A cooking appliance and operating method thereof

Abstract

A cooking device according to an embodiment of the present disclosure may include a power supply unit, an inverter that switches a voltage input through the power supply unit, a working coil that generates a magnetic field when current is supplied from the inverter, a controller that controls the switching frequency of the inverter, and a voltage charging / discharging circuit that charges and discharges an input voltage input through the power supply unit to reduce ripple of the resonant current flowing through the working coil.

Description

Technology Field

[0001] The present disclosure relates to a cooking appliance and a method of operating the same. More specifically, it relates to a cooking appliance that heats food using an induction heating method and a method of operating the same. Background Technology

[0002] Various types of cooking appliances are used to heat food in homes and restaurants. Traditionally, gas ranges using gas as fuel have been widely used; however, recently, devices that use electricity instead of gas to heat objects, such as cooking vessels like pots, are becoming more popular.

[0003] Methods of heating an object using electricity are broadly divided into resistance heating and induction heating. The electric resistance method heats an object by transferring heat generated when an electric current is passed through a metal resistance wire or a non-metallic heating element, such as silicon carbide, to the object (e.g., a cooking vessel) through radiation or conduction. The induction heating method, on the other hand, is a method in which an eddy current is generated in an object made of metal components by utilizing the magnetic field generated around a coil when high-frequency power of a predetermined magnitude is applied to the coil, thereby heating the object itself.

[0004] Recently, induction heating methods are being applied to most cooking appliances.

[0005] Conventional household induction heating cooking appliances operate using AC power supplied to homes with a frequency of 50 Hz or 60 Hz. At this time, the frequency of the voltage input to the DC capacitor is twice the frequency of the system. Consequently, the resonant current delivering current to the container through high-speed switching contains a frequency component of 100 Hz or 120 Hz, and this frequency component exists within the human audible frequency range (20 Hz to 20 kHz). As a result, the frequency of the current delivered to the container causes discomfort to the user, who perceives noise. The problem to be solved

[0006] The present disclosure aims to provide an induction heating cooking device that reduces noise caused by system frequency. means of solving the problem

[0007] The present disclosure aims to reduce noise caused by grid frequency through a voltage charging / discharging circuit and Constant Envelope Pulse Frequency Modulation (CE-PFM) switching modulation.

[0008] A cooking device according to an embodiment of the present disclosure may include a power supply unit, an inverter that switches a voltage input through the power supply unit, a working coil that generates a magnetic field when current is supplied from the inverter, a controller that controls the switching frequency of the inverter, and a voltage charging / discharging circuit that charges and discharges an input voltage input through the power supply unit to reduce ripple of the resonant current flowing through the working coil.

[0009] The voltage charging / discharging circuit can perform a charging operation when the input voltage is greater than a preset reference voltage, and a discharging operation when the input voltage is less than or equal to the reference voltage.

[0010] The reference voltage can be the RMS value of the input voltage.

[0011] The cooking appliance may further include a voltage sensing unit that detects the input voltage.

[0012] The controller can maintain a constant applied voltage to the inverter by using the charging voltage through the voltage charging / discharging circuit during the discharge operation.

[0013] The controller can perform frequency control to adjust the switching frequency of the inverter to reduce the ripple of the resonant current.

[0014] The controller can adjust the switching frequency based on the input voltage.

[0015] The controller can increase the switching frequency when the input voltage increases and decrease the switching frequency when the input voltage decreases.

[0016] The controller can adjust the switching frequency based on the resonant current flowing through the working coil.

[0017] When the controller performs frequency control, it can perform frequency reduction control after performing frequency increase control.

[0018] The voltage charging / discharging circuit can be formed as a buck-boost converter.

[0019] The controller operates at a predetermined cycle, and each cycle may include a first section in which the voltage charging / discharging circuit performs a charging operation while simultaneously adjusting the switching frequency of the inverter based on the input voltage, and a second section in which the voltage charging / discharging circuit performs a discharging operation.

[0020] The first section may include a frequency increase section in which the switching frequency increases and a frequency decrease section in which the switching frequency decreases. Effects of the invention

[0021] According to an embodiment of the present disclosure, by controlling the voltage gain of the resonant network through switching frequency control to keep the resonant current constant, there is an advantage in that noise caused by the grid frequency is reduced.

[0022] According to an embodiment of the present disclosure, power is supplied to the inverter from an internal capacitor of the voltage charging / discharging circuit to maintain a constant magnitude of the voltage applied to the inverter, thereby having the advantage of reducing noise caused by grid frequency. Brief explanation of the drawing

[0023] FIG. 1 is a perspective view showing a cooking appliance and a cooking container according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view of a cooking device and a cooking container according to an embodiment of the present disclosure. FIG. 3 is a diagram showing a circuit of a cooktop according to an embodiment of the present disclosure. FIG. 4 is a drawing showing the output characteristics of a cooktop according to an embodiment of the present disclosure. FIG. 5 is an exemplary drawing showing a circuit diagram of a cooking appliance according to a first embodiment of the present disclosure. Figure 6 is an example diagram showing the circuit diagram of a cooking device when the voltage charging / discharging circuit is a buck-boost circuit. Figure 7 is a diagram showing the output waveform according to the operation of a conventional cooking device. FIG. 8 is a drawing showing an output waveform according to an operation according to a first embodiment of the present disclosure. FIG. 9 is a control block diagram for explaining the operation method of a cooking appliance according to an embodiment of the present disclosure. FIG. 10 is a flowchart illustrating the operation method of a cooking appliance according to an embodiment of the present disclosure. FIG. 11 is a drawing showing an output waveform according to an operation according to a second embodiment of the present disclosure. Figure 12 shows the simulation results of a conventional induction heating cooking device. FIG. 13 is the result of a simulation of an induction heating cooking device according to the second embodiment of the present disclosure. Specific details for implementing the invention

[0024] Hereinafter, embodiments related to the present disclosure will be described in more detail with reference to the drawings. The suffixes "module" and "part" for components used in the following description are assigned or used interchangeably solely for the ease of drafting the specification and do not have distinct meanings or roles in themselves.

[0025] Hereinafter, a cooking appliance and a method of operation thereof according to an embodiment of the present disclosure will be described. Hereinafter, the term “cooking appliance” may refer to an induction heating type cooktop, but is not limited thereto.

[0026] FIG. 1 is a perspective view showing a cooking appliance and a cooking container according to an embodiment of the present disclosure, and FIG. 2 is a cross-sectional view of a cooking appliance and a cooking container according to an embodiment of the present disclosure.

[0027] A cooking container (1) can be positioned on top of a cooking device (10), and the cooking device (10) can heat the cooking container (1) positioned on top.

[0028] First, the method of heating the cooking container (1) by the cooking device (10) is explained.

[0029] As illustrated in FIG. 1, the cooking device (10) can generate a magnetic field (20) such that at least a portion of it passes through the cooking container (1). At this time, if the material of the cooking container (1) contains an electrical resistance component, the magnetic field (20) can induce an eddy current (30) in the cooking container (1). This eddy current (30) generates heat in the cooking container (1) itself, and since this heat is transmitted through conduction or radiation to the interior of the cooking container (1), the contents of the cooking container (1) can be cooked.

[0030] Meanwhile, if the material of the cooking container (1) does not contain an electrical resistance component, eddy current (30) is not generated. Therefore, in this case, the cooking device (10) cannot heat the cooking container (1).

[0031] Accordingly, the cooking vessel (1) that can be heated by this cooking device (10) may be a metal vessel such as a stainless steel vessel or an enamel or cast iron vessel.

[0032] Next, the method by which the cooking device (10) generates a magnetic field (20) is explained.

[0033] As shown in FIG. 2, the cooking device (10) may include at least one of a top plate (11), a working coil (150), and a ferrite core (13).

[0034] The top plate (11) can support the cooking vessel (1) on which the cooking vessel (1) is placed. That is, the cooking vessel (1) can be placed on the upper surface of the top plate (11). A heating area in which the cooking vessel (1) is heated can be formed on the top plate (11).

[0035] Additionally, the top plate (11) can be formed of reinforced glass made of a ceramic material that synthesizes various minerals. Accordingly, the top plate (11) can protect the cooking appliance (10) from external impacts.

[0036] In addition, the top plate (11) can prevent foreign substances such as dust from entering the cooking device (10).

[0037] A working coil (150) may be located below the top plate (11). Current may or may not be supplied to this working coil (150) to generate a magnetic field (20). Specifically, current may or may not flow through the working coil (150) depending on the on / off state of the internal switching element of the cooking appliance (10).

[0038] When current flows through the working coil (150), a magnetic field (20) is generated, and this magnetic field (20) can generate an eddy current (30) by encountering an electrical resistance component contained in the cooking container (1). The eddy current heats the cooking container (1), and accordingly, the contents of the cooking container (1) can be cooked.

[0039] In addition, the heat output of the cooking device (10) can be adjusted according to the amount of current flowing through the working coil (150). As a specific example, the more current flowing through the working coil (150), the more magnetic field (20) is generated, and accordingly, the magnetic field passing through the cooking container (1) increases, so the heat output of the cooking device (10) can be increased.

[0040] The ferrite core (13) is a component for protecting the internal circuit of the cooking device (10). Specifically, the ferrite core (13) acts as a shield to block the effect of the magnetic field (20) generated from the working coil (150) or the electromagnetic field generated from the outside on the internal circuit of the cooking device (10).

[0041] To this end, the ferrite core (13) can be formed from a material with very high permeability. The ferrite core (13) serves to guide the magnetic field flowing into the interior of the cooking device (10) to flow through the ferrite core (13) without being radiated. The way the magnetic field (20) generated in the working coil (150) moves through the ferrite core (13) may be as shown in FIG. 2.

[0042] Meanwhile, the cooking device (10) may include additional components in addition to the top plate (11), working coil (150), and ferrite core (13) described above. For example, the cooking device (10) may further include an insulating material (not shown) located between the top plate (11) and the working coil (150). That is, the cooktop according to the present disclosure is not limited to the cooking device (10) shown in FIG. 2.

[0043] Additionally, the cooking device (10) may include a temperature sensor for estimating the temperature of the cooking container (1). For example, the temperature sensor (170) can estimate the temperature of the cooking container (1) by sensing the temperature of the top plate (11) by being located at the center of the working coil (150) as shown in FIG. 1.

[0044] FIG. 3 is a diagram showing a circuit of a cooktop according to an embodiment of the present disclosure.

[0045] The circuit diagram of the cooking device (10) shown in FIG. 3 is merely an example for convenience of explanation, and therefore the present disclosure is not limited thereto.

[0046] Referring to FIG. 3, an induction heating type cooktop may include at least some or all of a power supply unit (110), a rectifier unit (120), a DC link capacitor (130), an inverter (140), a working coil (150), and a resonant capacitor (160).

[0047] The power supply unit (110) can receive external power. The power received by the power supply unit (110) from the outside may be AC ​​(Alternation Current) power.

[0048] The power supply unit (110) can supply alternating current voltage to the rectifier unit (120).

[0049] The rectifier (120) is an electrical device for converting alternating current into direct current. The rectifier (120) converts the alternating current voltage supplied through the power supply (110) into a direct current voltage. The rectifier (120) can supply the converted voltage to the DC terminals (121).

[0050] The output terminal of the rectifier (120) can be connected to the DC terminal (121). The DC terminal (121) output through the rectifier (120) can be called a DC link. The voltage measured at the DC terminal (121) is called the DC link voltage.

[0051] The DC link capacitor (130) serves as a buffer between the power supply unit (110) and the inverter (140). Specifically, the DC link capacitor (130) is used to maintain the DC link voltage converted through the rectifier unit (120) and supply it to the inverter (140).

[0052] The inverter (140) serves to switch the voltage applied to the working coil (150) so that a high-frequency current flows through the working coil (150). The inverter (140) may include a semiconductor switch, and the semiconductor switch may be an IGBT (Insulated Gate Bipolar Transistor) or WBG (Wide Band Gab) device, but since this is merely exemplary, it is reasonable to assume that it is not limited thereto. Meanwhile, the WBG device may be SiC (Silicon Carbide) or GaN (Gallium Nitride), etc. By driving the semiconductor switch, the inverter (140) causes a high-frequency current to flow through the working coil (150), and accordingly, a high-frequency magnetic field is formed in the working coil (150).

[0053] The working coil (150) may or may not have current flowing through it depending on whether the switching element is driven. When current flows through the working coil (150), a magnetic field is generated. The working coil (150) can generate a magnetic field as current flows to heat the cooking device.

[0054] One side of the working coil (150) is connected to the connection point of the switching element of the inverter (140), and the other side is connected to the resonant capacitor (160).

[0055] The switching element is driven by a driving unit (not shown), and the switching element is controlled by the switching time output from the driving unit, so that the switching elements operate alternately and apply a high-frequency voltage to the working coil (150). And, since the on / off time of the switching element applied by the driving unit (not shown) is controlled in a gradually compensated manner, the voltage supplied to the working coil (150) changes from a low voltage to a high voltage.

[0056] The resonant capacitor (160) may be a component to serve as a buffer. The resonant capacitor (160) controls the saturation voltage rise rate during the turn-off of the switching element, thereby affecting energy loss during the turn-off time.

[0057] In the case of a cooking device (10) configured with a circuit diagram as shown in FIG. 3, the resonance frequency is determined by the inductance value of the working coil (150) and the capacitance value of the resonance capacitor (160). Then, a resonance curve is formed around the determined resonance frequency, and the resonance curve can represent the output power of the cooking device (10) according to the frequency band.

[0058] Next, FIG. 4 is a drawing showing the output characteristics of a cooktop according to an embodiment of the present disclosure.

[0059] First, the Q factor (quality factor) may be a value indicating the sharpness of resonance in a resonant circuit. Therefore, in the case of a cooking device (10), the Q factor is determined by the inductance value of the working coil (150) included in the cooking device (10) and the capacitance value of the resonant capacitor (160). The resonance curve differs depending on the Q factor. Accordingly, the cooking device (10) has different output characteristics depending on the inductance value of the working coil (150) and the capacitance value of the resonant capacitor (160).

[0060] Figure 4 shows an example of a resonance curve according to the Q factor. Generally, the larger the Q factor, the sharper the shape of the curve, and the smaller the Q factor, the broader the shape of the curve.

[0061] The horizontal axis of the resonance curve represents frequency, and the vertical axis can represent output power. The vertical axis can also represent voltage gain.

[0062] The frequency at which maximum power is output on the resonance curve is called the resonance frequency (f0).

[0063] Generally, the cooking device (10) uses a frequency in the right region relative to the resonance frequency (f0) of the resonance curve. Also, the cooking device (10) may have a minimum operating frequency and a maximum operating frequency that can be operated pre-set.

[0064] When the cooking device (10) receives a heating command, it can determine the operating frequency according to the heat level set in the heating command. Specifically, the cooking device (10) can adjust the output power by lowering the operating frequency as the set heat level is higher and increasing the operating frequency as the set heat level is lower. That is, when the cooking device (10) receives a heating command, it can implement a heating mode that operates in any one of the operating frequency ranges according to the set heat level.

[0065] The cooking device (10) can operate at a frequency corresponding to the range from the maximum operating frequency (fmax) to the minimum operating frequency (fmin). That is, the operating frequency range of the cooking device (10) can be from the maximum operating frequency (fmax) to the minimum operating frequency (fmin).

[0066] The maximum operating frequency (fmax) may be the maximum switching frequency of the IGBT. The maximum switching frequency of the IGBT may refer to the maximum frequency that can be driven, taking into account the voltage withstand capability and capacitance of the IGBT switching device.

[0067] For example, the maximum operating frequency (fmax) may be 75 kHz and the minimum operating frequency (fmin) may be approximately 20 kHz. However, the above-described maximum operating frequency (fmax) and minimum operating frequency (fmin) are merely exemplary values ​​and are not limited thereto.

[0068] Meanwhile, conventional cooking appliances operate using AC power supplied to households with frequencies such as 50 Hz or 60 Hz. The frequency of the voltage input to the DC capacitor is twice the frequency of the grid. Consequently, the resonant current that delivers current to the container through high-speed switching contains frequency components of 100 Hz or 120 Hz. Since these frequency components fall within the human audible frequency range (20 Hz to 20 kHz), noise is generated.

[0069] The present disclosure can reduce noise caused by grid frequency by applying at least one of a voltage charging / discharging circuit and Constant Envelope Pulse Frequency Modulation (CE-PFM) switching modulation.

[0070] According to the first embodiment, the present disclosure can reduce noise caused by system frequency by applying a voltage charging / discharging circuit.

[0071] A cooking device (10) according to the first embodiment of the present disclosure may further include a voltage charging / discharging circuit (1000).

[0072] FIG. 5 is an exemplary drawing showing a circuit diagram of a cooking appliance according to a first embodiment of the present disclosure.

[0073] For example, the cooking device (10) may include a power supply unit (110), a rectifier unit (120), a DC link capacitor (130), an inverter (140), a working coil (150), a resonant capacitor (160), and a voltage charging / discharging circuit (1000). Since the remaining components, excluding the voltage charging / discharging circuit (1000), are the same as those described above, a redundant description will be omitted.

[0074] The voltage charging / discharging circuit (1000) can charge the voltage and discharge the charged voltage. The voltage charging / discharging circuit (1000) can alternately perform voltage charging operations and voltage discharging operations.

[0075] The voltage charging / discharging circuit (1000) may be a Line-frequency Noise Suppressor (LNS) circuit. As an example, the voltage charging / discharging circuit (1000) may be a buck-boost circuit.

[0076] Figure 6 is an example diagram showing the circuit diagram of a cooking device when the voltage charging / discharging circuit is a buck-boost circuit.

[0077] However, this is merely an example, and it is reasonable to assume that the voltage charging / discharging circuit (1000) is not limited to a buck-boost circuit. However, for the convenience of explanation, the explanation will be given by assuming that the voltage charging / discharging circuit (1000) is a buck-boost circuit with reference to FIG. 6.

[0078] The voltage charging / discharging circuit (1000) is a first and second capacitor (C LNS1 )(C LNS2 ), first and second switches (Q1)(Q2) and inductor (L DSC It can be composed of the first capacitor (C). LNS1 ) can be a DC link capacitor (130).

[0079] Second capacitor (C LNS2 The inductor (L) and the first switch (Q1) are connected in series, and the second switch (Q2) can be connected in parallel to them. DSC One end of ) is connected between the first switch (Q1) and the second switch (Q2), and the other end is connected to the first capacitor (C LNS1 It can be connected to one end of ).

[0080] Second capacitor (C LNS2 The operation of charging and discharging voltage in ) can be repeated. As the first switch (Q1) and the second switch (Q2) operate alternately, the second capacitor (C LNS2 Voltage can be charged / discharged in ).

[0081] Second capacitor (C LNS2 When ) is discharged, the resonant current (I resThe envelope of ) can be formed as direct current (DC). Accordingly, the resonant current (I res The ripple of ) can be reduced, thereby reducing noise.

[0082] According to the second embodiment, the present disclosure can reduce noise caused by grid frequency by further applying Constant Envelope Pulse Frequency Modulation (CE-PFM) switching modulation to the voltage charging / discharging circuit.

[0083] Figure 7 is a diagram showing the output waveform according to the operation of a conventional cooking device.

[0084] Referring to Fig. 7, the switching frequency (f sw ) is constant, and the resonant current (I res The envelope of ) can be formed as AC. That is, the resonant current (I res Ripples exist in ), and noise is generated as a result.

[0085] FIG. 8 is a drawing showing an output waveform according to an operation according to a first embodiment of the present disclosure.

[0086] Referring to FIG. 8, the second capacitor (C) is formed by the alternating operation of the first switch (Q1) and the second switch (Q2). LNS2 It can be confirmed that voltage charging and discharging are repeated in the ) . The second capacitor (C LNS2 While the voltage is being charged in ), the resonant current (I res The envelope of ) is formed as AC, but the second capacitor (C LNS2 While the voltage is being discharged in ), the resonant current (I res It can be confirmed that the envelope DC of ) is formed.

[0087] Accordingly, compared with the output waveform of FIG. 7, at least the second capacitor (C LNS2 It can be confirmed that noise is reduced in the voltage discharge section of ).

[0088] Meanwhile, according to a second embodiment of the present disclosure, switching frequency control is further applied to the resonant current (I res Noise can be further reduced due to ).

[0089] According to the second embodiment of the present disclosure, the cooking device (10) can further reduce noise by controlling the switching frequency while charging and discharging voltage through the voltage charging / discharging circuit (1000).

[0090] FIG. 9 is a control block diagram for explaining the operation method of a cooking appliance according to an embodiment of the present disclosure, and FIG. 10 is a flowchart illustrating the operation method of a cooking appliance according to an embodiment of the present disclosure.

[0091] Meanwhile, the circuit diagram of the cooking device according to the second embodiment may be the same as that of the first embodiment.

[0092] The cooking device (10) may include an inverter (140), a voltage sensing unit (180), a controller (190), and a voltage charging / discharging circuit (1000).

[0093] The inverter (140) can switch the voltage input through the power supply unit (110).

[0094] The voltage sensing unit (180) can detect the input voltage.

[0095] The controller (190) can control the inverter (140) and the voltage sensing unit (180), etc. The controller (190) can control the switching frequency of the inverter (140).

[0096] The burner of the cooking appliance (10) can be turned on (S101).

[0097] When the burner of the cooking appliance (10) is turned on, the voltage detection unit (180) can detect the input voltage (S103).

[0098] Input voltage (V s ) may be a voltage supplied through the power supply unit (110). The controller (190) can control the voltage detection unit (180) to detect the input voltage when the burner is turned on.

[0099] The controller (190) detects the input voltage and can determine whether the detected input voltage is greater than a preset reference voltage.

[0100] The reference voltage may be a preset voltage to determine the operation of the voltage charging / discharging circuit (1000). The reference voltage may be a constant. The reference voltage may be set differently depending on the size of the burner, the specifications of the inverter (140), etc.

[0101] For example, the reference voltage can be the RMS value of the input voltage. That is, the reference voltage can be the RMS voltage of the input voltage.

[0102] The controller (190) can perform charging and CE-PFM operations when the input voltage is greater than the reference voltage (S107).

[0103] The controller (190) can control the voltage charging / discharging circuit (1000) to perform a charging operation when the input voltage is greater than the reference voltage, and can control the inverter (140) to perform a CE-PFM operation.

[0104] The charging operation is performed on the second capacitor (C LNS2 The operation is to charge the voltage in the inverter (140), and the CE-PFM operation may be an operation to control the switching frequency of the inverter (140) to a constant level.

[0105] That is, the controller (190) has a resonant current (I res Frequency control can be further performed to adjust the switching frequency of the inverter (140) to reduce the ripple of ).

[0106] Meanwhile, step S107 may be the first section (S1) of FIG. 11. That is, in step S107, the output waveform may be the same as the first section (S1) of FIG. 11.

[0107] The controller (190) can perform discharge operation and PFM operation if the input voltage is below the reference voltage (S109).

[0108] The controller (190) can control the voltage charging / discharging circuit (1000) to perform a discharge operation when the input voltage is below the reference voltage, and can control the inverter (140) to perform a PFM operation.

[0109] The discharge operation is the second capacitor (C LNS2 The voltage charged in the inverter (140) is discharged, and the PFM operation may be an operation that variably controls the switching frequency of the inverter (140).

[0110] Meanwhile, step S109 may be the second section (S2) of FIG. 11. That is, in step S109, the output waveform may be the same as the second section (S2) of FIG. 11.

[0111] As described above, through frequency control as well as voltage charging / discharging operation, the resonant current (I) in the voltage charging section res Noise can be reduced by forming the envelope of ) into DC.

[0112] FIG. 11 is a drawing showing an output waveform according to an operation according to a second embodiment of the present disclosure.

[0113] In FIG. 11, the first section (S1) is a section in which the voltage charging / discharging circuit (1000) performs a charging operation, and the second capacitor (C LNS2 It may be a section where voltage is charged to ). The controller (190) uses the input voltage (Vs) in the first section (S1) to charge the second capacitor (C LNS2 It can charge the input voltage to a preset reference voltage (V). The first section (S1) is the input voltage to a preset reference voltage (V LNS(Target) It may be a section larger than ). The first section (S1) may be an output waveform resulting from performing step S107 of FIG. 10. The first section (S1) may be a section for performing frequency increase control.

[0114] The second section (S2) is a section in which the voltage charging / discharging circuit (1000) performs a discharge operation, and the second capacitor (C LNS2) may be a section where the charging voltage is discharged. The second section (S2) may be a section where the input voltage is below a preset reference voltage. The second section (S2) is a section where the input voltage is below the preset reference voltage (V LNS(Target) It may be a section below ). The second section (S2) may be an output waveform resulting from performing step S109 of FIG. 10. The second section (S2) may be a section for performing frequency reduction control.

[0115] In the second section (S2), the second capacitor (C LNS2 As the charging voltage of ) discharges, the resonant current (I res Since the envelope of ) is formed as DC, the frequency can be controlled to be constant. That is, the controller (190) can control the switching frequency to be constant in the second section (S2).

[0116] The controller (190) adjusts the switching frequency in the first section (S1) to resonant current (I res The envelope of ) can be formed as DC.

[0117] For example, when the actual voltage is greater than the RMS voltage of the system, the controller (190) [determines] the internal capacitor (C) of the voltage charging / discharging circuit (1000). LNS2 Charging ) and adjusting the voltage gain of the resonant network by adjusting the switching frequency of the inverter (140) to resonant current (I res ) can be controlled consistently.

[0118] That is, the first section (S1) may be a charging section of the voltage charging / discharging circuit (1000) and a frequency adjustment section.

[0119] The first section (S1) can be divided into a frequency increase section (S11) and a frequency decrease section (S12).

[0120] The frequency increase section (S11) is a section for increasing the switching frequency, and the frequency decrease section (S12) may be a section for decreasing the switching frequency.

[0121] First, the frequency increase section (S11) is explained. This is a section where the input voltage increases, and as the input voltage increases, the resonant current (I res As ) also increases, the envelope fluctuates. Therefore, the controller (190) can increase the switching frequency when the input voltage increases to lower the voltage gain of the resonant network. As the voltage gain decreases, the resonant current (I res ) is reduced so that the envelope can be formed similarly to DC.

[0122] Next, the frequency reduction section (S12) is described. This is a section where the input voltage decreases, and when the input voltage decreases, the resonant current (I res As ) also decreases, the envelope fluctuates. Therefore, the controller (190) can increase the voltage gain of the resonant network by reducing the switching frequency when the input voltage decreases. As the voltage gain increases, the resonant current (I res As ) increases, the envelope can be formed similarly to DC.

[0123] Accordingly, in the first section (S1), the controller (190) can perform frequency reduction control after performing frequency increase control.

[0124] Meanwhile, there may be various ways for the controller (190) to adjust the switching frequency in the first section (S1). That is, there may be various ways for the controller (190) to variably control the switching frequency in the first section (S1).

[0125] According to one embodiment, the controller (190) can adjust the switching frequency based on the input voltage. The controller (190) can control the switching frequency to follow the input voltage. The controller (190) can increase the switching frequency of the inverter (140) as the input voltage increases, and decrease the switching frequency of the inverter (140) as the input voltage decreases.

[0126] There can be various ways to vary the switching frequency.

[0127] For example, the controller (190) can control the switching frequency to increase in proportion to the input voltage.

[0128] As another example, the controller (190) can determine whether to increase or decrease the input voltage at predetermined intervals, and if the input voltage increases, increase the switching frequency from the current value by a predetermined value, and if the input voltage decreases, decrease the switching frequency from the current value by a predetermined value.

[0129] According to another embodiment, the controller (190) has a resonant current (I res The switching frequency can be adjusted based on ). The controller (190) can adjust the switching frequency based on the resonant current (I res The switching frequency can be controlled to increase or decrease in proportion to ).

[0130] The controller (190) can control the switching frequency to the maximum when the input voltage is at its maximum value.

[0131] That is, in the first section (S1), the controller (190) can vary the driving frequency of the inverter (140) to vary the voltage gain. Due to the variation in voltage gain, the resonant current (I res Fluctuations in the envelope of ) can also be eliminated. That is, the resonant current (I res The envelope of ) can be formed similarly to when the input voltage is DC.

[0132] The controller (190) in the second section (S2) has a second capacitor (C LNS2 Using ), the first capacitor (C LNS1 The voltage of ) can be fixed as the input voltage (Vs). That is, the controller (190) can maintain the applied voltage to the inverter (140) constant by using the charging voltage through the voltage charging / discharging circuit (1000) during the discharge operation.

[0133] For example, when the actual voltage is less than or equal to the RMS voltage (reference voltage) of the power supply, the controller (190) [describes] the internal capacitor (C) of the voltage charging / discharging circuit (1000). LNS2 Power is supplied from ) to the inverter (140) to the first capacitor (C LNS1 The voltage of ) can be controlled so that the input voltage RMS magnitude is maintained.

[0134] That is, the controller (190) is the second capacitor (C LNS2 When the inverter (140) is operated using the charging voltage of ), a constant first capacitor (C LNS1 Resonant current (I) without frequency variation of inverter (140) at the voltage of ) res ) can be maintained constant. That is, the resonant current (I res The envelope of ) becomes constant.

[0135] In summary, the controller (190) operates at a predetermined cycle, and each cycle may include a first section (S1) in which the voltage charging / discharging circuit (1000) performs a charging operation while simultaneously adjusting the switching frequency of the inverter (140) based on the input voltage, and a second section (S2) in which the voltage charging / discharging circuit (1000) performs a discharging operation. And, in the first and second sections (S1)(S2), the resonant current (I res It can be confirmed that the ripple of ) is minimized, and the resulting noise reduction can be confirmed.

[0136] FIG. 12 is the result of a simulation of a conventional induction heating cooking device, and FIG. 13 is the result of a simulation of an induction heating cooking device according to the second embodiment of the present disclosure.

[0137] Resonant current (I res The squared value of ) is a numerical value representing the noise resulting from the operation of the cooking appliance. At 120 Hz, the resonant current (I res If we look at the squared value of ), it is 872 in the conventional case, but 46.7 in the present disclosure, confirming that the noise is significantly reduced.

[0139] The above description is merely an illustrative explanation of the technical concept of the present disclosure, and those skilled in the art to which the present disclosure pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present disclosure without departing from its nature.

[0140] Accordingly, the embodiments disclosed in this disclosure are intended to explain, not limit, the technical concept of this disclosure, and the scope of the technical concept of this disclosure is not limited by these embodiments.

[0141] The scope of protection of the present disclosure shall be interpreted by the claims below, and all technical ideas within the equivalent scope shall be interpreted as being included within the scope of rights of the present disclosure.

Claims

Claim 1 A cooking device comprising: a power supply unit; an inverter that switches a voltage input through the power supply unit; a working coil that generates a magnetic field when current is supplied from the inverter; a controller that controls the switching frequency of the inverter; and a voltage charging / discharging circuit that charges and discharges an input voltage input through the power supply unit to reduce ripple of the resonant current flowing through the working coil. Claim 2 A cooking device according to claim 1, wherein the voltage charging / discharging circuit performs a charging operation when the input voltage is greater than a preset reference voltage and performs a discharging operation when the input voltage is less than or equal to the reference voltage. Claim 3 A cooking device according to claim 2, wherein the reference voltage is the RMS value of the input voltage. Claim 4 A cooking device according to claim 2, further comprising a voltage sensing unit for detecting the input voltage. Claim 5 A cooking device according to claim 2, wherein the controller maintains a constant applied voltage to the inverter by utilizing the charging voltage through the voltage charging / discharging circuit during the discharge operation. Claim 6 A cooking device according to claim 1, wherein the controller performs frequency control to adjust the switching frequency of the inverter for reducing the ripple of the resonant current. Claim 7 In claim 6, the controller controls the switching frequency based on the input voltage. Claim 8 A cooking device according to claim 7, wherein the controller increases the switching frequency when the input voltage increases and decreases the switching frequency when the input voltage decreases. Claim 9 A cooking device according to claim 6, wherein the controller adjusts the switching frequency based on the resonant current flowing through the working coil. Claim 10 A cooking device according to claim 6, wherein the controller, when performing the frequency control, performs frequency increase control and then performs frequency decrease control. Claim 11 A cooking device according to claim 1, wherein the voltage charging / discharging circuit is formed as a buck-boost converter. Claim 12 A cooking device according to claim 1, wherein the controller operates at a predetermined cycle, and each cycle includes a first section in which the voltage charging / discharging circuit performs a charging operation while simultaneously adjusting the switching frequency of the inverter based on the input voltage, and a second section in which the voltage charging / discharging circuit performs a discharging operation. Claim 13 A cooking device according to claim 12, wherein the first section comprises a frequency increasing section in which the switching frequency increases and a frequency decreasing section in which the switching frequency decreases.

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