Design And Development Of Power System For RTMS Equipment Based On Highly Efficient Push-pull Structure

With the progress of modern society and the faster pace of people’s life,the incidence rate of mental or neurological diseases has sharply increased.Transcranial magnetic stimulation(TMS)is a new noninvasive,painless,noninvasive biological stimulation technology,which has a wide range of applications in the medical diagnosis and clinical treatment of mental or neurological diseases.It is also one of the main directions of brain function research.As an important part of transcranial magnetic stimulator,the output performance of pulsed power system will directly affect the output index and treatment range of TMS equipment.According to the research for market demand,the output performance index of repetitive transcranial magnetic stimulation(rTMS)equipment is proposed with maximum stimulation frequency 25 Hz,maximum discharge current 1500 A,maximum discharge voltage1200 V and maximum magnetic field 0.5T.The design,optimization and development of pulsed power system are carried out,in order to reduce the volume,complexity,cost of rTMS equipment and enhance its reliability.The pulsed power system of rTMS equipment is composed of front rectifier circuit,charging circuit and pulsed discharge circuit.After analysis of the working mechanism of push-pull switching power supply and the mechanism of biphasic wave stimulation discharge circuit generating neuron membrane potential,the front boost PFC rectifier circuit,push-pull charging circuit and biphasic wave discharge circuit are proposed as the circuit topology of the power supply system.the Boost PFC rectifier circuit solves the problem that the power factor of the AC-DC conversion can not achieve the standard.The push-pull charging circuit ensures the convenience and reliability of the control system,and is also conducive to reducing the volume and cost of the system.The biphasic wave discharge circuit has high energy utilization rate,which is conducive to improving the efficiency of the system.According to the design index of rTMS equipment,the parameters of charging and discharging circuit components are calculated and designed.RC snubber circuit and parallel damping resistor are used to optimize the charging circuit,which can effectively reduce the overvoltage caused by oscillation on MOSFET and rectifier diode.It can also protect the switching devices.In addition,according to the turn off process,the fast thyristor is selected as the main discharge switch,with corresponding peripheral protection circuit being designed.In terms of system control,this paper establishes the small signal model of push-pull circuit.In simulation,the average current control strategy is adopted to stabilize the maximum charging voltage to1200 V and the charging current to 1A,which effectively improves the charging accuracy and efficiency of the charging circuit.According to the designed circuit topology,simulation model of charge and discharge is built,by which the theoretical feasibility of rTMS power system and closed-loop control is verified.In the design of hardware,the paper choose stm32f429 as the control core.The capacitor charging module based on push-pull circuit,the pulsed discharge module based on fast thyristor,and the control system based on signal acquisition,switch drive and temperature detection are designed.The dimensions of prototype is390×420×890(mm).By preliminary test,PFC rectifier circuit and discharge circuit are reliable.At last,the output performance of the device is tested in different stimulation modes.The maximum discharge voltage,current,frequency and magnetic field of the prototype are 1100 V,1500A,25 Hz and 0.40 T respectively.The test results show that the rTMS equipment designed in this paper is feasible and can almost satisfy the market demand.