WO2019132810A1

WO2019132810A1 - An induction heater and a coffee machine using the same

Info

Publication number: WO2019132810A1
Application number: PCT/TR2018/050578
Authority: WO
Inventors: Sercan SINIRLIOGLU; Ulas OKTAY; Hakan Suleyman YARDIBI; Arif Hakki POLAT; Mustafa SEKER
Original assignee: Arcelik Anonim Sirketi
Priority date: 2017-12-25
Filing date: 2018-10-10
Publication date: 2019-07-04
Also published as: TR201721434A2

Abstract

The present invention relates to an induction heater (1) suitable for use in heating ferromagnetic containers, comprising a resonance circuit (4) having an induction coil (2) and two resonance capacitors (3) connected in series to the induction coil (2), an inverter circuit (6) having two power switches (5) driving the resonance circuit (4), and a control unit (8) having a driver circuit (7) switching the power switch (5) to a closed and an open position according to a desired frequency value.

Description

AN INDUCTION HEATER AND A COFFEE MACHINE USING THE SAME

The present invention relates to an induction heater used in heating ferromagnetic containers, and a coffee machine using said heater.

Induction coils are known to be more efficient compared to resistance heaters. However, special containers should be used in induction heaters. Induction heaters function according to the principle of heating a cooking container made of ferromagnetic material such as cast iron or steel, by the magnetic field generated by an induction coil. In the state of the art, half bridge series resonant (HBSR) circuits composed of two power switches and two resonance capacitors, and single switch quasi resonant (SSQR) circuits composed of one power switch and one resonance capacitor, are used to drive a single induction coil. When it is desired to drive a plurality of induction coils, a separate inverter circuit should be used for each one of the induction coils. Since an induction coil is driven in heavy currents and high frequencies, it is necessary to use power switches resistant to heavy currents, capable of switching on/off in high frequencies. This extremely increases the costs of induction heaters. Therefore, using induction heaters in low-cost products such as small household appliances, substantially increases the production costs.

State of the art international patent application no. W02006008583 discloses a coffee machine in which the heater used in cooking coffee is an induction heater.

State of the art international patent application no. WO2013064333 discloses an induction cooking range having a control unit enabling driving an induction coil by means of an inverter circuit.

State of the art international patent application no. W02012089707 discloses an induction heater using auxiliary capacitors to stabilize voltage values.

The aim of the present invention is to realize a cost advantageous induction heater using a low number of circuit members, and a coffee machine using said induction heater.

The induction heater realized to achieve the aim of the present invention and disclosed in the claims, comprises a plurality of induction coils connected to each other, switches in an amount equal to the number of induction coils, enabling the induction coils to be individually short- circuited, and a control unit enabling driving a plurality of induction coils by means of a single inverter circuit. The control unit enables driving the induction coils individually or multiply simultaneously, in a coequal driving frequency. In an embodiment of the invention, the control unit drives a plurality of induction coils by turning on a desired number of induction coils by switching the switches on and off.

In another embodiment of the invention, the induction coils are connected to each other in series, and each switch is connected in parallel to an induction coil. In another embodiment of the invention, the induction coils are connected in series, and the switches are connected to the induction coils in parallel. When the switches are in the open position, the natural resonance frequency of the resonance circuit composed of a capacitor and the induction coils, increases in the case the induction coils are connected in series, and decreases in the case the induction coils are connected in parallel. In this case, in order to drive the induction coils with a power identical to the amount of power applied when the induction coils are driven individually, the same amount of power is transmitted to the containers being heated, by varying the driving frequency applied to the resonance circuit.

In another embodiment of the invention are used: auxiliary capacitors connected in parallel to the resonance circuit and enabling varying the capacitance value of the system, and an auxiliary capacitor circuit having a switch enabling turning the auxiliary capacitors on and off. By means of the auxiliary capacitor circuit, changing of the system's natural frequency due to variation of the inductance value according to series or parallel connection of the induction coils, is compensated. When the inductance value decreases, the capacitance of the system is increased by turning the auxiliary capacitors on, enabling the natural resonance frequency to be kept the same. Thus, a plurality of induction coils can be driven so as to transmit equal power to the containers being heated, without changing the driving frequency applied when driving the induction coils individually. In a version of this embodiment, the control unit controls turning the auxiliary capacitor circuit on and off by controlling the switch.

In another embodiment of the invention, all the switches are relays. This enables the control unit to control the switches quickly and easily, and the switches to be switched to the open or closed position when desired conditions are formed.

The coffee machine of the invention comprises an induction heater having a control unit enabling driving a plurality of induction coils with equal amounts of power by means of a single inverter circuit, and a plurality of coequal containers having identical ferromagnetic characteristics. In the coffee cooking process, the induction heater operates with a constant power value, without requiring any adjustments to change the power. The induction heater capable of driving a plurality of induction heaters in equivalent power, can thereby be used in a coffee machine. The user places a plurality of containers at the same time respectively on the induction heaters and starts the cooking process, and the control unit enables transmitting all induction coils equal and identical power just as driving a single induction coil, by means of a single inverter circuit. When it is desired to turn on the other induction coils while a single induction coil is operating, transmitting equal power to all induction coils continues by changing the driving frequency or by using the auxiliary capacitor circuit as explained above.

In another embodiment of the invention, the control unit sequentially sends at the beginning of the cooking process a signal to the induction coils, and whether there is a container on an induction coil is determined according to the feedback of said signal. A container being placed offset/improperly on an induction coil can be determined from the feedback of a signal by employing usage of equivalent containers in the coffee machine. The ferromagnetic characteristics of said equivalent containers is saved in the memory of the control unit. The ferromagnetic characteristics of the container on an induction coil obtained from the feedback of a signal, is compared to the presaved data, and a difference indicates an improper placement of said container. In this case, the user is alerted and is expected to correct the position of the container.

In another embodiment of the invention, a mechanical or an electronic detector is used for determining whether there is a container on an induction coil. The detector generates a signal when a container is placed coaxially with an induction coil. If there is a difference between the feedback of the signal from the detector and the signal sent by the control unit to the induction coil, the control unit gives an error alert and does not start the cooking process.

The induction heater of the invention makes it possible to drive a plurality of induction coils by means of a single inverter circuit, improving the production costs of induction heaters and coffee machines by reducing the number of high-cost power switches such as IGBTs.

An induction heater realized to achieve the aim of the present invention is illustrated in the accompanying drawings, wherein:

Figure 1 is a schematic view of the circuit of the induction heater in an embodiment.

Figure 2 is a schematic view of the circuit of the induction heater in another embodiment.

The elements in the figures are numbered individually and the correspondence of these numbers are given hereinafter. 1- Induction heater

2- Induction coil

3- Resonance capacitor

4- Resonance circuit

5- Power switch

6- Inverter circuit

7- Driver circuit

8- Control unit

9- Switch

10- Auxiliary capacitor

11- Auxiliary capacitor circuit

The induction heater (1) is suitable for use in heating ferromagnetic containers, and comprises a resonance circuit (4) having an induction coil (2) and two resonance capacitors (3) connected in series to the induction coil (2), an inverter circuit (6) having two power switches (5) driving the resonance circuit (4), and a control unit (8) having a driver circuit (7) switching the power switch (5) to a closed and an open position according to a desired frequency value. First, the alternative current signal received from the mains is rectified by means of the inverter circuit (6), and then an alternative current signal is generated again in a frequency value determined by the driver circuit (7). When a container with ferromagnetic properties is placed on the induction coil (2), the resonance frequency of the resonance circuit (4) is determined, and the control unit (8) drives the induction coils (2) within proximity of the resonance frequency by means of the driver circuit (7). The amplitude of the power transmitted to the induction coils (2) is adjusted according to the difference between the driving frequency and the resonance frequency.

The induction heater (1) of the invention comprises at least one coequal induction coil (2) connected to the induction coil (2), and switches (9) of an amount equal to the number of induction coils (2), enabling the induction coils (2) to be short-circuited. In the invention, a plurality of coequal induction coils (2) having identical characteristics are connected to a single inverter circuit (6). Switches (9) enabling each one of the induction coils (2) to be short- circuited and turned off, are used in order to drive the induction coils (2) individually. When all switches (9) are on, all induction coils (2) are driven by a single inverter circuit (6), in an equivalent frequency. Provided that identical containers are used on each induction coil (2), driving the induction coils (2) in an equivalent frequency means heating all containers to the same extent. By bringing to the closed position, the switch (9) connected to an unused induction coil (2), the related induction coil (2) is short-circuited.

In an embodiment of the invention, the control unit (8) enables driving the induction coils (2) simultaneously or individually, by controlling the switches (9). The switches (9) are controlled by the control unit (8). According to the preference of a user, the control unit (8) brings a related switch (9) to the open or closed position, enabling a desired induction coil (2) to be turned on or off.

In another embodiment of the invention, the induction coils (2) are connected to each other in series, and the switches (9) are connected to each induction coil (2) in parallel. In this embodiment, the natural resonance frequency of the resonance circuit (4) decreases when it is desired to turn on a plurality of induction coils (2). In this case, in order to transmit to two or more induction coils (2), the same power provided by the driving frequency used when driving a single induction coil (2), the driving frequency should be reduced.

In another embodiment of the invention, the induction coils (2) are connected to each other in parallel, and the switches (9) are connected to each induction coil (2) in series. In this embodiment, the natural resonance frequency increases compared to using a single induction coil (2). The driving frequency is increased in order to prevent overloading power to the induction coils (2).

In the case disclosed in the two embodiments above, equal heating of the containers on the induction coils (2) becomes possible by varying the driving frequency.

In another embodiment of the invention, the induction heater (1) comprises an auxiliary capacitor circuit (11) connected in parallel to the resonance circuit (4), having auxiliary capacitors (10), each one of which is connected in parallel to one of the resonance capacitors (3) and a switch (9) connected in series to the auxiliary capacitors (10). In this embodiment, the natural resonance frequency changing due to individually or multiply using the induction coils (2) connected in series or in parallel, is enabled not to change by means of the auxiliary capacitor circuit (11). When two induction coils (2) connected in parallel are used, the inductance value and therefore the natural resonance frequency of the system is reduced by half by turning both induction coils (2) on, and in this case, the auxiliary capacitor circuit (11) is turned on by means of a switch (9), increasing the capacitance value of the system, and thereby enabling maintaining the natural resonance frequency of the system. When using induction coils (2) connected in series, the auxiliary capacitor circuit (11) is used when a single induction coil (2) is turned on, and if a plurality of induction coils (2) are being used, since the inductance of the system will increase, in order not to change the natural resonance frequency, the capacitance of the system is reduced by turning the auxiliary capacitor circuit (11) off, enabling maintaining the natural resonance frequency. This embodiment makes it unnecessary to vary the driving frequency, and one or more induction coils (2) can be driven in the same driving frequency.

In a version of this embodiment, the control unit (8) turns the auxiliary capacitor circuit (11) on or off by controlling the switch (9). The control unit (8) enables keeping the natural resonance frequency the same for a single or a plurality of induction coils (2) by controlling the switch (9), enabling driving a plurality of induction coils (2) by means of a single inverter circuit (6) without requiring changing the driving frequency.

In another embodiment of the invention, all switches (9) are relays. All switching can be performed by the control unit (8) thanks to being capable of controlling the switches (9) electronically.

The coffee machine of the invention comprises an induction heater (1) such as the above- disclosed ones, and containers (not shown in the figures) having equivalent ferromagnetic characteristics, heated by the induction coils (2), in an amount equal to the number of induction coils (2). The coffee machine (not shown in the figures) is suitable for cooking Turkish coffee. Turkish coffee is cooked in containers called“cezve”, and heating intensity is kept constant during the heating/cooking process. When it is desired to simultaneously cook Turkish coffee in a plurality of“cezve”s, it is sufficient to heat all“cezve”s with equivalent power. The above-disclosed induction heater (1) enables driving a plurality of induction coils (2) in the same frequency by using a single inverter circuit (6), and using identical containers, or in other terms “cezve”s with equivalent ferromagnetic characteristics in the coffee machine, makes it possible to heat all containers with equivalent power. Therefore, the induction heater (1) comprising a plurality of induction coils (2) driven by a single inverter circuit (6), can conveniently be used in the coffee machine which does not require heating with differing amounts of power, thereby improving the production cost of the coffee machine. In another embodiment of the invention, the ferromagnetic characteristics of equivalent containers is saved in the memory of the control unit (8). By this, it can be detected whether the containers used for cooking coffee are actually suitable for cooking coffee. A user is enabled to be alerted in case he/she mistakenly places a container with different characteristics on an induction coil (2).

In another embodiment of the invention, the control unit (8) enables sequentially sending a pulse signal to the induction coils (2) in the beginning of the heating/cooking process, and enables determining the ferromagnetic characteristics of the containers on the induction coils (2) from the feedback of said signal. With this embodiment, the control unit (8) sends a pulse signal to the induction coils (2), and the ferromagnetic characteristics of a container placed on an induction coil (2) is determined according to the feedback signal arising from the interaction of the signal with the containers.

In another embodiment of the invention, the control unit (8) compares the ferromagnetic characteristics value saved in its memory to the measured ferromagnetic characteristics value, and determines offset placement of a container on an induction coil (2) if the values differ. Whether a container is placed correctly, i.e. coaxially on an induction coil (2) is detected by comparing the ferromagnetic characteristics information received from the above-disclosed feedback signal, with the ferromagnetic characteristics of the containers preferably presented to the user together with the coffee machine. When a container is placed offset, i.e. improperly on an induction coil (2), the ferromagnetic characteristics information received from the feedback signal is worse than the value saved in the memory of the control unit (8) for the same container. In this case, the control unit (8) determines improper placement of the container on the induction coil (2).

In a version of this embodiment, the control unit (8) enables alerting the user upon improper placement of a container on an induction coil (2). The power transmitted to a container changes when the container is placed offset, effecting the cooking duration and the taste of the coffee. The control unit (8) alerts the user in such a case, enabling the user to correct the placement of the container. In another version of this embodiment, the control unit (8) does not start the heating/cooking process upon determining improper placement of a container.

In another embodiment of the invention, the coffee machine comprises a detector (not shown in the figures) triggered by placement of a container on an induction coil (2), and the control unit (8) does not start the heating/cooking process upon determining offset placement of the container during the detector is generating signal. The detector may be mechanical or electronic, and generates a signal when a container is placed correctly, coaxially on an induction coil (2). The case in which the detector generates a signal and offset placement of the container is determined according to the comparison made by the control unit (8), indicates that a different container is placed on the induction coil (2). Particularly in cooking Turkish coffee, the taste of the coffee is determined by parameters such as the container used, the heating power applied to the container, and the cooking duration. Therefore, the control unit (8) does not start the cooking process since the desired coffee taste and froth cannot be obtained when coffee is cooked by placing a container with different ferromagnetic characteristics on an induction coil (2).

The induction heater (1) of the invention enables driving a plurality of induction coils (2) by means of a single inverter circuit (6), substantially reducing the cost of the induction heater (1). In the coffee machine in which equal power is transmitted to the containers being heated, also the cost of the coffee machine is reduced by using the induction heater (1) of the invention, and a more compact coffee machine is enabled to be produced by reducing the number of circuit members used.

Claims

1. An induction heater (1) suitable for use in heating ferromagnetic containers, comprising a resonance circuit (4) having an induction coil (2) and two resonance capacitors (3) connected in series to the induction coil (2), an inverter circuit (6) having two power switches (5) driving the resonance circuit (4), and a control unit (8) having a driver circuit (7) switching the power switch (5) to a closed and an open position according to a desired frequency value, characterized by at least one coequal induction coil (2) connected to the induction coil (2), and by the switches (9) of an amount equal to the number of induction coils (2), enabling the induction coils (2) to be short-circuited.

2. An induction heater (1) according to claim 1, characterized by the control unit (8) enabling the induction coils (2) to be driven simultaneously or individually, by controlling the switches (9).

3. A device (1) according to claim 1 or 2, characterized by the induction coils (2) connected to each other in series and by the switches (9) connected to each one of the induction coils (2) in parallel.

4. A device (1) according to claim 1 or 2, characterized by the induction coils (2) connected to each other in parallel and by the switches (9) connected to each one of the induction coils (2) in series.

5. A device (1) according to any one of the preceding claims, characterized by an auxiliary capacitor circuit (11) connected in parallel to the resonance circuit (4), having auxiliary capacitors (10) each one of which is connected in parallel to one of the resonance capacitors (3) and a switch (9) connected in series to the auxiliary capacitors (10).

6. An induction heater (1) according to claim 5, characterized by the control unit (8) turning the auxiliary capacitor circuit (11) on or off by controlling the switch (9).

7. An induction heater (1) according to any one of the preceding claims, characterized by the switches (9) which are relays.

8. A coffee machine comprising an induction heater (1) according to any one of the preceding claims, characterized by the containers in an amount equal to the number of the induction coils (2), having equivalent ferromagnetic characteristics, heated by the induction coils (2).

9. A coffee machine according to claim 8, characterized by the control unit (8) saving in its memory the ferromagnetic characteristics of the equivalent containers.

10. A coffee machine according to claim 9, characterized by the control unit (8) enabling sequentially sending a pulse signal to the induction coils (2) at the beginning of the heating/cooking process, and enabling determining from the feedback of said signal, the ferromagnetic characteristics of the containers on the induction coils (2).

11. A coffee machine according to claim 10, characterized by the control unit (8) comparing the ferromagnetic characteristics value saved in its memory to the measured ferromagnetic characteristics value, and determining offset placement of a container on an induction coil (2) if the values differ.

12. A coffee machine according to claim 11, characterized by the control unit (8) enabling alerting the user when a container is placed offset on an induction coil (2).

13. A coffee machine according to claim 12, characterized by a detector triggered by placement of a container on an induction coil (2), and by the control unit (8) not starting the heating/cooking process upon determining offset placement of the container when the detector is generating signal.