Abstract:
The present disclosure relates to an induction cooktop. The induction cooktop comprises a ceramic cooking surface in connection with a housing. A plurality of inductors is disposed in the housing and each of the inductors is in communication with an automatic control system. The automatic control system is configured to check for the presence of a cooking pan on the cooktop in order to prevent the inductors from activating in the absence of the cooking pan. The automatic control system is activated upon receiving an activation command.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part of U.S. application Ser. No. 14/435,814, entitled “INDUCTION COOKING TOP,” and filed Oct. 14, 2013 which is a National Phase Entry of International Application No. PCT/IB2013/059340 filed Oct. 14, 2013, which claims priority to Italian Application No. TO2012A000896 filed Oct. 15, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to an induction cooktop and more particularly to a controller for an induction cooktop. 
       BACKGROUND 
       [0003]    Induction cooktops are devices which exploit the phenomenon of induction heating for food cooking purposes. Induction cooktops comprise a top made of glass-ceramic material upon which cooking units are positioned (hereinafter “pans”). Moreover there are provided inductors comprising coils of copper wire where an oscillating current (e.g. an alternating current) is circulated producing an oscillating electromagnetic field. 
         [0004]    The electromagnetic field has the main effect of inducing a parasitic current inside the pan, which is made of an electrically conductive ferromagnetic material. The parasitic current circulating in the pan produces heat by dissipation; such heat is generated only within the pan and it acts without heating the cooktop. 
         [0005]    This type of flameless cooktop has a better efficiency than electric cooktops (i.e. a greater fraction of the absorbed electric power is converted into heat that heats the pan). In addition, induction cooktops are safer to use due to the absence of hot surfaces or flames, reducing the risk of burns for the user or of fire. The presence of the pan on the cooktop causes the magnetic flux close to the pan itself causing the power to be transferred towards the pan. The greater the size of the pan, the higher the power that can be transferred. 
         [0006]    Since heat is generated by induced currents, a cooktop control system may be utilized to monitor currents flowing through the coils; in this way, the power supplied to each inductor can be adjusted. Moreover such current monitoring may provide for the control system to automatically detect a presence of a pan over the inductors and to automatically turn off the inductors in response to the absence of the pan on the cooktop. A drawback arising from the automatic detection, is that it is possible for small pans not to be detected by the control system. In such conditions, the presence of a small pan that is not detected by the control system may lead to the cooktop control system failing to activate the inductors. That is, the control system may fail to activate the passage of the current through the coils of the inductors and fail to heat the small pan. 
         [0007]    The disclosure provides for a control system configured to provide an improved method of presence detection for pans, particularly small pans. The modification provides for improved detection and operation of an induction cooktop. 
       SUMMARY 
       [0008]    According to one aspect of the present invention, an induction cooktop is disclosed. The induction cooktop comprises a ceramic cooking surface in connection with a housing. A plurality of inductors is disposed in the housing and each of the inductors is in communication with an automatic control system. The automatic control system is configured to check for the presence of a cooking pan on the cooktop in order to prevent the inductors from activating in the absence of the cooking pan. The automatic control system is activated upon receiving an activation command. 
         [0009]    According to another aspect of the present invention, a method of controlling a cooktop is disclosed. The method comprises detecting a small pan on a cooking surface of the cooktop. In response to the detection of the small pan, the method continues by controlling a pan detection setting. I response to the pan detection setting, the method continues by selectively supplying a driving current to an inductor of the cooktop. The pan detection setting corresponds to a small pan operating range having a phase angle approximately between 84 and 88 degrees. 
         [0000]    According to yet another aspect of the present invention, a controller for identifying a small pan condition for an induction cooktop is disclosed. The controller is in communication with a plurality of inductors and a user interface. The controller is configured to selectively activate each of the inductors in response to a combination of an input and a presence of a pan proximate the inductor. The input is received at the user interface identifying an inductor of the plurality of inductors to activate. The presence of the pan proximate the inductor is in response to a detection signal corresponding to a pan presence. The controller is configured to identify the pan presence in response to a phase angle between a zero-crossing of an induced current in the inductor and a leading edge of a square wave of a voltage across an inverter switch configured to provide current to the inductor. 
         [0010]    These and other objects of the present disclosure may be achieved by means of a cooktop incorporating the features set out in the appended claims, which are an integral part of the present description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Further objects and advantages of the present disclosure may become more apparent from the following detailed description and from the annexed drawing, which is provided by way of a non-limiting example, wherein: 
           [0012]      FIG. 1  is a top view of a cooktop according to the present disclosure; 
           [0013]      FIG. 2  is a schematic representation of an inductor and an example of a driving circuit; 
           [0014]      FIG. 3  is a representation of phase control parameter; 
           [0015]      FIG. 4  is a plot of prior art control scheme for a controller of an induction cooktop; and 
           [0016]      FIG. 5  is a plot of a modified control scheme for a controller of an induction cooktop providing for use of a small pan in accordance with the disclosure. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0017]    For purposes of description herein the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the device as oriented in  FIG. 1 . However, it is to be understood that the device may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
         [0018]    Referring to  FIG. 1 , a top view of a cooktop  10  is shown. The cooktop  10  may comprise a plurality of cooking hobs  12  oriented on a ceramic plate  14 . Beneath the ceramic plate  14  and corresponding to each of the hobs  12 , a plurality of induction coils  16  may be disposed in a housing  18 . The induction coils  16  may be in communication with a controller  20  configured to selectively activate the induction coils  16  in response to an input to a user interface  22 . The controller  20  may correspond to an automatic control system configured to activate one or more of the induction coils  16  in response to an input or user selection. Additionally, the controller  20  may only activate an induction coil upon identifying a presence of a ferromagnetic pan  24  proximate a selected hob of the plurality of hobs  12 . The disclosure provides for an induction cooktop  10  operable to detect and activate a selected hob in response to the pan  24  corresponding to a small pan. Such pans may not be sensed by conventional induction cooktops due to safety systems that may mistakenly sense that no pan is present. 
         [0019]    The user interface  22  may correspond to a touch interface configured to perform heat control and selection of the plurality of hobs  12  as illustrated in a plurality of instructive decals  26  disposed on a cooking surface  28  of the cooktop. The user interface  22  may comprise a plurality of sensors  30  configured to detect a presence of an object, for example a finger of an operator, proximate thereto. The sensors  30  may correspond to any form of sensors. In an exemplary embodiment, the sensors  30  may correspond to capacitive, resistive, and/or optical sensors. In an exemplary embodiment, the sensors  30  correspond to capacitive proximity sensors. 
         [0020]    The user interface  22  may further comprise a display  32  configured to communicate at least one function of the cooktop  10 . The display may correspond to various forms of displays, for example, light emitting diode (LED) display, a liquid crystal display (LCD), etc. In some embodiments, the display may correspond to a segmented display configured to depict one or more alpha-numeric characters to communicate a cooking function of the cooktop  10 . The display may further be operable to communicate one or more error messages or status messages of the cooktop  10 . 
         [0021]    Referring now to  FIG. 2 , a schematic view of an electronic circuit  42  in communication with the controller  20  is shown. The controller  20  is configured to apply the alternating current to drive each of the induction coils  16 . As illustrated, an equivalent circuit model  44  of an exemplary induction coil  46  is shown and denoted as the equivalent inductance L eq  and the equivalent resistance R eq . The induction coil is further modeled having the equivalent capacitance C divided in the paths as C/2. 
         [0022]    The controller  20  is configured to selectively drive the induction coil  46  in response to a detection of a user input into the user interface  22  and a detection of a pan  24  on the cooking surface  28 . The induction coil  46  is driven in this example with a half bridge inverter  48 . The controller  20  is configured to monitor the current i L  driven through the induction coil  46 . Additionally, the controller  20  is configured to monitor the voltage V S2  on a lower switch  50  of the half bridge inverter  48 . The phase angle between the zero-crossing of the current i L  and the leading edge of the square wave of V S2  can be derived from the current i L  and the voltage V S2  . See  FIG. 3  for a schematic representation of phase parameter. 
         [0023]    Though a half bridge inverter is referred to herein, various driving circuits may be similarly utilized to control the induction coil  46  as described herein. For example, the induction coil  46  may correspond to a full bridge inverter or a quasi-resonant converter. The controller  20  may utilize a variety of sensor circuits to monitor the current i L  and the voltage V S2 . Additionally, the controller  20  may comprise one or more processors or circuits configured to derive the identify the zero-crossing of the current i L  and the leading edge of the voltage V S2 . 
         [0024]    Referring now to  FIG. 3 , an exemplary plot of the current i L  and the voltage V S2  is shown. The controller  20  may monitor the phase angle  58  between the zero-crossing  60  of the current i L  and the leading edge  62  of the square wave of V S2 . Based on the phase angle  58 , the controller may identify various states of the cooktop  10 . For example, if the phase angle  58  is approximately 90 degrees, the controller  20  may identify that the pan  24  is not present proximate an active or selected induction coil. Additionally, if the phase angle  58  is significantly less than  90  degrees the controller  20  may identify normal operation of the cooktop  10 . As discussed in reference to  FIG. 5 , the controller  20  may be configured to provide for an identification of a pan not being present while providing for operation of the cooktop with the small pan  24 . 
         [0025]    The phase angle  58  identified in  FIG. 3  corresponds to a low phase angle that is significantly less than 90 degrees and may correspond to normal operation of the cooktop  10 . The control scheme applied by the controller  20  may provide for the detection of the phase angle  58  as well as the amplitude of the current to distinguish normal operation of the cooktop  10  in accordance with the disclosure. As discussed herein, the controller  20  may provide for the detection of the small pan  24  to improve operation of the cooktop  10  and enable utilization of the small pan  24  to improve the versatility of the cooktop  10 . 
         [0026]    Referring now to  FIG. 4 , a plot of prior art control scheme  72  for a controller of an induction cooktop is shown. The control scheme  72  utilizes the phase angle between the zero-crossing  60  of the current i L  and the leading edge  62  of the square wave of V S2  as a first variable. In addition to the phase angle, the control scheme  72  utilizes the current i L  drawn by an induction coil to define operating parameters of an induction coil. In this way, the controller may be operable to distinguish normal operation of the cooktop, but may not provide for operation with a small pan. 
         [0027]    The normal operation zone  74  of the control scheme  72  may correspond to the phase angle  58  ranging from approximately 0 degrees to 85 degrees with the current i L  approximately less than 40 amps. Between a phase angle  58  of approximately 45 degrees and 85 degrees with the current i L  approximately between 30 and 40 amps, the controller may activate a peak current limitation  76 . Additionally, the controller  20  may identify the phase angle  58  approximately between 85 degrees and 90 degrees with the current i L  approximately between 0 and 40 amps as a first no pan detected range  78  of operation. In response to this condition, the controller may fail to activate a selected induction coil even if a small pan is present. As such, the control scheme  72  may fail to provide for operation of an induction cooktop with small pans. 
         [0028]    Therefore, the control scheme  72  may not provide for activation of an induction coil in the presence of a pan having such a size to have a surface in contact with the induction cooktop smaller than a size threshold (for example 50 cm 2 ). Such a size threshold may correspond to a working point falling in the area “NO PAN DETECTED” in the PHASE range 85°-90°. This can be an undesired operation, since in this case the user would like the system to operate and to activate; however, the activation may be limited for safety purposes. 
         [0029]    The control scheme  72  of the controller may further provide for an activated peak current  80  limitation to be activated in response to the phase angle  58  approximately between 0 degrees and 60 degrees with the current i L  approximately between 40 and 95 amps. Additionally, the controller may activate a second no pan detected range  82  of operation in response to the phase angle  58  approximately between 60 degrees and 75 degrees with the current i L  approximately between 40 and 95 amps. Finally a safety warning zone  84  may correspond to the phase angle  58  approximately between 75 degrees and 90 degrees with the current i L  approximately between 40 and 95 amps. 
         [0030]    Referring now to  FIG. 5 , a plot of a modified control scheme  92  for the controller  20  of the induction cooktop  10  is shown. The control scheme may provide for enhanced operation by including a small pan operating range  94 . The modified control scheme  82  similarly utilizes the phase angle between the zero-crossing  60  of the current i L  and the leading edge  62  of the square wave of V S2  as a first variable. In addition to the phase angle  58 , the modified control scheme  82  utilizes the current i L  drawn by an induction coil to define operating parameters of an induction coil. As further discussed, the controller  20  may provide for operation of the cooktop with the pan  24  and other small pans. 
         [0031]    The normal operation zone  96  of the modified control scheme  92  may correspond to the phase angle  58  ranging from approximately 0 degrees to 85 degrees with the current i L  approximately less than 40 amps. Between a phase angle  58  of approximately 45 degrees and 85 degrees with the current i L  approximately between 30 and 40 amps, the controller may activate a peak current limitation  98 . Additionally, the controller may identify the phase angle  58  approximately between 88 degrees and 90 degrees with the current i L  approximately between 0 and 40 amps as a first no pan detected range  100  of operation. In response to this condition, the controller  20  may accurately identify a pan not present proximate a selected induction coil. 
         [0032]    The controller  20  may identify the small pan operating range  94  in response to the phase angle  58  approximately between 84 degrees and 88 degrees with the current i L  approximately less than 30 amps. The small pan operating range may further correspond to the phase angle  58  approximately between 85 degrees and 87 degrees. In this way, the controller  20  may be advantageously configured to operate at least one induction coil of the cooktop  20  to provide for operation with the small pan  24 . 
         [0033]    The modified control scheme  92  of the controller  20  may further provide for an activated peak current  102  limitation to be activated in response to the phase angle  58  approximately between 0 degrees and 60 degrees with the current i L  approximately between 40 and 95 amps. Additionally, the controller  20  may activate a second no pan detected range  104  of operation in response to the phase angle  58  approximately between 60 degrees and 75 degrees with the current i L  approximately between 40 and 95 amps. Finally a safety warning zone  106  may correspond to the phase angle  58  approximately between 75 degrees and 90 degrees with the current i L  approximately between 40 and 95 amps. 
         [0034]    In some embodiments, the control scheme may further provide for the controller  20  to periodically update to the detection of the small pan periodically during a cooking operation. That is, the controller  20  may continue to periodically monitor the phase angle  58  and the current i L  throughout operation of each of the induction coils  16  or inductors of the cooktop  10 . In response to identifying an inductor having a phase angle greater than 88 degrees for a predetermined time, the controller  20  may deactivate the inductor. The time interval for the predetermined time may vary. In some implementations, the time interval may be approximately 5 seconds. 
         [0035]    It will be understood by one having ordinary skill in the art that construction of the described device and other components is not limited to any specific material. Other exemplary embodiments of the device disclosed herein may be formed from a wide variety of materials, unless described otherwise herein. 
         [0036]    For purposes of this disclosure, the term “coupled” (in all of its forms, couple, coupling, coupled, etc.) generally means the joining of two components (electrical or mechanical) directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components (electrical or mechanical) and any additional intermediate members being integrally formed as a single unitary body with one another or with the two components. Such joining may be permanent in nature or may be removable or releasable in nature unless otherwise stated. 
         [0037]    It is also important to note that the construction and arrangement of the elements of the device as shown in the exemplary embodiments is illustrative only. Although only a few embodiments of the present innovations have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, the length or width of the structures and/or members or connector or other elements of the system may be varied, the nature or number of adjustment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures, and combinations. Accordingly, all such modifications are intended to be included within the scope of the present innovations. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the desired and other exemplary embodiments without departing from the spirit of the present innovations. 
         [0038]    It will be understood that any described processes or steps within described processes may be combined with other disclosed processes or steps to form structures within the scope of the present device. The exemplary structures and processes disclosed herein are for illustrative purposes and are not to be construed as limiting. 
         [0039]    It is also to be understood that variations and modifications can be made on the aforementioned structures and methods without departing from the concepts of the present device, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise. 
         [0040]    The above description is considered that of the illustrated embodiments only. Modifications of the device will occur to those skilled in the art and to those who make or use the device. Therefore, it is understood that the embodiments shown in the drawings and described above is merely for illustrative purposes and not intended to limit the scope of the device, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents.