Research On High-frequency Induction Heating LLC Voltage-fed Inverters Parallel Operation

High frequency induction heating power supply is widely used in mental treatment industrial nowadays, so research on it is important more than ever. Firstly, the topology and circuit specification of the LLC resonant topology characteristic of voltage-fed inverter is discussed briefly in this paper, and analyzed the inverter power output, current and voltage. In order to realize the power control, analyzed the two LLC resonant inverter parallel system.This paper proposes a novel approach to control and regulate the inverter output power by controlling the phase-shift between two-inverters. At the same time use the advantage of LLC load resonant circuit current transformation, cancel the volume and low efficiency of high-frequency transformer.And two parallel connection LLC voltage-fed resonant inverters are adopted to improve power capacity.The paper studies digital control scheme of resonance inverter frequency-racking based on digital phase-locked loop. Through analyzed the digital phase lock loop structure and working principle, and put forward a kind of digital based on FPGA phase lock loop control method. Design hardware circuit of the system, and the digital phase lock control section is designed by using VHDL. The simulation results are proved the validity of the design. Then do the experiment by using the FPGA as control chip. Finally a prototype of two parallel connection LLC voltage-fed resonant inverters is designed and validated, the prototype experimental results validate the proposed approach feasibility.