Induction cooktop
By introducing parallel buffer capacitors and damping circuits into the power converter of the induction cooker, the problems of voltage overshoot and ringing noise are solved, resulting in lower EMC emissions and lower power dissipation, thus protecting electronic components.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ELECTROLUX APPLIANCES
- Filing Date
- 2024-10-15
- Publication Date
- 2026-05-26
Smart Images
Figure CN122095745A_ABST
Abstract
Description
Technical Field
[0001] This invention relates generally to the field of induction cooktop technology.
[0002] More specifically, the present invention relates to an electric power converter configured to supply high-frequency power to the heating coil of an induction cooker. Background Technology
[0003] Induction cooktops for food preparation are well known in the art and typically include a heating zone associated with an induction load. To heat cookware placed on the heating zone, the induction load is electrically coupled to an electronic drive unit for driving alternating current through the induction load.
[0004] Alternating current generates a time-varying magnetic field. Due to the inductive coupling between the inductive load and the cookware component placed above the inductive load, the magnetic field generated by the inductive load induces eddy currents circulating in the cookware component.
[0005] Due to the resistance of the cookware components, the presence of eddy currents generates heat within the cookware components.
[0006] It is also known that the electronic drive unit of an induction cooktop typically includes power converters, which include switching devices such as fast-switching insulated-gate bipolar transistors (IGBTs). During their switching, IGBTs are susceptible to voltage overshoot due to the rapid release of energy stored in stray inductance.
[0007] The technical problem with induction cooktops is that when voltage overshoot causes an overshoot voltage outside the operating range of the electronic components of the power converter, the electronic components of the power converter are often damaged.
[0008] In light of this, some proposed solutions envision using circuits configured to reduce stray inductance in power converters, for example, by using laminated copper plates on printed circuit boards. However, in addition to stray inductance, induction cooktops are partially affected by voltage overshoot due to their inductive load.
[0009] To reduce voltage overshoot, it is known that the power converters in induction cooktops include so-called buffer circuits, the architecture of which depends on the type of electronic components to be protected.
[0010] Some known snubber circuits for diodes include circuits with capacitors and resistors, i.e., RC circuits, which attenuate overvoltage spikes that occur during the reverse recovery process, but have some technical problems.
[0011] In practice, capacitors cause voltage and current oscillations, a phenomenon known as "ringing" noise. This noise flows through the printed circuit board, causing electromagnetic compatibility (EMC) problems, especially for circuits and appliances electrically connected to the printed circuit board.
[0012] Furthermore, the resistors in induction cooktops with RC buffers operate under high-frequency switching conditions, resulting in high power dissipation. Summary of the Invention
[0013] Therefore, the object of the present invention is to provide an electric power converter having one or more buffer circuits, which mitigates at least some of the disadvantages of electric power converters with buffer circuits as known in the prior art.
[0014] According to the present invention, an induction heating cooker is provided for this purpose, the induction heating cooker comprising at least one induction load and at least one power converter, the at least one power converter being configured to provide electrical power to the induction load and comprising at least one converter circuit and at least one converter control module, the at least one converter control module being configured to control the converter circuit by at least one control signal to regulate the electrical power supplied to the induction load, wherein the converter circuit comprises: at least one switching circuit having at least one converter switch, the at least one converter switch being controlled by the control signal and connected to a first terminal of the induction load via a converter line; and at least one buffer circuit comprising at least one damping circuit connected in parallel to the converter switch.
[0015] It is important to point out that reducing the ringing amplitude and time will reduce EMC emissions measured according to standard tests, allowing for a competitive advantage using simpler and cheaper input filters.
[0016] Preferably, the damping circuit is connected in parallel to the buffer capacitor.
[0017] Preferably, the switching circuit includes a pair of converter switches, which are selectively controlled by the control signal and connected in series with each other through a first node. The first node is connected to the first terminal of the inductive load through the converter line. The buffer circuit includes a pair of buffer capacitors and a pair of damping circuits. The pair of buffer capacitors are connected in series with each other through a second node, which is connected to the converter line. The pair of damping circuits are connected in parallel to both the buffer capacitors and the converter switches.
[0018] Preferably, the pair of converter switches includes a high-side switch and a low-side switch connected in series between a first power supply line with a high voltage and a second power supply line with a low voltage. The high-side switch and the low-side switch are connected to each other through the first node. The buffer circuit includes a high-side buffer capacitor and a low-side buffer capacitor connected in series and connected in parallel with the high-side switch and the low-side switch, respectively. The pair of damping circuits includes a high-side damping circuit and a low-side damping circuit. The high-side damping circuit is connected in parallel with the high-side switch and the high-side buffer capacitor, and the low-side damping circuit is connected in parallel with the low-side switch and the low-side buffer capacitor.
[0019] Preferably, the damping circuit includes a damping capacitor, a damping resistor, and a damping unidirectional current conduction device.
[0020] Preferably, the damping capacitor and the corresponding unidirectional current conduction device are connected in series between the converter line and the first power supply line or the second power supply line.
[0021] Preferably, the damping resistor and the opposite damping capacitor are connected in parallel with each other.
[0022] Preferably, the damping unidirectional current conduction device includes a first terminal connected to a corresponding damping resistor and a second terminal connected to the converter line.
[0023] Preferably, the switching circuit includes only a single converter switch.
[0024] Preferably, the power converter is a half-bridge and includes a single converter circuit.
[0025] Preferably, the power converter is a full-bridge converter and includes two converter circuits having output terminals connected to each other, and converter terminals connected to corresponding first and second terminals of the inductive load.
[0026] Preferably, the power converter includes three converter circuits connected to corresponding inductive loads; each converter circuit has no output terminal and is connected to a first terminal of the inductive load via the converter terminal; the second terminal of the inductive load is connected to the second converter terminal of the inductive load.
[0027] Preferably, the converter switch is an insulated gate bipolar transistor (IGBT) and / or a field-effect transistor with a corresponding anti-parallel diode.
[0028] Preferably, the damping capacitor has a capacitance between about 1 nanofarad and about 1 microfarad, and more preferably between about 30 nanofarads and about 500 nanofarads.
[0029] Preferably, the damping resistor has a resistance between about 0.2 ohms and about 100 ohms, preferably between about 0.8 ohms and 20 ohms.
[0030] Unless otherwise explicitly stated, embodiments of the present invention may be freely combined with each other. Attached Figure Description
[0031] Various aspects of the invention, including its specific features and advantages, will be readily understood from the following detailed description and accompanying drawings, in which:
[0032] Figure 1 An induction cooker made according to the teachings of the present invention is illustrated schematically.
[0033] Figure 2 The circuit diagram shows the converter circuit of the power converter of the induction cooker manufactured according to the first embodiment of the present invention.
[0034] Figure 3 The circuit diagram of the converter circuit for the power converter of the induction cooker manufactured according to the second embodiment of the present invention is shown.
[0035] Figure 4 The circuit diagram of the power converter of the induction cooker manufactured according to the third embodiment of the present invention is shown.
[0036] Figure 5 The circuit diagram of the power converter of the induction cooker manufactured according to the fourth embodiment of the present invention is shown.
[0037] Figure 6 The circuit diagram of the power converter of the induction cooker manufactured according to the fifth embodiment of the present invention is shown. Detailed Implementation
[0038] The invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments are illustrated. However, the invention should not be construed as being limited to the embodiments set forth herein. Throughout the following description, similar reference numerals are used where applicable to denote similar elements, parts, items, or features.
[0039] Figures 1 to 6 An induction heating device made according to the present invention is shown.
[0040] refer to Figure 1 The heating device includes an induction cooktop 1, which includes a cooktop plate 2 and one or more heating zones 4 (shown by dashed lines), which are arranged on the cooktop plate 2 and configured to support corresponding cookware (not shown).
[0041] refer to Figure 1 In the exemplary embodiment shown, each heating zone 4 is associated with at least one inductive load 3 configured to heat a cooking appliance component. Preferably, the inductive load 3 may be arranged below the cooktop 2.
[0042] exist Figure 1 In the example shown, the induction cooktop 1 further includes a user interface 5, which is included, for example, in the control panel of the induction cooktop 1.
[0043] User interface 5 can be configured to allow users to input / set commands to the induction cooktop 1 to execute cooking cycles.
[0044] refer to Figure 1 and Figure 2 The induction cooker 1 further includes a control circuit 10, which is equipped with an electric power converter 100 and an electronic control unit 101.
[0045] The power converter 100 is electrically connected to the inductive load 3 and is configured to supply electrical power to the inductive load 3 itself. It should be understood that the inductive load 3 may include one or more induction coils (not shown). It should also be understood that the inductive load 3 may further include one or more, preferably two, resonant capacitors. Figure 5 and Figure 6 ).
[0046] The electronic control unit 101 is configured to control the power converter 100 in order to regulate the heating power supplied by the inductive load 3 to the cookware component (not shown) during cooking.
[0047] Figure 2 This is a circuit diagram showing an electric power converter 100 according to an embodiment of the present invention.
[0048] exist Figure 2 In the exemplary embodiment shown, the power converter 100 includes an input stage 7, a converter circuit 8, and a converter control module 9 (inverter).
[0049] Input stage 7 is configured to provide a predetermined power supply voltage V1 to converter circuit 8. For example, input stage 7 can be connected to mains voltage (not shown), i.e., AC mains voltage (220 V), and is configured to rectify the mains voltage and output a DC power supply voltage V1 with a predetermined value. The power supply voltage V1 can be obtained, for example, by rectifying one or more phases of a single-phase or three-phase AC mains voltage.
[0050] The converter circuit 8 is configured to receive the power supply voltage V1 provided by the input stage 7 and to supply high-frequency current to the heating coil 3 based on the converter control signal CC.
[0051] The converter control module 9 is configured to control the converter circuit 8. Preferably, the converter control module 9 is configured to provide a control signal CC to the converter circuit 8 in order to control the high-frequency current to be supplied to the inductive load 3.
[0052] refer to Figure 2 In the illustrated embodiment, the converter circuit 8 has an electronic architecture corresponding to that of a half-bridge converter circuit.
[0053] The converter circuit 8 includes a first input terminal 15 and a second input terminal 16. Figure 2 In the example shown, the first input terminal 15 may have a first potential associated with voltage V1, while the second input terminal 16 may be connected to a terminal (ground terminal) having a second potential lower than the first potential (i.e., ground potential (V=0)). The input stage 7 supplies electrical power to the converter circuit 8 via the first input terminal 15 and the second input terminal 16.
[0054] Preferably, in Figure 2 In the example shown, the converter circuit 8 further includes a first output terminal 35, a second output terminal 36, and a third output terminal 37. Figure 2 In the configuration, the first output terminal 35 and the second terminal 36 are connected to the first terminal of the inductive load 3. The third terminal 37 is connected to the second terminal of the inductive load 3.
[0055] According to the present invention, the converter circuit 8 may include a switching circuit provided with one or more converter switches.
[0056] The converter switch is configured to selectively and alternately turn on and off based on the control signal CC generated by the converter control module 9.
[0057] according to Figure 2 In the illustrated embodiment, the converter circuit 8 includes two converter switches.
[0058] like Figure 2 As shown in the exemplary embodiment, the converter circuit 8 includes a first converter switch 11 (high-side switch) and a second converter switch 12 (low-side switch), which are connected in series between a first line 13 and a second line 14, and the first line and the second line are further connected to corresponding input terminals 15 and 16.
[0059] exist Figure 2 In the example shown, the first converter switch 11 and the second converter switch 12 are connected to each other via node 17, which is in turn connected to the third output terminal 37 via line 24.
[0060] Preferably, the first converter switch 11 and the second converter switch 12 may include insulated gate bipolar transistors (IGBTs).
[0061] In this configuration, the first converter switch 11 and the second converter switch 12 can be implemented such that their electrical behavior is controlled by the gate drivers of the converter control module 9, which operate on their respective gates, for example by setting the gate-emitter voltage.
[0062] according to Figure 2 In the example shown, the converter circuit 8 further includes a first anti-parallel diode 18 and a second anti-parallel diode 19. The first anti-parallel diode 18 is connected to the first converter switch 11 in reverse parallel.
[0063] The second anti-parallel diode 19 is connected to the second converter switch 12 in reverse parallel.
[0064] It should be understood that an insulated gate bipolar transistor (IGBT) can conduct current only in the forward direction; the first anti-parallel diode 18 and the second anti-parallel diode 18, which are connected in reverse parallel with the first converter switch 11 and the second converter switch 12, are configured to supply negative current to the load through node 23 and protect the load from damage caused by current flowing in the reverse direction.
[0065] Furthermore, it should be understood that the present invention is not limited to the converter switches 11, 12 including insulated gate bipolar transistors (IGBTs), but according to different embodiments of the present invention, alternatively or additionally, the converter switches 11, 12 may include field-effect transistors, such as metal oxide semiconductor field-effect transistors (MOSFETs) as MOS controlled thyristors (MCTs) or static induction thyristors (SITs).
[0066] The first converter switch 11 and the second converter switch 12 are configured to alternately turn on and off, wherein the turning on of converter switch 11 and the turning off of converter switch 12 occur simultaneously, and vice versa.
[0067] Preferably, the first converter switch 11 and the second converter switch 12 can be alternately turned on and off.
[0068] It should be understood that the symmetrical on-time of the first converter switch 11 and the second converter switch 12 can maximize the output power delivered to the inductive load 3 connected to the converter circuit 8.
[0069] However, it should also be understood that the first converter switch 11 and the second converter switch 12 can also be controlled based on asymmetrical on and off.
[0070] like Figure 2As shown, the converter circuit 8 further includes a buffer circuit 20.
[0071] according to Figure 2 In an exemplary embodiment, the buffer circuit 20 includes two buffer capacitors 21 and 22.
[0072] Buffer capacitors 20 and 21 are connected in series between the first line 13 and the second line 14 via node 23, which is then connected to node 17 and the third output terminal 37 via line 24.
[0073] Specifically, the voltage V1 at the first line 13 is approximately equal to the voltage at the first input terminal 15; the voltage at the second line 14 is approximately equal to the voltage at the input terminal 16; and the voltages at lines 24 and the third output terminal 37 are equal to the voltage V3 at node 23. It should be understood that the voltage V3 at node 23 is controlled by the switching modes of the first converter switches 11 and 12 (controlled using a gate driver), the buffer circuit 20, and the power supply voltage V1 provided at the first input terminal 15.
[0074] Preferably, the first buffer capacitor 21 and the second buffer capacitor 22 may have a capacitance ranging from about 10 nanofarads (10⁻⁹ farads) to about 47 nanofarads (nF), preferably from about 10 nanofarads to about 33 nanofarads (nF).
[0075] According to the present invention, the buffer circuit 20 further includes a damping circuit 38.
[0076] according to Figure 2 The exemplary embodiment shown includes a damping circuit 38 comprising a high-side damping circuit 25 and a low-side damping circuit 26.
[0077] The high-side damping circuit 25 is connected in parallel to the buffer capacitor 21 and in parallel to the first converter switch 11.
[0078] The low-side damping circuit 26 is connected in parallel to the buffer capacitor 22 and in parallel to the second converter switch 12.
[0079] As in Figure 2 As shown in the exemplary embodiment, the damping circuit 25 includes a damping capacitor 27, a damping resistor 28, and a damping unidirectional current conduction device, which is preferably a damping diode 29.
[0080] according to Figure 2 In the exemplary embodiment shown, the damping capacitor 27 and the damping diode 29 are connected in series between line 13 and line 24.
[0081] exist Figure 2In this circuit, the damping diode 29 includes a cathode connected to the damping capacitor 27 and an anode connected to node 23 via line 24. The damping resistor 28 is connected in parallel to the damping capacitor 27.
[0082] It should be understood that the present invention is not limited to the series connection of the damping diode 29 and the damping capacitor 27 in the above order, but such series connection can be reversed.
[0083] Referring to the low-side damping circuit 26, the low-side damping circuit includes a damping capacitor 30, a damping resistor 31, and a unidirectional current conduction device, which is preferably a damping diode 32.
[0084] Damping capacitor 30 and damping diode 32 are connected in series between line 24 and line 14.
[0085] exist Figure 2 In an exemplary embodiment, the damping diode 32 includes an anode connected to the damping capacitor 30 and a cathode connected to the node 23 via line 24. A damping resistor 31 is connected in parallel to the damping capacitor 30.
[0086] It should be understood that the present invention is not limited to the series connection of the damping diode 32 and the damping capacitor 30 in the above order, but such series connection can be reversed.
[0087] Preferably, the first damping capacitor 27 and the second damping capacitor 30 may have a capacitance between about 1 nanofarad and about 1 microfarad, preferably between about 30 nanofarads and about 500 nanofarads.
[0088] Preferably, the first damping resistor 28 and the second damping resistor 31 may have a resistance between about 0.2 ohms and about 100 ohms, preferably between about 0.8 ohms and 20 ohms.
[0089] Conveniently, the first buffer capacitor 21 and the second buffer capacitor 22 of the buffer circuit 20 are connected in parallel to the first converter switch 11 and the second converter switch 12, respectively, and are connected to each other through node 23. This allows the first converter switch 11 and the second converter switch 12 to perform soft switching, which mitigates the large voltage transients following rapid switching, thereby helping to protect the converter circuit 8 from damage. In other words, soft switching conveniently reduces losses on the one hand and protects the circuit from damage on the other.
[0090] The applicant has discovered that the buffer capacitors 21 and 22 implement "zero-voltage switching". In detail, the tests performed by the applicant demonstrate that, without the buffer capacitors 21 and 22, hard switching exists during the turn-off period. Under hard switching conditions, the switch must withstand high voltage and high current, resulting in high power dissipation on the power switch.
[0091] More specifically, by utilizing buffer capacitors 21 and 22, the voltage remains constant during the turn-off period, resulting in high current but low voltage, which significantly reduces power dissipation on the switching device. The technical effect obtained by connecting the high-side damping circuit 25 and the low-side damping circuit 26 in parallel to the buffer capacitors 21 and 22, as well as the first switching device 11 and the second switching device 12, is to functionally decouple both damping circuits 25 and 26 from overshoot mitigation caused by the first buffer capacitor 21 and the second buffer capacitor 22.
[0092] In practice, the high-side damping circuit 25 and the low-side damping circuit 26 operate based on a voltage range corresponding to the (maximum) difference between the overshoot / undershoot voltage and the power supply voltage V1 (level / ground) provided via the first input terminal 15 and the second input terminal 16, while the first buffer capacitor 21 and the second buffer capacitor 22 can be configured to operate based on the power supply voltage V1. In this way, low-voltage damping capacitors 27 and 30 can be selected for both the high-side damping circuit 25 and the low-side damping circuit 26, thereby conveniently reducing the size and cost of the high-side damping circuit and the low-side damping circuit.
[0093] It is important to note that the voltage across the buffer capacitors 21 and 22 and the damping circuits 25 and 26 is the same (supply voltage V1 + overshoot / undershoot). The advantage lies within the damping network: the damping capacitors 27 and 30 and the damping resistors 28 and 31 act only on the overshoot / undershoot voltage, while the damping diodes withstand the supply voltage V1. More specifically, both damping circuits 25 and 26 operate at their maximum voltage (supply voltage V1 + overshoot voltage, which is much smaller than the supply voltage V1, so ignoring the overshoot is acceptable), the same as that of the power switches 11 and 12 and the buffer capacitors 21 and 22.
[0094] Inside the damping network, during the idle state (diode reverse, first stage), diodes 29 and 32 will withstand the maximum voltage, and in the same stage, the voltage applied to capacitors 27 and 30 and resistors 28 and 31 is 0 V.
[0095] During the second and third stages of the damping network, the maximum voltage applied to capacitors 27 and 30 and resistors 28 and 31 is only the overshoot voltage (which is reached during the transition between the second and third stages).
[0096] The overshoot voltage is much smaller than V1, so low-voltage capacitors can be used. The advantage is that ceramic capacitors suitable for high frequencies can be used, and larger capacitances can be achieved with small package sizes and low-cost components. In practice, high-voltage ceramic capacitors are available, but they are larger and more expensive than low-voltage ceramic capacitors.
[0097] Furthermore, the first buffer capacitor 21 and the second buffer capacitor 22 advantageously enable soft switching of the first converter switch 11 and the second converter switch 12. Conveniently, the high-side damping circuit 25 and the low-side damping circuit 26 may include passive electronic components. Conveniently, the high-side damping circuit 25 and the low-side damping circuit 26 can achieve ringing reduction through the damping circuits 25 and 26 themselves.
[0098] Conveniently, the first damping capacitor 27 and the second damping capacitor 30 are implemented as low-voltage capacitors, which are configured to withstand the maximum overshoot voltage and the maximum undershoot voltage, respectively.
[0099] The following will refer to Figure 2 The operation of the induction cooker 1 having the above configuration is described.
[0100] During operation, the converter control module 9 selectively controls the first converter switch 11 and the second converter switch 12 so that they are alternately turned on and off based on a frequency that depends on a predetermined current frequency.
[0101] exist Figure 2 In the process, when the first converter switch 11 (high-side switch) is turned on and the second converter switch 12 (low-side switch) is turned off, the current flowing through the heating coil induction and the load resistor connected to the load 3 of the power converter 100 can increase.
[0102] When the first converter switch 11 is turned off, current can flow through the heating coil induction 3 (load resistor) and the buffer circuit 20, thereby reducing undershoot voltage and ringing.
[0103] The same considerations apply when the first converter switch 11 is off and the second converter switch 12 is on, and vice versa.
[0104] After such a switching operation, the voltage at the second output terminal 37 gradually decreases / increases through the first buffer capacitor 21 and the second buffer capacitor 22 to the ground / power supply voltage V1, and then undershoots / overshoots.
[0105] The timing of the gate driver and the dimensions of the first damping capacitor 27, the first damping diode 29, the first damping resistor 28, the second damping capacitor 30, the second damping diode 32, and the second damping resistor 31 can sufficiently reduce ringing.
[0106] The operation of the damping circuit 38 of the converter circuit 8 can be described by assuming three phases depending on the state / operation of the damping diodes 29 and 32 and the state / operation of the damping capacitors 27 and 30.
[0107] When the damping diode 29 or 32 is reverse biased and discharges relative to the damping capacitor 27 or 31, the damping circuit 38 is in the first stage.
[0108] In the first stage, damping resistors 28 and 31 hold damping capacitors 27 and 30 at 0 V, while damping diodes 29 and 32 withstand all the power supply voltage V1. Specifically, damping diode 32 is turned off.
[0109] When the first converter switch 11 or the second converter switch 12 is turned off, resulting in a voltage change at node 23, the damping circuit 38 remains in the first stage.
[0110] It should be understood that when the first damping diode 29 is in a reverse bias state and the damping circuit 38 is in a stable state where the first damping capacitor 27 is substantially discharged, there is essentially no current flowing through the first damping resistor 28, and the voltage at the first damping capacitor 27 can be zero volts.
[0111] Conversely, when the second damping diode 32 is in a reverse-biased state and the damping circuit 38 is in a stable state where the second damping capacitor 30 is essentially discharged, virtually no current can flow through the second damping resistor 31, and the voltage at the second damping capacitor 30 can be zero volts.
[0112] The damping circuit 38 conveniently reduces ringing through subsequent iterations between the second and third stages.
[0113] When damping diodes 29 or 32 are forward biased, damping circuit 38 is in the second stage. Specifically, damping circuit 38 enters the second stage when the voltage at node 23 completes the transition to the supply voltage or ground voltage, and then either overshoots or undershoots. For example, after transitioning from a high voltage V1 to zero voltage, node 23 will undershoot, falling below 0 V.
[0114] In this case, the low-side damping circuit 26 connected in parallel with the second converter switch 12 changes from the first stage to the second stage, wherein the damping diode 32 is forward biased and the damping capacitor 30 is charged at an undercharge voltage level.
[0115] Conversely, after the transition from 0 V to a high voltage V1, node 23 will overshoot above the supply voltage V1, and the high-side damping circuit 25, connected in parallel with the first converter switch 11, will transition from the first stage to the second stage and charge the damping capacitor 27. During the second stage, the first damping diode 29 will be forward biased, and the first damping capacitor 27 will be charged by a momentary overshoot voltage higher than V1.
[0116] When damping diode 29 or 32 is reverse biased and the corresponding damping capacitors 27 and 30 are charged, damping circuit 38 is in its third stage. Specifically, in this stage, damping capacitor 32 is turned off.
[0117] Once the damping capacitor 27 is charged to the maximum overshoot voltage, node 23 oscillates, thereby biasing the damping diode at the reverse voltage.
[0118] In this state, the damping circuit 38 moves to the third stage, in which the damping capacitor 27 is charged and the damping diode 29 is reverse-biased. During the third stage, the damping resistor 28 discharges the damping capacitor 27, thereby dissipating the stored energy. Specifically, the first damping diode 29 is reverse-biased, and the first damping capacitor 27 is discharged by the first damping resistor 28.
[0119] After the completion of the second and third stages, the instantaneous overshoot voltage in the subsequent second stage is less than the instantaneous overshoot voltage in the previously completed second stage.
[0120] It should be understood that during the voltage oscillation at node 23, the damping circuit 38 will repeat the second and third stages until the ringing is small enough to prevent the damping diode 29 from being forward biased.
[0121] The damping circuit 38 alleviates ringing by iterating between the second and third stages of the three operating phases, wherein: during the dead time interval after the first converter switch 11 and the second converter switch 12 are turned off and subsequently the first converter switch 11 is turned on; buffer capacitors 21 and 22 supply current to node 23 until the anti-parallel diode 18 of the first converter switch 11 is forward biased, and until the voltage V3 at node 23 reaches the supply voltage V1 and ringing at node 23 begins.
[0122] When the voltage oscillation at node 23 ends and the buffer circuit 20 is in the third stage, the damping resistor 28 causes the damping capacitor 27 to discharge completely, thereby returning the damping circuit 38 to the first stage.
[0123] The damping circuit 38 is in the first stage before a new transition to the same polarity, so that the function is ready again.
[0124] In the third stage, the damping circuit 38, the first damping resistor 28 / the second damping resistor 31 advantageously dissipate only a small amount of electrical power because the electrical energy stored in the first damping capacitor 27 / the second damping capacitor 30 is very small (which is essentially related to overshoot / undershoot voltage).
[0125] In the third stage, when the instantaneous overshoot voltage or instantaneous undershoot voltage is too small to forward bias the first damping diode 29 or the second damping diode 32 respectively, the damping circuit 38 stops the iteration between the second and third stages.
[0126] After the overshoot, the damping circuit 38 reduces ringing through subsequent iterations between the second and third stages, in which the damping diode 32 is forward biased and the damping capacitor 30 is charged with a momentary undershoot voltage lower than the supply voltage.
[0127] The damping circuit 38 reduces ringing after the switching of the first converter switch 11 and / or the second converter switch 12, and the first buffer capacitor 21 and the second buffer capacitor 22 are configured to reduce losses on the first converter switch 11 and / or the second converter switch 12.
[0128] The power converter manufactured according to the present invention has many advantages: the snubber capacitor used for soft-switching assistance maintains low losses in the IGBT during turn-off, while the damping network reduces maximum overshoot and subsequent ringing time. The capacitor in the damping network requires a low maximum rated voltage: it should only withstand overshoot / undershoot voltages. Power dissipation on the resistor is low: during overshoot / undershoot, it should only dissipate the energy stored in the capacitor. Reduced ringing amplitude and time will decrease EMC emissions measured according to standard tests, allowing for a competitive advantage using simpler and cheaper input filters.
[0129] Figure 3 The illustrated embodiment relates to an electric power converter 110, which is similar to... Figure 2 The power converter 100 is shown, and where possible, the power converter parts will be identified with the same reference numerals as the corresponding parts marked power converter 110.
[0130] The power converter 110 differs from the power converter 100 in that it includes two converter circuits 8 that are symmetrically connected to each other to form a “full bridge” circuit (topology) connected to the inductive load 3.
[0131] In detail, according to Figure 3 In the illustrated embodiment, the first output terminal 35 of the first converter circuit 8 is connected to the first output terminal 35 of the second converter circuit 8, the second output terminal 36 of the first converter circuit 8 is connected to the second output terminal 36 of the second converter circuit 8, the third output terminal 36 of the first converter circuit 8 is connected to the first terminal of the inductive load 3, and the third output terminal 36 of the second converter circuit 8 is connected to the second terminal of the inductive load 3.
[0132] Figure 4 The illustrated embodiment relates to an electric power converter 200, which differs from the electric power converter 100 in that it includes three converter circuits 8, which are controlled by corresponding converter control modules 9 and provide power to as many induction coils 3 as possible.
[0133] In detail, Figure 4 In the exemplary embodiment shown, the power converter 200 includes three converter circuits 8 configured to supply power to three inductive loads 3. Specifically, in Figure 4 In an exemplary embodiment, each inductive load 3 includes a first terminal and a second terminal. The first terminal is connected to the third output terminal 37 of the corresponding converter circuit 8, and the second terminal is connected to the second terminal of the other inductive load 3. Terminals 35 and 36 of the converter circuit are open-circuited.
[0134] This invention helps reduce EMC conducted emissions according to CISPR 14-1 standards or equivalents. The buffer circuit is configured to provide soft-switching assistance (to maintain low IGBT losses). Furthermore, compared to existing designs and the eventual external harness filter, this circuit allows for the use of cheaper components to reduce emissions at critical frequencies.
[0135] Reducing ringing amplitude and time will decrease EMC emissions measured according to standard tests, allowing for a competitive advantage using simpler and cheaper input filters.
[0136] In detail, the snubber capacitor used for soft turn-off assistance maintains low losses in the IGBT during turn-off, while the damping network reduces maximum overshoot and subsequent ringing time. The capacitor in the damping network requires a low maximum rated voltage: it should only withstand overshoot voltage. Low power dissipation on the resistor: during overshoot, it should only dissipate the energy stored in the capacitor.
[0137] Clearly, changes and modifications can be made to the induction cooktop without departing from the scope of this invention.
[0138] Figure 5 The illustrated embodiment relates to an electric power converter 300, which is connected to... Figure 2 The power converter 100 of the illustrated embodiment differs in that it includes a converter circuit 8 with a “single switch” topology and a single buffer circuit 26.
[0139] also, Figure 5 The power converter 300 shown is Figure 2 The difference in the power converter 100 of the illustrated embodiment is that the converter circuit 8 does not have buffer capacitors 21 and 22.
[0140] More in detail, Figure 5 In an exemplary embodiment, the converter circuit 8 includes a single converter switch 12 connected to the input terminal 16. Figure 2 (The low-side switch). Converter switch 12 is connected to node 17, which in turn is connected to output terminal 37 via line 24.
[0141] according to Figure 5 In the example shown, converter circuit 8 further includes an anti-parallel diode 19.
[0142] The converter circuit 8 is provided with a buffer circuit 20 excluding the buffer capacitor 22.
[0143] according to Figure 5 In the example shown, the buffer circuit 20 includes a damping circuit 26, which is provided with a damping capacitor 30, a damping resistor 31, and a unidirectional current conduction device, which is preferably a damping diode 32.
[0144] Figure 6 The illustrated embodiment relates to an electric power converter 400, which is connected to... Figure 5 The difference in the power converter 300 of the illustrated embodiment is that the power converter includes a converter circuit 8 with a buffer capacitor 22.
[0145] More in detail, Figure 6 In an exemplary embodiment, the converter circuit 8 includes a single converter switch 12 connected to the input terminal 16. Figure 2 (The low-side switch). Converter switch 12 is connected to node 17, which in turn is connected to output terminal 37 via line 24.
[0146] according to Figure 6 In the example shown, the converter circuit 8 further includes an anti-parallel diode 19. The converter circuit 8 is provided with a buffer circuit 20 that does not include a buffer capacitor 22.
[0147] according to Figure 6 In the example shown, the buffer circuit 20 includes a damping circuit 26 comprising a damping capacitor 30, a damping resistor 31, and a unidirectional current conduction device, preferably a damping diode 32. The damping circuit 26 is connected in parallel to the buffer capacitor 22 and also in parallel to the converter switch 12.
Claims
1. An induction heating cooker (1), the induction heating cooker comprising at least one induction load (3) and at least one power converter (100)(110)(200)(300)(400), the at least one power converter being configured to supply electrical power to the induction load (3), and comprising at least one converter circuit (8) and at least one converter control module (9), the at least one converter control module being configured to control the converter circuit (8) via at least one control signal (CC) to regulate the electrical power supplied to the induction load, in, The converter circuit (8) includes: At least one switching circuit, wherein the at least one switching circuit is provided with at least one converter switch (11) (12), the at least one converter switch being controlled by the control signal (CC) and connected to the first terminal of the inductive load (3) via converter line (24), and At least one buffer circuit (20) includes at least one damping circuit (25) (26) which is connected in parallel to the converter switch (11) (12).
2. The induction heating stove according to claim 1, wherein, The damping circuit (25) (26) includes a damping capacitor (27) (30), a damping resistor (28) (31), and a damping unidirectional current conduction device (29) (32).
3. The induction heating stove according to claim 2, wherein, The buffer circuit (20) includes at least one buffer capacitor (21) (22).
4. The induction heating stove according to claim 3, wherein, The damping circuits (25) and (26) are connected in parallel to the buffer capacitors (21) and (22).
5. The induction heating cooker (1) according to any one of the preceding claims, wherein, The switching circuit is provided with a pair of converter switches (11) (12), which are selectively controlled by the control signal (CC) and connected in series with each other through the first node (17), which is connected to the first terminal of the inductive load (3) through the converter line (24). The buffer circuit (38) is provided with a pair of buffer capacitors (21) (22), which are connected in series with each other through a second node (23), which is connected to the converter line (24). And a pair of damping circuits (25) and (26), which are connected in parallel to both the buffer capacitor (21) and (22) and the converter switch (11) and (12).
6. The induction heating stove according to claim 5, wherein, The pair of converter switches (11) (12) includes a high-side switch (11) and a low-side switch (12), which are connected in series between a first power supply line with a high voltage and a second power supply line with a low voltage. The high-side switch and the low-side switch are connected to each other through the first node (17). The buffer circuit (20) includes a high-side buffer capacitor (21) and a low-side buffer capacitor (22), which are connected in series with each other and connected in parallel with the high-side switch (11) and the low-side switch (12), respectively. The pair of damping circuits (25) (26) includes a high-side damping circuit (25) and a low-side damping circuit (26), the high-side damping circuit being connected in parallel to the high-side switch (11) and the high-side buffer capacitor (21), and the low-side damping circuit being connected in parallel to the low-side switch (12) and the low-side buffer capacitor (22).
7. The induction heating stove according to claim 2, wherein, The damping capacitors (27) and (30) and the corresponding unidirectional current conduction devices (29) and (32) are connected in series between the converter line (24) and the first power supply line (13) or the second power supply line (14).
8. The induction heating stove according to claim 2 or 7, wherein, The damping resistors (28) and (31) and the corresponding damping capacitors (27) and (30) are connected in parallel to each other.
9. The induction heating stove according to claim 2, wherein, The damped unidirectional current conduction device (29) (32) includes a first terminal connected to the corresponding damping resistor (28) (31) and a second terminal connected to the converter line (24).
10. The induction heating stove according to claim 1, wherein, The switching circuit consists of only a single converter switch.
11. The induction heating stove according to claim 1, wherein, The power converter (100) is a half-bridge and includes a single converter circuit (8) having output terminals (35, 36) connected to the load.
12. The induction heating stove according to claim 1, wherein, The power converter is a full-bridge converter and includes two converter circuits (8) having output terminals (35) (36) connected to each other respectively, and converter terminals (37) connected to the corresponding first and second terminals of the inductive load (3).
13. The induction heating stove according to claim 11, wherein, The power converter includes three converter circuits (8) connected to corresponding inductive loads (3); each converter circuit (8) has no output terminal (35) (36) and is connected to the first terminal of the inductive load (3) via the converter terminal (37); the second terminal of the inductive load (3) is connected to the second converter terminal (37) of the inductive load.
14. The induction heating cooker according to any one of the preceding claims, wherein, The converter switches (11) and (12) are insulated gate bipolar transistors (IGBTs) and / or field-effect transistors with corresponding anti-parallel diodes (18) and (19).
15. The induction heating stove according to claim 2, wherein, The damping capacitors (27) and (30) have a capacitance ranging from about 1 nanofarad to about 1 microfarad, preferably from about 30 nanofarads to about 500 nanofarads.
16. The induction heating stove according to claim 2, wherein, The damping resistors (28) and (31) have a resistance between about 0.2 ohms and about 100 ohms, preferably between about 0.8 ohms and 20 ohms.