Study On High Voltage DC Power Supply Of Medical X-ray Machine

Medical X-ray machine provides a powerful technical support and guarantee for accurate diagnosis of certain human diseases in modern disease diagnosis. However, clinical application investigation shows that the X-ray source of medical X-ray machine has some defects such as low efficiency, high energy consumption, poor quality of imaging, bad control stability, lower repeat rate, which makes the X-ray machine efficient application in medical field restricted by different degree. High voltage source is the key component of X-ray machines, and its output voltage ripple and adjustability decide the imaging quality and the range of disease diagnosis. For the output voltage characteristic (ripple and adjustability) of X-ray high-voltage source, this paper does a deep research on the influence factors on the output voltage characteristics of high voltage source in X-ray machine and the effect of improvement from the related theoretical analysis and simulation model, respectively, combined with specific experimental platform.The output adjustability of high voltage source in X-ray machine can be realized by the control of high frequency inverter. Smart system configuration and optimal control strategy are to guarantee the reality of good output voltage adjustability. This paper adopted power factor correction (PFC) principle to realize both system power factor correction and output voltage adjustment, and three-phase isolated PFC Cuk high-power circuit was designed and its principle was analyzed. Combined with the characteristics of isolated Cuk circuit, the strategy of one-cycle control power factor correction circuit was employed to educe the one-cycle control equation of Isolated Cuk circuit for the establishment of one-cycle control model. The small signal expression of one-cycle control model circuit was educed to establish the corresponding small signal model and acquire its transfer function of voltage loop, and its PI compensation parameters were calculated. One-cycle control scheme of three-phase isolated PFC Cuk high-power circuit was designed to establish simulation model for the research on the adjustability of output voltage and the correction ability circuit of power factor.Taking advantage of the single-phase full-bridge LLC resonant inverter, a three phase four-leg full-bridge LLC resonant inverter was designed to study the system loss, the symmetry and frequency characteristics of the output voltage. With the help of voltage multiplier, a three-phase two-way symmetrical series voltage multiplier was built to obtain a better output voltage ripple performance, and its running regulations was analyzed and the main output parameters were educed. The system simulation model was established to study further, compared with the single-phase two-way symmetrical multiplier and series three phase voltage multiplier.A single-phase isolated Cuk PFC simulation circuit was established and its simulation was demonstrated. Its main circuit parameters and control loop parameters were calculated, and the magnetic components of main circuit were designed and the control loop was built by employing discrete components. Appropriate independent components were employed to build up this simulation experiments platform, and then the analog output voltage adjustability and power factor correction capability were studied and compared with the digital simulation to verify that this PFC circuit can achieve both high power factor and better performance of output voltage for the high voltage source in X-ray machine while to confirm the correctness of theoretical analysis in this paper.