Induction heating circuit and control method

Abstract

The present invention discloses an induction heating circuit, comprising an industrial frequency AC power supply, which is sequentially connected to a rectifier circuit, an inverter circuit, and a primary coil, wherein the primary coil is coupled to a relay coil. The present invention also discloses a control method for the induction heating circuit, which can effectively heat cookware with low resistivity and low magnetic permeability by selecting an operating mode according to the equivalent resistance after rectification of the induction heating circuit, thereby improving the cookware load adaptability of traditional induction cookers. Based on the primary-side induction coil and the secondary load-side induction coil of the induction heating circuit, the present invention adds a relay coil between the primary-side coil and the cookware load.

Description

Technical Field

[0001] The invention belongs to the technical field of small and medium power induction heating methods, relates to an induction heating circuit, and also relates to a control method of the induction heating circuit. Background Art

[0002] At present, induction cookers are one of the main heating methods in home kitchens. Existing induction heating cookers can only effectively heat pots made of ferromagnetic materials or pots specially designed for induction cookers, and cannot heat pots with low magnetic permeability. In addition, there are problems with the universality of the use of induction cookers from different brands, so induction cookers have poor adaptability to pots with different magnetic permeabilities. Summary of the Invention

[0003] An object of the present invention is to provide an induction heating circuit that, by adding a relay coil in the circuit topology, improves the load adaptability of an induction cooker to heat cookware with different magnetic permeabilities. Another object of the present invention is to propose a control method for the induction heating circuit that selects an operating mode by analyzing the size of the equivalent resistance after rectification, thereby solving the problem of circuit resonant current.

[0004] The technical solution adopted by the present invention is that the induction heating circuit includes an industrial frequency AC power supply, which is sequentially connected to a rectifier circuit, an inverter circuit, and a primary coil, and the primary coil is coupled to a relay coil.

[0005] The rectifier circuit includes a thyristor a, which is connected to a thyristor c, a thyristor b, and a thyristor d in sequence through a wire;

[0006] The inverter circuit includes a MOSFET switch tube a, which is connected in series with MOSFET switch tubes c, MOSFET switch tubes b, and MOSFET switch tubes d through wires. One end of the filter capacitor is respectively connected to the input end of the MOSFET switch tube a and the output end of the thyristor, and the other end is respectively connected to the output end of the MOSFET switch tube a and the input end of the thyristor.

[0007] The primary coil includes a resistor a, which is connected to the primary side coil and capacitor a through a wire. Capacitor a is connected in parallel with switch a, capacitor b, switch b and capacitor c. The access end of resistor a is connected to the output end of MOSFET switch tube b.

[0008] The relay coil includes a resistor b, which is connected in series with the relay side coil and capacitor d through a wire. Capacitor d is connected in parallel with switch c, capacitor e, switch d and capacitor f. The relay side coil is coupled to the primary coil.

[0009] Another technical solution of the present invention is: a control method for an induction heating circuit, which uses the above-mentioned induction heating circuit and is specifically performed in the following steps:

[0010] Step 1: First, start the induction heating circuit;

[0011] Step 2: Use current Hall effect devices and voltage Hall effect devices to respectively collect the input voltage V of the rectifier circuit in the induction heating circuit. in and input current I in Data, by calculating the input voltage V in and input current I in The data is used to obtain the equivalent resistance R after rectification. eq-1 ;

[0012] Step 3: The induction heating circuit is based on the equivalent resistance R eq-1 Select the working mode of the inverter circuit. The working modes of the inverter circuit are triple frequency mode, double frequency mode, half bridge mode and full bridge mode. eq-1 is the equivalent resistance after rectification.

[0013] Step 4: The induction heating circuit is based on the multiple relationship between the current frequency of the primary coil and the MOSFET switching tube frequency, and the equivalent resistance R after rectification is calculated. eq-1 , select the working mode in step 3, and adjust the power required by the induction heating circuit through PFM, that is, frequency modulation and power modulation.

[0014] The triple frequency mode of the inverter circuit in the induction heating circuit, when the current frequency of the primary coil is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit in the induction heating circuit min When the capacitance of the primary coil and the relay coil is switched, the equivalent resistance R eq-1 ≤R eq-1 , tM, the induction heating circuit works in the triple frequency mode, and the power required by the induction heating circuit is adjusted by PFM, that is, frequency modulation and power modulation. eq-1 is the equivalent resistance after rectification, R eq-1 , tM is the equivalent resistance of the induction heating circuit working in the triple frequency mode.

[0015] The double frequency mode of the inverter circuit in the induction heating circuit, the current frequency of the primary coil is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit in the induction heating circuit min When the capacitance of the primary coil and the relay coil is switched, the equivalent resistance R of the primary side of the induction heating circuit is measured. eq-1 ≤R eq-1 ,dM, the induction heating circuit works in the double frequency mode, and the power required by the induction heating circuit is adjusted by PFM, that is, frequency modulation and power modulation. eq-1 , dM is the equivalent resistance of the induction heating circuit working in the double frequency mode, R eq-1 is the equivalent resistance after rectification.

[0016] In the half-bridge mode of the inverter circuit in the induction heating circuit, when the current frequency of the primary coil is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit in the induction heating circuit min When the equivalent resistance R eq-1 When the equivalent resistance is minimum, the induction heating circuit works in half-bridge mode, and the power required by the induction heating circuit is adjusted by PFM, i.e. frequency modulation and power regulation. eq-1 ,HM is the equivalent resistance of the induction heating circuit working in half-bridge mode, and then the required power is adjusted by frequency modulation and power regulation.

[0017] In the full-bridge mode of the inverter circuit in the induction heating circuit, when the current frequency of the primary coil is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit in the induction heating circuit min When the equivalent resistance R eq-1 ,HM<R eq-1 <R eq-1 ,FM, the induction heating circuit works R eq-1 ,FM is the equivalent resistance of the induction heating circuit working in full-bridge mode, R eq-1 is the equivalent resistance after rectification, R eq-1 ,HM is the equivalent resistance of the induction heating circuit working in half-bridge mode.

[0018] The beneficial effects of the present invention are as follows: based on the primary side induction coil and the secondary load side induction coil of the induction heating circuit of the prior art, the present invention adds a relay coil between the primary side coil and the cookware load;

[0019] The operating mode is selected according to the equivalent resistance after rectification of the induction heating circuit. This induction heating circuit has a total of four operating modes, which can effectively heat low-resistivity and low-magnetic permeability cookware, improving the cookware load adaptability of traditional induction cookers. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a circuit diagram of the induction heating circuit of the present invention;

[0021] Figure 2 Schematic diagram of the induction heating method of the present invention;

[0022] Figure 3 Schematic diagram of circuit topology of the control method of the induction heating circuit of the present invention.

[0023] In the figure, 1. Industrial frequency AC high voltage power supply, 2. Rectifier circuit, 3. Inverter circuit, 4. Primary coil, 5. Relay coil;

[0024] 201. Thyristor a, 202. Thyristor b, 203. Thyristor c, 204. Thyristor d, 301. Filter capacitor, 302. MOSFET switch a, 303. MOSFET switch b, 304. MOSFET switch c, 305. MOSFET switch d, 401. Primary-side coil, 402. Resistor a, 403. Capacitor a, 404. Switch a, 405. Capacitor b, 406. Switch b, 407. Capacitor c, 501. Relay-side coil, 502. Resistor b, 503. Capacitor d, 504. Switch c, 505. Capacitor e, 506. Switch d, 507. Capacitor f. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The present invention is used for the circuit of induction heating of electromagnetic cooker, such as Figure 1 As shown, it includes an industrial frequency AC power supply 1. After the industrial frequency AC power supply 1 passes through a rectifier circuit 2 composed of four thyristors, a voltage V is obtained after the rectifier circuit 2. in After being connected in parallel with the filter capacitor 301, it passes through the inverter circuit 3 composed of four MOSFET switches, connecting the resistor a402 of the primary coil 4, the primary side coil 401, the capacitor a403, the switch a404, the capacitor b405, the switch b406, and the capacitor c407 in parallel to form a closed loop. The relay coil structure is composed of the resistor b502, the relay side coil 501, the capacitor d503, the switch c504, the capacitor e505, the switch d506, and the capacitor f507 in parallel to form a closed loop. The resistance and inductance on the pot side include a closed loop consisting of the pot side coil Lp and the pot side resistor Rp.

[0027] like Figure 2 As shown in the figure, the induction heating circuit first selects the working mode according to the equivalent resistance of the rectifier side of the heating topology, and then adjusts the transmission power by frequency modulation and power modulation in the steady state, that is, R eq-1 Respectively with R eq-1 ,FM,R eq-1 ,HM,R eq-1 ,dM、R eq-1 ,tM to compare and select the corresponding working mode. eq-1 ,FM is the equivalent resistance in full-bridge mode, R eq-1 , HM is the equivalent resistance in full-bridge mode, R eq-1 ,dM equivalent resistance in double frequency mode, R eq-1 ,tM is the equivalent resistance in triple frequency mode.

[0028] By comparing the calculated equivalent resistance with the equivalent resistance in the four modes, the control method of the MOSFET switches in inverter circuit 3 is changed to enable inverter circuit 3 to operate in full-bridge mode, half-bridge mode, double frequency mode, and triple frequency mode, respectively. The circuit then switches the resonant capacitance of the coil according to the resonant frequency of the induction heating circuit in each mode, achieving resonant tank matching in each mode and thus achieving heating for different cookware.

[0029] Induction heating circuits are often used in household appliances such as induction cookers. The impact of noise must be considered during design. Since the human ear can hear sound frequencies between 20Hz and 20kHz, the operating frequency of the inverter in a typical household induction cooker is slightly greater than 20kHz. Therefore, the minimum switching frequency of the MOSFET switching device in this heating circuit is 25kHz.

[0030] The specific steps of the control method of the induction heating circuit of the present invention are:

[0031] Step 1: First, start the induction heating circuit with the relay coil 5;

[0032] Step 2: Use current Hall effect devices and voltage Hall effect devices to respectively collect the input voltage V on the rectifier side of the induction heating circuit topology. in and input current I in The size of the input voltage V in and input current I in The collection of Figure 1 As shown, the ratio of input voltage to input current is calculated to obtain the equivalent resistance R after rectification. eq-1 ;

[0033] Step 3: Select the working mode according to the calculated equivalent resistance. The working modes of the induction heating circuit inverter circuit 3 include triple frequency mode, double frequency mode, half-bridge mode and full-bridge mode.

[0034] In step 4, the system selects the system operating mode based on the multiple relationship between the current frequency of the primary coil 4 and the switching frequency, as well as the size relationship between the equivalent resistance calculated after rectification, and adjusts the required system power according to the PFM mode.

[0035] The specific process of step 3 in the control method of the induction heating circuit of the present invention is as follows:

[0036] Step 3.1: When the current frequency of the primary coil 4 is the minimum switching frequency f of the inverter circuit switch in the circuit topology, min When the capacitance of the primary coil 4 and the relay coil 5 is switched, the equivalent resistance R eq-1 ≤R eq-1 ,tM, where Req-1 is the equivalent resistance after rectification, R eq-1 , tM is the equivalent resistance of the system working in triple frequency mode, then the induction heating circuit works in triple frequency mode, and then the required power is adjusted by frequency and power modulation.

[0037] Step 3.2, the current frequency of the primary coil 4 is the minimum switching frequency f min When the capacitance of the primary coil 4 and the relay coil 5 is switched, the equivalent resistance R of the primary side of the induction heating circuit is measured. eq-1 ≤R eq-1 ,dM, the induction heating circuit works in the double frequency mode, and then adjusts the required power by frequency and power modulation.

[0038] Step 3.3, the current frequency of the primary coil 4 is the minimum switching frequency f min When the equivalent resistance R eq-1 ≤R eq-1 ,HM, the induction heating circuit works in half-bridge mode, where R eq-1 ,HM is the equivalent resistance of the induction heating circuit working in half-bridge mode, and then the required power is adjusted by frequency modulation and power regulation.

[0039] Step 3.4, the current frequency of the primary coil 4 is the minimum switching frequency f min When the equivalent resistance R eq-1 ,HM<R eq-1 <R eq-1 ,FM, the induction heating circuit works in full-bridge mode, where R eq-1 ,FM is the equivalent resistance of the induction heating circuit working in full-bridge mode, and then the system adjusts the required power by frequency modulation and power regulation.

[0040] For example, we choose the input of the induction heating circuit to be single-phase 220V, 50HZ AC, the rated power of the device is 2100W, and the minimum operating frequency of the switching device is 25KHz, that is, f min The value of is 25KHz. Therefore, the minimum operating frequency of the switch tube of this induction heating circuit is set to f min The minimum operating frequency is 25kHz, the minimum operating frequency at 2 times the frequency is 50kHz, and the minimum operating frequency at 3 times the frequency is 75kHz.

[0041] Therefore, in the calculation of the load parameters on the rectifier side of the induction heating circuit, the inverter circuit 3 of the induction heating circuit is calculated in full-bridge mode. The maximum equivalent resistance after rectification in full-bridge mode is:

[0042]

[0043] In the half-bridge mode, the double frequency mode and the triple frequency mode, the equivalent resistance of the rectifier circuit 2 of the induction heating circuit is one quarter of the equivalent resistance in the full-bridge mode, which is 5.76Ω.

[0044] The specific working process at this time is: after starting the induction heating circuit, respectively collect the magnitude of the input voltage and input current on the rectifier side of the circuit topology, and perform relevant calculations on the ratio of the input voltage and input current to obtain the equivalent resistance R after rectification. eq-L When the equivalent resistance at the switching frequency or 2 times the switching frequency or 3 times the switching frequency is less than 5.76Ω, the circuit operates in half-bridge mode or double frequency mode or triple frequency mode; when the equivalent resistance R after rectification is actually detected eq-l When the resistance is greater than 5.76Ω and less than 23Ω at the switching frequency, the circuit operates in full-bridge mode and the power supply can output the rated power.

[0045] That is, when the current frequency of the primary coil 4 in the induction heating circuit is 75KHz, the control switch is used to complete the capacitor switching of the primary coil 4 and the relay coil 5, and the equivalent resistance measured at this time is 5.76Ω less than 23Ω, then the induction heating circuit operates in triple frequency mode. When the current frequency of the primary coil 4 in the induction heating circuit is 50KHz, the control switch is used to complete the capacitor switching of the primary coil 4 and the relay coil 5, and the equivalent resistance measured at this time is less than 5.76Ω, then the induction heating circuit operates in double frequency mode. When the current frequency of the primary coil 4 in the induction heating circuit is 25KHz, the equivalent resistance measured at this time is less than 5.76Ω, and the induction heating circuit operates in half-bridge mode. When the rectifier circuit 2 of the induction heating circuit measures an equivalent resistance greater than 5.76Ω and less than 23Ω, the circuit operates in full-bridge mode.

[0046] like Figure 3 As shown, the cookware load-side coil, relay coil 5, primary coil 4, capacitors a403, b405, and c407 are the resonant capacitors on the primary side, and capacitors d503, e505, and f507 are the resonant capacitors on the relay coil side. When the induction heating circuit operates in different modes, the capacitors are switched on and off by controlling switches a404, b406, c504, and d506 to match the resonant frequency of the induction heating circuit, thereby improving the load adaptability of the induction heating circuit. LP represents the mutual inductance between the primary coil 4 and the cooker, M UP represents the mutual inductance between the relay coil 5 and the cooker, M LU represents the mutual inductance between the primary coil 4 and the cookware. When the cookware is heated, the primary coil 4 and the relay coil 5 heat the cookware simultaneously.

[0047] The circuit and control method of induction heating of the present invention work as follows:

[0048] Adding a relay coil and analyzing the equivalent resistance on the rectifier side of the induction heating circuit topology controls the switching frequency of the inverter circuit's switching transistors, solving the heating problem for low-permeability cookware. The induction heating circuit control system with the relay coil 5 is activated. The input voltage and input current on the rectifier side of the circuit topology are collected, and the ratio of the input voltage to the input current is calculated to obtain the equivalent resistance after rectification. The system selects an operating mode based on the calculated equivalent resistance. The inverter circuit's operating modes include triple frequency mode, double frequency mode, half-bridge mode, and full-bridge mode. The system selects the operating mode based on the multiple relationship between the current frequency of the primary coil 4 and the switching frequency, as well as the calculated equivalent resistance after rectification. The system adjusts the required system power using PFM (frequency modulation and power modulation).

[0049] The induction heating circuit and control method of the present invention have the following advantages: the induction heating circuit is equipped with a relay coil. To address the problem that the materials of cookware heated by traditional induction heating circuits are limited, the relay coil is added to increase the magnetic field strength, and the operating mode of the induction heating circuit is selected according to the size of the equivalent resistance after circuit rectification, thereby effectively improving the applicability of induction cookware.

Claims

1. Induction heating circuit, characterized in that, The invention comprises an industrial frequency AC power supply (1), the industrial frequency AC power supply (1) being connected in sequence to a rectifier circuit (2), an inverter circuit (3) and a primary coil (4), wherein the primary coil (4) is coupled to a relay coil (5); The primary coil (4) includes a resistor a (402), the resistor a (402) is connected to the primary side coil (401) and the capacitor a (403) in sequence through a wire, the other end of the capacitor a (403) is connected to the capacitor b (405), the switch a (404) is connected to the capacitor b (405) through a wire, the switch a (404) is connected to the switch b (406), the switch a (404) is connected to the capacitor c (407) through a wire, and the access end of the resistor a (402) is connected to the output end of the MOSFET switch tube b (303); The relay coil (5) includes a resistor b (502), and the resistor b (502) forms a closed loop with the relay side coil (501) and the capacitor d (503) through a wire. The two ends of the capacitor d (503) are respectively connected to the input end of the switch c (504) and the output end of the capacitor e (505). The output end of the switch c (504) is connected to the input end of the capacitor e (505). The input end of the switch c (504) is also connected to the input end of the switch d (506). The output end of the switch d (506) is connected to the input end of the capacitor f (507). The output end of the capacitor f (507) is connected to the output end of the capacitor e (505). The relay side coil (501) is coupled with the primary side coil (401).

2. The induction heating circuit according to claim 1, characterized in that: The rectifier circuit (2) comprises a thyristor a (201), wherein the thyristor a (201) is sequentially connected to a thyristor c (203), a thyristor b (202), and a thyristor d (204) via a wire, and the thyristor b (202) and the thyristor d (204) are respectively connected to a filter capacitor (301) of an inverter circuit (3) via a wire.

3. The induction heating circuit according to claim 2, characterized in that: The inverter circuit (3) comprises a MOSFET switch tube a (302), wherein the MOSFET switch tube a (302) is sequentially connected to a MOSFET switch tube b (303), a MOSFET switch tube c (304), and a MOSFET switch tube d (305) via a wire to form a closed loop; one end of the filter capacitor (301) is respectively connected to the input end of the MOSFET switch tube a (302) and the output end of the thyristor b (202), and the other end is respectively connected to the output end of the MOSFET switch tube a (304) and the input end of the thyristor b (202).

4. A control method for an induction heating circuit, characterized in that: The method uses the induction heating circuit according to any one of claims 1 to 3, and is specifically carried out in the following steps: Step 1, first start the induction heating circuit; Step 2: Use current Hall effect devices and voltage Hall effect devices to respectively collect the input voltage V of the rectifier circuit (2) in the induction heating circuit. in and input current I in data, by calculating the input voltage V in and the input current I in The data is used to obtain the equivalent resistance R after rectification. eq-1 , where V in is the input voltage, I in is the input current; Step 3: The induction heating circuit is based on the equivalent resistance R after rectification. eq-1 Selecting an operating mode of the inverter circuit (3), wherein the operating modes of the inverter circuit (3) include a triple frequency mode, a double frequency mode, a half-bridge mode, and a full-bridge mode; Step 4: The induction heating circuit is based on the multiple relationship between the current frequency of the primary coil (4) and the MOSFET switching tube frequency, and the equivalent resistance R after rectification is calculated. eq-1 , select the working mode described in step 3, and adjust the power required by the induction heating circuit through PFM, that is, frequency modulation and power modulation.

5. The control method of the induction heating circuit according to claim 4, characterized in that: In the triple frequency mode of the inverter circuit (3) in step 3, when the current frequency of the primary coil (4) is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit (3) in the induction heating circuit min When the capacitance of the primary coil (4) and the relay coil (5) is switched, the equivalent resistance R eq-1 ≤R eq-1 , tM, the induction heating circuit works in the triple frequency mode, and the power required by the induction heating circuit is adjusted by PFM, that is, frequency modulation and power modulation. eq-1 is the equivalent resistance after rectification, R eq-1 ,tM is the equivalent resistance of the induction heating circuit working in the triple frequency mode.

6. The control method of the induction heating circuit according to claim 4, characterized in that: In the double frequency mode of the inverter circuit (3) in step 3, the current frequency of the primary coil (4) is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit (3) in the induction heating circuit. min When the capacitance of the primary coil (4) and the relay coil (5) is switched, the equivalent resistance R of the primary side of the induction heating circuit is measured. eq-1 ≤R eq-1 ,dM, the induction heating circuit works in the double frequency mode, and the power required by the induction heating circuit is adjusted by PFM, that is, frequency modulation and power modulation. eq-1 , dM is the equivalent resistance of the induction heating circuit working in the double frequency mode, R eq-1 is the equivalent resistance after rectification.

7. The control method of the induction heating circuit according to claim 4, characterized in that: In the half-bridge mode of the inverter circuit (3) in step 3, the current frequency of the primary coil (4) is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit (3) in the induction heating circuit. min When the equivalent resistance R eq-1 ≤R eq-1 ,HM, the induction heating circuit works in half-bridge mode, and the power required by the induction heating circuit is adjusted by PFM, that is, frequency modulation and power regulation. eq-1 , HM is the equivalent resistance of the induction heating circuit working in half-bridge mode, R eq-1 is the equivalent resistance after rectification.

8. The control method of the induction heating circuit according to claim 4, characterized in that: In the full-bridge mode of the inverter circuit (3) in step 3, the current frequency of the primary coil (4) is the minimum switching frequency f of the MOSFET switch tube of the inverter circuit (3) in the induction heating circuit. min When the equivalent resistance R eq-1 ,HM<R eq-1 <R eq-1 ,FM, the induction heating circuit works R eq-1 ,FM is the equivalent resistance of the induction heating circuit working in full-bridge mode, R eq-1 is the equivalent resistance after rectification, R eq-1 ,HM is the equivalent resistance of the induction heating circuit working in half-bridge mode.

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