Induction hob and method for determining current of induction hob

Abstract

An induction hob (1) comprises: one or more induction coils (3); a mains supply power line (11) configured to supply an alternating main current (I1); a rectifying circuit (13) configured to rectify an AC main current (I1) supplied by the mains supply line (11) to output a rectified main current (I1); a drive circuit (14) electrically connected to the rectification circuit (13) by means of two rectified current lines, one of which is a ground voltage line (19), said drive circuit (14) comprising electronic switches (U1, U2) selectively controlled to regulate the AC secondary current supplied to the respective induction coils (3); an electronic control unit (10) configured to selectively control electronic switches (U1, U2) of a drive circuit (14) to regulate the secondary current flowing through the induction coil (3); a resistance device (22) having a predetermined resistance and electrically associated with the ground voltage line (19) upstream of the drive circuit (14); an electronic measurement unit (16) electrically connected to the ground voltage line (19) to measure a voltage drop (VD) across the resistive element (22) and to provide an electrical signal (VM) indicative of the measured voltage drop (VD) to the electronic control unit (10). The electronic control unit (10) is configured to determine the main current (I1) based on the electrical signal (VM).

Description

Technical Field

[0001] The present invention generally relates to the field of induction cooktops. More specifically, the present invention relates to determining the mains current supplied to an induction cooktop from a mains line. Background Art

[0002] Induction cooktops for preparing food are well known in the prior art. Typically, an induction cooktop includes a heating zone associated with an induction coil. To heat a cookware item placed on the heating zone, the induction coil is electrically coupled to an electronic drive unit for driving an alternating current through the induction coil.

[0003] The alternating current generates a time-varying magnetic field. Due to the inductive coupling between the induction coil and the cookware item placed above the induction coil, the magnetic field generated by the induction coil causes eddy currents to circulate in the cookware item. Due to the resistance of the cookware item, the presence of the eddy currents generates heat within the cookware item.

[0004] The induction cooktop further includes a measurement circuit that measures the total current supplied to the induction coil of the induction cooktop. The measurement circuit is configured to control the total current when the measured current does not meet a predetermined safety condition (i.e., the total current exceeds a current threshold).

[0005] A known measurement system includes a transformer having a primary winding electrically coupled to a mains line supplying a mains voltage to a first bridge rectifier of the induction cooktop, and a secondary winding electrically connected to a current measurement circuit via a second bridge rectifier.

[0006] The disadvantages are that the transformer and the second bridge rectifier circuit in the measurement system are expensive and prone to failure, requiring maintenance work and associated costs. Summary of the Invention

[0007] Accordingly, it is an object of the present invention to provide an induction cooktop provided with a measurement circuit that is not only simple but also less expensive than the measurement system disclosed above.

[0008] To this end of the present invention, as defined in the relevant independent claims, and preferably but not necessarily as defined in any of the dependent claims, there is provided an induction cooktop provided with a measurement circuit and a method for determining the current supplied to an induction cooktop.

[0009] The claims describe preferred embodiments of the present invention and form an integral part of this specification.

[0010] Unless otherwise explicitly stated, the embodiments of the present invention may be freely combined with each other.

[0011] According to one aspect of the present invention, the present invention relates to an induction cooker, which includes, and the induction cooker includes: one or more induction coils; a mains power supply line configured to supply an alternating main current; a rectification circuit configured to rectify the alternating main current supplied by the mains supply line to output a rectified main current; one or more drive circuits electrically connected to the rectification circuit through two rectified current lines, one of the rectified current lines being a ground voltage line, the drive circuit including one or more electronic switches selectively controlled to regulate the alternating secondary current supplied to each induction coil; an electronic control unit configured to selectively control the one or more electronic switches of the drive circuit to regulate the secondary current flowing through the induction coil; a resistance element having a predetermined resistance and electrically associated with the ground voltage line upstream of the drive circuit; an electronic measurement unit electrically connected to the ground voltage line to measure the voltage drop across the resistance element and provide an electrical value / signal indicating the measured voltage drop to the electronic control unit; the electronic control unit being configured to determine the main current based on the electrical value / signal.

[0012] Preferably, the induction cooker includes an induction printed circuit board provided with at least the rectification circuit, the drive circuit, and one or more circuit traces, one of the circuit traces being a ground trace, the ground trace being the ground voltage line; the resistance element is a part of the ground trace having the predetermined resistance.

[0013] Preferably, the electronic measurement unit is electrically connected to the end of the part of the ground trace of the printed circuit board.

[0014] Preferably, the ground trace of the ground voltage line has a first terminal connected to the terminal with negative voltage of the rectification circuit and a second terminal connected to the terminal with ground voltage of the drive circuit.

[0015] Preferably, the electronic measurement unit has two terminals electrically connected to both ends of the part of the ground trace and is configured to measure the voltage drop across the part.

[0016] Preferably, the ground trace of the induction printed circuit board does not include any shunt resistors.

[0017] Preferably, the ground voltage line is a low-frequency line.

[0018] Preferably, the resistive element includes a shunt resistor configured to have the predetermined resistance and arranged in series with the ground voltage line along the ground voltage line; the electronic measurement unit has two terminals electrically connected to both ends of the shunt resistor.

[0019] Preferably, the electronic measurement unit includes an operational amplifier stage, and both ends of the operational amplifier stage are connected to both ends of the resistive element.

[0020] Preferably, the operational amplifier stage is configured to provide the value / signal by performing voltage offset addition on the measured voltage drop.

[0021] The present invention further relates to a method for determining the mains current supplied to an induction cooker through a mains supply line, wherein the mains supply line is configured to supply an alternating main current to the induction cooker, and the induction cooker includes: a rectifying circuit configured to rectify the alternating main current supplied by the mains supply line to output a rectified main current; a driving circuit electrically connected to the rectifying circuit through two power supply lines, one of the power supply lines being a ground voltage line, and the driving circuit includes one or more electronic switches selectively controlled to regulate the alternating secondary current supplied to each induction coil; an electronic control unit configured to selectively control the one or more electronic switches of the driving circuit to regulate the secondary current flowing through the induction coil, and the method includes: arranging a resistive element having a predetermined resistance on the ground voltage line upstream of the driving circuit; measuring the voltage drop across both ends of the resistive element by an electronic measurement unit electrically connected to the ground voltage line to provide a signal / value indicating the measured voltage drop to the electronic control unit; and determining the main current by the electronic control unit based on the signal / value.

[0022] Preferably, the induction cooker includes an induction printed circuit board provided with at least the rectifying circuit, the driving circuit, and circuit traces, wherein the ground voltage line consists of a ground trace; the method includes the step of electrically connecting the electronic measurement unit to a portion of the ground trace having the predetermined resistance; and the resistive element consists of the portion of the ground trace of the printed circuit board.

[0023] Preferably, the method further includes the steps of connecting a first end of the ground trace to a terminal having a negative voltage of the rectifying circuit and connecting a second end of the ground trace of the ground voltage line to a terminal having a ground voltage of the driving circuit.

[0024] Preferably, the resistance element consists of a shunt resistor connected in series with the ground voltage line along the ground voltage line.

[0025] Preferably, the method further includes the step of performing voltage offset addition on the measured voltage drop through an operational amplifier stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Aspects of the present invention, including its specific features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0027] Figure 1 An induction cooker provided according to the present invention is schematically shown.

[0028] Figure 2 A block diagram of a circuit and an induction heating cooker according to some embodiments of the present invention is shown.

[0029] Figure 3 A circuit diagram of a rectification circuit, a drive circuit, and a driver unit of an induction cooker according to a first embodiment of the present invention is shown.

[0030] Figure 4 An example of a measurement circuit of the induction cooker of the present invention is shown.

[0031] Figure 5 An example of a circuit diagram of a rectification circuit, a drive circuit, and a driver unit of an induction cooker according to a second embodiment of the present invention is shown. DETAILED DESCRIPTION

[0032] The present invention will now be described more fully with reference to these drawings, in which example embodiments are shown. However, the present invention should not be construed as being limited to the embodiments set forth herein. Throughout the following description, like reference numerals are used to denote like elements, parts, objects, or features when applicable.

[0033] Reference Figure 1 , the numeral 1 as a whole represents an induction cooker made according to the present invention.

[0034] The induction cooker 1 may include a plurality of heating zones 4 (shown in dashed lines) arranged on the cooker top 2.

[0035] Reference Figure 1 In the exemplary embodiment shown, each heating zone 4 is associated with at least one induction coil 3. Preferably, the induction coil 3 is arranged below the cooker top 2.

[0036] In Figure 1 In the example shown, the induction cooker 1 further includes a user interface 5. The user interface 5 may be configured to allow a user to input / set commands for operating the induction cooker 1.

[0037] The user interface 5 can be further configured to provide the user with information about the operation of the induction cooker 1.

[0038] This information can conveniently include graphical information, and the user interface can include, for example, a touch screen display.

[0039] Figure 2 is a block diagram showing the configuration of the induction cooker 1 according to an embodiment of the present invention. Referring to Figure 2 , the induction cooker 1 includes two mains supply power lines 11, an electronic control unit 10, a rectification unit 13, one or more drive circuits 14 ( Figure 2 and Figure 3 only one is shown in Figure 2 and Figure 3 ), one or more driver units 15 (

[0040] only one is shown in

[0041] and a measurement unit 16.

[0042] As Figure 3 shown in the example of Figure 3 , the rectification unit 13 may include a plurality of diodes that are connected to each other to form a bridge rectifier. As

[0043] shown in the example of Figure 3 , the rectification unit 13 includes: two nodes 13a that are respectively electrically connected to the supply mains supply power line 11; and two nodes 13b that are electrically connected to two terminals 14a of the drive circuit 14 through a power supply line. Figure 3 shown in

[0044] The drive circuit 14 is electrically connected to the induction coil 3 and is configured to supply electric power, that is, current and voltage, to the induction coil 3.

[0045] InFigure 3 In the example shown, the drive circuit 14 includes two power lines 20 electrically connected to the power supply lines 18, 19, and a switching stage 21 electrically connected to the power lines 20.

[0046] The switching stage 21 may include one or more switching devices U1 and U2.

[0047] In Figure 3 the example shown, the switching stage 21 includes a plurality of switching devices U1 and U2, and two capacitor branches, the two capacitor branches including a pair of corresponding capacitors C1, C2 and C3, C4.

[0048] In Figure 3 the example shown, the switching devices U1 and U2 are connected in series between the power lines 20. The switching devices U1 and U2 may include transistors. For example, the transistors may include insulated gate bipolar transistors (IGBTs) or other similar transistors. It should be understood that the present invention is not limited to bipolar transistors, but other transistors or similar electronic switches may be contemplated.

[0049] In Figure 3 the example shown, the ends of the capacitor branches are electrically connected to the power lines 20. The capacitors C1, C2 and C3, C4 of the capacitor branches are connected in series through a common node 21, and these common nodes are connected to the ends of the induction coil 3.

[0050] In Figure 3 the example shown, the driver unit 15 is configured to receive a control signal S1 from the electronic control unit 10 and generate a drive signal SD for controlling the switching devices U1 and U2 based on the control signal S1.

[0051] The drive signal SD may include pulse signals configured to cause the switching devices U1 and U2 to operate alternately based on a high switching frequency to provide an alternating current flowing through the induction coil 3, thereby generating a high-frequency magnetic flux.

[0052] It should be understood that according to possible embodiments (not shown), if the switching stage 21 includes one switching device, the drive signal SD may include a pulse signal configured to cause the switching device to operate based on a high switching frequency to provide an alternating current flowing through the induction coil 3, thereby generating a high-frequency magnetic flux.

[0053] Referring Figure 1 、 Figure 2 and Figure 3 , the electronic control unit 10 is electrically connected to the user interface 5 to receive commands issued by the user for operating the induction cooker 1.

[0054] The electronic control unit 10 can provide a control signal S1 based on a command received from the user interface 5.

[0055] Reference Figure 2 and Figure 3 , the induction cooker 1 can include a resistive element 22.

[0056] The resistive elements 22 are electrically connected (in series) along the ground line 19. Preferably, the resistive elements 22 are configured to have a predetermined resistance.

[0057] According to Figure 3 the preferred embodiment shown, the induction cooker 1 includes an induction printed circuit board PCB, which is at least provided with a rectifier circuit 13, a drive circuit 14, and circuit traces (printed circuits / lines / branches) that electrically connect the electronic components of the printed circuit board PCB. At least one of the circuit traces 19a of the printed circuit board is a ground trace. The ground trace 19a is the ground line 19.

[0058] The resistive element 22 is conveniently part 22a (i.e., a piece or a portion) of the ground trace 19a and has a predetermined resistance. In other words, part 22a of the ground trace 19a forms the resistive element 22.

[0059] The electronic measurement unit 16 is electrically connected to the end of part 22a of the ground trace 19a of the ground line 19 and is configured to measure the voltage drop VD across part 22a of the ground trace 19a to provide a voltage signal VM indicating the measured voltage drop VD to the electronic control unit 10.

[0060] The electronic control unit 10 is configured to receive the voltage signal VM, determine the measured voltage drop VD based on the voltage signal VM, and determine the total current I1 based on the measured voltage drop VD and the predetermined resistance.

[0061] It is to be understood that the total current I1 determined by the electronic control unit 10 represents the total current consumption of the induction cooker 1.

[0062] It is to be further understood that the total current determined by the electronic control unit 10 can indicate the DC supply current I1 and / or the mains AC current I1 provided by the network AC to the induction cooker 1.

[0063] According to an exemplary embodiment, part 22a of the ground trace 19a of the printed circuit board PCB used by the electronic measurement unit 16 to determine the voltage drop VD can be defined / constructed to have a predetermined resistance. The predetermined resistance can be approximately 0.0123 Ohm.

[0064] It is to be further understood that according to Figure 3In the illustrated embodiment (where the resistive element 22 is part 22a of the ground trace 19a of the printed circuit board PCB), the ground line 19 does not include any shunt resistors.

[0065] The applicant has found that it is convenient to use part 22a of the ground trace 19a as a resistor element to determine / measure the current consumption of the induction cooker 1, as it allows for cost reduction.

[0066] In fact, the total current consumption can be determined by using components (i.e., the traces of the printed circuit board of the induction cooker 1) without adding additional electronic components (such as additional resistors) along the line.

[0067] Reference Figure 4 In the illustrated exemplary embodiment, the measuring unit 16 includes a terminal 16a having a supply voltage Vcc (e.g., 5V), a terminal 16b having a ground terminal GT (having a ground voltage VG (0V)), two terminals 16c electrically connected to the first and second ends of the resistive element 22, and a terminal 16d that provides a determined voltage signal VM to the electronic control unit 10.

[0068] Reference Figure 4 In the illustrated exemplary embodiment, the electronic measuring unit 16 further includes an operational amplifier stage 16h and two resistor branches 16e and 16f. The resistor branch 16e includes two resistors R2 and R3, which are connected between the terminal 16a and the first end of the resistive element 22. The resistors R2 and R3 are connected in series with each other through a common node 16g. The common node 16g is electrically connected to the inverting input terminal In of the operational amplifier stage 16h - electrically connected.

[0069] The resistor branch 16f includes two resistors R4 and R5, which are connected in series between the terminal 16a and the second end 16c of the resistive element 22. The resistors R4 and R5 are connected to each other through a common node 16s. The common node 16s is electrically connected to the non-inverting input terminal In of the operational amplifier stage 16h + electrically connected.

[0070] The resistors R2 and R4 are configured to operate as pull-up resistors. The pull-up resistors R21 and R4 are configured to add an offset to the voltage, so that it is always higher than 0V.

[0071] This has the technical effect of providing a positive voltage VM to the electronic control unit at the input terminal in the case where the electronic control unit 10 includes a microcontroller or a microprocessor. In other words, this has the technical effect of using the integrated components of an existing microcontroller without adding additional circuitry.

[0072] This solves the technical problem of the microcontroller operating with a negative voltage at the input. In fact, a negative voltage causes the microcontroller to have an integrated differential (AD) input with a gain amplifier. However, the integrated differential (AD) input increases the cost.

[0073] It is further to be understood that the voltage drop VD on the ground trace 19a is low and may be affected by noise. According to a first embodiment of the present invention, the electronic measurement unit 16 is conveniently configured to perform differential measurement for noise suppression and voltage shift for realizing negative voltage measurement. By using the operational amplifier stage 16h and utilizing the internal functions of the microcontroller of the electronic control unit 10, differential measurement and gain amplification can be conveniently performed.

[0074] Reference Figure 4 In the exemplary embodiment shown, the electronic measurement unit 16 further includes two capacitors C5 and C6. The capacitor C5 is electrically connected between the node 16g and the ground terminal 16b. The capacitor C6 is electrically connected between the node 16s and the ground terminal 16b.

[0075] According to the exemplary embodiment, the electronic measurement unit 16 is configured to: measure the voltage difference between the voltage on the inverting In - input and the voltage on the non-inverting In + input of the operational amplifier stage 16h respectively, and provide a differential value / signal VM preferably indicating the voltage difference at the input of the microcontroller of the electronic control unit 10.

[0076] According to the exemplary embodiment, the microcontroller of the electronic control unit 10 may be configured to integrate the differential value / signal VM, i.e., through an integrated AD converter module (not shown), and amplify the differential value based on the programmed gain factor of the operational amplifier stage 16h (e.g., when available).

[0077] It is to be understood that in the "zero current" state (i.e., when the current flowing through the ground line 19 is zero), the differential value / signal VM measured between the non-inverting In - input and the inverting input In + of the operational amplifier stage 16e may be different from zero due to the tolerances of the electronic components of the electronic measurement unit 16.

[0078] To compensate for the tolerance, the electronic control unit 10 can execute an automatic calibration algorithm (software). It is to be understood that the calibration can be conveniently performed at the factory or can be performed during runtime using the automatic calibration algorithm. When the automatic calibration is performed and the total current is determined to be zero, the electronic measurement unit 16 can determine the offset (voltage) based on the difference measured at the input terminal. Preferably, the difference can be stored in a memory (not shown) of the electronic control unit 10. The electronic control unit 10 can be configured to apply the difference as an offset when the induction cooktop 1 is operating, such that the total current I1 is calculated based on the measured value and the stored offset determined during calibration.

[0079] It is to be understood that, alternatively, the algorithm parameters can also be calibrated into the memory during factory production to compensate for the tolerance.

[0080] Figure 5 An embodiment of the induction cooktop 1 is shown, which Figure 3 differs from the embodiment shown in that the resistive element 22 includes a shunt resistor RS, which is connected in series along the ground line 19 upstream of the drive circuit 14. The terminals of the electronic measurement unit 16 are electrically connected to the ends of the shunt resistor RS. Preferably, the shunt resistor RS has a resistance of approximately 0.1 Ohm.

[0081] Compared with the circuits of the prior art, the advantage of the present invention lies in cost savings.

[0082] Obviously, changes and variations can be made to the cooking appliance, the method, and the electronic system, yet this does not depart from the scope of the present invention.

Claims

1. An induction cooker (1), comprising: - one or more induction coils (3), - a mains power supply line (11) configured to supply an alternating main current (I1), - a rectifier circuit (13) configured to rectify the alternating main current (I1) supplied by the mains supply line (11) to output a rectified main current (I1), - one or more drive circuits (14) electrically connected to the rectifier circuit (13) through two rectified current lines, one of the rectified current lines being a ground voltage line (19), the drive circuit (14) comprising one or more electronic switches (U1, U2) selectively controlled to regulate the alternating secondary current supplied to each induction coil (3), - an electronic control unit (10) configured to selectively control the one or more electronic switches (U1, U2) of the drive circuit (14) to regulate the secondary current flowing through the induction coil (3), - a resistive element (22) having a predetermined resistance and electrically associated with the ground voltage line (19) upstream of the drive circuit (14), - an electronic measurement unit (16) electrically connected to the ground voltage line (19) to measure the voltage drop (VD) across the resistive element (22) and provide an electrical value / signal (VM) indicative of the measured voltage drop (VD) to the electronic control unit (10); The electronic control unit (10) is configured to determine the main current (I1) based on the electrical value / signal (VM).

2. The induction cooker according to claim 1, comprising an induction printed circuit board (PCB) provided with at least the rectifier circuit (13), the drive circuit (14) and one or more circuit traces, one of the circuit traces being a ground trace (19a), the ground trace being the ground voltage line (19); the resistive element being a portion (22a) of the ground trace (19a) having the predetermined resistance.

3. The induction cooker according to claim 2, wherein, The electronic measurement unit (16) is electrically connected to an end of the portion (19a) of the ground trace (22a) of the printed circuit board (PCB).

4. The induction cooker according to claim 3, wherein, The ground trace (19a) of the ground voltage line (19) has a first terminal connected to a terminal of the rectifier circuit (13) having a negative voltage and a second terminal connected to a terminal of the drive circuit (14) having a ground voltage (VG).

5. The induction cooker according to claim 2 or 3, wherein, The electronic measurement unit (16) has two terminals electrically connected to both ends (16c) of the portion (22a) of the ground trace (19a) and is configured to measure the voltage drop (VD) across the portion (19a).

6. The induction cooker according to any one of the preceding claims 2 to 5, wherein, The ground trace (19a) of the induction printed circuit board (PCB) does not include any shunt resistors.

7. The induction cooker according to any one of the preceding claims, wherein, The ground voltage line (19) is a low-frequency line.

8. The induction cooker according to claim 1, wherein, The resistor element (22) includes a shunt resistor (RS) which is configured to have the predetermined resistance and is arranged in series with the ground voltage line (19) along the ground voltage line; the electronic measurement unit (16) has two terminals electrically connected to both ends (16c) of the shunt resistor (RS).

9. The induction cooker according to any one of the preceding claims, wherein, The electronic measurement unit (16) includes an operational amplifier stage (16h) whose both ends are connected to both ends of the resistor element (22).

10. The induction cooker according to claim 9, wherein, The operational amplifier stage (16h) is configured to provide the value / signal (VM) by performing voltage offset addition on the measured voltage drop (VD).

11. A method for determining the mains current (I1) supplied to an induction cooker (1) via a mains supply line (11), wherein, The mains supply line (11) is configured to supply an alternating main current (I1) to the induction cooker (1), and the induction cooker (1) includes: - A rectifier circuit (13) which is configured to rectify the alternating main current (I1) supplied by the mains supply line (11) to output a rectified main current (I1), - Driver circuits (14) which are electrically connected to the rectifier circuit (13) through two power supply lines, one of the power supply lines being the ground voltage line (19); the driver circuits (14) include one or more electronic switches (U1, U2) which are selectively controlled to regulate the alternating secondary current supplied to each induction coil (3), - An electronic control unit (10) which is configured to selectively control the one or more electronic switches (U1, U2) of the driver circuits (14) to regulate the secondary current flowing through the induction coil (3), The method includes: - Arranging a resistor element (22) having a predetermined resistance on the ground voltage line (19) upstream of the driver circuits (14), - Measuring the voltage drop (VD) across both ends of the resistor element (22) by an electronic measurement unit (16) electrically connected to the ground voltage line (19) to provide a signal / value (VM) indicating the measured voltage drop (VM) to the electronic control unit (10), - Determining the main current (I1) by the electronic control unit (10) based on the signal / value (VM).

12. The method according to claim 11, wherein, The induction cooker (1) includes an induction printed circuit board (PCB) which is at least provided with the rectifier circuit (13), the driver circuits (14) and circuit traces, wherein the ground voltage line (19) consists of a ground trace; The method includes the step of electrically connecting the electronic measurement unit (16) to a portion (19a) of the ground trace having the predetermined resistance; the resistor element (22) consists of the portion (19a) of the ground trace of the printed circuit board (PCB).

13. The method according to claim 12, comprising the steps of connecting the first end of the ground trace to the terminal having a negative voltage of the rectifier circuit (13) and connecting the second end of the ground trace of the ground voltage line (19) to the terminal having a ground voltage (VG) of the drive circuit (14).

14. The method according to claim 11, wherein The resistive element (22) consists of a shunt resistor (RS) connected in series with the ground voltage line along the ground voltage line (19).

15. The method according to any one of the preceding claims 11 to 14, comprising the step of performing voltage offset addition on the measured voltage drop by an operational amplifier stage (16h).

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