The Research On Adaptive Tracking Control Of Resonant Frequency Of EMAT For High Temperature

This paper investigates the problem of electromagnetic ultrasonic transducer (EMAT) conversion efficiency degradation caused by changes in the resonance frequency. In a high temperature environment, the internal parameters of EMAT will change with temperature, and other parameters of the lift-off change, resulting in a drift natural resonance frequency. To be able to detect the thickness of the high temperature of continuous casting billet, it is necessary to online real-time tracking of the resonance frequency of the EMAT, in order to improve the efficiency of the transducer, which produce high quality ultrasonic signal.Firstly, on the one hand, the purpose of EMAT impedance matching in the initial temperature is to make the EMAT system to achieve the requirement of the ultrasonic nondestructive testing, and make its internal current of EMAT coil maximize when resonance occurs, on the other hand, the dynamics model of EMAT coil is established.Secondly, when the external temperature increases, EMAT system resonance frequency is changed, this time the adaptive neural network control strategy is adopted to track the resonance frequency of the system to realize the system resonance. Although system eventually can track the resonant frequency, its dynamic performance cannot be guaranteed in the process of operation. Therefore, we put forward a new design scheme of using transient performance indicators transformation mechanism, the original system is converted to unfettered. Then the stability of new system can be prove by using Lyapunov stability theory, which indirectly proves that the EMAT system can track the resonant frequency, and transient performance of the system can be guaranteed in the process of system operation, which means that the tracking error should converge to an arbitrarily predefined small residual set, with convergence rate no less than a prespecified value, exhibiting a maximum overshoot less than a sufficiently small prespecified constant.Finally, we design the excitation power supply of EMAT system and study its internal parameters. According to the parameters of the experimental measurements and the control algorithm presented in this paper, we use Matlab simulation to study clarify and verify the approach. The result is consistent with the theoretical analysis.