Design Of High Output Voltage DC Power Supply For Medical X-ray System

With the development of medical imaging diagnostic technology,high output voltage DC power supply in medical X-ray machine has received extensive attention.This high voltage power supply needs not only high reliability,high efficiency and small size,but also low ripple,fast dynamic response and steady output voltage in a wide load range.The transformer in high voltage power supply needs a high conversion ratio.So its leakage inductance and parasitic capacitance is indeed not negligible.High voltage spike and circulation problem may happen in this system if traditional PWM converter is used.LCC resonant converter has three resonant components and parasitic elements of the high-voltage transformers can be used,so it is adopted as power conversion topology in this thesis.In this thesis,the operation principle is analyzed in detail and a AC equivalent model is established using first harmonic approximation.Then,the voltage gain characteristic curve of LCC resonant converter is deduced.Meanwhile,the digital control method is adopted to realize variable frequency control so that the switches can realize zero-voltage switching from zero to full load.After that,the small-signal model on the basis of extended describing function is derived and verified.Based on the model,the the transform function between output voltage and switching frequency is given,and the PID compensator is designed,making system with good dynamic performance.According to high voltage and low current of high output voltage DC power supply for medical X-ray machine,positive and negative bidirectional twelvefold voltage multiplying rectifying circuit is used.So the transformation ratio and secondary side voltage can be reduced,improving system reliability.Besides,the losses of the LCC resonant converter is analyzed and calculated,and the loss distribution is depicted,which provides basis for system efficiency optimal design.Finally,according to the principles of analysis and parameter design,a full digital controlled prototype is designed and its hardware and software design are explained in details.Experiments are done with this prototype,results show that calculation and simulation matches experimental results,which effectively proves the validity of analysis.