Research On High-voltage High-power Parallel Resonant SCR Induction Heating Power Supply

Thyristor is still widely used in the field of power and intermediate frequency induction heating power supply with its large capacity, high voltage, high frequency and so on. Especially in the case of the same capacity, compared with self turn-off devices(such as power MOSFET, IGBT), thyristor has incomparable advantages in the cost. Thyristor intermediate frequency induction heating power supply is mainly used for melting, diathermy and quenching, and has a very real sense in replacing high-polluting heating methods such as coking coal heating, so should be developed furthermore. At present, the induction heating power supply mainly depends on the bridge rectifier to regulate output power, but followed by the great increase in reactive power flowing through equipments and transmission grid, making the input voltage drop a lot and harmonic pollution aggravate. As a result, it is not conductive to improve the quality of electricity and operating conditions of electrical equipment. In this paper, high-voltage power inverter is presented to achieve constant output power regulation.Firstly, this paper proposes the development of intermediate frequency induction heating power supply, then theoretical basis is described, at the same time the characteristics and applications of induction heating technology is also summarized.Additionally, the inverter structure in main circuit, operating principle and working conditions of thyristor intermediate frequency power supply is analyzed. On the other hand, a mathematical model of the inverter working conditions is established, and the method of undetermined coefficients is applied to solve transient and steady-state expressions using the Mathematic8software. Finally, the simulation results are realistic.Again, the analysis of the existing control strategies of induction heating is presented, and the advantages and disadvantages of these methods are also compared. A phase-locked loop circuit is designed to control the inverter in this paper, and maintains constant power during heating process. Simulation model based on Matlab/Simulink tool is established and experiment is conducted on the prototype. The correction of control scheme is verified through simulation and experiment results.Finally, a design of the main circuit using the thyristors in series for each arm is proposed. Static and dynamic working conditions of the thyristors in series are analyzed using Matlab/Simulink software. The distribution of current, voltage and capacitance between two series thyristors should be considered in the design of protection circui.