JP7761982B2 - electromagnetic power supply - Google Patents

Description

An embodiment of the present invention relates to an electromagnetic power supply device.

Electromagnet power supplies for voltage-source power conversion devices are known that supply an electromagnet with a current that corresponds to a current pattern that changes in a stepwise manner. In such electromagnet power supplies, two chopper circuits are connected in series. One chopper circuit operates during the period when the current command value changes in a stepwise manner. This chopper circuit is called, for example, a forcing circuit. The other chopper circuit operates during the period when the current command value is constant. This chopper circuit is called, for example, a flat maintenance circuit.

In this way, by providing two chopper circuits connected in series, it is possible to obtain high responsiveness of the load current to changes in the current command value, and to control the load current with high precision relative to a constant current command value. Such electromagnet power supply units are used, for example, in medical scanning electromagnets.

The forcing circuit performs an output operation to output voltage during the period when the current command value changes in a step-like manner, and performs a stopping operation to stop voltage output by making the output side conductive (bypass) during the period when the current command value remains constant.

The forcing circuit switches from output operation to stopping operation when the current deviation, which represents the difference between the target current value and the current output current value, falls below a threshold. At this time, jitter caused by the sampling time of the current deviation can cause the timing of the forcing circuit's switch from output operation to stopping operation to be unstable, which could reduce the stability of the output current supplied to the electromagnet.

For this reason, it is desirable to further improve the stability of the output current in electromagnetic power supplies.

Japanese Patent Application Publication No. 1-279311

Embodiments of the present invention provide an electromagnetic power supply device that can further improve the stability of the output current.

According to an embodiment of the present invention, there is provided a main circuit section connected to an electromagnet and supplying a current to the electromagnet according to a current pattern that changes stepwise, a current detector that detects the current flowing through the electromagnet, and a control section that receives an input of the current pattern and controls the operation of the main circuit section based on the input current pattern and the detection result of the current detector, wherein the main circuit section has a forcing circuit that operates during a period when the current pattern changes stepwise, and a flat maintaining circuit that is connected in series with the forcing circuit and operates during a period when the current pattern is constant, and the control section causes the forcing circuit to perform an output operation that outputs a voltage during a period when the current pattern changes stepwise, and causes the output side to be conductive during a period when the current pattern is constant. and causes the forcing circuit to perform a stopping operation to stop output of the voltage by switching the current pattern to a target current value , acquires a current deviation representing the difference between a target current value represented by the current pattern and the current output current value detected by the current detector at a predetermined sampling period, calculates a time for the current deviation to reach the predetermined threshold based on the current value of the current deviation, a predetermined threshold, and a rate of change of the current deviation each time the current value of the current deviation is acquired, and after causing the forcing circuit to perform the output operation, if the current deviation reaches the predetermined threshold before the next acquisition of the current value of the current deviation, switches the forcing circuit from the output operation to the stopping operation at a timing when the arrival time calculated from the timing of acquisition of the current value of the current deviation has elapsed .

Embodiments of the present invention provide an electromagnetic power supply device that can further improve the stability of the output current.

1 is a circuit diagram schematically illustrating an electromagnetic power supply device according to an embodiment. FIG. 2 is a circuit diagram schematically illustrating a main circuit section. 3A and 3B are graphs that schematically show an example of the operation of the control unit. 10 is a graph schematically illustrating an example of the operation of the control unit. 10 is a graph schematically illustrating an example of the operation of the control unit. 10 is a graph schematically showing an example of a reference operation of a control unit.

Each embodiment will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing.
In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

FIG. 1 is a circuit diagram that schematically illustrates an electromagnetic power supply device according to an embodiment.
As shown in Fig. 1, the electromagnet power supply device 10 includes a main circuit unit 12 and a control unit 14. The main circuit unit 12 is connected to an electromagnet 2, which is a load, and supplies a current to the electromagnet 2 according to a current pattern that changes stepwise. The main circuit unit 12 operates the electromagnet 2 by supplying the current. The main circuit unit 12 is, for example, a voltage-type power conversion device. The control unit 14 controls the operation of the main circuit unit 12. More specifically, the control unit 14 controls the operation of the main circuit unit 12 to supply current to the electromagnet 2.

The main circuit section 12 has a forcing circuit 16 and a flat maintenance circuit 18. The flat maintenance circuit 18 is connected in series with the forcing circuit 16. The forcing circuit 16 operates during periods when the current pattern (current command value) changes stepwise. The flat maintenance circuit 18 operates during periods when the current pattern (current command value) is constant.

For example, reactors 21 and 22 are provided on the output side of the forcing circuit 16. For example, reactors 23 and 24 are provided on the output side of the flat maintenance circuit 18. Reactors 21 to 24 are, for example, reactors for smoothing ripple. The flat maintenance circuit 18 is connected in series with the forcing circuit 16 via reactors 22 and 23, for example. The forcing circuit 16 and flat maintenance circuit 18 (main circuit section 12) are connected to the electromagnet 2 via reactors 21 and 24.

The electromagnet power supply device 10 further includes, for example, a DC power supply 30 and a DC power supply 40. The forcing circuit 16 is connected to the electromagnet 2, which is a load, and also to the DC power supply 30. The forcing circuit 16 operates to change the current supplied to the electromagnet 2 in a step-like manner by switching between supplying and stopping the DC voltage supplied from the DC power supply 30 to the electromagnet 2. The current supplied from the main circuit unit 12 to the electromagnet 2 changes in a step-like manner when the forcing circuit 16 is outputting a DC voltage.

The DC power supply 30 includes, for example, a transformer 31, a rectifier 32, a reactor 33, and a capacitor 34. The rectifier 32 is connected to the AC power supply 4 via the transformer 31. The rectifier 32 rectifies the AC power supplied from the AC power supply 4 and converts it into rectified power. The reactor 33 and capacitor 34 smooth the rectified power converted by the rectifier 32 and convert it into DC power. In this way, the DC power supply 30 supplies DC power to the forcing circuit 16.

The flat maintenance circuit 18 is connected to the electromagnet 2, which serves as a load, and also to a DC power supply 40. The flat maintenance circuit 18 controls the current supplied to the electromagnet 2 to be a constant current according to the current command value represented by the current pattern by switching between supplying and stopping the DC voltage supplied from the DC power supply 40 to the electromagnet 2.

The DC power supply 40 includes, for example, a transformer 41, a rectifier 42, a reactor 43, and a capacitor 44. The configuration of the DC power supply 40 is similar to that of the DC power supply 30, so a detailed description will be omitted. As a result, the DC power supply 40 supplies DC power to the flat maintenance circuit 18.

The configuration of the DC power supplies 30, 40 is not limited to the above, and any configuration that can supply DC power to the forcing circuit 16 and the flat maintenance circuit 18 may be used. Furthermore, the electromagnet power supply device 10 does not necessarily have to include the DC power supplies 30, 40. The forcing circuit 16 and the flat maintenance circuit 18 may receive DC power from an external DC power supply.

FIG. 2 is a circuit diagram schematically showing the main circuit section.
As shown in FIG. 2, the forcing circuit 16 has four full-bridge-connected switching elements 50a to 50d and four rectifying elements 52a to 52d connected in anti-parallel to the four switching elements 50a to 50d, respectively.

Similarly, the flat maintenance circuit 18 has four full-bridge-connected switching elements 54a-54d and four rectifying elements 56a-56d connected in anti-parallel to each of the four switching elements 54a-54d.

The forcing circuit 16 and the flat maintenance circuit 18 are, in other words, chopper circuits. The forcing circuit 16 is, in other words, the first chopper circuit, and the flat maintenance circuit 18 is, in other words, the second chopper circuit.

In the forcing circuit 16, the connection point between the upper (high-side) switching element 50a and the lower (low-side) switching element 50c, and the connection point between the upper switching element 50b and the lower switching element 50d, respectively, form a pair of output points 16a and 16b. Similarly, in the flat maintenance circuit 18, the connection point between the upper switching element 54a and the lower switching element 54c, and the connection point between the upper switching element 54b and the lower switching element 54d, respectively, form a pair of output points 18a and 18b.

Output point 18a of flat maintenance circuit 18 is connected to output point 16b of forcing circuit 16 via reactors 22 and 23. This connects the output side of flat maintenance circuit 18 in series with the output side of forcing circuit 16. Output point 16a of forcing circuit 16 is connected to one end of electromagnet 2 via reactor 21. Output point 18b of flat maintenance circuit 18 is connected to the other end of electromagnet 2 via reactor 24. This connects the output sides of forcing circuit 16 and flat maintenance circuit 18, which are connected in series, with electromagnet 2, and power output from forcing circuit 16 and flat maintenance circuit 18 is supplied to electromagnet 2.

Each switching element 50a-50d, 54a-54d has a pair of main terminals and a control terminal. Depending on the voltage input to the control terminal, each switching element 50a-50d, 54a-54d switches between an ON state, in which current flows between the pair of main terminals, and an OFF state, in which current is blocked between the pair of main terminals. The OFF state does not necessarily have to be a state in which current flow between the main terminals is completely blocked, but may also be a state in which a weak current flows between the main terminals to the extent that it does not affect the operation of the main circuit unit 12. The ON state is, in other words, a first state in which current flows between the main terminals, and the OFF state is, in other words, a second state in which current flows between the main terminals in a smaller amount than in the first state.

Each of the switching elements 50a-50d, 54a-54d is a self-excited semiconductor switching element such as an IGBT (Insulated Gate Bipolar Transistor). However, the switching elements 50a-50d, 54a-54d are not limited to this and may be any switching element that can be controlled to switch between an on state and an off state.

In the forcing circuit 16 and flat maintenance circuit 18 of the full-bridge circuit, the direction of the current supplied to the electromagnet 2 can be controlled by switching each of the switching elements 50a-50d, 54a-54d. However, the configuration of the forcing circuit 16 and flat maintenance circuit 18 is not limited to the above, and any configuration can be used that can appropriately supply current to the electromagnet 2 in accordance with the step-like changing current pattern.

The control unit 14 is connected to the control terminals of each of the switching elements 50a-50d, 54a-54d, and controls the operation of the forcing circuit 16 and the flat maintenance circuit 18 by controlling the switching between the on and off states of each of the switching elements 50a-50d, 54a-54d.

The control unit 14 controls the switching between the on and off states of each of the switching elements 50a to 50d in the forcing circuit 16, thereby controlling the operation of changing the current supplied to the electromagnet 2 in a stepwise manner.

In addition, the control unit 14 causes the forcing circuit 16 to perform an output operation that outputs a voltage during a period in which the current pattern changes stepwise, and also causes the forcing circuit 16 to perform a stop operation that stops the voltage output by making the output side conductive (bypass) during a period in which the current pattern is constant. The output operation is, in other words, a forcing operation.

In this example, the pair of output points 16a, 16b can be brought into a conductive state by turning on the upper switching elements 50a, 50b and turning off the lower switching elements 50c, 50d, or conversely, turning off the upper switching elements 50a, 50b and turning on the lower switching elements 50c, 50d.

The control unit 14 controls the on/off switching of each of the switching elements 54a-54d of the flat maintenance circuit 18, thereby controlling the current supplied to the electromagnet 2 to be a constant current corresponding to the current pattern when the current pattern is for a fixed period. The control unit 14 controls the current supplied to the electromagnet 2 to be a constant current corresponding to the current pattern, for example, by quickly switching the on/off states of each of the switching elements 54a-54d. The control unit 14 controls the current supplied to the electromagnet 2 to be a constant current corresponding to the current pattern, for example, by performing ACR (Auto Current Regulator) control on the flat maintenance circuit 18.

As shown in FIG. 1, the electromagnet power supply device 10 further includes a current detector 60. The current detector 60 detects the current flowing through the electromagnet 2 and inputs the detection result to the control unit 14.

3A and 3B are graphs that schematically show an example of the operation of the control unit.
Fig. 3(a) schematically shows an example of a current pattern input to the control unit 14 and an example of an output current supplied from the main circuit unit 12 to the electromagnet 2. Fig. 3(b) shows an enlarged view of the area surrounded by the dashed line in Fig. 3(a).

As shown in Figures 3(a) and 3(b), a current pattern that changes stepwise is input to the control unit 14. The current pattern is input to the control unit 14 as needed, for example, from a higher-level controller via communication. In other words, the control unit 14 receives the current pattern input from an external device such as a higher-level controller by communicating with the external device. The current pattern is, in other words, a current command value that indicates the magnitude of the current to be supplied to the electromagnet 2. In other words, the control unit 14 receives the current command value input from the external device by communicating with the external device.

The current pattern (current command value) may be input to the control unit 14 in advance and stored in a memory unit of the control unit 14 or in another memory unit connected to the control unit 14, for example. The method of inputting the current pattern to the control unit 14 is not limited to the above, and any method that can appropriately input the current pattern to the control unit 14 may be used.

The control unit 14 controls the operation of the main circuit unit 12 (forcing circuit 16 and flat maintenance circuit 18) based on the input current pattern and the detection results of the current detector 60.

The control unit 14 causes the forcing circuit 16 to perform a stop operation to turn on the output side during periods when the current pattern is constant, and controls the operation of the flat maintenance circuit 18 based on the detection results of the current detector 60 so that the current supplied to the electromagnet 2 is a constant current according to the current pattern.

As shown in Figure 3(a), when changing the polarity of the current supplied to the electromagnet 2, the control unit 14 changes the polarity of the voltage output from the flat maintenance circuit 18 depending on whether a positive polarity current is supplied to the electromagnet 2 or a negative polarity current is supplied to the electromagnet 2.

FIG. 4 is a graph schematically showing an example of the operation of the control unit.
3A, 3B, and 4, the control unit 14 causes the forcing circuit 16 to perform an output operation to output a voltage when the current pattern changes stepwise. The control unit 14 changes the polarity of the voltage output from the forcing circuit 16 when the current supplied to the electromagnet 2 is lower than the current pattern and when the current supplied to the electromagnet 2 is higher than the current pattern. For example, when the current supplied to the electromagnet 2 is lower than the current pattern and the current supplied to the electromagnet 2 is to be increased toward a target current value, the control unit 14 causes the forcing circuit 16 to output a voltage of positive polarity. On the other hand, when the current supplied to the electromagnet 2 is higher than the current pattern and the current supplied to the electromagnet 2 is to be decreased toward a target current value, the control unit 14 causes the forcing circuit 16 to output a voltage of negative polarity.

When the forcing circuit 16 is caused to perform an output operation, the flat maintenance circuit 18 may continue to control the current supplied to the electromagnet 2 to a constant level, or may perform a stop operation to keep the output side conductive.

In Figures 3(b) and 4, the forcing-on period during which the forcing circuit 16 performs output operation is represented by the period indicated by arrow (1), and the flat operation period during which the flat maintenance circuit 18 performs operation to control the current to a constant level is represented by the period indicated by arrow (2). Note that in Figure 3(b), the timing of the start of the forcing-on period is shown slightly delayed from the timing of the change in the current pattern, taking into account the response delay between the timing of the change in the current pattern and the timing of the operation of the forcing circuit 16.

After causing the forcing circuit 16 to perform an output operation, the control unit 14 switches the forcing circuit 16 from an output operation to a stop operation when the current deviation, which represents the difference between the target current value represented by the current pattern and the current output current value detected by the current detector 60, reaches a predetermined threshold. In other words, the control unit 14 switches from the forcing-on period to the flat operation period when the current deviation reaches a predetermined threshold. In other words, the control unit 14 switches the forcing circuit 16 from an output operation to a stop operation when the current supplied to the electromagnet 2 reaches the target current value.

The threshold value may be set to zero deviation based on the target current value, or may be set to switch to a stopping operation early, taking into account overshoot (undershoot) of the current deviation due to delays in the operation of the forcing circuit 16. For example, as shown in Figure 4, when switching the forcing circuit 16 from output operation to stopping operation, it may be necessary to keep the current deviation within a specified range. The specified range is, for example, within ±0.1% of the rated current value. The rated current value is the current supplied to the electromagnet 2 when the forcing circuit 16 performs an output operation. In such cases, the threshold value may be set appropriately, taking into account overshoot of the current deviation, so that the current deviation falls within the specified range.

FIG. 5 is a graph schematically showing an example of the operation of the control unit.
5, the control unit 14 acquires the current deviation value at a predetermined sampling period. In other words, the control unit 14 acquires the detected value of the current flowing through the electromagnet 2 from the current detector 60 at a predetermined sampling period. The control unit 14 acquires the detected value of the current flowing through the electromagnet 2 from the current detector 60 at a predetermined sampling period, for example, and acquires the current deviation value at the predetermined sampling period by calculating the difference between the detected current value and the target current value each time the control unit 14 acquires the detected current value from the current detector 60. The control unit 14 calculates the current deviation value at the predetermined sampling period, for example, using the following formula:
Current deviation = target current value - detected current value

Each time the control unit 14 acquires the current deviation's current value, the control unit 14 calculates the time required for the current deviation to reach the threshold value based on the current deviation's current value, the threshold value, and the rate of change of the current deviation. The control unit 14 calculates the threshold value arrival time using, for example, the following formula.
Time to reach threshold = (current deviation current value - threshold) ÷ rate of change of current deviation

For example, suppose the current current deviation is 2A, the threshold is 1A, and the rate of change of the current deviation is 1A/μs. In this case, the time to reach the threshold can be calculated as (2A - 1A) ÷ 1A/μs = 1μs.

The sign of the current value of the current deviation may change depending on whether the current pattern is increasing or decreasing, and the direction in which current is supplied to electromagnet 2 (current polarity). Therefore, the current value of the current deviation is, more specifically, the absolute value of the current deviation. Similarly, the sign of the rate of change of the current deviation may also change depending on whether the current pattern is increasing or decreasing. More specifically, the rate of change of the current deviation is the absolute value of the slope of the change in the current deviation.

As shown in FIG. 5, after causing the forcing circuit 16 to perform an output operation, if the current deviation reaches a predetermined threshold before the next acquisition of the current value of the current deviation, the control unit 14 switches the forcing circuit 16 from an output operation to a stop operation at the timing when the arrival time calculated from the timing of acquisition of the current value of the current deviation has elapsed.

When the output voltage output from the main circuit unit 12 to the electromagnet 2 is V, the output current output from the main circuit unit 12 to the electromagnet 2 is i, the inductance component of the electromagnet 2 is L, the resistance component of the electromagnet 2 is R, and the rate of change of the output current i output to the electromagnet 2 is di/dt, the output voltage V can be expressed by the following equation. Note that when the forcing circuit 16 is performing an output operation, the output voltage V is, in other words, the output voltage of the forcing circuit 16.
V=L・di/dt+R・i
By modifying the above equation, the rate of change di/dt can be expressed by the following equation: That is, the rate of change of the current deviation can be obtained by the following equation.
di/dt=(VR・i)/L

The output voltage V, output current i, inductance component L, and resistance component R can be obtained as design values for the electromagnet power supply unit 10. Therefore, the rate of change of the current deviation can be a predetermined value calculated in advance using the above formula. The control unit 14 stores the pre-calculated rate of change of the current deviation, for example, in an internal memory unit or an external memory unit connected via wiring, and calculates the threshold arrival time based on the stored rate of change of the current deviation.

In this way, the rate of change of the current deviation depends on the output voltage of the forcing circuit 16. In other words, the rate of change of the current deviation depends on the output voltage of the DC power supply 30. In the electromagnetic power supply 10, the duration of the forcing-on period (the time during which the output current is changed in steps) may be predetermined. In this case, the rate of change of the current deviation is determined according to the duration of the predetermined forcing-on period. In other words, the output voltage of the forcing circuit 16 and the output voltage of the DC power supply 30 are determined according to the duration of the predetermined forcing-on period. The duration of the forcing-on period is sometimes referred to as, for example, the excitation speed.

The rate of change of the current deviation may be calculated based on the previous current deviation value, the current current deviation value, and the sampling period, each time the current current deviation value is acquired. That is, the rate of change of the current deviation may be calculated using the following formula each time the current current deviation value is acquired.
Current deviation change rate = (current deviation value from previous time - current deviation value from this time) / sampling period

However, there is a possibility that noise due to measurement errors may be superimposed on the current value of the current deviation detected by the current detector 60. For this reason, it is preferable to set the rate of change of the current deviation to a predetermined value calculated in advance based on the output voltage V, output current i, inductance component L, and resistance component R. This makes it possible, for example, to suppress the effects of measurement errors and more appropriately calculate the time it takes for the current deviation to reach the threshold value. Furthermore, it is also possible to reduce the computational load on the control unit 14.

FIG. 6 is a graph schematically showing an example of a reference operation of the control unit.
In the example shown in FIG. 6 , after the control unit 14 causes the forcing circuit 16 to perform an output operation, each time the control unit 14 acquires the current value of the current deviation, it determines whether the acquired current value of the current deviation has reached a threshold value, and switches the forcing circuit 16 from an output operation to a stop operation in response to determining that the threshold value has been reached.

In the reference operation shown in FIG. 6, as shown in FIG. 6, due to jitter caused by the sampling period of the current deviation, the timing at which the forcing circuit 16 switches from output operation to stopped operation may be delayed from the timing at which it should switch to stopped operation (the point at which it should be turned off) when the current value of the current deviation reaches the threshold value. In other words, in the reference operation, the timing at which the forcing circuit 16 switches from output operation to stopped operation may vary within the range from the timing at which the current deviation is sampled to the timing at which the next current deviation is sampled.

As such, in the reference operation, the timing at which the forcing circuit 16 switches from output operation to stop operation (forcing-off timing) is unstable, and as a result, the behavior of the overshoot in the current deviation when switching from output operation to stop operation may be unstable. For example, when the forcing circuit 16 switches from output operation to stop operation, the current deviation may not fall within a predetermined range, such as ±0.1% of the rated current value.

For example, as shown in Figure 3(a), there are cases where the cycle of the current pattern change (the cycle from one forcing-on period to the next) is relatively high, at tens of kHz or more, and the duration of the forcing-on period is required to be short, on the order of a few microseconds. In such a case, if the sampling cycle for acquiring the current value of the current deviation is set to about 1 microsecond, the sampling cycle becomes long relative to the change in current deviation, and the problem of variation in the timing at which the forcing circuit 16 is switched from output operation to stop operation becomes pronounced. In the reference operation, if the cycle of the current pattern change is high, there is a high possibility that the current deviation will not fall within the specified range when forcing is off.

One possible solution is to increase the sampling period for acquiring the current current deviation value. However, if the control unit 14 attempts to increase the sampling period while maintaining high resolution of the current current deviation value, the configuration of the control unit 14 would become more complex. For example, new components such as AD converters would have to be developed, which would increase the manufacturing costs of the control unit 14.

In contrast, in the electromagnet power supply device 10 according to this embodiment, each time the control unit 14 acquires the current value of the current deviation, it calculates the time it takes for the current deviation to reach the threshold value based on the current value of the current deviation, the threshold value, and the rate of change of the current deviation. After causing the forcing circuit 16 to perform an output operation, if the current deviation reaches the predetermined threshold value before the next acquisition of the current value of the current deviation, it switches the forcing circuit 16 from output operation to stop operation when the calculated arrival time has elapsed since the acquisition of the current value of the current deviation.

This stabilizes the timing at which the forcing circuit 16 switches from output operation to stop operation, and also stabilizes the overshoot behavior of the current deviation when switching from output operation to stop operation. For example, when the forcing circuit 16 switches from output operation to stop operation, the current deviation can be appropriately kept within a specified range.

As a result, it is possible to provide an electromagnet power supply unit 10 that can further improve the stability of the output current supplied to the electromagnet 2. For example, even when the current pattern changes frequently, it is possible to reduce the need to increase the sampling period and improve the stability of the output current with a relatively simple configuration.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

DESCRIPTION OF SYMBOLS 2...Electromagnet, 4...AC power supply, 10...Electromagnet power supply device, 12...Main circuit section, 14...Control section, 16...Forcing circuit, 18...Flat maintenance circuit, 21-24...Reactor, 30, 40...DC power supply, 31, 41...Transformer, 32, 42...Rectifier, 33, 43...Reactor, 34, 44...Capacitor, 50a-50d, 54a-54d...Switching element, 52a-52d, 56a-56d...Rectifying element, 60...Current detector

Claims (3)

a main circuit section connected to the electromagnet and supplying a current to the electromagnet according to a current pattern that changes stepwise;
a current detector for detecting a current flowing through the electromagnet;
a control unit that receives the current pattern and controls the operation of the main circuit unit based on the input current pattern and the detection result of the current detector;
Equipped with
The main circuit section includes:
a forcing circuit that operates during a period in which the current pattern changes stepwise;
a flat-maintaining circuit connected in series with the forcing circuit, the flat-maintaining circuit operating for a fixed period of time;
and
the control unit causes the forcing circuit to perform an output operation to output a voltage when the current pattern is changing stepwise, and causes the forcing circuit to perform a stop operation to make an output side conductive and stop the output of the voltage when the current pattern is in a fixed period ; acquires a present value of a current deviation that represents a difference between a target current value represented by the current pattern and a present output current value detected by the current detector at a predetermined sampling period; and each time the present value of the current deviation is acquired, calculates a time period for the current deviation to reach the predetermined threshold based on the present value of the current deviation, a predetermined threshold, and a rate of change of the current deviation; and after causing the forcing circuit to perform the output operation, if the current deviation reaches the predetermined threshold before the next acquisition of the present value of the current deviation, switches the forcing circuit from the output operation to the stop operation at a timing when the arrival time calculated from the timing of acquisition of the present value of the current deviation has elapsed . a main circuit section having a forcing circuit and a flat maintaining circuit, and supplying a current to the electromagnet according to a target current value that changes stepwise;
a current detector for detecting a current flowing through the electromagnet;
a control unit that controls the operation of the main circuit unit based on the target current value and the current value detected by the current detector;
Equipped with
The control unit
When the target current value changes, the forcing circuit is controlled to output a voltage so that the current flowing through the electromagnet becomes the target current value;
acquiring a current deviation, which is a difference between the target current value and the current value detected by the current detector, at a predetermined sampling period;
each time the current deviation is acquired, a time required for the current deviation to reach the predetermined threshold is calculated based on the current deviation, a predetermined threshold, and a rate of change of the current deviation;
If the current deviation reaches the predetermined threshold value before the next sampling period, stopping the output of voltage from the forcing circuit at the timing when the time calculated from the timing of acquiring the current deviation has elapsed until the current deviation reaches the predetermined threshold value ;
an electromagnet power supply device that, when the output of voltage from the forcing circuit is stopped, controls the flat maintaining circuit to supply a constant current to the magnet based on the target current value until the target current value changes. 3. The electromagnet power supply device according to claim 1, wherein the control unit calculates a time until the current deviation reaches the predetermined threshold value by using a rate of change of the current deviation that is calculated in advance based on an output voltage output from the main circuit unit to the electromagnet, an output current output from the main circuit unit to the electromagnet, an inductance component of the electromagnet, and a resistance component of the electromagnet.