高频感应加热电源一般采用高频变压器进行负载匹配.变压器成本高、体积大,不利于电源小型化.为提高电源利用率,获取最大功率,利用静电耦合方式代替高频变压器,实现负载匹配.对三阶谐振(LLC)电路进行特性分析,并利用改进型脉冲密度调制(PDM)方法来调节功率输出,降低了功率半导体器件的开关损耗.采用电容电流作为锁相控制变量进行频率跟踪控制,避免了因控制量过小而失锁的问题.仿真结果表明,LLC电路经过合理的参数设置,可以取代高频变压器,实现负载匹配;结合改进型PDM控制方式,可使逆变器输出电流更加均匀.LLC电路在高频感应加热电源领域具有很大潜力.%Generally,the load matching of high frequency induction heating power supply is achieved by using high frequency transformer,while high cost and bulky of such transformer is not conducive to miniaturization of the power supply.In order to improve the utilization rate of power supply and obtain the maximum power,instead of the high frequency transformer,load matching is realized by using electrostatic coupling method. The characteristics of three-order resonant (LLC) circuit are analyzed,and the power output is adjusted by improved pulse density modulation (PDM) method to reduce the switching loss of power semiconductor device.To avoid the loss of lock caused by the too small control amount,the frequency tracking control of phase locked control variable is conducted by adopting the capacitance current. The simulation results show that through the reasonable parameter setting,the LLC circuit can replace the high frequency transformer to achieve load matching; and by combining the improved PDM control method,the output current of inverter is more uniform.Therefore,the LLC circuit has great potential for application in high-frequency induction heating power supply.
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