A Study Of Variable Load Of Electromagnetic Thermal Excitation Power Controller

The improving demand of product quality make non-destructive testing more and more important, the non-destructive testing method based on infrared thermal imaging has become the emerging field. The infrared thermal imaging defect detection method requires short heating time of excitation power supply,and needs to replace different material load. The load inductance, resistance parameter may vary greatly, the load resonant frequency will change when heated. The usually way to achieve maximum output power of excitation power supply is frequency tracking. But when in high frequency or frequency changes big, especially in power up, the frequency tracking system may track slower or even not on the track. It exist the disadvantage of narrow tracking range and poor adaptability.This dissertation takes the power supply controller as the main research object, researching the effect of frequency tracking in variable load conditions and solving the problem of power to start slowly and poor tracking. At the same time the application of power supply controller is simply discussed, it analyze the effect of infrared thermal imaging detection based on two kinds of heating form induction heating and hysteresis loss. The main research contents have the following aspects:(1) An improved digital phase-locked loop is designed based on traditional PLL. It briefly describes the working principle and performance, and set up its mathematical model. The phase lock structure is verified by simulation, and it constructs the theoretical foundation for the following.(2) According to the demand of the system this dissertation designs and makes the hardware circuit of the power source controller, concluding design of the main points of power circuit, main control circuit, and phase detection circuit. Because of the A/D conversion results error, a correction algorithm was designed to improve the precision to 2%. Aim at the demand of power supply start fast, stable output, it designs a combination of dichotomy and PI frequency tracking algorithm, and writes the machine program.(3) The experimental platform is built to verify the performance of frequency tracking in different load conditions. The power supply start time control is around 10 ms, and the output frequency stability is within 200 Hz.