Development Of Scanning Magnet Power Supply For Proton Therapy Head

Proton therapeutic head is the key component of proton medical equipment.The scanning magnet power supply provides high precision,low ripple and fast changing excitation current for the scanning magnet of therapeutic head,which is the guarantee for the scanning magnet to accurately control the proton beam deflection and expansion in proton medical treatment,thereby affecting the final therapeutic effect.In this paper,a hybrid cascaded scanning magnet power supply based on high and low voltage H-bridge is developed,including hardware structure and control strategy.The high voltage H-bridge ensures the dynamic requirements of current,and the low voltage H-bridge realizes the accuracy requirements of current.Firstly,the main topology of the power supply is determined after analyzing the advantages and disadvantages of each power supply scheme by studying the power supply schemes of scanning magnet at home and abroad.The scanning magnet power supply is mainly composed of input rectifier,H-bridge circuit,output filter circuit and closed-loop control module.Different from the traditional transformer isolation and diode uncontrolled rectifier circuit,the power supply adopts three mutually isolated rectifier modules to make the power supply more compact and efficient.The low voltage H bridge adopts interleaved parallel technology to reduce the output current ripple and improve the output current switching frequency.The control adopts double closed-loop control of current and voltage,and the working principle of the power supply is analyzed in detail.Secondly,the input and output filter circuit of H-bridge circuit is designed.Aiming at the problem of DC capacitor voltage pump caused by the actual operation of the power supply,the corresponding solutions are given to avoid the damage of components caused by voltage pump.For the design of the output filter,based on the Bode diagram in the frequency domain analysis,it is found that the output filter will cause the output oscillation of the power supply,and finally the capacitor current active damping compensation is used to suppress the output oscillation.Double closed loop control of voltage and currentFinally,Matlab/Simulink is used to carry out the simulation and verification,and the software and hardware are designed from a practical point of view.A prototype of scanning magnet power supply is built,and relevant experimental tests are carried out.The simulation and experimental results show that the accuracy of the developed scanning magnet power supply is 23 ppm,the ripple is 24 ppm,and the current change rate reaches 156 k A / s under the rated output current,which meets the design requirements.