Research Of Dual-frequency Induction Heating Power Supply

Induction heating power supply(IHPS) modules based on the principle of electromagnetic induction have been widely used in smelting, diathermy, quenching and many other applications, showing the advantages of mimimal environmental impact, high thermal efficiency, flexible control, high reliability, precise parameter adjustability etc. In order to meet different heating needs in different settings, research on all kinds of induction heating topologies is gaining momentum. As the structures of the workpieces become increasingly complex and more and more workpieces are made of multi-metal alloys, heating these workpieces usually needs multiple alternating currents with different frequencies. This paper summarizes the work of developping a novel dual-frequency IHPS module, aiming at addressing the deficiency of single-frequency induction heating power supply module in delivering satisfactory heating and quenching for workpieces with uneven surfaces(such as gears and aircraft engine parts). Employing a composite resonant inverter, this IHPS module can be controlled to output two currents with different frequencies simultaneously, or output either of the current separately.This study focused on the topology, operation states, soft switching and components’ voltage stresses of the inverter of the IHPS module, as well as its digital feedback control system. A comparison of several power regulation mechanisms revealed that inserting a DC chopper circuit between the inverter circuit and the rectifier circuit would be conducive to reducing EMI, improving the overall system effieciency and simplifying the design of the digital feedback control system. A BUCK chopper circuit was chosen for power regulation based on this conclusion.The two operation states of the composite inverter(i.e. dual-frequency mode and single frequency mode) were investigated thoroughly and relevant parameters were determined through theoretical analysis. An ideal simulation model for the main topology of dual-frequency IHPS module was established on the Matlab/Simulink simulation platform using these parameters. Finally, on the basis of theory analysis and simulation, a DSP-based prototype of dual-frequency IHPS module was developed, which comprises main circuit, control circuit, drive circuit and sampling circuit. The waveforms obtained in experiment showed good agreement with the ones obtained though theoretical analysis and simulation. In the last part, this paper gives a review of the theory analysis, simulation and experimental verification in this study, together with some suggestions on how to improve the design in order to address the deficiencies of the prototype.