JP3608868B2 - Power supply device for magnetic resonance imaging apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply apparatus for a magnetic resonance imaging apparatus (hereinafter referred to as an MRI apparatus), and more particularly to a power supply apparatus suitable for various power supplies necessary for generating a static magnetic field, a gradient magnetic field, and a high-frequency magnetic field that require high power.
[0002]
[Prior art]
The MRI apparatus applies a high-frequency magnetic field in a pulsed manner to an inspection object placed in a static magnetic field, detects a nuclear magnetic resonance signal generated from the inspection object, and reconstructs a spectrum and an image based on the detection signal. In the MRI apparatus, a superconducting or normal conducting coil for generating a static magnetic field as a coil for generating a magnetic field, a gradient magnetic field coil for generating a gradient magnetic field superimposed on the static magnetic field, and a high frequency for generating a high-frequency magnetic field. A coil is provided. These magnetic field generating coils are provided with a switching power source for controlling the magnitude and timing of an applied current in order to generate a magnetic field having a predetermined magnetic field strength.
[0003]
As a switching power supply for generating a magnetic field of such an MRI apparatus, a configuration of a switching power supply for generating a gradient magnetic field is shown in FIG. The switching power supply includes contacts 11 to 16 connected to the three-phase AC commercial power supply 10, current limiting means for preventing inrush current connected in series to the contacts 11 to 13, respectively, resistors 17 to 19 here, and a rectifier circuit 120, a smoothing capacitor 71, and a current amplifier 40, and the output of the current amplifier 40 is applied to the gradient magnetic field coil 70. The current amplifier 40 is controlled by the control circuit control circuit 50 so that a current having an arbitrary waveform is applied to the gradient coil 70. As the rectifier circuit 120, a full-wave rectifier circuit using a diode bridge composed of diodes 124 to 128 as shown, a voltage control type rectifier circuit using a thyristor, a voltage control using a switching regulator, and the like are used.
[0004]
[Problems to be solved by the invention]
In recent years, high-speed imaging methods such as EPI (Echo Planer Imaging) have been developed for MRI apparatuses, and as a result, an increase in output current and a reduction in the rise time of gradient magnetic field coils are required, resulting in an increase in current and voltage. There is a tendency.
[0005]
In order to improve the current changing speed of the output current amplifier, it is necessary to increase the input voltage. However, in the rectifier circuit using the conventional thyristor or the like as shown in FIG. 5, the voltage can only be boosted to about 1.4 times the power supply voltage even at the peak charge. It was necessary to add additional circuits such as circuit systems, chopper circuits, and transformers.
[0006]
Also, the increase in capacity of power supply facilities has become a problem due to the increase in output power. Therefore, an object of the present invention is to provide a high voltage, large capacity power supply device for an MRI apparatus.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a power supply device for an MRI apparatus according to the present invention is connected to a commercial AC power source through a contact, an AC / DC converter for converting AC to DC, and an output of the AC / DC converter. A power supply device for a magnetic resonance imaging apparatus, comprising: a current amplifier that supplies a current of an arbitrary waveform to a magnetic field generating coil of the apparatus; and a control circuit that controls switching of the current amplifier, and prevents inrush current connected in parallel to the contacts And a second contact connected in series with the current control means. The AC / DC converter includes a bridge circuit in which a plurality of pairs of diodes are connected in parallel and at least one diode of the pair of diodes. A semiconductor switching element connected in parallel; and a reactor connected between the AC input side of the bridge circuit and the contact. And control means for driving and controlling the quenching element, said control means, in which and a sequencer connected to the control circuit and the contacts of the current amplifier.
[0008]
By combining a diode bridge and a semiconductor switching element connected in parallel to the diode and a reactor connected on the AC input side, energy can be stored in the reactor when a predetermined semiconductor switching element is short-circuited. This stored energy can be added to the original output of the AC / DC converter. As a result, the output voltage of the AC / DC converter can be increased. Since the energy stored in the reactor depends on the short circuit time of the semiconductor switching element, a desired output voltage can be obtained by controlling the short circuit and the open circuit by the control means. Therefore, even with a small capacity power supply facility, a high voltage can be supplied more safely with fewer components without adding a chopper circuit or the like, and the output current supplied to the magnetic field generating coil can be changed at high speed. it can.
[0009]
As a result, an output current having a desired waveform can be supplied to the gradient magnetic field coil with high responsiveness, so that it is possible to provide an MRI apparatus that is inexpensive and highly reliable and that can execute a high-speed imaging sequence such as EPI. .
[0010]
Further, in the power supply device of the present invention, the sequencer 1) short-circuits the contact connected in series with the current limiting means for preventing inrush current by a signal requesting power-on or power-on. When the voltage detector reaches a constant output voltage or both of the conditions are satisfied, the contact directly connecting the commercial power source and the reactor is short-circuited, and 3) after a certain time, the AC / DC converter is An operation signal is sent to the control means for driving control, and when the desired output voltage is reached by the voltage detector, a signal notifying that the operation is possible is sent to the control circuit for controlling the current amplifier. 4) A signal for notifying the control circuit that controls the current amplifier that the operation is impossible by a power-off signal and an operation end signal are sent to the control means for driving and controlling the AC / DC converter. After a certain time, a constant output voltage is reached by the voltage detector or both conditions are met, thereby opening the contact directly connecting the commercial power source and the reactor, and 6) after a certain time or voltage detector When a constant output voltage is reached or both of the conditions are satisfied, the contact connected to the current limiting means for preventing inrush current is opened.
[0011]
Connection between the power supply by providing such a sequencer, Ri Do is possible to control the switching control of the control and current amplifier of the switching elements sequentially, it is possible to safely Turn on and turn off.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 is a diagram showing an embodiment of a power supply device of the present invention, and shows a power supply device 1 for generating a gradient magnetic field using a three-phase power supply facility. The power supply device 1 includes contacts 11 to 16 connected to a three-phase AC commercial power supply 10, current limiting means for preventing inrush current connected in series to the contacts 11 to 13, here resistors 17 to 19, and a voltage type An AC / DC converter 20, a smoothing capacitor 71, a current amplifier 40, and a control circuit 50 for the current amplifier 40 are provided. The output of the current amplifier 40, which is an amplifier, is connected to a gradient magnetic field coil 70. Yes. In addition, the same number was shown about the element of the structure similar to the conventional power supply device shown in FIG.
[0014]
Contacts 14 to 16 that directly connect the commercial power supply 10 and the input side of the voltage type AC / DC exchanger 20 are main power supply contacts of the power supply apparatus. Further, the contacts 11 to 13 which connect the commercial power supply 10 and the input side of the voltage type AC / DC exchanger 20 via resistors 17 to 19 are inrush currents to the smoothing capacitor 71 via the diode of the voltage type AC / DC exchanger 20I. Is connected as a current limiting means for preventing inflow, and is connected when the power is turned on.
[0015]
The voltage-type AC / DC exchanger 20 is a semiconductor connected in parallel with reactors 21 to 23 connected to the AC input side and a full-bridge flywheel diode (hereinafter simply referred to as a diode) connected to the reactor and generating a DC voltage. It consists of switching elements 24-29, here IGBTs (Insulated Gate Bipolar Transistors). In such a combination of a diode and a switching element, when the switching element is short-circuited, current is allowed to flow in one direction via the switching element, and when the switching element is opened, the diode is connected to the switching element. Allow current to flow in the other direction.
[0016]
The voltage type AC / DC converter 20 further includes a control circuit 30 and a sequencer 60 as control means for driving and controlling each switching element, and the voltage detector 72 detects the output voltage of the voltage type AC / DC exchanger 20.
[0017]
The sequencer 60 is also connected to the contacts 11 to 16 that connect the three-phase AC commercial power supply 10 and the voltage-type AC / DC converter 20 and the control circuit 50 of the current amplifier 40, and the drive timing of the contacts and the switching timing of the control circuit 50 are set. While controlling, the detection value from the voltage detector 72 is input, and the control circuit 30 of the voltage type | mold AC / DC exchanger 20 is controlled based on this.
[0018]
As shown in FIG. 2, the sequencer 60 includes a SwR signal 120 that controls on / off of the contacts 11 to 13 that connect the three-phase AC commercial power supply 10 and the voltage-type AC / DC converter 20 via a resistor, and three-phase. A SwT signal 121 for on / off control of the contacts 14 to 16 that directly connect the AC commercial power supply 10 and the voltage type AC / DC converter 20 and a Conv for on / off control of the control circuit 30 of the voltage type DC / AC converter 20. A signal 122, an Amp signal 123 for controlling on / off of the control circuit 50 of the current amplifier 40, and a ready signal 124 indicating that the power supply device 1 for the nuclear magnetic resonance imaging apparatus is ready are output to the outside. Abnormal signals 125 and 126 for requesting abnormal termination processing from, a detection value 128 from the voltage detector 72, and the power supply device 1 for the nuclear magnetic resonance imaging apparatus are operated from the outside. Inputting a power signal 127 for causing the.
[0019]
The sequencer 60 operates as shown in the state transition diagram shown in FIG. 3 by these input signals and an internal timer, and sequentially controls so that the entire power supply device 1 for the nuclear magnetic resonance imaging apparatus can be safely started and terminated. To do. As shown in the lower right legend, a square box represents a state and an arrow represents a transition. The symbol attached to the arrow indicates the state transition condition on the upper side and the operation for changing the state on the lower side.
[0020]
When the power is turned on, the initial state starts from the position indicated by the start position 100 and transitions to the inspection state 101. In this state, the abnormal signals 125 and 126 from the respective control circuits are inspected, and if normal (inspection normal end condition), the state transits to the standby state 102. Thereafter, contacts 11 to 13 connected in series with current limiting means 17 to 18 are short-circuited (SwR signal 120 is turned on) by external power-on signal 127, current limiting means 17 to 18, contacts 11 to 13, reactor 21. To 23, and the capacitor 71 is charged through a diode connected in reverse parallel to the switching elements 24 to 29 (limited charge state 103). When the charging voltage reaches a certain voltage, a certain time elapses, or both conditions are satisfied, the commercial power supply 10 and the contacts 14 to 16 directly connected to the reactors 21 to 23 are short-circuited (SwT signal). 121 is turned on), and the capacitor 71 is peak-charged by a diode connected in reverse parallel to the switching elements 24-29 (fully charged state 104). After a predetermined time has elapsed after the contacts 14 to 16 are short-circuited, the Conv signal 122 for turning on / off the control circuit 30 of the voltage type DC / AC converter 20 is turned on, and the voltage type DC / AC converter 20 performs boosting (boosting) State 105). When the output voltage reaches a desired voltage, an Amp signal 123 is sent to the control circuit 50 of the current amplifier 40 to notify that the input voltage of the current amplifier becomes a desired voltage and the current amplifier is ready for operation. (Voltage stable state 106).
[0021]
When the power is shut off, the Amp signal 123 and the Conv signal 122 are turned off by the power-off signal 127 to inform that the current amplifier has become inoperable, and the voltage-type DC / AC converter 20 stops the voltage boost (stops the voltage boost) State 107). After a predetermined time has elapsed, the contacts 14 to 16 directly connected to the commercial power supply 10 and the reactors 21 to 23 are opened (the SwT signal 121 is turned off), and the discharge state 108 is obtained. Thereafter, when a certain time has elapsed, the contacts 11 to 13 connected in series with the current limiting means 17 to 18 are opened (the SwR signal 120 is turned off), and the standby state 102 is resumed.
[0022]
The case where an error is detected or the power-off signal 127 is received during the state transition is as shown in the figure.
[0023]
2 and 3, it is activated by an external power-on signal 127. However, the power-on signal 127 may be issued by itself when the sequencer main power is turned on. The ready signal to be output to the outside is not necessarily provided for the sake of convenience. Although the state is changed by the internal timer, the state may be changed only by the detection value from the voltage detector 72 without using an external timer or a timer. The error processing is performed by inputting an error signal from each control circuit, but it is not always necessary, and the abnormal boost stop state 109, the abnormal discharge state 110, and the inspection state 101 may be omitted.
[0024]
Next, the operation of the power supply device having such a configuration will be described.
FIG. 4 shows a time-axis waveform of the voltage as viewed from the midpoint of the power supply of each phase of the three-phase AC commercial power supply 10, and is input to the input side terminals 20a, 20b, and 20c of the voltage type AC / DC exchanger 20, respectively. U-phase, V-phase, and W-phase voltages are shown. Let this voltage be U>V> W at time t. In this case, as shown in FIG. 5 (a), when the upper IGBT 28 connected to the W phase is short-circuited, the voltage difference EWU between the terminals 20a and 20c is connected to the reactor 21 and the IGBT 24 connected to the U phase. The power supply voltage EWU is short-circuited through the diode, the IGBT 28, and the reactor 23 connected to the W phase. For this reason, a short circuit current flows between them, and energy is stored in the reactors 21 and 23. Similarly, due to the voltage difference EWV between the terminals 20b and 20c, a short-circuit current flows through the reactor 22 connected to the V phase, the diode connected to the IGBT 26, the IGBT 28, and the reactor 23 connected to the W phase. Energy is stored.
[0025]
Thereafter, by opening the IGBT 28, the energy stored in each of the reactors 21 to 23 is discharged through the diode connected in parallel to the IGBTs 24 and 26, the smoothing capacitor 71, and the diode connected to the IGBT 29. To charge as voltage energy.
[0026]
Further, as shown in FIG. 5B, when the lower IGBT 25 connected to the W phase is short-circuited, the voltage difference EWU between the terminal terminals 20a and 20c is connected to the reactor 21, IGBT 25, and IGBT 29 connected to the U phase. A short-circuit current flows through the connected diode and the reactor 23 connected to the W phase, and energy is stored in the reactors 21 and 23. Further, due to the voltage difference EVU between the terminals 20a and 20b, a short-circuit current flows through the reactor 21 connected to the U phase, the diode 25 connected to the IGBT 25, the IGBT 27, and the reactor 22 connected to the V phase, and the reactors 21 and 22 are energized. Is stored.
[0027]
Thereafter, by opening the IGBT 25, the energy stored in each of the reactors 21 to 23 is charged as voltage energy in the capacitor 71 in the same manner as in FIG.
[0028]
Next, as shown in FIG. 5C, when the upper IGBT 26 connected to the V-phase is short-circuited, the voltage difference EVU between the terminal terminals 20a and 20b causes the reactor 21 and the IGBT 24 connected to the U-phase to be connected. A short-circuit current flows through the diode 22 connected in parallel, the IGBT 26, and the reactor 22 connected to the V phase, and energy is stored in the reactors 21 and 22. After that, by opening the IGBT 26, the energy stored in each of the reactors 21 and 22 is discharged through the diode connected in parallel to the IGBT 24, the smoothing capacitor 71, and the diode connected to the IGBT 27, and then to the capacitor 71. Charge as voltage energy.
[0029]
Further, as shown in FIG. 5 (d), when the lower IGBT 27 connected to the W phase is short-circuited, the reactor 22, IGBT 27 connected to the V phase due to the voltage difference EWV between the terminal terminals 20b and 20c, A short-circuit current flows through a diode connected in parallel to the IGBT 29 and a reactor 23 connected to the W phase, and energy is stored in the reactors 22 and 23. After that, by opening the IGBT 26, the energy stored in each of the reactors 22 and 23 is discharged through the diode connected in parallel to the IGBT 26, the smoothing capacitor 71, and the diode connected to the IGBT 29, and then to the capacitor 71. Charge as voltage energy.
[0030]
Thus, the energy stored in the capacitor 71 due to the potential difference between the phases by short-circuiting and opening these IGBTs 25 to 28 within the time when the voltages of the U phase, the V phase, and the W phase are U>V> W. In addition, the energy stored in the reactor is charged. The control circuit 30 controls short-circuiting and opening-up of switching elements such as IGBTs so that the capacitor 71 is charged with desired electrical energy. Here, the longer the switch ON time (short circuit time), the greater the energy stored in the reactor.
[0031]
Further, by controlling the switching duty of the IGBTs 24 to 29, the input current waveform can be controlled simultaneously with the output voltage. Therefore, by controlling the input voltage waveform and the input current waveform to be in phase, the device The power factor can be improved. As a result, large output power can be obtained even in a facility having a small power supply capacity.
[0032]
1 uses a bridge in which a switching element and a diode are combined, and connects the reactor between the connection point of each diode pair constituting the bridge and the input terminal, thereby switching the switching element. When the switch is turned on, energy is stored in the reactor, and when the switching element is turned off, the capacitor 71 can be charged with this energy. Therefore, a voltage of 1.4 times or more of the power supply voltage is stored, and a high voltage power supply can be performed. The voltage stored in the capacitor 71 is applied to the gradient coil 70 when the output amplifier 40 is switched by the control circuit 50, and at this time, the output current can be changed at high speed.
[0033]
In the embodiment shown in FIG. 1, the case where the commercial power source has three phases has been described. However, the present invention is not limited to three phases and may be a single phase. In addition to IGBTs, switching elements such as bipolar transistors and MOSFETs can also be used as the switching elements. Further, in the embodiment of FIG. 1, the case where such a combination of the switching element and the flywheel diode is used on both the upper side and the lower side of each arm of the bridge has been described, but it is not necessary to perform step-down control of the output voltage. It is also possible to replace the upper or lower side with a diode. As a result, the cost can be reduced with simplified control.
[0034]
FIG. 6 shows a case where a single-phase commercial power source is used, IGBTs 24 and 26 are used only on the upper side of the bridge arm, and diodes 125 and 127 are used on the lower side. In FIG. 6, only the AC / DC converter 20 ′ and the smoothing capacitor 71 are shown, but a commercial AC power supply is connected to the input side terminals 20e and 20f of the AC / DC converter 20 ′ via contacts. The output side of the capacitor 71 is connected to the gradient coil through an output amplifier, and the control circuit (30) for controlling the driving of the IGBT constituting the bridge of the AC / DC converter 20 ′ is connected. Further, the control circuit of these output amplifiers and the control circuit of the AC / DC converter 20 ′ are controlled by commands of the sequencer as in the embodiment of FIG. Further, in this embodiment, the reactor 21 is connected to only one of the input side terminals, but the reactor may be connected to both sides as in the embodiment of FIG.
[0035]
In such a power supply device of FIG. 6, the IGBT 26 is short-circuited in a time when the input voltage value of one terminal 20e is higher than the input voltage value of the other terminal 20f, whereby the reactor 21, the diode connected to the IGBT 24, and the IGBT 26 A short-circuit current flows through, energy is accumulated in the reactor 21, and the energy is charged in the capacitor 71 by opening the IGBT 26. In addition, when the input voltage value of the terminal 20f is higher than the input voltage value of the terminal 20e, the IGBT 24 is short-circuited, whereby a short-circuit current flows through the diode connected to the IGBT 26, the IGBT 24, and the reactor 21, and energy is supplied to the reactor 21. Is stored, and the energy is charged in the capacitor 71 by opening the IGBT 24. By controlling the IGBT on the terminal having the lower voltage value to be short-circuited and opened, a voltage higher than the power supply voltage is accumulated in the capacitor 71, so that a large output power is obtained as in the embodiment of FIG. be able to.
[0036]
【The invention's effect】
As described above, according to the present invention, as an AC / DC converter, a voltage obtained by combining a bridge circuit of a switching element arm connected in parallel with a flywheel diode and a reactor connected to the AC input side of the bridge circuit. Type AC / DC converter, and the switching element is controlled by the control means so that the output voltage of the AC / DC converter becomes a desired value. A high voltage can be supplied to the connected current amplifier, whereby the output current to the magnetic field generating coil can be changed at high speed.
[0037]
Further, since the gradient magnetic field current can be changed at high speed, it is possible to provide an MRI apparatus that is highly reliable and that can handle a high-speed imaging sequence such as EPI at low cost.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a power supply device for an MRI apparatus according to the present invention. FIG. 2 is a diagram showing input / output signals of a sequencer in the power supply device of FIG. 4 is a diagram showing input voltage waveforms in the power supply device of FIG. 1. FIGS. 5A to 5D are diagrams for explaining drive control of switching elements in the power supply device of FIG. 1. FIG. FIG. 7 is a block diagram showing an embodiment of a power supply device for an MRI apparatus according to FIG. 7 is a block diagram showing a conventional power supply device.
10 Commercial power supply 11-13 Contact (second contact)
14-16 Contact 17 Resistance (Current limiting means)
20, 20 ′ Voltage type AC / DC converters 21 to 23 Reactors 24 to 29 Switching element 30 Control circuit (control means)
40 Output current amplifier (current amplifier)
50 control circuit 60 sequencer (control means)
70 Gradient magnetic field coil (magnetic field generating coil)
71 Capacitor 72 Voltage detector

Claims (1)

An AC / DC converter that is connected to a commercial AC power source through a contact and converts AC to DC, and a current amplifier that inputs the output of the AC / DC converter and supplies a current of arbitrary waveform to the magnetic field generating coil of the magnetic resonance imaging apparatus And a power supply device for a magnetic resonance imaging apparatus comprising a control circuit for switching and controlling the current amplifier,
A bridge circuit in which a current limiting means for preventing inrush current connected in parallel to the contact and a second contact connected in series with the current control means are provided, and the AC / DC converter includes a plurality of diodes connected in parallel And a semiconductor switching element connected in parallel to at least one diode of the pair of diodes, and a reactor connected between the AC input side of the bridge circuit and the contact, and controls driving of the semiconductor switching element Means and a sequencer connected to the control means, the contact point and the control circuit of the current amplifier, the sequencer comprising:
1) Short-circuit a contact connected in series with the current limiting means for preventing inrush current by a power-on or power-on request signal,
2) short-circuiting the contact directly connecting the commercial power source and the reactor after a certain period of time or a constant output voltage is reached by the voltage detector, or both conditions are satisfied,
3) Further, after a certain time, an operation signal is sent to the control means for driving and controlling the AC / DC converter, and when the desired output voltage is reached by the voltage detector, the control circuit for controlling the current amplifier is operable. Send a signal that there is,
4) On the other hand, by a power-off signal, a signal that informs the control circuit that controls the current amplifier that it cannot operate, and an operation end signal that is sent to the control means that drives and controls the AC / DC converter,
5) Open a contact directly connecting the commercial power source and the reactor after a certain period of time or when a constant output voltage is reached by the voltage detector, or both conditions are met,
6) A contact connected to the current limiting means for preventing the inrush current is opened when a constant output voltage is reached by a voltage detector after a certain period of time or when both conditions are satisfied. A power supply device for a magnetic resonance imaging apparatus.

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