METHOD FOR OPERATING AN INDUCTION HOB AND INDUCTION HOB

Abstract

The invention relates to a method for operating an induction hob (1), the induction hob (1) comprising a power circuit portion (2) with at least one switching element adapted to provide pulsed electric power to an induction coil (3) and a control entity (4) for controlling operating parameters of the switching element, the method comprising the steps of: performing a control loop with control cycles in order to detect coupling changes between the induction coil (3) and a piece of cookware, said control cycles comprising the steps of: receiving frequency information (f.sub.curr) and power information (P.sub.curr) at said control entity (4); calculating at least one relation coefficient (Ds′, Ds″) based on said frequency information (f.sub.curr) and said power information (P.sub.curr); and comparing said relation coefficient (Ds′, Ds″) with a relation coefficient boundary, thereby deriving a comparison result; deciding, based on the comparison result, whether to: perform a new control cycle of said control loop or whether to stop said control loop and said provision of pulsed electric power to the induction coil (3) and restart said control loop after updating an operating parameter of the switching element.

Claims

1. A method for operating an induction hob, comprising the steps of: performing a control loop with control cycles to detect coupling changes between an induction coil and a piece of cookware; calculating a relation coefficient based on one or more operating parameters of said induction coil during each of said control cycles; and determining whether to perform a new control cycle of said control loop based on a comparison between the relation coefficient and a relation coefficient boundary.

2. The method according to claim 1, said one or more operating parameters comprising frequency information and power information relating to operation of said induction coil.

3. The method according to claim 1, further comprising stopping said control loop and ceasing to power said induction coil after the determining step if it is determined not to perform the new control cycle.

4. The method according to claim 3, further comprising restarting the control loop after updating an a new value of off-time of pulsed electric power supplied via a switching element that supplies such pulsed electric power to the induction coil.

5. The method according to claim 2, wherein said frequency information is indicative of a current frequency of pulsed electric power provided to the induction coil, and wherein said power information is indicative of power currently provided to the piece of cookware.

6. The method according to claim 2, wherein said frequency information includes frequency trend information indicating a frequency change between different ones of said control cycles.

7. The method according to claim 2, wherein said power information includes power trend information indicating a power change between different ones of said control cycles.

8. The method according to claim 2, wherein the relation coefficient is calculated based on a multiplication of the frequency information and the power information.

9. The method according to claim 2, wherein said frequency information includes frequency trend information indicating a frequency change between different ones of said control cycles, wherein said power information includes power trend information indicating a power change between said different ones of said control cycles, and wherein the relation coefficient is calculated based on a multiplication of said frequency trend information and said power trend information.

10. The method according to claim 1, wherein the relation coefficient comprises a first relation coefficient value (Ds′) calculated based on the following formula: ${\mathrm{Ds}}^{\prime }\left[\%\right]=\frac{\mathrm{Fs}*\mathrm{Ps}}{100\%};$ wherein: Fs is a quotient between a current frequency of pulsed electric power provided to the induction coil and a prior frequency of pulsed electric power provided to the induction coil in a prior said control cycle, and Ps is a quotient between a value indicative of a current estimated power provided to the piece of cookware and a value indicative of a prior estimated power provided to the induction coil in the prior control cycle, wherein the relation coefficient boundary includes a first relation coefficient boundary value, and wherein the first relation coefficient value is compared to the first relation coefficient boundary value.

11. The method according to claim 10, wherein the relation coefficient comprises a second relation coefficient value (Ds″) calculated based on the following formula: ${\mathrm{Ds}}^{″}\left[\%\right]=100\%+\left\{\left(100\%-\mathrm{Fs}\left[\%\right]\right)*\left(100\%-\mathrm{Ps}\left[\%\right]\right)\right\};$ wherein the relation coefficient boundary includes a second relation coefficient boundary value, and wherein the second relation coefficient value is compared to the second relation coefficient boundary value.

12. The method according to claim 2, wherein the relation coefficient is calculated based on a multiplication of frequency deviations of the frequency information from a frequency target value and power deviations of the power information from a power target value.

13. The method according to claim 1, wherein within said control loop, on-time of pulsed electric power supplied to the induction coil is varied.

14. The method according to claim 1, wherein off-time of pulsed electric power supplied to the induction coil remains unchanged within the control loop.

15. The method according to claim 1, wherein said relation coefficient boundary is chosen based on current operating conditions of a power circuit comprising a switching element configured to provide pulsed electric power to the induction coil.

16. The method according to claim 1, wherein said relation coefficient boundary is chosen based on characteristics of the induction coil and/or a chosen power level.

17. The method according to claim 1, wherein said control loop is run as long as said relation coefficient boundary is crossed.

18. The method according to claim 1, wherein stability of a value indicative of estimated power provided to the piece of cookware is checked within the control loop.

19. An induction hob comprising: an induction coil; a power circuit comprising a switching element configured to provide pulsed electric power to the induction coil; and a control entity for controlling operating parameters of said switching element, the control entity being configured to: perform a control loop with control cycles to detect coupling changes between the induction coil and a piece of cookware; calculate a relation coefficient based on one or more operating parameters of said induction coil during each of said control cycles; and determine whether to perform a new control cycle of said control loop based on a comparison between the relation coefficient and a relation coefficient boundary.

20. The induction hob according to claim 19, said one or more operating parameters comprising frequency information and power information relating to operation of said induction coil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0069] FIG. 1 shows an example block diagram of an induction hob;

[0070] FIG. 2 shows a flow chart of a control loop cycle performed in an induction hob; and

[0071] FIG. 3 shows a flow chart of a method for operating an induction hob including a control loop for determining dynamic coupling state changes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0072] The present invention will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. However, this invention should not be construed as limited to the embodiments set forth herein. Throughout the following description similar reference numerals have been used to denote similar elements, parts, items or features, when applicable.

[0073] FIG. 1 discloses a schematic diagram of an induction hob 1. The induction hob 1 comprises one or more induction coils 3 above which a piece of cookware can be placed in order to be heated. Furthermore, the induction hob 1 comprises a power circuit portion 2, said power circuit portion 2 being adapted to provide pulsed electric power to an oscillation circuit electrically coupled with the induction coil 3. In order to generate said pulsed electric power, the power circuit portion 2 comprises one or more switching elements. Said switching elements may be, for example, IGBTs.

[0074] The induction hob 1 comprises a user interface 5 for receiving user input. Said user interface 5 may be a touch-sensitive interface or a switch- or knob-based user interface. Based on said user interface 5, the user may provide a power request for a heating zone associated with the induction coil 3.

[0075] In order to reduce interruptions of provision of pulsed electric power for determining off-time of pulsed electric power, the induction hob 1 performs a control loop. Aim of said control loop is to detect coupling changes between the induction coil 3 and the piece of cookware and initiate an interruption only if strictly required. The control loop takes advantage of the physical delay of a quasi-resonant converter included in the power circuit portion 2 of the induction hob. It is worth mentioning that due to minor modifications of one or more operating parameters of the switching element, coupling changes between the induction coil 3 and the piece of cookware can be compensated without any interruption of power circuit portion (provision of pulsed electric power). Said minor modifications of one or more operating parameters are performed by a control loop.

[0076] FIG. 2 illustrates steps performed through a control cycle of a control loop.

[0077] Before starting the control loop, the coupling between the induction coil 3 and the piece of cookware has to be determined. Said determination may be a measuring step. Based on said measurement result, an off-time (T_off) of pulsed electric signal provided to the switching element can be defined. In other words, the period of time in a duty cycle in which the switching signal provided to the switching element is low, can be determined based on the coupling state between the induction coil 3 and the piece of cookware. In order to obtain a reliable result of coupling state, multiple measurements for determining the coupling between the induction coil 3 and the piece of cookware may be performed.

[0078] In addition, a frequency range of the frequency of the pulsed electric power signal provided to the induction coil 3 (which is correlated with the frequency of the switching signal provided to the switching element) is determined. More in detail, a minimum driving frequency and a maximum driving frequency is determined. Said minimum driving frequency/maximum driving frequency values are used within the control loop to provide a power to the piece of cookware according to the user's power request.

[0079] After determining the coupling conditions (specifically off-time (T_off)) and the frequency range, the power circuit portion 2 may start the provision of power to the induction coil based on pulse width modulation (PWM) scheme. Specifically, electric power may be provided to the induction coil based on free running PWM mode. Said free running PWM mode is advantageous because it enhances the robustness of power control. In addition, it is possible to monitor and adjust pot/coil coupling state depending on pot position/detection.

[0080] After starting the provision of power to the induction coil by the power circuit portion 2, the control loop is started according to FIG. 2. Said control loop may be performed by said control entity 4, specifically a micro-processor-based control entity.

[0081] In a first step, frequency and power information are received (S10). Said frequency information may be the current frequency of the electric current provided through the induction coil 3, i.e. the frequency which is currently applied/measured in the present control cycle. Similarly, said power information may be the current electric power provided to the induction coil, respectively, the piece of cookware, i.e. the provided electric power in the present control cycle. Said power information may be provided by a power estimation entity.

[0082] According to embodiments, said frequency and power information may be directly used for calculating at least one relation coefficient (S11). According to other embodiments, trend information may be calculated based on said frequency and power information. Said trend information may be indicative for the change of frequency/power between two or more control cycles. For example, said trend information may be indicative for an increase/decrease of frequency/power over time.

[0083] According to an embodiment, frequency trend information may be calculated by the following formula:

[00003]$\begin{array}{cc}\mathrm{Fs}=\frac{f_{\mathrm{curr}}\left[Hz\right]}{f_{\mathrm{prev}}\left[Hz\right]};& \left(\mathrm{formula}1\right)\end{array}$

[0084] wherein

[0085] f.sub.curr is the frequency in the present control cycle; and

[0086] f.sub.prev is the frequency in the previous control cycle.

[0087] Similarly, according to an embodiment, power trend information may be calculated by the following formula:

[00004]$\begin{array}{cc}Ps=\frac{P_{\mathrm{curr}}\left[W\right]}{P_{\mathrm{prev}}\left[W\right]};& \left(\mathrm{formula}2\right)\end{array}$

[0088] wherein

[0089] P.sub.curr is the power in the present control cycle; and

[0090] P.sub.prev is the power in the previous control cycle.

[0091] Based on said frequency and power information (which can be directly frequency/power values or frequency/power trend information), one or more relation coefficients are calculated.

[0092] A first relation coefficient Ds′ may be indicative for the change of a multiplication result obtained by multiplying frequency information and power information. Said first relation coefficient Ds′ may provide proportional trend information.

[0093] Specifically, said first relation coefficient Ds′ may be calculated based on the following formula:

[00005]$\begin{array}{cc}{\mathrm{Ds}}^{\prime }\left[\%\right]=\frac{\mathrm{Fs}*\mathrm{Ps}}{100\%};& \left(\mathrm{formula}3\right)\end{array}$

[0094] wherein Fs and Ps are calculated according to formulas 1 and 2.

[0095] In addition, a second relation coefficient Ds″ may be calculated. Said second relation coefficient Ds″ may provide parabolic trend information.

[0096] Specifically, said second relation coefficient Ds″ may be calculated based on the following formula:

[00006]$\begin{array}{cc}{\mathrm{Ds}}^{″}\left[\%\right]=100\%+\left\{\left(100\%-\mathrm{Fs}\left[\%\right]\right)*\left(100\%-\mathrm{Ps}\left[\%\right]\right)\right\};& \left(\mathrm{formula}4\right)\end{array}$

[0097] wherein Fs and Ps are calculated according to formulas 1 and 2.

[0098] In order to determine whether only slight changes of coupling between the induction coil 3 and the piece of cookware occurred which are not critical for the power circuit portion 2, i.e. the control loop can be continued, or coupling changes occurred which require an update of off-time (T_off), at least one relation coefficient is compared with a relation coefficient boundary (S12). Depending on the situation, respectively, working mode of the induction hob 1 (e.g. power level, temperature of the coil etc.), only the first or the second relation coefficient may be used for comparing with a respective relation coefficient boundary. In addition, also both relation coefficients may be used and compared with respective relation coefficient boundaries. Said relation coefficient boundaries may provide an upper boundary, a lower boundary or a range in which the respective relation coefficient should be included. The relation coefficient boundary may be determined considering coil characteristics, for example coil size, ohmic resistance of the induction coil and/or inductance value of the induction coil.

[0099] Based on said comparison step (S12) a comparison result is obtained. Said comparison result may indicate whether the relation coefficient crosses the relation coefficient boundary or not.

[0100] Based on said comparison result, a decision step can be performed (S13). In case that the relation coefficient boundary is not crossed, the control loop can be continued and a new control cycle is started. The other way round, if the relation coefficient boundary is crossed, said control loop may be stopped, at least one operating parameter is updated and the control loop is started based on said updated operating parameter(s).

[0101] According to an embodiment, in case of crossing the relation coefficient boundary, an operating parameter depending on the coupling state between the induction coil and the piece of cookware (specifically off-time T_off) can be updated. In addition, the frequency range (minimum driving frequency/maximum driving frequency) may also be updated.

[0102] Finally, the control loop is restarted based on said at least one updated operational parameter.

[0103] FIG. 3 shows an embodiment of a method for dynamic pot detection at an induction hob 1.

[0104] After starting, an input may be received at the user interface 5 (S20). Said input may be a power request for powering one or more induction coils associated with a heating zone. In case that the power request is not zero (S21), the coupling state between the induction coil and the piece of cookware is determined. Said coupling state may be determined based on one, preferably multiple coupling measurements. After performing said coupling measurements, off-time (T_off) currently required for the measured coupling state is determined (S22).

[0105] Following up, minimum frequency/maximum frequency of electric current provided to the induction coil may be determined based on said off-time (T_off) (S23). Based on said parameters, the power provision to the induction coil is started (S24). Said power provision may be started in free running pulse width modulation (PWM) mode.

[0106] After starting the power provision to the induction coil, the control loop (as indicated by the dashed box) as mentioned before is started. First of all, frequency information and power information is calculated (S25). Said calculation may include the calculation of frequency trend information Fs and power trend information Ps as mentioned before.

[0107] In order to obtain reliable results, a check may be made if calculated (specifically estimated) power information is stable (S26). If not, the method returns to step S25.

[0108] If calculated power information is stable, dynamic pot detection process is enabled to operate (S27). This means that only after power stabilization is achieved, parameters regarding dynamic pot detection are monitored.

[0109] Afterwards, upper-mentioned relation coefficients Ds′ and Ds″ are calculated (S28). As mentioned before, said relation coefficients are indicative for dynamic changes of the coupling between the piece of cookware and the induction coil.

[0110] In step S29 it is checked if the relation coefficient(s) cross(es) the relation coefficients boundary or not. If not, it is deemed that only slight changes in coupling state have occurred and the control loop can therefore start with a new control cycle without interrupting the power circuit portion. Otherwise, in case that the relation coefficients boundary is not met, the provision of pulsed electric power to the induction coil is stopped (S30) and the method returns to step S21 because a significant change of coupling state have been detected which may be detrimental for the switching elements included in the power circuit portion 2. Therefore, in case that the power request is not zero, T_off, respectively, the coupling characteristics between the induction coil and the piece of cookware is determined again (S22). Otherwise, in case that the power request is zero, the power circuit portion is deactivated, i.e. the provision of electric power to the induction coil is stopped (S31) and the method is terminated.

[0111] It should be noted that the description and drawings merely illustrate the principles of the proposed invention. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the invention.

LIST OF REFERENCE NUMERALS

[0112] 1 induction hob [0113] 2 power circuit portion [0114] 3 induction coil [0115] 4 control entity [0116] 5 user interface