EP2887763A1

EP2887763A1 - Method, apparatus and computer program product for controlling a heat source associated with heat inertia

Info

Publication number: EP2887763A1
Application number: EP13198275.3A
Authority: EP
Inventors: Bogumil Tulin; Martin Kessler; Bryan Thomas Phillips
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2013-12-19
Filing date: 2013-12-19
Publication date: 2015-06-24

Abstract

The invention presents a method, apparatus or kitchen hob (300) and a computer program product (370) to improve temperature control of a heat source (310, ..., 330), taking heat inertia of the heat source and a total thermal system of masses associated to a heating process in e.g. a kitchen hob into account. The invention takes care of the heat inertia present in the heat source and a total thermal system of masses associated to a heating process and correspondingly provides a transition phase (255) between a higher temperature level and a lower temperature level, wherein the power supplied to the heat source is controlled differently. In particular, in pulse-width control sub-phases with ascending power phases over time are provided after e.g. preferably a break when transiting from a higher power level to a lower power level. In this manner, temperature overshooting can be avoided, energy can be saved and a consumer using a kitchen hob does not have to frequently adjust the power level, because this is automatically effected according to the present invention.

Description

In modern household environments, such as kitchens, often radiant heat sources are used in kitchen hobs or ovens. Such radiant heat sources are usually made out of metal with a distinct mass, and when they are heated, they demonstrate a heat inertia in a form that they need a certain time to adapt to a certain temperature once a certain electric power level is applied, and on the other hand when the electric power is switched off, they still stay warm for a longer time depending on their mass and their respective temperature. In an oven environment the thermal properties of the heater add up to the ones of the housing and the food to be prepared to form a system heat transmission inertia.
Respective considerations are even more important in the absence of a temperature sensor when applying open loop control.
In glass ceramic hobs, where such radiant heat sources are often used for cooking purposes, it is desired that the power level that is adjusted by a user or operator who is in the process of preparing a food dish, should reflect in a temperature change in the heat source timely and correctly in terms of increase or decrease of the temperature of the heated food.
With the limited presence of natural resources and the lack of cheap energy, it is also a prerogative that household appliances use as little energy as possible to fulfill their desired purpose. In the case of kitchen ovens and glass ceramic hobs, usually a higher energy amount is required to heat food to prepare a roast or bake a cake or the like. Devices that have a high energy saving rating, meaning that they preserve energy when in use, are attractive to the customer, not only because they are technically more sophisticated, but also because they save energy and thus costs. On the other hand, such devices are more suitable to perform their tasks, because they provide a better consumer experience in terms of temperature control during a cooking process.
Thus, there is a need on the market for sophisticated temperature control mechanisms that improve the temperature behavior of radiant heat devices and /or associated system components like cooking cavity and food subjected to a heating process in terms of following of the control commands set by an input device by a user, while at the same time saving energy.
In the prior art, document EP 0442139 A2 discusses a method and an apparatus for control of the power that is supplied to at least one load. A principle is to cut half waves of a symmetrical oscillation packet control, while at the same time satisfying a requirement regarding the switch-off times and a DIN standard. No other related prior art is known.
The invention is based on the problem to provide a better power control for a heat source that in particular helps saving energy.
This problem is solved by a method for controlling a heat source associated with heat inertia according to claim 1, by an apparatus or a kitchen hob according to claim 13 and by a computer program product according to claim 15.
Advantageous further developments are given in the dependent claims.
Advantageously, a method according to the present invention contemplates for a transition phase between two power levels in which the heat source is operated differently than at the initial power level and at the desired final power level. Such a transition phase allows for an adaptation of the power control to compensate for heat inertia of the heat source and a total thermal system of masses associated to a heating process involved in terms avoiding a temperature overshooting as much as possible. Favorably, the initialization of a transition phase is triggered by the setting of a lower power level.
Favorably, according to a further development of an embodiment of a method according to the present invention in the transition phase, the heat source is operated at no or a lower second power level in order to adapt to the heat inertia, which provides additional thermal energy in the heating process and can thus be exploited to save energy. Eventually, this leads to a better correspondence of the power control curve and the temperature control curve.
Beneficially, according to a further development of an embodiment according to the method of the present invention, in the transition phase the heat source is lesser switched on and longer switched off than at the initial power level and at the power level to be achieved in order to operate it at a lower power level.
Favorably, according to a further development of an embodiment of the method according to the present invention, at the beginning of the transition phase there is a time period where no power is supplied to the heat source in order to control it and to take care of the compensation of the heat inertia and to use the thermal energy amount present in the thermal system including the heat source and e.g. the other heated masses like food and oven cavity to arrive at the final power level to be established according to a control signal.
Advantageously, according to a further development of an embodiment of the method of the present invention pulse-width modulation is used to control switching on and off of the heat source. Such technology is known in the art and thus components are available to perform power control in an adequate and reliable manner suitable for consumer applications.
Beneficially, according to a further development of the method according to the present invention, the duty cycle of a pulse-width modulation changes in the transition phase in order to compensate for the thermal inertia of the thermal system including the heat source and e.g. the other heated masses like food and oven cavity.
Advantageously, according to a further development of the method according to the present invention, the duty cycle of the pulse-width modulation changes in a dynamic manner to better be able to closely control a temperature curve to follow a power control curve towards a value to be achieved as a final power and temperature level.
Beneficially, according to a further development of the method according to the present invention, in the transition phase, multiple sub-phases are present with an ascending power phase. In this manner, a good guidance of the heat source in terms of a temperature curve to be followed can be achieved.
Preferably, according to a further development of the method of the present invention, the start of the transition phase is controlled in dependency of a control signal issued to set a first lower power level. This, because this is the first point in time when the system knows that it should adapt to a different power level and thus the transition phase can optimally be used. It also allows a precise control to arrive at the final power level.
Beneficially, according to a further development of the method according to the present invention, in the transition phase, the adaptation from one power level to the next power level is controlled in dependency of the heat inertia of the thermal system including the heat source and e.g. the other headed masses like food and oven cavity. This allows for a good adaptation of the temperature curve that the heat source follows from the temperature associated to the initial power level to the temperature associated to the final power level.
Beneficially, according to a further development of the method according to the present invention, the heat source is controlled to avoid temperature overshooting or non achieving, when a different power level is selected by adaptively controlling the power to the heat source in the transition phase.
Beneficially, according to a further development of the method according to the present invention, by controlling the intermittently supplied power in the transition phase, the heat source is controlled to follow a temperature curve as closely as possible. This can be done by taking the heat inertia of the thermal system including the heat source and e.g. the other heated masses like food and oven cavity into account to a maximum degree and dimensioning the power to be supplied to the thermal system of heated masses adaptively and optimally for a given system heat inertia.
Advantageously, the apparatus or kitchen hob according to the present invention comprises a minimum number of components to execute the method according to the present invention. In this manner, a technically relatively simple device can be presented that is attractive for the customer as it features the benefits such as better user experience and power saving provided by the instant invention.
Favorably, the apparatus or kitchen hob according to the present invention comprises a reader for a storage medium, because in this manner the instructions how the heat source can be controlled in the transition phase and a behavior in the initial power level and the final power level can be changed or serviced. In this manner, it is also possible to adapt individual heat sources, e.g. plural heating elements allocated to different heating zones of a glass ceramic hob to their individual heat inertia, especially once such a radiant heat source had to be replaced due to service.
Advantageously, a computer program product according to the present invention comprises a storage medium and instructions to carry out the method steps as process steps, once these instructions are read and executed by a computing device. In this manner, during service and manufacturing as well as at home in use, the power control of the heat source can always be adapted to the latest state of the art research results in terms of actual and desired heat behavior of the heat source, e.g. in a kitchen environment.
Subsequently, the invention will further be explained on the basis of drawings and embodiments, wherein

Fig. 1: shows a conventional power control;
Fig. 2: shows a power control according to an embodiment of the present invention; and
Fig. 3: shows an apparatus or kitchen hob according to the present invention.

As Fig. 1 shows, at an initial higher power level 117, the corresponding pulse-width modulated power 112 basically shows a power curve 120 at full load. This leads to a temperature curve 110 with a maximum gradient depending on the heat inertia of the heat source. Such a heat source can be, for example, a heater of a glass ceramic kitchen hob in a particular heating zone or the heater of an oven. On the right axis, the time t is indicated. The maximum or higher power level is indicated by 145, and the first lower power level is indicated with reference numeral 150. As can be seen, the pulse-width modulated power contains valleys 130 and peaks 125. A peak may have a width of 135 and a valley may have a width of 140. Not necessarily, those dimensions have to be the same.
As can further be recognized in Fig. 1 according to measurements, a transition from a high power level to a lower power level can directly lead to an overshooting of a temperature curve until the final temperature 180 is achieved that corresponds to the first lower power level. This overshooting is indicated by reference sign 170, and the area under the curve corresponds to the energy that is consumed due to the overshooting.
Conventionally, a control of a kitchen hob is performed by an electronic embedded system. In a conventional boiling or frying process, power is set initially to a maximum or to a high power level for heating e.g. the food fast, and after reaching a certain temperature, the power level is set to a lower one. Usually, this is managed by observation by an operator being in front of the cooking hob adjusting the power control of the heating zone correspondingly. Such a control leads to a waste of energy as a consequence of the heat inertia of the heating device, e.g. a radiant heater.
As Fig. 2 shows, control of power levels and associated temperature of a heating device can be performed differently, if the present invention is applied here in a preferred embodiment as an example.
Reference signs throughout the drawings as long as they are the same mean the same. Thus, some of the indications in the diagram in Fig. 2 are the same as the ones in Fig. 1.
Here, however, a temperature curve 210 is indicated corresponding to an initial higher power level 245, a transition phase 255 and a first lower power level 250. As can be seen, the overshooting in the temperature curve 290 is much smaller than the one in Fig. 1. This is achieved by controlling the power supplied to the heat source in a transition phase 255, differently then as under the power control that is performed at a higher power level 245 and later at the first power level 250 respectively.
Preferably, the transition phase starts once a signal is generated to change the power level of the heat source. This can be initiated by an operator or a cook changing the power to be supplied to a e.g. heating zone by means of an input provided for that purpose at a e.g. kitchen hob.
This point in time is indicated with 244. Then, preferably, a break 260 is taking place in order to allow the thermal system including the heat source and e.g. the other heated masses like food and oven cavity to cool down and to make use of the energy saved in the thermal system including the heat source and e.g. the other heated masses like food and oven cavity due to its heat inertia. Then, a sequence of pulses 280, 288 and 290 follow that are separated by corresponding valleys 265, 270 and 275. As can be seen, the small sub-phases as they may also be called 280, 288 and 290 have an ascending power phase represented by the width of the respective pulses 280, 288 and 290. Beneficially, the ascending power phase can be achieved by a dynamic duty cycle management of the main power.
In the subsequent first lower power level, the pulses are e.g. evenly spread as also shown in Fig. 1 having a width 235 of a peak and a valley 40. By such a transition phase, a temperature overshoot is limited respectively suppressed, and thermal losses to the environment are lowered. As a consequence, power consumption is lowered as well. Beneficially, the power control in the transition phase can be adapted to the requirements of an optimum curve shape of the temperature curve, decisions can also be taken how complex an algorithm of power control should be and the trade-offs between the desire to have an optimum curve shape and a less complex algorithm can be taken into account in designing the power control. Advantageously, a user experience of a kitchen hob with a power control according to the present invention is better, as a user does not have to switch the power level manually, once e.g. the boiling temperature is reached.
Fig. 3 shows an apparatus or kitchen hob according to an embodiment of the present invention. The kitchen hob 300 in this example has four cooking zones 310 to 325 and an oven 330. The skilled person is aware that individual components of the hob shown in this embodiment like cooking zones 310 to 325 and oven 330 can be provided separately and also controlled individually in further developments of kitchen appliances according to the market demand without limiting the invention.
It further comprises a control board 335 with switches 340 and a display 337. It also has a controller 345 to control the power of each of the heating zones that are preferably present in the form of radiant heaters individually, and it also has a reader for a computer storage medium, e.g. a smartcard reader or an optical drive. From there read in data or instructions can be forwarded and stored into an internal non volatile memory to be used in the open loop control for heating of a thermal system including the heat source and e.g. the other heated masses like food and oven cavity or heating zone.
Further, Fig. 3 shows a corresponding computer program product 370 which is present in the form of e.g. a smartcard, and has on it instructions 375 and 380 stored to operate the power control of the kitchen hob respectively its individual components like e.g. cooking zones 310 to 325 and an oven 330 according to the present invention. This computer storage medium can be inserted into a slot of the reader 350 and can be read by the controller 345 of a kitchen hob in order to perform adequate power control of the heating zones of the kitchen hob in the manner as described above when explaining the method of the present invention and its embodiments.
A kitchen hob according to the present invention saves power and provides a better cooking experience to a customer as it avoids overshooting and thus long cooking or boiling periods which may lead to the spilling of fluids or other cooking substances.

List of reference numerals

110: temperature curve
112: power curve
117: power level
145: high power level
120: power curve at high power level
125: peak of pulse-width modulated power
130: valley of pulse-width modulated power
135: width of peak of pulse-width modulated power
140: width of valley of pulse-width modulated power
150: first lower power level
180: temperature corresponding to first lower power level
170: area on the temperature curve corresponding to heat inertia
t: time axis
210: temperature curve of improved heat control method
245: higher power level
250: first lower power level
255: transition phase
290: area under temperature curve
244: start of transition phase
288, 290: sub-phases with ascending power phase
260: break
265, 270, 275: valleys between sub-phases
235: width of peak
240: width of valley corresponding to pulse-width modulation for power control to adjust a first lower power level
300: apparatus or kitchen hob
310,...; 325: heating zones of a glass ceramic hob
330: oven
335: control panel
340: switch
350: reader
345: controller
375, 380: instructions
370: storage medium

Claims

A method for controlling a heat source (310, ..., 330) associated with heat inertia comprising:
- setting (340) a higher power level (245),

- setting a first lower power level (250), wherein at the first power level the heat source is intermittently powered to control the heat source,

- providing a transition phase (255) after setting the first lower power level (250), wherein the heat source is controlled differently than at the higher power level and at the first lower power level.
The method according to claim 1, wherein in the transition phase (255) the heat source (310, ..., 330) is controlled at no or at a lower second power level that is lower than the first power level (250).
The method according to claim 2, wherein the heat source (310, ..., 330) is lesser switched on and longer switched off than at the first power level (250) for intermittently powering it.
The method according to any one of the previous claims, where at the begin of the transition phase (255) a break (260) is provided in which no power is supplied to the heat source in control of the heat source (310, ..., 330).
The method according to any one of the previous claims, wherein the intermittently powering is controlled in the form of a pulse-width modulation with a duty cycle corresponding to the respective power level.
The method according to claim 6, wherein the duty cycle changes in the transition phase (255).
The method according to any one of the claims 5 to 6, wherein the duty cycle is dynamic.
The method according to claim 7, wherein the duty cycle is present in the form of sub-phases, respectively having an ascending power phase over time.
The method according to any one of the previous claims wherein the transition phase (255) is started in dependency of a signal generated to set the first power level (250)..
The method according to any one of the previous claims wherein in the transition phase (255) the power of the heat source (310, ..., 330) is controlled in dependency of the heat inertia.
The method according to any one of the previous claims, wherein the power in the transition phase (255) is controlled to avoid overshooting of the temperature of the heat source (310, ..., 330).
The method to any one of the previous claims, wherein the power in the transition phase (255) is controlled to adapt the temperature of a heat source (310, ..., 330) to a predefined temperature curve (210).
An apparatus or kitchen hob (300), at least comprising:
- a heat source (310, ..., 330),

- a controller (345) to control the heat source (310, ..., 330),

- an input (340) to set a power level,
wherein the controller (345) is adapted to perform the method according to any one of the claims 1 to 12.
The apparatus according to claim 13, further comprising a reader (350) for a data storage medium (370).
A computer program product, comprising a data storage medium (370) that comprises instructions (375, 380) that when read and executed by a computing device (345) carry out the method steps according to any one of the claims 1 to 12 as process steps.