WO2013064329A1

WO2013064329A1 - An induction heating cooker

Info

Publication number: WO2013064329A1
Application number: PCT/EP2012/069843
Authority: WO
Inventors: Namik Yilmaz; Metin OZTURK; Hakan Suleyman YARDIBI
Original assignee: Arcelik Anonim Sirketi
Priority date: 2011-11-03
Filing date: 2012-10-08
Publication date: 2013-05-10
Also published as: EP2774259B1; EP2774259A1; TR201718435T3

Abstract

The present invention relates to an induction heating cooker (1) comprising a bridge rectifier (3) that converts the alternative current to direct current, a DC-line inductor (4) and a DC-line capacitor (5) disposed at the output of the bridge rectifier (3), a parallel resonant circuit (8) having an induction coil (6) and a resonant capacitor (7) connected in parallel to the induction coil (6), a power switch (9) having an IGBT (Insulated Gate Bipolar Transistor) and a freewheel diode (D) connected in parallel to the IGBT, which changes to the conducting state in the closed position and provides the resonant capacitor (7) to be charged, providing the delivery of the energy stored in the resonant capacitor (7) to the vessel (K) by means of the induction coil (6) in the open position, and wherein the current passing through the power switch (9) can be detected in the open and closed positions of the power switch (9).

Description

AN INDUCTION HEATING COOKER

The present invention relates to an induction heating cooker comprising electronic elements that carry high current.

The induction heating cooker functions according to the principle of heating a cast iron or steel ferromagnetic cooking container with the magnetic field effect generated by the induction coil. In order to drive the induction coils generating magnetic field, high amount of electric current is passed through the power switch (IGBT-Insulated Gate Bipolar Transistor, diode or Mosfet) on the circuit board. In the state of the art, the half bridge series resonant (HBSR) circuits realized by using two power switches and two resonant capacitors, and the single switch quasi resonant (SSQR) circuits realized by one power switch and one resonant capacitor are used for driving a single induction coil. The single switch quasi resonant (SSQR) circuits are preferred due to cost advantage however they function in narrower energy frequency range as compared with two-power-switch structure and the maximum power obtained is limited. In the single switch quasi resonant circuits, the power switch draws high amplitude capacitor charge currents and the said high currents cause the power switch to be damaged and shorten the life span of the induction heating cooker. Therefore, the destructive peak currents passing through the power switch are required to be detected and the peak currents are prevented from being generated by adjusting the time the power switch remains closed during which it conducts the current and the time it remains open during which it cuts off the current. In the state of the art, current detection resistors connected in series to the power switch are used for detecting the current on the power switch. Additional components are needed for bringing the voltage measured on the current detection resistors connected in series to the power switch to a level so as to be processed by the control unit and thus the cost of the circuit board increases.

In the United States Patent Application No. US2010006563, an induction heating device operating method is explained. In the induction heating device, the current detection resistor connected in series to the power switch is used for detecting the current passing through the power switch.

The aim of the present invention is the realization of an induction heating cooker wherein the electric current passing through the power switch is detected.

The induction heating cooker realized in order to attain the aim of the present invention, explicated in the first claim and the respective claims thereof comprises a bridge rectifier that converts the alternative mains current to direct current, a DC-line inductor and a DC-line capacitor disposed at the output of the bridge rectifier and which deliver DC voltage in a certain frequency range by filtering the voltage generated in the DC-line, a parallel resonant circuit having an induction coil and a resonant capacitor, a power switch having an IGBT which drives the parallel resonant circuit and a freewheel diode connected in parallel to the IGBT and a voltage change detection circuit connected in parallel to the DC-line capacitor and which detects the voltage changes on the DC-line capacitor. The control unit calculates the current that passes through the freewheel diode and the IGBT, which are the components of the power switch, in the open and closed positions of the power switch according to the signals received from the voltage change detection circuit.

In an embodiment of the present invention, the voltage change detection circuit comprises a voltage divider circuit which reduces the DC-line voltage to an easily-detectable level and a derivation circuit which is connected in series to the voltage divider circuit and calculates the change of the voltage with respect to time (dv/dt).

The voltage divider circuit comprises three resistors connected in series, that do not require special design and two capacitors connected in parallel to the resistors. The derivation circuit comprises a resistor and a capacitor connected in series.

In the induction heating cooker of the present invention, for detecting the current passing through the power switch, considering that the current passing through the power switch also passes through the DC-line capacitor under all circumstances, a voltage change detection circuit which detects the voltage changes on the DC-line capacitor is used instead of high cost current detectors such as current transformers or shunt resistors and thus the currents passing through the power switch can be detected. The voltage change detection circuit consists of low cost standard resistance and capacitance elements.

The induction heating cooker realized in order to attain the aim of the present invention is illustrated in the attached figures, where:

Figure 1 – is the schematic view of an induction heating cooker.

The elements illustrated in the figures are numbered as follows:

Induction heating cooker
Mains filtering circuit
Bridge rectifier
DC-line inductor
DC-line capacitor
Induction coil
Resonant capacitor
Parallel resonant circuit
Power switch
Collector node
Voltage measuring unit
Drive circuit
Control unit
Voltage change detection circuit
Voltage divider circuit
Derivation circuit

The induction heating cooker (1) comprises a filtering circuit (2) that filters the AC mains voltage, a bridge rectifier (3) that converts the alternative current to direct current, a DC-line inductor (4) and a DC-line capacitor (5) disposed at the output of the bridge rectifier (3) and which deliver DC voltage in a certain frequency range by filtering the voltage generated in the DC-line, a parallel resonant circuit (8) having an induction coil (6) that provides the vessel (K) placed thereon to be heated and a resonant capacitor (7) connected in parallel to the induction coil (6), a power switch (9) having an IGBT (Insulated Gate Bipolar Transistor) and a freewheel diode (D) connected in parallel to the IGBT, which changes to the conducting state in the closed position and provides the resonant capacitor (7) to be charged, providing the delivery of the energy stored in the resonant capacitor (7) to the vessel (K) by means of the induction coil (6) in the open position, a collector node (10) disposed between the power switch (9) and the parallel resonant circuit (8), whereon the resonant voltage (Vce) is generated in the open position of the power switch (9), a voltage measuring unit (11) that detects the resonant voltage (Vce) on the collector node (10), a drive circuit (12) that provides the power switch (9) to be driven with the required level of drive voltage (Vge) and a control unit (13), preferably a microcontroller, that regulates the operation of the power switch (9) by controlling the drive circuit (12).

In the induction heating cooker (1), energy is stored by charging the resonant capacitor (7) when the power switch (9) is in the closed position and meanwhile current passes through the IGBT on the power switch (9). When the power switch (9) is in the open position, the resonant capacitor (7) is being discharged, meanwhile the resonant voltage (Vce) is generated on the collector node (10) and the current completes its cycle by passing through the freewheel diode (D) connected in parallel to the IGBT.

The induction heating cooker (1) of the present invention comprises a voltage change detection circuit (14) connected in parallel to the DC-line capacitor (5) and which detects the voltage changes on the DC-line capacitor (5) and the control unit (13) which detects the value of the current that passes through the IGBT and the freewheel diode (D) in the open and closed positions of the power switch (9) according to the signals received from the voltage change detection circuit (14).

In the open position of the power switch (9) where the current is conducted through the freewheel diode (D) and in the closed position where the current is conducted through the IGBT, the currents that pass through the power switch (9) also pass through the DC-line capacitor (5) and complete their cycles. The current that passes through the power switch (9) passes through the DC-line capacitor (5) under all circumstances. The voltage change detection circuit (14) detects the voltage changes on the DC-line capacitor (5), and the control unit (13) evaluates the data received from the voltage change detection circuit (14) and detects the value of the current that passes through the DC-line capacitor (5) and hence (since the current of same value passes therethrough) the current that passes through the power switch (9). The DC-line capacitor (5) is used as “current detector”.

The voltage change detection circuit (14) consists of standard electronic components that do not require special design and cost advantage is provided.

In an embodiment of the present invention, the voltage change detection circuit (14) comprises a voltage divider circuit (15) which divides and reduces the DC-line voltage to an easily-detectable level, for example from 300 volt to 5 volt and a derivation circuit (16) which is connected in series to the voltage divider circuit (15) and which transmits the information of voltage differentiation on the DC-line capacitor (5) to the control unit (13).

The voltage divider circuit (15) comprises three resistors (R1, R2, R3) connected in series, a first capacitor (C1) connected in parallel to the first and second resistors (R1, R2), between the input node of the first resistor (R1) and the output node of the second resistor (R2) and a second capacitor (C2) connected in parallel to the second and third resistors (R2, R3), between the input node of the second resistor (R2) and the output note of the third resistor (R3).

The derivation circuit (16) comprises a third capacitor (C3) connected in series to the resistors (R1, R2, R3) in the voltage divider circuit (15) and a fourth resistor (R4) which is connected between the output node of the third capacitor (C3) and the ground (GND).

In the induction heating cooker (1) of the present invention, for detecting the current passing through the power switch (9) which carries high-value current, high cost elements such as current transformers or shunt resistors which require special design and which are connected in series to the power switch (9) are not used, the DC-line capacitor (5) is also used as a current detector besides its own function and the voltage changes on the DC-line capacitor (5) are easily detected by the voltage change detection circuit (14). The voltage change detection circuit (14) consists of standard resistance and capacitance elements that do not require special design and cost advantage is provided.

It is to be understood that the present invention is not limited by the embodiments disclosed above and a person skilled in the art can easily introduce different embodiments. These should be considered within the scope of the protection postulated by the claims of the present invention.

Claims

An induction heating cooker (1) comprising a bridge rectifier (3) that converts the alternative current to direct current, a DC-line inductor (4) and a DC-line capacitor (5) disposed at the output of the bridge rectifier (3), a parallel resonant circuit (8) having an induction coil (6) and a resonant capacitor (7), a power switch (9) having an IGBT and a freewheel diode (D) connected in parallel to the IGBT, which changes to the conducting state in the closed position and provides the resonant capacitor (7) to be charged, providing the delivery of the energy stored in the resonant capacitor (7) to the vessel (K) by means of the induction coil (6) in the open position and a control unit (13) which regulates the operation of the power switch (9), characterized by a voltage change detection circuit (14) connected in parallel to the DC-line capacitor (5) and which detects the voltage changes on the DC-line capacitor (5) and the control unit (13) which detects the value of the current that passes through the IGBT and the freewheel diode (D) in the open and closed positions of the power switch (9) according to the signals received from the voltage change detection circuit (14).
An induction heating cooker (1) as in Claim 1, characterized by the voltage change detection circuit (14) that comprises a voltage divider circuit (15) which divides the DC-line voltage and a derivation circuit (16) which is connected in series to the voltage divider circuit (15) and which transmits the information of voltage differentiation on the DC-line capacitor (5) to the control unit (13).
An induction heating cooker (1) as in Claim 2, characterized by the voltage divider circuit (15) that comprises three resistors (R1, R2, R3) connected in series, a first capacitor (C1) connected in parallel to the first and second resistors (R1, R2), between the input node of the first resistor (R1) and the output node of the second resistor (R2) and a second capacitor (C2) connected in parallel to the second and third resistors (R2, R3), between the input node of the second resistor (R2) and the output note of the third resistor (R3).
A induction heating cooker (1) as in Claim 2 or 3, characterized by the derivation circuit (16) that comprises a third capacitor (C3) connected in series to the resistors (R1, R2, R3) in the voltage divider circuit (15) and a fourth resistor (R4) which is connected between the output node of the third capacitor (C3) and the ground (GND).