X-ray CT device, x-ray diagnostic device, and control method for x-ray diagnostic device

Abstract

To enable an inverter circuit of an X-ray high voltage device to prevent a switching loss from increasing even when a load varies.SOLUTION: An X-ray CT device comprises an X-ray tube and an X-ray high voltage device for supplying high voltage power supply to the X-ray tube. The X-ray high voltage device comprises a DC power supply, a full-bridge circuit, a transformer, an auxiliary inductor, a switch for turning on / off the auxiliary inductor, and a controlling unit. The full-bridge circuit has a first arm and a second arm. The first arm is composed of a first switching element and a second switching element connected in series. The second arm is composed of a third switching element and a fourth switching element connected in series. To the first, second, third, and fourth switching elements, first, second, third, and fourth capacitors are connected in parallel, respectively.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray CT apparatus, an X-ray diagnostic apparatus, and a method for controlling an X-ray diagnostic apparatus. [Background technology]

[0002] 2. Description of the Related Art X-ray diagnostic apparatuses, such as X-ray CT (Computed Tomography) apparatuses, X-ray angiography apparatuses, and X-ray TV apparatuses, have an X-ray tube that generates X-rays and an X-ray high voltage device that supplies a high voltage to the X-ray tube.

[0003] Many X-ray high voltage devices used in X-ray diagnostic equipment are configured with a converter circuit, an inverter circuit, a transformer, and a rectifier circuit. The converter circuit first converts the AC from the commercial power source into DC. The inverter circuit converts the DC converted by the converter circuit into AC (pulse signal) of a specified frequency and voltage by switching it with a switching element. The converted AC signal is then converted to a specified voltage by a transformer, and finally the AC is converted to DC of the specified voltage by the rectifier circuit.

[0004] The X-ray high voltage device includes electronic components such as coils, capacitors, and transformers. The higher the switching frequency of the switching elements, the more miniaturized these electronic components can be.

[0005] However, in general, increasing the switching frequency increases switching loss, so a technique called zero voltage switching (ZVS) is known as a technique for reducing switching loss.

[0006] On the other hand, it is known that zero voltage switching does not necessarily produce the expected effect when the load fluctuates, for example when the output of the X-ray tube, such as the tube voltage or tube current, changes, and switching losses increase. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-073532 A Summary of the Invention [Problem to be solved by the invention]

[0008] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to prevent an increase in switching loss in an inverter circuit of an X-ray high voltage device even when the load fluctuates. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0009] An X-ray CT apparatus according to an embodiment includes an X-ray tube, an X-ray high voltage device that supplies a high voltage power source to the X-ray tube, and a control unit. The X-ray high voltage device has a DC power source, a first arm, and a second arm, and is a full bridge circuit connected to the DC power source, the first arm being configured by connecting a first switching element and a second switching element in series, the second arm being configured by connecting a third switching element and a fourth switching element in series, first, second, third, and fourth capacitors being connected in parallel to the first, second, third, and fourth switching elements, respectively, and the switching of each of the first and second switching elements and the switching of each of the third and fourth switching elements are controlled by a control circuit. The switching element includes a full bridge circuit in which different switching elements are controlled with different phase differences, a transformer having one end of a primary winding connected to a connection point between the first switching element and the second switching element and the other end of the primary winding connected to a connection point between the third switching element and the fourth switching element, an auxiliary inductor configured to be connectable in parallel to the primary winding of the transformer, and a switch configured to turn on and off the electrical connection between the auxiliary inductor and the primary winding, and the control unit controls the on and off of the switch. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram showing an example of the configuration of an X-ray CT apparatus according to a first embodiment. [Diagram 2] FIG. 1 is a block diagram showing an example of the configuration of an X-ray high voltage device. [Diagram 3] FIG. 2 is a diagram for explaining the operational concept of zero voltage switching. [Figure 4] 5 is a timing chart showing operation timings of a phase-shift full-bridge circuit according to an embodiment. [Diagram 5] FIG. 1 is a first diagram illustrating the operation of each switching mode of a full-bridge circuit. [Figure 6] FIG. 2 is a second diagram illustrating the operation of each switching mode of the full-bridge circuit. [Figure 7]FIG. 3 is a third diagram illustrating the operation of each switching mode of the full-bridge circuit. [Figure 8] FIG. 4 is a fourth diagram illustrating the operation of each switching mode of the full-bridge circuit. [Figure 9] 6 is a flowchart showing a first operation example of connecting and disconnecting an auxiliary inductor. [Figure 10] 10 is a flowchart showing a second operation example of connecting and disconnecting an auxiliary inductor. [Figure 11] 10 is a flowchart showing a third operation example of connecting and disconnecting an auxiliary inductor. [Figure 12] 10 is a flowchart showing a fourth operation example of connecting and disconnecting an auxiliary inductor. [Figure 13] FIG. 11 is a block diagram showing an example of the arrangement of an X-ray CT apparatus according to a second embodiment. [Figure 14] FIG. 11 is a diagram for explaining the operation concept of the X-ray high voltage generator according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of an X-ray diagnostic apparatus will be described with reference to the drawings. The X-ray diagnostic apparatus of the embodiment includes an X-ray CT apparatus, an X-ray angiography apparatus, an X-ray TV apparatus, and a general X-ray imaging apparatus, but the embodiment of an X-ray CT apparatus will be described in detail below.

[0012] (First embodiment) Fig. 1 is a block diagram showing an example of the configuration of an X-ray CT apparatus 1 according to the first embodiment. As shown in Fig. 1, the X-ray CT apparatus 1 includes a gantry 10, a bed 30, and a console 40. The gantry 10 includes a rotating frame 13, and components such as an X-ray generator 20, an X-ray high voltage device 21, and an X-ray detector 25 that are mounted and fixed to the rotating frame 13. The gantry 10 is also called a gantry.

[0013] As shown in FIG. 1, in this embodiment, the direction of the rotation axis of the rotating frame 13 when the rotating frame 13 is in a non-tilted state, or the longitudinal direction of the table top 33 of the bed device 30, is defined as the z-axis direction, the direction of an axis perpendicular to the z-axis direction and horizontal to the floor surface is defined as the x-axis direction, and the direction of an axis perpendicular to the z-axis direction and perpendicular to the floor surface is defined as the y-axis direction.

[0014] The X-ray generating device 20 includes an X-ray tube 11, a wedge 16, and a collimator 17. The X-ray tube 11 is a vacuum tube that generates X-rays by application of high voltage from an X-ray high voltage device 21. The X-rays irradiated from the X-ray tube 11 pass through the wedge 16 and the collimator 17, then pass through the subject P and reach the X-ray detection device 25.

[0015] The wedge 16 is a filter for adjusting the amount of X-rays irradiated from the X-ray tube 11. For example, the wedge 16 is a filter for attenuating the X-rays irradiated from the X-ray tube 11 so that the X-rays irradiated from the X-ray tube 11 to the subject P have a predetermined distribution. For example, the wedge 16 is formed by processing aluminum.

[0016] The collimator 17 is used to narrow the irradiation range of the X-rays transmitted through the wedge 16, and is sometimes called an X-ray movable aperture. The collimator 17 narrows the irradiation range of the X-rays by forming a slit by combining multiple lead plates or the like, for example.

[0017] The X-ray detection device 25 includes an X-ray detector 12 and a DAS (Data Acquisition System) 18. The X-ray detector 12 detects X-rays that have passed through the subject P, and converts them into an electrical signal corresponding to the amount of X-rays.

[0018] The X-ray detector 12 has an X-ray detection element row in which a plurality of X-ray detection elements are arranged in the channel direction along one arc centered on the focal point of the X-ray tube 11. Furthermore, the X-ray detector 12 has a structure in which a plurality of X-ray detection element rows are arranged in a slice direction perpendicular to the channel direction.

[0019] The X-ray detector 12 is configured to include, for example, a grid, a scintillator array, and an optical sensor array. The grid is disposed on the X-ray incident surface of the scintillator array, and has an X-ray shielding plate having a function of absorbing scattered X-rays. The grid is sometimes called a collimator (one-dimensional collimator or two-dimensional collimator). The scintillator array is an array of multiple scintillators. Each scintillator has a scintillator crystal that outputs light with a photon amount corresponding to the amount of incident X-rays. The optical sensor array is an array of multiple optical sensors. Each optical sensor converts the light output from the scintillator into an electrical signal corresponding to the amount of light. Instead of the above-mentioned configuration of the scintillator and the optical sensor, a configuration having a semiconductor element that directly converts the incident X-ray into an electrical signal may be used.

[0020] The DAS 18 is configured to include an amplifier circuit, an AD conversion circuit, a data transfer circuit, etc. The electrical signals output from each X-ray detection element of the X-ray detector 12 are amplified by the amplifier circuit, and then converted from analog signals to digital signals by the AD conversion circuit, generating detection data.

[0021] The detection data generated by the DAS 18 is transmitted, for example, by optical communication from a transmitter having a light-emitting diode (LED) provided on the rotating frame 13 to a receiver having a photodiode provided on a non-rotating portion (e.g., a fixed frame) of the gantry 10, and then transferred to the console device 40. The fixed frame is a frame that rotatably supports the rotating frame 13. Note that the method of transmitting the detection data from the rotating frame 13 to the non-rotating portion of the gantry 10 is not limited to optical communication, and any method of non-contact data transmission may be used.

[0022] The control device 15 has, for example, a processor provided on a control board, a memory circuit, and a driving mechanism such as a motor and an actuator. The control device 15 has a function of receiving an input signal from an input interface 43 attached to the console device 40 or the gantry device 10 and controlling the gantry device 10 and the bed device 30. For example, the control device 15 receives an input signal and controls the rotation of the rotating frame 13, the tilt of the gantry device 10, and the operation of the bed device 30 and the tabletop 33. The control device 15 may be provided in the gantry device 10 as shown in FIG. 1, or may be provided in the console device 40.

[0023] The bed device 30 is a device on which the subject P to be scanned is placed and moved, and includes a base 31, a bed driving device 32, a top board 33, and a support frame .

[0024] The base 31 is a housing that supports the support frame 34 so as to be movable in the vertical direction (y direction). The bed driving device 32 is a motor or actuator that moves the top board 33, on which the subject P is placed, in the longitudinal direction (z direction) of the top board 33. The top board 33, which is provided on the upper surface of the support frame 34, is a plate on which the subject P is placed.

[0025] The bed driving device 32 may move the support frame 34 in the longitudinal direction (z direction) of the tabletop 33 in addition to the tabletop 33. The bed driving device 32 may also move the base 31 of the bed device 30 together. When the present invention is applicable to upright CT, a method of moving a patient movement mechanism corresponding to the tabletop 33 may be used.

[0026] The console device 40 has a memory 41, a display 42, an input interface 43, a network connection circuit 44, and a processing circuit 45. In this specification and the drawings, the console device 40 is described as being separate from the gantry device 10, but the gantry device 10 may include some or all of the components of the console device 40. Also, in this specification and the drawings, the console device 40 is described below as a single console that executes all of the functions, but these functions may be executed by multiple consoles.

[0027] The memory 41 includes a processor-readable recording medium, such as a semiconductor memory element such as a random access memory (RAM), a flash memory, a hard disk, an optical disk, etc. The memory 41 also stores, for example, projection data, reconstructed image data, and previously acquired volume data of the subject P.

[0028] The display 42 displays various kinds of information. For example, the display 42 outputs medical images (CT images) generated by the processing circuit 45, a GUI (Graphical User Interface) for receiving various operations from a user, and the like. For example, the display 42 is a liquid crystal display, a CRT (Cathode Ray Tube) display, an OLED (Organic Light Emitting Diode) display, or the like. The display 42 may be provided on the gantry device 10. The display 42 may be a desktop type, or may be configured as a tablet terminal capable of wireless communication with the main body of the console device 40.

[0029] The input interface 43 receives various input operations from the user, converts the received input operations into electrical signals, and outputs the electrical signals to the processing circuit 45. For example, the input interface 43 receives from the user collection conditions for collecting projection data, reconstruction conditions for reconstructing CT images, image processing conditions for generating post-processed images from CT images, and the like. For example, the input interface 43 is realized by a mouse, a keyboard, a trackball, a switch, a button, a joystick, a touchpad for performing input operations by touching an operation surface, a touchscreen in which a display screen and a touchpad are integrated, a non-contact input circuit using an optical sensor, and a voice input circuit. The input interface 43 may be provided in the gantry device 10. The input interface 43 may be configured by a tablet terminal capable of wireless communication with the main body of the console device 40.

[0030] The network connection circuit 44 implements various information communication protocols according to the form of the network. The network connection circuit 44 connects the X-ray CT apparatus 1 to other devices such as an image server according to the various protocols. This connection can be an electrical connection via an electronic network. Here, the electronic network means a general information communication network using electrical communication technology, and includes a wireless / wired hospital backbone LAN (Local Area Network) and the Internet network, as well as a telephone communication line network, an optical fiber communication network, a cable communication network, and a satellite communication network.

[0031] The processing circuit 45 reads and executes the programs stored in the memory 41 to control the overall operation of the X-ray CT apparatus 1. It is Sessa.

[0032] (X-ray high voltage device) Next, a description will be given of the configuration and operation of the X-ray high voltage device 21 of the X-ray CT apparatus 1 according to the first embodiment. FIG.

[0033] The X-ray high voltage device 21 includes an AC / DC converter 200, a full bridge circuit 210, a transformer 220, and a rectifier circuit 230. The X-ray high voltage device 21 may further include a load measuring circuit 250 and a control circuit 240.

[0034] The AC / DC converter 200 converts, for example, a three-phase AC power supply or a single-phase AC power supply into a DC power supply of a predetermined voltage. The AC / DC converter 200 functions as a DC power supply that is input to a full-bridge circuit 210.

[0035] The full bridge circuit 210 is a circuit that functions as an inverter circuit of the X-ray high voltage device 21. The full bridge circuit 210 has a first arm 211 and a second arm 212. The first arm is configured by connecting a first switching element Q1 and a second switching element Q2 in series. The second arm is configured by connecting a third switching element Q3 and a fourth switching element Q4 in series.

[0036] The first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4 are, for example, semiconductor switching elements such as MOSFETs (Metal-Oxide-Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).

[0037] A first diode D1, a second diode D2, a third diode D3, and a fourth diode D4 are connected in parallel to the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4, respectively. The first, second, third, and fourth diodes D1, D2, D3, and D4 are, for example, body diodes (or parasitic diodes) of the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4, respectively.

[0038] A first capacitor C1, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4 are connected in parallel to the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4, respectively. The first, second, third, and fourth capacitors C1, C2, C3, and C4 are, for example, external capacitors for the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4, respectively, but may be parasitic capacitors of the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4, respectively.

[0039] On / off signals based on switching timing described later are applied to the gates of the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4, respectively, and the DC power supply input to the full bridge circuit 210 is converted into an AC pulse power supply.

[0040] The switching timing of each of the first and second switching elements Q1, Q2 constituting the first arm and the switching timing of each of the third and fourth switching elements Q3, Q4 constituting the second arm are controlled with a predetermined phase difference α, as described later.

[0041] The output of the full-bridge circuit 210 is input to the transformer 220. More specifically, one end of a primary winding 221 of the transformer 220 is connected to a connection point between a first switching element Q1 and a second switching element Q2, and the other end of the primary winding 221 is connected to a connection point between a third switching element Q3 and a fourth switching element Q4.

[0042] The voltage of the AC pulse power supply output from the full bridge circuit 210 is converted by the transformer 220 into a voltage according to the winding ratio of the primary side and the secondary side.

[0043] The X-ray high voltage device 21 of the embodiment is configured to include an auxiliary inductor 300. The auxiliary inductor 300 is connected in series with an auxiliary inductor switch 301. When the switch 301 is turned on, the auxiliary inductor 300 is connected in parallel with the primary winding 221 of the transformer 220. On the other hand, when the switch 301 is turned off, the auxiliary inductor 300 is disconnected from the full bridge circuit 210 and the transformer 220. The operation of the switch 301 and the function and effect of the auxiliary inductor 300 will be described later.

[0044] The AC pulse output from the transformer 220 is converted to DC by the rectifier circuit 230 and input to the X-ray tube 11 as a DC high voltage power supply.

[0045] The load measurement circuit 250 measures the load of the X-ray tube 11 as seen from the X-ray high voltage device 21. The higher the tube voltage supplied to the X-ray tube 11, the higher the load, and the lower the tube voltage, the lower the load. Also, the higher the tube current supplied to the X-ray tube 11, the higher the load, and the lower the tube current, the lower the load. There are no particular limitations on the method of measuring the load of the X-ray tube 11, but for example, the level of the load of the X-ray tube 11 can be measured by measuring the current value of the AC pulse output from the full bridge circuit 210.

[0046] The control circuit 240 outputs on / off signals to be applied to the gates of the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4, respectively, and also outputs on / off signals to the switch 301 for the auxiliary inductor.

[0047] The X-ray high voltage device 21 uses a phase-shift full bridge circuit 210, and this phase-shift full bridge circuit (PSFB: Phase Shift Full Bridge) can reduce losses due to switching and improve power supply efficiency by realizing zero voltage switching. However, it is known that in a conventional full bridge circuit, when the load of the X-ray tube 11 becomes low, zero voltage switching cannot be realized and power supply efficiency decreases.

[0048] In contrast, the X-ray high voltage device 21 of the embodiment realizes zero voltage switching and maintains high power efficiency regardless of the load on the X-ray tube 11. Below, the zero voltage switching will be explained, and the detailed operation of the phase-shift full-bridge circuit will be explained with reference to Figs. 3 to 8.

[0049] 3A and 3B are diagrams for explaining the operation concept of zero voltage switching. As shown in Fig. 3A, the drain-source voltage of the switching element is Vds, and the drain-source current is Ids.

[0050] Hard switching, as shown in Figure 3(b), refers to a switching operation in which the switching element turns on and the drain-source current Ids starts to increase before the drain-source voltage Vds becomes zero, or the drain-source voltage Vds rises from zero before the switching element turns off and the drain-source current Ids becomes zero. In hard switching, the drain-source voltage Vds and the drain-source current Ids overlap, so power due to the overlap region of the voltage Vds and current Ids occurs as switching loss.

[0051] In contrast, soft switching refers to a switching operation in which the drain-source voltage Vds becomes zero, and then the switching element turns on, increasing the drain-source current Ids, or the drain-source voltage Vds rises from zero, and then the switching element turns off, and then the drain-source current Ids becomes zero, as shown in FIG. 3(c). In soft switching, the drain-source voltage Vds and the drain-source current Ids do not overlap, so no switching loss occurs. Soft switching is also called zero voltage switching (ZVS). Hereinafter, zero voltage switching may be simply called ZVS.

[0052] Fig. 4 is a timing chart showing the operation timing of the phase-shift type full bridge circuit 210 in the X-ray high voltage device 21 according to the embodiment. Fig. 4 is a timing chart showing the on / off states of the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4 in the full bridge circuit 210. In addition to mode 1, mode 2, mode 3, and mode 4, there are 12 switching modes, including intermediate modes 1-2-1 and 1-2-2 between mode 1 and mode 2, intermediate modes 2-3-1 and 2-3-2 between mode 2 and mode 3, intermediate modes 3-4-1 and 3-4-2 between mode 3 and mode 4, and intermediate modes 4-1-1 and 4-1-2 between mode 4 and mode 1, depending on the on / off states of the first, second, third, and fourth switching elements Q1, Q2, Q3, and Q4.

[0053] 4 is the phase difference α between the first arm and the second arm, that is, the phase difference α between the switching timing of each of the first and second switching elements Q1 and Q2 constituting the first arm and the switching timing of each of the third and fourth switching elements Q3 and Q4 constituting the second arm. By adjusting this phase difference α, the output voltage of the transformer 220 can be adjusted.

[0054] 5 to 8 are diagrams explaining the operation of each switching mode, which will be explained in order below. In mode 1 shown in Fig. 5(a), the first switching element Q1 and the fourth switching element Q4 are both ON, and current flows through Q1, the transformer, and Q4 in that order.

[0055] Here, as shown in intermediate mode 1-2-1 in Fig. 5(b), when Q1 is turned off, the mode transitions to intermediate mode 1-2-1 in Fig. 5(b). At the moment Q1 is turned off, the voltage across Q1 is maintained at 0V, so ZVS is established.

[0056] In the intermediate mode 1-2-1, the inductor of the primary winding 221 of the transformer 220 tries to keep a current flowing by the internal energy. At this time, Q1 is turned off and no current flows, so the current flows through a path that charges the first capacitor C1 and discharges the second capacitor C2 of the second switching element Q2.

[0057] When the charging and discharging of the first and second capacitors C1 and C2 is completed, the mode transitions to intermediate mode 1-2-2. In intermediate mode 1-2-2, the inductor of the primary winding 221 continues to pass current, and as shown in FIG. 5(c), current flows through the diode D2 of the second switching element Q2.

[0058] In the intermediate mode 1-2-2 state, the second switching element Q2 is turned on, and the mode transitions to mode 2. Fig. 6(a) is a diagram showing the current flow in mode 2, where the current flows through Q2, the transformer, and Q4 in that order. When the second switching element Q2 is turned on, a current flows through the diode D2, so the voltage across Q2 is approximately 0 volts, and ZVS is established.

[0059] Here, when Q4 turns off, the mode transitions from mode 2 to intermediate mode 2-3-1. Even when Q4 turns off, the inductor of the primary winding 221 tries to continue to pass current, so that current continues to flow through the path that charges the fourth capacitor C4 of Q4 and the path that discharges the third capacitor C3 of Q3, as shown in FIG. 6(b). While C4 and C3 are charging and discharging, the potential at the midpoint between Q3 and Q4 gradually changes from 0V to Vin (the output voltage of the AC / DC converter 200). At the moment Q4 turns off, the voltage across Q4 is maintained at 0V, so ZVS is established.

[0060] When the charging and discharging of the fourth and third capacitors C4 and C3 are completed, the mode transitions to intermediate mode 2-3-2. In intermediate mode 2-3-2, the inductor of the primary winding 221 continues to pass current, and as shown in FIG. 6(c), current flows through the diode D3 of the third switching element Q3.

[0061] In the intermediate mode 2-3-2 state, the third switching element Q3 turns on, and the mode transitions to mode 3. Fig. 7(a) is a diagram showing the current flow in mode 3, in which the direction of the current flowing through the primary winding 221 is reversed, and the current flows through Q3, the transformer, and Q2 in that order. When the third switching element Q3 turns on, a current flows through the diode D3, so the voltage across Q3 is approximately 0 volts, and ZVS is established.

[0062] Here, when Q2 turns off, the mode transitions from mode 3 to intermediate mode 3-4-1. Even when Q2 turns off, the inductor of the primary winding 221 tries to continue to pass current, so as shown in FIG. 7(b), current continues to flow through the path that charges the second capacitor C2 of Q2 and the path that discharges the first capacitor C1 of Q1. While C2 and C1 are charging and discharging, the potential at the midpoint between Q1 and Q2 gradually changes from 0V to Vin. At the moment Q2 turns off, the voltage across Q2 is maintained at 0V, so ZVS is established.

[0063] When the charging and discharging of the second and first capacitors C2 and C1 is completed, the mode transitions to the intermediate mode 3-4-2. In the intermediate mode 3-4-2, the inductor of the primary winding 221 continues to pass a current, and as shown in FIG. 7(c), a current flows through the diode D1 of the first switching element Q1.

[0064] In the intermediate mode 3-4-2 state, the first switching element Q1 turns on, and the mode transitions to mode 4. Fig. 8(a) is a diagram showing the current flow in mode 4, where the current flows through Q3, the transformer, and Q1 in that order. When the first switching element Q1 turns on, a current flows through the diode D1, so the voltage across Q1 is approximately 0 volts, and ZVS is established.

[0065] Here, when Q3 turns off, the mode transitions from mode 4 to intermediate mode 4-1-1. Even when Q3 turns off, the inductor of the primary winding 221 tries to continue to pass current, so as shown in FIG. 8(b), current continues to flow through the path that charges the third capacitor C3 of Q3 and the path that discharges the fourth capacitor C4 of Q4. While C3 and C4 are charging and discharging, the potential at the midpoint between Q3 and Q4 gradually changes from 0V to Vin. At the moment Q3 turns off, the voltage across Q3 is maintained at 0V, so ZVS is established.

[0066] When the charging and discharging of the third and fourth capacitors C3 and C4 is completed, the mode transitions to the intermediate mode 4-1-2. In the intermediate mode 4-1-2, the inductor of the primary winding 221 continues to pass a current, and as shown in FIG. 8(c), a current flows through the diode D4 of the fourth switching element Q4.

[0067] In this state, the voltage across the fourth switching element Q4 is approximately 0 V, and by turning on the fourth switching element Q4, ZVS is established. By turning on the fourth switching element Q4, the mode returns from the intermediate mode 4-1-2 to the mode 1 shown in Fig. 5(a). Thereafter, the modes 1 to 4-1-2 are repeated.

[0068] Here, in order for ZVS to be established when each switching element is turned on, the voltage across each switching element at the time of turn-on must be approximately 0 V. In order to make the voltage across each switching element approximately 0 V, the capacitor corresponding to the switching element is fully charged and discharged before the switching element is turned on, and the diode corresponding to the switching element is made conductive.

[0069] An important point here is that the capacitor is charged and discharged by the internal energy stored in the inductor of the primary winding 221 of the transformer 220. For example, as shown in intermediate mode 1-2-1 shown in FIG. 5(b), it is necessary to charge and discharge the capacitor C2 of the second switching element Q2 and the capacitor C1 of the first switching element Q1 connected in series to the second switching element Q2 by the internal energy stored in the inductor of the primary winding 221 just before turning on the second switching element Q2 and transitioning to mode 2. In order to completely charge and discharge the capacitors C2 and C1, the energy stored in the inductor of the primary winding 221 must be greater than the energy required to charge and discharge the capacitors C2 and C1.

[0070] Also, for example, immediately before turning on the third switching element Q3 to transition to mode 3, as shown in intermediate mode 2-3-1 in Fig. 6(b), it is necessary to charge and discharge the capacitor C3 of the third switching element Q3 and the capacitor C4 of the fourth switching element Q4 connected in series to the third switching element Q3 by the internal energy stored in the inductor of the primary winding 221. In order to completely charge and discharge the capacitors C3 and C4, the energy stored in the inductor of the primary winding 221 must be greater than the energy required to charge and discharge the capacitors C3 and C4.

[0071] The same applies to the intermediate mode 3-4-1 shown in FIG. 7(b) and the intermediate mode 4-1-1 shown in FIG. 8(b).

[0072] Thus, in order to establish ZVS when the first to fourth switching elements Q1-Q4 are turned on, the energy stored in the inductor of the primary winding 221 must be greater than the energy required to charge and discharge the first capacitor C1 and the second capacitor C2, or the energy required to charge and discharge the third capacitor C3 and the fourth capacitor C4.

[0073] However, the energy stored in the inductor of the primary winding 221 changes according to the current flowing through the primary winding 221, and the current flowing through the primary winding 221 changes according to the load of the X-ray tube 11. Therefore, in an operation mode in which the load of the X-ray tube 11 is low, such as an operation mode in which the tube voltage of the X-ray tube 11 is low or an operation mode in which the tube current is small, the energy stored in the inductor of the primary winding 221 becomes small, and there is a risk that ZVS cannot be realized.

[0074] Therefore, in the embodiment of the X-ray high voltage device 21, when the load on the X-ray tube 11 is low, an auxiliary inductor 300 is connected in parallel to the primary winding 221 to increase the energy stored in the inductor of the primary winding 221.

[0075] It is possible to keep the auxiliary inductor 300 connected at all times regardless of the load on the X-ray tube 11. In this case, however, more energy than necessary will be consumed when the load is high, resulting in a decrease in power supply efficiency.

[0076] 9 to 12 are flowcharts showing some example operations relating to the connection and disconnection of the auxiliary inductor 300. FIG.

[0077] 9 is a flowchart relating to the first operation example. In the first operation example, in step ST100, the switch 301 for the auxiliary inductor 300 is turned off as an initial state, and the auxiliary inductor is separated.

[0078] In the next step ST101, the operation mode of the X-ray tube 11 is acquired. In the next step ST102, it is determined whether the operation mode of the X-ray tube 11 is a low-load mode. The low-load mode is, for example, a mode in which the X-ray tube 11 is operated at a tube voltage lower than a predetermined tube voltage or at a tube current lower than a predetermined tube current.

[0079] When the operation mode of the X-ray tube 11 is the low-load mode, by turning on the switch 301 for the auxiliary inductor 300, energy is stored in both the inductor of the primary winding 221 and the auxiliary inductor 300, making it possible to realize ZVS that could not be realized by only the auxiliary inductor 300. Each process shown in Fig. 9 is performed by, for example, the control circuit 240 of the X-ray high voltage device 21.

[0080] 10 is a flowchart relating to the second operation example. In the second operation example, in step ST200, similarly to the first operation example, the switch 301 for the auxiliary inductor 300 is turned off as an initial state, and the auxiliary inductor is disconnected.

[0081] In the next step ST201, the load of the X-ray tube 11 is measured. As described above, for example, the load measuring circuit 250 of the X-ray high voltage device 21 measures the current value of the AC pulse output from the full bridge circuit 210 to measure the level of the load of the X-ray tube 11.

[0082] Then, in the next step ST202, it is determined whether or not the measured load is lower than a predetermined value. If the measured load is lower than the predetermined value, in step ST203, the switch 301 for the auxiliary inductor 300 is turned on, so that energy is stored in both the inductor of the primary winding 221 and the auxiliary inductor 300, and it becomes possible to realize ZVS, which could not be realized by the auxiliary inductor 300 alone.

[0083] 11 is a flowchart of the third operation example. The third operation example is a combination of the first and second operation examples. In step ST300, similarly to the first operation example, the switch 301 for the auxiliary inductor 300 is turned off as an initial state, and the auxiliary inductor is disconnected.

[0084] In the next step ST301, the operation mode of the X-ray tube 11 is obtained in step ST101. In addition, in step ST302, the load of the X-ray tube 11 is measured. Then, in the next step ST303, it is determined whether or not the measured load is lower than a predetermined value. If the measured load is lower than the predetermined value, in step ST304, the switch 301 for the auxiliary inductor 300 is turned on, so that energy is stored in both the inductor of the primary winding 221 and the auxiliary inductor 300, and it becomes possible to realize ZVS, which could not be realized by the auxiliary inductor 300 alone.

[0085] 12 is a flowchart relating to the fourth operation example. In step ST400, the operation mode of the X-ray tube is acquired.

[0086] In the next step ST401, the switch 301 for the auxiliary inductor 300 is set to on or off depending on the operation mode. For example, when the operation mode is the high-load mode, the switch 301 is set to off, and when the operation mode is the low-load mode, the switch 301 is set to on.

[0087] In step ST402, it is determined whether or not a predetermined time has elapsed in the set operation mode. If the predetermined time has elapsed, the load of the X-ray tube 11 is measured in step ST403, as in the second operation example, and it is determined in step ST404 whether or not the measured load is lower than a predetermined value. If the measured load is lower than the predetermined value, the switch 301 for the auxiliary inductor 300 is turned on in step ST405. As a result, energy is stored in both the inductor of the primary winding 221 and the auxiliary inductor 300, making it possible to realize ZVS, which could not be realized by the auxiliary inductor 300 alone.

[0088] In the fourth operation example, even if the load on the X-ray tube 11 decreases due to aging or temperature change after being set to a certain operation mode, ZVS can be realized.

[0089] Second Embodiment Fig. 13 is a block diagram showing a configuration example of an X-ray CT apparatus 1 according to the second embodiment. The difference from the first embodiment (see Fig. 2) is that a plurality of auxiliary inductors that can be connected in parallel with the primary winding 221 of the transformer 220 are provided. The number of auxiliary inductors is not particularly limited, but for example, in the example shown in Fig. 13, three auxiliary inductors, auxiliary inductors 300, 302, and 304, are provided.

[0090] Further, each of the multiple auxiliary inductors is provided with a switch for independently turning on and off an electrical connection with the primary winding 221. For example, in the example shown in Fig. 13, auxiliary inductors 300, 302, and 304 are provided with switches 301, 303, and 305, respectively.

[0091] Moreover, the control circuit 240 of the X-ray high voltage device 21 according to the second embodiment is configured to be able to control the on / off of each of the multiple switches in accordance with the multiple operation modes of the X-ray tube 11. With this configuration, even if the magnitude of the load on the X-ray tube 11 differs stepwise between the multiple operation modes, it is possible to realize ZVS while maintaining the power supply efficiency at an appropriate level.

[0092] Furthermore, the control circuit 240 of the X-ray high voltage device 21 according to the second embodiment may be configured to control the on / off of each of the multiple switches depending on the magnitude of the load measured by the load measurement circuit 250. With this configuration, even if the magnitude of the load on the X-ray tube 11 varies among multiple values, it is possible to realize ZVS while maintaining the power supply efficiency at an appropriate level.

[0093] (Third embodiment) 14 is a diagram for explaining the operation concept of the X-ray high voltage device 21 of the X-ray CT device 1 according to the third embodiment. Some X-ray CT devices 1 have an operation mode in which the tube voltage of the X-ray tube 11 is switched between a high voltage (high kV) and a low voltage (low kV) at high speed during one rotation of the X-ray tube 11 to image the subject. Such an operation mode is called a fast kV switching mode or a dual energy mode.

[0094] In the Fast kV switching mode, during the period when the tube voltage of the tube 11 is low, the energy stored in the inductor of the primary winding 221 becomes low, and as a result, ZVS may not be achieved in each switching element of the full bridge circuit 210.

[0095] Therefore, in the X-ray high voltage device 21 according to the third embodiment, periods of high voltage and low voltage in the Fast kV switching mode are detected, and during the low voltage period, the switch 301 for the auxiliary inductor 300 is turned on.

[0096] As a result, in both the high voltage and low voltage periods in the Fast kV switching mode, ZVS can be realized while maintaining the power supply efficiency at an appropriate level, and an increase in switching loss in the full bridge circuit 210 can be prevented.

[0097] The AC / DC converter and the control circuit in the above-described embodiments are an example of the DC power supply and the control unit in the claims.

[0098] According to at least one of the X-ray CT apparatuses of the embodiments described above, in the inverter circuit of the X-ray high voltage device, an increase in switching loss can be prevented even when the load fluctuates.

[0099] Although some embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0100] 1 X-ray CT device 10 Mounting device 11 X-ray tube 21 High voltage X-ray device 210 Full Bridge Circuit 211 First Arm 212 Second Arm 220 Transformer 221 Primary winding 240 Control circuit 250 Load measurement circuit 300 Auxiliary Inductor 301 Switch for auxiliary inductor Q1-Q4 1st-4th switching elements C1-C4 1st-4th capacitor D1-D4 1st-4th diode

Claims

1. An X-ray high voltage device that supplies a high voltage power source to the X-ray tube, and a control unit, The X-ray high voltage device A DC power source; A full bridge circuit having a first arm and a second arm and connected to the DC power supply, the first arm is configured by connecting a first switching element and a second switching element in series, the second arm is configured by connecting a third switching element and a fourth switching element in series, and is controlled in a phase different from that of the first arm; a first capacitor, a second capacitor, a third capacitor and a fourth capacitor are connected in parallel to the first switching element, the second switching element, the third switching element and the fourth switching element, respectively; A full bridge circuit; a transformer, one end of a primary winding of which is connected to a connection point between the first switching element and the second switching element, and the other end of which is connected to a connection point between the third switching element and the fourth switching element; an auxiliary inductor configured to be connected in parallel with the primary winding of the transformer; a switch configured to turn on and off an electrical connection between the auxiliary inductor and the primary winding; The control unit controls the on / off of the switch. X-ray CT device.

2. the control unit controls the on / off of the switch in accordance with an operation mode of the X-ray tube; when the X-ray tube is in a low-load mode in which the load is lower than a predetermined load, the switch is turned on, and when the X-ray tube is in an operation mode other than the low-load mode, the switch is turned off. The X-ray CT apparatus according to claim 1 .

3. a load measurement circuit for measuring a load of the X-ray tube; the control unit turns on the switch when the load of the X-ray tube detected by the load measurement circuit is lower than a predetermined value, and turns off the switch when the load of the X-ray tube is higher than the predetermined value. The X-ray CT apparatus according to claim 1 .

4. a load measurement circuit for measuring a load of the X-ray tube; the control unit turns the switch on and off in response to an operation mode of the X-ray tube and a load detected by the load measurement circuit. The X-ray CT apparatus according to claim 1 .

5. the control unit turns on the switch when the load detected by the load measuring circuit is lower than each of a plurality of predetermined values ​​corresponding to the plurality of operation modes in each of the plurality of operation modes according to the level of the load of the X-ray tube, and turns off the switch when the load detected by the load measuring circuit is higher than each of the plurality of predetermined values.

5. The X-ray CT apparatus according to claim 4.

6. the control unit sets the switch to on or off in accordance with an operation mode of the X-ray tube, and after the operation mode has continued for a predetermined time, determines whether to maintain or change the on / off state of the switch based on the level of the load detected by the load measuring circuit.

5. The X-ray CT apparatus according to claim 4.

7. A plurality of auxiliary inductors configured to be connected in parallel to the primary winding of the transformer; and a plurality of switches configured to turn on and off electrical connection between each of the plurality of auxiliary inductors and the primary winding. The X-ray CT apparatus according to claim 1 .

8. The control unit is controlling the on / off of each of the plurality of switches in accordance with a plurality of operation modes of the X-ray tube; The X-ray CT apparatus according to claim 7.

9. a load measurement circuit for measuring a load of the X-ray tube; the control unit controls the on / off of each of the plurality of switches in response to a level of a load of the X-ray tube detected by the load measurement circuit. The X-ray CT apparatus according to claim 7.

10. The control unit is in an operation mode in which imaging is performed by alternately switching between a high voltage mode and a low voltage mode at high speed, the switch is turned off in the high voltage mode and the switch is turned on in the low voltage mode; The X-ray CT apparatus according to claim 1 .

11. An X-ray high voltage device that supplies a high voltage power source to the X-ray tube, and a control unit, The X-ray high voltage device is A DC power source; A full bridge circuit having a first arm and a second arm, the first arm is configured by connecting a first switching element and a second switching element in series, the second arm is configured by connecting a third switching element and a fourth switching element in series, The switching of each of the first and second switching elements and the switching of each of the third and fourth switching elements are controlled with different phase differences. A full bridge circuit; a transformer, one end of a primary winding of which is connected to a connection point between the first switching element and the second switching element, and the other end of which is connected to a connection point between the third switching element and the fourth switching element; an auxiliary inductor configured to be connected in parallel with the primary winding of the transformer; a switch configured to turn on and off an electrical connection between the auxiliary inductor and the primary winding; The control unit controls the on / off of the switch. X-ray diagnostic equipment.

12. A DC power source; A full bridge circuit having a first arm and a second arm, the first arm is configured by connecting a first switching element and a second switching element in series, the second arm is configured by connecting a third switching element and a fourth switching element in series, The switching of each of the first and second switching elements and the switching of each of the third and fourth switching elements are controlled with different phase differences. A full bridge circuit; a transformer, one end of a primary winding of which is connected to a connection point between the first switching element and the second switching element, and the other end of which is connected to a connection point between the third switching element and the fourth switching element; an auxiliary inductor configured to be connected in parallel with the primary winding of the transformer; a switch configured to turn on and off an electrical connection between the auxiliary inductor and the primary winding, Detecting at least one of an operation mode of the X-ray diagnostic apparatus and a load of an X-ray tube; controlling the switch to be turned on or off in response to at least one of the operation mode and the load of the X-ray tube; A method for controlling an X-ray diagnostic apparatus.

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