Cold cathode ray machine digital control system based on high-frequency inversion and pulse modulation

Abstract

The invention relates to the technical field of ray detection, and particularly discloses a cold cathode ray machine digital control system based on high-frequency inversion and pulse modulation, which specifically comprises a master control and calculation module, a high-frequency high-voltage inversion and modulation module, a pulse driving and field emission control module and a precise sensing and acquisition module which are in communication connection with one another, a safety interlocking and state monitoring module; and a man-machine interface and communication module. According to the invention, a closed-loop control scheme of high-frequency inversion, pulse modulation and cathode state is provided for the first time, the problem of separation of independent operation of a power supply, a controller and an emitter of a traditional system is solved, and cross-module collaborative optimization is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of X-ray detection technology, in particular to a portable X-ray detection device control system, and more particularly to a digital control system for a cold cathode X-ray machine based on high-frequency inversion and pulse modulation. BACKGROUND

[0002] The high-voltage power supply of a conventional cold cathode portable X-ray machine generally adopts a silicon-based IGBT or MOSFET to form an industrial frequency or intermediate frequency inversion topology. Due to the switching loss and frequency characteristics of semiconductor devices, the operating frequency is usually lower than 50 kHz, resulting in a large volume of transformers and filter elements, and the power density is difficult to break through 1 kW / kg, which seriously restricts the lightweight and portability of the device. At the same time, the existing control system relies on analog circuits or fixed parameter digital PWM regulation, and the adjustment range of pulse width and repetition frequency is narrow, and lacks adaptive ability to the cold cathode field emission characteristics. This rigid control mode causes three core defects: first, the transient instability of cathode electron emission causes X-ray dose rate drift, resulting in imaging gray scale distortion; second, the electron beam focus thermal diffusion under wide pulse operation limits the spatial resolution to below 3LP / mm, which cannot meet the microstructure detection requirements; third, the cathode life is significantly shortened due to continuous overcurrent impact. In addition, the high-voltage closed-loop response delay of the existing power supply topology is more than 100 μs, which cannot realize pulse-level real-time regulation, further exacerbating the uncontrollability of the output energy. Although in recent years some research has tried to introduce a digital control chip, its algorithm only realizes open-loop pulse width modulation, and does not establish a multi-parameter coordination mechanism with the cathode state and dose feedback, and does not solve the core contradiction of deep integration of high frequency and digitization. Therefore, there is an urgent need for a control system that integrates wide-bandgap semiconductor high-frequency inversion technology and intelligent adaptive pulse modulation, which breaks through the technical bottlenecks of power density, resolution and reliability through topology innovation and algorithm coordination. SUMMARY

[0003] In order to solve the problem of deep integration of high frequency and digitization in the existing portable X-ray detection device technology, the present application provides a digital control system for a cold cathode X-ray machine based on high-frequency inversion and pulse modulation, which mainly innovates in intelligent pulse modulation and control, and high-frequency, digitization and semiconductor high-voltage power supply, as follows: First, the algorithm for adjusting the pulse frequency, width and amplitude according to the target material thickness and density in real time is developed in the intelligent pulse modulation and control, and the dynamic pulse parameter adjustment problem is solved; secondly, through real-time acquisition of dose feedback, the pulse output is closed-loop controlled to ensure that the exposure dose is accurate and constant each time, and is not affected by power fluctuations or temperature, and the adaptive dose control problem is solved. Furthermore, the application adopts GaN / SiC wide bandgap semiconductor devices to realize a high-voltage power supply with a MHz-level switching frequency. The volume and weight of the transformer and filter elements are greatly reduced, and the power density and response speed are improved. The high-precision closed-loop control of high voltage is realized by using a high-speed digital signal processor, the stability and anti-interference ability are improved, and the parameter remote configuration and update are facilitated.

[0004] In order to achieve the above purpose, the technical scheme adopted by the present application is: The application provides a cold cathode ray machine digital control system based on high-frequency inversion and pulse modulation, and specifically comprises the following: A main control and calculation module is used for receiving instructions from a human-computer interface and a communication module and receiving real-time data from a precision sensing and acquisition module and a safety interlocking and state monitoring module, and specifically comprises an MPU main processor for adaptive pulse parameter calculation, dose management, user interface, communication protocol stack management and data recording, a real-time coprocessor FPGA for executing millisecond / microsecond-level real-time closed-loop control algorithms, pulse parameter calculation and safety logic processing, and connected with the MPU main processor through a high-speed bus to share memory communication, high-speed memory RAM, nonvolatile storage and a precision clock source; A high-frequency high-voltage inversion and modulation module comprises a digital controller for receiving instructions from the main control and calculation module and generating PWM / pulse control signals, a wide bandgap semiconductor driver for providing isolation protection, a wide bandgap semiconductor power stage module for core power conversion, a high-frequency power transformer for high-frequency, high-efficiency and high-insulation voltage boosting, and a multi-stage sampling resonance network module for sampling anode high voltage to a low-voltage measurable range and performing filtering processing; A pulse driving and field emission control module is used for providing high voltage for field emission of cathodes and anodes of the ray machine, and specifically comprises a pulse interface and logic unit for receiving high-voltage pulses output by the high-frequency high-voltage inversion and modulation module and performing logic on-off control, a gate / extraction voltage control circuit for providing accurate and fast response gate voltage or extraction voltage to the cold cathode, a cathode biasing and stabilizing circuit for providing a direct current bias potential of the cathode and a local feedback signal for stabilizing field emission, and a cathode current measurement circuit for measuring the cathode emission current emission current sampling circuit, and processing instructions of the master and computing module, controlling the gate / extractor driving circuit, and reading the cathode emission current , calculating the emission stability index, and communicating with the master and computing module in real time microcontroller logic unit; precise sensing and acquisition module, including the anode high voltage down to low voltage high voltage voltage divider, and emission current sensor, dose rate sensor interface, temperature sensor interface, high-speed analog-to-digital converter, and signal conditioning and isolation; safety interlock and state monitoring module, including the safety logic controller connected with the precise sensing and acquisition module, and executing the hard safety logic independent of the master and computing module.

[0005] human-computer interface and communication module, including the main processor interface for connecting with the master and computing module, wireless communication unit, display unit, input unit, cloud platform interface and audio output interface.

[0006] Preferably, the adaptive pulse parameter , , The algorithm used for calculation is as follows: wherein, represents the pulse amplitude setting voltage value calculated in the kth control cycle, with the unit of V; represents the expected emission current value, represents the average emission current measured in the kth control cycle, with the unit of A; , represents the proportional and integral gain; represents the control cycle time, with the unit of s;∑ represents the error integral from the start to the current cycle k; wherein, represents the duration of a single high voltage pulse, with the unit of us or ns; is the pulse width calibration coefficient, determined by the cathode characteristics; is the system reference resolution, is the actual demand resolution, with the unit of LP / mm; represents the repetition frequency of the pulse sequence, with the unit of Hz or kHz; is the frequency scaling factor, determined by the response speed of the high voltage power supply, is the equivalent attenuation coefficient of the target material; is the equivalent attenuation coefficient of the detected material.

[0007] Preferably, the dose management adopts integral calculation of cumulative dose and compares with the target dose , then controls the exposure time or adjusts the pulse parameters to achieve the target dose, the cumulative dose is calculated by integral as follows: is the feedback dose rate, unit: Gy / s.

[0008] Preferably, the multi-stage sampling resonant network module in the high-frequency high-voltage inverter and modulation module adopts LLC resonant converter output voltage , which is calculated by the following formula: is the output DC bus voltage, is the input DC voltage, unit: V; N represents the turns ratio of transformer secondary / primary; M is the voltage gain, which is related to the switching frequency; Q is the quality factor; ; is the normalized frequency, ; is the resonant frequency, .

[0009] Preferably, the multi-stage sampling resonant network module in the high-frequency high-voltage inverter and modulation module adopts PWM duty cycle control model to calculate the output voltage : , wherein, is the topology factor, when the full-bridge structure is , N is the turns ratio of transformer secondary / primary; represents the PWM signal duty cycle and satisfies 0<D<1; the digital PI control algorithm is as follows: , wherein, represents the duty cycle setting of the kth period; is the anode voltage feedback of the kth period, unit: V; , respectively represent the proportional and integral gain of the voltage loop; represents the control period, unit: s.

[0010] Preferably, the gate / extracting pole control circuit in the pulse driving and field emission control module controls the field emission current density J The equation is as follows: wherein, J represents the emission current density, unit: A / m 2 ; A represents the effective emission area constant, unit: A·m -2 ·V -2 ; represents the field enhancement factor; E represents the applied electric field intensity, unit: V / m.

[0011] Advantages: 1. The application first proposes a "high-frequency inverter, pulse modulation and cathode state" closed-loop control scheme, solves the fragmentation problem of independent operation of the power supply, control and transmitter of the traditional system, and realizes cross-module collaborative optimization.

[0012] 2. The application reduces the corresponding delay from the traditional 100us level to below 5us through algorithm optimization, significantly speeds up, and can realize pulse-level real-time regulation; at the same time, the current and voltage precision regulation is also significantly improved, and the dose can be accurately and stably output.

[0013] 3. Based on the accurate current, voltage and dose precision regulation, the application can further improve the spatial resolution and time resolution, further reduce the minimum detectable defect, and improve the dynamic imaging capability from the traditional static to real-time imaging. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0015] Figure 1 is the system principle block diagram of the application. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, not all embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0017] Therefore, the following detailed description of embodiments of the application provided in the accompanying drawings is not intended to limit the scope of the application claimed, but merely represents selected embodiments of the application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0018] Embodiment 1: The present application provides a cold cathode ray machine digital control system based on high-frequency inverter and pulse modulation, specifically comprising: Master Control & Computation Module, in order to facilitate subsequent description, avoid long text statements, affect understanding, in the embodiment part, it will be referred to as MCC in the future, for real-time receiving instructions from human-computer interface and communication module and receiving real-time data from precision sensing and collecting module and safety interlocking and state monitoring module, specifically including MPU main processor for adaptive pulse parameter calculation, dose management, user interface, communication protocol stack management and data recording, this embodiment adopts high-performance multi-core ARM Cortex-A or RISC-V SoC, and realizes in the mode of Linux or RTOS; and real-time coprocessor FPGA for executing millisecond / microsecond level real-time closed loop control algorithm, pulse parameter calculation, safety logic processing, which is connected with MPU main processor through high-speed bus shared memory communication. Although real-time coprocessor FPGA is not the main processor MPU, its role is irreplaceable, and it is the core of information processing of the whole system. High-speed FPGA or real-time MCU with FPU / DSP, such as Cortex-M7 / M4, is used for executing millisecond / microsecond level real-time closed loop control algorithm, pulse parameter calculation, safety logic processing. The MPU communicates through high-speed bus, such as PCIe, AXI, shared memory communication. High-speed memory RAM, traditional DDR3 / 4, non-volatile storage eMMC or plugable SD card, is used for storing system configuration, calibration data, algorithm model, running log. And provide system synchronization clock precise clock source. Since the present system is a highly integrated system, in order to facilitate the understanding of those skilled in the art, at the same time, it is also convenient to further elaborate the present application, the working principle and the role played in the whole system will be elaborated in the following embodiment, taking functional module as the unit. From the role of the whole system, MCC plays the role of the central nervous system, which is used for receiving HCI instructions and real-time data of PSA / SISM. It undertakes a large number of core operations, mainly including calculating target dose , target imaging characteristics, such as material attenuation coefficient or penetration , resolution , real-time feedback , Dynamic calculation of optimal pulse parameters , , ; also includes providing a set value to the HFHI , and based on closed-loop adjustment. And by integrating the cumulative dose and compared with the target dose , control the exposure time or adjust the pulse parameters to achieve the target dose.

[0019] High-frequency high-voltage inverter and modulation module, English full name High-Frequency High-Voltage Inverter & Modulation Module, in the embodiment part, hereinafter referred to as HFHI, including a digital controller for receiving instructions from the master control and calculation module and generating PWM / pulse control signals, referred to as DCtrl, a special high-voltage control ASIC or high-speed MCU / FPGA of the digital controller and the FPGA of the MCC are closely coordinated; receiving instructions from the MCC, including , , , to generate PWM / pulse control signals.

[0020] Wide-bandgap semiconductor driver with isolation protection, referred to as WGD, in this embodiment, high-speed and high-drive-capacity SiCMOSFET or GaNHEMT gate driver is adopted. Wide-bandgap semiconductor power stage module for core power conversion, referred to as WGP, which is implemented based on SiCMOSFET or GaNHEMT full-bridge, half-bridge or LLC resonant inverter topology structure. High-frequency power transformer for high-frequency, high-efficiency, high-isolation voltage boost, referred to as HFT, using low-loss magnetic cores such as nanocrystalline, ferrite and litz wire winding; and a multi-stage sampling resonant network module for scaling down the sampled anode high voltage to a low-voltage measurable range and performing filtering processing, which specifically includes a filter using a resonant network / high-frequency rectification filter circuit based on LLC resonant topology, a high-voltage sampling unit and a primary current sampling unit; the high-voltage sampling unit uses a precise high-voltage voltage dividing resistor network to scale down the sampled anode high voltage to a low-voltage measurable range , and the primary current sampling unit uses a current transformer CT or a low-inductance sampling resistor combined with an isolation amplifier to measure the inverter primary current The main functions and working principle of HFHI include high-frequency inversion, rectification and filtering / resonant conversion, pulse modulation, and high-voltage closed-loop control; among them, the high-frequency inversion process is performed by DCtrl based on the target output voltage. The pulse parameters are used to generate a high-frequency PWM signal. WGD drives the WGP switch, and HFT boosts the primary low-voltage high-frequency AC to the secondary high-voltage high-frequency AC. The rectification and filtering / resonant conversion process involves the secondary high voltage being rectified and filtered, or directly obtaining a stable high voltage through a resonant network. The pulse modulation process involves DCtrl controlling the switching timing of WGP to modulate the stable high voltage to meet the requirements. , , Required high voltage pulse Sequence. For example, amplitude modulation is achieved by changing the PWM duty cycle or phase shift angle, and pulse width and frequency are controlled by switching timing. The high-voltage closed-loop control process includes reading via DCtrl. (represent = * ) and with By comparing and adjusting PWM parameters in real time, such as duty cycle D, switching frequency, or phase shift angle, the output voltage can be stabilized.

[0021] The Field Emission Driver & Control Module (FDEC), used in the embodiments section, provides high voltage for field emission to the cathode and anode of the X-ray machine. Specifically, it includes a module for receiving high-voltage pulses output from the high-frequency high-voltage inverter and modulation module. The pulse interface and logic unit (PIL) for logic on / off control provides precise and fast-response gate voltage. Or extract pressure The gate / extraction electrode control circuit for the cold cathode, abbreviated as GDC / EDC, provides the DC bias potential of the cathode and the local feedback signal for stabilizing field emission. The cathode bias and stabilization circuit, abbreviated as CBS, is used to measure the cathode emission current. The emission current sampling circuit and the instructions from the main control and computing module control the gate / extraction electrode drive circuit, and read the cathode emission current. The microcontroller logic unit (μCL) calculates launch stability parameters and communicates with the main control and computing modules in real time. Its working principle is briefly described as follows: High-voltage pulse application: The high-voltage pulse... Safe and precise application to the cold cathode structure (typically, the cathode is at a negative high voltage relative to the gate / anode). Gate / extraction electrode control: based on fine-tuning instructions from the MCC. Fine adjustment or Optimized field distribution, control of emission current density and focal spot size. Emission current monitoring: high precision, high speed measurement of cathode emission current per pulse Waveform, including amplitude, rise / fall time, stability. Emission stability evaluation: μCL real-time analysis of cathode emission current Waveform, if exceeds system threshold, set alarm to MCC. Fast shutdown: can quickly cut off high voltage pulse when detecting unstable emission or receiving safety instruction Pathway to cathode or gate voltage of clamping.

[0022] Precision Sensing & Acquisition Module, in the embodiment part, hereinafter referred to as PSA; including the anode high voltage Fall to low voltage High voltage voltage divider, and emission current sensor, dose rate sensor interface, temperature sensor interface, high-speed analog-to-digital converter, and signal conditioning and isolation; this part of the embodiment uses existing technology in technology, mainly completes signal conversion: various physical quantities (high voltage, current, dose rate, temperature) are converted into analog electrical signals by sensors. Precision conditioning: amplify, filter, and linearize weak or high common-mode signals to meet the ADC input range. Electrical isolation: provides safety isolation between high voltage / power parts and low voltage digital control parts to prevent ground loop interference and high voltage intrusion. High-speed synchronous acquisition: ADC synchronously digitizes all sensor signals at a high sampling rate under precise clock control; data transmission: digitized data stream is transmitted to MCC in real time through a high-speed interface.

[0023] Safety interlock and status monitoring module, in the embodiment part, hereinafter referred to as SISM; including a safety logic controller connected to the precision sensing and acquisition module and executing independent hard safety logic of the main control and computing module. Specifically includes safety logic controller: high-reliability PLC, safety MCU or special safety relay logic, executes independent hard safety logic of MCC. Safety input interface: connects all safety-related sensors: door interlock switch, emergency stop button, vacuum level sensor relay output, over-temperature sensor, dose accumulation overrun signal, etc. Safety output interface: drives safety relays, contactors, audible and visual alarms. Hardware watchdog: monitors the running status of MCC and SLC itself, triggers reset or safety shutdown if timeout without response. Health monitoring sensor interface: connects vibration sensors, more precise temperature / humidity sensors, etc. This part is only a functional integration, and there is no algorithm innovation in technology, and the working principle is not substantially different from existing technology, which will not be described here.

[0024] Human-Computer Interface & Communication Module, in the embodiment part, hereinafter referred to as HCI, including a main processor interface for connecting with the main control and computing module, a wireless communication unit, a display unit, an input unit, a cloud platform interface and an audio output interface. This part is also functionally integrated, and there is no innovation in the algorithm and structure part in the technology, and there is no substantial difference in working principle with the prior art, which will not be described here.

[0025] Embodiment 2: This embodiment provides a specific optimization algorithm on the basis of embodiment 1, mainly including the technical content of the present application in solving self-adaptation, high precision and fast response, which makes new innovative contributions to the prior art, specifically including the self-adaptive pulse parameter , , The algorithm used for calculation is as follows: Among them, represents the pulse amplitude setting voltage value calculated in the kth control period, unit: V; represents the expected emission current value, represents the average emission current measured in the kth control period, unit: A; , represents the proportional and integral gain; represents the control period time, unit: s; ∑ represents the error integral from the start to the current period k; Among them, represents the duration of a single high-voltage pulse, unit: us or ns; is a pulse width calibration coefficient, determined by the cathode characteristics; is the system reference resolution, is the actual required resolution, unit: LP / mm; represents the repetition frequency of the pulse sequence, unit: Hz or kHz; is a frequency scaling factor, determined by the response speed of the high-voltage power supply, is the equivalent attenuation coefficient of the target material; is the equivalent attenuation coefficient of the detected material.

[0026] In this embodiment, the dose management adopts integral calculation of cumulative dose And the target dose Comparatively, the exposure time is controlled or the pulse parameters are adjusted to reach the target dose, and the cumulative dose The integral calculation is as follows: The feedback dose rate is Gy / s.

[0027] Preferably, the multi-stage sampling resonant network module in the high-frequency high-voltage inverter and modulation module adopts an LLC resonant converter output voltage The output voltage is calculated by the following formula: The output DC bus voltage is V. The input DC voltage is V; N represents the transformer secondary / primary turns ratio; M is the voltage gain, which is related to the switching frequency; Q is the quality factor; ; The normalized frequency is ; The resonant frequency is .

[0028] In this embodiment, the multi-stage sampling resonant network module in the high-frequency high-voltage inverter and modulation module adopts a PWM duty cycle control model to calculate the output voltage : Wherein, is the topology factor, and when the full-bridge structure is N is the transformer secondary / primary turns ratio; represents the PWM signal duty cycle and satisfies 0<D<1; the digital PI control algorithm is as follows: Wherein, represents the kth cycle duty cycle setting; is the kth cycle anode voltage feedback, V. , represent the voltage loop proportional and integral gain, respectively; represents the control period, s.

[0029] In this embodiment, the gate / extractor control circuit in the pulse drive and field emission control module controls the field emission current density J The equation is as follows: Wherein, J represents the emission current density, A / m 2; A represents an effective emitting area constant, unit: A m -2 ·V -2 ; represents the field enhancement factor; E represents the applied electric field intensity, unit: V / m.

[0030] The above only represents the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A digital control system for a cold cathode ray machine based on high frequency inverter and pulse modulation, characterized in that: Comprise: Master control and computing module, for receiving instructions from human-computer interface and communication module in real time and receiving real-time data from precision sensing and collecting module and safety interlocking and state monitoring module, specifically including MPU main processor for adaptive pulse parameter calculation, dose management, user interface, communication protocol stack management and data recording, real-time coprocessor FPGA connected with MPU main processor through high-speed bus shared memory communication for executing millisecond / microsecond level real-time closed-loop control algorithm, pulse parameter calculation and safety logic processing, and high-speed memory RAM, non-volatile storage and precision clock source; The high-frequency high-voltage inverter and modulation module includes a digital controller for receiving instructions from the master and calculation module and generating PWM / pulse control signals, a wide-bandgap semiconductor driver providing isolation protection, a wide-bandgap semiconductor power stage module for core power conversion, a high-frequency power transformer for high-frequency, high-efficiency, high-isolation voltage boosting, and a multi-stage sampling resonance network module for sampling the anode high voltage Downscale to low-voltage measurable range , and a multi-stage sampling resonance network module for filtering and processing The application relates to a pulse driving and field emission control module for providing high voltage for field emission of cathodes and anodes of a ray machine, which comprises a high-voltage pulse output for receiving high-frequency high-voltage inverter and modulation module output A pulse interface and logic unit for logic on-off control, which provides accurate and fast response gate voltage Or extraction pressure A gate / extraction electrode control circuit for a cold cathode, a cathode biasing and stabilizing circuit for providing a direct current biasing potential of the cathode and a local feedback signal for stabilizing field emission of the cathode, an emission current sampling circuit for measuring the emission current of the cathode A microcontroller logic unit for processing instructions of a host and calculation module, controlling the gate / extraction electrode driving circuit, calculating an emission stability index by reading the emission current of the cathode and communicating with the host and calculation module in real time ​ A precision sensing and acquisition module, including a high voltage divider to reduce anode high voltage to low voltage a high voltage divider to reduce anode high voltage to low voltage a high voltage divider to reduce anode high voltage to low voltage, an emission current sensor, a dose rate sensor interface, a temperature sensor interface, a high speed analog to digital converter, and signal conditioning and isolation; Safety interlocking and state monitoring module, comprising a safety logic controller connected with the precision sensing and collecting module and executing a hard safety logic independent of the master control and computing module.

2. Human-computer interface and communication module, comprising a main processor interface for connecting with the master control and computing module, a wireless communication unit, a display unit, an input unit, a cloud platform interface and an audio output interface.

3. The digital control system for cold cathode ray machine based on high frequency inverter and pulse modulation according to claim 1, characterized in that: The adaptive pulse parameters , , The algorithm employed for the calculation is as follows: wherein, represents the pulse amplitude setting voltage value calculated in the kth control cycle, unit: V; represents the expected emission current value, represents the average emission current measured in the kth control cycle, unit: A; , represents the proportional and integral gain; represents the control cycle time, unit: s; ∑ represents the error integral from the start to the current cycle k; wherein, represents the duration of a single high voltage pulse, in us or ns; is a pulse width calibration coefficient, determined by the cathode characteristics; is the system reference resolution, is the actual required resolution, in LP / mm; is the repetition frequency of the representative pulse sequence, in Hz or kHz; is the frequency scaling factor, determined by the response speed of the high voltage power supply, is the equivalent attenuation coefficient of the target material; is the equivalent attenuation coefficient of the detected material.

4. The digital control system for cold cathode ray machine based on high frequency inverter and pulse modulation according to claim 1, characterized in that: The dose management employs an integration to calculate a cumulative dose and compares it to a target dose and controls the exposure time or adjusts the pulse parameters to reach the target dose, the cumulative dose is integrated as follows: is the feedback dose rate in Gy / s.

5. The digital control system for cold cathode ray machine based on high frequency inverter and pulse modulation according to claim 1, characterized in that: The LLC resonant converter output voltage is adopted in the multi-stage sampling resonant network module in the high-frequency high-voltage inverter and modulation module The calculation is obtained by the following formula: is an output DC bus voltage, is an input DC voltage, in V; N represents the transformer secondary / primary turns ratio; M is the voltage gain, which is related to the switching frequency; Q is the quality factor; ; is the normalized frequency, ; is the resonance frequency, .

6. The digital control system for cold cathode ray machine based on high frequency inverter and pulse modulation according to claim 1, characterized in that: The multi-stage sampling resonant network module in the high-frequency high-voltage inverter and modulation module adopts a PWM duty cycle control model to calculate an output voltage : wherein, is the topology factor, and for full-bridge topology N is the transformer secondary / primary turns ratio; D represents the duty cycle of the PWM signal and satisfies 0 < D < 1; and a digital PI control algorithm is as follows: wherein, represents the duty cycle setting of the kth cycle; is the anode voltage feedback of the kth cycle, in V; , respectively represent the voltage loop proportional and integral gains; represents the control period, in s.

7. The digital control system for cold cathode ray machine based on high frequency inverter and pulse modulation according to claim 1, characterized in that: The pulse driving and field emission control module controls the field emission current density by the gate / extractor control circuit J The equation is as follows: wherein J represents the emission current density, unit: A / m 2 ; A represents the effective emission area constant, unit: A·m -2 · V -2 ; represents the field enhancement factor; E represents the applied electric field intensity, unit: V / m.

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