WO2019145321A1

WO2019145321A1 - Induction cooker

Info

Publication number: WO2019145321A1
Application number: PCT/EP2019/051558
Authority: WO
Inventors: Kun DENG; Hongxuan Zhang; Peng Wu; Zhenquan WU
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2018-01-29
Filing date: 2019-01-23
Publication date: 2019-08-01
Anticipated expiration: 2020-07-29
Also published as: CN110099468A

Abstract

The disclosure relates to an induction cooker. According to one embodiment of the disclosure, the induction cooker comprises a pair of terminals for receiving electric power from a DC power source, a switch heating unit and a control unit; wherein the switch heating unit comprises an LC parallel resonant unit and a switch unit; the LC parallel resonant unit comprises a resonant capacitor and a coil panel; the LC parallel resonant unit is connected in series with the switch unit; the switch unit is configured to switch between an ON state and an OFF state so that the switch heating unit can start and stop receiving the electric power respectively; and the control unit is configured to and output a programmable pulse signal to the switch unit to control, by the programmable pulse signal, the switch unit to switch to the ON state or the OFF state. The technical solution of the disclosure has at least one of the following advantageous technical effects: a high electric power conversion efficiency, operation without needing mains electricity, an accurate power control and a simple structure.

Description

Induction cooker

TECHNICAL FIELD

[01] The disclosure relates generally to an induction cooker, and particularly to an induction cooker capable of generating a high-frequency time-varying magnetic field for heating using electric power from a DC power source.

BACKGROUND ART

[02] In recent years, induction cookers as cookware have been used more and more widely. Generally, during operation of an induction cooker, the induction cooker will receive AC mains electricity. An internal circuit of the induction cooker will convert the AC mains electricity to DC electricity, and then invert the DC electricity to high-frequency AC electricity at an appropriate frequency (e.g., 20-30 kHz) . The flow of the high-frequency AC electricity in a coil will generate a high-frequency alternating magnetic field which will induce, at a bottom of a pot on a panel of the induction cooker, an eddy current for heating the pot.

SUMMARY OF THE INVENTION

[03] A brief summary of the disclosure is given below to provide a basic understanding to some aspects of the disclosure. It should be understood that the summary is not exhaustive. It does not intend to define a key or important part of the disclosure, nor does it intend to limit the scope of the disclosure. The object of the summary is only to present some concepts, in a simplified manner, as a preamble of the more detailed description that follows.

[04] In view of the desire for use of an induction cooker in an environment without mains electricity, the inventor designs technical solutions below.

[05] According to one aspect of the disclosure, an induction cooker is provided. The induction cooker comprises a pair of terminals, a switch heating unit and a control unit; wherein the pair of terminals comprises a positive terminal and a negative terminal for receiving electric power from a DC power source; the switch heating unit comprises an LC parallel resonant unit and a switch unit; the LC parallel resonant unit comprises a resonant capacitor and a coil panel, and the resonant capacitor and the coil panel are connected in parallel between a first coil terminal and a second coil terminal for the coil panel; the LC parallel resonant unit is connected in series with the switch unit; the switch unit is configured to switch between an ON state and an OFF state so that the switch heating unit can start and stop receiving the electric power from the DC power source respectively; and the control unit is configured to generate a programmable pulse signal and output the programmable pulse signal to the switch unit to control, by the programmable pulse signal, the switch unit to switch to the ON state or the OFF state so that the coil panel generates a high-frequency time-varying magnetic field for heating using the electric power from the DC power source.

[06] In one embodiment, the DC power source is a battery. The battery is preferably a rechargeable battery.

[07] In one embodiment, the induction cooker further comprises a case and the DC power source, wherein the DC power source is a battery, and the battery is disposed within the case.

[08] In one embodiment, the switch unit comprises a first switch, the first switch is an IGBT element, a collector of the first switch is electrically connected with the second coil terminal, and the first switch is configured so that a gate voltage of the first switch is controlled by the programmable pulse signal.

[09] In one embodiment, the switch unit further comprises a second switch, the second switch is an IGBT element, and the first switch is connected in parallel with the second switch.

[10] In one embodiment, the switch unit further comprises a switch driving circuit. The programmable pulse signal is output to a gate of the first switch via the switch driving circuit, and the switch driving circuit comprises a complementary amplification circuit for amplifying the programmable pulse signal. The switch driving circuit further comprises an inverse transistor, and the programmable pulse signal is input to the complementary complication circuit via the inverse transistor.

[11] In one embodiment, the induction cooker further comprises a current detection unit and a voltage detection unit, wherein the current detection unit is configured to detect a current flowing through the switch heating unit to output a current signal indicative of the current, the voltage detection unit is configured to detect a potential difference between the positive terminal and the negative terminal to output a potential difference signal indicative of the potential difference, and the current detection unit and the voltage detection unit are connected with the control unit so that the control unit can obtain the current signal and the potential difference signal from the current detection unit and the voltage detection unit respectively to perform closed-loop control with respect to power of the induction cooker.

[12] In one embodiment, the induction cooker further comprises a voltage sampling circuit, wherein the voltage sampling circuit is configured to sample a first voltage at the first coil terminal and a second voltage at the second coil terminal respectively to obtain a first voltage signal indicative of the first voltage from a first output node of the voltage sampling circuit and obtain a second voltage signal indicative of the second voltage from a second output node of the voltage sampling circuit, and the voltage sampling circuit is connected with the control unit so that the control unit can obtain the first voltage signal and the second voltage signal from the voltage sampling circuit; and the first output node is electrically connected with the second output node via an isolation capacitor.

[13] In one embodiment, the control unit generates the programmable pulse signal based on the current signal, the potential difference signal, the first voltage signal and the second voltage signal.

[14] In one embodiment, the programmable pulse signal is a rectangular pulse signal, and the control unit is configured to: after a first predetermined period of time for which a difference between the first voltage signal and the second voltage signal has been less than a first voltage threshold approximate to zero, flip a level of the programmable pulse signal, and maintain the flipped level for a second predetermined period of time.

[15] In one embodiment, the induction cooker further comprises an electric power conversion unit, wherein the electric power conversion unit is electrically connected with the positive terminal and the negative terminal to convert a first DC voltage supplied by the DC power source to a second DC voltage and a third DC voltage lower than the second DC voltage.

[16] In one embodiment, the induction cooker further comprises a program read and write unit, wherein the program read and write unit is electrically connected with the electric power conversion unit to receive electric power with the third DC voltage, and the program read and write unit is connected with the control unit so that the program read and write unit can read a control program within the control unit, write the control program within the control unit, and/or modify the control program within the control unit.

[17] In one embodiment, the control unit is configured to, in response to detection that a magnitude of a drop of a voltage to ground of the positive terminal from a constant voltage value within a predetermined period of time after the voltage to ground of the positive terminal has maintained the constant voltage value for a period of time greater than a first time threshold is greater than a drop threshold, set a pot detection flag as "TRUE" stored in the control unit so that, in a case where the pot detection flag is "TRUE", the control unit outputs the programmable pulse signal to generate the high-frequency time-varying magnetic field for heating by the coil panel.

[18] In one embodiment, the switch unit is composed of the first switch and a switch driving circuit for amplifying the programmable pulse signal .

[19] In one embodiment, the switch unit is configured to control the programmable pulse signal so that in use of the induction cooker to perform heating, a voltage at the first coil terminal is always not lower than a voltage at the second coil terminal.

[20] In one embodiment, the positive terminal is connected to the negative terminal sequentially via the switch unit and the LC parallel resonant unit, or the positive terminal is connected to the negative terminal sequentially via the LC parallel resonant unit and the switch unit .

[21] The technical solution according to the disclosure has at least one of the following advantageous technical effects: a high electric power conversion efficiency, operation without needing mains electricity, an accurate power control and a simple structure.

BRIEFT DESCRIPTION OF THE DRAWINGS

[22] The disclosure could be better understood with reference to the descriptions made in combination with the appended drawings hereinafter. It should be appreciated that the appended Drawings is not necessarily scaled. In the appended Drawings:

[23] FIG. 1 is a structure block diagram showing an operating principle of an induction cooker according to one embodiment of the disclosure;

[24] FIG.2 is a structure block diagram showing an operating principle of an induction cooker according to another embodiment of the disclosure ;

[25] FIG. 3 is a schematic view showing a switch unit according to one embodiment of the disclosure;

[26] FIG. 4 is a schematic view of showing a switch unit according to another embodiment of the disclosure;

[27] FIG. 5 schematically shows changes of a programmable pulse signal, a gate voltage of a first switch, and a collector voltage of the first switch with time in FIG. 4;

[28] FIG. 6 shows a circuit for closed-loop control according to one embodiment of the disclosure; and

[29] FIG. 7 shows an electric power conversion unit according to one embodiment of the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[30] Exemplary embodiments of the disclosure will be described in combination with the appended drawings below. For the sake of clarity and conciseness, the specification does not describe all features of actual embodiments. However, it should be understood that in developing any such an actual embodiment, many decisions specific to the embodiment may be made, so as to achieve specific objects of a developer, and these decisions possibly vary as embodiments are different .

[31] It should also be noted that, to avoid the disclosure from being obscured due to unnecessary details, only those device structures closely related to the solutions according to the disclosure are shown in the appended drawings, while other details not closely related to the disclosure are omitted.

[32] The disclosure provides an induction cooker operable in an environment without mains electricity. The induction cooker can be used as a stove for cooking without needing connection to mains electricity network, and is especially adapted for use in a field environment .

[33] Differing from an conventional induction cooker which is required to convert received AC mains electricity to DC electricity before converting the DC electricity to high-frequency AC electricity for generating a high-frequency alternating magnetic field, the induction cooker according to the disclosure can be directly connected with a DC power source to receive DC electric power, and use a controlled switch unit and an LC parallel resonant unit to convert the received DC electric power to appropriate high-frequency time-varying DC electric power to generate a high-frequency alternating magnetic field for heating a pot. The DC power source may be a battery, and is preferably a rechargeable battery.

[34] FIG. 1 is a structure block diagram showing an operating principle of an induction cooker 1 according to one embodiment of the disclosure. As shown in FIG. 1, the induction cooker 1 comprises a pair of terminals for receiving electric power from a DC power source 17, a switch heating unit HU and a control unit 15. The pair of terminals comprises a positive terminal P+ and a negative terminal P-.The positive terminal P+ and the negative terminal P- are electrically connectable to a positive pole and a negative pole of a DC power source 17 respectively. The switch heating unit HU comprises an LC parallel resonant unit 11 and a switch unit 13. The LC parallel resonant unit 11 comprises a resonant capacitor C2 and a coil panel CP. The resonant capacitor C2 and the coil panel CP are connected in parallel between a first coil terminal PI and a second coil terminal P2 for the coil panel CP. The LC parallel resonant unit 11 is connected in series with the switch unit 13. The switch unit 13 is configured to be switchable between an ON state and an OFF state so that the switch heating unit HU can start and stop receiving electric power from the DC power source 17 respectively. The control unit 15 can generate a programmable pulse signal Spp and output the programmable pulse signal Spp to the switch unit 13. The control unit 15 can control, by the programmable pulse signal Spp, the switch unit 13 to switch to the ON state or the OFF state so that the coil panel CP generates a high-frequency time-varying magnetic field for heating using the electric power from the DC power source 17. The switch unit 13 may comprise at least one switch.

[35] In FIG. 1, exemplarily, the switch unit 13 can switch electrical a connection between the second coil terminal P2 and the negative terminal P- between the ON state and the OFF state. The control unit 15 can control the switch unit 13 to switch electrical connection between the second coil terminal P2 and the negative terminal P-, so as to allow the coil panel CP to generate a high-frequency time-varying magnetic field for heating using the electric power from the DC power source. The nominal output voltage (hereinafter referred to as "first DC voltage VI") of the DC power source 17 is for example 60 V. In FIG. 1, the positive terminal P+ is connected to the negative terminal P- sequentially via the LC parallel resonant unit 11 and the switch unit 13.

[36] Without needing an AC-to-DC electric power transformation, the induction cooker of the disclosure directly uses the DC power source, and transforms the electric power from the DC power source to high-frequency time-varying (for example at a frequency of 20 kHz) electric power, thus making it possible to improve conversion efficiency of converting the electric power from the power source to heat energy for cooking.

[37] In one embodiment, a power source adapter for converting AC mains electricity to an appropriate DC voltage can be provided for the induction cooker of the disclosure. The positive terminal P+ and the negative terminal P- can be electrically connected with a positive pole and a negative pole of an electric power output end of the power source adapter respectively. In this way, the induction cooker of the disclosure can, like the conventional induction cooker, also perform operations while being connected to AC mains electricity.

[38] The induction cooker of the disclosure may comprise the DC power source, wherein the DC power source includes a battery. The battery may be disposed within the case of the induction cooker, or the battery is an external battery at the outside of the case of the induction cooker. Alternatively, the induction cooker may not be provided with a dedicated battery, but uses an appropriate battery configured for other equipments in the prior art. Further, the induction cooker of the disclosure may be designed to be provided with a plurality of DC voltage input interfaces (i.e., a plurality of pairs of terminals for inputting electric power) . Each DC voltage input interface receives electric power of one kind of DC voltage. In this way, the universality of the induction cooker is improved.

[39] In the disclosure, a position where the switch unit is connected is not limited to the position as shown in FIG. 1. The position of the switch unit can be adjusted while ensuring a switching function of the switch unit. FIG. 2 is a structure block diagram showing an operating principle of an induction cooker 1 according to another embodiment of the disclosure. As shown in FIG. 2, the induction cooker 1 comprises a pair of terminals for receiving electric power from a DC power source 17, a switch heating unit HU' and a control unit 15. The pair of terminals comprises a positive terminal P+ and a negative terminal P- . The positive terminal P+ and the negative terminal P- are electrically connectable to a positive pole and a negative pole of a DC power source 17 respectively. The switch heating unit HU' comprises an LC parallel resonant unit 11 and a switch unit 13. The LC parallel resonant unit 11 comprises a resonant capacitor C2 and a coil panel CP. The resonant capacitor C2 and the coil panel CP are connected in parallel between a first coil terminal PI and a second coil terminal P2 for the coil panel CP. The LC parallel resonant unit 11 is connected in series with the switch unit 13. The switch unit 13 is configured to be switchable between an ON state and an OFF state so that the switch heating unit HU' can start and stop receiving electric power from the DC power source 17 respectively The control unit 15 can generate a programmable pulse signal Spp and output the programmable pulse signal Spp to the switch unit 13. The control unit 15 can control, by the programmable pulse signal Spp, the switch unit 13 to switch to the ON state or the OFF state so that the coil panel CP generates a high-frequency time-varying magnetic field for heating using the electric power from the DC power source 17. In comparison with the induction cooker 1 in FIG. 1, a position where the switch unit 13 of the switch heating unit HU' of the induction cooker 1 is connected changes. In FIG. 2, the positive terminal P+ is connected to the negative terminal P+ sequentially via the switch unit 13 and the LC parallel resonant unit 11.

[40] In one embodiment, the switch unit 13 comprises a first switch. The first switch may be a switch element such as an IGBT element, a power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and the like.

[41] In one embodiment, the first switch is an IGBT element. A collector of the first switch is electrically connected with the second coil terminal P2, an emitter of the first switch SW1 is electrically connected with the negative terminal P-, and a gate voltage of the first switch SW1 is controlled by the programmable pulse signal Spp. For example, when the programmable pulse signal Spp is at a high level, the gate of the first switch SW1 is at a high level, the first switch SW1 is switched on, and the electrical connection state between the second coil terminal P2 and the negative terminal P- is a connected state, so as to charge the LC parallel resonant unit 11; and when the programmable pulse signal Spp is at a low level, the gate of the first switch SW1 is at a low level, the first switch SW1 is switched off, the electrical connection state between the second coil terminal P2 and the negative terminal P- is a disconnected state, and the LC parallel resonant unit 11 is discharged .

[42] In one embodiment, the control unit 11 may be configured to control the programmable pulse signal Spp so that in use of the induction cooker according to the disclosure to perform heating, a voltage at the first coil terminal PI is always not lower than a voltage at the second coil terminal P2. This can simplify the structure of the switch unit.

[43] To broaden an adjustable range of power according to the disclosure, the switch unit 13 can comprise a plurality of switch elements, wherein the plurality of switch elements are connected in parallel .

[44] FIG. 3 is a schematic view showing a switch unit 133 according to one embodiment of the disclosure. The switch unit 133 is one exemplary implementation of the switch unit 13 in FIGs. 1 and 2. As shown in FIG. 3, the switch unit 133 comprises a first switch SW1 and a second switch SW2. Exemplarily, both the first switch SW1 and the second switch SW2 are IGBT elements. The first switch SW1 is connected in parallel with the second switch SW2. A gate G of the second switch SW2 is connected with a gate G of the first switch SW1, a collector C of the second switch SW2 is connected with a collector C of the first switch SW1, and an emitter E of the second switch SW2 is connected with an emitter E of the first switch SW1. The two connected gates receive the programmable pulse signal Spp. The two connected emitters are electrically connected with the negative terminal P- . The two connected collectors are electrically connected with the second coil terminal P2. Alternatively, the number of the parallelly connected switch elements of the switch unit may be more than two, so as to allow the induction cooker according to the disclosure to have a larger adjustable range of power. It should be noted that the switch unit 133 is not limited to the structure as shown in FIG. 3 and that the switch unit 133 may include more constituent parts such as a switch driving unit. In addition, FIG. 3 shows a connection manner adapted for the switch unit in FIG. 1. When the switch unit 133 is used as the switch unit in FIG. 2, the two connected gates receive the programmable pulse signal Spp; the two connected emitters are electrically connected with the first coil terminal PI; and the two connected collectors are electrically connected with the positive terminal P+ .

[45] The IGBT used in the disclosure is not limited to the structure as shown in FIG. 3. For example, the IGBT used in the disclosure may not comprise an anti-parallel diode as shown in FIG. 3.

[46] A singlechip microcomputer can serve as the control unit 15 according to the disclosure. When a voltage of the programmable pulse signal Spp supplied by the control unit 15 is insufficient to control the first switch SW1, a switch driving circuit can be arranged for the switch unit 13. FIG. 4 is a schematic view of showing a switch unit 134 according to another embodiment of the disclosure. The switch unit 134 comprises a first switch SW1 and a switch driving circuit 41. In FIG. 4, the first switch SW1 is exemplarily shown as an IGBT element. The switch driving circuit 41 comprises an inverse transistor Q03 and a complementary amplification circuit 411 comprising transistors Q01 and Q02. A voltage of a driving power source of the switch driving circuit 41 is a second DC voltage V2 such as 18 V. The programmable pulse signal Spp is output to a gate G of the first switch SW1 via the inverse transistor Q03 and the complementary amplification circuit 411. The complementary amplification circuit 411 amplifies the inverted programmable pulse signal Spp to an appropriate range, so that a voltage of the gate of the first switch SW1 is in an appropriate range to control the first switch SW1 to be in a switched-on state or a switched-off state, so as to enable the electrical connection state between the second coil terminal P2 and the negative terminal P- to be controllable.

[ 47 ] The inverse transistor Q03 is exemplarily used in FIG. 3. However, in the disclosure, the inverse transistor Q03 may also be omitted. For example, the inverse transistor Q03 is omitted by adjusting the generation logic of the programmable pulse signal Spp.

[48] FIG. 3 exemplarily shows grounding through the emitter E of the first switch SW1, the negative terminal P- being also grounded, so as to realize switching between an ON state and an OFF state so that the switch heating unit can start and stop receiving electric power from the DC power source respectively. However, the manner of electrical connection of the switch unit according to the disclosure is not limited hereto.

[49] In one embodiment, the switch unit of the induction cooker according to the disclosure is composed of the first switch (e.g., an IGBT element) and a switch driving circuit for amplifying the programmable pulse signal, so as to minimize the number of power switch elements to reduce the cost of the induction cooker.

[50] FIG. 5 schematically shows changes of a programmable pulse signal Spp, a gate voltage V_G of a first switch, and a collector voltage V_c of the first switch along with time t in FIG. 4. As shown in FIG. 5, the programmable pulse signal Spp exemplarily may be a rectangular pulse signal, whose level changes between a high level and a low level with the time t . Due to the use of the inverse transistor Q03, a waveform of the gate voltage V_G of the first switch is opposite to a waveform of the programmable pulse signal Spp; that is, the gate voltage V_G is at a low level when the programmable pulse signal Spp is at a high level, and the gate voltage V_G is at a high level when the programmable pulse signal Spp is at a low level. The collector voltage V_G of the first switch SW1 is a DC voltage whose amplitude changes at a high frequency (e.g. 20-30 kHz) with time. When the gate voltage V_G is at a high level, the collector voltage V_G is a voltage approximate to zero or equal to zero. When the gate voltage V_G is at a low level, the collector voltage V_G gradually increases and reaches a maximum, and then gradually decreases and reaches a value approximate to zero or equal to zero. Heating power of the induction cooker can be adjusted by adjusting a duty cycle of the programmable pulse signal Spp.

[51] To accurately control the heating power according to the disclosure, closed- loop control can be performed on the heating power . FIG. 6 shows a circuit 60 for closed-loop control according to one embodiment of the disclosure. As shown in FIG. 6, a capacitor EC52 is connected between the positive terminal P+ and the negative terminal P- . The capacitor EC52 is advantageous to keeping a voltage between the positive terminal P+ and the negative terminal P- stable.

[52] The circuit 60 comprises a current detection unit 61 and a voltage detection unit 63. The current detection unit 61 is used for detecting a current (i.e., a current flowing through the switch heating unit) flowing through an electrical connection circuit between the switch unit (not shown in FIG. 6) and the negative terminal P- to output a current signal Sc indicative of the current. The voltage detection unit 63 is used for detecting a potential difference between the positive terminal P+ and the negative terminal P- to output a potential difference signal Sp indicative of the potential difference. The current detection unit 61 and the voltage detection unit 63 are connected with the control unit (not shown in FIG. 6) so that the control unit can obtain the current signal Sc and the potential difference signal Sd from the current detection unit 61 and the voltage detection unit 63 respectively to perform closed-loop control with respect to power of the induction cooker. In the present embodiment, the switch unit may adopt the switch unit 134 as shown in FIG. 4, and the voltage Vc at the second coil terminal P2 corresponds to the collector voltage of the first switch SW1. The switch unit can be connected with the negative terminal P- via a grounding terminal of the switch unit.

[53] To accurately control a level flipping timing of the programmable pulse signal Spp, the circuit 60 is further provided with a voltage sampling circuit 65. The voltage sampling circuit 65 sample a first voltage at the first coil terminal PI and a second voltage at the second coil terminal P2 respectively to obtain a first voltage signal Svl indicative of the first voltage from a first output node nl of the voltage sampling circuit 65 and obtain a second voltage signal Sv2 indicative of the second voltage from a second output node n2 of the voltage sampling circuit 65. The voltage sampling circuit 65 is connected with the control unit so that the control unit can obtain the first voltage signal Svl and the second voltage signal Sv2 from the voltage sampling circuit 65. The first output node nl is electrically connected with the second output node n2 via an isolation capacitor C12.

[54] To protect the induction cooker, the circuit 60 comprises a protection unit 67. The protection unit 67 comprises a fuse FI, and protection didoes D01, D02, D05 and D06.

[55] To further protect the induction cooker to prevent a voltage surge from damaging the induction cooker, the circuit 60 further comprises a surge protection unit 69. The surge protection unit 69 is electrically connected between the positive terminal P+ and the negative terminal P- . The surge protection unit 69 is connected with the control unit so that the control unit can obtain a surge voltage signal Ss indicative of a voltage between the positive terminal P+ and the negative terminal P- from the surge protection unit 69. For example, when the surge voltage signal Ss is greater than a predetermined value SsO, the control unit can output the programmable pulse signal Spp which makes the switch unit disconnected for a period tO of time. In FIG. 6, the surge protection unit 69 is electrically connected to the negative terminal P- through the grounding terminal and the negative terminal P- . [56] Although the circuit 60 in FIG. 6 comprises the current detection unit 61, the voltage detection unit 63, the voltage sampling circuit 66, the protection unit 67 and the surge protection unit 69, in actual applications some of the above units or all of the above units may be selected to be used. Besides, the configuration manner of the respective units is not limited to the configuration manner as shown in FIG. 6 either, and it is possible to add or reduce elements or to adjust a connection relationship.

[57] According to one embodiment of the disclosure, the programmable pulse signal Spp is a rectangular pulse signal, and the control unit is configured to: after a first predetermined period of time for which a difference between the first voltage signal and the second voltage signal has been less than a first voltage threshold approximate to zero, flip the level of the programmable pulse signal, and maintain the flipped level for a second predetermined period of time. By accurately controlling a timing of flipping to a high level and a timing of flipping to a low level, the power of the induction cooker and the electric power conversion efficiency are controlled.

[58] If the voltage of the DC electricity received from the positive terminal P+ and the negative terminal P- fails to satisfy the requirements of the induction cooker of the disclosure, an electric power conversion unit can also be arranged in the induction cooker of the disclosure. FIG. 7 shows an electric power conversion unit 70 according to one embodiment of the disclosure. The electric power conversion unit 70 comprises a switch chip 71 and a voltage regulator chip 73. An input node ns of the electric power conversion unit 70 is electrically connected with the positive terminal P+ . The electric power conversion unit 70 converts a first DC voltage VI supplied from the positive terminal P+ to a second DC voltage V2 (e.g., 18V) and a third DC voltage V3 (e.g., 5V) lower than the second DC voltage V2.

[59] In one embodiment, the switch unit 1 in the disclosure can further comprise a switch temperature detection unit. The switch temperature detection unit is electrically connected with the electric power conversion unit 70 to receive electric power with the third DC voltage V3. The switch temperature detection unit detects a temperature of the switch unit 13 (e.g., the first switch SW1) . The switch temperature detection unit is connected with the control unit 15 so that the control unit 15 can obtain a first temperature signal indicative of the temperature of the switch unit 13 from the switch temperature detection unit. When the first temperature signal is greater than a predetermined value Tl, the control unit 15 can control the switch unit 13 to be in a disconnected state for a predetermined period tpl of time . When the first temperature signal is less than a predetermined value T2, the control unit 15 can control the switch unit 13 to be in a high-frequency switching state to ensure the induction cooker according to the disclosure to normally perform a heating operation.

[60] In one embodiment, the switch unit 13 in the disclosure can further comprise a panel supporting a cooker and a panel temperature detection unit. The panel temperature detection unit is electrically connected with the electric power conversion unit 70 to receive electric power with the third DC voltage V3. The panel temperature detection unit detects a temperature of the panel, and the panel temperature detection unit is connected with the control unit 15 so that the control unit 15 can obtain a second temperature signal indicative of the temperature of the panel from the panel temperature detection unit. When the second temperature signal is greater than a predetermined value T3, the control unit 15 can control the switch unit 13 to be in a disconnected state for a predetermined period tp2 of time . When the first temperature signal is less than a predetermined value T4, the control unit 15 can control the switch unit 13 to be in a high-frequency switching state to ensure the induction cooker according to the disclosure to normally perform a heating operation.

[61] In one embodiment, the switch driving circuit 133 in FIG. 3 can be electrically connected with the electric power conversion unit 70 to receive electric power with the second DC voltage V2.

[62] In one embodiment, the induction cooker in the disclosure can further comprise a panel supporting a cooker and a key communication unit comprising at least one key. The at least one key is arranged on the panel to receive a user input. The key communication unit is electrically connected with the electric power conversion unit 70 to receive electric power with the third DC voltage V3. The key communication unit is connected with the control unit 15 so that the control unit 15 can obtain a user input signal indicative of the user input from the key communication unit. The control unit performs corresponding processing under a predetermined rule according to the user input signal.

[63] In one embodiment, the induction cooker in the disclosure further comprises a fan for cooling the coil panel and a fan driving unit. The fan driving unit is electrically connected with the electric power conversion unit 70 to receive electric power with the second DC voltage V2. The fan driving unit is communicatively connected with the control unit to control an operating state of the fan by the control unit.

[64] In one embodiment, the induction cooker in the disclosure can further comprise a program read and write unit. The program read and write unit is electrically connected with the electric power conversion unit 70 to receive electric power with the third DC voltage V3. The program read and write unit is connected with the control unit 15 so that the program read and write unit can read a control program within the control unit 15, write the control program within the control unit 15, and/or modify the control program within the control unit 15.

[65] In one embodiment, the control unit 15 of the induction cooker in the disclosure is configured to, in response to detection that an magnitude of a drop of a voltage to ground of the positive terminal from a constant voltage value within a predetermined period of time after the voltage to ground of the positive terminal P+ has maintained the constant voltage value (e.g., the first DC voltage VI ) for a period of time greater than a first time threshold is greater than a drop threshold, set a pot detection flag as "TRUE" stored in the control unit so that, in a case where the pot detection flag is "TRUE", the control unit 15 output the programmable pulse signal Spp to generate the high-frequency time-varying magnetic field for heating by the coil panel CP. The stable value may be greater than the predetermined period of time.

[66] Those skilled in the art could understand that more control functions can be set for the control unit. For example, the control unit is configured so that: after the induction cooker is started through a switch key on the panel of the induction cooker, the control unit acquires the remaining electricity amount of the rechargeable battery, and in a case where the remaining electricity amount is insufficient to drive the fan for cooling the coil panel to operate for a period of time long enough, sets a heating power selection key or a heating power adjustment key on the panel to be disabled.

[67] As can be seen from the foregoing descriptions, the technical solution of the disclosure has at least one of the following advantageous technical effects: a high electric power conversion efficiency, operation without needing mains electricity, an accurate power control and simple structure.

[68] It should be understood that the different embodiments or features described herein may be combined, where feasible, unless otherwise indicated.

[69] Although the disclosure has been disclosed above by describing the detailed embodiments of the disclosure, it should be understood that those skilled in the art could carry out various modifications, improvements or equivalents for the disclosure within the spirit and scope of the appended claims. Such modifications, improvements or equivalents should also be regarded as being included within the scope of protection of the disclosure.

[70] It should be emphasized that when being used herein, terms "include/comprise" indicate existence of features, elements or assemblies, without excluding existence or addition of one or more other features, elements or assemblies.

Claims

1. An induction cooker (1, 1' ) , comprising a pair of terminals, a switch heating unit (HU, HU') and a control unit (15);

wherein the pair of terminals comprises a positive terminal (P+) and a negative terminal (P-) for receiving electric power from a DC power source (17);

the switch heating unit comprises an LC parallel resonant unit (11) and a switch unit (13, 133, 134);

the LC parallel resonant unit comprises a resonant capacitor (C2) and a coil panel (CP) , and the resonant capacitor and the coil panel are connected in parallel between a first coil terminal (PI) and a second coil terminal (P2) for the coil panel;

the LC parallel resonant unit is connected in series with the switch unit (13) ;

the switch unit is configured to switch between an ON state and an OFF state so that the switch heating unit can start and stop receiving the electric power from the DC power source respectively; and

the control unit is configured to generate a programmable pulse signal (Spp) and output the programmable pulse signal to the switch unit to control, by the programmable pulse signal, the switch unit to switch to the ON state or the OFF state so that the coil panel generates a high-frequency time-varying magnetic field for heating using the electric power from the DC power source.

2. The induction cooker according to claim 1, further comprising a case and the DC power source, wherein the DC power source comprises a battery, and the battery is disposed within the case.

3. The induction cooker according to claim 1, wherein the switch unit (133, 134) comprises a first switch (SW1), the first switch is an IGBT element, a collector of the first switch is electrically connected with the second coil terminal, and the first switch is configured so that a gate voltage (V_G) of the first switch is controlled by the programmable pulse signal.

4. The induction cooker according to claim 3, wherein the switch unit (134) further comprises a second switch (SW2) , the second switch is an IGBT element, and the first switch is connected in parallel with the second switch.

5. The induction cooker according to claim 3, wherein the switch unit (134) further comprising a switch driving circuit (41), the programmable pulse signal is output to a gate of the first switch via the switch driving circuit, and the switch driving circuit comprises a complementary amplification circuit (411) for amplifying the programmable pulse signal.

6. The induction cooker according to claim 5, wherein the switch driving circuit further comprises an inverse transistor (Q03) , and the programmable pulse signal is input to the complementary complication circuit via the inverse transistor.

7. The induction cooker according to claim 1, further comprising a current detection unit (61) and a voltage detection unit (63), wherein the current detection unit is configured to detect a current flowing through the switch heating unit to output a current signal (Sc) indicative of the current, the voltage detection unit is configured to detect a potential difference between the positive terminal and the negative terminal to output a potential difference signal (Sp) indicative of the potential difference, and the current detection unit and the voltage detection unit are connected with the control unit so that the control unit can obtain the current signal and the potential difference signal from the current detection unit and the voltage detection unit respectively to perform closed-loop control with respect to power of the induction cooker.

8. The induction cooker according to claim 7, further comprising a voltage sampling circuit (65) , wherein the voltage sampling circuit is configured to sample a first voltage at the first coil terminal and a second voltage at the second coil terminal respectively to obtain a first voltage signal indicative of the first voltage from a first output node (nl) of the voltage sampling circuit and obtain a second voltage signal indicative of the second voltage from a second output node (n2) of the voltage sampling circuit, and the voltage sampling circuit is connected with the control unit so that the control unit can obtain the first voltage signal and the second voltage signal from the voltage sampling circuit; and the first output node is electrically connected with the second output node via an isolation capacitor (C12) .

9. The induction cooker according to claim 8, wherein the control unit generates the programmable pulse signal based on the current signal, the potential difference signal, the first voltage signal and the second voltage signal.

10. The induction cooker according to claim 9, wherein the programmable pulse signal is a rectangular pulse signal, and the control unit is configured to: after a first predetermined period of time for which a difference between the first voltage signal and the second voltage signal has been less than a first voltage threshold approximate to zero, flip a level of the programmable pulse signal, and maintain the flipped level for a second predetermined period of time .

11. The induction cooker according to claim 1, further comprising an electric power conversion unit (70), wherein the electric power conversion unit is electrically connected with the positive terminal and the negative terminal to convert a first DC voltage (VI) supplied by the DC power source to a second DC voltage (V2) and a third DC voltage (V3) lower than the second DC voltage.

12. The induction cooker according to claim 11, wherein the switch unit comprises a switch temperature detection unit, the switch temperature detection unit is electrically connected with the electric power conversion unit to receive electric power with the third DC voltage, the switch temperature detection unit is configured to detect a temperature of the switch unit, and the switch temperature detection unit is connected with the control unit so that the control unit can obtain a first temperature signal indicative of the temperature of the switch unit from the switch temperature detection unit .

13. The induction cooker according to claim 11, further comprising a panel supporting a cooker and a panel temperature detection unit, wherein the panel temperature detection unit is electrically connected with the electric power conversion unit to receive electric power with the third DC voltage, the panel temperature detection unit is configured to detect a temperature of the panel, and the panel temperature detection unit is connected with the control unit so that the control unit can obtain a second temperature signal indicative of the temperature of the panel from the panel temperature detection unit .

14. The induction cooker according to claim 11, further comprising a switch driving circuit, wherein the switch unit comprises a first switch, the first switch is an IGBT element, the programmable pulse signal is output to a gate of the first switch via the switch driving circuit, the switch driving circuit comprises a complementary amplification circuit for amplifying the programmable pulse signal, and the switch driving circuit is electrically connected with the electric power conversion unit to receive electric power with the second DC voltage.

15. The induction cooker according to claim 15, further comprising a panel supporting a cooker and a key communication unit comprising at least one key, wherein the at least one key is arranged on the panel to receive a user input, the key communication unit is electrically connected with the electric power conversion unit to receive electric power with the third DC voltage, and the key communication unit is connected with the control unit so that the control unit can obtain a user input signal indicative of the user input from the key communication unit.

16. The induction cooker according to claim 11, further comprising a fan for cooling the coil panel and a fan driving unit, wherein the fan driving unit is electrically connected with the electric power conversion unit to receive electric power with the second DC voltage, and the fan driving unit is configured to be communicatively connected with the control unit to control an operating state of the fan by the control unit.

17. The induction cooker according to claim 11, further comprising a program read and write unit, wherein the program read and write unit is electrically connected with the electric power conversion unit to receive electric power with the third DC voltage, and the program read and write unit is connected with the control unit so that the program read and write unit can read a control program within the control unit, write the control program within the control unit, and/or modify the control program within the control unit.

18. The induction cooker according to claim 1, further comprising a surge protection unit (69), wherein the surge protection unit is electrically connected between the positive terminal and the negative terminal, and the surge protection unit is connected with the control unit so that the control unit can obtain a surge voltage signal indicative of a voltage between the positive terminal and the negative terminal from the surge protection unit.

19. The induction cooker according to claim 1, wherein the control unit is configured to, in response to detection that a magnitude of a drop of a voltage to ground of the positive terminal from a constant voltage value within a predetermined period of time after the voltage to ground of the positive terminal has maintained the constant voltage value for a period of time greater than a first time threshold is greater than a drop threshold, set a pot detection flag as "TRUE" stored in the control unit so that, in a case where the pot detection flag is "TRUE", the control unit outputs the programmable pulse signal to generate the high-frequency time-varying magnetic field for heating by the coil panel.

20. The induction cooker according to claim 1, wherein the DC power source includes a rechargeable battery.

21. The induction cooker according to claim 1, wherein the switch unit is composed of a first switch and a switch driving circuit for amplifying the programmable pulse signal.

22. The induction cooker according to claim 1, wherein the control unit is configured to control the programmable pulse signal so that in use of the induction cooker to perform heating, a voltage at the first coil terminal is always not lower than a voltage at the second coil terminal.

23. The induction cooker according to claim 1, wherein the positive terminal is connected to the negative terminal sequentially via the switch unit and the LC parallel resonant unit, or the positive terminal is connected to the negative terminal sequentially via the LC parallel resonant unit and the switch unit.