Power Transmission Characteristics on Load Fluctuation and their Improvements of a High Frequency Induction Heating System Using the Distributed Constant Line

Abstract

In order to improveme the characteristics of high-frequency power supply from an inverter to a resonance load circuit, the authors have been studying a system, consisting of a voltage-fed type inverter, a 1/4 wave-length distributed constant line, and a parallel resonance load circuit, as a new induction heating system. This paper describes a theoretical study performed on the power transmission characteristics of the whole system including the power transmission line, against load fluctuations occurring as conditions of the heated object change.
Our study has clarified, first, differences as well as problems in characteristics between the case where the inverter operating frequency is kept constant, and the case where inverter operating frequency follows the load resonance frequency. Second, it has been confirmed that power transmission characteristics can be always kept optimum under optimum load conditions, given by improved impedance characteristics of the load circuit against load fluctuations. Finally, we have introduced a new even-number parallel resonance circuit method as a method of approximately reallzing a circuit having such characteristics, analyzed the operating characteristics of this circuit method, and confirmed the usefulness of this method.