Research On The Starting Method Of Thyristor Power Supply For Medium Frequency Induction Heating Under Heavy Load Conditions

Due to its advantages of being high in heating temperature, quick in heating speed,and easy in controlling the heating process as well as protecting environment and savingenergy etc, the power supply of thyristor medium frequency induction heating has beenwidely used in the field of industrial production, such as metal smelting, diathermy, heattreatment and so on. With its continuous expanding application, the power demand forsupply would get greatly increasing, and a better startup performance of power supplywould be required, especially in start safe and reliability under heavy load conditions. Inthis paper, we studied on the startup methods of power supply for thyristor mediumfrequency induction heating, proposed a safe and reliable startup method of powersupply for thyristor medium frequency induction heating. The simulation resultsshowed that the method could have better performance to start the inverter under heavyload conditions. The completed works of topic research concretely is as the following.Firstly, based on the mathematical model of load circuit of parallel and seriesinverter, the paper analyzed the dynamic characteristic of the inverter load and themathematical description, under heavy load condition it would be difficult to start. themathematical analysis demonstrated that the smaller equivalent impedance is，the morestrenuous oscillation damped，and the inverter is more difficult to be started.Based on the research of startup method in parallel inverter，the paper confirmedthe reliable commutation in the startup process of the inverter, which is the key toachieve a successful startup of the inverter. The commutation is performed by thyristorof the parallel inverter with load voltage, while the commutation in series inverter isperformed by thyristor with load current. The reason, why the parallel inverter isdifficult to start under heavy load condition, is that the load circuit can not provideenough voltage to make the inverter reliable commutation.Aimed at the puzzle of being difficult to start for parallel inverter under heavy load,we proposed a method of auxiliary bridge in IGBT inverter to start, and it couldeffectively improve the performance of parallel inverter start, especially under heavyload condition with the auxiliary bridge in IGBT inverter. Under different loadconditions based on Matlab/Simulink simulation platform, the paper analyzed relationsbetween the minimum load equivalent resistance of the inverter could start and thepower supply starting ability, the comparative simulation results showed that the start performance of the proposed method under heavy load conditions is better thancurrently available methods.Finally, in consideration of the nonlinear parameters in the process of starting leadto the bad starting ability, the paper studied the fuzzy control technology in the startupprocess of the inverter, completed the design of the fuzzy controller, and conducted thecomparison experiments respectively by traditional control and fuzzy control algorithm,the simulation results showed that the fuzzy control is better than traditional control incontrol performance, it provide a feasible thought for inverter start.