JP6636223B1 - Gradient magnetic field power supply device and magnetic resonance imaging diagnostic apparatus including the same - Google Patents

Abstract

The gradient magnetic field power supply device (100) includes an alternating current between a first inverter circuit (INV1) having a plurality of switching elements made of a silicon semiconductor and a second inverter circuit (INV2) having a plurality of switching elements made of a wide band gap semiconductor. The output terminals are connected in series to supply power to the gradient coil (50). The control device (30) has a current rise period (Ta), a constant current output period (Tb), and a current fall period (Tc). The current rise period (Ta) and the current fall period (Tc) )), The switching state of the first and second inverter circuits (INV1, INV2) is fixed to output a constant voltage, and during the constant current output period (Tb), the first inverter circuit (INV1) outputs 0 voltage. At the same time, high frequency switching control of the second inverter circuit (INV2) is performed based on the constant current command value.

Description

  The present application relates to a gradient magnetic field power supply device and a magnetic resonance imaging apparatus including the same.

A magnetic resonance image diagnostic apparatus (hereinafter, referred to as an MRI apparatus) is an image diagnostic apparatus using a nuclear magnetic resonance method. Nuclear magnetic resonance is a phenomenon in which a nuclear spin placed in a static magnetic field resonates with an electromagnetic wave having a specific frequency (Larmor frequency). In an MRI apparatus, nuclear spins are excited by nuclear magnetic resonance, and a magnetic resonance signal generated with subsequent relaxation is acquired and converted into image data.
As the gradient magnetic field coil, which is one of the components of the MRI apparatus, three-axis coils of X-axis, Y-axis, and Z-axis are used, and power is supplied from these devices to the three-axis gradient magnetic field. Are synthesized. These gradient magnetic fields are applied to the subject while being superimposed on a strong static magnetic field.

  The gradient magnetic field superimposed on the static magnetic field is required to be sufficiently larger than the variation of the static magnetic field, and a large current needs to flow through the gradient coil. In addition, a high-precision current with small ripple is required for the current flowing through the gradient magnetic field coil in order to suppress the fluctuation amount of the gradient magnetic field. Further, in order to increase the speed of imaging in the MRI apparatus, a high slew rate due to a high voltage is required for the gradient magnetic field. For this reason, it is required that the gradient magnetic field power supply device can output a large current with high accuracy and can output a high voltage.

In the conventional gradient magnetic field power supply described in Patent Literature 1, a plurality of power stages having a full bridge circuit that generates a drive waveform by switching a high voltage supplied from a high voltage source are connected in cascade, Output is enabled.
Further, in the conventional power supply device described in Patent Document 2, a plurality of switching power supplies are connected in parallel, and each switching power supply is drive-controlled with its phase shifted. As a result, the output ripple is increased in frequency and reduced.

JP 2009-39247 A JP-A-8-111139

In the conventional gradient magnetic field power supply described in Patent Literature 1, a high voltage can be output by increasing the number of power stages, but this increases the size of the apparatus. Also, it has been difficult to improve the current output accuracy.
In the conventional power supply device described in Patent Document 2, there is a limit in outputting a high voltage and a large current.

The present application discloses a technique for solving the above-described problem, and provides a high-voltage and large-current output, high-precision current control, and a small-sized gradient magnetic field power supply device. The purpose is to provide.
Further, it is another object of the present invention to provide an MRI apparatus which includes this gradient magnetic field power supply apparatus and can perform high-speed and high-quality imaging.

A first gradient magnetic field power supply device disclosed in the present application includes a first inverter circuit having a first DC voltage section and a plurality of switching elements, a second inverter circuit having a second DC voltage section and a plurality of switching elements, A current detection unit for detecting an output current, and a control device for controlling the output of the first and second inverter circuits are provided. The plurality of switching elements of the first inverter circuit are made of a silicon semiconductor, and the plurality of switching elements of the second inverter circuit are made of a wide band gap semiconductor having a wider band gap than a silicon semiconductor. An AC output terminal of the first inverter circuit and an AC output terminal of the second inverter circuit are connected in series to supply power to the gradient coil. The control device performs constant current control when power is supplied to the gradient magnetic field coil. In the constant current control, the switching state of the first inverter circuit is fixed, and a constant voltage is output from the first inverter circuit. At the same time, the high frequency switching control of the second inverter circuit is performed based on the constant current command value.

  Also, a second gradient magnetic field power supply device disclosed in the present application is a first inverter circuit having a first DC voltage section and a plurality of switching elements, and a second inverter circuit having a second DC voltage section and a plurality of switching elements. A current detection unit for detecting an output current; and a control device for controlling the output of the first and second inverter circuits. The AC output terminal of the first inverter circuit and the AC output terminal of the second inverter circuit The ends are connected in series to supply power to the gradient coil. The control device has a current rising period, a constant current output period following the current rising period, and a current falling period following the constant current output period, and generates the trapezoidal wave current that is the output current. The output of the first and second inverter circuits is controlled so as to output to the gradient coil. In the current rising period and the current falling period, the control device fixes each switching state of the first and second inverter circuits and sets a constant voltage by a sum of output voltages of the first and second inverter circuits. Output is performed. In the constant current output period, constant current control is performed in which the first inverter circuit outputs 0 voltage and the second inverter circuit performs high-frequency switching control based on a constant current command value.

  Further, a magnetic resonance imaging apparatus disclosed in the present application includes the first or second gradient magnetic field power supply device and the gradient magnetic field coil which is supplied with power from the gradient magnetic field power supply and is excited.

ADVANTAGE OF THE INVENTION According to the gradient magnetic field power supply apparatus disclosed by this application, the output of a high voltage and a large current, and a highly accurate current control are attained with a small apparatus structure.
Further, according to the magnetic resonance imaging diagnostic apparatus disclosed in the present application, high-speed and high-quality imaging can be performed.

FIG. 2 is a diagram showing a circuit configuration of the gradient magnetic field power supply device according to the first embodiment. FIG. 3 is a diagram showing an output current waveform of the gradient magnetic field power supply device according to the first embodiment. FIG. 5 is a waveform chart of each section for explaining the operation of the gradient magnetic field power supply device according to the first embodiment. FIG. 5 is a waveform chart of each section for explaining the operation of the gradient magnetic field power supply device according to the first embodiment. FIG. 3 is a control block diagram of a second inverter circuit in the constant current control according to the first embodiment. FIG. 9 is a diagram showing a circuit configuration of a gradient power supply according to a second embodiment. FIG. 13 is a diagram showing a cross current path of a second inverter circuit according to the second embodiment. FIG. 13 is a diagram showing a cross current path of a second inverter circuit according to the second embodiment. FIG. 13 is a diagram showing a cross current path of a second inverter circuit according to the second embodiment. FIG. 13 is a diagram illustrating a configuration of a second inverter circuit according to a second embodiment. FIG. 13 is a current path diagram illustrating cross current suppression control of a second inverter circuit according to a second embodiment. FIG. 13 is a current path diagram illustrating cross current suppression control of a second inverter circuit according to a second embodiment. FIG. 13 is a current path diagram illustrating cross current suppression control of a second inverter circuit according to a second embodiment. FIG. 13 is a current path diagram illustrating cross current suppression control of a second inverter circuit according to a second embodiment. FIG. 13 is a configuration diagram illustrating another example of the second inverter circuit according to the second embodiment. FIG. 9 is a diagram illustrating a circuit configuration of a gradient magnetic field power supply device according to a third embodiment. FIG. 13 is a diagram illustrating a configuration of a second inverter circuit according to a third embodiment. FIG. 14 is a waveform chart of each section for explaining the operation of the gradient magnetic field power supply device according to the fourth embodiment. FIG. 13 is a diagram showing an overall configuration of an MRI apparatus according to a sixth embodiment.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a circuit configuration of the gradient power supply according to the first embodiment.
As shown in FIG. 1, the gradient magnetic field power supply device 100 includes a first inverter circuit INV1 and a second inverter circuit INV2, and an AC output terminal of the first inverter circuit INV1 and an AC output terminal of the second inverter circuit INV2. Are connected in series to supply power to the gradient coil 50. Further, the gradient magnetic field power supply device 100 includes a control device 30 that controls the output of the first inverter circuit INV1 and the second inverter circuit INV2, and a current that detects an output current Iout output from the gradient magnetic field power supply device 100 to the gradient magnetic field coil 50. And a detection unit 40.

The first inverter circuit INV1 is a full bridge circuit including a plurality of switching elements 11, 12, 13, and 14 made of a silicon semiconductor and a first DC voltage unit 10, and converts DC power of the first DC voltage unit 10 into AC power. Convert and output. In this case, an IGBT (Insulated Gate Bipolar Transistor) in which diodes are connected in anti-parallel is used as the switching elements 11 to 14, but other switching elements such as a thyristor may be used as long as they have a high withstand voltage.
In the first inverter circuit INV1, an AC output terminal of a first leg (11-12) composed of two series switching elements 11 and 12 and a second leg (13-14) composed of two series switching elements 13 and 14 are provided. Three levels of voltages of + V1, -V1, and 0 are output between the AC output terminal. V1 is the voltage of the first DC voltage unit 10, and is set to, for example, 1200V.

  The second inverter circuit INV2 is a full bridge circuit including a plurality of switching elements 21, 22, 23, and 24 made of a wide bandgap semiconductor having a wider band gap than a silicon semiconductor, and a second DC voltage unit 20, and a second DC circuit. The DC power of the voltage section 20 is converted into AC power and output. In this case, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) composed of silicon carbide (SiC) and having a diode connected between the source and the drain is used for the switching elements 21 to 24. The switching elements 21 to 24 may be made of other wide band gap semiconductors such as gallium nitride, and are not limited to MOSFETs.

In the second inverter circuit INV2, an AC output terminal of a first leg (21-22) composed of two series switching elements 21 and 22 and a second leg (23-24) composed of two series switching elements 23 and 24 are provided. Three levels of voltages of + V2, -V2, 0 are output between the AC output terminal. V2 is the voltage of the second DC voltage unit 20, which is lower than the voltage V1 of the first DC voltage unit 10 of the first inverter circuit INV1, for example, 800V.
Note that the first and second inverter circuits INV1 and INV2 are full-bridge circuits, but are not limited to full-bridge circuits as long as they are three-level inverters.

  The value of the output current Iout detected by the current detection unit 40 is input to the control device 30. Then, based on the output current (value) Iout and the output current command Iout * as a constant current command value, the switching elements 11 to 14, 21 to 24 of the first and second inverter circuits INV1 and INV2 are supplied to The gate signals G11 to G14 and G21 to G24 are generated to control the output of the first and second inverter circuits INV1 and INV2.

Next, the operation of the gradient magnetic field power supply device 100 will be described. As an example, an operation when the gradient magnetic field power supply device 100 outputs an output current Iout which is a trapezoidal wave current as shown in FIG. 2 to the gradient magnetic field coil 50 will be described.
FIG. 3 is a waveform diagram of each section for explaining the operation of the gradient magnetic field power supply device 100. Here, the output current Iout, the output voltage V-INV1 of the first inverter circuit INV1, the output voltage V-INV2 of the second inverter circuit INV2, the gate signals G11 to G14, G21 to the switching elements 11 to 14, 21 to 24 are provided. G24 to G24.
As shown in the figure, the control device 30 includes a current rising period Ta, a constant current output period Tb following the current rising period Ta, and a current falling period Tc following the constant current output period Tb. A trapezoidal wave current (output current Iout) is output from the first and second inverter circuits INV1 and INV2, which are main circuits.

In the current rising period Ta, the control device 30 performs constant voltage control that outputs a constant voltage (V1 + V2) based on the sum of the output voltages of the first and second inverter circuits INV1 and INV2.
The first inverter circuit INV1 outputs the voltage V1 of the first DC voltage unit 10 by fixing the switching elements 11 and 14 to the ON state and the switching elements 12 and 13 to the OFF state. The second inverter circuit INV2 outputs the voltage V2 of the second DC voltage unit 20 by fixing the switching elements 21 and 24 to the ON state and the switching elements 22 and 23 to the OFF state.

  Since the first inverter circuit INV1 and the second inverter circuit INV2 are connected in series, a voltage (V1 + V2) based on the sum of the output voltages of the first and second inverter circuits INV1 and INV2 is output from the gradient magnetic field power supply device 100, The gradient magnetic field coil 50 is excited. Then, output current Iout rapidly increases toward output current command Iout *. At this time, the current gradient (current per unit time: (dI / dT)) is determined from the output voltage (V1 + V2) and the inductance of the gradient coil 50.

In the constant current output period Tb, the control device 30 performs constant current control in which the first inverter circuit INV1 outputs 0 voltage and the second inverter circuit INV2 performs high-frequency switching control based on the output current command Iout *.
The first inverter circuit INV1 outputs 0 voltage by fixing the switching elements 12 and 14 to the on state and fixing the switching elements 11 and 13 to the off state. The high frequency switching control of the second inverter circuit INV2 is performed so that the output current Iout follows the output current command Iout *. In this case, the second inverter circuit INV2 performs high-frequency switching by shifting the first leg (21-22) and the second leg (23-24) by half a cycle, and the frequency of the output voltage V-INV2 is equal to 2 times the switching frequency. Double.

  Note that when the output voltage V-INV2 of the second inverter circuit INV2 is applied to the gradient coil 50, a ripple current having the same frequency as the frequency of the output voltage V-INV2 is superimposed on the output current Iout, but not shown. The ripple component is removed by the filter circuit, and the output current Iout can be converted to a highly accurate DC current. Since the output current command Iout * is constant, the output current Iout is maintained at a constant DC current with high accuracy.

In the current falling period Tc, the control device 30 performs an operation reverse to that of the current rising period Ta, and outputs a constant voltage (−V1−V2) based on a sum of output voltages of the first and second inverter circuits INV1 and INV2. Performs constant voltage control.
The first inverter circuit INV1 fixes the switching elements 11 and 14 in the off state and the switching elements 12 and 13 in the on state, and outputs the voltage V1 of the first DC voltage unit 10 with the opposite polarity. The second inverter circuit INV2 fixes the switching elements 21 and 24 in the off state and the switching elements 22 and 23 in the on state, and outputs the voltage V2 of the second DC voltage unit 20 with the opposite polarity. Then, the voltage (−V1−V2) is output from the gradient magnetic field power supply device 100, and the gradient magnetic field coil 50 is demagnetized. Then, the output current Iout rapidly decreases.

As described above, the control device 30 outputs the trapezoidal wave current (output current Iout) including the current rising period Ta, the constant current output period Tb, and the current falling period Tc.
The gradient magnetic field power supply device 100 obtains the output current Iout according to the imaging required for the MRI apparatus, that is, uses the output current command Iout * which is a constant current command value according to the imaging. The control device 30 determines the level of the sum of the output voltages of the first and second inverter circuits INV1 and INV2 based on the output current command Iout * in the current rising period Ta and the current falling period Tc. The output voltage levels of the second inverter circuits INV1 and INV2 are determined. Then, constant voltage control is performed based on each output voltage level.

  The levels of the sum of the output voltages of the first and second inverter circuits INV1 and INV2 are nine levels of 0, ± V1, ± (V1−V2), ± V2, ± (V1 + V2), in particular, V1 = 2 (V2 ), There are seven levels of 0, ± V1, ± V2, ± (V1 + V2). From the plurality of voltage levels, the level of the sum of the output voltages of the first and second inverter circuits INV1, INV2 is determined according to the output current command Iout *.

A case where the level of the output current Iout is lower than the case shown in FIG. 3 will be described below with reference to FIG. In this case, the sum of the output voltages of the first and second inverter circuits INV1 and INV2 is determined to be (V1−V2) according to the output current command Iout *.
In the current rising period Ta, the control device 30 performs constant voltage control that outputs a constant voltage (V1−V2) based on the sum of the output voltages of the first and second inverter circuits INV1 and INV2.
The first inverter circuit INV1 outputs the voltage V1 of the first DC voltage unit 10 by fixing the switching elements 11 and 14 to the ON state and the switching elements 12 and 13 to the OFF state. The second inverter circuit INV2 fixes the switching elements 22 and 23 to the ON state and the switching elements 21 and 24 to the OFF state, and outputs the voltage V2 of the second DC voltage unit 20 with the opposite polarity. Then, a voltage (V1−V2) based on the sum of the output voltages of the first and second inverter circuits INV1 and INV2 is output from the gradient magnetic field power supply device 100, and the gradient magnetic field coil 50 is excited. Then, output current Iout rapidly increases toward output current command Iout *.

In the constant current output period Tb, the control device 30 causes the first inverter circuit INV1 to output 0 voltage and switches the second inverter circuit INV2 to high frequency switching based on the output current command Iout *, as in the case shown in FIG. Control, constant current control.
The first inverter circuit INV1 outputs 0 voltage by fixing the switching elements 12 and 14 to the on state and fixing the switching elements 11 and 13 to the off state. The high frequency switching control of the second inverter circuit INV2 is performed so that the output current Iout follows the output current command Iout *.

In the current falling period Tc, the control device 30 performs an operation opposite to that of the current rising period Ta, and outputs a constant voltage (−V1 + V2) based on the sum of the output voltages of the first and second inverter circuits INV1 and INV2. Perform control.
The first inverter circuit INV1 fixes the switching elements 11 and 14 in the off state and the switching elements 12 and 13 in the on state, and outputs the voltage V1 of the first DC voltage unit 10 with the opposite polarity. The second inverter circuit INV2 outputs the voltage V2 of the second DC voltage unit 20 by fixing the switching elements 22 and 23 to the off state and fixing the switching elements 21 and 24 to the on state. Then, the voltage (−V1 + V2) is output from the gradient magnetic field power supply device 100, and the gradient magnetic field coil 50 is demagnetized. Then, the output current Iout rapidly decreases.

Next, the details of the constant current control during the constant current output period Tb will be described.
FIG. 5 is a control block diagram of the second inverter circuit INV2 in the constant current control. As shown in FIG. 5, in the control device 30, a difference between the output current command Iout * and the output current Iout is calculated by a subtracter 31, and the difference is PI-controlled by a proportional-integral (PI) controller 32. The control amount 32a is calculated. That is, the control amount 32a is calculated by feedback control in which the output current Iout follows the output current command Iout *.

  In addition, feedforward control for compensating for various voltage drops that occur when current flows is performed together with the feedback control. A feedforward term 33a based on a voltage drop generated by the resistance component Rcoil of the gradient coil 50, and a feedforward term based on a voltage drop generated by flowing a current through the on-resistance Rds of the switching elements 21 to 24 of the second inverter circuit INV2. The term 33b is added by the adder 34a. Further, a feedforward term 33c for compensating for a voltage drop between the collector-emitter voltage Vce and the emitter-collector voltage Vec caused by the current flowing through the switching elements 11 to 14 of the first inverter circuit INV1 is added to the adder 34b. And add. Further, an adder 34c adds a feedforward term 33d based on a voltage drop generated by a dead time Td at the time of switching of the switching elements 21 to 24 of the second inverter circuit INV2.

As described above, the value 33 obtained by adding the feedforward terms 33a to 33d for compensating for various voltage drops is added to the control amount 32a by the feedback control in the adder 35, and the voltage command Vout * is calculated. The voltage command Vout * is divided by the voltage V2 of the second DC voltage unit 20 in the divider 36, and a duty ratio D of the second inverter circuit INV2 is generated.
As described above, the control device 30 combines the feedback control and the feedforward control, calculates the voltage command Vout * of the output voltage V-INV2, and generates the duty ratio D of the second inverter circuit INV2. Then, the control device 30 generates gate signals G21 to G24 to the switching elements 21 to 24 of the second inverter circuit INV2 based on the duty ratio D, and performs high-frequency switching control of the switching elements 21 to 24.

  In addition, the feedforward control combined with the feedback control is described by adding the four types of feedforward terms 33a to 33d. However, the present invention is not limited to this combination, and compensates for a voltage drop generated when current flows. Anything is fine.

Next, switching from constant voltage control during the current rising period Ta to constant current control during the constant current output period Tb will be described.
When the output current Iout reaches the set current value IA in the constant voltage control during the current rising period Ta, the control device 30 switches from the constant voltage control to the constant current control in which the output current Iout follows the output current command Iout *. Then, the process proceeds to the constant current output period Tb. Set current value IA is set in advance to a current value smaller than output current command Iout *.
By such control switching, the output current Iout does not overshoot beyond the output current command Iout *, and the output current Iout can be quickly started.
Note that the set current value IA is not unnecessarily small as long as the overshoot of the output current Iout can be avoided, and is preferably a value close to the output current command Iout *.

Further, the switching from the constant voltage control in the current rising period Ta to the constant current control in the constant current output period Tb may be performed by setting a switching time in advance. In the constant voltage control in the current rising period Ta, the control device 30 switches to the constant current control in which the output current Iout follows the output current command Iout * when the set time TA elapses, and shifts to the constant current output period Tb. In this case, a set time TA shorter than the time when the output current Iout reaches the output current command Iout * is set in advance, and the set time TA is a time corresponding to the current rise period Ta.
Also in this case, the output current Iout does not exceed the output current command Iout * and does not overshoot, and the output current Iout can be quickly started.
Note that the set time TA is not unnecessarily short as long as the overshoot of the output current Iout can be avoided, and is preferably a value close to the time required to reach the output current command Iout *.

  Switching from the constant current control in the constant current output period Tb to the constant voltage control in the current fall period Tc is usually performed based on a preset time.

As described above, in the gradient magnetic field power supply device 100 according to the present embodiment, the switching elements 11 to 14 of the first inverter circuit INV1 are made of a silicon semiconductor, and the switching elements 21 to 24 of the second inverter circuit INV2 are made of a wide band gap semiconductor. The AC output terminal of the first inverter circuit INV1 and the AC output terminal of the second inverter circuit INV2 are connected in series to supply power to the gradient coil 50.
The switching elements 21 to 24 made of a wide band gap semiconductor are suitable for high frequency switching because they have a lower on-resistance and much smaller switching loss than silicon semiconductors, and are also suitable for miniaturization. The gradient magnetic field power supply device 100 is a combination of a first inverter circuit INV1 made of a silicon semiconductor and a second inverter circuit INV2 made of a wide band gap semiconductor suitable for high-frequency switching operation. Therefore, an increase in the size of the device configuration is suppressed, a high voltage and a large current can be output with a small device configuration, and highly accurate current control is also possible.

The control device 30 has a current rising period Ta, a constant current output period Tb, and a current falling period Tc. Then, in the current rising period Ta and the current falling period Tc, constant voltage control for outputting a constant voltage based on the sum of the output voltages of the first and second inverter circuits INV1 and INV2 is performed. As a result, a high voltage can be output, and the output current Iout can be quickly raised or lowered.
In the constant current output period Tb, the first inverter circuit INV1 outputs 0 voltage, and only the second inverter circuit INV2 performs high-frequency switching control based on the output current command Iout * which is a constant current command value. Thereby, low-loss and high-precision current control can be achieved. In addition, since the constant current output period Tb is performed after the current rising period Ta, high-precision current control with a large current becomes possible.

  Further, the control device 30 determines each output voltage level of the first and second inverter circuits INV1 and INV2 based on the output current command Iout * during the current rise period Ta and the current fall period Tc, and sets the constant. Control the voltage. For this reason, the output voltage levels of the first and second inverter circuits INV1 and INV2 can be easily and appropriately determined in accordance with the required output current command Iout *, and the constant voltage control can be performed. Can be started or shut down reliably.

  Further, in the constant current output period Tb, the control device 30 can control the output current Iout at high speed and with high accuracy by performing the constant current control by a combination of the feedback control and the feedforward control.

  Further, by setting the voltage V1 of the first DC voltage unit 10 of the first inverter circuit INV1 higher than the voltage V2 of the second DC voltage unit 20 of the second inverter circuit INV2, a low voltage can be applied to the constant current control by high-frequency switching. V2 is used, and the high voltage V1 can be used only for constant voltage control. As a result, the load on the switching elements 21 to 24 of the second inverter circuit INV2 can be reduced, and both the constant voltage control and the constant current control can be performed effectively, so that the device configuration can be reduced in size.

  Note that the voltage V1 is not limited to being higher than the voltage V2, and the control device 30 controls the first and second inverter circuits INV1 and INV2 in the same manner as in this embodiment, so that a high voltage and a large current can be obtained. Output is possible and high-precision current control becomes possible.

  Further, in this embodiment, only the case where the gradient magnetic field power supply device 100 outputs the output current Iout which is a trapezoidal wave current is shown, but a current other than the trapezoidal wave can be output if necessary.

Embodiment 2 FIG.
FIG. 6 is a diagram showing a circuit configuration of the gradient power supply according to the second embodiment. In the second embodiment, a plurality of second inverter circuits using switching elements made of a wide band gap semiconductor are configured in parallel. The description of the same parts as those in the first embodiment will be appropriately omitted.
As shown in FIG. 6, the gradient magnetic field power supply device 100A includes a first inverter circuit INV1 and a second inverter circuit INV2A, and includes an AC output terminal of the first inverter circuit INV1 and an AC output terminal of the second inverter circuit INV2A. Are connected in series to supply power to the gradient coil 50. The first inverter circuit INV1 is the same as in the first embodiment, and is a full bridge circuit including a plurality of switching elements 11, 12, 13, and 14 made of a silicon semiconductor, and a first DC voltage unit 10.

The second inverter circuit INV2A is configured by connecting a plurality of (in this case, two) similar unit circuits 2A and 2B in parallel at connection points AA and BB. The connection points AA and BB serve as AC output terminals of the second inverter circuit INV2A.
Each of the unit circuits 2A and 2B has the same configuration as the second inverter circuit INV2 of the first embodiment. That is, the unit circuit 2A is a full bridge circuit including a plurality of switching elements 21a, 22a, 23a, 24a made of a wide band gap semiconductor such as a SiC-MOSFET and the second DC voltage unit 20A, and the second DC voltage unit. 20A DC power is converted into AC power and output. Similarly, the unit circuit 2B is a full bridge circuit including a plurality of switching elements 21b, 22b, 23b, 24b made of a wide band gap semiconductor and the second DC voltage unit 20B, and converts the DC power of the second DC voltage unit 20B into AC. Convert to electric power and output. Further, second DC voltage unit 20A and second DC voltage unit 20B are connected in parallel.

  Further, the gradient magnetic field power supply device 100A includes a control device 30A that controls the output of each of the unit circuits 2A and 2B in the first inverter circuit INV1 and the second inverter circuit INV2A, and outputs the gradient magnetic field power supply device 100A to the gradient magnetic field coil 50. And a current detection unit 40 for detecting the output current Iout to be output.

The unit circuits 2A and 2B in the second inverter circuit INV2A include AC output terminals A1 and B1 of the first legs (21a-22a) and (21b-22b), and second legs (23a-24a) and (23b- Voltages of three levels of + V2, -V2, 0 are output between the AC output terminals A2, B2 of 24b).
Note that the voltage V2 of the second DC voltage units 20A and 20B is lower than the voltage V1 of the first DC voltage unit 10 of the first inverter circuit INV1.

  The value of the output current Iout detected by the current detection unit 40 is input to the control device 30A. Then, based on this output current (value) Iout and the output current command Iout * as a constant current command value, each of the unit circuits 2A and 2B in the first inverter circuit INV1 and the second inverter circuit INV2A It generates gate signals G11 to G14, G21a to G24a, and G21b to G24b to the switching elements 11 to 14, 21a to 24a, 21b to 24b, and controls the output of the first and second inverter circuits INV1, INV2A.

Next, the operation of the gradient power supply device 100A will be described.
The control device 30A has a current rising period Ta, a constant current output period Tb, and a current falling period Tc, similarly to the first embodiment, and includes the first and second inverter circuits INV1, which are main circuits. A trapezoidal wave current (output current Iout) is output from INV2A. Control device 30A controls first inverter circuit INV1 in the same manner as in the first embodiment. Further, the unit circuits 2A and 2B in the second inverter circuit INV2A are controlled in the same manner as the second inverter circuit INV2 according to the first embodiment, and the cross current suppression control between the unit circuits 2A and 2B is also performed.

When the unit circuits 2A and 2B are connected in parallel, the current flowing in the second inverter circuit INV2A is shunted. However, due to a difference in impedance between the parallel unit circuits 2A and 2B or a slight shift in switching timing, etc. Cross flow occurs.
7 to 9 are diagrams illustrating examples of the path of the cross current Ia in the second inverter circuit INV2A. In this case, in the unit circuit 2A, the switching elements 21a and 24a are on, and the switching elements 22a and 23a are off. In the unit circuit 2B, the switching elements 21b and 24b are on and the switching elements 22b and 23b are off.
The cross current Ia of any path is a reactive current circulating in the second inverter circuit INV2A without a current flowing through the gradient coil 50, and is not detected by the current detection unit 40.

Next, the control of the cross flow between the unit circuits 2A and 2B will be described.
As shown in FIG. 10, there are provided current detectors 41 to 44 for detecting circuit currents I1 to I4 input and output to the first and second legs of each of the unit circuits 2A and 2B of the second inverter circuit INV2A. In this case, the current detector 41 detects a circuit current I1 flowing between the AC output terminal A1 of the unit circuit 2A and the connection point AA. The current detector 42 detects a circuit current I2 flowing from the AC output terminal B1 of the unit circuit 2B to the connection point AA. The current detector 43 detects a circuit current I3 flowing between the AC output terminal A2 of the unit circuit 2A and the connection point BB. The current detector 44 detects a circuit current I4 flowing between the AC output terminal B2 of the unit circuit 2B and the connection point BB.

  Note that the current detectors 41 to 44 are configured to detect currents flowing through the reactors L1 to L4, which are inductance components. As a result, the inductance component is inserted into the path of the cross current Ia, and the cross current is suppressed.

The control device 30A calculates the duty ratio so that the circuit currents I1 to I4 follow the circuit current command based on the output current command Iout * in the constant current output period Tb, and uses the duty ratio to perform the operation of each unit circuit. The first and second legs 2A and 2B are subjected to high-frequency switching control. At this time, the switching of the second legs (23a-24a) and (23b-24b) of each of the unit circuits 2A and 2B is adjusted to perform the cross current suppression control. The circuit current command of each of the unit circuits 2A and 2B is obtained by dividing the output current command Iout * by the number of parallel units of the unit circuits 2A and 2B, and in this case, Iout * / 2.
FIGS. 11 to 14 are current path diagrams illustrating the cross current suppression control of the second inverter circuit INV2A. In this case, for convenience, reactors L1 to L4 are illustrated, and illustration of current detectors 41 to 44 is omitted.

The control device 30A inputs the values of the circuit currents I1 to I4, which are the input / output currents of the unit circuits 2A and 2B, and sets the duty so that the circuit currents I1 to I4 follow the circuit current command (Iout * / 2). Calculate the ratio. This constant current control can be performed by combining feedback control and feedforward control as in the first embodiment.
The first legs (21a-22a) and (21b-22b) of each of the unit circuits 2A and 2B perform high-frequency switching control using the calculated duty ratio. That is, the switching elements 21a and 22a of the first leg (21a-22a) of the unit circuit 2A are controlled by the duty ratio calculated so that the circuit current I1 follows the circuit current command (Iout * / 2). The switching elements 21b and 22b of the first leg (21b-22b) of the unit circuit 2B are controlled by a duty ratio calculated so that the circuit current I2 follows the circuit current command (Iout * / 2).

On the other hand, in the second legs (23a-24a) and (23b-24b) used for the cross current suppression control, the circuit currents I3 and I4 are compared, and if there is no difference, the duty ratio calculated by the constant current control described above is used. High-frequency switching control. That is, the second legs (23a-24a) of the unit circuit 2B are connected to the second legs (23b-24b) of the unit circuit 2B such that the circuit current I3 follows the circuit current command (Iout * / 2). The current I4 is controlled so as to follow the circuit current command (Iout * / 2).
When a difference occurs between the circuit currents I3 and I4, a cross current occurs between the parallel unit circuits 2A and 2B. Therefore, the switching timing in the high-frequency switching control using the calculated duty ratio is adjusted as follows. I do.

FIGS. 11 to 14 are current path diagrams for explaining the cross current suppression control of the second inverter circuit INV2A. The output current Iout is the main current of the second inverter circuit INV2A and flows between the two unit circuits 2A and 2B. 4 shows a current path of the cross current Ia.
In the case shown in FIG. 11, the switching elements 21a, 24a, 21b, 24b are on and the cross current Ia flows, so that the circuit current I3 flowing through the reactor L3 is larger than the circuit current I4 flowing through the reactor L4. The AC output terminal B2 of the second leg (23b-24b) of the unit circuit 2B has a higher potential than the AC output terminal A2 of the second leg (23a-24a) of the unit circuit 2A.
In this case, the on-time of the switching element 24a, which is a flow element of the cross current Ia, in the second leg (23a-24a) of the unit circuit 2A is reduced, so that the second leg (23a-24a) of the unit circuit 2A is reduced. The potential of the AC output terminal A2 can be increased.

In the case shown in FIG. 12, the switching elements 22a, 23a, 22b, and 23b are on and the cross current Ia flows, so that the circuit current I3 flowing through the reactor L3 is larger than the circuit current I4 flowing through the reactor L4. The AC output terminal B2 of the second leg (23b-24b) of the unit circuit 2B has a higher potential than the AC output terminal A2 of the second leg (23a-24a) of the unit circuit 2A.
In this case, by shortening the on-time of the switching element 23b, which is a flow element of the cross current Ia, in the second leg (23b-24b) of the unit circuit 2B, the second leg (23b-24b) of the unit circuit 2B is reduced. The potential of the AC output terminal B2 can be lowered.

In the case shown in FIGS. 11 and 12, the circuit current I3 is larger than the circuit current I4 and the cross current Ia is detected, but neither of the two types of cross current path is detected. Therefore, when detecting that the circuit current I3> the circuit current I4, the control device 30A detects the switching element 24a on the low voltage side in the second leg (23a-24a) of the unit circuit 2A and the switching element 24a of the unit circuit 2B. The ON time of both the switching element 23b on the high voltage side in the second leg (23b-24b) is reduced.
Thereby, the potential difference between the AC output terminal A2 of the second leg (23a-24a) of the unit circuit 2A and the AC output terminal B2 of the second leg (23b-24b) of the unit circuit 2B is reduced, and the cross current Ia is suppressed. Is done.

The on-time of the switching elements 24a and 23b can be easily reduced by, for example, delaying the turn-on timing. At this time, the amount of shortening of the on-time of the switching elements 24a and 23b may be a fixed value or may be varied according to the difference between the circuit currents I3 and I4.
The switching elements 23a and 24b whose on-time is not adjusted in each of the second legs (23a-24a) and (23b-24b) are controlled by the on-time based on the calculated duty ratio.

  In order to suppress the cross current Ia, if the dead time of each of the second legs (23a-24a) and (23b-24b) can be secured, the ON time of the switching elements 24b and 23a, which are the flow elements of the cross current Ia, is increased. But it is possible.

In the case shown in FIG. 13, the switching elements 21a, 24a, 21b, and 24b are on and the cross current Ia flows, so that the circuit current I4 flowing through the reactor L4 is larger than the circuit current I3 flowing through the reactor L3. The AC output terminal A2 of the second leg (23a-24a) of the unit circuit 2A has a higher potential than the AC output terminal B2 of the second leg (23b-24b) of the unit circuit 2B.
In this case, by shortening the ON time of the switching element 24b, which is a flow element of the cross current Ia, in the second leg (23b-24b) of the unit circuit 2B, the second leg (23b-24b) of the unit circuit 2B is reduced. The potential of the AC output terminal B2 can be increased.

In the case shown in FIG. 14, the switching elements 22a, 23a, 22b, and 23b are on and the cross current Ia flows, so that the circuit current I4 flowing through the reactor L4 is larger than the circuit current I3 flowing through the reactor L3. The AC output terminal A2 of the second leg (23a-24a) of the unit circuit 2A has a higher potential than the AC output terminal B2 of the second leg (23b-24b) of the unit circuit 2B.
In this case, the on-time of the switching element 23a, which is a flow element of the cross current Ia, in the second leg (23a-24a) of the unit circuit 2A is shortened, so that the second leg (23a-24a) of the unit circuit 2A is reduced. The potential of the AC output terminal A2 can be lowered.

In the case shown in FIGS. 13 and 14, the circuit current I3 is smaller than the circuit current I4 and the cross current Ia is detected, but it is not determined which of the two types of cross current path. For this reason, when detecting that the circuit current I3 <the circuit current I4, the control device 30A detects the switching element 23a on the high voltage side in the second leg (23a-24a) of the unit circuit 2A and the switching device 23a of the unit circuit 2B. The on-time of both the switching element 24b on the low voltage side in the second leg (23b-24b) is shortened.
Thereby, the potential difference between the AC output terminal A2 of the second leg (23a-24a) of the unit circuit 2A and the AC output terminal B2 of the second leg (23b-24b) of the unit circuit 2B is reduced, and the cross current Ia is suppressed. Is done.

The on-time of the switching elements 23a and 24b can be easily reduced by, for example, delaying the turn-on timing. At this time, the amount of shortening of the on-time of the switching elements 23a and 24b may be a fixed value or may be varied according to the difference between the circuit currents I3 and I4.
The switching elements 24a and 23b whose ON times are not adjusted by the second legs (23a-24a) and (23b-24b) are controlled by the ON time based on the calculated duty ratio.

  Also in this case, the suppression of the cross current Ia can be achieved by increasing the on-time of the switching elements 23b and 24a, which are the flow elements of the cross current Ia, if the dead time of each of the second legs (23a-24a) and (23b-24b) can be secured. It is also possible.

  In the above embodiment, the cross flow suppression control is performed using the second legs (23a-24a) and (23b-24b). However, the second legs (23a-24a) and (23b- 24b) may be controlled by the ON time based on the calculated duty ratio, and the cross flow suppression control may be performed using each of the first legs (21a-22a) and (21b-22b).

  Also in the second embodiment, the switching elements 11 to 14 of the first inverter circuit INV1 are made of a silicon semiconductor, and the switching elements 21a to 24a and 21b to 24b of the second inverter circuit INV2A are made of a wide band gap semiconductor. The AC output terminal of the inverter circuit INV1 and the AC output terminal of the second inverter circuit INV2A are connected in series to supply power to the gradient coil 50. The control device 30A has a current rising period Ta, a constant current output period Tb, and a current falling period Tc. In the current rising period Ta and the current falling period Tc, the first and second inverter circuits are provided. Constant voltage control is performed to output a constant voltage based on the sum of the output voltages of INV1 and INV2A. Then, in the constant current output period Tb, the first inverter circuit INV1 outputs zero voltage, and the second inverter circuit INV2A performs high-frequency switching control based on the output current command Iout * which is a constant current command value. As a result, similarly to the first embodiment, an increase in the configuration is suppressed, a high voltage and a large current can be output with a small device configuration, and a highly accurate current control can be performed.

  In this embodiment, the second inverter circuit INV2A is configured by connecting a plurality of (in this case, two) similar unit circuits 2A and 2B in parallel at connection points AA and BB. The current flowing through the switching elements 21a to 24a and 21b to 24b in 2B can be reduced, and in this case can be reduced to half. Thereby, conduction loss generated in the switching elements 21a to 24a and 21b to 24b can be reduced. In addition, since the current ratings required for the switching elements 21a to 24a and 21b to 24b are reduced, the switching elements 21a to 24a and 21b to 24b having good on-resistance characteristics and switching loss characteristics can be applied, and the second inverter circuit INV2A Loss can be reduced. Thereby, the cooler can be downsized, and the device configuration can be downsized.

  In the constant current output period Tb, the control device 30A changes the cross current Ia flowing between the unit circuits 2A and 2B to the high voltage side and the low voltage side of each of the second legs (23a-24a) and (23b-24b). The suppression control is performed by adjusting the ON time of one switching element. The cross current Ia flowing between the unit circuits 2A and 2B is a reactive current, which promotes an increase in loss and heat generation in the switching elements 21a to 24a and 21b to 24b. A high gradient magnetic field power supply device 100A is obtained. Further, the currents flowing through the unit circuits 2A and 2B in the second inverter circuit INV2A are balanced, and highly accurate and reliable constant current control can be realized.

  In addition, since the second DC voltage units 20A and 20B of the unit circuits 2A and 2B are connected in parallel, only one of the second DC voltage units 20A needs to be supplied with power from an external power supply. The overall device configuration can be simplified.

  Since the current detectors 41 to 44 for detecting the circuit currents I1 to I4 are provided, the current detection unit 40 for detecting the output current Iout does not directly measure the output current Iout, but the circuit currents I1 to I4. May be calculated from

Conversely, if there is a current detection unit 40 that detects the output current Iout, the current detectors 41 to 44 need only be at least M−1 when the number of parallel units M of the unit circuits 2A and 2B is M. In this case, if at least one of the circuit currents I1 and I2 and one of the circuit currents I3 and I4 can be measured, the remaining circuit current can be calculated.
FIG. 15 shows a case where reactors L1 and L4 are provided, and reactors L2 and L3 are omitted. In this case, the circuit currents I1 and I4 flowing through the reactors L1 and L4 are detected, and the circuit currents I2 and I3 are calculated.

  Further, in the present embodiment, the control device 30A performs the crossflow suppression control, but there is also an effect of the crossflow suppression by the inductance components of the reactors L1 to L4. Therefore, reactors L1 to L4 may be inserted separately from current detectors 41 to 44. In this case, the capacity of reactors L1 to L4 can be reduced by the cross flow suppression control by control device 30A.

  Furthermore, even when the control device 30A does not perform the crossflow suppression control, the crossflow can be suppressed by inserting the reactors L1 to L4. If at least one of the reactors L1 to L4 is inserted in each cross flow path, there is a cross flow suppression effect.

Embodiment 3 FIG.
FIG. 16 is a diagram showing a circuit configuration of the gradient power supply according to the third embodiment. In the second embodiment, the second DC voltage units 20A and 20B of the unit circuits 2A and 2B are connected in parallel. However, in the third embodiment, the unit circuits 2A and 2B of the second inverter circuit INV2B are connected in parallel. Each of the second DC voltage units 20C and 20D of 2B has an independent configuration. Other circuit configurations are the same as those of the second embodiment.

In this embodiment, since the plurality of second DC voltage units 20C and 20D are each configured independently and there is no connection between the second DC voltage units 20C and 20D, the number of cross current paths flowing between the unit circuits 2A and 2B is reduced. Be reduced. For example, the cross flow path shown in FIGS. 7 to 9 of the second embodiment is only the cross flow path shown in FIG.
Further, as in the second embodiment, by inserting reactors L1 to L4 into the cross flow path, the cross flow is suppressed by the inductance components of reactors L1 to L4.

In this embodiment, since the cross current path and the main current path overlap, the cross current is suppressed by controlling the output current Iout which is the main current. Therefore, the cross flow suppression control described in the second embodiment is not performed.
Further, since the circuit currents I1 to I4, which are the input / output currents of the unit circuits 2A and 2B, are I1 = I3 and I2 = I4, only the current detectors 41 and 42 are provided, and the current detectors 43 and 44 are omitted. You.

The control device 30A calculates the duty ratio such that the circuit currents I1 and I2, which are the input and output currents of the unit circuits 2A and 2B, follow the circuit current command (Iout * / 2) during the constant current output period Tb. Then, the first and second legs of each of the unit circuits 2A and 2B are subjected to high-frequency switching control based on the ON time based on the calculated duty ratio.
Thus, the currents flowing through the unit circuits 2A and 2B in the second inverter circuit INV2A are balanced, and highly accurate and reliable constant current control can be realized, and the same effect as that of the second embodiment can be obtained. Further, since the number of cross flow paths is small, loss can be easily reduced.

Also in this embodiment, similarly to the second embodiment, by inserting reactors L1 to L4 into the cross flow path, there is an effect of suppressing the cross flow due to the inductance components of reactors L1 to L4.
Further, since the number of cross flow paths is reduced, the number of reactors L1 to L4 can also be reduced. When the number of unit circuits 2A and 2B is two in parallel, as shown in FIG. 17, if one reactor L1 is provided, the cross current can be suppressed.

Embodiment 4 FIG.
In the second embodiment, the case where the plurality of unit circuits 2A and 2B are configured in parallel to form the second inverter circuits INV2A and INV2B has been described. In this embodiment, the control device 30A of the gradient power supply device 100A provides a phase difference in the switching cycle of the plurality of unit circuits 2A and 2B during the constant current output period Tb.
In this case, it is assumed that the cross flow suppression control is not performed, but at least one reactor L1 to L4 is inserted in each cross flow path.

  FIG. 18 is a waveform chart of each part for explaining the operation of the gradient magnetic field power supply device 100A according to the fourth embodiment. Here, the output current Iout, the output voltage V-INV1 of the first inverter circuit INV1, the output voltage V-INV2A of the second inverter circuit INV2A, and the switching elements 11 to 14 in the first inverter circuit INV1 and the second inverter circuit INV2A. , 21a to 24a, 21b to 24b, G21a to G14, G21a to G24a, and G21b to G24b.

As shown in the figure, the control device 30 has a current rising period Ta, a constant current output period Tb, and a current falling period Tc, and includes first and second inverter circuits INV1 and INV2A as main circuits. Outputs a trapezoidal wave current (output current Iout).
In the current rising period Ta, the control device 30A controls the constant voltage based on the sum of the output voltages of the first and second inverter circuits INV1 and INV2A, in this case, (V1 + V2), as in the first embodiment. I do.

In the constant current output period Tb, the control device 30A performs constant current control in which the first inverter circuit INV1 outputs 0 voltage and high frequency switching control of the second inverter circuit INV2A is performed based on the output current command Iout *.
The second inverter circuit INV2A detects circuit currents I1 and I2, which are output currents of the unit circuits 2A and 2B, and controls the circuit currents I1 and I2 to follow the output current command (Iout * / 2). . At this time, the gate signals G21a to G24a and G21b to G24b are generated by shifting the phase of the switching cycle of the unit circuit 2A and the phase of the switching cycle of the unit circuit 2B by (1/4) cycle.

In this case, in each of the unit circuits 2A and 2B, the first legs (21a to 22a) and (21b to 22b) and the second legs (23a to 24a) and (23b to 24b) are shifted by a half cycle to perform high-frequency switching. Therefore, the frequency of the output voltage V-INV2A is four times the switching frequency.
This leads to an increase in the frequency of the ripple current superimposed on the output current Iout, and it is possible to further improve the accuracy of the output current Iout by reducing the size of a filter circuit (not shown) or reducing the ripple current. Conversely, when the ripple current is satisfied at a higher frequency, the switching frequency of the second inverter circuit INV2 can be reduced. Thereby, the loss of the switching elements 21a to 24a and 21b to 24b can be reduced, and the cooler can be downsized.

The control according to the above embodiment can be applied to the configuration of the gradient magnetic field power supply device 100B according to the third embodiment, and the same effect can be obtained.
Although the control without using the cross current suppression control is shown, the cross current suppression control described in the second embodiment may be performed together, and more accurate current control can be performed with low loss.

Embodiment 5 FIG.
In each of the first to fourth embodiments, the switching elements 11 to 14 of the first inverter circuit INV1 are made of a silicon semiconductor, and the switching elements 21 to 24 of the second inverter circuit INV2 are made of a wide band gap semiconductor. However, the present invention is not limited to this. For example, the switching elements 11 to 14 and 21 to 24 of both the first and second inverter circuits INV1 and INV2 may be made of a wide band gap semiconductor, or both may be made of a silicon semiconductor. Is also good. Also in this case, by performing the same control as in each of the above embodiments, it is possible to output a high voltage and a large current and to control the current with high accuracy, and to reduce the size of the device configuration.

Embodiment 6 FIG.
FIG. 19 is a diagram showing an overall configuration of an MRI apparatus according to the sixth embodiment. In this case, an MRI apparatus 1 including the gradient magnetic field power supply device 100 according to the first embodiment is shown. However, a configuration including the gradient magnetic field power supply devices 100A and 100B according to the second to fifth embodiments has the same configuration.
The MRI apparatus 1 includes a static magnetic field coil 201 for generating a static magnetic field for the subject M, a static magnetic field power supply 200 for exciting the static magnetic field coil 201, and a gradient magnetic field coil for generating a gradient magnetic field for the subject M 50, a gradient magnetic field power supply 100 for exciting the gradient magnetic field coil 50, a transmission coil 202 and a transmission unit 205 for irradiating the subject M with an RF (Radio Frequency) pulse, and a reception for receiving a nuclear magnetic resonance signal A coil 203 and a receiving unit 206; an image data generating unit 207 for processing received nuclear magnetic resonance signals to generate image data; a display unit 208 for displaying the image data; and a transmitting unit 205 for the gradient magnetic field power supply device 100 , A sequencer 210 for controlling the image data generation unit 207, and a bed 204 on which the subject M is arranged.

In order to generate the gradient magnetic field in the X-axis direction, the Y-axis direction, and the Z-axis direction orthogonal to each other, a gradient magnetic field power supply device 100 and a gradient magnetic field coil 50 for three axes are provided. As the gradient magnetic field coil 50, air-core coils of three axes of X-axis, Y-axis, and Z-axis are used, and pulse electric power is supplied from these to the gradient magnetic field power supply device 100 to synthesize a three-axis gradient magnetic field. Then, it becomes possible to set the slice selection gradient magnetic field, the phase encoding gradient magnetic field, and the frequency encoding gradient magnetic field orthogonal to each other in any direction. The gradient magnetic field in each direction is applied to the subject M while being superimposed on a strong static magnetic field.
Nuclear spin is excited by nuclear magnetic resonance in which a nuclear spin placed in a static magnetic field resonates with an electromagnetic wave of a specific frequency (Larmor frequency), and a nuclear magnetic resonance signal generated by subsequent relaxation is received by a receiving coil 203 and a receiving unit. The image data generation unit 207 converts the image data into image data.

  As described above, the gradient magnetic field power supply device 100 has a small device configuration, can output a large current with high accuracy, and can output a high voltage. Therefore, it is possible to superimpose a gradient magnetic field that is sufficiently larger than the variation amount of the static magnetic field, thereby suppressing the variation amount of the gradient magnetic field and increasing the slew rate. As a result, the MRI apparatus 1 capable of high-speed, high-quality imaging can be obtained, and miniaturization of the MRI apparatus 1 is promoted.

Although this application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments may apply to particular embodiments. However, the present invention is not limited thereto, and can be applied to the embodiment alone or in various combinations.
Accordingly, innumerable modifications not illustrated are envisioned within the scope of the technology disclosed herein. For example, a case where at least one component is deformed, added or omitted, and a case where at least one component is extracted and combined with components of other embodiments are included.

DESCRIPTION OF SYMBOLS 1 MRI apparatus, 2A, 2B unit circuit, 10 1st DC voltage part, 11-14 Switching element, 20, 20A, 20B, 20C, 20D 2nd DC voltage part, 21-24, 21a-24a, 21b-24b Switching Element, 30, 30A Controller, 40 Current detector, 41-44 Current detector, 50 Gradient magnetic field coil, 100, 100A, 100B Gradient magnetic field power supply, INV1 first inverter circuit, INV2, INV2A, INV2B Second inverter circuit , L1 to L4 reactors.

Claims (15)

A first inverter circuit having a first DC voltage section and a plurality of switching elements, a second inverter circuit having a second DC voltage section and a plurality of switching elements, a current detection section for detecting an output current; A control device for controlling the output of the second inverter circuit,
The plurality of switching elements of the first inverter circuit are made of a silicon semiconductor, and the plurality of switching elements of the second inverter circuit are made of a wide band gap semiconductor having a wider band gap than a silicon semiconductor;
An AC output terminal of the first inverter circuit and an AC output terminal of the second inverter circuit are connected in series to supply power to a gradient coil ,
The control device performs constant current control when power is supplied to the gradient magnetic field coil. In the constant current control, the switching state of the first inverter circuit is fixed, and a constant voltage is output from the first inverter circuit. Controlling the high frequency switching of the second inverter circuit based on a constant current command value;
Gradient magnetic field power supply. The control device includes:
A current rising period, a constant current output period following the current rising period, and a current falling period following the constant current output period, the trapezoidal wave current being the output current is supplied to the gradient coil. Controlling the output of the first and second inverter circuits so as to output the signals;
In the current rising period and the current falling period, a constant voltage for fixing each switching state of the first and second inverter circuits and outputting a constant voltage based on a sum of output voltages of the first and second inverter circuits. Control,
And in the constant current output period, as the constant current control, causes said first inverter circuit 0 voltage output, said second inverter circuit, high-frequency switching control based on the constant current command value,
The gradient magnetic field power supply device according to claim 1. The first and second inverter circuits can output three levels of voltages of positive, negative and 0, respectively.
The control device includes:
Determining each output voltage level of the first and second inverter circuits during the current rising period and the current falling period based on the constant current command value;
In the current rise period and the current fall period, the constant voltage control is performed based on the determined output voltage levels.
The gradient magnetic field power supply device according to claim 2. A voltage of the first DC voltage unit is higher than a voltage of the second DC voltage unit;
The gradient magnetic field power supply device according to claim 2 or 3. The control device, during the constant current output period, feedback control in which the output current detected by the current detection unit follows the constant current command value, and feedforward control that compensates for a voltage drop in a current path. Performing the constant current control by a combination of
The gradient magnetic field power supply device according to claim 2. The control device, in the constant voltage control during the current rising period, when the output current detected by the current detection unit reaches a set current value smaller than the constant current command value, the constant voltage control To switch to the constant current control and shift to the constant current output period,
The gradient magnetic field power supply device according to claim 2. The second inverter circuit is configured by connecting a plurality of unit circuits in parallel,
Each of the unit circuits includes the second DC voltage unit and the plurality of switching elements made of the wide band gap semiconductor.
The gradient magnetic field power supply device according to any one of claims 2 to 6. Each of the unit circuits has two parallel first and second legs formed by the plurality of switching elements,
The current detection unit further detects each circuit current input / output to / from the first and second legs of each of the unit circuits,
The control device includes:
In the constant current output period, a duty ratio is calculated so that each circuit current follows a circuit current command based on the constant current command value, and the first and second duty ratios of the unit circuits are calculated using the duty ratio. High frequency switching control of two legs,
At the time of the high-frequency switching control, the ON time of one of the high-voltage side and the low-voltage side switching element of the second leg according to the difference between the circuit currents input to and output from the second leg of each unit circuit By adjusting the cross current flowing between the plurality of unit circuits,
The gradient magnetic field power supply device according to claim 7. The control device determines one of the high-voltage side and the low-voltage side switching element of the second leg according to a magnitude relationship between the circuit currents input to and output from the second leg of each unit circuit. Reduce the ON time of the determined switching element,
The gradient magnetic field power supply device according to claim 8. Each of the second DC voltage units of the plurality of unit circuits includes an independent DC voltage,
The gradient magnetic field power supply device according to claim 7. The second DC voltage units of the plurality of unit circuits are connected in parallel,
The gradient magnetic field power supply device according to any one of claims 7 to 9. Inserting at least one inductance component into the path of each cross current flowing between the plurality of unit circuits;
The gradient magnetic field power supply device according to any one of claims 7 to 11. The control device, during the constant current output period, provides a phase difference in the switching cycle of the plurality of unit circuits,
The gradient magnetic field power supply device according to any one of claims 7 to 12. A first inverter circuit having a first DC voltage section and a plurality of switching elements, a second inverter circuit having a second DC voltage section and a plurality of switching elements, a current detection section for detecting an output current; A control device for controlling the output of the second inverter circuit, wherein an AC output terminal of the first inverter circuit and an AC output terminal of the second inverter circuit are connected in series to supply power to the gradient coil;
The control device includes:
A current rising period, a constant current output period following the current rising period, and a current falling period following the constant current output period, the trapezoidal wave current being the output current is supplied to the gradient coil. Controlling the output of the first and second inverter circuits so as to output the signals;
In the current rising period and the current falling period, a constant voltage for fixing each switching state of the first and second inverter circuits and outputting a constant voltage based on a sum of output voltages of the first and second inverter circuits. Control,
In the constant current output period, the first inverter circuit outputs 0 voltage, and performs high-frequency switching control of the second inverter circuit based on a constant current command value.
Gradient magnetic field power supply. The gradient magnetic field power supply device according to any one of claims 1 to 14, and the gradient magnetic field coil which is supplied with power and excited by the gradient magnetic field power supply device,
Magnetic resonance imaging diagnostic device.

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