The Development Of High-power Pulsed Induction Heating Power Supply For Active Thermography

Aiming at the problems of the low electromagnetic coupling efficiency and the poor heating uniformity in the traditional water-cooled copper tube induction heating power,a pulsed exciting power supply with a U-shaped yoke probe is used,and the key technologies of power topology,drive circuit and frequency tracking control are researched.Firstly,the detection theory of pulsed eddy current thermography was introduced,based on this,combined with the special requirements about power density,start-up time and heating uniformity of pulsed eddy current thermography,a high power pulse induction heating power supply is proposed,a probe structure with excitation coil twining the U-shaped yoke is put forward,and the electromagnetic thermal coupling simulation of the probe and sample was analyzed by COMSOL 5.2.;the power supply modules are introduced and calculated in detail by theoretical analysis,the working state of series resonant circuit and the buffer circuit are emphatically analyzed and simulated by Pspice;the driver circuit based on KA962 F is designed and the influence of the parasitic parameters on driving circuit are also analyzed and simulated.Besides,in order to solve the problems of poor stability,weak anti-interference ability and no artificial frequency tracking strategy of the traditional all-digital phase-locked loop frequency tracking technology,a modified all digital fixed-angle frequency tracking technology is proposed.As a consequence of it,the theoretical analysis of all digital fixed-angle frequency tracking technology is addressed in detail.The mathematical expression between system control parameters and the steady and dynamic performance of the system are established.Then the influences of the quality factor,initial frequency and stepped frequency on the dynamic performance of the system are further analyzed.In the end,on the basis of sufficient theoretical analysis and simulation research,a prototype of 20kHz/10 kW pulsed power supply is designed and the power performance is tested,and the pulse eddy thermography experiment is carried out by the power.The result of which shows that the performance of the driving circuit is stable,the modified all digital fixed-angle frequency tracking technology can achieve the frequency tracking quickly in 5 ms,and the tiny metal crack about 0.5 mm depth and 5 mm length can be detected.