EP3383131A1

EP3383131A1 - Inductive cooking device and method

Info

Publication number: EP3383131A1
Application number: EP17163004.9A
Authority: EP
Inventors: Hüseyin Cem KIZILARI; Murat Aydin DURAN
Original assignee: Vestel Elektronik Sanayi ve Ticaret AS
Current assignee: Vestel Elektronik Sanayi ve Ticaret AS
Priority date: 2017-03-27
Filing date: 2017-03-27
Publication date: 2018-10-03

Abstract

The present invention provides an inductive cooking device (100, 200, 300) comprising a ground node (101, 201, 301), an energy supply device (102, 202, 302) comprising a positive port (103, 203, 303) and a negative port (104, 204, 304), wherein the negative port (104, 204, 304) is coupled to the ground node (101, 201, 301), an inductive coil arrangement (105, 205, 305) comprising an input port (106, 206, 306) and an output port (107, 207, 307), wherein the input port (106, 206, 306) is coupled to the positive port (103, 203, 303) and the output port (107, 207, 307) is coupled to the ground node (101, 201, 301), and a current sensor (109, 209, 309) configured to measure the current flowing between the output port (107, 207, 307) and the ground node (101, 201, 301). Further, the present invention provides a respective method.

Description

TECHNICAL FIELD

The invention relates to an inductive cooking device and a respective method.

BACKGROUND

Although applicable to any system that uses energy transfer via induction to heat an element, the present invention will be mainly described in combination with induction cookers.
Induction cookers are usually used to heat cooking vessels by magnetic induction. Usually a high frequency power signal is provided to an induction coil. This generates a magnetic field around the induction coil, which is magnetically coupled to a conductive cooking vessel, such as a pan, placed over the induction coil. The magnetic field then generates eddy currents in the cooking vessel, causing the cooking vessel to heat.
In particular, the output power of the induction coil is a function of the power signal input, the coil inductance, the resistance of the cooking vessel, and the resonance frequency of the system. In known induction cookers, the induction coil is usually driven with a power signal at the resonance frequency of the system. The closer the system is driven to its resonance frequency, the more efficient power can be delivered to the system.
For fine grained control of such an induction cooker a very accurate measurement of the currents through the system is necessary.
In US 2012 / 0 305 546 A1 a control system for an induction cooker is presented, where the current in the inverter circuit only is measured. However, this measurement does not allow measuring the current through the complete induction system. Detecting the pan removing (when pan on the cooktop is removed) is not easy with using such a traditional current sense method. Providing the shunt resistor between the switching element and the ground does not give information about the current, when the pan is removed, because the current does not pass only through the switching element. Instead the current passes through the entire resonant tank, i.e. switching circuit.
Accordingly, there is a need for an improved power control in induction cookers.

SUMMARY

The present invention provides an inductive cooking device with the features of claim 1 and a method with the features of claim 7.
Therefore the present invention provides an inductive cooking device. The inductive cooking device comprises a ground node, an energy supply device comprising a positive port and a negative port, wherein the negative port is coupled to the ground node, an inductive coil arrangement comprising an input port and an output port, wherein the input port is coupled to the positive port and the output port is coupled to the ground node, and a current sensor configured to measure the current flowing between the output port and the ground node.
Further, the present invention provides a method for controlling an inductive cooking device according to the present invention. The method comprises supplying electrical energy to an inductive coil arrangement via an energy supply device comprising a positive port and a negative port, wherein the negative port is coupled to a ground node, wherein the inductive coil arrangement comprises an input port and an output port, wherein the input port is coupled to the positive port and the output port is coupled to the ground node, measuring the current flowing between the output port and the ground node, and generating the a driving signal for the inductive coil arrangement based on the measured current.
Induction cookers usually use a fixed operating frequency range for the power signal, which drives the induction coils. The fixed operating frequency range usually starts at the resonance frequency of the induction coil and ends at a safety limit frequency. The maximum power efficiency of the power transfer to the cooking vessel is achieved at the resonance frequency of the system of induction coil and cooking vessel. Increasing the frequency will lower the efficiency of the energy transfer. However, at increased frequencies, the impedance of the induction coil will fall and the current through the induction coil will raise. Therefore, a maximum frequency is defined, which is not surpassed.
Further, the effect a cooking vessel has on the input impedance and the resonance frequency of the induction coil can be taken into account when selecting the fixed frequency range. The operating frequency range can e.g. be selected for a virtual idealized or standardized cooking vessel, which represents an average of the existing cooking vessels. Objects, which are placed over the induction coil to cook, like e.g. pans or pots, will be referred to as cooking vessels throughout this description.
When controlling the induction coil not only a frequency but also a duty cycle may be controlled.
The present invention is based on the finding that it is detrimental to the controlling of the inductive coil of the inductive cooking device if the current is measured inside of the inductive coil arrangement. In such arrangements not the entire current in the system is measured and therefore changes in the current flow may be rather small. However, small current changes may not adequately reflect changes in the load of the inductive cooking coil. The changes in current may e.g. be so small that no distinction can be made between the removal of a cooking vessel or the emptying of a cooking vessel.
Therefore, the present invention provides a topology, where the current sensor is arranged between the output port of the inductive coil arrangement and the ground node of the inductive coil arrangement.
With the arrangement according to the present invention the current that is sensed reflects the total current in the inductive cooking device. Therefore, signal amplitudes of the measured current will be high and therefore adequately reflect changes in the operation of the inductive cooking device, like e.g. the removal of a cooking vessel.
Further embodiments of the present invention are subject of the further subclaims and of the following description, referring to the drawings.
In an embodiment, the inductive coil arrangement may comprise a filter and a resonant converter. The filter serves for smoothing the input current and/or voltage for the resonant converter. The resonant converter will then drive the induction coil of the inductive coil arrangement with the help of a resonant circuit arrangement that includes the coil as inductive element.
In an embodiment, the inductive cooking device may comprise a controller, which is coupled to the current sensor and which is configured to control the resonant converter based on the measured current. The controller can e.g. control the duty cycle of a driving signal of the resonant converter or adapt the driving frequency for the resonant converter. Further, with the shunt resistor at the position according to the present invention it becomes possible to accurately detect if a cooking vessel is removed from the induction coil. The current sensor may be a shunt resistor that has a far better reliability and accuracy than e.g. current transformers, because current sense transformers' responses vary from device to device due to its complex arrangements. In addition, sensing current at the position that is presented in the present invention with a shunt resistor makes it possible to decide when the pan is removed due to the sensed current's significant change. The control depends on the current sensing because the aim is to stabilize the output power of the induction cooker, according to the different power levels specified. With a shunt resistor, it is possible to fix the power within 5% tolerance while the tolerance level is up to 15% in sensing methods with e.g. current transformers. Therefore, in traditional methods it is complicated to detect a current change and complex computations are needed when the pan is removed. However, with the present invention a removed pan can be easily detected due to the significant changes. A significant change can be sensed with the present invention because the total current to the resonant tank, e.g. the switching circuit, can be sensed in contrast to traditional methods. Due to the nature of the resonant converter, the currents on the branches of the resonant tanks change and it is not easy to detect the total current decrease from measuring only a branch. Also little changes of the sensed current are not enough for deciding if the pan is removed or not.
In an embodiment, the filter may comprise a filter inductance arranged between the input port and a converter input port of the resonant converter, and a capacitor arranged between the converter input port and a converter output port of the resonant converter, wherein the converter output port is further coupled to the output port. The inductance and the capacitor form an LC filter that smooths the input current or voltage to the resonant converter. Further, these components support the valley detection during the switching process of the resonant converter. The LC filter works as a low pass filter. It smooths the input of a comparator of the controller of the inductive cooking device. The comparator inputs are connected to the terminals of the induction coil. Without the LC filter there is lots of noise in the input signals of the comparator. Therefore, with the LC filter the noise is reduced and valley detection for determining the switching time is improved.
In an embodiment, the current sensor may comprise a shunt resistance. A shunt resistance provides a very reliable and economic way of measuring the current in the inductive cooking device. According to Ohm's law the voltage developed across the shunt resistance is proportional to the current through the shunt resistance and therefore the inductive coil arrangement. Further, since the shunt resistor measures the current flowing between the output port and the ground node, one node of the shunt resistor is coupled to the ground node. Therefore the voltage over the shunt resistor can easily be measured with e.g. an analog to digital converter or the like connected on the input side, i.e. the not ground-connected side, of the shunt resistor.
In an embodiment, the current sensor may comprise a contactless current sensing element. This allows sensing the current through the inductive coil arrangement without any loss in the current sensor, as happens with shunt resistors.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings. The invention is explained in more detail below using exemplary embodiments which are specified in the schematic figures of the drawings, in which:

Fig. 1: shows a block diagram of an embodiment of an inductive cooking device according to an embodiment of the present invention;
Fig. 2: shows a block diagram of another embodiment of an inductive cooking device according to an embodiment of the present invention;

Fig. 3: shows a block diagram of another embodiment of an inductive cooking device according to an embodiment of the present invention; and
Fig. 4: shows a flow diagram of an embodiment of a method according to an embodiment of the present invention.

In the figures like reference signs denote like elements unless stated otherwise.

DETAILED DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a block diagram of an embodiment of an inductive cooking device 100. The inductive cooking device 100 comprises a ground node 101, an energy supply 102 and an inductive coil arrangement 105.
The energy supply 102 comprises a positive port 103 and a negative port 104. The negative port 104 is coupled to the ground node 101. The inductive coil arrangement 105 comprises an input port 106 and an output port 107. The input port 106 is coupled to the positive port 103. A coil 108 is further coupled to the inductive coil arrangement 105. The inductive coil arrangement 105 provides the driving power to the coil 108, which servers to inductively transmit energy to the cooking vessel 150 and therefore heat up the cooking vessel 150.
The inductive cooking device 100 further comprises a current sensor 109. The current sensor 109 is coupled between the output port 107 and the ground node 101 and therefore senses the current between the output port 107 and ground node 101.
The current sensor 109 may comprise any type of current sensor 109, for example a contactless inductive current sensor that produces a voltage on its output that is proportional to the current between the output port 107 and the ground node 101. The current sensor 109 may also comprise a shunt resistor or the like.
In the inductive cooking device 100 the energy supply 102 only comprises the energy source that provides a direct voltage or current. Any other elements, like e.g. filters or the like are provided in the inductive coil arrangement 105.
Therefore, in the inductive cooking device 100 the current sensor 109 senses the overall current in the system instead of a specific current value of any one of the subcomponents of the inductive cooking device 100.
Based on the sensed current value e.g. a duty cycle of a driving signal of the inductive coil arrangement 105 or the driving frequency for the inductive coil arrangement 105 may e.g. be adapted. In the inductive cooking device 100, sensing current with current sensor 109 placed between the bridge rectifier's reference, which may be called ground, and the node that is placed after the bus capacitance Cbus, resonant capacitance Cr and the load allows sensing the total load current in the system instead of the traditional sensing only in single branches of the switching circuit and making complex calculations. The resulting increased current sensing amplitude allows easier sensing of the pan removal.
Fig. 2 shows a block diagram of another embodiment of an inductive cooking device 200. In the inductive cooking device 200 the energy supply 202 comprises a bridge rectifier with two mains inputs 215, 216, which allow connecting the energy supply 202 to a mains network. The energy supply 202 further comprises two outputs 203, 204.
The inductive coil arrangement 205 is coupled to the energy supply 202 with its input port 206 via the positive port 203. Further, the inductive coil arrangement 205 is coupled with its negative port 207 via the current sensor 209 to the ground node 201.
The inductive coil arrangement 205 comprises a filter 210 and a resonant converter 213. The filter 210 comprises a series coil 211 and a parallel capacitor 212. The series coil 211 is arranged between the input port 206 and the input to the resonant converter 213. The parallel capacitor 212 is arranged between the connection of the coil 211 to the resonant converter 213 and the output of the resonant converter 213 that is directly coupled to the negative port 207.
The inductive cooking device 200 further comprises a controller 214. The controller 214 reads the current values measured by the current sensor 209 and provides a control signal 220 to the resonant converter 213. The resonant converter 213 then drives the coil 208 according to the control signal 220.
Fig. 3 shows a block diagram of another embodiment of an inductive cooking device 300 that is based on the inductive cooking device 200.
In the inductive cooking device 300 the resonant converter 313 comprises a capacitor 317 in parallel to the coil 308. The parallel arrangement of coil 308 and capacitor 317 is provided at an input of the resonant converter 313. Between this arrangement and the output of the resonant converter 313 a switching device 319 with a parallel capacitor 318 are provided. It can be seen that the controller 314 controls the switching device 319 via the control signal 320. The controller 314 can e.g. modify the frequency or the duty cycle of the switching signal for the switching device 319.
Fig. 4 shows a flow diagram of an embodiment of a method for controlling an inductive cooking device 100, 200, 300. For sake of clarity the same reference signs as used with Figs. 1 - 3 will be used in the description of Fig. 4.
The method comprises supplying S1 electrical energy to an inductive coil arrangement 105, 205, 305 via an energy supply device 102, 202, 302 comprising a positive port 103, 203, 303 and a negative port 104, 204, 304, wherein the negative port 104, 204, 304 is coupled to a ground node 101, 201, 301, wherein the inductive coil arrangement 105, 205, 305 comprises an input port 106, 206, 306 and an output port 107, 207, 307, wherein the input port 106, 206, 306 is coupled to the positive port 103, 203, 303 and the output port 107, 207, 307 is coupled to the ground node 101, 201, 301. The method further comprises measuring S2 the current flowing between the output port 107, 207, 307 and the ground node 101, 201, 301. The current may e.g. be measured with a shunt resistance. Alternatively, the current may be measured with a contactless current sensing element.
Finally, the method comprises generating S3 a driving signal for the inductive coil arrangement 105, 205, 305 based on the measured current.
The method may further comprise filtering the electrical energy in the inductive coil arrangement 105, 205, 305 and driving a resonant converter 213, 313 in the inductive coil arrangement 105, 205, 305 with the driving signal.
Filtering may be performed with a filter inductance 211, 311 arranged between the input port 106, 206, 306 and a converter input port 106, 206, 306 of the resonant converter 213, 313, and with a capacitor 212, 312 arranged between the converter input port 106, 206, 306 and a converter output port 107, 207, 307 of the resonant converter 213, 313, wherein the converter output port 107, 207, 307 is further coupled to the output port 107, 207, 307.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art, that a variety of alternate and/or equivalent implementations exist. It should be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein.
The present invention provides an inductive cooking device 100, 200, 300 comprising a ground node 101, 201, 301, an energy supply device 102, 202, 302 comprising a positive port 103, 203, 303 and a negative port 104, 204, 304, wherein the negative port 104, 204, 304 is coupled to the ground node 101, 201, 301, an inductive coil arrangement 105, 205, 305 comprising an input port 106, 206, 306 and an output port 107, 207, 307, wherein the input port 106, 206, 306 is coupled to the positive port 103, 203, 303 and the output port 107, 207, 307 is coupled to the ground node 101, 201, 301, and a current sensor 109, 209, 309 configured to measure the current flowing between the output port 107, 207, 307 and the ground node 101, 201, 301. Further, the present invention provides a respective method.

List of reference signs

100, 200, 300: inductive cooking device
101, 201, 301: ground node
102, 202, 302: energy supply device
103, 203, 303: positive port
104, 204, 304: negative port
105, 205, 305: inductive coil arrangement
106, 206, 306: input port
107, 207, 307: output port
108, 208, 308: coil
109, 209, 309: current sensor

210, 310: filter
211, 311: filter inductance
212, 312: capacitor
213, 313: resonant converter
214, 314: controller

215, 216, 315, 316: mains input

317, 318: capacitor
319: switching device

220, 320: control signal

150, 350: cooking vessel

S1 - S3: method actions

Claims

Inductive cooking device (100, 200, 300) comprising:
a ground node (101, 201, 301),

an energy supply device (102, 202, 302) comprising a positive port (103, 203, 303) and a negative port (104, 204, 304), wherein the negative port (104, 204, 304) is coupled to the ground node (101, 201, 301),

an inductive coil arrangement (105, 205, 305) comprising an input port (106, 206, 306) and an output port (107, 207, 307), wherein the input port (106, 206, 306) is coupled to the positive port (103, 203, 303) and the output port (107, 207, 307) is coupled to the ground node (101, 201, 301), and

a current sensor (109, 209, 309) configured to measure the current flowing between the output port (107, 207, 307) and the ground node (101, 201, 301).
Inductive cooking device (100, 200, 300) according to claim 1, wherein the inductive coil arrangement (105, 205, 305) comprises a filter (210, 310) and a resonant converter (213, 313).
Inductive cooking device (100, 200, 300) according to claim 2, comprising a controller (214, 314), which is coupled to the current sensor (109, 209, 309) and which is configured to control the resonant converter (213, 313) based on the measured current.
Inductive cooking device (100, 200, 300) according to any one of claims 2 and 3, wherein the filter (210, 310) comprises a filter inductance (211, 311) arranged between the input port (106, 206, 306) and a converter input port (106, 206, 306) of the resonant converter (213, 313), and a capacitor (212, 312) arranged between the converter input port (106, 206, 306) and a converter output port (107, 207, 307) of the resonant converter (213, 313), wherein the converter output port (107, 207, 307) is further coupled to the output port (107, 207, 307).
Inductive cooking device (100, 200, 300) according to any one of the preceding claims, wherein the current sensor (109, 209, 309) comprises a shunt resistance.
Inductive cooking device (100, 200, 300) according to any one of the preceding claims, wherein the current sensor (109, 209, 309) comprises a contactless current sensing element.
Method for controlling an inductive cooking device (100, 200, 300) according to any one of the preceding claims, the method comprising:
supplying (S1) electrical energy to an inductive coil arrangement (105, 205, 305) via an energy supply device (102, 202, 302) comprising a positive port (103, 203, 303) and a negative port (104, 204, 304), wherein the negative port (104, 204, 304) is coupled to a ground node (101, 201, 301), wherein the inductive coil arrangement (105, 205, 305) comprises an input port (106, 206, 306) and an output port (107, 207, 307), wherein the input port (106, 206, 306) is coupled to the positive port (103, 203, 303) and the output port (107, 207, 307) is coupled to the ground node (101, 201, 301),

measuring (S2) the current flowing between the output port (107, 207, 307) and the ground node (101, 201, 301), and

generating (S3) a driving signal for the inductive coil arrangement (105, 205, 305) based on the measured current.
Method according to claim 7, comprising filtering the electrical energy in the inductive coil arrangement (105, 205, 305) and driving a resonant converter (213, 313) in the inductive coil arrangement (105, 205, 305) with the driving signal.
Method according to claim 8, wherein filtering is performed with a filter inductance (211, 311) arranged between the input port (106, 206, 306) and a converter input port (106, 206, 306) of the resonant converter (213, 313), and a capacitor (212, 312) arranged between the converter input port (106, 206, 306) and a converter output port (107, 207, 307) of the resonant converter (213, 313), wherein the converter output port (107, 207, 307) is further coupled to the output port (107, 207, 307).
Method according to any one of the preceding claims 7 to 9, wherein the current is measured with a shunt resistance.
Method according to any one of the preceding claims 7 to 9, wherein the current is measured with a contactless current sensing element.