| Nuclear fusion is to overcome the electrostatic repulsion between ions by heating the plasma to a certain temperature,a fusion reaction occurs,and nuclear energy is generated.Ion cyclotron resonance heating is an auxiliary heating method commonly used in fusion devices to heat plasma.In the process of heating the plasma,the high-frequency transmitter feeds power to the antenna system via the transmission line,thereby heating the plasma.When the characteristic impedance of the transmission line is equal to the input impedance of the antenna,the transmission efficiency is the largest and the heating efficiency is the highest.During the heating process,the plasma parameters change rapidly,and the input impedance of the antenna also changes rapidly.If the line impedance cannot follow the change,the heating efficiency will seriously decrease.Therefore,the heating efficiency of the plasma is closely related to the impedance matching of the ICRH device.This thesis uses simulation software to simulate the impedance matching system of the ICRH device of the H1 stellarator.The main contents are as follows:Firstly,the finite element analysis software comsol was used to build the antenna simulation model in the ICRH device of H1 star simulator.The input impedance of the antenna was obtained.The electromagnetic field distribution of the antenna was analyzed.The influence of different geometric parameters of the antenna on the input impedance of the antenna was studied.Then,a simulation model of ICRH antenna and plasma coupling is established in comsol software.Through simulation analysis,the plasma electron density changes with time are studied,and the antenna input impedance changes with electron density are obtained.Aiming at the method of controlling the rotation of the vacuum adjustable capacitor screw by the stepper motor,adjusting the capacitance capacity,and achieving the impedance matching,the double closed-loop feedback control of the current speed of the stepper motor is studied,and the fuzzy PID control screw of the stepper motor is designed.The simulink module builds simulation models for PID control and fuzzy PID control of stepper motors respectively,and compares the effects of fuzzy PID control and traditional PID control on adjustable capacitance control.The simulation results show that:(1)During the plasma heating process,the plasma electron density changes rapidly within a short period of time.Within the same time scale,it causes the antenna input impedance to decrease sharply,up to two orders of magnitude,which does not match the transmission line impedance seriously This will cause the power emitted by the high-frequency transmitter to not be effectively fed into the load,resulting in reduced heating efficiency.(2)The adjustable capacitor that realizes impedance matching is a highly nonlinear control object with high frequency and fast speed.Simulation results show that the speed of fuzzy PID control is much smoother than that of PID control,and the system disturbance is smaller.Even when the adjustable capacitance controlled by the stepper motor changes suddenly,fuzzy PID control performs better than PID control.The application of fuzzy PID control stepper motor solves the problem of stepping motor control out of step,thereby improving the heating efficiency of ICRH,which will help the stable operation of the star simulator ICRH device system. |
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