JPH105189A - Power power unit for magnetic resonance imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power power unit for an MRI device capable of stable output by a high speed response. SOLUTION: A power power unit 1 for an MRI device is provided with a voltage type AC-DC converter 10 to covert AC voltage supplied from a commercial AC power source 2 into DC voltage, a control means 20 to control the voltage type AC-DC converter 10 by using a current value of input current to the voltage type AC-DC converter 10, a voltage value of output voltage of the voltage type AC-DC converter 10 and a voltage command value inputted from an external part as input and an electric current amplifier 30 to amplify an output current of the voltage type AC-DC converter 10, and is also provided with an electric current detecting means 23 to detect an electric current inputted to the electric current amplifier 30. The control means 20 performs feedforward control on the voltage type AC-DC converter 10 so that an input current to the electric current amplifier 30 and an output current from the voltage type AC-DC converter 10 become equal to each other by inputting a detecting value of the electric current detecting means 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for a magnetic resonance imaging apparatus (hereinafter referred to as a "power supply for an MRI apparatus"), and is particularly characterized by control with good responsiveness for maintaining a stable output. It relates to an MRI apparatus.

[0002]

2. Description of the Related Art In an MRI apparatus, a high-speed imaging method such as an echo planar imaging method has been developed, and accordingly, an increase in an output current of a power supply for generating a magnetic field and a reduction in a rise time thereof are required. It tends to be. In order to improve the change speed of the output current of the power supply for generating a magnetic field, it is necessary to increase the input voltage and stabilize the input voltage.
Therefore, as a switching power supply for generating a magnetic field for generating a static magnetic field or a gradient magnetic field, a stabilized power supply apparatus for an MRI apparatus having a voltage-type AC / DC converter has been used.

FIG. 4 shows a known power supply device for generating a gradient magnetic field. This power supply 1 '
Converts the AC supplied from the commercial power supply 2 into DC by the voltage type AC / DC converter 10, smoothes it by the capacitor 21, amplifies it by the current amplifier 30, and then drives the gradient coil 3. AC / DC converter 10 used here
Are reactors 11 to 13 connected to the commercial power supply 2
A flywheel diode connected in full bridge to the reactors 11 to 13; and insulated gate bipolar transistors (IGBT) 14 to 19 which are switching elements connected in parallel to the flywheel diode.

The output voltage of such a voltage type AC / DC converter 10 is controlled by a control circuit 20 '. That is, the control circuit determines the input current to the voltage type AC / DC converter 10 detected by the current detectors 24 and 25 and the voltage detection means 2
The feedback control of the output voltage is performed based on the voltage of the capacitor 21 detected by Step 2 and a voltage command value input from the outside. This control is specifically performed by the reactors 11 to 13 connected to the commercial power supply and the switching element 14.
To 19, the voltage charged in the smoothing capacitor 21 is controlled to a high voltage by changing the duty of the switching elements 14 to 19.

The output current of the current amplifier 30 is feedback-controlled by the control circuit 40, and the amplification factor of the current amplifier 30 is determined based on the current value detected by the current detector 43 and the specified current value input from the outside. To control the current amplifier 30.

[0006]

In such a conventional power supply device, in controlling the output voltage of the voltage type AC / DC converter 10, feedback control is performed using the output voltage. As described below, the current has a plurality of delays in the control.

First, since the output voltage of the AC / DC converter 10 fluctuates in proportion to the integrated value of the load current which is the output of the current amplifier 30, when the feedback control is performed using this output voltage, the load current is output to the output. There is a first order delay before it takes effect. Further, a primary delay occurs when the duty, which is the control amount, is converted into an input current to the AC / DC converter 10, and a primary delay occurs when the input current is further converted into a voltage charged in the capacitor 21. As a result, the controlled output voltage has a third order delay with respect to the current (disturbance) flowing by driving the coil.

Due to such a control delay, the conventional power supply device cannot perform high-speed feedback control with respect to a change in load, and the output voltage sometimes becomes unstable. An object of the present invention is to provide a power supply device for an MRI apparatus that responds at high speed in order to solve such a problem.

[0009]

In order to achieve the above object, a power supply for an MRI apparatus according to the present invention is a power supply for supplying a direct current through a current amplifier to a magnetic field generating means for a magnetic resonance imaging apparatus. There is a voltage type AC / DC converter for converting an AC voltage supplied from a commercial AC power supply into a DC voltage, and a detection value of an input current to the voltage type AC / DC converter and an output voltage of the voltage type AC / DC converter. Control means for controlling the output voltage of the voltage type AC / DC converter using the detected value and a voltage command value inputted from the outside as inputs, and current detection for detecting the current inputted from the voltage type AC / DC converter to the current amplifier The control means uses the value of the input current detected by the current detector to control the output voltage, so that the current input to the current amplifier and the output current from the voltage type AC / DC converter are equal. It is to feed-forward control a voltage-type AC-DC converter for Kunar.

[0010] In the power supply device having such a configuration, the input current to the current amplifier detected by the current detection means is fed forward to the control means for controlling the output voltage. And a stable power supply device for the MRI apparatus can be provided. Particularly when used as a power supply for generating a gradient magnetic field, the gradient magnetic field current can be changed at a high speed,
Highly reliable M that can support high-speed sequences such as EPI
An RI device can be provided.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. It should be noted that FIG.
The same components as those described above are denoted by the same reference numerals.

The power supply device 1 for an MRI apparatus is connected to a three-phase AC commercial power supply 2 and is used to supply an output current to a gradient coil 3 as a load. The power supply device 1 includes a voltage type AC / DC converter 10 for converting an AC voltage supplied from a commercial power supply 2 into a DC voltage, and current detecting means 24 and 2 for detecting a current input to the AC / DC converter 10.
5, a capacitor 21 for smoothing the output voltage from the AC / DC converter 10, a voltage detector 22 for detecting the voltage of the capacitor 21, and a gradient magnetic field coil which amplifies the output current of the AC / DC converter 10 and serves as a load. 3; a current detector 23 for detecting a current input to the current amplifier 30; a current detector 43 for detecting an output current from the current amplifier 30; ,
Control for controlling the AC / DC converter 10 using the current value detected by the voltage detector 25, the voltage value detected by the voltage detector 22, the current value detected by the current detector 23, and the voltage command value input from the outside as inputs. The control circuit 40 includes a circuit 20 and a control circuit 40 that controls the current amplifier 30 using a current value detected by the current detector 43 and a current command value input from the outside as inputs. The control circuit 40 includes the current detector 4
3 and a current designation value inputted from the outside, and the amplification factor is obtained based on these inputs to control the current amplifier 30.

The AC / DC converter 10 includes reactors 11 to 13 connected to the commercial power supply 2 and reactors 11 to 13
And a IGBT 14 to 19, which are switching elements connected in parallel with the flywheel diode.

The power supply device 1 having such a configuration operates as follows. First, the AC supplied from the commercial power supply 2 is supplied to the IGBTs 14 to 19 via the reactors 11 to 13.
Input to the bridge circuit consisting of
The average potentials Eua and Eva between the upper and lower arms are controlled by controlling the on / off time of T14 to T19, that is, the duty.
And Ewa are determined, whereby a predetermined output voltage Ecl across both ends of the capacitor 21 is output. That is, the average potentials Eua, Eva and Ewa and the potential E of each phase of the commercial power supply 2
The integral of the difference between u, Ev and Ew is determined by the reactors 11 to 13
Is proportional to the currents Iu, Iv, and Iw flowing through the capacitor 21, and the sum of these one-way currents flows into the capacitor 21 as the output current Ia. Then, a voltage Ecl proportional to the integrated value of the current is applied to both ends of the capacitor 21.

The output voltage Ecl is applied to both ends of the current amplifier 30, and the control circuit 40 controls the amplification factor of the current amplifier 30 so that a predetermined current given to the gradient coil 3 by the current command value flows. Become.

Here, the detection value Ecl from the voltage detector 22, that is, the fluctuation of the voltage applied to both ends of the capacitor 21 connected to the output of the AC / DC converter 10 and smoothing the output voltage is represented by the following equation: That is, the AC / DC converter 1
It is proportional to the integral value of the sum of the output current Ia of 0 and the input current If of the current amplifier 30. The input current I of the current amplifier 30
f is a disturbance in the control system that controls the output current Ia via the output voltage Ecl. Input voltage Ecl of current amplifier 30
In order to maintain a stable voltage without fluctuation, it is only necessary to supply a current to the smoothing capacitor 21. Therefore, in the present invention, the input current If of the current amplifier 30 and the Control is performed so that the values of the output current Ia become equal.

For this reason, in this embodiment, the input current If to the current amplifier 30 is detected by the current detector 23 and used for control by the control circuit 20. The use of the currents Iu and Iv input to the voltage-type AC / DC converter 10 detected by the current detectors 24 and 25 and the voltage Ecl across the capacitor 21 detected by the voltage detection means 22 is the same as in the related art. It is.

The control by the control circuit 20 will be described with reference to FIG. U phase used in this description,
The v-phase and the w-phase represent each phase of a three-phase AC commercial power supply.

First, a proportional integral (PI) is calculated from the output voltage Ecl detected by the voltage detector 22 and the voltage command value Eclr.
The current value Ir as an input target is calculated so that the difference between the two becomes zero by the control. In this embodiment, the input current If, which is a disturbance, is input to the current amplifier 30 by feedforward and added to the current value Ir, and the proportional gain K
The current value Ir ′ to be input is calculated by multiplying by m. Then, the current value Ir ′ is multiplied by sin (ωt) and sin (ωt−2π / 3), respectively, to calculate the u-phase and v-phase target currents Iur and Ivr of the commercial power supply 2. Further, the current Iu flowing through the reactor 11 and the current Iv flowing through the reactor 12 are fed back, and the difference between the target current Iur and the current Iu and the difference between the target current Ivr and the current Iv are respectively multiplied by a proportional gain Kc to perform proportional (P) control. Thus, the duty for each phase of the commercial power supply 2 is calculated.

From the relationship between the duty and the output voltage Ecl, the average potentials Eua, Eva and Ewa between the upper and lower arms of the IGBTs 14 to 19 are determined. Average potential Eua, Eva
The integration of the difference between Ewa and Ewa and the potentials Eu, Ev and Ew of the respective phases of the commercial power supply 2 is based on the current I
It is proportional to u, Iv, and Iw, and the sum of these unidirectional currents flows into the capacitor 21 as the output current Ia.

On the other hand, the current amplifier 3
Although the input current If to 0 is generated, in such control, since the input current If to the current amplifier 30 and the output current Ia from the voltage type AC / DC converter 10 are controlled to be equal, No current flows through the capacitor 21, and the output voltage Ecl is kept constant without fluctuation.

As described above, in the control according to the present invention, the feed-forward control of the input current If to the current amplifier 30, which is a disturbance, can reduce the control delay of the output voltage Ecl due to the disturbance. On the other hand, the input currents Iu, Iv and Iw of each phase flowing into the AC / DC converter 10 controlled by changing the duty have a first-order lag. Therefore, when the feedforward control is performed in the power supply device for an MRI apparatus according to the present invention, the output voltage Ecl is determined only by the primary delay of the input currents Iu, Iv and Iw of each phase.
Can be controlled to be constant. Therefore, voltage control can be performed with good responsiveness.

The power supply device for an MRI apparatus according to the present invention is not limited to the configuration shown in FIG. 1. For example, FIG. 1 shows a reactor connected to the commercial power supply 2 provided in all phases. , At least two reactors are required.
Also, the commercial power supply 2 may be a single-phase one instead of a three-phase one. In this case, it is necessary to provide at least one reactor connected to the commercial power supply 2.

In the voltage type AC / DC converter 10, elements other than the IGBTs 14 to 19 may be used as switching elements. For example, a field effect transistor (MOSFET) capable of switching at a higher speed than the IGBT.
May be used. In addition, one of the upper and lower arms
A diode can be used without using a switching element such as a BT, and in this case, there is an advantage that it can be replaced with an inexpensive component.

Further, in this embodiment, a current detector 23 is provided near the input terminal to the current amplifier 30 to detect the input current If to the current amplifier 30, so that the input current If is directly detected. However, the current detector 23 is provided at a position for detecting the output current of the capacitor 21 connected to the output of the voltage type AC / DC converter 10 and is detected as the sum with the output current Ia from the voltage type AC / DC converter 10. It is also possible. In this case as well, the same effects as in the embodiment of FIG. 1 can be obtained. However, since the current flowing through the capacitor 21 is an alternating current, the configuration of a detector such as a current transformer becomes easy, and the detection becomes easy.

FIG. 3 shows an embodiment of a power supply device incorporating such a changeable element. In this embodiment, a single-phase AC commercial power supply 2 "is used, and the reactor is one.
Connected. In addition, the voltage type AC / DC converter 1
0 "is composed of four arms, and the upper arm has full-bridge diodes 114 and 11 for generating a DC voltage.
6 and IGBTs 15 and 17 connected to the lower arm in parallel with the flywheel diode. Further, the current detector 23 ″ as a means for detecting the input current If to the current amplifier 30 is a voltage-type AC / DC converter 10
Is provided at a position for detecting the output current of the capacitor 21 connected to the output of. In this case, the current detected by the current detector 23 "is the sum of the input current If to the current amplifier 30 and the output current Ia from the AC / DC converter 10, and the detected value is fed to the control circuit 20". Be worded.

That is, in the power supply device shown in FIG. 3, the control circuit 20 "controls the input current If, which is a disturbance, in a feed-forward manner, similarly to the control circuit 20 of the embodiment shown in FIG. The current detected by the capacitor 23 ", that is, the current flowing through the capacitor 21 is controlled to be zero. This means that the input current If to the current amplifier 30 and the voltage type AC / DC converter 10 in the power supply device shown in FIG.
The output voltage Ecl of the voltage-type AC / DC converter 10 ″ can be maintained constant. Similarly, the control circuit 20 ″ can also maintain the output voltage Ecl of the voltage-type AC / DC converter 10 ″ constant. A point for controlling the gain of the AC / DC converter 10 by calculating an input target current value Ir from the output voltage Ecl detected by the voltage detector 22 and the voltage command value Eclr so that the difference between the two becomes zero. Is similar to the control circuit 20 of FIG.

Further, in each of the embodiments shown in FIGS. 1 and 3, when the control circuits 20, 20 "control the current value Ir from the output voltage Ecl and the voltage command value Eclr, the proportional integration as shown in FIG. Not only the (PI) control but also a known control method such as proportional / integral / differential (PID) control can be adopted.

[0029]

The power supply for an MRI apparatus according to the present invention is an MR apparatus.
In controlling the output voltage of the voltage type AC / DC converter that supplies power to the current amplifier connected to the magnetic field generating means for the I device, using its detection value and a voltage command value input from the outside as an input, it is a disturbance. By detecting the input current to the current amplifier and feeding it forward to the control system, it is possible to control the output current from the voltage type AC / DC converter and the input current to the current amplifier to be equal, thereby delaying the control. Can be reduced. For this reason, it is possible to provide a power supply for a magnetic field generator with extremely high responsiveness. Therefore, according to the power supply device of the present invention, the current for generating a magnetic field can be changed at a high speed, which is suitable for a high-speed sequence such as an echo planar imaging method. In addition, the output from the current amplifier becomes stable, and a device with a low current change rate can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a power supply device for an MRI apparatus of the present invention.

FIG. 2 is a control block diagram of a voltage type AC / DC converter according to the present invention.

FIG. 3 is a diagram showing another embodiment of the power supply device for an MRI apparatus of the present invention.

FIG. 4 is a diagram showing a conventional power supply device for an MRI apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power supply device for MRI apparatus 2 Commercial power supply 10 Voltage-type DC / AC converter 20, 20 "Control circuit (Control means) 23 Current detector (Current detecting means) 30 Current amplifier 40 Control circuit.

Claims (1)

[Claims] 1. A power supply device for supplying a DC current to a magnetic field generating means for a magnetic resonance imaging apparatus via a current amplifier, wherein a voltage type AC / DC converter for converting an AC voltage supplied from a commercial AC power supply into a DC voltage. And a voltage-type AC / DC converter which receives a detected value of an input current to the voltage-type AC / DC converter, a detected value of an output voltage of the voltage-type AC / DC converter, and a voltage command value input from outside. Control means for controlling the output voltage of the power supply, comprising: a current detector for detecting a current input to the current amplifier from the voltage-type AC-DC converter, the control means, the control means, In the control, using the detected value of the input current detected by the current detector, the current input to the current amplifier and the output current from the voltage type AC / DC converter become equal. A power supply device for a magnetic resonance imaging apparatus characterized in that the voltage type AC / DC converter is feed-forward controlled as described above.