Dual frequency heating, melting and stirring with electric induction power
First Claim
1. A method of dual frequency electric induction heating, melting or stirring of a composition or workpiece in an inductive load circuit, the method comprising the step of inserting a dual frequency switch at the output of a H-bridge inverter to the inductive load circuit, the H-bridge inverter having a resonant load tuning capacitance connected across the direct current input to the H-bridge inverter and a tank capacitance connected across the legs of the H-bridge inverter, the dual frequency switch having a low frequency switch position and a high frequency switch position, where in the high frequency switch position the H-bridge inverter operates as a half bridge inverter with each of the legs of the H-bridge inverter connected in parallel by the dual frequency switch, and in the low frequency switch position the H-bridge inverter operates as a full bridge inverter.
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Abstract
A dual frequency output is provided from a DC to AC inverter. An H-bridge inverter is provided with switching arranged to reconfigure the inverter from half-bridge to full bridge so that the inverter'"'"'s output can be switched from high frequency to low frequency, respectively. A resonant load tuning capacitance is utilized across the input of the inverter subsequent to the DC link input (for example from an AC utility fed rectifier) to the inverter. The inductive load circuit at the output of the inverter may be one or more induction coils surrounding a crucible in which an electrically conductive material is placed, or susceptor, or one or more inductors used to heat treat an electrically conductive material. In an alternative arrangement an H-bridge inverter is utilized in both the high and low frequency modes while a tank capacitance is in the circuit, or shorted out of the circuit, respectively, in the high or low frequency modes.
6 Citations
13 Claims
- 1. A method of dual frequency electric induction heating, melting or stirring of a composition or workpiece in an inductive load circuit, the method comprising the step of inserting a dual frequency switch at the output of a H-bridge inverter to the inductive load circuit, the H-bridge inverter having a resonant load tuning capacitance connected across the direct current input to the H-bridge inverter and a tank capacitance connected across the legs of the H-bridge inverter, the dual frequency switch having a low frequency switch position and a high frequency switch position, where in the high frequency switch position the H-bridge inverter operates as a half bridge inverter with each of the legs of the H-bridge inverter connected in parallel by the dual frequency switch, and in the low frequency switch position the H-bridge inverter operates as a full bridge inverter.
- 9. A method of dual frequency electric induction heating, melting or stirring, of a composition or workpiece in an inductive load circuit, the method comprising the step of inserting a dual frequency switch across a tank capacitance of a full bridge inverter having a resonant load tuning capacitor connected across the direct current input of the full bridge inverter, the dual frequency switch having a low frequency switch position and a high frequency switch position, where in the high frequency switch position the tank capacitance is in the inverter circuit and in the low frequency switch position the dual frequency switch shorts out the tank capacitance.
Specification