Technical Field
[0001] The present disclosure relates to an induction cooker and a method of operating an
induction cooker.
Background
[0002] Induction cookers are known in which a varying electric current is passed through
an induction coil, the coil therefore producing a corresponding varying electromagnetic
field. The varying electromagnetic field induces a varying eddy current in a ferromagnetic
cooking vessel or the like when the cooking vessel placed in close proximity to the
induction coil, which in turn heats the cooking vessel and therefore the contents
of the cooking vessel. One or more transistors may be used to control the power that
is provided to the induction coil by varying the current that is provided to the induction
coil.
Summary
[0003] The present invention is defined by the features of the claims. The document
EP 2 605 614 A1 discloses the preamble of claim 1. According to a first aspect disclosed herein,
there is provided an induction cooker, the induction cooker comprising:
an induction coil arranged to receive a varying electric current and to produce a
corresponding varying electromagnetic field;
a power circuit constructed and arranged to provide the varying electric current;
the power circuit comprising at least a first transistor and a second transistor which
are each arranged in series with the induction coil and which are arranged in parallel
to each other, the transistors being controllable so as to control the current that
is provided to the induction coil by the power circuit;
a first current sensor for sensing the current flowing through the first transistor;
a second current sensor for sensing the current flowing through the second transistor;
and
a controller for controlling the power circuit, the controller being arranged to compare
a current flowing through the first transistor and a current flowing through the second
transistor, and to cause an indication to be output in the case that the current flowing
through the first transistor and the current flowing through the second transistor
differ by more than a threshold.
[0004] In an example, the transistors of the power circuit are power transistors.
[0005] In an example, the transistors of the power circuit are insulated-gate bipolar transistors.
[0006] In an example, the induction coil is a coil of a resonant converter, the resonant
converter comprising a capacitor in parallel with the induction coil.
[0007] In an example, the induction cooker comprises a display device, wherein the controller
is arranged such that the indication is a visual indication that is provided to the
display device for display.
[0008] According to a second aspect disclosed herein, there is provided a method of operating
an induction cooker, the induction cooker comprising a power circuit constructed and
arranged to provide a varying electric current to an induction coil of the induction
cooker, the power circuit comprising at least a first transistor and a second transistor
which are each arranged in series with the induction coil and which are arranged in
parallel to each other, the transistors being controllable so as to control the current
that is provided to the induction coil by the power circuit, the method comprising:
sensing a current flowing through the first transistor;
sensing a current flowing through the second transistor;
comparing the current flowing through the first transistor and the current flowing
through the second transistor; and
outputting an indication in the case that the current flowing through the first transistor
and the current flowing through the second transistor differ by more than a threshold.
Brief Description of the Drawings
[0009] To assist understanding of the present disclosure and to show how embodiments may
be put into effect, reference is made by way of example to the accompanying drawings
in which:
Figure 1 shows schematically a circuit diagram of an example of an induction cooker
according to an aspect disclosed herein;
Figure 2 shows schematically a plan view of an induction coil; and
Figures 3A and 3B show examples of differences in currents flowing through switching
transistors.
Detailed Description
[0010] Referring to Figure 1, there is shown a circuit diagram of an example of an induction
cooker 10 according to an aspect disclosed herein. The induction cooker 10 has an
induction coil 12. As will be discussed further below, a varying electric current
is provided to the induction coil 12, which therefore produces a corresponding varying
electromagnetic field. When a ferromagnetic object is placed close to the induction
coil 12 and therefore in the varying electromagnetic field, a corresponding varying
eddy current is induced in the ferromagnetic object, which therefore heats the ferromagnetic
object. The ferromagnetic object may be a cooking vessel such as a cooking pot or
saucepan or frying pan, etc., etc.
[0011] In the example shown, the induction coil 12 is in parallel with a capacitor 14. The
induction coil 12 and the capacitor 14 form a resonant converter (which term as used
herein includes so-called "quasi-resonant" converters unless the context requires
otherwise) which resonates at a specific frequency.
[0012] Many induction cookers are intended to be run from an AC (alternating current) mains
electric power supply. However, the current is not used directly from the mains power
supply as the mains power supply is typically at a frequency of between 50 to 60 Hz
or so, which can cause an unpleasant audible hum if used directly to power the induction
coil 12. Accordingly, in this example, the incoming AC mains power 16 is passed through
a filter 18 and then to a rectifier 20, which may for example be a diode bridge rectifier,
which rectifies the AC to DC (direct current). In the example shown, the direct current
is then provided via a series choke coil 22 to the induction coil 12.
[0013] As mentioned, a varying current must be provided to the induction coil 12 in order
to produce the required varying electromagnetic field. This is often achieved by regulating
or varying the current at a constant voltage. This is often achieved in practice by
using a converter having a transistor which is controlled to switch on and off as
necessary to produce a varying electric current. Because the power levels are high,
the switching transistor that is used is typically a "power" transistor which is capable
of withstanding the high voltages and/or high currents that are used. By way of example
only, the total power of the induction cooker 10 may be say 3500W and the currents
flowing through the switching transistor(s) may be say 15A.
[0014] Power transistors are relatively expensive components, and a power transistor that
can withstand very high currents is very expensive. Accordingly, two or more transistors,
such as power transistors, may be used in parallel in the converter effectively to
"share" the current that is being supplied, which helps to keep down the costs as
transistors having a lower specification may be used instead of a single, high specification
transistor.
[0015] The use of two switching transistors in the converter portion in the present example
is indicated in Figure 1, it being understood that other examples may use more than
two switching transistors. In particular, there is shown two switching transistors
24, 26. Each switching transistor 24, 26 is connected in series with the induction
coil 10 on the return line to the rectifier 20. The switching transistors 24, 26 are
in parallel with each other. The switching transistors 24, 26 are controlled by a
main controller (not shown in Figure 1) to switch on and off at the necessary times
in order to provide the desired power to the induction coil 12.
[0016] The switching transistors 24, 26 may be for example so-called power transistors.
Suitable examples include MOSFETs (metal-oxide-semiconductor field-effect transistors)
and IGBTs (insulated-gate bipolar transistors). As is known, MOSFETs are typically
described in terms of the gate, source and drain of the MOSFET and IGBTs are typically
described in terms of the base, collector and emitter of the IGBT. For present purposes,
these terms are in essence equivalent to each other. Thus, in the present specification,
which is given in terms of using IGBTs as specific examples of the switching transistors
24, 26, the language of "base, collector and emitter" will be used, it being understood
that this will be interpreted as "gate, source and drain" in the case of MOSFETs being
used as the switching transistors 24, 26.
[0017] Given the symmetry in their layout and connections, it would be expected that the
current flowing through the two switching transistors 24, 26 would be the same. However
it has been found that in practice the current flowing through the two switching transistors
24, 26 may be different, for example because of variations in manufacturing tolerances
of various components or errors during manufacture. This is undesirable as it is likely
to mean that one of the switching transistors 24, 26 may be subjected to a greater
load than the other and is therefore more likely to fail over time, leading to a shortened
lifetime before repair or replacement is necessary.
[0018] Accordingly, in accordance with examples of aspects described herein, the induction
cooker 10 is arranged so that the currents flowing through the two switching transistors
24, 26 are compared. In the case that the currents flowing through the switching transistors
24, 26 differ by more than a threshold, then an indication may be output. The indication
may be for the benefit of the user (owner) of the induction cooker 10 as it may effectively
indicate that some repair or replacement will be required. The indication may be for
the benefit of the manufacturer of the induction cooker 10 as it may be used during
final testing of the induction cooker 10 following manufacture to effectively indicate
that some modification of the components or circuit of the induction cooker 10 is
required.
[0019] In the example shown, a current detector 28, 30 is provided for each switching transistor
24, 26 to measure the current flowing through the switching transistors 24, 26. The
current detectors 28, 30 are connected in series with the respective switching transistors
24, 26. The measured current from each current detector 28, 30 is passed to a comparator,
which may be implemented as part of the main controller or by a separate comparator
component. If it is determined that the currents flowing through the switching transistors
24, 26 differ by more than a threshold, then a corresponding indication is caused
to be output by the controller. The indication may be output as for example a warning
or alarm sound. Alternatively or additionally, the indication may be output as for
example a visual display on a display device, such as a display device of the induction
cooker 10. An appropriate value for the threshold can be set by the manufacturer.
The threshold may be for example some percentage, such that an indication is output
if the two currents differ by more than 5% or 10% or 15%, etc.
[0020] The currents flowing through the switching transistors 24, 26 may be measured continuously
by the current detectors 28, 30. Alternatively, the currents may be measured at intervals,
such as for example every 10ms, which would be particularly appropriate in the case
that the mains power supply is a 50Hz AC. The currents may be measured during the
zero-crossing points of the 10ms period, which is advantageous as there should be
no or little noise at the noise zero-crossing points. The comparison between the two
currents flowing through the switching transistors 24, 26 may be such that it is not
initially carried for a time period following initial powering of the induction coil
12. This is to enable the powering of the induction coil 12 to settle down after first
being powered. It can happen for example that noise levels in the detected currents
are high during this initial period. The initial time period when no comparison is
made may for example be around 1 second or so. The comparison between the two currents
flowing through the switching transistors 24, 26 may be such that it is only carried
out for a time period following initial powering of the induction coil 12. In the
case that no comparison is made for an initial time period, this time period when
a comparison is made may follow that initial time period. The time period when a comparison
is made may be for example a few seconds, such as for example 5 seconds. In this time
in this example where the currents are measured every 10ms, the controller receives
approximately 3000 sensed current values, which provides a good measure and averaging
of the current difference.
[0021] The current detectors 28, 30 may be or comprise one or more current shunt resistors.
A shunt resistor is a low resistance, precision resistor which may be used to measure
AC or DC electrical currents by the voltage drop those currents create across the
resistance. The resistance may be for example in the region of a few milliohm.
[0022] The current detectors 28, 30 for detecting the currents in the switching transistors
24, 26 may be provided as part of the induction cooker 10 for other purposes. For
example, in induction cookers, a feedback system may be used for controlling the switching
on and off of the switching transistors 24, 26 to achieve the desired power output.
Such a feedback system uses measured values of the currents flowing through the switching
transistors 24, 26. Such a feedback system may also be used to detect when a cooking
vessel has been removed from the induction cooker 10 as removal of the cooking vessel
causes rapid and significant changes in the current flowing through the switching
transistors 24, 26.
[0023] As a particular example of errors that may occur during manufacture of the induction
cooker 10, the switching transistors 24, 26 may be in thermal contact with respective
heat sinks for removing excess heat from the switching transistors 24, 26 during operation,
and it can happen that the thermal contact between one or both of the switching transistors
24, 26 and the heat sinks is poor. This will manifest itself by different currents
flowing through the switching transistors 24, 26, which will therefore be brought
to the attention of the manufacturer during testing.
[0024] As another example of errors that may occur during manufacture of the induction cooker
10, errors may arise in the induction coil 12, either during manufacture of the induction
coil 12 itself or during assembly of the induction coil 12 into the induction cooker
10. An example of an induction coil 12 is shown schematically in Figure 2. The induction
coil 12 of this example has inner, middle and outer portions. First and second electrical
connectors 122, 124 are provided at the two ends of the coil 12 for connecting the
coil 12 into the circuit of the induction cooker 10. It is important that the induction
coil 12 is inserted in the correct direction or orientation into the induction cooker
10, and in particular that the two electrical connectors 122, 124 are connected the
right way round to the resonant capacitor 14 and the switching transistors 24, 26.
If for some reason the induction coil 12 has not been manufactured correctly, such
as not having a uniform direction for the winding of the coil, or is installed incorrectly
into the induction cooker 10, this will manifest itself by different currents flowing
through the switching transistors 24, 26.
[0025] This difference in the currents through the switching transistors 24, 26 in the case
that the induction coil 12 has been manufactured or installed correctly and incorrectly
are illustrated in Figures 3A and 3B. Figure 3A shows the difference (measured as
a percentage) between the measured currents passing through the switching transistors
24, 26 in the case that the induction coil 12 has been manufactured and installed
correctly. As can be seen, the difference is less than around 1.7% of the value of
the current flowing through one or other of the switching transistors 24, 26. In contrast,
Figure 3B shows the difference (measured as a percentage) between the measured currents
passing through the switching transistors 24, 26 in the case that the induction coil
12 has been manufactured and/or installed incorrectly. As can be seen, the current
difference is large, typically above around 15% in this example. As such, the controller
of the induction cooker 10 quickly turns off the current through the switching transistors
24, 26 (at just less than 58 ms from when the comparison is first made in the example
shown). An indication is also provided, which in this case is likely to be for the
attention of the manufacturer as this is ideally carried out during testing following
manufacture.
[0026] It will be understood that the processor or processing system or circuitry referred
to herein may in practice be provided by a single chip or integrated circuit or plural
chips or integrated circuits, optionally provided as a chipset, an application-specific
integrated circuit (ASIC), field-programmable gate array (FPGA), digital signal processor
(DSP), graphics processing units (GPUs), etc. The chip or chips may comprise circuitry
(as well as possibly firmware) for embodying at least one or more of a data processor
or processors and a digital signal processor or processors, which are configurable
so as to operate in accordance with the exemplary embodiments. In this regard, the
exemplary embodiments may be implemented at least in part by computer software stored
in (non-transitory) memory and executable by the processor, or by hardware, or by
a combination of tangibly stored software and hardware (and tangibly stored firmware).
The examples described herein are to be understood as illustrative examples of embodiments
of the invention.
1. An induction cooker (10), the induction cooker comprising:
an induction coil (12) arranged to receive a varying electric current and to produce
a corresponding varying electromagnetic field;
a power circuit constructed and arranged to provide the varying electric current;
the power circuit comprising at least a first transistor (24) and a second transistor
(26) which are each arranged in series with the induction coil (12) and which are
arranged in parallel to each other, the transistors (24, 26) being controllable so
as to control the current that is provided to the induction coil (12) by the power
circuit, characterised by:
a first current sensor (28) for sensing the current flowing through the first transistor
(24);
a second current sensor (30) for sensing the current flowing through the second transistor
(26); and
a controller for controlling the power circuit, the controller being arranged to compare
a current flowing through the first transistor (24) and a current flowing through
the second transistor (26), and to cause an indication to be output in the case that
the current flowing through the first transistor (24) and the current flowing through
the second transistor (26) differ by more than a threshold.
2. An induction cooker (10) according to claim 1, wherein the transistors (24, 26) of
the power circuit are power transistors.
3. An induction cooker (10) according to claim 1 or claim 2, wherein the transistors
(24, 26) of the power circuit are insulated-gate bipolar transistors.
4. An induction cooker (10 according to any of claims 1 to 3, wherein the induction coil
(12) is a coil of a resonant converter, the resonant converter comprising a capacitor
(14) in parallel with the induction coil (12).
5. An induction cooker (10) according to any of claims 1 to 4, comprising a display device,
wherein the controller is arranged such that the indication is a visual indication
that is provided to the display device for display.
6. A method of operating an induction cooker (10), the induction cooker (10) comprising
a power circuit constructed and arranged to provide a varying electric current to
an induction coil (12) of the induction cooker (10), the power circuit comprising
at least a first transistor (24) and a second transistor (26) which are each arranged
in series with the induction coil (12) and which are arranged in parallel to each
other, the transistors (24, 26) being controllable so as to control the current that
is provided to the induction coil (12) by the power circuit,
characterised by: the method comprising:
sensing a current flowing through the first transistor (24);
sensing a current flowing through the second transistor (26);
comparing the current flowing through the first transistor (24) and the current flowing
through the second transistor (26); and
outputting an indication in the case that the current flowing through the first transistor
(24) and the current flowing through the second transistor (26) differ by more than
a threshold.
7. A method according to claim 6, wherein the transistors of the power circuit are power
transistors (24, 26).
8. A method according to claim 6 or claim 7, wherein the transistors of the power circuit
are insulated-gate bipolar transistors (24, 26).
9. A method according to any of claims 6 to 8, comprising outputting the indication as
a visual indication on a display device.
1. Induktionskocher (10), wobei der Induktionskocher umfasst:
eine Induktionsspule (12), die dazu eingerichtet ist, einen veränderlichen elektrischen
Strom zu empfangen und ein entsprechendes veränderliches elektromagnetisches Feld
zu erzeugen;
eine Leistungsschaltung, die dazu konstruiert und eingerichtet ist, den veränderlichen
elektrischen Strom zu liefern;
wobei die Leistungsschaltung mindestens einen ersten Transistor (24) und einen zweiten
Transistor (26) umfasst, die jeweils in Reihe mit der Induktionsspule (12) und parallel
zueinander eingerichtet sind, wobei die Transistoren (24, 26) so steuerbar sind, dass
sie den Strom steuern, der der Induktionsspule (12) durch die Leistungsschaltung zugeführt
wird, gekennzeichnet durch:
einen ersten Stromsensor (28) zum Erfassen des durch den ersten Transistor (24) fließenden
Stroms;
einen zweiten Stromsensor (30) zum Erfassen des durch den zweiten Transistor (26)
fließenden Stroms und
eine Steuereinheit zum Steuern der Leistungsschaltung, wobei die Steuervorrichtung
dazu eingerichtet ist, einen durch den ersten Transistor (24) fließenden Strom und
einen durch den zweiten Transistor (26) fließenden Strom zu vergleichen und zu bewirken,
dass eine Anzeige ausgegeben wird, falls der durch den ersten Transistor (24) fließende
Strom und der durch den zweiten Transistor (26) fließende Strom um mehr als einen
Schwellenwert voneinander abweichen.
2. Induktionskocher (10) nach Anspruch 1, wobei die Transistoren (24, 26) der Leistungsschaltung
Leistungstransistoren sind.
3. Induktionskocher (10) nach Anspruch 1 oder Anspruch 2, wobei die Transistoren (24,
26) der Leistungsschaltung bipolare Transistoren mit isoliertem Gate sind.
4. Induktionskocher (10) nach einem der Ansprüche 1 bis 3, wobei die Induktionsspule
(12) eine Spule eines Resonanzwandlers ist, wobei der Resonanzwandler einen Kondensator
(14) parallel zur Induktionsspule (12) umfasst.
5. Induktionskocher (10) nach einem der Ansprüche 1 bis 4, umfassend eine Anzeigevorrichtung,
wobei die Steuervorrichtung so eingerichtet ist, dass die Anzeige eine visuelle Anzeige
ist, die der Anzeigevorrichtung zur Anzeige bereitgestellt wird.
6. Verfahren zum Betreiben eines Induktionskochers (10), wobei der Induktionskocher (10)
einen Stromkreis umfasst, der dazu konstruiert und eingerichtet ist, einer Induktionsspule
(12) des Induktionskochers (10) einen veränderlichen elektrischen Strom zuzuführen,
wobei die Leistungsschaltung mindestens einen ersten Transistor (24) und einen zweiten
Transistor (26) umfasst, die jeweils in Reihe mit der Induktionsspule (12) und parallel
zueinander eingerichtet sind, wobei die Transistoren (24, 26) dazu steuerbar sind,
den Strom zu steuern, der der Induktionsspule (12) durch die Leistungsschaltung zugeführt
wird,
dadurch gekennzeichnet, dass das Verfahren umfasst:
Erfassen eines durch den ersten Transistor (24) fließenden Stroms;
Erfassen eines durch den zweiten Transistor (26) fließenden Stroms;
Vergleichen des durch den ersten Transistor (24) fließenden Stroms und des durch den
zweiten Transistor (26) fließenden Stroms; und
Ausgeben einer Anzeige, falls sich der durch den ersten Transistor (24) fließende
Strom und der durch den zweiten Transistor (26) fließende Strom um mehr als einen
Schwellenwert unterscheiden.
7. Verfahren nach Anspruch 6, wobei die Transistoren der Leistungsschaltung Leistungstransistoren
(24, 26) sind.
8. Verfahren nach Anspruch 6 oder 7, wobei die Transistoren der Leistungsschaltung bipolare
Transistoren mit isoliertem Gate (24, 26) sind.
9. Verfahren nach einem der Ansprüche 6 bis 8, umfassend das Ausgeben der Anzeige als
visuelle Anzeige auf einer Anzeigevorrichtung.
1. Plaque de cuisson à induction (10), la plaque de cuisson comprenant :
une bobine d'induction (12) conçue pour recevoir un courant électrique variable et
produire un champ électromagnétique variable correspondant ;
un circuit d'alimentation conçu et disposé pour fournir le courant électrique variable
;
le circuit d'alimentation comprenant au moins un premier transistor (24) et un second
transistor (26) qui sont chacun disposés en série avec la bobine d'induction (12)
et qui sont disposés en parallèle l'un par rapport à l'autre, les transistors (24,
26) pouvant être commandés de manière à commander le courant qui est envoyé à la bobine
d'induction (12) par le circuit d'alimentation,
caractérisé par :
un premier capteur de courant (28) pour détecter le courant circulant dans le premier
transistor (24) ;
un second capteur de courant (30) pour détecter le courant circulant dans le second
transistor (26) ; et
un contrôleur pour commander le circuit d'alimentation, le contrôleur étant conçu
pour comparer un courant circulant dans le premier transistor (24) et un courant circulant
dans le second transistor (26) et pour qu'une indication soit émise dans le cas où
le courant circulant dans le premier transistor (24) et le courant circulant dans
le second transistor (26) diffèrent de plus d'un certain seuil.
2. Plaque de cuisson à induction (10) selon la revendication 1, dans laquelle les transistors
(24, 26) du circuit d'alimentation sont des transistors de puissance.
3. Plaque de cuisson à induction (10) selon la revendication 1 ou la revendication 2,
dans laquelle les transistors (24, 26) du circuit d'alimentation sont des transistors
bipolaires à grille isolée.
4. Plaque de cuisson à induction (10) selon l'une quelconque des revendications 1 à 3,
dans laquelle la bobine d'induction (12) est une bobine d'un convertisseur résonant,
le convertisseur résonant comprenant un condensateur (14) en parallèle avec la bobine
d'induction (12) .
5. Plaque de cuisson à induction (10) selon l'une quelconque des revendications 1 à 4,
comprenant un dispositif d'affichage, dans laquelle le contrôleur est disposé de sorte
que l'indication est une indication visuelle qui est envoyée au dispositif d'affichage
en vue de l'affichage.
6. Procédé de fonctionnement d'une plaque de cuisson à induction (10), la plaque de cuisson
à induction (10) comprenant un circuit d'alimentation conçu et disposé pour fournir
le courant électrique variable à une bobine d'induction (12) de la plaque de cuisson
à induction (10), le circuit d'alimentation comprenant au moins un premier transistor
(24) et un second transistor (26) qui sont chacun disposés en série avec la bobine
d'induction (12) et qui sont disposés en parallèle l'un par rapport à l'autre, les
transistors (24, 26) pouvant être commandés de manière à commander le courant qui
est envoyé à la bobine d'induction (12) par le circuit d'alimentation,
caractérisé en ce que le procédé consiste à :
détecter un courant circulant dans le premier transistor (24) ;
détecter un courant circulant dans le second transistor (26) ;
comparer le courant circulant dans le premier transistor (24) et le courant circulant
dans le second transistor (26) ; et
émettre une indication dans le cas où le courant circulant dans le premier transistor
(24) et le courant circulant dans le second transistor (26) diffèrent de plus d'un
certain seuil.
7. Procédé selon la revendication 6, dans lequel les transistors du circuit d'alimentation
sont des transistors (24, 26) de puissance.
8. Procédé selon la revendication 6 ou la revendication 7, dans lequel les transistors
du circuit d'alimentation sont des transistors (24, 26) bipolaires à grille isolée.
9. Procédé selon l'une quelconque des revendications 6 à 8, consistant à émettre l'indication
sous forme d'une indication visuelle sur un dispositif d'affichage.