Induction heating (IH) converters commutate close to resonant frequency to supply maximum power to the workpiece. Therefore, the correct identification of the tank’s resonant frequency is a matter of vital importance in most IH converters. Detection of resonant frequency is based on the calculation of the phase-shift between two electric variables. In order to control this phase-shift between two electric variables, most IH converters use a PLL system.
Most PLL systems used in IH converters are analog PLLs that use integrated circuits from the CD4046 circuit family and analog low pass filters. Although analog control has demonstrated to be effective and accurate, it is less flexible and robust to the degradation of the components than digital control. Due to the advantages of digital control presented above, DSPs or field-programmable gate arrays (FPGAs) have been used to implement PLLs. But as hardware components are used, the change of components is needed in the case of changing parameters. In software PLL systems, many of the parameters used during the control, like frequency, dead time or filters, can be adjusted with no changes in hardware.
Kwon Chang Hyok, a researcher at the Faculty of Mechanical Science and Technology, has proposed a method for implementing the resonant frequency tracking control, the main control in IH systems used in various sectors of the national economy, by using a software PLL algorithm, conducted a simulation to evaluate the stability and reliability of control, and verified them through several experiments in the IH system with LLC.
The proposed software PLL algorithm can be applied to induction heating systems as well as to various fields where phase-shift control of both signal waveforms is necessary.
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