JPH0527128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a control device for a coil that generates a magnetic field using a direct current.

[Prior art and its problems]

FIG. 2 is a block diagram showing a conventional example of controlling a magnetic field generating coil by magnetic field control. The smoothed DC power is converted into desired DC power by so-called chopper control that changes the ratio of the on time and off time of the transistor 6, and is applied to the coil 8. Here, numeral 7 is a freewheel diode.

The strength of the magnetic field generated by the coil 8 when a direct current flows is detected by the magnetic field detector 11, amplified by the magnetic field amplifier 12, and then transmitted to the magnetic field setting device 1.
The magnetic field adjuster 14 outputs a control signal that makes the difference between the two values zero. The output signal from the magnetic field adjuster 14 is sent to the base drive circuit 15 to turn on and off the transistor 6 as appropriate, so that the strength of the magnetic field generated by the coil 8 can be maintained at the value set by the magnetic field setting device 13. can.

However, the magnetic field detector 11 for detecting the strength of the magnetic field uses a Hall element or a system that utilizes the nuclear magnetic resonance phenomenon. Methods that utilize this phenomenon require certain periodic operations for measurement, which not only makes it impossible to measure continuously but also has the disadvantage of slow response speed. It is difficult to control.

FIG. 3 is a block diagram showing a conventional example of controlling a magnetic field generating coil by current control, in which AC power from an AC power source 2 is converted into DC power by an insulating transformer 3 and a rectifier 4, and then by a smoothing capacitor 5. The smoothing and further conversion to desired DC power through the transistor 6 and freewheeling diode 7 to excite the capacitor 8 are the same as in the conventional example shown in FIG. 2 described above. The conventional example shown in FIG. 3 focuses on the fact that there is a proportional relationship between the magnitude of the current flowing through the coil 8 and the strength of the magnetic field.The conventional example shown in FIG. The deviation between the current setting value determined by the current setting device 23 and this detected current value is input to the current regulator 24, and the control output signal from the current regulator 24 is sent to the transistor 6 via the base drive circuit 15. The current flowing through the coil 8 is controlled to a desired value by supplying the current to the base and turning the transistor 6 on and off as appropriate.

Although the conventional example shown in Fig. 3 is capable of high-speed control, the strength of the magnetic field changes due to changes in coil dimensions due to temperature, residual magnetization of the iron core, etc., so it is difficult to control the strength of the magnetic field to a desired value. It has the disadvantage that it cannot be maintained.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for a magnetic field generating coil that has a fast response speed and can control the strength of a magnetic field with high precision.

[Key points of the invention]

This invention detects the current flowing through a magnetic field generating coil and the generated magnetic field, calculates the theoretical value of the required current from the detected magnetic field value, compares the theoretical current value with the detected current value, and calculates the difference between the two. is added to the current set value to perform current adjustment operation, and the difference between the two currents mentioned above is updated at a predetermined time using a sample and hold circuit to improve control accuracy and to This is intended to avoid interfering with speed response.

[Embodiments of the invention]

FIG. 1 is a block diagram showing an embodiment of the present invention, and the content of the present invention will be described below with reference to FIG.

In FIG. 1, AC power from an AC power source 2 is converted into DC power by an isolation transformer 3 and a rectifier 4, which serve as both insulation and transformer, and a ripple component is removed by a smoothing capacitor 5, resulting in smooth DC power. Become. The transistor 6 repeats on/off operations at high speed, and by changing the ratio between the on time and the off time, the current value flowing through the coil 8 is controlled along with the action of the freewheeling diode 7.

The current flowing through the coil 8 is detected by the shunt 21 and the isolation amplifier 22, and the deviation between this detected current value and the current setting value set by the current setting device 23 is determined by the proportional-integral calculator. The current regulator 24 outputs a control signal that makes the input deviation zero, but this output signal is given to the base circuit of the transistor 6 via the base drive circuit 15. The transistor 6 controls the current flowing through the coil 8 to match the value set by the current setting device 23.
On the other hand, since the strength of the magnetic field generated by the coil 8 is detected by the magnetic field detector 11, the theoretical value of the current to be passed through the coil 8 is determined by the virtual current calculator 31 from the detected magnetic field value obtained via the magnetic field amplifier 12. Calculated. The deviation between the theoretical current value obtained in this way and the above-mentioned detected current value is input to the sample and hold circuit 32.

When the sample command circuit 33 sends a sample command to the sample hold circuit 32 at a predetermined timing, the input signal at that time is output from the sample hold circuit 32 and added to the above-mentioned current detection value and current setting value to adjust the current. 24. That is, isolation amplifier 2
The difference between the detected current value outputted by 2 and the theoretical current value outputted by the virtual current calculator 31 is the magnetic field error,
The magnitude of the current setting value is adjusted by this magnetic field error at the time when the sample command signal is issued. Here, if the time interval of the sample command signal outputted from the sample command circuit 33 is set to an appropriate length, even the magnetic field detector 11 with a slow response speed can sufficiently respond and correct the error.

Note that the above-mentioned sample command may be issued only twice: when starting the coil 8 and when starting normal operation after completion of warm-up. That is, the sample command at the first start is a so-called initial reset, and warm-up operation is performed so that current control is performed with the current setting value corrected for the residual magnetization of the coil 8 as the target value. It will start. When the temperature of the coil 8 rises due to this warm-up operation and becomes constant, the warm-up is complete, so at this point the second
A second sample command is issued, and a correction is made for the relationship between the strength of the magnetic field and the magnitude of the current that deviates from the planned value. After the current setting value is corrected in this way, the operating state is entered by constant current control.

〔Effect of the invention〕

According to this invention, the current setting value of the loop that controls the current flowing through the magnetic field generating coil to a constant current is corrected by the difference between the detected current value and the theoretical current value. After warm-up is completed and the steady state is reached, constant magnetic field control is applied, so compared to a case where constant current control is performed from the beginning, there is less influence from changes in the coil outline and residual magnetization of the magnetic material around the coil. can be removed. In addition, the difference between the detected current value and the theoretical current value for correction is processed through a sample and hold circuit.
Since the current setting value is corrected appropriately according to the sample command, it is possible to use a detector with a slow response speed, such as a magnetic field detector that uses nuclear magnetic resonance phenomena, and it is possible to use a magnetic field detector with a large drift. The stability of the magnetic field generated by the coil during operation can be ensured, and the accuracy determined by these magnetic field detectors can be ensured. Furthermore, since direct current can be detected at high speed, a high response speed can be ensured even against power supply voltage fluctuations and various disturbances.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a conventional example of controlling a magnetic field generating coil by magnetic field control, and Fig. 3 is a block diagram of a conventional example of controlling a magnetic field generating coil by current control. FIG. 2 is a block diagram showing an example. 2... AC power supply, 3... Isolation transformer, 4... Rectifier, 5... Smoothing capacitor, 6... Transistor, 7... Freewheel diode, 8... Coil, 11... Magnetic field detector, 12... ...Magnetic field amplifier, 13...Magnetic field setting device, 14...Magnetic field adjuster,
15... base drive circuit, 21... shunt, 22
...Isolation amplifier, 23...Current setting device, 24...
Current regulator, 31...Virtual current calculator, 32...
Sample hold circuit, 33...Sample command circuit.

Claims (1)

[Claims] 1. A coil that generates a magnetic field by passing a direct current, comprising a current detector that detects the direct current flowing through the coil and a magnetic field detector that detects the strength of the magnetic field generated by the coil. , a current regulator that inputs the deviation between the current setting value determined by the current setting device and the current detection value detected by the current detector and outputs a control signal to make the DC current flowing through the coil match the current setting value; a virtual current calculator that calculates a theoretical DC current value corresponding to the strength of the magnetic field obtained by the magnetic field detector; and a virtual current calculator that calculates a theoretical current value output by the virtual current calculator and a current detected value from the current detector. A magnetic field generator comprising: a sample hold circuit that inputs a difference and outputs a difference input signal to be added to or subtracted from the current setting value when a sample command signal from a sample command circuit is given. Coil control device. 2. The control device according to claim 1, wherein the sample command circuit is a sample command circuit that provides a sample command signal to the sample hold circuit at the time of starting the coil and at the completion of warm-up of the magnetic field. Generator coil control device.