Control unit of induction heating unit, induction heating system, and method of controlling induction heating unit

• US 9,247,590 B2
• Filed: 11/22/2010
• Issued: 01/26/2016
• Est. Priority Date: 12/14/2009
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Nippon Steel & Sumitomo Metal Corporation (Nippon Steel Corporation)
• Inventors: Fukutani, Kazuhiko, Mayumi, Yasuhiro, Takechi, Toshiya, Umetsu, Kenji
• Primary Examiner(s): Ross, Dana
• Assistant Examiner(s): MILLER, RENEE LAROSE
• Application Number:
  US13/514,738
• Publication Number:
  US 20120305547A1
• Time in Patent Office: 1,891 Days
• US Class Current: 1/1
• CPC Class Codes: C21D 1/04 with simultaneous application of supersonic waves, magnetic or electric fields
• CPC Class Codes: C21D 1/42 Induction heating
• CPC Class Codes: C21D 11/00 Process control or regulation for heat treatments
• CPC Class Codes: C21D 9/56 Continuous furnaces for strip or wire
• CPC Class Codes: C21D 9/60 with induction heating
• CPC Class Codes: H05B 6/04 Sources of current
• CPC Class Codes: H05B 6/06 Control, e.g. of temperature, of power
• CPC Class Codes: H05B 6/10 Induction heating apparatus, other than furnaces, for specific applications
• CPC Class Codes: H05B 6/104 metal pieces being elongated like wires or bands
• CPC Class Codes: H05B 6/362 with flat coil conductors
• CPC Class Codes: Y02P 10/25 Process efficiency

Abstract

A control unit of an induction heating unit controls AC power output to a heating coil of a transverse type induction heating unit that allows an alternating magnetic field to intersect a sheet surface of a conductive sheet that is being conveyed to inductively heat the conductive sheet. The control unit includes: a magnetic energy recovery switch that outputs AC power to the heating coil; a frequency setting unit that sets an output frequency in response to at least one of the relative permeability, resistivity, and sheet thickness of the conductive sheet; and a gate control unit that controls a switching operation of the magnetic energy recovery switch on the basis of the output frequency set by the frequency setting unit.

Claims

1. An induction heating system which allows an alternating magnetic field to intersect a sheet surface of a conductive sheet which is being conveyed to inductively heat the conductive sheet, the induction heating system comprising:

an induction heating unit including a heating coil which is disposed to face the sheet surface of the conductive sheet; and

a control unit which controls an AC power to output to the heating coil,

wherein the induction heating unit includes;

a core around which the heating coil is wound; and

a shielding plate which is disposed to face a region including an edge of the conductive sheet in a width direction, the shielding plate having a depressed portion at a surface which faces the conductive sheet, and the shielding plate being formed from a metal that is a paramagnetic substance or a diamagnetic substance, and

wherein the control unit includes;

a magnetic energy recovery switch which outputs the AC power to the heating coil;

a frequency setting unit which sets an output frequency in response to at least one of a relative permeability, a resistivity, and a sheet thickness of the conductive sheet; and

a gate control unit which controls a switching operation of the magnetic energy recovery switch on the basis of the output frequency set by the frequency setting unit.

2. The induction heating system according to claim 1,

wherein the shielding plate is disposed in such a manner that a region, which is closer to the edge of the conductive sheet than a region in which an eddy current flowing to the conductive sheet becomes a maximum, and the depressed portion face each other.

3. The induction heating system according to claim 1,

wherein an inner-side edge out of edges of the depressed portion, which is on a closer side of a central portion in the width direction of the conductive sheet, is disposed in such a manner that the edge of the conductive sheet is closer to the inner-side edge than a region in which the eddy current flowing to the conductive sheet becomes a maximum, and

an outer-side edge out of the edges of the depressed portion, which is on a farther side of the central portion in the width direction of the conductive sheet, is disposed in such a manner that the edge of the conductive sheet is closer to the outer-side edge than a region through which the eddy current flows to the edge of the conductive sheet.

4. The induction heating system according to claim 1,

wherein the frequency setting unit acquires an attribute information which specifies the relative permeability, the resistivity, and the sheet thickness of the conductive sheet, and selects a frequency corresponding to the acquired attribute information as the output frequency with reference to a table in which the relative permeability, the resistivity, and the sheet thickness of the conductive sheet, and the frequency are correlated with each other and are registered in advance.

5. The induction heating system according to claim 1,

wherein the control unit further comprises:

an output current setting unit which sets an output current value in response to at least one of the relative permeability, the resistivity, and the sheet thickness of the conductive sheet;

a current measuring unit which measures an alternating current which flows through the induction heating unit; and

a power supply unit which supplies a DC power to the magnetic energy recovery switch and adjusts the alternating current which is measured by the current measuring unit to the output current value which is set by the output current setting unit,

wherein the magnetic energy recovery switch is supplied with the DC power by the power supply unit and outputs the AC power to the heating coil.

6. The induction heating system according to claim 5,

wherein the output current setting unit acquires an attribute information which specifies the relative permeability, the resistivity, and the sheet thickness of the conductive sheet, and selects a current value corresponding to the acquired attribute information as the output current value with reference to a table in which the relative permeability, the resistivity, and the sheet thickness of the conductive sheet, and the current value are correlated with each other and are registered in advance.

7. The induction heating system according to claim 1, further comprising:

an output transformer which is disposed between the magnetic energy recovery switch and the induction heating unit, lowers an AC voltage which is output from the magnetic energy recovery switch, and outputs the lowered AC voltage to the heating coil.

8. The induction heating system according to claim 5,

wherein the magnetic energy recovery switch includes:

first and second AC terminals which are connected to one end and an other end of the heating coil, respectively;

first and second DC terminals which are connected to an output terminal of the power supply unit;

a first reverse conductivity type semiconductor switch which is connected between the first AC terminal and the first DC terminal;

a second reverse conductivity type semiconductor switch which is connected between the first AC terminal and the second DC terminal;

a third reverse conductivity type semiconductor switch which is connected between the second AC terminal and the second DC terminal;

a fourth reverse conductivity type semiconductor switch which is connected between the second AC terminal and the first DC terminal; and

a capacitor which is connected between the first and second DC terminals,

wherein the first reverse conductivity type semiconductor switch and the fourth reverse conductivity type semiconductor switch are connected in series in such a manner that conduction directions at the time of a switch-off become opposite to each other,

the second reverse conductivity type semiconductor switch and the third reverse conductivity type semiconductor switch are connected in series in such a manner that conduction directions at the time of the switch-off become opposite to each other,

the first reverse conductivity type semiconductor switch and the third reverse conductivity type semiconductor switch have the same conduction direction at the time of the switch-off as each other,

the second reverse conductivity type semiconductor switch and the fourth reverse conductivity type semiconductor switch have the same conduction direction at the time of the switch-off as each other, and

the gate control unit controls a switching operation time of the first and third reverse conductivity type semiconductor switches and a switching operation time of the second and fourth reverse conductivity type semiconductor switches on the basis of the output frequency which is set by the frequency setting unit.