KR20080093318A - Induction heating circuit - Google Patents

Abstract

An induction heating circuit is provided to increase power output and to reduce current consumption by using resonant components. An induction heating circuit(200) includes a voltage source(202), a transformer(204), first and second capacitors(206,210), an inductor(208), and a transistor(211). The transformer includes a first heating coil(212) as a first coil and a metal vessel(213) as a second coil. The first heating coil is adjacent to an object to heat. The first capacitor is a resonant component and is connected to the transformer in parallel. The second capacitor is connected to the transistor in parallel. The inductor is an additional heating coil and is connected to the first heating coil and the first capacitor.

Description

Induction Heating Circuits {INDUCTION HEATING CIRCUIT}

FIG. 1 illustrates an induction heating cooker having a metal bowl and a heating coil which together form a transformer.

FIG. 2 is a circuit diagram illustrating a simple equivalent circuit for the heating cooker and the metal container as one transformer.

3 is a circuit diagram illustrating a half-bridge type circuit that can be used as a heating circuit.

4 is a circuit diagram illustrating a circuit of a Class-E converter type as an induction heating circuit.

5A through 5C are circuit diagrams illustrating an induction heating circuit according to embodiments of the present invention.

FIG. 6 is a partial view illustrating a rice cooker having a first heating coil provided at the bottom of the metal container and a second heating coil provided around the side of the metal container, according to an embodiment of the present invention.

7A-7C are circuit diagrams illustrating equivalent circuits associated with the cooker of FIG. 6.

FIG. 8 is a circuit diagram illustrating an equivalent circuit for the heating coil and metal container of FIG. 6.

9 is a circuit diagram showing a heating coil and a metal container.

10 is a circuit diagram illustrating a heating circuit according to the prior art.

FIG. 11 is a graph illustrating an operating waveform of the circuit of FIG. 10.

12 is a circuit diagram illustrating a heating circuit according to another embodiment of the present invention.

13 is a circuit diagram illustrating circuits used in a rice cooker according to the prior art.

14 is a waveform diagram of a simulation with the circuits of FIG. 13.

15 is a circuit diagram illustrating circuits that may be used to heat a cooker in accordance with one embodiment of the present invention.

16 is a waveform diagram of a simulation with the circuits of FIG. 15.

The present invention relates to an induction heating circuit.

Induction heating circuits can be used in many electrical devices. One such use is in induction heated cooking utensils, such as rice cookers. The cooker has a housing surrounding the metal container, a heating coil, and a ceramic provided between the heating coil and the metal container.

FIG. 1 illustrates an induction heating cooker having a metal bowl and a heating coil which together form a transformer. The turns ratio is n: 1 (n is the number of coil turns). 2 is a circuit diagram illustrating a simple equivalent circuit for the heating cooker and metal container as one transformer. At this time, R 'is a resistance value of the metal container. The heating coil corresponds to the primary coil side of the transformer, and the metal container corresponds to the secondary coil side of the transformer. An alternating current (AC) voltage is applied from the power supply circuit to the heating coil. The alternating voltage is transferred to a secondary coil, ie the metal container. The magnitude of the alternating voltage delivered to the secondary coil side is reduced to 1 / n. Since the metal container has a low resistance value, a large current flows through the metal container. This current is reduced to 1 / n in the primary coil, ie the heating coil.

There are several methods of applying alternating current to the primary coil of the transformer, ie the heating coil. Such circuits generally include switching semiconductor elements (transistors or switches), or capacitors and inductors. Semiconductor devices operate in switch mode, not in linear mode.

3 is a circuit diagram illustrating a half-bridge type circuit 150 that can be used as a heating circuit. The circuit 150 includes a voltage source 152, transistors 150 connected in a half bridge configuration, and a blocking capacitor 158 for blocking direct current. Resistor R 'represents the secondary coil side of transformer 156, i.e., the resistance of the metal container. Since the voltage applied to the switching element does not greatly exceed the DC link voltage, an element having a low breakdown voltage can also be used. The output voltage is symmetrical in terms of the polarity of the voltage. One disadvantage of such half bridge type circuits is that they require two transistors and a complex drive circuit to control the switching elements. Because of the low output voltage, the required number of turns of the coil is small and the current of the primary coil is large.

4 is a circuit diagram illustrating a circuit 180 of a Class-E converter type as an induction heating circuit. The circuit 180 includes a voltage source 182, a transformer 184, a transistor 186, and a capacitor 188 connected in parallel with the transistor 186. Since the circuit 180 uses only one transistor, the manufacturing cost is low. The output voltage is substantially fixed and greater than the output voltage of the half bridge type circuit. Since the transistor 186 sees a voltage much higher than the DC connection voltage, it needs to have a high breakdown voltage.

It is an object of the present invention to provide an induction heating circuit.

The present invention claims all rights of US Provisional Application No. 60 / 792,154, filed April 14, 2006, which is incorporated herein by reference.

The heating circuit according to an embodiment of the present invention includes a first heating coil provided around an object to be heated. A first capacitor is provided in parallel with the first heating coil, wherein the first capacitor is a resonant element. An inductor is coupled to the first heating coil and the first capacitor.

According to an embodiment, a second heating coil is coupled to said first heating coil, said second heating coil comprising a heating coil provided around said conductive container. A switch is coupled to the inductor and a second capacitor is provided in parallel to the switch. The heating circuit includes a sensor for detecting whether the slope of the current has a negative value, and a gate driver configured to output a control signal for energizing or disconnecting the switch.

Induction heating circuit according to an embodiment of the present invention, the first heating coil provided in the lower portion of the conductive container for heating the conductive container, the second heating coil provided around the body of the conductive container, and the first At least one capacitor defining a resonant loop with one heating coil, the second heating coil, or both.

According to an embodiment, the induction heating circuit further comprises first, second and third nodes, wherein the first capacitor and the first heating coil are provided between the first and second nodes, and the second A heating coil is provided between the second and third nodes. The heating circuit includes a second capacitor, one end of which is connected to the first node and the other end of which is connected to the third node.

According to an embodiment, said induction heating circuit further comprises first, second, third and fourth nodes, wherein said first heating coil is provided between said first and second nodes, and said second heating A coil is provided between the second node and the third node. One side of the first capacitor is connected to the first node and the other side is connected to the third node. The second capacitor has one side connected to the second node and the other side connected to the fourth node. A switch is provided between the third node and the fourth node, wherein the third node is located between the second heating coil and the switch.

According to an embodiment, said induction heating circuit comprises first, second, third and fourth nodes. A first capacitor is connected to the second node, one side of which is located between the first and second heating coils, and the other side of the first capacitor, to the fourth node. The second capacitor is connected at one end thereof to the third node and at the other end thereof to the fourth node. A switch is provided between the third and fourth nodes.

The present invention relates to an induction heating circuit. 5A is a circuit diagram illustrating an induction heating circuit 200 according to an embodiment of the present invention. The heating circuit 200 is associated with a class-two converter type circuit having one or more resonant components, ie a capacitor and an inductor. These resonant elements can increase the power output and allow the circuit to operate using smaller currents.

The heating circuit 200 may include a voltage source 202, a transformer (or heating coil) 204, a first capacitor 206, an inductor 208, and a second capacitor coupled in parallel to the transformer (or heating coil) 204. Two capacitors 210 and a transistor 211. The second capacitor 210 is connected in parallel to the transistor 211. The first capacitor 206 is a resonant element. The transformer (or heating coil) 204 has a first heating coil 212 as a primary coil and a metal container 213 as a secondary coil. The inductor 208 may be an additional heating coil. Here, in the present embodiment, the heating coil is intended to describe what is viewed from the primary coil side of the transformer, and the term 'heating coil' may be used in a part that can replace the term 'transformer'.

5B is a circuit diagram illustrating a circuit diagram of an induction heating circuit 230 according to an embodiment of the present invention. The heating circuit 230 includes a first capacitor 232 connected in parallel to the heating coil 234, and a second capacitor 236 connected in parallel to the combination of the heating coil 234 and the inductor 238. . The heating coil 234 is part of any transformer. The switch 240 is connected to a node between the second capacitor 236 and the inductor 238. The switching 240 may be an insulated gate bipolar transistor (IGBT) or a bipolar junction transistor (BJT). Diode 242 is connected in anti-parallel to the switch 240. The first and second capacitors 232 and 236 are resonant capacitors. This configuration makes it possible to use capacitors with low voltage ratings as the first and second capacitors 232, 236.

5C is a circuit diagram illustrating a circuit diagram of an induction heating circuit 250 according to another embodiment of the present invention. The heating circuit 250 includes a first capacitor 252 connected in parallel to a heating coil 254, and a second capacitor 256 connected in parallel to a combination of the heating coil 254 and the inductor 258. . The inductor 258 is provided on top of the heating coil 254 in this embodiment, ie closer to the positive rail of the transformer. The switch 260 is connected to a node common to the first capacitor 252, the second capacitor 256, and the heating coil 254. The switching 260 may be an insulated gate bipolar transistor or a bipolar junction transistor. Diode 262 is connected in anti-parallel to switch 260. The first and second capacitors 252 and 256 are resonant capacitors.

6 is a rice cooker having a first heating coil 302 provided at the bottom of the metal container 304 and a second heating coil 306 provided around the side surface of the metal container 304, according to one embodiment of the invention. A partial diagram illustrating 300.

FIG. 7A is a circuit diagram illustrating an equivalent circuit 301 related to the rice cooker 300 of FIG. 6. The circuit 301 may include a voltage source 312, a first transformer (ie, a first heating coil) 314, a first capacitor 316, and a second transformer coupled in parallel with the first heating coil 314. That is, the second heating coil 318, the second capacitor 320, and the transistor 321 are included. The capacitors 316 and 320 are resonant elements.

The second heating coil 318 is wrapped around the metal container 304, so that the energy consumed by the heating coil, that is, heat generated by the parasitic resistance component of the heating coil, can be more efficiently used. The capacitor 320 is provided to be parallel to the transistor 321. Alternatively, the first heating coil 314 may be a heating coil that surrounds the metal container, and the second heating coil 318 may be a heating coil provided under the metal container.

FIG. 7B is a circuit diagram illustrating another equivalent circuit 330 associated with the cooker 300 of FIG. 6. The circuit 330 includes a first capacitor 332 coupled in parallel to a first heating coil 334, and a second capacitor coupled in parallel to the combination of the first and second heating coils 334, 338. 336). The capacitors and heating coils are resonant elements. The switch 340 is connected to a node between the second capacitor 336 and the second heating coil 338. Diode 342 is connected in anti-parallel with respect to switch 340. The capacitors and heating coils are resonant elements forming a resonant loop.

FIG. 7C is a circuit diagram illustrating another equivalent circuit 350 associated with the cooker 300 of FIG. 6. The circuit 350 includes a first capacitor 352 coupled in parallel to a first heating coil 354, and a second capacitor coupled in parallel to the combination of the first and second heating coils 354, 358. 356). The second heating coil is provided closer to the positive terminal than the upper portion of the first heating coil, that is, the first heating coil 354 in this embodiment. The switch 360 is connected to a common node of the first capacitor 352, the second capacitor 356, and the first heating coil 354. Diode 362 is connected in anti-parallel to the switch 360.

Some advantages of the circuit 301 are as follows. The circuit 301 shows low peak current and RMS current even at relatively high output power. Such circuits may use cheaper transistors. The conduction loss and switching loss of the transistor are reduced.

FIG. 8 is a circuit diagram illustrating an equivalent circuit for the heating coil and metal container of FIG. 6. L _m represents the magnetizing inductance on the primary coil side. Transformer 352 can be viewed as an ideal n: 1 transformer with infinite magnetization inductance. R 'represents the resistive component of a metal container. The resistor R 'looks as if R = n * n * R' when viewed from the primary coil side. Accordingly, the heating coil and the metal container may be treated like the circuit 360 in which the inductor L _m and the resistor R are connected in parallel, as shown in FIG. 9.

10 is a circuit diagram illustrating a heating circuit 400 according to the prior art. The heating circuit 400 is a class-two type circuit and includes a voltage source 402, an inductor L _m , a resistor R, a transistor 404, a diode 406 and a capacitor 408. The inductor L _m and the resistor R are connected in parallel between the voltage source 402 and the node 410. The transistor 404 and capacitor 408 are connected in parallel between the node 410 and ground. The capacitor 408 is a resonant element. The diode 406 may be a body diode of the transistor 404 or may be a separate diode.

Looking at the operation, the switch voltage V _sw is not deep negative. The diode 410 prevents the switch voltage V _sw from having a large negative value. FIG. 11 is a graph illustrating an operating waveform of the circuit 400 of FIG. 10. The circuit is an induction heating circuit of the Class-E converter type. Since the average voltage across the inductor L _m should be 0 in the steady state of the repetitive operation, the average voltage value of the switch voltage V _sw is equal to the DC voltage V _DC . If the resistor R is not too small, the switch can be turned on while the diode conducts current.

At time t0, the inductor current I _LM becomes zero and the diode stops conducting. From time t0 to t1, the inductor current I _LM increases linearly with a slope of V _dc / L _m . At time t1, the switch Sw is turned off. From time t1 to t2, the inductor current I _LM increases and reaches a maximum at time t2. From time t2 to t3, the inductor current I _LM decreases and reaches zero at time t3. Between times t3 and t4, the inductor current I _LM decreases and reaches a negative peak at time t4. Between time t4 and t5 the inductor current I _LM increases. At time t5, the switch voltage V _SW becomes zero and the diode starts to conduct inductor current. Between times t5 and t6, the inductor current I _LM increases linearly with a slope of V _DC / L _m . At time point t6, the initial state t0 is returned.

When the voltage V _DC is 0V, the voltage V _DC -V _SW is the output voltage. The output voltage is reduced to 1 / n. A large current flows through the secondary coil of the transformer (ie the heating coil), ie the metal container. If such a current is too large, the resonant circuit loses much of its energy, and the switch voltage VSW does not return to zero at time t5. In this case, the switch will not turn on at zero volts and will result in significant switching losses.

12 is a circuit diagram illustrating a heating circuit according to another embodiment of the present invention. The resonant circuit including the _capacitor C _r1 and the inductance L _m1 vibrates at the same frequency as the switching frequency of the switch Sw. The switch Sw is turned on when the voltage V _O2 applied to the switch becomes zero. The switch is turned off when the current flowing in the switch begins to decrease. This switching method is one of many possible methods.

13 is a circuit diagram illustrating circuits used in a rice cooker according to the prior art. A heating circuit 500 is used to heat the metal vessel of the cooker and includes a switch Z1. The switch is an insulated gate bipolar transistor (IGBT). The sensor 502 is used to send a signal G_ON when the output voltage becomes negative. The gate driver 504 outputs a control signal G used to turn on the switch Z1 in accordance with the signal G_ON. The gate driver 504 may be configured to be turned on or off periodically without any input from the sensor 502. FIG. 14 is a waveform diagram of a simulation with the circuits 500, 502, 504 of FIG. 13.

15 is a circuit diagram illustrating circuits that may be used to heat a cooker in accordance with one embodiment of the present invention. Heating circuit 600 is used to heat the metal container of the cooker. The circuit 600 includes a switch Z1 and an inductor L _S1 . The switch Z1 is controlled by the input signal G. The inductor L _S1 is used to detect the derivative of the total current. Sensor 602 receives signal D1 and determines whether the derivative of the switch current has a negative slope. The gate driver 604 outputs a control signal used to turn on the switch Z1 of the circuit 600 according to the signals received from the sensor 602. The gate driver 604 may be configured to be turned on or off periodically without any input signal from the sensor 602. FIG. 16 is a waveform diagram of a simulation with the circuits 600, 602, 604 of FIG. 15.

Table 1 below shows simulation results of the circuits 500 and 600. The parameters of the circuits were chosen such that the output power and operating frequency were similar.

First Embodiments 500, 502, 504 Second Embodiments 600, 602, 604 frequency 23 kHz 23 kHz Output power 1.23 kW 1.28kW Voltage of switch 920 V 930 V Current switch 38A 18.5A diode 19A 4.0A RMS current switch 12.3A 7.9A diode 4.5A 0.6 A Average current switch 5.8A 4.3A diode 1.5A 0.1 A

Switching power loss is almost proportional to the maximum current value. The conduction loss of a unipolar device is equal to the product of the (effective current) ² and the on-resistance. The conduction loss of a bipolar device is the product of the average current and the on-voltage during energization. For both insulated gate bipolar transistors (IGBTs) and for anti-parallel diodes, the conduction loss will be some value between these two conduction loss formulas. Table 2 below compares the power losses.

First Switches 500, 502, 504 Second switches 600, 602, 604 Reduction ratio Switching loss Switch (A * Pz) 38 18.5 45% Diode (A * Pd) 19 4.0 21% Conduction Loss A (unipolar) Switch (A * A * Ronz) 151 62 41% Diode (A * A * Rond) 20 0.36 2% Conduction Loss B (Bipolar) Switch (A * Vonz) 5.8 4.3 74% Diode (A * Vond) 15 0.1 One%

In Table 2 above, Pz is a switching loss per peak current of the switch, Pd is a switching loss per maximum current of the diode, Ronz is a resistance when the switch is energized, and Rond is the diode. Is the resistance when energizing, Vonz is the voltage when the switch is energized, and Vond is the voltage when the diode is energized.

Induction heating circuit according to an embodiment of the present invention has a high efficiency, it is possible to use a device having a low breakdown voltage.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (20)

A first heating coil provided around the object to be heated; A first capacitor provided in parallel with the first heating coil and being a resonant element; And And an inductor coupled to the first heating coil and the first capacitor. The apparatus of claim 1, further comprising: a switch coupled to the inductor; And a second capacitor provided in parallel with respect to the coupling of the first heating coil and the inductor. The heating circuit of claim 2, wherein the switch is an insulated gate bipolar transistor or implemented as a bipolar junction transistor. The heating circuit according to claim 1, wherein the circuit is configured to inductively heat a cookware having a conductive container, and the object to be heated is the conductive container. The heating circuit of claim 4, wherein the first heating coil is provided below the conductive container, and the heating circuit further comprises a diode connected in anti-parallel to the switch. The heating circuit of claim 4, further comprising a second heating coil coupled to the first heating coil and provided around the conductive container. The method of claim 6, wherein the inductor is the second heating coil, The heating circuit comprises: a switch coupled to the second heating coil; And a second capacitor provided in parallel with respect to the combination of the first and second heating coils. 8. The heating circuit of claim 7, wherein said switch is implemented with an insulated gate bipolar transistor or a bipolar junction transistor. 8. The heating circuit of claim 7, further comprising diodes connected in anti-parallel to the switch. 8. The heating circuit of claim 7, wherein the first and second heating coils are connected to each other and adjacent to each other. 8. The heating circuit of claim 7, wherein the heating circuit is coupled with a sensor that detects whether the slope of the current has a negative value and is coupled with a gate driver configured to output a control signal that energizes or disconnects the switch. . A first heating coil provided under the conductive container to heat the conductive container; A second heating coil provided around the body of the conductive container; And An induction heating circuit comprising at least one capacitor defining a resonant loop with the first heating coil, the second heating coil, or both. 13. The induction heating circuit according to claim 12, further comprising a first capacitor provided in parallel to the first heating coil and being a resonant element, wherein the at least one capacitor. The method of claim 13, further comprising first, second and third nodes, wherein the first capacitor and the first heating coil are provided between the first and second nodes, and the second heating coil is the second. And an induction heating circuit provided between the third nodes. The induction heating circuit of claim 14, further comprising a second capacitor connected at one side to the first node and at the other end to the third node. 13. The apparatus of claim 12, further comprising first, second, third and fourth nodes, wherein the first heating coil is provided between the first and second nodes, and wherein the second heating coil is the second node. And an induction heating circuit provided between the third nodes. The induction heating circuit of claim 16, further comprising a first capacitor connected at one side to the first node and at the other side to the third node. 18. The induction heating circuit of claim 17, further comprising a second capacitor connected at one side to the second node and at the other end to the fourth node. 18. The induction heating circuit of claim 17, further comprising a switch provided between the third node and a fourth node, wherein the third node is located between the second heating coil and the switch. 17. The apparatus of claim 16, further comprising: a first capacitor connected at one side to the second node positioned between the first and second heating coils and at the other end to the fourth node; A second capacitor having one side connected to the third node and the other side connected to the fourth node; And An induction heating circuit further comprising a switch provided between said third and fourth nodes.

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