Detection method to prevent electromagnetic stove from burning dry with empty pot

Abstract

The present invention provides a detection method for preventing an electromagnetic cooker from burning dry due to an empty pot. The method comprises an IGBT inverter module, a high-frequency LC oscillator circuit, a sampling circuit, and an MCU digital processing circuit. The cookware is placed on a wire reel L in the high-frequency LC oscillator circuit. The MCU digital processing circuit is connected to a drive circuit, which is in turn connected to the IGBT inverter module, which is in turn connected to the high-frequency LC oscillator circuit. The sampling circuit includes high-frequency current and frequency sampling circuits and an input AC power supply voltage and current sampling circuit. The MCU digital processing circuit controls the drive circuit based on data from the two sampling circuits, causing the IGBT inverter module to output a constant power. The MCU digital processing circuit collects current and frequency data from the LC oscillator circuit at set intervals and stores the data in memory. When the collected LC oscillator circuit frequency change value exceeds a set value, the electromagnetic cooker is determined to be in an empty pot and burning dry condition. Advantageously, the entire process has a fast response time: it only takes a few seconds to detect that the cookware is in an empty pot and implement pot protection, thereby extending the cookware's service life and preventing fires and injuries caused by high temperatures due to an unprotected empty pot. The manufacturing cost of the induction cooker can also be reduced by removing the stovetop protection temperature sensor.

Description

Technical Field

[0001] The invention relates to electromagnetic cooker technology, in particular to a detection method for preventing an electromagnetic cooker from burning an empty pot dry. Background Art

[0002] In recent years, induction cooktops have become increasingly popular in kitchens across restaurant chains, hotels, and cafeterias, gaining widespread popularity for their safety, environmental friendliness, energy efficiency, and lack of open flames. However, all induction cooktops on the market rely on temperature sensors on the cooktop surface to detect whether the pot is burning dry. However, the choice of pots for induction cooktops is open, and users often do not use the pots provided by the manufacturer. Furthermore, for cost reasons, single-bottom pots are often preferred. Because the temperature sensor cannot directly measure the pot's temperature, the thermal response time is very slow. When the induction cooktop's output power is high, a dry pot can easily burn red in just a few seconds, before the temperature sensor's temperature has significantly changed, making effective protection impossible. This makes it difficult to provide timely protection when the pot is burning dry when no one is around, resulting in damage to the pot. In severe cases, the high temperature can cause fires and injuries. Summary of the Invention

[0003] To address the aforementioned problems with electromagnetic cookers, the present invention provides a detection method for preventing an electromagnetic cooker from burning dry when the pot is empty. The method comprises an IGBT inverter module, a high-frequency LC oscillation circuit, a sampling circuit, and an MCU digital processing circuit. The pot is placed on a wire reel L in the high-frequency LC oscillation circuit. The MCU digital processing circuit is connected to a drive circuit, which is connected to the IGBT inverter module, which is connected to the high-frequency LC oscillation circuit. The sampling circuit comprises a high-frequency current and frequency sampling circuit and an input AC power supply voltage and current sampling circuit. The MCU digital processing circuit controls the drive circuit based on data from the two sampling circuits, causing the IGBT inverter module to output constant power. The MCU digital processing circuit collects current and frequency data from the LC oscillation circuit at set intervals and stores the data in a memory in sequence. When the collected change in the LC oscillation circuit frequency is greater than a set value, it is determined that the electromagnetic cooker is in an empty pot and burning dry state. The method comprises the following steps:

[0004] (1) The MCU digital processing circuit controls the drive circuit based on the data collected by the sampling circuit, so that the IGBT inverter module outputs constant power to the high-frequency LC oscillation circuit;

[0005] (2) The MCU digital processing circuit collects the current and frequency of the LC oscillation circuit every 100ms;

[0006] (3) The MCU digital processing circuit calculates the frequency change of the high-frequency LC oscillation circuit every 500ms;

[0007] (4) If the frequency of the LC oscillation circuit acquired in the first 100 ms is f1, the frequency of the LC oscillation circuit acquired in the fifth 100 ms is f5, and the difference between f5 and f1 is less than 500, return to step (1);

[0008] (5) If the difference between f5 and f1 in step (4) is greater than 500, it is determined that the electromagnetic cooker is in a dry-burning state, and the MCU digital processing circuit controls the drive circuit to shut down the output power of the IGBT inverter module.

[0009] Induction cooktops use electromagnetic induction heating technology to rapidly heat ferromagnetic cookware. The cookware and the cooktop's high-frequency LC oscillator circuit form an integrated whole. Changes in the cookware's material, distance, and other factors affect the circuit's operating state. The primary factors affecting the circuit's operation are the cookware's magnetic permeability and inductance. The temperature characteristics of metal materials indicate that when the cookware's temperature is below its Curie temperature, its magnetic permeability increases slightly with increasing temperature. When the temperature reaches the Curie temperature, the cookware's magnetic permeability and inductance decrease dramatically, affecting the LC oscillator circuit's operation.

[0010] Before the cookware temperature reaches the Curie temperature, the operating frequency of the cooker's high-frequency LC oscillator circuit decreases slightly to maintain a constant output power. Once the cookware temperature reaches the Curie temperature, the operating frequency of the cooker's high-frequency LC oscillator circuit increases significantly to stabilize the cooker's output power, as the cookware's magnetic permeability and inductance change. This change occurs within two seconds. It is based on this principle that the technical solution of the present invention is proposed.

[0011] The advantages of the present invention are that it samples the high-frequency current and grid input voltage and current in real time, and periodically records the operating frequency of the high-frequency LC oscillation circuit. This allows the determination of whether the induction cooker is in an empty pot and dry-burning state using only the internal algorithm of the MCU. The entire process has a fast response time, requiring only a few seconds to implement protection. Furthermore, as the output power of the induction cooker increases, the protection becomes faster, thereby extending the service life of the cooker and preventing fires and personal injuries caused by high temperatures resulting from an unprotected empty pot and dry-burning. Removing the stovetop protection temperature sensor can also reduce the manufacturing cost of the induction cooker, contributing to reduced environmental pollution and energy conservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a framework diagram of the present invention;

[0013] Figure 2 It is a principle circuit diagram;

[0014] Figure 3It is a detection flow chart;

[0015] Description of the numbers in the figure:

[0016] 1-Rectifier circuit; 2-Filter circuit; 3-High-frequency LC oscillation circuit; 4-IGBT inverter module; 5-Drive circuit; 6-Input voltage and current sampling circuit; 7-High-frequency current and frequency sampling circuit; 8-MCU digital processing unit; 9-Cookware; 10-Mutual inductor; L-High-frequency oscillation coil, i.e., the induction cooker wire reel. DETAILED DESCRIPTION

[0017] Please attach Figure 1 、 2 As shown in Figure 3, the present invention includes an IGBT inverter module 4, a high-frequency LC oscillation circuit 3, sampling circuits 6, 7, and an MCU digital processing circuit 8. The cookware 9 is placed on the wire reel L in the high-frequency LC oscillation circuit. The MCU digital processing circuit 8 is connected to the drive circuit 5, which is connected to the IGBT inverter module 4. The IGBT inverter module 4 is connected to the high-frequency LC oscillation circuit 3. The sampling circuit includes a high-frequency current and frequency sampling circuit 7 and an input AC power supply voltage and current sampling circuit 6. The MCU digital processing circuit 8 controls the drive circuit 5 based on the data from the two sampling circuits 6 and 7, so that the IGBT inverter module 4 outputs constant power. The MCU digital processing circuit 8 collects the current and frequency data of the LC oscillation circuit 3 at set intervals and stores them in memory in sequence. When the collected frequency of the LC oscillation circuit is greater than the set value, it is determined that the induction cookware is in an empty pot dry-burning state. The specific detection process is:

[0018] (1) The MCU digital processing circuit controls the drive circuit based on the data collected by the sampling circuit, so that the IGBT inverter module outputs constant power to the high-frequency LC oscillation circuit;

[0019] (2) The MCU digital processing circuit collects the current and frequency of the LC oscillation circuit every 100ms;

[0020] (3) The MCU digital processing circuit calculates the frequency change of the high-frequency LC oscillation circuit every 500ms;

[0021] (4) If the frequency of the LC oscillation circuit collected in the first 100 ms is f1, the frequency of the LC oscillation circuit collected in the fifth 100 ms is f5, and the difference between f5 and f1 is less than 500, return to step (1);

[0022] (5) If the difference between f5 and f1 in step (4) is greater than 500, it is determined that the induction cooker is in an empty pot dry-burning state, and the MCU digital processing circuit controls the drive circuit to shut down the output power of the IGBT inverter module.

[0023] Please see the attached Figure 3 The detection process shown in the figure:

[0024] Label 1 is circuit start;

[0025] Label 2 is sampling circuit sampling;

[0026] Label 3 is the MCU instructing the driving circuit to make the IGBT inverter module operate at constant power;

[0027] Reference numeral 4 is a sampling circuit that collects the current and frequency of the LC oscillation circuit every 100ms;

[0028] Mark 5 is the frequency change of the high-frequency LC oscillation circuit calculated by the MCU every 500ms;

[0029] Label 6: The difference between f5 and f1 is less than 500, and the process returns to step (3).

[0030] f1 is the frequency of the LC oscillation circuit collected in the first 100ms;

[0031] f5 is the frequency of the LC oscillation circuit collected in the fifth 100ms;

[0032] Label 7 indicates that if the difference between f5 and f1 is greater than 500, the MCU instructs the drive circuit to shut down the power output of the IGBT inverter module.

[0033] The difference between the frequencies f5 and f1 is greater than 500, and is usually 500H in the present invention. Z .

Claims

1. A detection method for preventing an empty pot from burning dry on an electromagnetic cooker, comprising an IGBT inverter module, a high-frequency LC oscillating circuit, a sampling circuit, and an MCU digital processing circuit. The pot is placed on a wire reel L in the high-frequency LC oscillating circuit. An MCU digital processing circuit is connected to a drive circuit, which is connected to the IGBT inverter module, which is connected to the high-frequency LC oscillating circuit. The sampling circuit includes a high-frequency current and frequency sampling circuit and an input AC power supply voltage and current sampling circuit. The MCU digital processing circuit controls the drive circuit based on data from the two sampling circuits, causing the IGBT inverter module to output a constant power. The MCU digital processing circuit collects current and frequency data from the LC oscillating circuit at set intervals. , and stored in the memory in sequence. When the collected change value of the LC oscillation circuit frequency is greater than the set value, it is determined that the induction cooker is in an empty pot dry-burning state; the cooker and the high-frequency LC oscillation circuit of the induction cooker form a whole. When the material and distance of the cooker change, the operating frequency of the high-frequency LC oscillation circuit is different. The magnetic permeability and inductance coefficient of the cooker itself affect the operating frequency of the high-frequency LC oscillation circuit. Before the temperature of the cooker reaches the Curie temperature point, in order to keep the output power of the induction cooker constant, the operating frequency of the high-frequency LC oscillation circuit of the induction cooker will be slightly reduced; when the temperature of the cooker reaches the Curie temperature point, in order to stabilize the output power of the induction cooker, the operating frequency of the high-frequency LC oscillation circuit of the induction cooker will increase significantly with the change of the magnetic permeability and inductance coefficient of the cooker. The following steps are involved: (1) The MCU digital processing circuit controls the drive circuit based on the data collected by the sampling circuit, so that the IGBT inverter module outputs constant power to the high-frequency LC oscillation circuit; (2) The MCU digital processing circuit collects the current and frequency of the LC oscillation circuit every 100ms; (3) The MCU digital processing circuit calculates the frequency change of the high-frequency LC oscillation circuit every 500ms; (4) If the frequency of the LC oscillation circuit collected in the first 100 ms is f1, the frequency of the LC oscillation circuit collected in the fifth 100 ms is f5, and the difference between f5 and f1 is less than 500, return to step (1); (5) If the difference between f5 and f1 in step (4) is greater than 500, it is determined that the electromagnetic cooker is in the empty pot dry-burning state, and the MCU digital processing circuit controls the drive circuit to shut down the output power of the IGBT inverter module; whether the electromagnetic cooker is in the empty pot dry-burning state can be determined only by the internal algorithm of the MCU; The high-frequency current and grid input voltage and current are sampled in real time, and the operating frequency of the high-frequency LC oscillation circuit is recorded regularly.

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