Induction cooktop and method for automatically configuring operating parameters of an induction cooktop

Abstract

An induction cooktop includes: an induction heater (3), selected from one of a plurality of induction heater families; a control unit (15); a switching current generator (17), operable by the control unit (15) to energize the induction heater (3); and a memory device (30), containing identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32) of reference values of at least one characteristic parameter (R, X). Each induction heater family is identified by at least one respective identification range (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32) of reference values. The control unit (15) is configured to: cause the switching current generator (17) to apply a test signal (ST) to the induction heater (3); determine an actual value of the at least one characteristic parameter characteristic parameter (R, X) of the induction heater (3) from a response of the induction heater (3) to the test signal (ST); identify the induction heater family of the induction heater (3) from a comparison of the actual value and the identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32) of reference values; and set operating parameters corresponding to the identified induction heater family.

Description

TECHNICAL FIELD

[0001] The present invention relates to an induction cooktop and method for automatically configuring operating parameters of an induction cooktop.BACKGROUND

[0002] As it is known, an induction cooktop may comprise a control unit and switching current generators, sharing common mains line, rectifier and DC link and configured to energize induction heaters, which include respective inductors and are often referred to as "pancake coils".

[0003] In order to cope with the ever increasing market demand for different product layouts and features, the switching generators are designed to be flexibly connectable to several kinds of induction heaters, which may range over a large variety of dimensions, shape and rated powers. However, electrical, mechanical and thermal performances of different induction heaters widely vary as well and switching generators need to be configured before use to match the parameters of specific induction heaters actually coupled. The process by which the switching generators are configured to be able to properly drive the induction heaters is named "End Of Line Coil Parameter Setting" or "Service Coil Parameter Setting", depending on whether it is carried out at the manufacturing site or after servicing a faulty cooktop.

[0004] By way of example, a switching generator may be configured to deliver a peak power of 3 kW to a 240 mm coil but may limit the output power not to exceed 1,5 kW when coupled to a 145 mm coil. Other operating parameters that may require adjustment in accordance with the type of induction heater include booster time, availability of special functions, pan detection activation thresholds, power vs user selected level table, etc.

[0005] Several methods are known to configure the switching generators, but the available solutions suffer from limitations and do not prove satisfactory in many aspects.

[0006] According to a first known solution, the characteristics of the induction heaters are directly input by sending configuration commands trough a communication port or a digital bus or otherwise stored in a programmable nonvolatile memory. A drawback resides in that the switching generator needs to be coupled to external equipment specifically designed to communicate with the control unit. Physical connectors are required for this purpose and result in increased costs for additional components and assembly operations and time.

[0007] Another known method is based on jumper switch setting. A number of physical jumpers are manually set by an operator to define the selected configuration. However, also the process of adding or removing jumpers is time consuming and ultimately is not effective on a large scale.

[0008] In another solution, resistors encoding the induction heater types are associated with individual induction heaters. The processing unit is configured to measure the resistance of the encoding resistors and to set operating parameters accordingly. Again, additional cost and greater layout complexity are involved. In fact, not only encoding resistors, but also dedicated connection lines and contact pins must be provided.SUMMARY OF THE INVENTION

[0009] It is an aim of the present invention to provide an induction cooktop and a method for automatically configuring operating parameters of an induction cooktop that allow the above limitations to be overcome or at least reduced.

[0010] According to the present invention there are provided an induction cooktop and a method of automatically configuring operating parameters of an induction cooktop as defined in claims 1 and 11, respectively.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will now be described with reference to the accompanying drawings, which show a number of non-limitative embodiments thereof, in which: figure 1 is a simplified block diagram of an induction cooktop; figure 2 is a circuit diagram of the induction cooktop of figure 1, in accordance with an embodiment of the present invention; figure 3 is a flow chart of a method for automatically configuring operating parameters of an induction cooktop in accordance with an embodiment of the present invention; figure 4 is a graph showing quantities relating to the induction cooktop of figure 2; figure 5 is a graph showing quantities relating to an induction cooktop in accordance with an alternative embodiment of the present invention; figure 6 is a graph showing quantities relating to an induction cooktop in accordance with another alternative embodiment of the present invention; figure 7 is a circuit diagram of the induction cooktop of figure 1, in accordance with a further embodiment of the present invention; and figures 8 and 9 are graphs showing quantities relating to the induction cooktop of figure 7. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0012] With reference to figure 1, an induction cooktop is designated as a whole by number 1 and comprises a glass-ceramic plate 2, at least a pair of induction heaters 3 and at respective cooking zones below the plate 2, and a converter 5, configured to couple to a supply line (mains) 7 through a coupling interface 8 to receive an AC supply voltage V AC and to independently energize the induction heaters 3. The coupling interface 8 allows connection to the supply line 7 and may include a terminal block and EMI (Electro-Magnetic Interference) suppression filters (not shown). In embodiments not shown, an induction cooktop may include a plurality of induction heaters, each induction heater being supplied by one mains phase. A user interface 9 allows users to select average power levels to be delivered to the induction heaters 3.

[0013] In use, induction cooking vessels 10, 11 are arranged at the cooking zones in positions corresponding to respective induction heaters 3. When the induction heaters 3 are energized, Eddy currents are induced in the cooking vessels 10, 11, which are thus heated.

[0014] In accordance with a non-limiting embodiment of the present invention illustrated in figure 2, the converter 5 comprises a rectifier 13, a DC link capacitor 14, a control unit 15 and power switches 17, coupled to a respective one of the induction heaters 3. For the sake of simplicity, in what follows reference will be made to just one of the induction heaters 3 and the respective power switches 17. It is understood that this cannot be in any manner considered limiting and the following discussion applies to any one of the induction heaters that may be present in the induction cooktop 1.

[0015] The induction heater 3 forms a resonant tank 19 with respective resonant capacitors 18. The resonant tank 19 is driven by the power switches 17, which are operated as switching current generators by the control unit 15 through respective control terminals 17a. In the embodiment of figure 2, the converter 5 (more specifically the control unit 15 and the first power switches 17) may be in half-bridge configuration. The power switches 17 may be devices of any suitable kind, such as IGBTs or power MOSFETs. It is also understood that the converter is not limited to the half-bridge configuration and other configuration may be exploited as well.

[0016] In operation, the rectifier 13 and the DC link capacitor 14 supply a rectified voltage to rails 20, 21 and the control unit 15 controls the power switches 17 to energize the induction heaters 3 and deliver power to the cooking vessels 10, 11 in accordance with user's requests.

[0017] The converter 5 further includes sensors configured to sense a response of the induction heater 3 to test signals, in a non-limiting example a current sensor 22 for current flowing through the power switches 17, a voltage sensor 23 for a voltage on a common node 19a of the tank circuit 19, to which the induction heater 3 and the resonant capacitors 18 are connected, and temperature sensors 25, thermally coupled to the induction heater 3. The temperature sensors 25 may be of a resistive type, for example NTC (Negative Temperature Coefficient) or PTC (Positive Temperature Coefficient) resistors and are normally embedded in the induction heaters 3. The current sensor 22, and the voltage sensor 23 and the temperature sensor 25 are coupled to respective sense inputs of the control unit 15. The control unit 15 may use temperature signals provided by the temperature sensors 25 to include temperature limitation within temperature control functions.

[0018] Several types of induction heaters may be associated with the converter 16. Induction heaters of different induction heater families may widely vary as to dimension, shape and rated power. Since electrical, mechanical and thermal performance of the induction heaters also vary accordingly, configuration of the control unit 15 needs to be adapted to the specific induction heater which has been in fact coupled to the converter 5.

[0019] For this purpose, the control unit 15 comprises a non-volatile memory device 30 that contains: 1) instructions for carrying out an automatic configuration procedure; the automatic configuration procedure may be activated once the induction heater 3 has been connected to the converter 5 either in factory before first use or after installation during maintenance operations; 2) identification ranges of reference values of at least one characteristic parameter, wherein each induction heater family is identified by at least one respective identification range of reference values; 3) configuration settings for each induction heater family; the configuration settings may include operating parameters specific to each induction heater family such as and not limited to resonance frequency, operating frequency ranges, maximum rated power, allowable temperature ranges.

[0020] With reference to figure 3, the control unit 15 activates the automatic configuration procedure (block 50), e.g. in response to a command input by an operator through the user interface 9 or another communication interface, here not shown.

[0021] The control unit 15 drives the power switches 17 to apply a test signal S T to the induction heater 3 under inspection (block 55). The test signal S T may be a switching current with controlled amplitude and switching frequency. Examples of possible test signal S T will be presented later on.

[0022] A response of the induction heater 3 to the test signal S T is recorded by the control unit 15 (block 60) and used to determine an actual value P A of the characteristic parameter (or parameters, in accordance with design preferences) of the induction heater 3 (block 65). The steps of applying a test signal S T , recoding the response of the induction heater 3 and determining an actual value P A of the characteristic parameter(s) may be iteratively repeated in different conditions (for example, with different test signal S T , at different frequencies, with or without a reference load coupled to the induction heater 3).

[0023] The control unit 15 identifies the induction heater family of the induction heater 3 (block 70) from a comparison of the determined actual value P A of the characteristic parameter(s) and the identification ranges specific to each induction heater family.

[0024] Then, configuration settings of the identified induction heater family are selected (block 75) and the corresponding operating parameters are set (block 80), so that the induction heater 3 actually coupled to the converter 5 may be properly controlled.

[0025] In one embodiment (figure 3), the characteristic parameters are defined by a resistive component (resistance) R and an inductive component (reactance) X of the complex impedance Z = R + jX = R + jωL of the induction heater 3 (L being the self-inductance of the induction heater 3). The complex impedance Z, i.e. the resistance R, the reactance X as a whole and specifically the self-induction L, depend on frequency and on external conditions, such as the presence and characteristics of an associated load. The associated load may be a cooking vessel and the characteristics may include e.g. electric resistivity, magnetic permeability, displacement with respect to the induction heather.

[0026] The control unit 5 may be configured to send one or more test signals S T , in order to determine the complex impedance Z in one or more corresponding operating conditions, as illustrated in figure 4. More specifically, figure 4 shows identification ranges of reference values for three exemplary induction heater families in two different operating conditions and three measurements of actual values of different induction heaters for each family and each operating condition. The first induction heater family is identified by values of the characteristic parameters R, X in an identification range RNG ω11 , in the first operating condition and in an identification range RNG ω12 in the second operating condition. Likewise, the second induction heater family and the third induction heater family are identified by values of the characteristic parameters R, X respectively in identification ranges RNG ω21 , RNG ω31 in the first operating condition and in identification ranges RNG ω22 , RNG ω32 in the second operating condition. It is understood that the number of induction heater families and the number of identification ranges of reference values (i.e. of different test conditions) for each family may be flexibly selected in accordance with design preferences.

[0027] The operating conditions may be defined, for example, by test signals S T at a first frequency ω 1 and at a second frequency ω 2 . Advantageously, the first frequency ω 1 may be a resonance frequency of the resonant tank 19 formed by the induction heater 3 and the resonant capacitors 18. While determining a single actual value of the characteristic parameters is generally sufficient to identify the correct induction heater family, at least two actual values may be useful to discriminate neighboring families in case the identification ranges partially overlap.

[0028] As shown in figure 5, in another embodiment the control unit 15 drives the power switches 17 to carry out a discrete or continuous scan over a frequency range Q, records the response of the induction heater 3 and determines the actual values of the characteristic parameters at each step of the scan (here, again the resistive component R and the inductive component X of the complex impedance Z). In this case, identification ranges RNG 1 , RNG 2 , RNG 3 are defined by regions that include expected measurements or, in other words, the whole trajectory in response to a variable-frequency test signal S T ', e.g. with from an initial frequency ω I to a final frequency ω F of the scan.

[0029] As an alternative, a first reference load L 1 (including no load) and a second reference load L 2 may be associated with the induction heater 3 in the first operating condition and in the second operating condition, respectively. A reference load may be defined e.g. by one or more of size, shape, material and relative position of a reference body (such as, but not necessarily, a cooking vessel) with respect to the induction heater. Corresponding identification ranges RNG L11 , RNG L12 , RNG L21 , RNG L22 , RNG L31 , RNG L32 of reference values identify respective families of induction heaters 3, as illustrated in figure 6.

[0030] With reference to figures 7-9, in another embodiment at least one parameter which is a function of, but is not coinciding with the complex impedance Z is determined as the characteristic parameter by the control unit 15. In this case, a converter 105 in single-ended quasi-resonant configuration comprises a rectifier 113, a DC link capacitor 114, a control unit 115 and power switches 117, coupled to respective induction heaters 103. The induction heaters 103 with respective resonant capacitors 118 form resonant tanks 119, driven by the power switches 117, which are operated as switching current generators by the control unit 115 through respective control terminals 117a.

[0031] In operation, the rectifier 113 and the DC link capacitor 114 supply a rectified voltage to rails 120, 121 and the control unit 115 controls the power switches 117 to energize the induction heaters 103 and deliver power to the cooking vessels 110, 111 in accordance with user's requests.

[0032] The converter 105 further includes sensors configured to sense a response of each of the induction heaters 103 to test signals, in a non-limiting example current sensors 122 for currents flowing through the power switches 117, voltage sensor 123 for voltages on the induction heaters 103 and temperature sensors 125, thermally coupled to respective induction heaters 103. The temperature sensors 125 may be NTC or PTC resistors and are normally embedded in the induction heaters 103. The current sensors 122, the voltage sensors 123 and the temperature sensors 125 are coupled to respective sense inputs of the control unit 115. The control unit 115 may use temperature signals provided by the temperature sensors 125 to include temperature limitation within temperature control functions.

[0033] The control unit 115 comprises a non-volatile memory device 130 that contains: 1) instructions for carrying out an automatic configuration procedure; 2) identification ranges of reference values of at least one characteristic parameter; 3) configuration settings for each induction heater family.

[0034] In one embodiment, the control unit 115 may record damped oscillation of the current flowing in the induction heaters 103 or a voltage on conduction terminals (collector or drain) of the power switch 117 coupled to the respective induction heaters 103 in quasi-resonant voltage, in response to a test signal S T ". For the sake of simplicity, the following description will be focused on just one of the induction heaters 103, but it is understood that the same applies to any other induction heater 103 in the cooktop. By way of non-limiting example, figure 8 shows the voltages V on conduction terminals of power switches 117 coupled to a first induction heater (IH 1 ) and to a second induction heater (IH 2 ) having different complex impedance, which result in different damping (due to different resistive components) and different natural frequency (due to different inductive components). The test signal S T " may be a squared current pulse, applied to the control terminal 117a of the switch 117, having a duration t ON . Here, the duration t ON is selected such that the resulting oscillating voltage in response to the test signal S T " does not reach 0 V. The induction heater 103 is energized by the power switch 117 when the test signal S T " is applied and releases stored energy when the test signal S T " ends. The control unit 115 then uses the recorded response to determine actual values of a decay rate 2, and a natural frequency ω N of the damped oscillation, which are known to be dependent on the resistive component and inductive component of the complex impedance, respectively.

[0035] Identification ranges RNG ωξ1 , RNG ωξ2 , RNG ωξ3 may be defined by regions that include expected measurements of the decay rate 2, and the natural frequency ω N in response to at least one test signal S T ".

[0036] In one embodiment, families of induction heaters 103 are selected, which include temperature sensors 125 all of one and the same type (i.e. all NTC or all PTC temperature sensors), but having different resistance values given the same temperature. More precisely, at a given temperature, all the temperature sensors 125 in each family have the same resistance value, but resistance values of temperature sensors 125 of different families are different as well. The control unit 115 uses the resistance values of temperature sensors 125 to increase reliability of discrimination based solely on the complex impedance or a parameter which is a function of complex impedance of the induction heaters 103.

[0037] The invention advantageously allows to automatically identify the type of induction heaters and to configure the switching current generators accordingly, without the need for external equipment and communication ports (e.g. to input configuration commands) or additional components, such as jumpers or coding resistors with relevant dedicated connection lines. Complex impedance is in fact an intrinsic property of the induction heaters and, given the same operating conditions, induction heaters of different families generally have complex impedances sufficiently spaced apart to allow discrimination. Hence, complex impedance or quantities dependent on complex impedance may be determined by the control unit by driving the power switches to apply suitable test signals as in the examples presented and by recording the response of the induction heaters to the test signals. Complexity of induction cooktops may be thus reduced and the layout simplified, to the benefit of cost. Moreover, the configuration procedure may be fully automated and carried out rapidly. Also, specific training is not required for operators.

[0038] Finally, it is clear that modifications and variants can be made to the cooktop and to the method described herein without departing from the scope of the present invention, as defined in the appended claims.

[0039] For example, any suitable combination of different operating conditions may be exploited to refine identification of induction heater families in accordance with design preferences. In particular, identification may be based on test signals at different frequencies in combination with different reference loads for half-bridge converters. Likewise, the test for quasi-resonant converters may be repeated with different reference loads.

Examples

Embodiment Construction

[0012]With reference to figure 1, an induction cooktop is designated as a whole by number 1 and comprises a glass-ceramic plate 2, at least a pair of induction heaters 3 and at respective cooking zones below the plate 2, and a converter 5, configured to couple to a supply line (mains) 7 through a coupling interface 8 to receive an AC supply voltage V AC and to independently energize the induction heaters 3. The coupling interface 8 allows connection to the supply line 7 and may include a terminal block and EMI (Electro-Magnetic Interference) suppression filters (not shown). In embodiments not shown, an induction cooktop may include a plurality of induction heaters, each induction heater being supplied by one mains phase. A user interface 9 allows users to select average power levels to be delivered to the induction heaters 3.

[0013]In use, induction cooking vessels 10, 11 are arranged at the cooking zones in positions corresponding to respective induction heaters 3. When the inducti...

TECHNICAL FIELD

[0001] The present invention relates to an induction cooktop and method for automatically configuring operating parameters of an induction cooktop.BACKGROUND

[0002] As it is known, an induction cooktop may comprise a control unit and switching current generators, sharing common mains line, rectifier and DC link and configured to energize induction heaters, which include respective inductors and are often referred to as "pancake coils".

[0003] In order to cope with the ever increasing market demand for different product layouts and features, the switching generators are designed to be flexibly connectable to several kinds of induction heaters, which may range over a large variety of dimensions, shape and rated powers. However, electrical, mechanical and thermal performances of different induction heaters widely vary as well and switching generators need to be configured before use to match the parameters of specific induction heaters actually coupled. The process by which the switching generators are configured to be able to properly drive the induction heaters is named "End Of Line Coil Parameter Setting" or "Service Coil Parameter Setting", depending on whether it is carried out at the manufacturing site or after servicing a faulty cooktop.

[0004] By way of example, a switching generator may be configured to deliver a peak power of 3 kW to a 240 mm coil but may limit the output power not to exceed 1,5 kW when coupled to a 145 mm coil. Other operating parameters that may require adjustment in accordance with the type of induction heater include booster time, availability of special functions, pan detection activation thresholds, power vs user selected level table, etc.

[0005] Several methods are known to configure the switching generators, but the available solutions suffer from limitations and do not prove satisfactory in many aspects.

[0006] According to a first known solution, the characteristics of the induction heaters are directly input by sending configuration commands trough a communication port or a digital bus or otherwise stored in a programmable nonvolatile memory. A drawback resides in that the switching generator needs to be coupled to external equipment specifically designed to communicate with the control unit. Physical connectors are required for this purpose and result in increased costs for additional components and assembly operations and time.

[0007] Another known method is based on jumper switch setting. A number of physical jumpers are manually set by an operator to define the selected configuration. However, also the process of adding or removing jumpers is time consuming and ultimately is not effective on a large scale.

[0008] In another solution, resistors encoding the induction heater types are associated with individual induction heaters. The processing unit is configured to measure the resistance of the encoding resistors and to set operating parameters accordingly. Again, additional cost and greater layout complexity are involved. In fact, not only encoding resistors, but also dedicated connection lines and contact pins must be provided.SUMMARY OF THE INVENTION

[0009] It is an aim of the present invention to provide an induction cooktop and a method for automatically configuring operating parameters of an induction cooktop that allow the above limitations to be overcome or at least reduced.

[0010] According to the present invention there are provided an induction cooktop and a method of automatically configuring operating parameters of an induction cooktop as defined in claims 1 and 11, respectively.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will now be described with reference to the accompanying drawings, which show a number of non-limitative embodiments thereof, in which: figure 1 is a simplified block diagram of an induction cooktop; figure 2 is a circuit diagram of the induction cooktop of figure 1, in accordance with an embodiment of the present invention; figure 3 is a flow chart of a method for automatically configuring operating parameters of an induction cooktop in accordance with an embodiment of the present invention; figure 4 is a graph showing quantities relating to the induction cooktop of figure 2; figure 5 is a graph showing quantities relating to an induction cooktop in accordance with an alternative embodiment of the present invention; figure 6 is a graph showing quantities relating to an induction cooktop in accordance with another alternative embodiment of the present invention; figure 7 is a circuit diagram of the induction cooktop of figure 1, in accordance with a further embodiment of the present invention; and figures 8 and 9 are graphs showing quantities relating to the induction cooktop of figure 7. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0012] With reference to figure 1, an induction cooktop is designated as a whole by number 1 and comprises a glass-ceramic plate 2, at least a pair of induction heaters 3 and at respective cooking zones below the plate 2, and a converter 5, configured to couple to a supply line (mains) 7 through a coupling interface 8 to receive an AC supply voltage V AC and to independently energize the induction heaters 3. The coupling interface 8 allows connection to the supply line 7 and may include a terminal block and EMI (Electro-Magnetic Interference) suppression filters (not shown). In embodiments not shown, an induction cooktop may include a plurality of induction heaters, each induction heater being supplied by one mains phase. A user interface 9 allows users to select average power levels to be delivered to the induction heaters 3.

[0013] In use, induction cooking vessels 10, 11 are arranged at the cooking zones in positions corresponding to respective induction heaters 3. When the induction heaters 3 are energized, Eddy currents are induced in the cooking vessels 10, 11, which are thus heated.

[0014] In accordance with a non-limiting embodiment of the present invention illustrated in figure 2, the converter 5 comprises a rectifier 13, a DC link capacitor 14, a control unit 15 and power switches 17, coupled to a respective one of the induction heaters 3. For the sake of simplicity, in what follows reference will be made to just one of the induction heaters 3 and the respective power switches 17. It is understood that this cannot be in any manner considered limiting and the following discussion applies to any one of the induction heaters that may be present in the induction cooktop 1.

[0015] The induction heater 3 forms a resonant tank 19 with respective resonant capacitors 18. The resonant tank 19 is driven by the power switches 17, which are operated as switching current generators by the control unit 15 through respective control terminals 17a. In the embodiment of figure 2, the converter 5 (more specifically the control unit 15 and the first power switches 17) may be in half-bridge configuration. The power switches 17 may be devices of any suitable kind, such as IGBTs or power MOSFETs. It is also understood that the converter is not limited to the half-bridge configuration and other configuration may be exploited as well.

[0016] In operation, the rectifier 13 and the DC link capacitor 14 supply a rectified voltage to rails 20, 21 and the control unit 15 controls the power switches 17 to energize the induction heaters 3 and deliver power to the cooking vessels 10, 11 in accordance with user's requests.

[0017] The converter 5 further includes sensors configured to sense a response of the induction heater 3 to test signals, in a non-limiting example a current sensor 22 for current flowing through the power switches 17, a voltage sensor 23 for a voltage on a common node 19a of the tank circuit 19, to which the induction heater 3 and the resonant capacitors 18 are connected, and temperature sensors 25, thermally coupled to the induction heater 3. The temperature sensors 25 may be of a resistive type, for example NTC (Negative Temperature Coefficient) or PTC (Positive Temperature Coefficient) resistors and are normally embedded in the induction heaters 3. The current sensor 22, and the voltage sensor 23 and the temperature sensor 25 are coupled to respective sense inputs of the control unit 15. The control unit 15 may use temperature signals provided by the temperature sensors 25 to include temperature limitation within temperature control functions.

[0018] Several types of induction heaters may be associated with the converter 16. Induction heaters of different induction heater families may widely vary as to dimension, shape and rated power. Since electrical, mechanical and thermal performance of the induction heaters also vary accordingly, configuration of the control unit 15 needs to be adapted to the specific induction heater which has been in fact coupled to the converter 5.

[0019] For this purpose, the control unit 15 comprises a non-volatile memory device 30 that contains: 1) instructions for carrying out an automatic configuration procedure; the automatic configuration procedure may be activated once the induction heater 3 has been connected to the converter 5 either in factory before first use or after installation during maintenance operations; 2) identification ranges of reference values of at least one characteristic parameter, wherein each induction heater family is identified by at least one respective identification range of reference values; 3) configuration settings for each induction heater family; the configuration settings may include operating parameters specific to each induction heater family such as and not limited to resonance frequency, operating frequency ranges, maximum rated power, allowable temperature ranges.

[0020] With reference to figure 3, the control unit 15 activates the automatic configuration procedure (block 50), e.g. in response to a command input by an operator through the user interface 9 or another communication interface, here not shown.

[0021] The control unit 15 drives the power switches 17 to apply a test signal S T to the induction heater 3 under inspection (block 55). The test signal S T may be a switching current with controlled amplitude and switching frequency. Examples of possible test signal S T will be presented later on.

[0022] A response of the induction heater 3 to the test signal S T is recorded by the control unit 15 (block 60) and used to determine an actual value P A of the characteristic parameter (or parameters, in accordance with design preferences) of the induction heater 3 (block 65). The steps of applying a test signal S T , recoding the response of the induction heater 3 and determining an actual value P A of the characteristic parameter(s) may be iteratively repeated in different conditions (for example, with different test signal S T , at different frequencies, with or without a reference load coupled to the induction heater 3).

[0023] The control unit 15 identifies the induction heater family of the induction heater 3 (block 70) from a comparison of the determined actual value P A of the characteristic parameter(s) and the identification ranges specific to each induction heater family.

[0024] Then, configuration settings of the identified induction heater family are selected (block 75) and the corresponding operating parameters are set (block 80), so that the induction heater 3 actually coupled to the converter 5 may be properly controlled.

[0025] In one embodiment (figure 3), the characteristic parameters are defined by a resistive component (resistance) R and an inductive component (reactance) X of the complex impedance Z = R + jX = R + jωL of the induction heater 3 (L being the self-inductance of the induction heater 3). The complex impedance Z, i.e. the resistance R, the reactance X as a whole and specifically the self-induction L, depend on frequency and on external conditions, such as the presence and characteristics of an associated load. The associated load may be a cooking vessel and the characteristics may include e.g. electric resistivity, magnetic permeability, displacement with respect to the induction heather.

[0026] The control unit 5 may be configured to send one or more test signals S T , in order to determine the complex impedance Z in one or more corresponding operating conditions, as illustrated in figure 4. More specifically, figure 4 shows identification ranges of reference values for three exemplary induction heater families in two different operating conditions and three measurements of actual values of different induction heaters for each family and each operating condition. The first induction heater family is identified by values of the characteristic parameters R, X in an identification range RNG ω11 , in the first operating condition and in an identification range RNG ω12 in the second operating condition. Likewise, the second induction heater family and the third induction heater family are identified by values of the characteristic parameters R, X respectively in identification ranges RNG ω21 , RNG ω31 in the first operating condition and in identification ranges RNG ω22 , RNG ω32 in the second operating condition. It is understood that the number of induction heater families and the number of identification ranges of reference values (i.e. of different test conditions) for each family may be flexibly selected in accordance with design preferences.

[0027] The operating conditions may be defined, for example, by test signals S T at a first frequency ω 1 and at a second frequency ω 2 . Advantageously, the first frequency ω 1 may be a resonance frequency of the resonant tank 19 formed by the induction heater 3 and the resonant capacitors 18. While determining a single actual value of the characteristic parameters is generally sufficient to identify the correct induction heater family, at least two actual values may be useful to discriminate neighboring families in case the identification ranges partially overlap.

[0028] As shown in figure 5, in another embodiment the control unit 15 drives the power switches 17 to carry out a discrete or continuous scan over a frequency range Q, records the response of the induction heater 3 and determines the actual values of the characteristic parameters at each step of the scan (here, again the resistive component R and the inductive component X of the complex impedance Z). In this case, identification ranges RNG 1 , RNG 2 , RNG 3 are defined by regions that include expected measurements or, in other words, the whole trajectory in response to a variable-frequency test signal S T ', e.g. with from an initial frequency ω I to a final frequency ω F of the scan.

[0029] As an alternative, a first reference load L 1 (including no load) and a second reference load L 2 may be associated with the induction heater 3 in the first operating condition and in the second operating condition, respectively. A reference load may be defined e.g. by one or more of size, shape, material and relative position of a reference body (such as, but not necessarily, a cooking vessel) with respect to the induction heater. Corresponding identification ranges RNG L11 , RNG L12 , RNG L21 , RNG L22 , RNG L31 , RNG L32 of reference values identify respective families of induction heaters 3, as illustrated in figure 6.

[0030] With reference to figures 7-9, in another embodiment at least one parameter which is a function of, but is not coinciding with the complex impedance Z is determined as the characteristic parameter by the control unit 15. In this case, a converter 105 in single-ended quasi-resonant configuration comprises a rectifier 113, a DC link capacitor 114, a control unit 115 and power switches 117, coupled to respective induction heaters 103. The induction heaters 103 with respective resonant capacitors 118 form resonant tanks 119, driven by the power switches 117, which are operated as switching current generators by the control unit 115 through respective control terminals 117a.

[0031] In operation, the rectifier 113 and the DC link capacitor 114 supply a rectified voltage to rails 120, 121 and the control unit 115 controls the power switches 117 to energize the induction heaters 103 and deliver power to the cooking vessels 110, 111 in accordance with user's requests.

[0032] The converter 105 further includes sensors configured to sense a response of each of the induction heaters 103 to test signals, in a non-limiting example current sensors 122 for currents flowing through the power switches 117, voltage sensor 123 for voltages on the induction heaters 103 and temperature sensors 125, thermally coupled to respective induction heaters 103. The temperature sensors 125 may be NTC or PTC resistors and are normally embedded in the induction heaters 103. The current sensors 122, the voltage sensors 123 and the temperature sensors 125 are coupled to respective sense inputs of the control unit 115. The control unit 115 may use temperature signals provided by the temperature sensors 125 to include temperature limitation within temperature control functions.

[0033] The control unit 115 comprises a non-volatile memory device 130 that contains: 1) instructions for carrying out an automatic configuration procedure; 2) identification ranges of reference values of at least one characteristic parameter; 3) configuration settings for each induction heater family.

[0034] In one embodiment, the control unit 115 may record damped oscillation of the current flowing in the induction heaters 103 or a voltage on conduction terminals (collector or drain) of the power switch 117 coupled to the respective induction heaters 103 in quasi-resonant voltage, in response to a test signal S T ". For the sake of simplicity, the following description will be focused on just one of the induction heaters 103, but it is understood that the same applies to any other induction heater 103 in the cooktop. By way of non-limiting example, figure 8 shows the voltages V on conduction terminals of power switches 117 coupled to a first induction heater (IH 1 ) and to a second induction heater (IH 2 ) having different complex impedance, which result in different damping (due to different resistive components) and different natural frequency (due to different inductive components). The test signal S T " may be a squared current pulse, applied to the control terminal 117a of the switch 117, having a duration t ON . Here, the duration t ON is selected such that the resulting oscillating voltage in response to the test signal S T " does not reach 0 V. The induction heater 103 is energized by the power switch 117 when the test signal S T " is applied and releases stored energy when the test signal S T " ends. The control unit 115 then uses the recorded response to determine actual values of a decay rate 2, and a natural frequency ω N of the damped oscillation, which are known to be dependent on the resistive component and inductive component of the complex impedance, respectively.

[0035] Identification ranges RNG ωξ1 , RNG ωξ2 , RNG ωξ3 may be defined by regions that include expected measurements of the decay rate 2, and the natural frequency ω N in response to at least one test signal S T ".

[0036] In one embodiment, families of induction heaters 103 are selected, which include temperature sensors 125 all of one and the same type (i.e. all NTC or all PTC temperature sensors), but having different resistance values given the same temperature. More precisely, at a given temperature, all the temperature sensors 125 in each family have the same resistance value, but resistance values of temperature sensors 125 of different families are different as well. The control unit 115 uses the resistance values of temperature sensors 125 to increase reliability of discrimination based solely on the complex impedance or a parameter which is a function of complex impedance of the induction heaters 103.

[0037] The invention advantageously allows to automatically identify the type of induction heaters and to configure the switching current generators accordingly, without the need for external equipment and communication ports (e.g. to input configuration commands) or additional components, such as jumpers or coding resistors with relevant dedicated connection lines. Complex impedance is in fact an intrinsic property of the induction heaters and, given the same operating conditions, induction heaters of different families generally have complex impedances sufficiently spaced apart to allow discrimination. Hence, complex impedance or quantities dependent on complex impedance may be determined by the control unit by driving the power switches to apply suitable test signals as in the examples presented and by recording the response of the induction heaters to the test signals. Complexity of induction cooktops may be thus reduced and the layout simplified, to the benefit of cost. Moreover, the configuration procedure may be fully automated and carried out rapidly. Also, specific training is not required for operators.

[0038] Finally, it is clear that modifications and variants can be made to the cooktop and to the method described herein without departing from the scope of the present invention, as defined in the appended claims.

[0039] For example, any suitable combination of different operating conditions may be exploited to refine identification of induction heater families in accordance with design preferences. In particular, identification may be based on test signals at different frequencies in combination with different reference loads for half-bridge converters. Likewise, the test for quasi-resonant converters may be repeated with different reference loads.

Examples

Embodiment Construction

[0012]With reference to figure 1, an induction cooktop is designated as a whole by number 1 and comprises a glass-ceramic plate 2, at least a pair of induction heaters 3 and at respective cooking zones below the plate 2, and a converter 5, configured to couple to a supply line (mains) 7 through a coupling interface 8 to receive an AC supply voltage V AC and to independently energize the induction heaters 3. The coupling interface 8 allows connection to the supply line 7 and may include a terminal block and EMI (Electro-Magnetic Interference) suppression filters (not shown). In embodiments not shown, an induction cooktop may include a plurality of induction heaters, each induction heater being supplied by one mains phase. A user interface 9 allows users to select average power levels to be delivered to the induction heaters 3.

[0013]In use, induction cooking vessels 10, 11 are arranged at the cooking zones in positions corresponding to respective induction heaters 3. When the inducti...

Claims

1. An induction cooktop comprising: an induction heater (3; 103), selected from one of a plurality of induction heater families; a control unit (15; 115); a switching current generator (17; 117), operable by the control unit (15; 115) to energize the induction heater (3; 103); and a memory device (30; 130), containing identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values of at least one characteristic parameter (R, X; ξ, ωN), each induction heater family of the plurality of induction heater families being identified by at least one respective identification range (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values; wherein the control unit (15; 115) is configured to: cause the switching current generator (17; 117) to apply a test signal (ST; ST'; ST") to the induction heater (3; 103); and determine an actual value of the at least one characteristic parameter characteristic parameter (R, X; ξ, ωN) of the induction heater (3; 103) from a response of the induction heater (3; 103) to the test signal (ST; ST'; ST"); identify the induction heater family of the induction heater (3; 103) from a comparison of the actual value and the identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values; and set operating parameters corresponding to the identified induction heater family.

2. The induction cooktop according to claim 1, wherein the at least one characteristic parameter is a function of a complex impedance (R, X) of the induction heater (3).

3. The induction cooktop according to claim 2, wherein the at least one characteristic parameter includes the complex impedance (R, X) of the induction heater (3).

4. The induction cooktop according to claim 2 or 3, comprising a resonant capacitor (118) coupled to the induction heater (103), wherein the at least one characteristic parameter includes a decay rate (ξ) and a natural frequency (ωN) of damped oscillations of a resonant circuit (119) formed by the induction heater (103) and the resonant capacitor (118).

5. The induction cooktop according to any one of the preceding claims, wherein the control unit (15; 115) is further configured to iteratively: cause the switching current generator (17; 117) to apply the test signal (ST; ST'; ST") to the induction heater (3) at least in a first operating condition and in a second operating condition; and determine the actual value of the at least one characteristic parameter (R, X; ξ, ωN) of the induction heater (3; 103) from the response of the induction heater (3; 103) to the test signal (ST; ST'; ST") at least in the first operating condition and in the second operating condition.

6. The induction cooktop according to claim 5, wherein the control unit (15; 115) is further configured to identify the induction heater family of the induction heater (3) from the comparison of the actual value at least in the first operating condition and in the second operating condition and of the identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values.

7. The induction cooktop according to claim 5 or 6, wherein the control unit (15) is further configured to drive the switching current generator (17) at a first frequency (ω1; ωI) in the first operating condition and at a second frequency (ω2; ωF) in the second operating condition.

8. The induction cooktop according to any one of claims 5 to 7, comprising a first reference load (L1) coupled to the induction heater (3; 103) in the first operating condition includes and a second reference load (L2) coupled to the induction heater (3; 103) in the second operating condition.

9. The induction cooktop according to any one of the preceding claims, wherein the control unit (15) is further configured to drive the power switch (17) to carry out a scan over a frequency range (Ω), to record the response of the induction heater (3) and to determine the actual value of the characteristic parameter (R, X) at each step of the scan.

10. The induction cooktop according to any one of the preceding claims, wherein the induction heater (3; 103) comprises a resistive temperature sensor (25; 125) and the control unit (15; 115) is further configured to sense a resistance value of the resistive temperature sensor (25; 115) and to use the sensed resistance value to identify the induction heater family of the induction heater (3; 103).

11. A method for automatically configuring operating parameters of an induction cooktop comprising: coupling an induction heater (3; 103), selected from one of a plurality of induction heater families, to a switching current generator (17; 117), whereby the switching current generator (17; 117) is operable to energize the induction heater (3; 103); storing identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values of at least one characteristic parameter (R, X; ξ, ωN), each induction heater family of the plurality of induction heater families being identified by at least one respective identification range (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values; causing the switching current generator (17; 117) to apply a test signal (ST; ST'; ST") to the induction heater (3; 103); and determining an actual value of the at least one characteristic parameter characteristic parameter (R, X; ξ, ωN) of the induction heater (3; 103) from a response of the induction heater (3; 103) to the test signal (ST; ST'; ST"); identifying the induction heater family of the induction heater (3; 103) from a comparison of the actual value and the identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGcoi2, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values; and setting operating parameters corresponding to the identified induction heater family.

12. The method according to claim 11, wherein the at least one characteristic parameter is a function of a complex impedance (R, X) of the induction heater (3).

13. The method according to claim 12, wherein the at least one characteristic parameter includes the complex impedance (R, X) of the induction heater (3).

14. The method according to claim 12 or 13, comprising coupling a resonant capacitor (18) to the induction heater (3), wherein the at least one characteristic parameter includes a decay rate (ξ) and a natural frequency (ωN) of damped oscillations of a resonant circuit (19) formed by the induction heater (3) and the resonant capacitor (18).

15. The method according to any one of claims 11 to 14, wherein further comprising iteratively: causing the switching current generator (17; 117) to apply the test signal (ST; ST'; ST") to the induction heater (3; 103) at least in a first operating condition and in a second operating condition; and determining the actual value of the at least one characteristic parameter (R, X; ξ, ωN) of the induction heater (3; 103) from the response of the induction heater (3; 103) to the test signal (ST; ST'; ST") at least in the first operating condition and in the second operating condition.

16. The method according to claim 15, further comprising identifying the induction heater family of the induction heater (3; 103) from the comparison of the actual value at least in the first operating condition and in the second operating condition and of the identification ranges (RNGω11, RNGω12, RNGω21, RNGω31, RNGω12, RNGω22, RNGω32; RNG1, RNG2, RNG3; RNGL11, RNGL12, RNGL21, RNGL31, RNGL12, RNGL22, RNGL32) of reference values.

17. The method according to claim 15 or 16, further comprising driving the switching current generator (17) at a first frequency (ω1; ωI) in the first operating condition and at a second frequency (ω2; ωF) in the second operating condition.

18. The method according to any one of claims 15 to 17, comprising coupling a first reference load (L1) to the induction heater (3; 103) in the first operating condition includes and coupling a second reference load (L2) to the induction heater (3; 103) in the second operating condition.

19. The method according to any one of claims 11 to 18, comprising driving the power switch (17) to carry out a scan over a frequency range (Ω), recording the response of the induction heater (3) and determining the actual value of the characteristic parameter (R, X) at each step of the scan.

20. The method according to any one of claims 11 to 19, wherein the induction heater (3; 103) comprises a resistive temperature sensor (25; 125) and wherein identifying the induction heater family of the induction heater (3; 103) comprises sensing a resistance value of the resistive temperature sensor (25; 125) and using the sensed resistance.

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