JP6556407B1 - Switching power supply apparatus and power supply apparatus for nuclear magnetic resonance imaging apparatus using the same - Google Patents

Abstract

A switching power supply (10) having a power converter (1) having a plurality of switching elements (SW11 to SW14) and a DC voltage source (2), and between the switching power supply (10) and a load (5) A measuring instrument (7) for measuring the current and voltage of the load (5) provided in series, and a control circuit (8) for controlling the operation of the plurality of switching elements (SW11 to SW14), 8), positive and negative voltages are output to the load (5), the amount and polarity of the current flowing through the load (5) are controlled by the difference between the positive and negative voltage output periods, and the switching power supply (10) The operation of the plurality of switching elements (SW11 to SW14) is controlled to the load (5) so that the sum of the output periods of the positive and negative voltages within the period T becomes smaller than one period T of the switching power supply (10). Flowing To reduce the flow ripple.

Description

  The present application relates to a switching power supply apparatus and a power supply apparatus for a nuclear magnetic resonance imaging apparatus using the same.

  An MRI (Magnetic Resonance Imaging) apparatus applies a high-frequency magnetic field in a pulsed manner to an inspection object placed in a static magnetic field, and detects and images a magnetic resonance signal generated by the inspection object. In addition, in order to acquire a magnetic resonance signal having position information, a gradient magnetic field having an intensity proportional to the distance is applied to the inspection target in addition to the static magnetic field. This MRI apparatus includes a superconducting or normal conducting coil for generating a static magnetic field as a magnetic field generating coil, a gradient magnetic field coil for generating a gradient magnetic field superimposed on the static magnetic field, and a high frequency coil for generating a high frequency magnetic field. It has been. The plurality of magnetic field generating coils include a switching power supply device for controlling the magnitude and timing of the applied current in order to generate a magnetic field having a predetermined magnetic strength.

In order to obtain position information with high accuracy and increase the resolution of an image, a power supply device for a gradient magnetic field of an MRI apparatus is required to have a pulse current waveform with a small current ripple.
There is disclosed a power supply device for a nuclear magnetic resonance imaging apparatus that has a plurality of switching power supply groups in which a plurality of switching power supplies are connected in parallel, and can obtain a high voltage and a large capacity by connecting the switching power supply groups in series. (Patent Document 1). With the disclosed configuration, current wraparound between switching power supply groups connected in parallel can be prevented, and the ripple of current flowing in the coil of the gradient magnetic field can be reduced by operating the phases of the switching power supply groups connected in parallel. It becomes possible.

  In addition, a switching amplification device is disclosed that can reduce the current ripple of the gradient coil by controlling the variable input power source connected to the full bridge inverter to adjust the input bus voltage (Patent Document 2). ). Further, the switching amplifier of Patent Document 2 includes a buck circuit having a voltage buck regulator, and the switching function is performed when the voltage is high and the bridge inverter performs the switching function when the voltage is low. By sharing the loss in two and reducing it, high-frequency operation, that is, operation with a steep rise is possible.

Japanese Patent No. 3591982 JP 2000-092856 A

In the amplifying device of Patent Document 2, it is not disclosed how to control the variable input power source connected to the inverter with a complicated device configuration and to reduce the current ripple of the gradient coil, and the output of the full bridge inverter It does not reduce current ripple.
In the power supply device of Patent Document 1, the current ripple of the gradient magnetic field coil as a load of the power supply device is reduced by a combination of a plurality of switching power supplies, and the current ripple of each switching power supply is not reduced. Therefore, the current ripple of each switching power supply may be large, and it is premised on the combination of a plurality of switching power supplies, which is a restriction on simplification of the device configuration and control. Further, reduction of the current ripple when the current flowing through the gradient magnetic field coil is small is an important issue for imaging in the MRI apparatus, but it has not been shown to reduce it.

  The present application discloses a technique for solving the above-described problem, and an object thereof is to provide a switching power supply device having a simple device configuration with a small current ripple of the switching power supply. It is another object of the present invention to provide a power supply device for a nuclear magnetic resonance imaging apparatus that can obtain a high-resolution image by using this switching power supply device.

A switching power supply device disclosed in the present application is provided between a switching power supply including a power converter having a plurality of switching elements and a DC voltage source, and a load connected in series to the switching power supply. A switching power supply comprising: a measuring instrument for measuring the current and voltage of the load, and a control circuit for controlling operations of the plurality of switching elements, wherein the control circuit has positive and negative voltages across the load. And controlling the operation of the plurality of switching elements so as to control the amount and polarity of the current flowing through the load according to the difference between the positive and negative voltage output periods, and the positive and negative voltage output corresponding to the amount of current flowing through the load. A command value for determining a period and a reference signal are generated, and the reference signal is generated at a cycle of 1 / n (n is an integer of 2 or more) of the cycle of the switching power supply. A voltage output period determined by comparing the command value and the reference signal is D, and from the voltage output period D, the voltage of the DC voltage source, the dead time of the plurality of switching elements, the resistance of the load, and The surplus period α (i) obtained by the amount of current flowing through the load is subtracted, one positive / negative voltage is set to the D−α (i) period in the first reference signal period, and the other positive / negative voltage is set to the remaining period. The operation of the plurality of switching elements is controlled so as to output during the period 1-D-α (i) .

  A power supply device for a nuclear magnetic resonance imaging apparatus disclosed in the present application includes the above-described switching power supply device, a coil for a nuclear magnetic resonance imaging apparatus that is the load, and a coil control device that controls the coil. The control circuit of the switching power supply device controls the operation of the plurality of switching elements of the switching power supply device based on the current command value output from the control device.

  According to the above configuration, the positive and negative voltages are output to the load, the amount and polarity of the current flowing through the load are controlled by the difference between the positive and negative voltage output periods, and the positive and negative voltages within one cycle of the switching power supply. Since the sum of the output periods is made smaller than one cycle of the switching power supply, it is possible to provide a switching power supply apparatus having a simple device configuration with a small current ripple. Further, since this switching power supply device is used, it is possible to provide a power supply device for a nuclear magnetic resonance imaging apparatus that can increase the resolution of an image even in a region where the current flowing through the coil is small.

1 is a configuration diagram illustrating a switching power supply device according to a first embodiment. It is a figure which shows the relationship between the operation | movement of the switching element which comprises the switching power supply apparatus which concerns on Embodiment 1, and an output voltage. 3 is a timing chart illustrating a basic operation sequence of the switching power supply device according to the first embodiment. 3 is a timing chart illustrating an operation sequence of the switching power supply device according to the first embodiment. FIG. 3 is a block diagram illustrating a configuration of a control circuit of the switching power supply device according to the first embodiment. 6 is a timing chart illustrating an operation sequence of the switching power supply device according to the second embodiment. It is a figure which shows the relationship between the output current (load current) by PWM control of a switching power supply device, and an output surplus period. FIG. 6 is a block diagram illustrating a configuration of a control circuit of a switching power supply device according to a second embodiment. FIG. 5 is a schematic configuration diagram showing a switching power supply device according to a third embodiment. It is the figure which showed the circuit structure of the power converter in FIG. It is a figure which shows the output current waveform of the switching power supply device which concerns on Embodiment 3, and sharing of a power converter. FIG. 10 is a diagram showing an operation pattern of the switching power supply device according to the third embodiment. FIG. 10 is a diagram showing an operation pattern of the switching power supply device according to the third embodiment. FIG. 10 is a diagram showing an operation pattern of the switching power supply device according to the third embodiment. FIG. 10 is a diagram showing an operation pattern of the switching power supply device according to the third embodiment. FIG. 10 is a diagram showing an operation pattern of the switching power supply device according to the third embodiment. It is a figure which shows the output voltage of the electric current rise part of the switching power supply which concerns on Embodiment 3. FIG. 12 is a timing chart showing an operation sequence of a current steady part (current flat part) of the switching power supply according to the third embodiment. 4 is a hardware configuration diagram of a control circuit of the switching power supply according to Embodiments 1 to 3. FIG. FIG. 6 is a configuration diagram illustrating a power supply device for an MRI apparatus according to a fourth embodiment.

  Hereinafter, the present embodiment will be described with reference to the drawings. The switching power supply device according to the embodiment will be described with reference to an example in which power is supplied to a coil for a gradient magnetic field device of an MRI (Magnetic Resonance Imaging) device, but is not limited thereto. In addition, in each figure, the same code | symbol shall show the same or an equivalent part.

Embodiment 1 FIG.
Hereinafter, the switching power supply according to Embodiment 1 will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of a switching power supply apparatus 100 according to the first embodiment. The switching power supply device 100 includes a power converter (inverter) 1 in which four switching elements indicated by SW11 to SW14 are configured in a full bridge type, and a DC voltage source 2 connected to the power converter 1, A measuring instrument 7 for measuring a current and a voltage flowing in a load 5 connected between AC output terminals Q1 and Q2 of the power converter 1, a current and a voltage measured by the measuring instrument 7, and a current command value are inputted. A control circuit 8 that outputs a gate signal to the switching elements SW11 to SW14 is provided. Here, the load 5 is a gradient magnetic field coil of the MRI apparatus, but the switching power supply apparatus 100 corresponds to a constant current power source or a constant voltage circuit that controls the amount of current to the coil that is the load 5 and the positive / negative direction. The switching elements SW11 to SW14 can use, for example, MOSFETs (Metal-Oxide-Semiconductor-Field-Effect-Transistors) as semiconductor switching elements.

Next, the basic operation of the switching power supply apparatus 100 will be described with reference to FIGS.
FIG. 2 is a diagram showing the relationship between the operation of the switching elements SW11 to SW14 constituting the power converter (inverter) 1 and the output voltage. Broken line arrows in the figure indicate the direction of current.
(1) Positive voltage output In order to make the polarity of the current flowing through the load 5 in FIG. 1 positive, the switching elements SW12 and SW13 are turned on so that a positive voltage is output from the power converter (inverter) 1. The switching elements SW11 and SW14 are turned off.
(2) Through state In order to disconnect the DC voltage source 2 from the load 5 to make a through state so that no voltage is applied, the switching elements SW11 and SW13 are turned on and the switching elements SW12 and SW14 are turned off. Alternatively, although not shown, the switching elements SW12 and SW14 are turned on and the switching elements SW11 and SW13 are turned off.
(3) Negative voltage output To make the polarity of the current flowing through the load 5 in FIG. 1 negative, the switching elements SW11 and SW14 are turned on so that a negative voltage is output from the power converter (inverter) 1. The switching elements SW12 and SW13 are turned off.

The amount of current in the positive direction to the load 5 is adjusted by adjusting the ratio of the period of (1) positive voltage output and (2) through state, and the amount of current in the negative direction to the load 5 is 3) The period ratio between negative voltage output and (2) through may be adjusted.
However, when the amount of current is extremely small or when the voltage of the DC voltage source 2 is high, a control limit is generated in which the output from the power converter 1 is not normal. Therefore, even when a current in the positive direction is supplied to the load 5 within one cycle in which the switching elements SW11 to SW14 operate, the above-described (1) positive voltage output, (2) through, and (3) negative voltage output 3 By adjusting one period and performing bipolar output, and even when a negative current flows through the load 5, the same adjustment and output can solve the problem of current control limitations at low currents.

  FIG. 3 is a timing chart showing a basic operation sequence of the switching power supply apparatus 100, and is an example using the bipolar output described above. The current flowing through the load 5 is divided into a steady state (current flat portion where the current rises and becomes a constant current) A when the amount of current is large and a steady state B when the amount of current is small. The D signal that determines the reference signal and the voltage output period, the output current average value and the output voltage, the transition of the current ripple corresponding to this output voltage, and the gate signal that operates the switching elements SW11 to SW14, respectively, are shown from the top. Yes. The current ripple is a fluctuation value on the average current value, but is shown here so as to understand the relationship with the output voltage.

First, a case where the current is large (A) will be described.
A rectangular waveform output voltage waveform is formed by PWM (Pulse Width Modulation) control based on a sawtooth signal as a reference signal and a D command in which a voltage output period D corresponding to a predetermined load current (large) is a command value. Is done. Specifically, at time t0, the switching elements SW12 and SW13 are turned on, the switching elements SW11 and SW14 are turned off, and a positive voltage is output. At time t101, the reference signal exceeds the D command, the switching elements SW12 and SW13 are turned off, the switching elements SW11 and SW14 are turned on, and a negative voltage is output. After the negative voltage is output until the period of 1-D, that is, t102, the positive voltage output period starts again. From time t0 to t102 is one cycle of the operation of the four switching elements (T: switching power supply cycle), and this operation sequence is repeated after time t102.
At this time, since the difference between the positive and negative output voltage periods in the rectangular wave shape is large, the average value of the output current becomes large, and the current ripple becomes large so as to follow the output voltage waveform.

Next, the case where the current is small (B) will be described.
A rectangular waveform output voltage waveform is formed by PWM control based on a sawtooth signal as a reference signal and a D command in which a voltage output period D corresponding to a predetermined load current (small) is a command value. Specifically, at time t0, the switching elements SW12 and SW13 are turned on, the switching elements SW11 and SW14 are turned off, and a positive voltage is output. At time t201, the reference signal exceeds the D command, the switching elements SW12 and SW13 are turned off, the switching elements SW11 and SW14 are turned on, and a negative voltage is output. After the negative voltage is output until the period 1-D, ie, time t202, the positive voltage output period starts again. The period from time t0 to t202 is one cycle of the operation of the four switching elements (T: switching power supply cycle), and this operation sequence is repeated after time t202.
Compared with the case (A) where the current is large, the rectangular wave-like negative output voltage period is longer, and the difference between the positive and negative output voltage periods is small, so the average value of the output current becomes smaller. Further, the current ripple is smaller than that in (A) when the current is large.

  In the above description, an example in which the electrode polarity is positive is shown. However, it can be seen that the direction of the current and the amount of current can be controlled by the difference between the positive voltage D period and the negative voltage 1-D period. However, in the basic operation of the switching power supply device 100 described above, even when the current is small, a positive voltage is output during a period (D) that is approximately half of one cycle, so that the current ripple is still large. Note that D and 1-D satisfy the relationship D> 1-D.

In order to reduce the current ripple, it is conceivable to shorten the cycle of the switching power supply, that is, increase the frequency, but there are problems such as an increase in loss of the switching element. In the present embodiment, the current ripple is reduced by controlling the positive and negative voltage output periods in the switching power supply cycle T to be short without changing (decreasing) the switching power supply cycle.
FIG. 4 is a timing chart showing an operation sequence of the switching power supply apparatus 100 according to the first embodiment. The current flowing through the load 5 is divided into a steady state A when the current is large and a steady state B-1 when the current is small.

First, a case where the current is large (A) will be described.
The sawtooth signal as the reference signal is generated with a period of ½ of the switching power supply period T in the basic operation described above, and a D command in which the voltage output period D corresponding to a predetermined load current (large) becomes a command value To do. A rectangular wave output voltage waveform is formed by PWM control based on this D command. Specifically, at time t0, the switching elements SW12 and SW13 are turned on, the switching elements SW11 and SW14 are turned off, and a positive voltage is output. At time t11, the reference signal exceeds the D command, and the switching element SW13 is turned off and the switching element SW14 is turned on in order to enter a through state in which positive and negative voltages are not applied. The time t12 when the second sawtooth signal rises is a T / 2 cycle, and a negative voltage is output during the period of output 1-D. That is, at time t12, the switching element SW11 is turned on and the switching element SW12 is turned off. At time t13, the negative voltage output period ends, the switching element SW13 is turned on, the switching element SW14 is turned off, and the through state is established. At time t14, the switching element SW11 is turned off, the switching element SW12 is turned on, and a positive voltage is output again. The switching power supply cycle T is from time t0 to t14, and this operation sequence is repeated after time t14.

Next, the case where the current is small (B-1) will be described.
The sawtooth signal as the reference signal is generated with a period that is 1/2 of the switching power supply period T, as in the case where the above-described current is large, and the voltage output period D corresponding to a predetermined load current (small) is the command value. It becomes D command which becomes. A rectangular wave output voltage waveform is formed by PWM control based on this D command. Specifically, at time t0, the switching elements SW12 and SW13 are turned on, the switching elements SW11 and SW14 are turned off, and a positive voltage is output. At time t21, the switching element SW13 is turned off and the switching element SW14 is turned on in order to enter a through state in which the reference signal exceeds the D command and no positive or negative voltage is applied. The time t22 at which the second sawtooth signal rises is a T / 2 cycle, and a negative voltage is output for a period of 1-D. That is, at time t22, the switching element SW11 is turned on and the switching element SW12 is turned off. At time t23, the negative voltage output period ends, the switching element SW13 is turned on, the switching element SW14 is turned off, and the through state is established. At time t24, the switching element SW11 is turned off, the switching element SW12 is turned on, and a positive voltage is output again. The switching power supply cycle T is from time t0 to t24, and this operation sequence is repeated after time t24.

In the operation sequence of FIG. 4, whether the current is large or small, the reference signal is generated with a period of ½ of the switching power supply period, and with the first reference signal, the positive / negative output voltage period is determined, Since the positive voltage is output during period D and the negative voltage is output during period 1-D at the timing of the second reference signal, the positive voltage output period is shortened. As in the basic operation, D and 1-D satisfy the relationship of D> 1-D.
When the current is large (A), the rectangular wave-shaped positive voltage output period is shorter than ½ of the switching power supply cycle, and even when combined with the rectangular wave negative voltage output period, it is about ½ of the switching power supply cycle. Thus, the current ripple is halved compared to the basic operation described above.
When the current is small (B-1) The rectangular wave-shaped positive voltage output period is about 1/4 of the switching power supply cycle, and even if it is added to the rectangular wave negative voltage output period, it is about 1/2 of the switching power supply cycle. Thus, the current ripple is halved compared to the basic operation described above.

FIG. 5 is a block diagram showing the configuration of the control circuit 8 of the switching power supply apparatus 100 according to the first embodiment. The signal for performing positive and negative bipolar output to the power converter 1 and the power according to the current of the load 5 are shown. The control calculation for outputting the signal which controls the voltage output period of the converter 1 is shown.
In the figure, the command value (load current command value) of the current flowing through the coil from the control device (not shown) for controlling the coil of the load 5, that is, the coil of the gradient magnetic field device, and the load current measurement measured by the measuring instrument 7. The value is input to the PI controller 81. The output of the PI controller 81 and the sawtooth signal generated by the reference signal generator 82 are input to the comparator 83, and a voltage is output from the switching power supply 10 so that a predetermined amount of current flows through the coil as the load 5. A D command that is a command value for the output voltage period is set. The output from the comparator 83 is input to the selector 84 as a command value D and a negative command value -D, 1-D obtained by adding 1 from the adder. Either a positive or negative signal is input to the selector 84 from the output positive / negative switching unit 85 that switches the polarity of the current of the coil that is the load 5. Entered. The gate signal generation unit 86 generates a gate signal that sets the on / off operation and the on / off period of the four switching elements SW11 to SW14, and operates the switching elements SW11 to SW14.

  Here, the magnitude | size of the electric current which flows into the coil of the gradient magnetic field apparatus which is the load 5 is demonstrated. The load current is a set of rectangular waveform pulses, and on average, it has a square waveform as shown in FIG. The square-wave flat portion has a predetermined current value according to the command value. For example, the maximum current is 500 to 600 A, and for example, 256 steps of current having different square-wave flat portions are flowed for MRI image creation. In the above description, when the current is large, the current is approximately 400 A or more close to the maximum current, and when the current is small, the current is approximately several A or 10 A or less close to the minimum value. Since the current ripple when the current is small greatly affects the resolution of the MRI image, it is particularly important to reduce the current ripple.

  As described above, in the first embodiment, the direction and amount of current can be controlled by the difference between the positive voltage output period and the negative voltage output period. Furthermore, the cycle of the reference signal that sets the output voltage period of the switching power supply is set to a period that is 1/2 of the switching power supply cycle. In the case of generation, the switching element is operated so as to output a positive voltage during the period D with the first reference signal that is the first half of the switching power supply cycle, and 1-D of the second reference signal that is the second half of the switching power supply cycle Since the switching element is operated so as to output a negative voltage during a period (D> 1-D), and the switching element is operated so as to be in a through state in which no voltage is applied except during a period during which positive and negative voltages are output. Without changing (decreasing) the switching power supply cycle, the positive voltage output period per switching power supply cycle is shortened, and the current rip There is reduced. As a result, it is possible to provide a switching power supply device having a simple device configuration with small load current ripple. In the case of generating a negative current by outputting a negative voltage, the switching element is operated so as to output a negative voltage during the period D with the first reference signal that is the first half of the switching power supply cycle. The switching element is operated so as to output a positive voltage during a period of 1-D (D> 1-D) with a certain second reference signal, and a through state in which no voltage is applied except during a period of outputting positive and negative voltages is established. The switching element may be operated.

  In the above description, the switching element is operated so as to output a negative voltage (D> 1-D) negative voltage (positive voltage at negative current) in accordance with the second reference signal which is the second half of the switching power supply cycle. However, it is not limited to this timing. A timing after the switching element is operated so as to output a positive voltage during the period D with the first reference signal that is the first half of the switching power supply cycle, and a period during which a through state is provided before and after the switching power supply cycle If it is.

In the above description, the reference signal is ½ the switching power supply cycle. However, the reference signal is not limited to the ½ cycle. 1 / n (n is an integer greater than or equal to 3), a positive voltage is output during the first reference signal period, a negative voltage is output during the remaining period, and a period during which no positive or negative voltage is output is set In this state, the current ripple can be reduced to 1 / n. Therefore, if the reference signal is made variable according to the load current, the current ripple can be adjusted and suppressed by the load current without changing the frequency of the switching power supply.
Note that setting the period of the reference signal to 1 / n of the switching power supply period is synonymous with the frequency of the reference signal being n times the switching power supply frequency.
Further, when n is increased, the current ripple is further reduced. However, it is preferable to set n within 10 so that the problem of the current control limit at the time of low current does not occur.

Embodiment 2. FIG.
Hereinafter, in the second embodiment, a switching power supply device capable of reducing the current ripple more than the switching power supply device according to the first embodiment when the current is small will be described with reference to FIGS. 6 to 8.
FIG. 6 is a timing chart showing an operation sequence of the switching power supply apparatus 100 according to the second embodiment. Regarding the current flowing through the load 5, the steady flow state B-2 when the amount of current is small is shown, but a part of the timing chart B-1 according to FIG. 4 of the first embodiment is also shown for comparison. Note that the basic configuration of the switching power supply apparatus 100 is the same as that of FIG.

  When the amount of current is small, as shown in the timing chart B-1, the positive voltage and negative voltage output period of the switching power supply approaches a substantially equal state. In order to allow a predetermined current to flow through the load 5, it is sufficient if the difference between the positive voltage and negative voltage periods of the switching power supply can ensure a certain period of time determined by the DC voltage source 2 and the current amount. If the period is defined as α (i) and is subtracted (subtracted) from the positive voltage and negative voltage output periods, the current ripple can be further reduced while controlling the current to the load 5.

  In the timing chart B-2 of FIG. 6, the positive voltage output period is D−α (i), which is shortened by α (i) compared to the positive voltage output period of B-1. Similarly, the negative voltage output period is 1-D-α (i), which is shortened by α (i) compared to the negative voltage output period of B-1. As in the case of the first embodiment, the sawtooth signal as the reference signal is generated with a period that is ½ of the switching power supply period T, and the voltage output period D corresponding to a predetermined load current (small) is commanded. The D command becomes a value. A rectangular wave output voltage waveform is formed by PWM control based on this D command.

The operation of the switching element is as follows.
At time t0, the switching elements SW12 and SW13 are turned on, the switching elements SW11 and SW14 are turned off, and a positive voltage is output for a period D−α (i). At time t31, the switching element SW13 is turned off and the switching element SW14 is turned on in order to enter a through state in which positive and negative voltages are not applied. The time t32 when the second sawtooth signal rises is a T / 2 period, and a negative voltage is output for a period of 1−D−α (i). That is, at time t32, the switching element SW11 is turned on and the switching element SW12 is turned off. At time t33, the negative voltage output period ends, the switching element SW13 is turned on, the switching element SW14 is turned off, and the through state is established. At time t34, the switching element SW11 is turned off, the switching element SW12 is turned on, and a positive voltage is output again. The switching power supply cycle T is from time t0 to t34, and this operation sequence is repeated after time t34.

  As shown in FIG. 6, in the timing chart B-2, the output period of the positive and negative voltages is further shortened, and the current ripple can be reduced as compared with the timing chart B-1.

Next, a method of calculating α (i) for the extra period will be described.
It is assumed that the current of the load 5 is IL, the voltage of the DC voltage source 2 is V, the switching power supply cycle is T, the resistance of the load 5 is R, and the dead time of the switching elements SW11 to SW14 is td. The equation of the relationship of the energy with which the power supply is charged / discharged is expressed by equation (1). Here, when viewed from the DC voltage source 2, the positive voltage output is regarded as discharging and the negative voltage output is regarded as charging.
From Expression (1), the relationship between currents IL and D is Expression (2).

Here, when the load current is a positive current, the conditional expression for enabling the switching power supply to output a positive voltage is expression (3) from the first term of expression (1), and the conditional expression for outputting a negative voltage is expression ( Equation (4) is derived from the second term of 1).
If α (i) satisfying these expressions (2) to (4) is set according to the load current, the current ripple of the load 5 can be further suppressed.

From Expression (2), the current IL flowing through the load 5 decreases as D approaches 0.5, and Conditional Expression (3) for the power converter 1 to output a positive voltage and Conditional Expression (4) for outputting a negative voltage. Α (i) satisfying can take a larger value as D approaches 0.5. This indicates that α (i) is limited under the condition of either formula (3) or formula (4) when the current flowing through the load 5 is large, that is, when D is large. When it is small, that is, when D approaches 0.5, α (i) can be increased, indicating that the current ripple of the load 5 can be further reduced.
FIG. 7 conceptually shows this relationship, and it can be seen that α (i) increases as the load current decreases.

FIG. 8 is a block diagram showing the configuration of the control circuit 8 of the switching power supply apparatus 100 according to the second embodiment. The power for the positive / negative bipolar output to the power converter 1 and the power according to the current of the load 5 is shown. The control calculation for outputting the signal which controls the voltage output period of the converter 1 is shown. The difference from FIG. 5 of the first embodiment is that it includes a D limiter 87 that calculates and outputs α (i) that satisfies the above formulas (2) to (4).
In the figure, the command value (load current command value) of the current flowing through the coil from the control device (not shown) for controlling the coil of the load 5, that is, the coil of the gradient magnetic field device, and the load current measurement measured by the measuring instrument 7. A value is input to the PI controller 81. The output of the PI controller 81 and the sawtooth signal generated by the reference signal generator 82 are input to the comparator 83, and an output that outputs a voltage from the switching power supply so that a predetermined amount of current flows through the coil as the load 5 is output. A D command that is a command value for the voltage period is set. The output from the comparator 83 is divided into two, ie, a command value D and 1-D obtained by adding 1 to the negative command value D from the adder. For each, the output α (i) from the D limiter 87 is Subtraction is performed, and D-α (i) and 1-D-α (i) are input to the selector 84. Either a positive or negative signal is input to the selector 84 from the output positive / negative switching unit 85 that switches the polarity of the current of the coil that is the load 5. Entered. The gate signal generation unit 86 generates a gate signal that sets the on / off operation and the on / off period of the four switching elements SW11 to SW14, and operates the switching elements SW11 to SW14.

  As described above, in the second embodiment, as in the first embodiment, the current direction and the current amount can be controlled by the difference between the positive voltage output period and the negative voltage output period, and the current ripple can be controlled. Reduction can be achieved. Furthermore, the voltage output period that satisfies the conditions of the expressions (2) to (4) is shortened according to the current command value of the load 5 from the voltage output periods D, 1-D (D> 1-D). ) Is subtracted to operate the switching element, the voltage output period can be further shortened and the current ripple can be further reduced. As a result, it is possible to provide a switching power supply device having a simple device configuration with a small current ripple of the switching power supply.

Embodiment 3 FIG.
Hereinafter, the switching power supply according to Embodiment 3 will be described with reference to FIGS. 9 to 14.
FIG. 9 is a schematic configuration diagram of a switching power supply apparatus 200 according to the third embodiment. In the figure, this switching power supply device 200 includes three power converters (inverters) 1, 3a, 3b, a DC voltage source 2 for the power converter 1, a DC voltage source 4 for the power converters 3a, 3b, and a reactor 6a. To 6d, a measuring instrument 7 for measuring a voltage output to the load and a load current flowing through the load, a load (coil of the gradient magnetic field device) 5, and a control circuit 8. Reactor 6a is connected to the input side of power converter 3a, reactor 6b is connected to the output side, reactor 6c is connected to the input side of power converter 3b, and reactor 6d is connected to the output side. These reactors 6a to 6d suppress the return current, and the current flowing between the common DC voltage source 4 and the power converters 3a and 3b is controlled. The power converter 3 a to which the reactors 6 a and 6 b are connected and the power converter 3 b to which the reactors 6 c and 6 d are connected are connected in parallel, and are connected in series between the power converter 1 and the load 5. The measured values of the current and voltage measured by the measuring instrument 7 and the current command value are input, and the power converters (inverters) 1, 3 a, 3 b of the power converters (inverters) 1, 3 a, 3 b are input so that a predetermined amount of current in a predetermined direction flows to the load 5 A control circuit 8 that outputs a gate signal to each switching element is provided. Here, if the voltage of the DC voltage source 2 is V1, and the voltage of the DC voltage source 4 is V2, the relationship is V1> V2.

FIG. 10 is a diagram showing each circuit configuration of power converters 1, 3a, 3b in FIG.
Each of the power converters 1, 3a, and 3b constitutes a full bridge type inverter using MOSFETs that are four switching elements. The power converter 1 includes switching elements SW11 to SW14 as in FIG. 1, the power converter 3a includes switching elements SW31 to SW34, and the power converter 3b includes switching elements SW35 to SW38. The power converter 3 a and the power converter 3 b are connected in parallel with the DC voltage source 4 in common, and the DC voltage source 2 is connected to the power converter 1. The power converter 1 and the power converters 3 a and 3 b are connected in series via the reactors 6 a to 6 d and the load 5.

  FIG. 11 is a diagram showing the output current waveform (load current waveform) of the switching power supply apparatus 200 and the sharing of the power converters 1, 3a, and 3b. A square-wave pulse current is generated by the power converters 1, 3a, 3b and applied to the coil of the gradient magnetic field device as the load 5. The current rising portion has a tin period, the falling portion has a tfin period, and the current is flat. Part (stationary part) tcon period.

In the tin period of the current rising part, in order to raise the current at high speed, the power converters 3a and 3b connected in parallel with the power converter 1 are connected in series so that a high voltage can be applied to the load 5. The voltage applied to the gradient coil of the load 5 and the application time are adjusted by combining the voltages of the power converters 1, 3a, and 3b, and the current rise time is adjusted.
Similarly to the current rise time tin period, the current fall time tfin period is adjusted by adjusting the voltage applied to the load 5 and the application time by combining the voltages of the power converters 1, 3a and 3b. Adjust the time.

12A to 12E show the operating state of each power converter of the switching power supply apparatus 200 during the tin period of the current rising portion in FIG. The bold arrows in each figure indicate the direction of current flow.
FIG. 12A shows the voltage V1 of the DC voltage source 2 and the voltage V2 of the DC voltage source 4 because the switching element of the power converter 1 is in a positive voltage application state and the switching elements of the power converters 3a and 3b are in a positive voltage application state. In this state, the total voltage is applied to the load 5. Specifically, the switching elements SW12 and SW13 of the power converter 1 are turned on to generate a DC voltage V1 between the input and output of the switching power supply, the switching elements SW32 and SW33 of the power converter 3a are turned on, and the power converter In this state, the switching elements SW36 and SW37 of 3b are turned on to generate a DC voltage V2 at the input and output of the switching power supply, and the total voltage V1 + V2 is applied to the load 5.

  12B shows a state in which only the voltage V1 of the DC voltage source 2 is applied to the load 5, and the operation of the switching element of the power converter 1 is the same as that of FIG. 12A. The switching elements SW32, SW34, SW36, and SW38 are turned on to show a through state in which no power passes. Although the figure shows a through state in which the lower arm is turned on, the upper arm may be turned on in the through state.

  FIG. 12C shows a state in which the power converter 1 is set to the through state, and the DC voltage V2 of the DC voltage source 4 that is a shared power source of the power converters 3a and 3b is applied to the load 5. Specifically, the switching elements SW12 and SW14 which are the lower arms of the power converter 1 are turned on so as not to pass through the power source, and the operation of the switching elements of the power converters 3a and 3b is as shown in FIG. 12A. It is the same.

  In FIG. 12D, both the power converter 1 and the power converters 3 a and 3 b are in a through state that does not pass through the power source, and the voltage of the DC voltage sources 2 and 4 is not applied to the load 5.

  FIG. 12E shows a state where a voltage difference V 1 −V 2 between the voltage V 1 of the DC voltage source 2 and the voltage V 2 of the DC voltage source 4 is applied to the load 5. Specifically, the switching elements SW12 and SW13 of the power converter 1 are turned on to output a positive voltage, and the switching elements SW31 and SW34 of the power converter 3a and the switching elements SW35 and SW38 of the power converter 3b are turned on, respectively. Output negative voltage.

  12A to 12E, it is possible to apply five levels of voltages of 0, V1-V2, V2, V1, and V1 + V2 to the load 5. Since the slope of the current is proportional to the voltage, the rise time tin and the fall time tfin are selectively combined to operate, and the current rise time and fall time are finely adjusted.

FIG. 13 is an enlarged view of the tin period of the current rising portion shown in FIG. 11, and shows an example in which the above-mentioned different voltage is applied to the load 5 to form a predetermined current gradient.
When the current is large, it is necessary to start up sharply and flow a large current, but overcurrent must also be avoided. A broken line current curve is formulated so that a predetermined current is obtained within a predetermined period (tin), and a predetermined voltage is output for a predetermined period so as to divide this curve and correspond to the current gradient of each divided region. That's fine. In this example, the switching element of each power converter is operated so that it is divided into four and any voltage of V1-V2, V2, V1, V1 + V2 is output as indicated by a rectangular wave.
Similarly, when the current is small, a current curve may be formulated, and the curve may be divided to output a predetermined voltage for a predetermined period so as to correspond to the current gradient for each divided region.
In order to simplify the description, an example of four divisions has been given, but it goes without saying that it can be further subdivided and adjusted.

Next, an operation sequence of the switching power supply device 200 during the tcon period of the current flat portion will be described.
FIG. 14 is a timing chart showing an operation sequence of the current flat part of the switching power supply apparatus 200. During this tcon period, the power converter 1 does not output the voltage of the DC voltage source 2 as shown in FIG. 2, and the SW11 and SW13 are turned on, or the SW12 and SW14 are turned on so as to pass the current. The connected power converters 3a and 3b perform operations based on PWM control that are out of phase with each other, and vary the amount of current and the polarity of current (only the forward current is shown in the figure).

  A sawtooth signal, which is a reference signal for operating the switching elements of the power converters 3a and 3b, is generated with a period of 1/4 of the switching power supply period T. That is, it is generated at a frequency four times the frequency of the switching power supply. A positive voltage output period D and a negative voltage output period 1-D are determined by the first sawtooth signal and the D command. A surplus period α (i) of the voltage output period satisfying the expressions (2) to (4) is calculated according to the current command value, and subtracted from the positive voltage output period D and the negative voltage output period 1-D, respectively. . The first sawtooth signal outputs a positive voltage during the period D-α (i) from the power converter 3a, and the second sawtooth signal generates a negative voltage during the period 1-D-α (i) from the power converter 3a. Is output. In the third sawtooth signal, a positive voltage is output from the power converter 3b for a period of D−α (i), and in the second sawtooth signal, a negative voltage is output from the power converter 3b for a period of 1−D−α (i). Is output.

  Specifically, at time t0, the switching elements SW32 and SW33 of the power converter 3a are turned on, the switching elements SW31 and SW34 are turned off, and a positive voltage is output for a period D−α (i). At a time t41, the switching element SW33 is turned off and the switching element SW34 is turned on in order to enter a through state in which positive and negative voltages are not applied. The time t42 when the second sawtooth signal rises is a T / 4 cycle, and a negative voltage is output for a period of 1−D−α (i). That is, at time t42, the switching element SW31 is turned on and the switching element SW32 is turned off. At time t43, the negative voltage output period ends, the switching element SW33 is turned on, the switching element SW34 is turned off, and the through state is established. During the period from time t0 to t44, the switching element of the power converter 3b is in a through state in which SW35 and SW37 are turned on or SW36 and SW38 are turned on and current is passed.

  The time t44 at which the third sawtooth signal rises is a T / 2 period. Here, the switching element SW35 of the power converter 3b is turned off, the switching element SW36 is turned on, and a positive voltage is applied during the period D-α (i). Output. At time t45, the switching element SW37 is turned off and the switching element SW38 is turned on in order to enter a through state in which positive and negative voltages are not applied. At the time t46 when the fourth sawtooth signal rises, a negative voltage is output for a period of 1−D−α (i). That is, at time t46, the switching element SW35 is turned on and the switching element SW36 is turned off. At time t47, the negative voltage output period ends, the switching element SW37 is turned on, the switching element SW38 is turned off, and the through state is established. At time t48, the positive voltage is output again from the power converter 3a. The switching power supply cycle T is from time t0 to t48, and this operation sequence is repeated after time t48.

  The above-described operation sequence is controlled by the control circuit 8, but if the reference signal is generated as a sawtooth signal having a period of T / 4 in FIG. 8 of the second embodiment, the control is executed by the same arithmetic processing. And a gate signal is generated.

  Although the current ripple is shown in FIG. 14, the switching frequency of the switching power supply constituted by each of the power converters 3a and 3b is the same as that of one basic operation of the power converter of FIG. It can be seen that it decreases to about / 4 or less. In FIG. 14, the magnitude of the current has been described without distinction. However, when the current becomes large, α (i) becomes small, and there is no influence on the current ripple without performing the subtraction process.

  As described above, according to the third embodiment, by using three power converters, the load current can be sharply raised. When the current is steady, two power conversions connected in parallel are possible. Since each switching element is operated so as to shorten the output period of the positive and negative voltages, the current ripple caused by each power converter is also reduced, and the switching power supply device in which the current ripple is also reduced as a whole device. Provision is possible. That is, in addition to the effects of the first and second embodiments, the effect that the load current can be sharply increased is added.

  In the above description, the switching element is operated so as to output a negative voltage during the period of 1-D-α (i) (D> 1-D) in accordance with the second and fourth reference signals. It is not limited to timing. After the switching element is operated so as to output a positive voltage during the period D-α (i) with the first and third reference signals, respectively, the through state before and after the switching power supply cycle T / 2 It suffices to provide a timing for providing a period. Further, there may be a through state before and after the positive and negative voltage output periods so that none of the output periods overlap.

In the above description, the reference signal is set to ¼ of the switching power supply cycle T. However, the reference signal is not limited to ¼ cycle. 1 / m (m is an integer of 5 or more), and the operation of the power converters 3a and 3b is switched in a period that is 1/2 of the switching power supply period T. In the power converter 3a, in the period of the first reference signal A period in which a positive voltage is output and a negative voltage is output in any of the T / 2 cycles may be set, and a period in which no positive / negative voltage is output may be set to a through state. The operation of the power converter 3b is the same. In this way, the current ripple can be reduced to 1 / m. Note that setting the period of the reference signal to 1 / m of the switching power supply period is synonymous with the frequency of the reference signal being m times the switching power supply frequency.
Further, when m is increased, the current ripple is further reduced. However, it is preferable to set m to an even number within 10 to the extent that the problem of the current control limit at low current does not occur.

  In the above-described first to third embodiments, an example in which a MOSFET is used as a semiconductor switching element has been described. However, the present invention is not limited to this, and an IGBT (Insulated Gate Bipolar Transistor) may be used, for example.

  As shown in FIG. 15, the control circuit 8 in the switching power supply device according to the first to third embodiments described above includes at least the following as hardware for executing functions. That is, the processing circuit includes an arithmetic processing device (computer) 801 such as a CPU (Central Processing Unit), a storage device 802 that exchanges data with the arithmetic processing device 801, and the like. As the arithmetic processing unit 801, various logic circuits such as an application specific integrated circuit (ASIC), an integrated circuit (IC), a digital signal processor (DSP), and a field-programmable gate array (FPGA), and various signal processing circuits 5, what can perform the arithmetic processing shown in FIG. 8 is provided. In addition, a plurality of the same type or different types of arithmetic processing devices may be provided, and each process may be shared and executed. As the storage device 802, a RAM (Random Access Memory) configured to be able to read and write data from the arithmetic processing device 801, a ROM (Read Only Memory) configured to be able to read data from the arithmetic processing device 801, or an HDD (Hard disk drive) etc. are provided.

Embodiment 4 FIG.
Although the switching power supply devices 100 and 200 according to the first to third embodiments have been described assuming that the output load 5 is a coil of a gradient magnetic field device of an MRI apparatus, the fourth embodiment is configured as a power supply device for an MRI apparatus. Will be described.
FIG. 16 is a configuration diagram of the MRI apparatus power supply apparatus 1000 according to the fourth embodiment. The MRI apparatus power supply apparatus 1000 includes the switching power supply apparatuses 100 and 200 according to any one of the first to third embodiments including the coil that is the load 5 and the coil control apparatus 500, and the current flowing from the coil control apparatus 500 to the coil 5. The command value may be output to the control circuit 8 of the switching power supply apparatus 100, 200. The coil control device 500 acquires a nuclear magnetic resonance signal from the coil 5, creates an image, and displays it on an image display device (not shown).

As described above, in order to create an MRI image, for example, it is necessary to pass a current of 256 steps ranging from several A to several hundred A through the coil, and in order to obtain a high resolution image, in particular, several A, 10 A or less. The current ripple should be reduced when the current is small. The switching power supplies according to the first to fourth embodiments can reduce the current ripple even when the current is small, and is preferably incorporated in the power supply apparatus for the MRI apparatus.
In addition, when the switching power supply device 200 according to the third embodiment is used, a steep current rise can be achieved, and a highly reliable power supply device for an MRI apparatus can be provided.

Although this disclosure describes various exemplary embodiments and examples, various features, aspects, and functions described in one or more embodiments may be described in terms of particular embodiments. The present invention is not limited to the application, and can be applied to the embodiments alone or in various combinations.
Accordingly, countless variations that are not illustrated are envisaged within the scope of the technology disclosed herein. For example, the case where at least one component is deformed, the case where the component is added or omitted, the case where the at least one component is extracted and combined with the component of another embodiment are included.

  1, 3a, 3b: Power converter, 2, 4: DC voltage source, 5: Load (coil), 6a, 6b, 6c, 6d: Reactor, 7: Measuring instrument, 8: Control circuit, 10: Switching power supply, 81: PI controller, 82: Reference signal generator, 83: Comparator, 84: Selector, 85: Output positive / negative switching unit, 86: Gate signal generation unit, 87: D limiter, 100, 200: Switching power supply device, 500: Coil control device, 801: Arithmetic processing device, 802: Storage device, 1000: Power supply device for MRI device, SW11, SW12, SW13, SW14, SW31, SW32, SW33, SW34, SW35, SW36, SW37, SW38: Switching element.

Claims (7)

Measures the current and voltage of the load provided between the switching power supply having a power converter having a plurality of switching elements and a DC voltage source, and the load connected in series to the switching power supply and the switching power supply A switching power supply comprising: a measuring instrument that controls the operation of the plurality of switching elements;
The control circuit includes:
The positive and negative voltages are output to the load, and the operations of the plurality of switching elements are controlled so as to control the amount and polarity of the current flowing through the load according to the difference between the positive and negative voltage output periods .
A command value for determining a positive / negative voltage output period corresponding to the amount of current flowing through the load and a reference signal are generated, and the reference signal is generated at a cycle of 1 / n (n is an integer of 2 or more) of the cycle of the switching power supply. As well as
The voltage output period determined by comparing the command value and the reference signal is D,
A first reference signal is subtracted from the voltage output period D by the voltage of the DC voltage source, the dead time of the plurality of switching elements, the resistance of the load and the amount of current flowing through the load. The operation of the plurality of switching elements is controlled so that one positive / negative voltage is output during the period D-α (i) and the other positive / negative voltage is output during the period 1-D-α (i). Switching power supply. A plurality of switching power supplies including a power converter having a plurality of switching elements and a DC voltage source, and the second and third switching power supplies connected in parallel are connected in series between the first switching power supply and the load. A measuring instrument for measuring current and voltage of the load provided between the load and the second and third switching power supplies connected in parallel, and the plurality of the switching power supplies A control circuit for controlling the operation of the switching element, and a switching power supply device comprising:
The control circuit includes:
Controlling the operation of the plurality of switching elements of the plurality of switching power supplies so as to output positive and negative voltages to the load and to control the amount and polarity of current flowing through the load according to the difference between the positive and negative voltage output periods,
When the current flowing through the load rises and falls, the first, second, and second output voltages from the first, second, and third switching power supplies have values corresponding to current gradients. Operating the plurality of switching elements of the switching power source of 3,
In the stationary part where the current flowing through the load reaches a predetermined current, the plurality of switching elements of the second and third switching power supplies connected in parallel are operated,
The sum of the output periods of the positive and negative voltages in one cycle of the second and third switching power supplies is smaller than one cycle of the switching power supply, and the second and third switching power supplies A switching power supply apparatus that controls operations of the plurality of switching elements of the second and third switching power supplies so as to shift a phase of an output period of positive and negative voltages. The switching power supply according to claim 2 , wherein the DC voltage sources of the second and third switching power supplies connected in parallel are common. The control circuit generates a command value and a reference signal for determining a positive / negative voltage output period corresponding to the amount of current flowing to the load in a stationary part where the current flowing to the load reaches a predetermined current value, The signal is generated with a period of 1 / m (m is an integer of 4 or more) of the period of the switching power supply, and one of the positive and negative voltages in the period of the first reference signal from one of the second and third switching power supplies. 4. The switching power supply device according to claim 2 , wherein operations of the plurality of switching elements are controlled so that the other positive and negative voltages are output in the remaining period. The control circuit is determined by comparing a command value for determining a positive / negative voltage output period corresponding to the amount of current flowing to the load and a reference signal in a stationary part where the current flowing to the load reaches a predetermined current value. When the voltage output period is D, one of positive and negative voltages is set to D period in the period of the first reference signal from one of the second and third switching power supplies, and the other positive and negative voltage is set to 1− in the remaining period. The switching power supply device according to claim 4 , wherein operations of the plurality of switching elements are controlled so as to output during a D period. In the steady portion where the current flowing through the load reaches a predetermined current value, the control circuit includes the voltage of the DC voltage source, the dead time of the plurality of switching elements, the resistance of the load from the positive / negative voltage output period D And a surplus period α (i) obtained by the amount of current flowing through the load is subtracted, and one of the positive and negative voltages in the period of the first reference signal from one of the second and third switching power supplies is expressed as D−α ( 6. The switching power supply device according to claim 5 , wherein operations of the plurality of switching elements are controlled so that the other positive and negative voltages are output for a period of 1-D-α (i) during the period i and the remaining period. A switching power supply device according to any one of claims 1 to 6 , a coil for a nuclear magnetic resonance imaging apparatus as the load, and a coil control device for controlling the coil, wherein the coil control device The control circuit of the switching power supply device controls the operation of the plurality of switching elements of the switching power supply device based on the output current command value.

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