Research On Control Strategy Of Medical High Voltage Power Supply

Modern medical laser equipment provides a new treatment for some human diseases.As the core device of medical laser equipment,DC high-voltage power supply has essential influence on laser generator,and the intensity and stability of laser are determined by DC high-voltage equipment.At present,75% of the medical laser equipment in China are all foreign-funded and joint-venture products.There are only a few local enterprises,and the quality requirements cannot be comparable to those of foreign products.High-voltage power supply in domestic medical field is monopolized by foreign countries and the cost is relatively high.Therefore,the research on improvement of DC high voltage power supply is the primary task of domestic enterprises in related fields.Traditional high-voltage power supplies are mostly oil-immersed and open-loop designs,which lead to large power supply volume,high voltage output ripple and instability.Thus,it will cause damage to electrical equipment and affect the quality of use.With the continuous emergence of new power electronic devices,switching tube technology is widely used in the design of DC high-voltage power supply.The output voltage is controlled by controlling the duty cycle of PWM waveform.At present,the more mature control method is closed-loop PID control,which has the advantages of simple programming,small controller volume and no need to establish the mathematical model of the controlled circuit.Although PID control can directly control the voltage without establishing a mathematical model,it is easy to generate overvoltage at the initial stage of voltage establishment to cause damage to medical equipment and affect the voltage quality.Aiming at the overvoltage problem,the variable speed PID algorithm and the integral separation PID control algorithm are studied and simulated experimentally.The experimental results show that the variable speed PID and the integral separation PID algorithm can solve the overvoltage problem of general PID control,however,the integral separation algorithm has the problem of high voltage ripple.The weighted integral separation algorithm is further proposed and simulated experimentally.The experimental results show that the weighted integral separation can solve the traditional PID overshoot problem,and the weighted integral separation algorithm has higher output voltage stability and better quality than the general integral separation and variable speed PID algorithm.In order to further reduce the voltage ripple and quickly establish the voltage,this paper analyzes and studies the fuzzy control algorithm and simulates it.The experimental results show that its dynamic response is poor at the initial stage of voltage establishment.Therefore,a fuzzy PID control with self-adjusting weight coefficient is proposed,which not only retains the advantages of fuzzy control,but also takes into account the fast adjustment of PID algorithm,meanwhile,it can establish voltage faster.It is found that the experimental results of weight coefficient self-adjusting fuzzy PID control and weighted integral separation algorithm are similar by comparing the two methods,both of which have higher practical value.Finally,the analysis and outlook are made,and the design deficiencies and the future development direction of high voltage power supply are put forward.