JP2022115528A - X-ray high voltage device and X-ray imaging device - Google Patents

Abstract

An object of the present invention is to reduce switching loss. SOLUTION: An X-ray high-voltage apparatus according to an embodiment has an inverter, a voltage generation circuit, and a control circuit. The inverter has a resonant circuit including a switching element and a resonant capacitor. A voltage generator circuit generates an input DC voltage to the inverter. The control circuit controls the input DC voltage so that the voltage value of the input DC voltage is lower than the product of the inverter current value of the inverter and the circuit constant of the resonance circuit. [Selection drawing] Fig. 2

Description

The embodiments disclosed in the specification and drawings relate to X-ray high voltage devices and X-ray imaging devices.

In the X-ray high-voltage apparatus, power loss and heat generation are required to be reduced in order to downsize the power supply. Some types of X-ray high-voltage devices are equipped with an inverter that converts a DC voltage into an AC voltage using a switching element. Inverters using switching elements are required to reduce switching losses such as power loss and heat generation accompanying switching between ON and OFF of the switching elements.

WO2013/172320

One of the problems to be solved by the embodiments disclosed in the specification and drawings is to reduce switching loss. However, the problems to be solved by the embodiments disclosed in this specification and drawings are not limited to the above problems. A problem corresponding to each effect of each configuration shown in the embodiments described later can be positioned as another problem.

An X-ray high voltage device according to an embodiment has an inverter, a voltage generation circuit, and a control circuit. The inverter has a resonant circuit including a switching element and a resonant capacitor. A voltage generator circuit generates an input DC voltage to the inverter. The control circuit controls the input DC voltage so that the voltage value of the input DC voltage is lower than the multiplication value of the inverter current value of the inverter and the circuit constant of the resonance circuit.

FIG. 1 is a diagram showing a configuration example of an X-ray computed tomography apparatus according to this embodiment. FIG. 2 is a diagram showing a structural example of the X-ray high voltage apparatus of FIG. FIG. 3 is a diagram showing the current and voltage in the circuit configuration of the inverter at high load in conventional operation. FIG. 4 is a diagram showing the current and voltage in the circuit configuration of the inverter at light load in conventional operation. FIG. 5 is a graph showing temporal changes in load voltage (tube voltage) and inverter current. FIG. 6 is a diagram showing a circuit configuration example of an AC/DC converter using a three-phase converter rectifier circuit. FIG. 7 is a diagram showing currents and voltages in the circuit configuration of the X-ray high-voltage apparatus under high load in an operation example according to this embodiment. FIG. 8 is a diagram showing currents and voltages in the circuit configuration of the X-ray high-voltage apparatus under light load in an operation example according to this embodiment. FIG. 9 is a graph showing temporal changes in load voltage, inverter current, and inverter input voltage in an operation example according to this embodiment. FIG. 10 is a diagram showing an example of a table of inverter current values for each imaging condition.

Hereinafter, embodiments of an X-ray high voltage device and an X-ray imaging device will be described in detail with reference to the drawings.

An X-ray high-voltage device according to this embodiment is mounted in an X-ray imaging device. The X-ray imaging apparatus according to the present embodiment is a medical image diagnostic apparatus that irradiates a subject with X-rays and performs imaging. The X-ray imaging apparatus according to this embodiment can be applied to an X-ray computed tomography apparatus and an X-ray diagnostic apparatus. In the following description, it is assumed that the X-ray imaging apparatus according to this embodiment is an X-ray computed tomography apparatus.

There are various types of X-ray computed tomography apparatuses (CT apparatuses), such as third-generation CT and fourth-generation CT, and any type can be applied to the present embodiment. Here, the third-generation CT is a Rotate/Rotate-Type in which the X-ray tube and the detector rotate around the subject as a unit. The fourth-generation CT is a Stationary/Rotate-Type in which a large number of X-ray detection elements arrayed in a ring are fixed and only the X-ray tube rotates around the subject.

FIG. 1 is a diagram showing a configuration example of an X-ray computed tomography apparatus according to this embodiment. As shown in FIG. 1, the X-ray computed tomography apparatus 1 has a gantry 10, a bed 30 and a console 40. As shown in FIG. In FIG. 1, for the convenience of explanation, a plurality of mounts 10 are drawn, but in reality, one or a plurality of mounts may be used. The gantry 10 is a scanning device having a configuration for X-ray CT imaging of the subject P. As shown in FIG. The bed 30 is a transport device for placing a subject P to be subjected to X-ray CT imaging and positioning the subject P. As shown in FIG. A console 40 is a computer that controls the gantry 10 .

As shown in FIG. 1, the gantry 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17 and a data acquisition circuit (Data Acquisition System). : DAS) 18.

The X-ray tube 11 irradiates the subject P with X-rays. The X-ray tube 11 includes a cathode that generates thermoelectrons, an anode that receives thermoelectrons flying from the cathode and generates X-rays, and a vacuum tube that holds the cathode and the anode.

The X-ray detector 12 detects X-rays emitted from the X-ray tube 11 and passed through the subject P, and outputs an electrical signal corresponding to the dose of the detected X-rays to the data acquisition circuit 18 . The X-ray detector 12 has a structure in which a plurality of X-ray detection element arrays each having a plurality of X-ray detection elements arranged in the channel direction are arranged in the slice direction (column direction). The X-ray detector 12 is, for example, an indirect conversion type detector having a grid, a scintillator array and a photosensor array.

The rotating frame 13 is an annular frame that rotatably supports the X-ray tube 11 and the X-ray detector 12 about a rotation axis (Z-axis). Rotating the rotation frame 13 about the rotation axis by the control device 15 causes the X-ray tube 11 and the X-ray detector 12 to rotate about the rotation axis.

The X-ray high voltage device 14 has a high voltage generator and an X-ray controller. The high voltage generator generates a high voltage to be applied to the X-ray tube 11 and a filament current to be supplied to the X-ray tube 11 . The X-ray control device controls the output voltage according to the X-rays emitted by the X-ray tube 11 . The high voltage generator is of inverter type. The X-ray high-voltage device 14 may be provided on the rotating frame 13 within the gantry 10 or may be provided on a fixed frame (not shown) within the gantry 10 .

The wedge 16 attenuates the X-rays so that the dose of the X-rays emitted from the X-ray tube 11 to the subject P has a predetermined distribution. For example, as the wedge 16, a metal plate such as aluminum is used for a wedge filter, a bow-tie filter, or the like. The collimator 17 limits the irradiation range of X-rays transmitted through the wedge 16 . The collimator 17 slidably supports a plurality of lead plates that shield X-rays, and adjusts the form of slits formed by the plurality of lead plates. Note that the collimator 17 may also be called an X-ray diaphragm.

The data acquisition circuit 18 reads from the X-ray detector 12 an electrical signal corresponding to the dose of X-rays detected by the X-ray detector 12 . The data acquisition circuit 18 amplifies the readout electrical signal and integrates the electrical signal over the view period to acquire detection data having a digital value corresponding to the X-ray dose over the view period. The detected data are called projection data. The data acquisition circuit 18 is implemented, for example, by an Application Specific Integrated Circuit (ASIC) incorporating circuit elements capable of generating projection data. Projection data is transmitted to the console 40 via a non-contact data transmission device or the like.

In this embodiment, the integrating X-ray detector 12 and the X-ray computed tomography apparatus 1 equipped with the integrating X-ray detector 12 will be described as an example. It is also applicable to photon counting X-ray detectors.

The control device 15 controls the X-ray high-voltage device 14 and the data acquisition circuit 18 in order to perform X-ray CT imaging under the imaging control of the processing circuit 44 of the console 40 . The control device 15 has a processor and drive mechanisms such as motors and actuators.

The bed 30 includes a base 31 , a support frame 32 , a top plate 33 and a bed driving device 34 . The base 31 is installed on the floor. The base 31 is a housing that supports the support frame 32 so as to be movable in the vertical direction (Y-axis direction) with respect to the floor surface. The support frame 32 is a frame provided on top of the base 31 . The support frame 32 supports the top plate 33 so as to be slidable along the rotation axis (Z-axis). The top plate 33 is a flexible plate on which the subject P is placed. The bed driving device 34 is housed within the housing of the bed 30 . The bed driving device 34 is a motor or an actuator that generates power for moving the support frame 32 on which the subject P is placed and the top plate 33 . The bed driving device 34 operates according to control by the console 40 or the like.

Console 40 has memory 41 , display 42 , input interface 43 and processing circuitry 44 . Data communication between the memory 41, the display 42, the input interface 43 and the processing circuit 44 is performed via a bus (BUS). Although the console 40 is described as being separate from the gantry 10, the gantry 10 may include the console 40 or a part of each component of the console 40. FIG.

The memory 41 is a storage device such as a hard disk drive (HDD), a solid state drive (SSD), or an integrated circuit storage device that stores various information. The memory 41 stores projection data and reconstructed image data, for example.

The display 42 displays various information. For example, the display 42 outputs a CT image generated by the processing circuit 44, a GUI (Graphical User Interface) for accepting various operations from the operator, and the like. Various arbitrary displays can be used as the display 42 as appropriate. For example, the display 42 can be a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electro luminescence display (OELD), or a plasma display. A projector may be used as the display 42 .

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 44 . Specifically, the input interface 43 is connected to input devices such as a mouse, keyboard, trackball, switch, button, joystick, touch pad, and touch panel display. Also, the input device connected to the input interface 43 may be an input device provided in another computer connected via a network or the like. The input interface 43 may be a speech recognizer that converts audio signals collected by a microphone into instructional signals.

The processing circuit 44 controls the operation of the entire X-ray computed tomography apparatus 1 according to the electric signal of the input operation output from the input interface 43 . The processing circuit 44 notifies the control device 15 of a command to perform X-ray CT imaging. The processing circuit 44 also reconstructs a CT image based on projection data acquired from the X-ray detector 12 via the data acquisition circuit 18 . For example, the processing circuit 44 has a processor such as a CPU (Central Processing Unit) as a hardware resource.

FIG. 2 is a diagram showing a configuration example of the X-ray high voltage device 14 according to this embodiment. As shown in FIG. 2, the X-ray high-voltage device 14 is connected to a commercial power source 51 and the X-ray tube 11 . The X-ray high voltage device 14 converts the AC voltage from the commercial power source 51 into a DC high voltage and applies it to the X-ray tube 11 . Specifically, the X-ray high voltage device 14 has an AC/DC converter 52 , an inverter 53 , a high voltage transformer 54 , a rectifier circuit 55 , a converter drive circuit 56 , an inverter drive circuit 57 and a control circuit 58 .

The input side of AC/DC converter 52 is connected to commercial power source 51 . AC/DC converter 52 converts AC voltage from commercial power source 51 into DC voltage. The output side of AC/DC converter 52 is connected to the input side of inverter 53 . AC/DC converter 52 is an example of a voltage generating circuit. Moreover, the AC/DC converter 52 and the commercial power supply 51 can also be called a voltage generation circuit. The voltage generator circuit generates an input DC voltage for inverter 53 .

Inverter 53 converts the input DC voltage from AC/DC converter 52 into an output AC voltage. Inverter 53 has a resonant circuit including a switching element and a resonant capacitor. A control signal is supplied from the inverter drive circuit 57 to the switching element to switch between ON and OFF. By switching on and off of the switching element, the input DC voltage is converted into an output AC voltage having a frequency higher than that of the commercial power supply 51 . Inverter 53 is a phase-shift inverter in which the voltage value of the output AC voltage of inverter 53 is adjusted by giving a phase difference between switching elements to control signals applied to the switching elements. The output side of the inverter 53 is connected to the input side of the high voltage transformer 54 .

A high-voltage transformer 54 boosts the output AC voltage from the inverter 53 . High-voltage transformer 54 has a primary coil, a secondary coil, and an iron core. The primary coil is wound with a primary winding and the secondary coil is wound with a secondary winding. The input side of the primary coil is connected to the output side of the inverter 53 . The primary coil receives an alternating voltage (primary voltage) from the inverter 53 and induces an alternating voltage (secondary voltage) in the secondary coil through the iron core according to the principle of electromagnetic induction. The amplification factor of the secondary voltage with respect to the primary voltage is determined according to the ratio of the number of turns of the secondary winding to the number of turns of the primary winding. The output side of the secondary coil is connected to the input side of the rectifier circuit 55 .

The rectifier circuit 55 rectifies and smoothes the output AC voltage from the high-voltage transformer 54 and converts it into an output DC voltage. The rectifier circuit 55 can have various configurations. The rectifier circuit 55 may be a circuit that performs only rectification and smoothing, or a circuit that performs boosting in addition to rectification and smoothing. As the rectifier circuit 55 that performs only rectification and smoothing, for example, a silicon rectifier, which is a high-voltage diode using a silicon semiconductor, may be used. As the rectifying circuit 55 for rectifying, smoothing, and boosting, a multiple booster circuit or the like is used in which a plurality of circuits each having a high voltage rectifying capacitor and a high voltage diode are connected in an arbitrary manner. The output side of the rectifier circuit 55 is connected to the X-ray tube 11 . The output DC voltage of the rectifier circuit 55 is applied to the X-ray tube 11 .

The X-ray tube 11 includes a cathode that generates thermoelectrons, an anode that receives thermoelectrons flying from the cathode and generates X-rays, and a vacuum tube that holds the cathode and the anode. The X-ray tube 11 is connected to an X-ray high voltage device 14 via a high voltage cable. An output DC voltage from a rectifier circuit 55 is applied between the cathode and the anode. The voltage applied between the cathode and anode is called the tube voltage. Thermal electrons fly from the cathode to the anode by applying a tube voltage. A tube current flows due to thermal electrons flying from the cathode to the anode. X-rays are generated by thermal electrons impinging on the anode.

Converter drive circuit 56 drives AC/DC converter 52 in accordance with a control signal from control circuit 58 to control the output DC voltage of AC/DC converter 52 , in other words, the input AC voltage to inverter 53 .

Inverter drive circuit 57 drives inverter 53 in accordance with a control signal from control circuit 58 to control the output AC voltage of inverter 53 . Specifically, the inverter drive circuit 57 supplies a control signal to each switching element included in the inverter 53 to switch ON and OFF of each switching element. At this time, the inverter drive circuit 57 provides a phase difference between the control signals to be supplied to each switching element and supplies the control signals to each switching element. By adjusting the phase difference between the control signals, the voltage value of the output AC voltage from inverter 53 is adjusted. Adjusting the voltage value of the output AC voltage from the inverter 53 based on the phase difference between the control signals supplied to the switching elements is called phase shift control.

Control circuit 58 controls converter drive circuit 56 and inverter drive circuit 57 . The control circuit 58 controls the detected value of the load voltage, the detected value of the current flowing through the inverter 53 (hereinafter referred to as inverter current), the detected value of the input DC voltage to the inverter 53, and the input AC current to the AC/DC converter 52. A detected value of the input AC voltage to the AC/DC converter 52 is obtained. Detected value of load voltage, Detected value of inverter current, Detected value of input DC voltage to inverter 53, Detected value of input AC current flowing through AC/DC converter 52, Detected value of input AC voltage to AC/DC converter 52 are detected by the detector for each. The load voltage is a general term for voltages applied to the high-voltage transformer 54, the rectifier circuit 55, and the X-ray tube 11 to which the power generated by the inverter 53 is supplied. Assume that the load voltage is the tube voltage of the X-ray tube 11 in the following embodiments.

The control circuit 58 controls the detected value of the load voltage, the detected value of the inverter current, the detected value of the input DC voltage to the inverter 53, the detected value of the input AC current to the AC/DC converter 52, and the input to the AC/DC converter 52. Based on the detected value of the AC voltage, the converter drive circuit 56 and the inverter drive circuit 57 are synchronously controlled so that the detected tube voltage value approaches the set tube voltage value. Specifically, the control circuit 58 adjusts the input DC voltage to the inverter 53 so that the tube voltage detection value and the tube voltage set value match. In parallel, the control circuit 58 controls the inverter drive circuit 57 so as to perform soft switching in order to reduce switching loss caused by switching ON and OFF of the switching element included in the inverter 53 . In order to increase the efficiency of soft switching, the control circuit 58 sets the voltage value of the input DC voltage to the inverter 53 to the product of the current value of the inverter current flowing through the inverter 53 and the circuit constant of the resonance circuit included in the inverter 53. The input DC voltage to the inverter 53 is controlled so as to fall below. Control circuit 58 is implemented by any circuit such as a digital feedback control circuit.

Next, the problem of soft switching will be described in detail with reference to FIGS. 3 and 4. FIG.

3 is a diagram showing the current and voltage in the circuit configuration of the inverter 53 at high load in conventional operation, and FIG. 4 is a diagram showing the current and voltage in the circuit configuration of the inverter 53 at light load in conventional operation. be. When the load is high, a relatively high voltage is applied to the load side, and when the load is light, a relatively low voltage is applied to the load side. 3 and 4, the AC/DC converter 52 is represented by a simple circuit symbol.

As shown in FIGS. 3 and 4, a DC bus capacitor C _in is provided between the AC/DC converter 52 and the inverter 53 . The output _DC voltage _VDC from the AC/DC converter 52 is applied to the DC bus capacitor Cin to store the charge supplied along with the application of the voltage _VDC . Inverter 53 illustratively has a resonant circuit with four arms. Each arm has switching elements S1-S4, diodes and resonant capacitors C1-C4 connected in parallel. The AC voltage generated by the inverter 53 is stepped up by the high voltage transformer 54 . The output side of the inverter 53 is connected to the input _side of the high voltage transformer 54 via the choke coil L1. _The choke coil L1 receives the inverter current and accumulates energy.

Zero voltage switching (ZVS) control and zero current switching (ZCS) control can be used as soft switching methods. Zero-voltage switching control reduces switching loss by causing voltage to resonate by transferring electric charges to and from a switching element and a resonance capacitor, and performing switching when the voltage of the switching element becomes approximately zero. Zero-current switching control reduces switching loss by performing switching at the timing when the inverter current becomes substantially zero. In the following description, it is assumed that zero voltage switching control is used.

The control circuit 58 utilizes the parallel resonance of the choke coil L1 and the resonant capacitors C1 _- S4 connected in parallel to the switching elements S1-S4 to perform zero voltage switching control by phase shift control. It controls the inverter drive circuit 57 . In the zero-voltage switching control, the energy accumulated in the choke coil L1 is used during the dead time provided immediately before turning on _each of the switching elements S1-S4, and the charge stored in the resonance capacitors C1-S4 is pull out. At this time, the inverter driving circuit 57 alternately turns ON and OFF the switching elements S1 and S2, and alternately turns ON and OFF the switching elements S3 and S4. The switching elements S1-S4 are turned ON by turning ON the control signal to the switching elements S1-S4. When the switching elements S1-S4 are switched ON, the charges stored in the resonance capacitors C1 _- S4 are discharged using the energy of the choke coil L1. When the switching elements S1-S4 are switched ON, the collector-emitter voltages of the switching elements S1-S4 are zero because the resonant capacitors C1-S4 are discharged. Thus, zero voltage switching is achieved.

A conditional expression for realizing zero voltage switching control (hereinafter referred to as a ZVS conditional expression) can be expressed by the following formula. _In the following formula, Li is the inductance value of the inductor such as the choke coil L1 in the inverter 53, _i is the current value of the inverter current, C is the capacitance of the resonance capacitor included in the inverter 53, and V _DC It is an input DC voltage value to the inverter 53 . According to the ZVS conditional expression, soft switching is realized when the energy stored in the inductor shown on the left side is larger than the energy stored in the resonant capacitor. The ZVS conditional expression below is a conditional expression for an arm including the switching element S3 and the switching element S4. The ZVS upper bound equation for the arm containing switching element S1 and switching element S2 is obtained by replacing C3 and _C4 in the equation below with C1 and _{C2 , respectively} .

FIG. 5 is a graph showing temporal changes in load voltage (tube voltage) and inverter current. As shown in FIG. 5, the load voltage rises toward the tube voltage set value from the start. The pulse width of the output AC voltage from the inverter 53 is relatively wide when the load voltage rises, but narrows as the load voltage approaches a steady state, and becomes narrow and constant when the load voltage reaches a steady state. Therefore, the inverter current also rises from the rise of the load voltage, reaches its peak at time t1, then decreases as it approaches a steady state, and converges to a small value when it reaches a steady state at time t2.

As shown in FIG. 5, when the load is high (during charging) shown in FIG. , enough energy can be stored in the inductor to store a voltage on the resonant capacitor. In this case, the left side becomes larger than the right side and soft switching is realized. On the other hand, when the load is light (steady state) shown in FIG. 4, the current value i of the inverter current flowing through the inductor is small, and the inductor cannot store enough energy to store the voltage in the resonant capacitor. In this case, the left side becomes smaller than the right side and soft switching cannot be achieved.

Therefore, the X-ray high voltage device 14 controls the input DC voltage to the inverter 53 according to the load condition. A three-phase converter rectifier circuit is used as the AC/DC converter 52 in order to control the input DC voltage.

FIG. 6 is a diagram showing a circuit configuration example of the AC/DC converter 52 using a three-phase converter rectifier circuit. As shown in FIG. 6, a three-phase alternating current consisting of U-phase, V-phase and W-phase is supplied from a commercial power source 51 to the input side of an AC/DC converter 52 . AC/DC converter 52 has two pairs of arms for each phase. Each arm has a switching element and a diode connected in anti-parallel to the switching element S1-S6. Three arms are bridge connected. The output side of AC/DC converter 52 is connected to the input side of inverter 53 via DC bus capacitor _Cin .

The output DC voltage of AC/DC converter 52 is determined by the combined voltage of the output voltages of the three arms. The output voltage of each arm is adjusted by switching ON and OFF of each pair of switching elements. Each switching element receives a control signal from the converter drive circuit 56 and switches between ON and OFF. By adjusting the ON time of the switching elements among the three arms, it is possible to adjust the voltage value of the output voltage of AC/DC converter 52 . An output DC voltage, which is the composite voltage of the output voltages of the three arms, is applied to the DC bus capacitor _Cin .

Control circuit 58 controls the DC bus voltage on DC bus capacitor _Cin . Specifically, the control circuit 58 acquires the detected value of the DC bus voltage _Vdc , which is the input DC voltage to the inverter 53, and instructs the control circuit 58 according to the difference between the detected value of the DC bus voltage _Vdc and the target value. The signal is provided to converter driver circuit 56 . Converter drive circuit 56 generates a control signal for each switching element S1-S6 according to each of the command signals for the U-phase, V-phase, and W-phase, supplies it to each switching element S1-S6, and supplies it to each switching element S1 - Drive S6. By driving the switching elements S1 to S6 according to the command signal, the input AC voltage applied to the DC bus capacitor _Cin is increased when the difference between the detected value of the DC bus voltage _Vdc and the target value is large. , the input AC voltage applied to the DC bus capacitor _Cin can be reduced when the difference value is small. _In this way it is possible to regulate the DC bus voltage _Vdc across the DC bus capacitor Cin.

Next, an operation example of the X-ray high-voltage device 14 according to this embodiment will be described separately for Example 1 and Example 2. FIG.

(Example 1)
FIG. 7 is a diagram showing the current and voltage in the circuit configuration of the X-ray high-voltage device 14 at high load in an operation example according to this embodiment, and FIG. FIG. 2 is a diagram showing the current and voltage in the circuit configuration of the X-ray high voltage device 14 at time. FIG. 9 is a graph showing temporal changes in load voltage, inverter current, and inverter input voltage in an operation example according to this embodiment.

The control circuit 58 controls the converter drive circuit 56 and the inverter drive circuit 57 so that the tube voltage detection value matches the set value _Vset . In parallel, the control circuit 58 detects the inverter current, which changes according to the load conditions, and the DC bus voltage, which is the input DC voltage to the inverter 53, compares them, and controls the converter to obtain the optimum DC bus voltage. It controls the drive circuit 56 .

During operation of the X-ray high voltage device 14, the control circuit 58 controls the converter drive circuit 56 and the inverter drive circuit 57 so that the detected value of the load voltage (tube voltage) matches the set value _Vset . During CT imaging, the control circuit 58 switches between light-load control and high-load control according to a change in the load voltage applied to the load to which the power generated by the inverter 53 is supplied. Light-load control is control of the input DC voltage so that the voltage value of the input DC voltage (DC bus voltage) is constant. The high-load control is control of the input DC voltage so that the voltage value of the input DC voltage (DC bus voltage) is less than the product of the inverter current value of the inverter 53 and the circuit constant of the resonance circuit.

The control circuit 58 monitors the detected value of the load voltage and determines whether the load is high or light. For example, the load is determined to be high until time t1 when the detected value of the load voltage reaches a predetermined percentage such as 80% of the set value _Vset , and the load is determined to be light after time t1. In addition, the control circuit 58 may monitor the detected value of the inverter current that changes according to changes in the load voltage to determine whether the load is high or light. For example, the load is determined to be high until time t1 when the detected value of the inverter current reaches the peak value, and the load is determined to be light after time t1. The load may be determined to be high until the peak value is reached and the detected value drops by a predetermined percentage of the peak value, and the load may be determined to be light after that point. Alternatively, it may be determined that the load is high until a predetermined time has elapsed from time t1 when the peak value is reached, and that the load is light after that time.

When the load is determined to be high, the control circuit 58 controls the input DC voltage of the inverter 53, that is, the DC bus voltage _Vdc of the DC bus capacitor Cin to reach the maximum value _Vmax as shown _in FIGS. The converter drive circuit 56 is controlled so that More specifically, the control circuit 58 acquires a detected value of the DC bus voltage _Vdc , which is the input DC voltage to the inverter 53, and adjusts the voltage according to the difference between the detected value of the DC bus voltage _Vdc and the target value _Vmax . command signal is supplied to the converter drive circuit 56 . Converter drive circuit 56 generates control signals for switching elements S1-S6 to drive switching elements S1-S6 in accordance with command signals for each of the U-phase, V-phase and W-phase. By driving the switching elements S1 to S6 according to the command signal, the input AC voltage applied to the DC bus capacitor _Cin is increased when the difference between the detected value of the DC bus voltage _Vdc and the target value _Vmax is large. , the input AC voltage applied to the DC bus capacitor _Cin can be reduced when the difference value is small. This allows the DC bus voltage _Vdc to be maintained at the maximum value _Vmax . Note that the maximum value V _max is set in advance according to the combination of the tube voltage set value V _set and the tube current set value.

When the load is determined to be light, the control circuit 58 controls the converter drive circuit 56 so that the input voltage (DC bus voltage V _dc ) of the inverter 53 drops from the maximum value V _max as shown in FIGS. to control. More specifically, control circuit 58 controls converter drive circuit 56 to control the DC bus voltage so that it falls below the product of the detected inverter current value and the circuit constant of the resonant circuit. For example, by applying the detected value of the inverter current and the circuit constant of the resonance circuit to the ZVS conditional expression, the target value of the DC bus voltage _Vdc that makes the right side smaller than the left side is obtained. That is, the target value of the DC bus voltage _Vdc is set to a value lower than the product of the detected value of the inverter current and the circuit constant of the resonance circuit in the inverter 53 . The circuit constant includes the capacitance of the switching element C and the _inductance of the inductor Li, as shown in the ZVS conditional expression. More specifically, the optimum DC bus voltage value for switching in the switching elements S3 and S4 is the inverter current value _i and (inductance of Li/ ₍ capacitance of the resonant capacitor C3 antiparallel to the switching element S3 and the capacitance of the resonance capacitor _C4 in parallel with the switching element S4). That is, the multiplication value is the upper limit of the voltage value of the optimum DC bus voltage. The lower limit of the voltage value of the optimum DC bus voltage may be set to a value not lower than the minimum value of the DC bus voltage at which the set tube voltage value and the set tube current value can be obtained. For example, the lower limit may be set to any value within the above range via the input interface 43 by the user.

The target value of the DC bus voltage V _dc is set to the DC bus voltage V _sta when the load condition substantially reaches or approaches the set value V _set . Converter drive circuit 56 drives AC/DC converter 52 so that DC bus voltage _Vdc approaches target value _Vsta . More specifically, the control circuit 58 acquires a detected value of the DC bus voltage _Vdc , which is the input DC voltage to the inverter 53, and determines the difference between the detected value of the DC bus voltage _Vdc and the target value _Vsta . command signal is supplied to the converter drive circuit 56 . Converter drive circuit 56 generates control signals for switching elements S1-S6 to drive switching elements S1-S6 in accordance with command signals for each of the U-phase, V-phase and W-phase. By driving the switching elements S1 to S6 according to the command signal, the input AC voltage applied to the DC bus capacitor _Cin is increased when the difference between the detected value of the DC bus voltage _Vdc and the target value _Vsta is large. , the input AC voltage applied to the DC bus capacitor _Cin can be reduced when the difference value is small. This allows the DC bus voltage _Vdc to transition to the target value _Vsta .

When the input voltage (DC bus voltage V _dc ) of the inverter 53 is smoothly shifted from the maximum value V _max to the steady-state value V _sta , the target value is set to gradually decrease from the maximum value V _max to the steady-state value V _sta . It may be set in several stages.

As described above, according to the first embodiment, according to the load state, the input DC voltage is adjusted so that the voltage value of the input DC voltage is lower than the multiplication value of the current value of the inverter current of the inverter 53 and the circuit constant of the resonant circuit. (DC bus voltage). As a result, the energy stored in the inductor can be made larger than the energy stored in the resonance capacitor even at light load when the load voltage reaches a steady state, so soft switching can be realized.

(Example 2)
As described above, the condition under which soft switching of the inverter 53 becomes difficult is when the load voltage reaches a steady state and the inverter current of the inverter 53 decreases. The maximum value of the voltage applied to the load and the maximum value of current flowing through the load are determined according to the set tube voltage value and the set tube current value of the imaging conditions, respectively. The control circuit 58 according to the second embodiment holds the inverter current value flowing through the inverter 53 under each imaging condition as prior data, and controls the converter drive circuit 56 at the timing when the detected value of the load voltage matches the set tube voltage value. , the input DC voltage (DC bus voltage) of the inverter 53 is adjusted according to the inverter current value of the advance data.

FIG. 10 is a diagram showing an example of a table of inverter current values for each imaging condition. As shown in the figure, the table associates the maximum current value "A" of the inverter current with each combination of the set tube voltage value [kv] and the set tube current value [mA]. For example, the combination of the set tube voltage value xkv and the set tube current value amA is associated with the maximum current value (1)A flowing through the inverter 53 . The maximum current value is defined as the inverter current value when the load is in a steady state under the set tube voltage value [kv] and the set tube current value [mA]. The table is generated in advance by measuring the maximum current value of the inverter current for each of multiple combinations of the set tube voltage value [kv] and the set tube current value [mA] at an arbitrary time such as during installation or maintenance. be.

During CT imaging, the control circuit 58 monitors the detected value of the inverter current. In the second embodiment, the control circuit 58 monitors the load voltage. For example, when the load tube voltage value is lower than the set tube voltage value, it is determined that the load is high, and the load tube voltage value reaches the set tube voltage value. If so, it is determined that the load is light.

When it is determined that the load is high, the control circuit 58 causes the converter drive circuit 56 to apply the DC bus voltage of the target value _Vmax corresponding to the set tube voltage value to the DC bus capacitor, as in the first embodiment. to drive the AC/DC converter 52 .

If the load is determined to be light, the control circuit 58 acquires the set tube voltage value and the set tube current value, and refers to the table using the combination of the set tube voltage value and the set tube current value as a search key. , to identify the maximum current value associated with the search key. The control circuit 58 controls the converter drive circuit 56 according to the specified maximum current value so as to achieve the DC bus voltage value determined by the maximum current value specified in the table and the ZVS conditional expression. /DC converter 52.

In the above table according to the second embodiment, each combination of the set tube voltage value [kv] and the set tube current value [mA] is associated with the maximum current value "A" of the inverter current. However, in the above table, the target value "V" of the DC bus voltage may be associated with each combination of the set tube voltage value [kv] and the set tube current value [mA]. The target value "V" is set to a DC bus voltage value lower than the product of the current value of the inverter current and the circuit constant of the resonant circuit. In this case, control circuit 58 controls converter drive circuit 56 to drive AC/DC converter 52 so that DC bus voltage _Vdc approaches target value _Vsta , as in the first embodiment. Soft switching can also be achieved by this method.

The table that associates the maximum current value or the target value of the DC bus voltage can also be realized by a machine learning model or a calculation formula.

In Examples 1 and 2, the AC/DC converter 52 is assumed to be a three-phase converter rectifier circuit. However, the AC/DC converter 52 is not limited to a three-phase converter rectifier circuit, and may be any circuit such as a step-up/step-down chopper circuit as long as the output voltage (input voltage of the inverter 53) can be adjusted.

A power factor correction circuit may be used as the AC/DC converter 52 . In this case, the AC/DC converter 52 has a voltage detector for the input alternating voltage to the AC/DC converter 52 and a current detector for the input alternating current. The control circuit 58 controls the AC/DC converter 52 through the converter drive circuit 56 so as to eliminate the phase shift between the detected waveform of the input AC voltage from the voltage detector and the detected waveform of the input AC current from the current detector. to control. This makes it possible to improve the deterioration of the power factor caused by the capacitive load _in the DC bus capacitor Cin.

According to at least one embodiment described above, switching loss can be reduced.

The term "processor" used in the above description includes, for example, CPU, GPU, or Application Specific Integrated Circuit (ASIC)), programmable logic device (for example, Simple Programmable Logic Device : SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA)). The processor realizes its functions by reading and executing the programs stored in the memory circuit. It should be noted that instead of storing the program in the memory circuit, the program may be directly installed in the circuit of the processor. In this case, the processor implements its functions by reading and executing the program embedded in the circuit. Also, functions corresponding to the program may be realized by combining logic circuits instead of executing the program. Note that each processor of the present embodiment is not limited to being configured as a single circuit for each processor, and may be configured as one processor by combining a plurality of independent circuits to realize its function. good. Furthermore, multiple components in FIGS. 1 and 2 may be integrated into a single processor to implement its functions.

While several embodiments have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations of embodiments can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

11 X-ray tube 14 X-ray high voltage device 51 Commercial power supply 52 AC/DC converter 53 Inverter 54 High voltage transformer 55 Rectifier circuit 56 Converter drive circuit 57 Inverter drive circuit 58 Control circuit

Claims (9)

an inverter having a resonant circuit including a switching element and a resonant capacitor;
a voltage generation circuit that generates an input DC voltage to the inverter;
a control circuit for controlling the input DC voltage so that the voltage value of the input DC voltage is lower than the multiplication value of the inverter current value of the inverter and the circuit constant of the resonance circuit;
An X-ray high voltage device comprising: The voltage generation circuit generates, as the input DC voltage, a DC bus voltage to be applied to a DC bus capacitor provided between the voltage generation circuit and the inverter,
wherein the control circuit controls the DC bus voltage;
An X-ray high voltage apparatus according to claim 1. The control circuit is configured such that the voltage value of the input DC voltage becomes constant according to changes in the load voltage applied to the load to which the power generated by the inverter is supplied or the current flowing through the inverter. 3. The X-ray high voltage according to claim 1, wherein the first control of the input DC voltage and the second control of the input DC voltage such that the voltage value of the input DC voltage is much lower than the multiplication value are switched. Device. 4. The X-ray high-voltage apparatus according to claim 3, wherein said control circuit executes said first control to reduce said input DC voltage when said load voltage is in a steady state. 2. The X-ray high voltage apparatus according to claim 1, wherein said voltage generation circuit includes an AC/DC converter including a three-phase converter rectifier circuit or a buck-boost chopper circuit. the inverter includes a plurality of the switching elements and a plurality of the resonance capacitors,
The resonance capacitor is provided in parallel with each of the plurality of switching elements,
An X-ray high voltage apparatus according to claim 1. further comprising a storage unit that stores a target current value flowing through the inverter for each combination of the load voltage value and the load current value;
The control circuit controls the voltage generation circuit according to a current target value corresponding to a combination of a detected load voltage value and a set load current value.
An X-ray high voltage apparatus according to claim 1. 2. The X-ray high voltage apparatus according to claim 1, wherein said circuit constant includes an inductance of said resonance circuit and a capacitance of said resonance capacitor. an X-ray tube for generating X-rays;
an X-ray high voltage device that applies a high voltage to the X-ray tube;
an X-ray detector for detecting X-rays generated from the X-ray tube and transmitted through a subject;
an image generator that generates an X-ray image of the subject based on an output signal from the X-ray detector;
The X-ray high voltage device is
an inverter having a resonant circuit including a switching element and a resonant capacitor;
a voltage generation circuit that generates an input DC voltage to the inverter;
a control circuit that controls the input DC voltage so that the voltage value of the input DC voltage is lower than the multiplication value of the inverter current value of the inverter and the circuit constant of the resonance circuit;
X-ray imaging device.

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