Electrical transmission or interconnection systems – Plural load circuit systems – Transformer connections
Reexamination Certificate
2002-08-12
2004-02-24
Riley, Shawn (Department: 2838)
Electrical transmission or interconnection systems
Plural load circuit systems
Transformer connections
C219S662000, C219S666000, C219S671000, C373S147000
Reexamination Certificate
active
06696770
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ac power supply for use in induction heating or melting applications wherein the induction power circuit is resonantly tuned.
BACKGROUND OF THE INVENTION
FIG. 1
illustrates a conventional power supply
110
that is used in induction heating or melting applications. The power supply consists of an ac-to-dc rectifier and filter section
112
, a dc-to-ac inverter section
120
and a tuning capacitor section
130
. For the power supply shown in
FIG. 1
, a three-phase diode bridge rectifier
114
converts three-phase (A, B, C) ac utility line power into dc power. Current limiting reactor L
108
smoothes out the ripple in the output dc current of the rectifier, and capacitor C
108
filters the ac component from the output dc voltage of the rectifier. The filtered dc output of the rectifier is inverted to ac by a full-bridge inverter consisting of solid state switches S
101
, S
102
, S
103
and S
104
and associated antiparallel diodes D
101
, D
102
, D
103
and D
104
, respectively. Alternating turn-on/turn-off cycles of switch pairs S
101
/S
103
and S
102
/S
104
produce a synthesized ac inverter output at terminals
3
and
4
.
Induction load coil L
101
represents the power coil used in the induction heating or melting application. For example, in an induction furnace, load coil L
101
, is wound around the exterior of a crucible in which metal charge has been placed. In an induction heating application, a metal workpiece, such as a strip or wire, may travel through a helical winding of load coil L
101
or otherwise be brought near to the coil to inductively heat the workpiece. Current supplied by the power supply and flowing through load coil L
101
creates a magnetic field that either directly heats the metal charge or workpiece by magnetic induction, or heats the workpiece by heat conduction from a susceptor that is heated by magnetic induction. Load coil L
101
, whether it be a single coil or an assembly of interconnected coil sections, has a very low operating power factor. Because of this, a tuning capacitor (or bank of capacitors), such as capacitor C
101
must be provided in the load coil circuit to improve the overall power factor of the load coil circuit. These tuning capacitors are a significant cost and volume component of the power supply. Therefore, there exists the need for a power supply for inductive heating or melting applications that utilizes smaller and less costly tuning capacitors.
An objective of the present invention is to provide a power supply for inductive heating or melting applications that utilizes a capacitor connected between the output of the rectifier and the input of the inverter to form a resonantly tuned circuit with the induction load coil used in the application.
BRIEF SUMMARY OF THE INVENTION
In one aspect, the present invention is apparatus for, and a method of, providing a power supply with rectifier and inverter sections for use with an induction load coil wherein a tuning capacitor is provided across the output of the rectifier and the input of the inverter to form a resonant circuit with the induction load coil. The induction load coil may comprise an active load coil connected to the output of the inverter, and a passive load coil connected in parallel with a capacitor to form a tank circuit. Other aspects of the invention are set forth in this specification and the appended claims.
REFERENCES:
patent: 4426564 (1984-01-01), Steigerwald et al.
patent: 5968398 (1999-10-01), Schmitt et al.
patent: 6546039 (2003-04-01), Fishman et al.
patent: 195 27 827 (1997-01-01), None
Fishman Oleg S.
Nadot Vladimir V.
Inductotherm Corp.
Post Philip O.
Riley Shawn
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