EP3461229B1

EP3461229B1 - Induction cooking hob

Info

Publication number: EP3461229B1
Application number: EP17192537.3A
Authority: EP
Inventors: Massimo Nostro; Laurent Jeanneteau; Massimo Zangoli; Adriano Scotto D'Apollonia; Alex Viroli; Luca DI CARLO
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2017-09-22
Filing date: 2017-09-22
Publication date: 2022-08-10
Anticipated expiration: 2037-09-22
Also published as: EP3461229A1; WO2019057653A1

Description

The present invention relates to an induction cooking hob comprising a plurality of heating units and a plurality of switching elements.
Document JP 2011/198621 A1 describes an electromagnetic cooker capable of effectively cooling a semiconductor switching element mounted on radiators by forming an air channel hardly leaking cooling wind from a cooling fan with the use of a pair of the radiators having a simple structure. The electromagnetic cooker is provided with a heating coil, an inverter circuit containing a plurality of switching elements supplying high-frequency current to the heating coil, at least a pair of radiators mounted on each of the switching elements and containing a plurality of heat radiating fins, and a cooling fan blasting air to the air channel formed between the pair of radiators by arranging at least one heat radiating fin of one of the radiators between heat radiating fins of the other radiator.
Document EP 1 679 938 A1 describes an induction heating cooking device having an inverter including a resonant circuit, and a heating output control part. The resonant circuit has a resonant capacitor and a heating coil that is magnetically coupled to a load. The inverter has first and second switching elements. The heating output control part performs control by inverting the rate values of the driving periods of the first and second switching elements. The driving of the inverter is thus controlled so that substantially the same heating output is obtained to average the losses of the first and second switching elements.
Document EP 2 746 672 A1 describes a cooktop with a control device for controlling inductors. The control device includes a single temperature sensor arranged in a cooling air stream generated by a fan, and arranged downstream of an end of a heat sink. A microcontroller is arranged in the cooling air stream generated by the fan, and arranged downstream of the end of the heat sink, where power supply to power components of the control device is limited by the microcontroller according to the value of temperature measured by the temperature sensor.
Document JP 2001 267056 A relates to an induction heating cooker having a frequency converter for turning on/off a switching semiconductor and supplying a high frequency current to a heating coil by resonance. A thermistor is connected to a copper foil of a printed circuit board in the vicinity of a solder connecting portion of an emitter terminal of a reverse conducting transistor by soldering the end portion to the copper foil. A collector and emitter terminal of the transistor, terminals of the reverse conducting transistor, and terminals of the thermistor are soldered.
Document EP 1 616 463 B1 is related to a high-frequency dielectric heating by using a magnetron, and to protecting a semiconductor switching element such as IGBT (insulated gate bipolar transistor) used in an inverter from being overheated. A heat-radiating portion of the IGBT that generates a high temperature is secured to heat-radiating fins, and three legs thereof are inserted in through holes in a printed circuit board and are soldered on the opposite side. A chip thermistor is directly soldered to a leg of the IGBT on a soldering surface on the back side of the printed circuit substrate.
Document EP 1 571 707 A2 is related to temperature detection for a semiconductor device used for a power conversion apparatus to drive an alternating current induction motor.
A problem with known cooking hobs is the fact that it is difficult to set the appropriate power for each heating unit so as to avoid any overheating of the switching elements which can lead to a malfunction or can destroy parts of the induction cooking hob and the comprised circuits or electrical components such as the switching elements itself.
It is an object of the present invention to provide an improved induction cooking hob which allows a more precise temperature estimation and power control of the switching elements.
The object of the present invention is achieved by the induction cooking hob according to claim 1. Preferred embodiments of the present invention are defined in the dependent claims.
The induction cooking hob according to the present invention includes a plurality of temperature sensors, wherein each of the temperature sensors is associated and thermally connected to one of the switching elements, wherein the temperature sensors are adapted to sense the temperature of the dedicated switching element.
Since each switching element is associated with a (separate) respective temperature sensor being thermally connected to the switching element, wherein the temperature sensor is adapted to sense the temperature of the switching element, a more precise temperature estimation and control of the switching element can be achieved. As a result the power fed into or through the switching elements can be better controlled and an overheating of the components of the induction cooking hob, especially of the related switching element, can be avoided.
In a first preferred embodiment, the induction cooking hob comprises induction coils, each induction coil being associated to one of the heating units, wherein a power generator is associated to each of the induction coils for feeding electrical power to the induction coil.
The temperature sensors preferably are thermistors.
The switching element is a semiconductor switching element, preferably an insulated-gate bipolar transistor (IGBT), or a relay.
In a further preferred embodiment of the present invention, the induction cooking hob comprises a resonant circuit, wherein the induction coil is part of the resonant circuit, and the resonant circuit further comprises a capacitor.
Preferably, the power generator comprises an inverter adapted to convert a direct current (DC) voltage into an alternating current (AC) voltage to be applied to the induction coil.
Further preferably, the inverter or each inverter comprises one or two switching elements, each of them being thermally connected to an associated temperature sensor which is adapted to sense the temperature of the associated switching element. This comprises the beneficial effect, that by assigning one thermistor to each and every switching element, the specific temperature load of every switching element can be estimated and controlled in an improved manner, thus avoiding an overheating of the respective switching element.
The switching elements and the associated temperature sensors can be mounted onto a printed circuit board (PCB) and preferably are surface mounted devices (SMD). This i.a. reduces production cost.
At least one cooling body can be mounted onto such a PCB and is thermally connected to at least one switching element. This leads to the benefit that the cooling body acts as a heating sink or passive heat exchanger that transfers the heat generated by the switching element to the surrounding air, thereby allowing regulation of the device's temperature at optimal levels.
A temperature sensor and at least one leg of the switching element (e.g. a IGBT) are sharing the same PCB pattern.
The temperature sensor and the switching element can be mounted on opposite sides of the PCB.
In general, an induction cooking hob according to the present invention preferably comprises:
at least one, preferably one or two power boards, each power board comprising:
at least one, preferably one or two power generators, each power generator being associated to one induction coil and comprising:
at least one, preferably one or two switching elements, each switching element being thermally connected to an associated temperature sensor, wherein the temperature sensor is adapted to sense the temperature of the respective switching element.
As a result the induction cooking hob includes one-to-one association between every switching element (preferably IGBTs) and one of the temperature sensors (preferably thermistors) leading to an improved power and temperature management of the switching elements.
A further temperature sensor is provided and placed in or nearby an air inlet or outlet of a cooling fan and adapted to measure the temperature of cooling air draw in or ejected by the fan. This leads to the benefit that the cooling fan can cool the switching element and the efficiency of the cooling can be controlled by measuring the respective air temperature.
In a further preferred embodiment the induction cooking hob further comprises a microcontroller being adapted to receive input signals from at least one temperature sensor and to control the electrical power that is delivered to a switching elements associated with the temperature sensor. This includes the benefit that a feedback control can be established wherein the electrical power that is directed towards the respective switching element or power generator / inverter can be controlled based on the detected temperature of the switching element.
Further preferably, the induction cooking hob further comprises at least one cooling body and a temperature sensor is provided per switching element or per generator or per cooling body, wherein the cooling body and the temperature sensor an the switching element preferably are mounted on a PCB.
The present invention will be described in further detail with reference to the accompanying drawings in which:

FIG. 1: illustrates a schematic circuit of an induction cooking hob according to a preferred embodiment of the present invention; and
FIG. 2: illustrates a schematic view onto a PCB carrying one switching element of F_IG. 1.

F_IG. 1 illustrates a schematic circuit diagram of the induction cooking hob according to the present invention.
On the left side, a thermistor circuit 10 is shown comprising a thermistor 12 connected to a potential V_CC 14 and a common ground 42. The thermistor 12 is arranged at or nearby a joint of a switching element such as an insulated-gate bipolar transistor (IGBT) 26. IGBT 26 is part of a power generator 20 or inverter which feeds electrical power to a resonant circuit 32 comprising an induction coil 34 and a capacitor 36. Induction coil 34 is associated to a heating unit 50 which can be used to heat a load 38 such as a pan or a pot or the like.
Power generator 20 can be realized by or comprise a half-bridge inverter 22 comprising an additional IGBT 24 and two diodes 28 and 30. Alternatively, the power generator 20 can also be realized by other means such as a quasi-resonant converter comprising only one switching element such as an IGBT.
Half-bridge inverter 22 is connected to a potential V_BUS 40 and also to common ground 42. The dotted line in F_IG. 1 illustrates that thermistor circuit 10 with thermistor 12 and power generator 20 comprising or consisting of half-bridge inverter 22 (or another type of inverter) not only share the same common electrical ground 42, but IGBT 26 and thermistor 12 are arranged at a small distance or in contact with each other so that thermistor 12 is also thermally connected to IGBT 26. Therefore, thermistor 12 can be used for detecting the specific temperature of IGBT 26.
Electrical connection 16 connects thermistor 12 to a microcontroller (not shown) which is used to control or feedback-control the electrical power provided to and fed into power generator 20. Due to the thermal connection of thermistor 12 to IGBT 26 a more precise temperature estimation of IGBT 26 is achieved. Therefore, power control and power delivery to the power generator 20 can be controlled in a more precise manner so as to avoid an overheating of IGBT 26 and/or other parts of the circuit. An improved power regulation and temperature control of the induction cooking hob is achieved. Thermistor 12 can be used to limit the maximum temperature of the components of the power generator20 by modulating the power by means of the controller, wherein the latter can be a microcontroller running a respective software or program.
Fig. 2 shows schematic view onto thermistor 12 and IGBT 26 of Fig. 1 which both are mounted onto a printed circuit board (PCB) 44.
Thermistor 12 as well as IGBT 26 are SMDs (Surface Mounted Devices). In the embodiment of Fig. 2 thermistor 12 and IGBT 26 are mounted on opposite sides of PCB 44. Thermistor 12 and IGBT 26 are arranged close to each other or in contact with each other so that thermistor 12 is thermally connected to IGBT 26. One leg 46 of IGBT 26 and thermistor 12 share the same pattern potential of PCT 44 which means that they are not only in electrical contact (see common ground 42 according to Fig. 1) but also in thermal contact with each other through the metallization of the PCB.
Fig. 2 also shows a heat radiating fin 48 of a cooling body which is thermally connected to IGBT 26 so as to act as a heat sink for IGBT 26.
To further reduce the thermal load of power generator 20 and half bridge inverter 22 a cooling fan can be provided which sucks in air and directs a respective air flow towards the components of power generator 20 such as towards IGBTs 24 and 26 and fin 48. A further temperature sensor is provided and placed in or nearby an air inlet of such a cooling fan and is adapted to measure the temperature of cooling air drawn in or ejected by the fan.
Further temperature sensors or thermistors can be provided in contact to PCB 44 or to fin 48 of the cooling body and used for detecting the temperature of the PCB or the cooling body.
A combination of all measurements of the comprised temperature sensors improves the overall power and temperature regulation.

List of reference signs:_

10: thermistor circuit
12: thermistor
14: V_cc
16: connection to microcontroller
20: power generator
22: half bridge inverter
24: IGBT
26: IGBT
28: diode
30: diode
32: resonant circuit
34: induction coil
36: capacitor
38: load
40: V_Bus
42: ground
44: PCB
46: leg
48: fin
50: heating unit

Claims

An induction cooking hob comprising a plurality of heating units (50), a plurality of switching elements, and a plurality of temperature sensors, wherein each of the temperature sensors is associated and thermally connected to one of the switching elements,
wherein the temperature sensors are adapted to sense the temperature of the dedicated switching element,

wherein a temperature sensor of the plurality of temperature sensors and at least one leg of the dedicated switching element are sharing the same printed circuit pattern, and

wherein a further temperature sensor is provided and placed in or nearby an air inlet or outlet of a cooling fan and adapted to measure the temperature of cooling air draw in or ejected by the fan.
The induction cooking hob of claim 1, wherein the induction cooking hob comprises induction coils (34), each induction coil being associated to one of the heating units, and wherein a power generator (20) is associated to each of the induction coils for feeding electrical power to the induction coil.
The induction cooking hob of anyone of the preceding claims, wherein at least one of the temperature sensors is a thermistor (12).
The induction cooking hob of anyone of the preceding claims, wherein at least one of the switching elements is a semiconductor switching element, preferably an insulated-gate bipolar transistor (IGBT) (24, 26), or a relay.
The induction cooking hob of anyone of the preceding claims 2-4, wherein the induction cooking hob comprises resonant circuits (32) wherein each induction coil (34) is part of a resonant circuit, each resonant circuit further comprising a capacitor (36).
The induction cooking hob of anyone of the preceding claims 2-5, wherein each power generator (20) comprises an inverter (22) adapted to convert a direct current (DC) voltage into an alternating current (AC) voltage to be applied to the induction coil (34).
The induction cooking hob of claim 6, wherein the inverter (22) comprises one or two switching elements, wherein at least one of them being thermally connected to an associated temperature sensor which is adapted to sense the temperature of the associated switching element.
The induction cooking hob of anyone of the preceding claims, wherein the switching elements and the associated temperature sensors are mounted onto a printed circuit board (PCB) (44) and the switching elements and / or temperature sensors preferably are surface mounted devices (SMDs).
The induction cooking hob of claim 8, wherein at least one cooling body is mounted onto the printed circuit board (PCB) (44) and is thermally connected to a switching element.
The induction cooking hob of anyone of the preceding claims 8 and 9, wherein the temperature sensor and the switching element are mounted on opposite sides of the PCB (44).
The induction cooking hob of anyone of the preceding claims, wherein the induction cooking hob comprises:
at least one, preferably one or two power boards, each power board comprising:
at least one, preferably one or two power generators (20), each power generator being associated to one induction coil (34) and comprising:
at least one, preferably one or two switching elements, at least one, preferably all switching elements being thermally connected to an associated temperature sensor, wherein the temperature sensor is adapted to sense the temperature of the respective switching element.
The induction cooking hob of anyone of the preceding claims, wherein the induction cooking hob further comprises a microcontroller being adapted to receive input signals from at least one temperature sensor and to control the electrical power that is delivered to a switching element associated with the temperature sensor.
The induction cooking hob of anyone of the preceding claims, wherein the induction cooking hob further comprises at least one cooling body and a temperature sensor is provided per heating unit or per switching element or per generator or per cooling body, wherein the cooling body and the temperature sensor and the switching element preferably are mounted on a PCB (44).