Autonomous Energy Matching Control in an LLC Induction Heating Generator

Abstract

Induction heating is one of the most effective methods of energy conversion from the electrical to thermal form, used in diverse industrial processes. In this paper the resonance generators for induction heating are considered for which the equivalent load resistance has a strong impact on the ability of the system to use optimally the potentially available power. The equivalent load resistance varies, depending on the type of induction heating system (IHS) and during the heating process itself. This paper presents an induction heat generator in which an L-LC resonance system (called the LLC system) plays an active role in energy matching. The LLC resonance system is analyzed from the point of view of both the functional dependencies describing the influence of frequency on the load resistance transformation, and the impact of the LLC setup on the sensitivity of the generator to changes in the charge resistance caused by heating. The procedure for initial selection of the resonance system parameters is presented. We also consider the possibility of automatic correction by the generator of the LLC system parameters, in order to limit the effect of changes in the IHS parameters on the degree of source–load energy matching. We describe cascade power control algorithms based on the use of Field Programmable Gate Array (FPGA) systems, which enable the optimal control of energy matching. Our study is based on theoretical considerations, numerical simulations, and experimental verification using a 30 kW model.