a desired current value can be further facilitated.

  If the permanent current switch 3 is in a superconducting state together with the superconducting coil 2, the value of the current flowing through the permanent current switch 3 cannot be directly measured. For this reason, when the current circulation loop A is opened, it is more difficult to match the current value flowing through the superconducting coil 2 with the output current value of the excitation power source 5. However, since the output voltage value from the excitation power source 5 to the superconducting coil 2 is limited to a value within the range of −3V to + 3V, it occurs at both ends of the superconducting coil 2 when the current circulation loop A is opened. The voltage value is in the range of −3V to + 3V. Therefore, it is possible to further reduce the burden associated with the work of matching the current value flowing through the superconducting coil 2 and the output current value of the excitation power source 5 when the current circulation loop A is opened.

[Second Embodiment]
(Configuration of superconducting magnet)
Next, a second embodiment of the present invention will be described. An excitation power source (excitation power source) 105 for the superconducting magnet according to the present embodiment is used for the superconducting magnet 101 as shown in FIG. The superconducting magnet 101 is different from the superconducting magnet 1 of the first embodiment in that it has a mechanical relay 10 provided outside the superconducting magnet 101 and connected in parallel to the permanent current switch 3. A semiconductor switch may be provided instead of the mechanical relay 10.

  The mechanical relay 10 is opened and closed by a coil 10a. When the mechanical relay 10 is closed, both ends of the output of the excitation power source 105 are short-circuited. When the permanent current switch 3 is opened and the mechanical relay 10 is closed, the circulating current IL circulating in the current circulating loop A circulates in the current circulating loop A ′. The mechanical relay 10 may be configured with an A contact or a B contact. When the mechanical relay 10 is configured with an A contact, the mechanical relay 10 is closed when the coil 10a is energized, and the mechanical relay 10 is opened when the coil 10a is not energized. When the mechanical relay 10 is configured with a B contact, the mechanical relay 10 is closed when the coil 10a is not energized, and the mechanical relay 10 is opened when the coil 10a is energized. In consideration of a power failure, the mechanical relay 10 is preferably configured with a B contact.

(Excitation power source configuration)
The excitation power source 105 is different from the excitation power source 5 of the first embodiment in that it includes an excitation circuit 11.

  The excitation circuit 11 is connected to the coil 10a by a conducting wire 12, and excites the coil 10a by energizing the coil 10a. The mechanical relay 10 is opened and closed by exciting / demagnetizing the coil 10a.

  The excitation power supply 105 is a bipolar power supply, and is different from the excitation power supply 5 of the first embodiment that is a unipolar power supply. As shown in FIG. 6, the excitation power source 105 includes a switching regulator (power source) 41, a first full bridge circuit 42, a second full bridge circuit 43, a switching control unit 44, a first driver unit 45, The two-driver unit 46, the first reactor 51, the second reactor 52, the smoothing capacitor 55, the first reactor 53, the second reactor 54, the smoothing capacitor 56, and the regenerative circuit 48 are provided.

  The switching regulator 41 is connected to the AC power source 31 and converts AC power output from the AC power source 31 into predetermined DC power. In the following description, the direction in which current flows from the joint portion 2a to the joint portion 2b of the permanent current switch 3 and the superconducting coil 2 is defined as the forward direction, and the direction in which current flows from the joint portion 2b to the joint portion 2a is defined as the reverse direction. To do.

  The first full bridge circuit 42 and the second full bridge circuit 43 each include four switching elements connected to the switching regulator 41.

  The first reactor 51 is connected between the first full bridge circuit 42 and the joint portion 2a. The second reactor 52 is connected between the first full bridge circuit 42 and the joint portion 2b. The first reactor 53 is connected between the second full bridge circuit 43 and the joint portion 2a. The second reactor 54 is connected between the second full bridge circuit 43 and the joint portion 2b.

  The smoothing capacitor 55 is connected with one end between the first reactor 51 and the joint portion 2a and the other end between the second reactor 52 and the joint portion 2b. Similarly, the smoothing capacitor 56 is connected between the first reactor 53 and the joint portion 2a as one end and between the second reactor 54 and the joint portion 2b as the other end.

  The switching control unit 44 outputs a PWM signal for turning on / off the switching element to the first full bridge circuit 42 and the second full bridge circuit 43. Specifically, the switching control means 44 includes a current detector 61, a target current value setting device 62, a current / voltage control circuit 63, a basic pulse generator 64, a first PWM signal converter 65, and a second PWM signal. And a converter 66.

  The current detector 61 is connected to the joint portion 2 b side of the superconducting coil 2, detects the current value flowing through the superconducting coil 2, and outputs the detected current value to the current voltage control circuit 63 through the line 116. The target current value setting unit 62 sets a target current value (set value) in advance, and sends a current command value for instructing to shift to the set current value to the input terminals 111a, To 111b. In the present embodiment, the set value is + 100A or −100A.

  Further, the current voltage control circuit 63 uses the difference value between the current value detected by the current detector 61 and the current command value output from the target current value setting unit 62 as a current error signal, and the first PWM signal converter 65 and the second PWM. The signal is output to the signal converter 66. Details of the current-voltage control circuit 63 will be described later.

  The basic pulse generator 64 outputs a pulse signal having a phase difference at a predetermined frequency to the first PWM signal converter 65 and the second PWM signal converter 66. Specifically, the pulse signal output to the second PWM signal converter 66 has a phase difference of 180 ° with respect to the pulse signal output to the first PWM signal converter 65.

  The first PWM signal converter 65 separates the current error signal output from the current-voltage control circuit 63 into a forward direction signal (plus side) and a backward direction signal (minus side). The first PWM signal converter 65 generates a forward PWM signal (switching signal) from the separated forward signal and the pulse signal output from the basic pulse generator 64, and also separates the separated backward signal and the basic signal. A PWM signal (switching signal) in the reverse direction is generated from the pulse signal output from the pulse generator 64. Similarly, the second PWM signal converter 66 generates a forward PWM signal (switching signal) and a reverse PWM signal (switching signal).

  The first driver unit 45 is connected between the switching control unit 44 and the first full bridge circuit 42. The second driver unit 46 is connected between the switching control unit 44 and the second full bridge circuit 43.

  The positive PWM signal output from the first PWM signal converter 65 controls ON / OFF of the two switching elements of the first full bridge circuit 42 via the first driver unit 45. When this system is ON, a current flows from the joint portion 2a of the superconducting coil 2 to the joint portion 2b. The reverse PWM signal output from the first PWM signal converter 65 controls the ON / OFF of the other two switching elements of the first full bridge circuit 42 via the first driver unit 45. When this system is ON, a current flows from the joint portion 2b of the superconducting coil 2 to the joint portion 2a. The same applies to the second PWM signal converter 66.

  The regenerative circuit 48 is connected between the plus side and the minus side of the switching regulator 41. The regenerative circuit 48 suppresses the voltage increase of the switching regulator 41 when the superconducting coil 2 is demagnetized.

(Current control circuit)
Next, the configuration of the current / voltage control circuit 63 will be described. As shown in FIG. 7, the current voltage control circuit 63 includes a current control circuit 131, a voltage limiting circuit 132, a transistor 127, and an analog switch 128.

  The current control circuit 131 includes four operational amplifiers 111 to 114 and a shunt resistor 115. The shunt resistor 115 is connected to the line 116, and converts the current value flowing through the superconducting coil 2 detected by the current detector 61 (more precisely, the output current value of the excitation power source 105) into a voltage value. The operational amplifier 114 inverts and amplifies this voltage.

  The current command value from the target current value setter 62 is input to the input terminals 111a and 111b of the operational amplifier 111 that is an adder. The operational amplifier 111 adds the voltage amplified by the operational amplifier 114 to the current command value (actually subtraction). The operational amplifier 111 outputs the difference between the current command value and the voltage amplified by the operational amplifier 114 as a current error signal.

  The operational amplifier 112 functions as an amplifier. The operational amplifier 113 functions as a buffer. The current error signal output from the operational amplifier 113 is input to the first PWM signal converter 65 and the second PWM signal converter 66 (see FIG. 6). Thereby, the current control circuit 131 controls the first full bridge circuit 42 and the second full bridge circuit 43 (see FIG. 6) so that the output current value of the excitation power source 105 becomes the set value (+ 100A or −100A). It will be. That is, the current control circuit 131 controls the output current value from the excitation power source 105 to the superconducting coil 2 to be the set value (+ 100A or −100A).

  The voltage limiting circuit 132 includes four operational amplifiers 121 to 124 and two diodes 125 and 126. The voltage limiting circuit 132 is connected to a point D between the operational amplifier 112 and the operational amplifier 113 in the current control circuit 131 via the analog switch 128.

  The voltage generated at both ends of the superconducting coil 2 (to be exact, the voltage generated at both ends of the superconducting coil 2 is connected to the input terminals 121a and 121b of the operational amplifier 121 via the line 129 (see FIG. 6). A voltage obtained by adding the generated voltage) is input as an applied voltage. This applied voltage corresponds to a voltage generated between the power cables 4a and 4b (see FIG. 5).

  A limit voltage is input to input terminals 122a and 122b of the operational amplifier 122 from a limit voltage value setter (not shown). In the present embodiment, the value of the limit voltage is +3 V, but is not limited to this. The operational amplifier 122 inverts the limit voltage plus and minus.

  The operational amplifier 123 receives the output of the operational amplifier 121 and the limit voltage. The operational amplifier 123 compares the output (applied voltage) of the operational amplifier 121 with the limit voltage. When the applied voltage is larger than +3 V (first threshold value) which is the value of the limit voltage, the output of the operational amplifier 123 becomes negative. If the output of the operational amplifier 123 is negative, a current flows through the diode 125. On the other hand, if the output of the operational amplifier 123 is positive, no current flows through the diode 125.

  The operational amplifier 124 receives the output of the operational amplifier 121 and the output of the operational amplifier 122. The operational amplifier 124 compares the output (applied voltage) of the operational amplifier 121 and the output (limited voltage) of the operational amplifier 122. In the operational amplifier 124, the limit voltage and the applied voltage are inverted. When the applied voltage is smaller than −3 V (second threshold), the output of the operational amplifier 124 becomes positive. If the output of the operational amplifier 124 is positive, a current flows through the diode 126. On the other hand, if the output of the operational amplifier 124 is negative, no current flows through the diode 126.

  In the above configuration, when the applied voltage is higher than the limit voltage value +3 V (first threshold), a current flows through the diode 125. When a current flows through the diode 125, the operational amplifier 113 functions as an adder, and the current error signal at point D is lowered. As a result, the output current value of the excitation power supply 105 becomes smaller than the set value (+ 100A or −100A), and as a result, the output voltage value of the excitation power supply 105 is lowered to + 3V. Therefore, when the output current value of the excitation power source 105 is smaller than the set value (+100 A or −100 A), the output voltage value of the excitation power source 105 is constant at + 3V. As described above, when the voltage value generated at both ends of the superconducting coil 2 is larger than the first threshold value (+3 V), the voltage limiting circuit 132 sets the output voltage value from the excitation power source 105 to the superconducting coil 2 as the first value. By clamping to the threshold value (+3 V), the output voltage value of the excitation power source 105 is limited so as not to be larger than the first threshold value (+3 V).

  On the other hand, when the applied voltage is smaller than −3 V (second threshold), a current flows through the diode 126. When a current flows through the diode 126, the operational amplifier 113 functions as an adder, and the current error signal at point D is raised. As a result, the output current value of the excitation power source 105 becomes larger than the set value (+ 100A or −100A), and as a result, the output voltage value of the excitation power source 105 is increased to −3V. Therefore, when the output current value of the excitation power source 105 is larger than the set value (+100 A or −100 A), the output voltage value of the excitation power source 105 becomes constant at −3V. As described above, the voltage limiting circuit 132 sets the second output voltage value from the excitation power source 105 to the superconducting coil 2 when the voltage value generated at both ends of the superconducting coil 2 is smaller than the second threshold value (−3 V). The output voltage value of the excitation power source 105 is limited so as not to become smaller than the second threshold value (−3 V).

  Further, when the applied voltage is a value within a range of −3 V or more and +3 V or less, no current flows through the diode 125 and the diode 126. Thereby, since the current error signal at point D does not change, the current control circuit 131 controls the output current value of the excitation power source 105 to be the set value (+ 100A or −100A). As a result, the output current value of the excitation power supply 105 becomes a set value (+100 A or −100 A). At this time, the output voltage value of the excitation power supply 105 takes such a value that no current flows through the diode 125 and the diode 126. That is, the output voltage value of the excitation power source 105 does not become larger than + 3V and does not become smaller than −3V. Therefore, when the output current value of the excitation power source 105 is the set value (+100 A or −100 A), the output voltage value of the excitation power source 5 is the second threshold value (−3 V) with the first threshold value (+3 V) as the upper limit value. Becomes a value within a range of −3V to + 3V. As described above, the voltage limiting circuit 132 does not clamp the output voltage value from the excitation power source 105 to the superconducting coil 2 when the applied voltage is a value in the range of −3V to + 3V. The output voltage value to the coil 2 is limited to a value within a range of −3V to + 3V with the first threshold (+ 3V) as the upper limit and the second threshold (−3V) as the lower limit.

  Here, clamping means that when a certain voltage value exceeds a predetermined voltage value, a portion of the voltage value exceeding the predetermined voltage value is cut so that the certain voltage value exceeds the predetermined voltage value. It means not to. In other words, when a certain voltage value exceeds a predetermined voltage value, a clamp is a voltage value that is lowered (or pushed up) to a predetermined voltage value. Means not to exceed.

  The transistor 127 is turned on when the voltage limit valid signal is input to the input terminals 127a and 127b, and is turned off when the voltage limit valid signal is not input to the input terminals 127a and 127b. Here, the transistor 127 is turned on for a certain period before and after opening the current circulation loop A '(see FIG. 5). For example, the transistor 127 is turned on 2 seconds before the mechanical relay 10 is opened, and turned off 1 minute after the mechanical relay 10 is opened. However, the transistor 127 may be configured to be turned off after the voltage generated at both ends of the superconducting coil 2 becomes equal to or lower than a certain value, or to be turned off according to an operator's judgment.

  The analog switch 128 is provided between a point D between the operational amplifier 112 and the operational amplifier 113 and between the two diodes 125 and 126. When the transistor 127 is turned on and the control terminal 128c is energized, the analog switch 128 conducts the terminal 128a and the terminal 128b. On the other hand, when the transistor 127 is turned off and the control terminal 128c is not energized, the analog switch 128 The terminal 128b is configured to be shut off.

  As a result, while the terminals 128a and 128b of the analog switch 128 are conductive (while the voltage limit enable signal is input to the transistor 127), the function of the voltage limit circuit 132 is enabled and the analog switch 128 is enabled. The function of the voltage limiting circuit 132 is disabled while the terminal 128a and the terminal 128b are not conducting (while the voltage limiting valid signal is not input to the transistor 127). As described above, the transistor 127 and the analog switch 128 enable the limitation by the voltage limiting circuit 132 in a certain period before and after opening the current circulation loop A ′, and invalidate the limitation by the voltage limiting circuit 132 in a period other than the certain period. Yes.

  With the above configuration, the output characteristics of the excitation power source 105 when the function of the voltage limiting circuit 132 is valid are as shown in FIG. 3 or FIG. Since the excitation power source 105 of the present embodiment is a bipolar power source, the set current value may be positive or negative. The output characteristics of the excitation power supply 105 when the set current value is positive are the same as those of the excitation power supply 5 of the first embodiment, as shown in FIG.

  On the other hand, FIG. 8 shows output characteristics of the excitation power source 105 when the set current value is negative. When the output current value of the excitation power source 105 is smaller than −100 A, the output voltage value of the excitation power source 105 is constant at +3 V, and when the output current value of the excitation power source 105 is larger than −100 A, the output of the excitation power source 105 The voltage value is constant at -3V. Thus, the excitation power supply 105 has a constant voltage characteristic. Further, when the output voltage value of the excitation power source 105 is a value in the range of −3 V or more and +3 V or less, the output current value of the excitation power source 105 is constant at −100 A. Thus, the excitation power source 105 has a constant current characteristic. That is, the excitation power source 105 is a constant voltage constant current power source.

  In general, it is desirable that the value of the limiting voltage is set to be equal to or less than the voltage value obtained by adding the voltage generated at the power cables 4 a and 4 b to the voltage generated at both ends of the superconducting coil 2 at the rated excitation speed of the superconducting magnet 101. Moreover, the structure which an operator directly sets the value of a limit voltage may be sufficient.

(Excitation power supply operation)
Next, the operation of the excitation power source 105 will be described. Since the operation of the excitation power source 105 when the set current value is positive is basically the same as the operation of the excitation power source 5 of the first embodiment, the description thereof is omitted. On the other hand, consider the case where the circulating current IL increases from −100 A to −90 A as the operation of the excitation power source 105 when the set current value is negative. The set value of current in the excitation power source 105 is −100A.

  In the superconducting magnet 101, as shown in FIG. 5, the circulating current IL circulates in the current circulation loop A including the superconducting coil 2 and the permanent current switch 3 by closing the permanent current switch 3. In this way, when circulating the circulating current IL in the current circulating loop A, the current continues to flow almost permanently without causing any loss by closing the current circulating loop A with the permanent current switch 3.

  On the other hand, when supplying current from the exciting power source 105 to the superconducting coil 2, first, the permanent current switch 3 is opened and the mechanical relay 10 is closed. As a result, the circulating current IL circulates in the current circulation loop A ′ including the superconducting coil 2 and the mechanical relay 10. Thus, when supplying current from the exciting power source 105 to the superconducting coil 2, the permanent current switch 3 is opened and the current circulation loop A ′ is opened and closed by the mechanical relay 10.

  When the permanent current switch 3 and the mechanical relay 10 are closed, when an abnormality occurs in either the excitation power source 105 or the superconducting magnet 101, the superconducting state is detected in the initial stage at the time of abnormality. Most of the current flows through the permanent current switch 3 having zero resistance. However, when the superconducting coil 2 is quenched, the permanent current switch 3 is often quenched with a slight delay, and in this case, a current flows through the mechanical relay 10. In addition, when the permanent current switch 3 and the mechanical relay 10 are closed, a current flows through the mechanical relay 10 even when an abnormality occurs in the permanent current switch 3 and a voltage is generated.

  Next, the excitation power source 105 is connected to both ends of the mechanical relay 10 by the power cables 4 a and 4 b, and a current of −100 A is supplied from the excitation power source 105 to the superconducting coil 2. The current supplied from the excitation power supply 105 flows in this order through the loop B including the excitation power supply 105, the power cable 4a, the mechanical relay 10, and the power cable 4b.

  Thereafter, the exciting circuit 11 excites the coil 10a and opens the mechanical relay 10, thereby opening the current circulation loop A '. Then, the current supplied from the excitation power source 105 flows through the loop C including the excitation power source 105, the power cable 4a, the superconducting coil 2, and the power cable 4b in this order.

  Here, as shown in FIG. 7, the voltage limit valid signal is input to the transistor 127 in a certain period before and after opening the current circulation loop A ′. As a result, the function of the voltage limiting circuit 132 is enabled. Therefore, the voltage value transiently generated at both ends of the superconducting coil 2 and the output voltage value of the excitation power supply 105 are each -3V due to the constant voltage characteristics of the excitation power supply 105. Further, due to the constant current characteristics of the superconducting coil 2, the current value flowing through the superconducting coil 2 and the output current value of the excitation power source 105 are each -90A. As a result, as shown in FIG. 8, the output of the excitation power source 105 is balanced at the a ″ point where the voltage value is −3 V and the current value is −90 A.

  Thereafter, when the inductance of the superconducting coil 2 is L, the current is I, and the time is t, the voltage of the superconducting coil 2 is −3V. The value of the current flowing through the coil 2 decreases and reaches -100A. In FIG. 8, the change is indicated by an arrow c ″.

  Thereafter, the voltage across the superconducting coil 2 increases and finally settles to 0V. In accordance with this, the output voltage value of the excitation power supply 105 increases with the constant current characteristic of the excitation power supply 105 while the output current value of the excitation power supply 105 remains constant at the set value (−100 A). In FIG. 8, the change is indicated by an arrow d ″. Here, if the resistance values of the power cables 4a and 4b are taken into consideration, the resistance value of the superconducting coil 2 is 0Ω, and the resistance values of the power cables 4a and 4b are about 0.01Ω. Eventually, the voltage value is about -1V and the current value is -100A and balance is made at the point b '.

  Note that while the output voltage value from the excitation power source 105 to the superconducting coil 2 is limited to a value within the range of −3V to + 3V, it is not possible to detect the generation of the voltage due to the quench generated in the superconducting coil 2. . Therefore, the period for limiting the output voltage value from the excitation power source 105 to the superconducting coil 2 is limited to a certain period before and after opening the current circulation loop A ′. Thus, quenching of the superconducting coil 2 can be detected while the output voltage value from the excitation power source 105 to the superconducting coil 2 is not limited.

  Further, while the current is being supplied from the exciting power source 105 to the superconducting coil 2, the exciting power source 105 and the superconducting power may be changed such that the current suddenly changes due to a trouble with the exciting power source 105 itself or the superconducting coil 2 is quenched. When an abnormality occurs in any of the magnets 101, both ends of the output of the excitation power source 105 are short-circuited by closing the mechanical relay 10. As a result, a current flows through the mechanical relay 10 and the excitation power source 105 and the superconducting coil 2 are substantially separated, so that the excitation power source 105 and the superconducting magnet 101 can be prevented from being damaged. Here, if the mechanical relay 10 is set to the B contact so that the mechanical relay 10 automatically closes in the event of a power failure, the excitation power source 105 and the superconducting magnet 101 can be more reliably prevented from being damaged. Note that a power failure detection circuit for detecting a power failure may be provided in the excitation power source 105 to control the mechanical relay 10.

  As described above, the current value flowing through the superconducting coil 2 settles to the set value. Thereafter, as shown in FIG. 5, the current circulation loop A is closed by turning on the permanent current switch 3. When all of the current flowing through the superconducting coil 2 circulates in the current circulation loop A via the permanent current switch 3, the excitation power source 105 is disconnected from the superconducting magnet 101 to complete the operation.

  As described above, the output voltage value from the excitation power source 105 to the superconducting coil 2 is limited to a value within the range of −3V to + 3V. Therefore, when the current circulation loop A ′ is opened while supplying current from the excitation power source 105 to the superconducting coil 2, the voltage value generated at both ends of the superconducting coil 2 becomes a value within a range of −3V to + 3V. If the value in the range of −3V or more and + 3V or less is a value that does not affect the superconducting state, even if a voltage is generated at both ends of the superconducting coil 2, the operator rushes through the current circulation loop A ′. There is no need to close. As a result, it is possible to reduce the burden associated with the work of matching the current value flowing through the superconducting coil 2 with the output current value of the excitation power source 105 when the current circulation loop A ′ is opened. Therefore, the operation of adjusting the current value flowing through the superconducting coil 2 to a desired current value can be facilitated.

  Further, the output current value from the exciting power source 105 to the superconducting coil 2 is controlled to be a set value (+100 A or −100 A). Therefore, if the current circulation loop A 'is opened, the current value flowing through the superconducting coil 2 finally settles to the set value. Thus, if the set value is set to a desired current value, the current flowing through the superconducting coil 2 does not have to be adjusted to the desired current value after opening the current circulation loop A ′. The current value becomes a desired current value. Therefore, the operation of adjusting the current value flowing through the superconducting coil 2 to a desired current value can be further facilitated.

  Further, when the voltage value generated at both ends of the superconducting coil 2 is larger than the first threshold value (+3 V) which is a positive value, the output voltage value to the superconducting coil 2 is clamped to the first threshold value (+3 V). The Further, when the voltage value generated at both ends of the superconducting coil 2 is smaller than the second threshold value (−3 V) which is a negative value, the output voltage value to the superconducting coil 2 becomes the second threshold value (−3 V). Clamped. Thereby, the output voltage value from the excitation power source 105 to the superconducting coil 2 is in the range of −3V to + 3V with the first threshold (+ 3V) as the upper limit and the second threshold (−3V) as the lower limit. Limited to value. Therefore, by changing at least one of the first threshold value and the second threshold value, the range in which the output voltage value from the excitation power source 105 to the superconducting coil 2 is limited can be easily changed.

(Modification of superconducting magnet)
Note that the superconducting magnet 101 may be configured as follows. That is, as shown in FIG. 9, the superconducting magnet 101 does not include the permanent current switch 3 and is configured to open and close the current circulation loop A ′ with the mechanical relay 10. A semiconductor switch may be used instead of the mechanical relay 10.

  While the current is being supplied from the exciting power source 105 to the superconducting coil 2, the exciting power source 105 and the superconducting power are rapidly changed due to a trouble in the exciting power source 105 itself or the superconducting coil 2 is quenched. When an abnormality occurs in any of the magnets 101, both ends of the output of the excitation power source 105 are short-circuited by closing the mechanical relay 10. As a result, a current flows through the mechanical relay 10 and the excitation power source 105 and the superconducting coil 2 are substantially separated, so that the excitation power source 105 and the superconducting magnet 101 can be prevented from being damaged.

(effect)
As described above, according to the excitation power source 105 for the superconducting magnet according to the present embodiment, when the voltage value generated at both ends of the superconducting coil 2 is larger than the first threshold value (+3 V) which is a positive value. The output voltage value to the superconducting coil 2 is clamped to the first threshold value (+ 3V). Further, when the voltage value generated at both ends of the superconducting coil 2 is smaller than the second threshold value (−3 V) which is a negative value, the output voltage value to the superconducting coil 2 becomes the second threshold value (−3 V). Clamped. Thereby, the output voltage value from the excitation power source 105 to the superconducting coil 2 is in the range of −3V to + 3V with the first threshold (+ 3V) as the upper limit and the second threshold (−3V) as the lower limit. Limited to value. Therefore, by changing at least one of the first threshold value and the second threshold value, the range in which the output voltage value from the excitation power source 105 to the superconducting coil 2 is limited can be easily changed.

  Further, while the output voltage value from the excitation power source 105 to the superconducting coil 2 is limited to a value within the range of −3V or more and + 3V or less, the generation of the voltage due to the quench generated in the superconducting coil 2 cannot be detected. . Therefore, the period for limiting the output voltage value from the excitation power source 105 to the superconducting coil 2 is limited to a certain period before and after opening the current circulation loop A '. Thus, quenching of the superconducting coil 2 can be detected while the output voltage value from the excitation power source 105 to the superconducting coil 2 is not limited.

  When circulating the current in the current circulation loop A, the current circulation loop A is closed by the permanent current switch 3 so that the current flows almost permanently without causing any loss. On the other hand, when a current is supplied from the exciting power source 105 to the superconducting coil 2, the permanent current switch 3 is opened and the current circulation loop A 'is opened and closed by the mechanical relay 10. When an abnormality occurs in either the excitation power supply 105 or the superconducting magnet 101 while the current is being supplied from the excitation power supply 105 to the superconducting coil 2, the mechanical relay 10 is closed, Both ends of the output of the excitation power supply 105 are short-circuited. As a result, a current flows through the mechanical relay 10 and the excitation power source 105 and the superconducting coil 2 are substantially separated, so that the excitation power source 105 and the superconducting magnet 101 can be prevented from being damaged.

(Modification of this embodiment)
The embodiment of the present invention has been described above, but only specific examples are illustrated, and the present invention is not particularly limited, and the specific configuration and the like can be appropriately changed in design. Further, the actions and effects described in the embodiments of the invention only list the most preferable actions and effects resulting from the present invention, and the actions and effects according to the present invention are described in the embodiments of the present invention. It is not limited to what was done.

  For example, the excitation power source 5 (see FIGS. 2 and 4) of the first embodiment may be connected to the superconducting magnet 101 (see FIGS. 5 and 9) of the second embodiment. Moreover, the structure which connects the excitation power supply 105 (refer FIG. 6) of 2nd Embodiment to the superconducting magnet 1 (refer FIG. 1) of 1st Embodiment may be sufficient.

DESCRIPTION OF SYMBOLS 1,101 Superconducting magnet 2 Superconducting coil 3 Permanent current switch 3a Superconducting wire 3b Heater 5,105 Excitation power supply 10 Mechanical relay 21 Power supply 22, 23, 29 Transistor 24 Diode array 25, 30 Voltage control circuit 26 Current control circuit 27 Shunt resistance 28 Reference Voltage Value Setting Unit 31 AC Power Supply 41 Switching Regulator 42 First Full Bridge Circuit 43 Second Full Bridge Circuit 44 Switching Control Unit 45 First Driver Unit 46 Second Driver Unit 51, 53 First Reactor 52, 54 Second Reactor 55, 56 Smoothing capacitor 61 Current detector 62 Target current value setting device 63 Current voltage control circuit 64 Basic pulse generator 65 First PWM signal converter 66 Second PWM signal converter 111-114 Operational amplifier 115 Shunt resistor 1 21-124 operational amplifiers 125, 126 diode 127 transistor 128 analog switch 131 current control circuit 132 voltage limiting circuit

Claims (7)

An excitation power supply for supplying current from the outside to the superconducting coil by connecting to both ends of the switch means provided in a part of the current circulation loop of the superconducting coil constituting the superconducting magnet,
An excitation power source for a superconducting magnet, comprising voltage limiting means for limiting an output voltage value to the superconducting coil to a value within a predetermined range.   2. The exciting power supply for a superconducting magnet according to claim 1, further comprising current control means for controlling the output current value to the superconducting coil to be a set value.   The voltage limiting means clamps the output voltage value to the superconducting coil at the first threshold value when the voltage value generated at both ends of the superconducting coil is larger than the first threshold value which is a positive value. When the voltage value generated at both ends of the superconducting coil is smaller than a second threshold value which is a negative value, the output voltage value to the superconducting coil is clamped to the second threshold value, thereby the superconducting coil. The output voltage value to is limited to a value within the predetermined range in which the first threshold value is an upper limit value and the second threshold value is a lower limit value. Excitation power source for superconducting magnets.   And further comprising a voltage limit limiting unit that enables the limitation by the voltage limiting unit during a certain period before and after opening the current circulation loop, and invalidates the limitation by the voltage limiting unit at a time other than the certain period. The exciting power supply for a superconducting magnet according to any one of claims 1 to 3.   The exciting power supply for a superconducting magnet according to any one of claims 1 to 4, wherein the switch means is a permanent current switch provided inside the superconducting magnet and containing a superconducting material.   The exciting power supply for a superconducting magnet according to any one of claims 1 to 4, wherein the switch means is a mechanical relay or a semiconductor switch provided outside the superconducting magnet. The switch means includes
A permanent current switch provided in the superconducting magnet and containing a superconducting material;
A mechanical relay or a semiconductor switch provided outside the superconducting magnet and connected in parallel to the permanent current switch;
Have
When circulating current in the current circulation loop, the current circulation loop is closed with the permanent current switch, while when supplying current from the excitation power source to the superconducting coil, the permanent current switch is opened and the permanent current switch is opened. The exciting power supply for a superconducting magnet according to any one of claims 1 to 4, wherein the current circulation loop is opened and closed by a mechanical relay or the semiconductor switch.