Research On Control Technique Of High Frequency Solid-State Induction Heating Power Supply

Induction heating power supply is widely used in industrial applications for its high efficiency, high heating speed, flexible control and clear heating conditions. Focusing on the existing problems and the hot researching emphasis, this paper deeply studies the rectifier, resonant inverter , resonant tank and control circuit of high-frequency solid-state induction heating power supply respectively. The main productions and conclusions are as the following:1. The topology structure and control technique of three-phase current source rectifier (CSR) are researched. A new SVPWM technique for multilevel three-phase CSR based on the concept of space vector integration is presented, which has the merits of clear concept, simple realization and universal adaptability. Through the new SVPWM technique, the multilevel three-phase converter realizes high power capability, low switching frequency and low grid current harmonic; A new over-modulation method for three-phase CSR is presented to expand its dc output range, which is suitable for application fields where the power source fluctuates severely; A new SCR multilevel three-phase CSR topology and its SVPWM technique are presented to realize high power capability, low costs.2. The switching processes and phase-locking control scheme of voltage-source resonant inverter is researched. The zero-voltage-switching (ZVS) strategy to minimize the power loss, as well as the realization of ZVS phase-locking control method is presented; The mathematical model of the all-digital phase-locked-loop (ADPLL) is established, and the stability and dynamic performances under different control parameters are analyzed deeply; The ADPLL realized by Field Programmable Gate Array (FPGA) is software programmed and operates as hardware mode. Contrasted with the traditional PLL, the ADPLL can increase the stability and accuracy of the inverter control circuit.3. The topology and control strategy of voltage-source LLC resonant circuit are researched, and some important conclusions are as the following: a) The LLC resonant circuit is easy to realize impedance-match between induction heating power supply and heated load, b) comparing with the LC resonant circuit, the LLC resonant circuit is immune to load faults, such as inductor coil open, short and strike, c) when the LLC inverter units are paralleled to increase power capability, the LLC inverter units are robust to output voltage phase error, amplitude error and trigger asynchrony; A double-closed-loop ADPLL control circuit based on the feedbacks of inverter output current and resonant capacitor voltage are designed. And, the switching state of power devices is optimized, which can make the power supply operating safely and efficiently.4. An all-digital controlled high frequency solid-state induction heating power supply topology is designed. And, the control system including three-phase CSR, resonant inverter and protection circuit is realized on one chip FPGA, which is called System on Chip (SoC). The control methods and conclusions proposed in this paper are verified by the topology tests.