JP2017150735A - Induction heating type steam generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating type steam generator which makes high frequency current supply circuit hard to break down due to abnormal heat generation without increasing a cost of the high frequency current supply circuit.SOLUTION: In an induction heating type steam generator, a control unit: detects that a heating body is put into an overheated state with a temperature there of higher than a Curie temperature when a current measurement measured by a current meter exceeds a first threshold set higher than an output corresponding current value corresponding to output of high frequency current; and controls the high frequency current in a manner that stops a supply thereof from the high frequency current supply circuit to an induction heating coil. In addition, the control unit controls the high frequency current in a manner that temporarily reduces the output thereof supplied from the high frequency current supply circuit to the induction heating coil when the current measurement measured by the current meter exceeds a second threshold set higher than the output corresponding current value and not more than the first threshold.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an induction heating steam generator used in a steam convection oven or the like.

  Patent Document 1 below discloses a steam generator used in a cooking device such as a steam convection oven. This steam generator includes a steam generation container that stores a predetermined amount of water to generate steam, an induction heating coil wound around the outer periphery of the steam generation container, and a high frequency that is housed in the steam generation container and is applied to the induction heating coil. A heating element that generates heat by supplying current, a high-frequency current supply circuit that supplies high-frequency current to the induction heating coil, and a control device that controls the operation of the high-frequency current supply circuit to control the supply of high-frequency current to the induction heating coil And. An eddy current flows in the heating element in the steam generation vessel due to the influence of the magnetic field generated when high-frequency current is supplied to the induction heating coil, and the surrounding water is heated by Joule heat generated when the eddy current flows. Steam is generated.

Japanese Patent Laying-Open No. 2015-017747

  In the steam generating apparatus of Patent Document 1 described above, water in the steam generating container is controlled to be a predetermined amount using a water level sensor in a water level detection tank provided adjacent to the water generating sensor. If the water is not properly supplied into the steam generating container, the heating body may be empty in the steam generating container and become overheated. If the temperature of the heating element exceeds the Curie temperature in the steam generation vessel, the heating element loses magnetism and the flowing eddy current decreases, and the high-frequency current supply circuit may generate an overcurrent due to a decrease in impedance. There was a risk that the current supply circuit would fail due to overcurrent. In order to prevent this, when the high-frequency current supplied from the high-frequency current supply circuit exceeds a threshold value that is larger than a predetermined ratio (eg, 130%) of the normal current according to the output, the heating body is heated to reduce the Curie temperature. It is detected that the overheated state has been exceeded, and the supply of the high frequency current from the high frequency current supply circuit to the induction heating coil is stopped.

  However, when a steam film is formed around the heating element in the steam generation container even though there is sufficient water (hot water) in the steam generation container, the water in the steam generation container Film boiling occurs at the contact surface with the vapor film, and the heating body may not be heat exchanged with the water in the vapor generation vessel and may be overheated. In this case, since the temperature rise of the heating element is more gradual than when the heating element is heated, the temperature of the heating element rises until the temperature exceeds the Curie temperature, but becomes longer than when the heating element is heated, and the high frequency current from the high frequency current supply circuit However, the high current state is maintained for a long time before the voltage rises to the threshold value described above, and the high frequency current supply circuit may be damaged due to abnormal heat generation. On the other hand, a failure due to abnormal heat generation can be avoided to some extent by increasing the transistors constituting the high-frequency current supply circuit or increasing the size of the radiator or cooling fan, but there is a problem that the cost is significantly increased. It is an object of the present invention to make a high-frequency current supply circuit less likely to fail due to abnormal heat generation without increasing the cost of the high-frequency current supply circuit in an induction heating type steam generator.

  In order to solve the above problems, a steam generation container for storing a predetermined amount of water to generate steam, an induction heating coil wound around the outer periphery of the steam generation container, and an induction heating coil housed in the steam generation container A heating element that generates heat by supplying a high-frequency current to the coil, a high-frequency current supply circuit that supplies a high-frequency current to the induction heating coil, an ammeter that measures the current supplied from the high-frequency current supply circuit to the induction heating coil, The control device that controls the operation of the current supply circuit to control the supply of high-frequency current to the induction heating coil, and the control device set the measured current value measured by the ammeter higher than the output-corresponding current value according to the output When the first threshold value is exceeded, it is detected that the heating body has overheated exceeding the Curie temperature, and the supply of high-frequency current from the high-frequency current supply circuit to the induction heating coil is stopped. An induction heating type steam generator that controls the second current threshold value, wherein the measured current value measured by the ammeter is higher than the output-corresponding current value and lower than the first threshold value. An induction heating type steam generator is provided which is controlled so as to temporarily reduce the output of the high frequency current supplied from the high frequency current supply circuit to the induction heating coil when the temperature exceeds the value.

  In the induction heating type steam generator configured as described above, when the measured current value measured by the ammeter exceeds the first threshold value set higher than the output corresponding current value according to the output, heating is performed. By detecting that the body has overheated above the Curie temperature and controlling the high-frequency current to be stopped from the high-frequency current supply circuit to the induction heating coil, an overcurrent is generated in the high-frequency current supply circuit. It is possible to prevent the steam generation container from becoming empty.

  However, when a steam film is formed around the heating element in the steam generation container, the heat of the heating element is not easily exchanged with the water in the steam generation container by the steam film, and the temperature of the heating element is Rise more slowly than when. At this time, there is a possibility that the high-frequency current flows from the high-frequency current supply circuit for a long time until the measured current value measured by the ammeter exceeds the first threshold, and the high-frequency current supply circuit abnormally generates heat. In contrast, in the steam generator of the present invention, when the measured current value measured by the ammeter exceeds the second threshold value set higher than the output-corresponding current value and below the first threshold value, the high-frequency current is Control was performed to temporarily reduce the output of the high-frequency current supplied from the supply circuit to the induction heating coil. As a result, even if a vapor film is formed around the heating body, the heat generation of the heating body is temporarily suppressed, so that the vapor film generated around the heating body in the steam generation container disappears and heating is performed. The body was heat exchanged with the surrounding water (hot water), so that the high-frequency current from the high-frequency current supply circuit was not maintained at a high current for a long time, and the high-frequency current supply circuit could be prevented from becoming abnormally heated. .

It is the schematic of the induction heating type steam generator of this invention. It is a graph which shows an output corresponding | compatible electric current value, a 1st threshold value, and a 2nd threshold value.

  Hereinafter, the induction heating type steam generator of the present invention is mainly incorporated in a heating cooker such as a steam convection oven. As shown in FIG. 1, an induction heating type steam generator 10 (hereinafter also simply referred to as a steam generator 10) includes a steam generation container 21 that stores a predetermined amount of water and generates steam, and a steam generation container. The induction heating coil 31 wound around the outer periphery of the heating element 21, the heating body 32 that is housed in the steam generation container 21 and generates heat by supplying the induction heating coil 31 with high frequency current, and the induction heating coil 31 receives high frequency current. A high-frequency current supply circuit 41 to be supplied, an ammeter 42 for measuring a current to be supplied from the high-frequency current supply circuit 41 to the induction heating coil 31, and an operation of the high-frequency current supply circuit 41 to control the high-frequency current in the induction heating coil 31. And a control device 43 for controlling supply.

  In this steam generator 10, in order to prevent the heating element 32 in the steam generation container 21 from being overheated exceeding the Curie temperature and generating an overcurrent in the high-frequency current supply circuit 41, the control device 43 includes: When the measured current value measured by the ammeter 42 exceeds the first threshold value set higher than the output-corresponding current value according to the output, the heating element 32 is in an overheated state exceeding the Curie temperature. It is detected and controlled to stop the supply of high-frequency current from the high-frequency current supply circuit 41 to the induction heating coil 31.

  Further, in this steam generator 10, a steam film is generated around the heating body 32 in the steam generation container 21, so that the heat of the heating body 32 is converted into water (hot water) in the steam generation container by the steam film. In order to prevent the high-frequency current supply circuit 41 from flowing out of the high-frequency current supply circuit 41 in a high current state for a long time and preventing the high-frequency current supply circuit 41 from generating abnormal heat, the control device 43 is measured by the ammeter 42. When the measured current value exceeds the second threshold value set higher than the output-corresponding current value and lower than the first threshold value, the output of the high-frequency current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31 is temporarily It is controlled so as to decrease. Below, the steam generator 10 of this invention is explained in full detail.

  As shown in FIG. 1, the steam generation container 21 has a cylindrical shape that is open at the top and bottom. The opening 21a at the upper end of the steam generating container 21 serves as a steam outlet, and the opening 21b at the lower end of the steam generating container 21 serves as a drain outlet. Connected to the upper part of the steam generating container 21 is a steam outlet tube 22 for sending steam into a cooking chamber (not shown). A drain cylinder 23 is connected to the lower part of the steam generation container 21, and water in the steam generation container 21 is drained by opening a drain valve 24 provided in the drain cylinder.

  A water level detection tank 25 is erected at a position adjacent to the steam generation container 21, and a lower part of the water level detection tank 25 is connected to a lower part of the steam generation container 21. A water level sensor 26 is attached in the water level detection tank 25, and the water level sensor 26 detects the water level in the steam generation container 21 by detecting the water level in the water level detection tank 25. The water level sensor 26 detects the lower limit water level L1 and the upper limit water level L2 in the steam generation container 21. Further, a water supply pipe 27 derived from a water supply source such as a water supply is connected to the water level detection tank 25, and a water supply valve 28 is interposed in the water supply pipe 27. When the water supply valve 28 is opened and water is supplied from the water supply pipe 27 to the water level detection tank 25, the water in the water level detection tank 25 flows into the steam generation container 21 from below so that the water level becomes the same. Thus, the water from the water supply pipe 27 is supplied to the steam generation container 21 through the water level detection tank 25.

  An induction heating coil 31 is wound around the outer periphery of the steam generation container 21, and a heating body 32 is provided in the steam generation container 21. The induction heating coil 31 generates a magnetic field around the heating body 32 when a high frequency current is supplied. The heating body 32 heats the water in the steam generation container 21, and includes a plurality of heating rods 32 a and a holder 32 b that supports the heating bars 32 a on the upper portion of the steam generation container 21. The heating rod 32a is a conductive metal rod-like member made of a magnetic member, extends in the axial direction of the steam generation vessel 21, and is equidistantly arranged on a concentric circle centering on the central axis of the cylindrical steam generation vessel 21. Has been placed. When a high frequency current is supplied to the induction heating coil 31 to generate a magnetic field around the heating rod 32a, an eddy current flows through the heating rod 32a due to the influence of the magnetic field. The heating rod 32a generates heat due to Joule heat generated by electric resistance when eddy current flows, and heats the water in the steam generation vessel 21.

  The steam generator 10 includes a high-frequency current supply circuit 41 that supplies a high-frequency current to the induction heating coil 31, an ammeter 42 that measures a current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31, and a high-frequency current supply circuit. The control apparatus 43 which controls the action | operation of 41 is provided. The high-frequency current supply circuit 41 generates a high-frequency current from a direct current, and a known IH inverter circuit is employed in this embodiment. The high-frequency current supply circuit 41 is supplied with a direct current from an inverter circuit that converts an alternating current from a power source into a direct current. The ammeter 42 measures the output current from the high-frequency current supply circuit 41 (current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31), and the current value measured by the ammeter 42 is the control device 43. Is output.

  The control device 43 is connected to the water level sensor 26, the water supply valve 28, the high frequency current supply circuit 41, and the ammeter 42. The control device 43 controls the opening and closing of the water supply valve 28 based on the detected water level of the water level sensor 26 by a built-in microcomputer, and controls the water level in the steam generation container 21 to be a predetermined water level (a predetermined amount of water). ing. Specifically, the control device 43 starts the water supply to the steam generation container 21 by opening the water supply valve 28 in response to the detection of the lower limit water level L1 by the water level sensor 26, and the detection of the upper limit water level L2 by the water level sensor 26. The water supply valve 28 is closed by input to stop water supply to the steam generation container 21 and the water level in the steam generation container 21 is controlled to be a predetermined water level (between L1 and L2).

  The control device 43 controls the operation of the high-frequency current supply circuit 41 so that a high-frequency current corresponding to the heat output of the heating body 32 is supplied from the high-frequency current supply circuit 41 to the induction heating coil 31. . Specifically, the control device 43 includes a set steam amount in a cooking chamber (not shown) input to the control device 43 from an operation panel (not shown), and a cooking chamber (not shown) input to the control device 43. ) To control the output of the high-frequency current supply circuit 41 so that the required amount of steam is generated in the cooking chamber.

  In addition, when a malfunction such as the water level sensor 26 or the water supply valve 28 occurs, there is a possibility that water is not properly supplied into the steam generation container 21. In this state, when the high frequency current is supplied from the high frequency current supply circuit 41 to the induction heating coil 31 and the heating rod 32a of the heating body 32 is continuously heated in the steam generation vessel 21, the heating rod 32a exchanges heat with water. It continues to generate heat without being overheated. When the heating rod 32a becomes overheated at a temperature equal to or higher than the Curie temperature, the eddy current that flows because the heating rod 32a loses magnetism decreases, and the high-frequency current supply circuit 41 generates an overcurrent due to a decrease in impedance. 41 may be damaged.

  For this reason, when the current value measured by the ammeter 42 exceeds the first threshold value set higher than the output-corresponding current value according to the output, the control device 43 causes the heating rod 32a of the heating body 32 to be magnetic. It is detected that the overheated state is lost, and the supply of the high-frequency current from the high-frequency current supply circuit 41 to the induction heating coil 31 is stopped. In this embodiment, the first threshold value is set to a current value 130% higher than the output corresponding current value corresponding to the output. Further, when the output of the high-frequency current supply circuit 41 is set to 20% or less of the maximum output in normal use by the control device 43, in order to prevent false detection due to the influence of noise and voltage fluctuation, the first step is performed. The threshold is not set.

  Further, when a steam film is formed around the heating rod 32a in the steam generation container 21 and film boiling occurs, the heat of the heating rod 32a is hardly exchanged with water by the steam film. At this time, the heating rod 32a enters an overheated state, although it is slower than when the heating rod 32a is operated as described above. At this time, since the temperature rise of the heating rod 32a is slower than when the heating rod 32a is empty, the input current of the high-frequency current supply circuit 41 measured by the ammeter 42 rises to the first threshold value described above. There is a possibility that the high-frequency current supply circuit 41 may abnormally generate heat by taking a long time or maintaining a high current state for a long time without increasing to the first threshold value.

  For this reason, when the current value measured by the ammeter 42 exceeds the second threshold value set higher than the output-corresponding current value corresponding to the output and lower than the first threshold value, the control device 43 determines the high-frequency current. Control is performed so that the output of the high-frequency current supplied from the supply circuit 41 to the induction heating coil 31 is temporarily reduced (in this embodiment, 60 seconds) (in this embodiment, the output current value is reduced to 50%). Yes. In this embodiment, the second threshold value is set to a current value that is 110% to 130% higher than the output-corresponding current value corresponding to the output, and the output by the high-frequency current from the high-frequency current supply circuit 41 is normal. When the maximum output is 30%, it is set 130% higher than the output-corresponding current value in the same way as the first threshold, and gradually when the output due to the high-frequency current from the high-frequency current supply circuit 41 becomes higher than the above 30%. It is set to be low, and is set to be 110% higher when the output by the high frequency current from the high frequency current supply circuit 41 is 100% (maximum output in normal use). Film boiling in the steam generation vessel 21 is less likely to occur when the output due to the high-frequency current from the high-frequency current supply circuit 41 is low, and is more likely to occur as the output due to the high-frequency current from the high-frequency current supply circuit 41 is higher. The second threshold value is set to be lower as the output due to the high-frequency current from the current supply circuit 41 is higher. Further, in the control device 43, when the output due to the high frequency current of the high frequency current supply circuit 41 is set to 30% or less of the maximum output in normal use, in order to prevent false detection due to the influence of noise and voltage fluctuation. The second threshold value is not set.

  The operation of the steam generator 10 configured as described above will be described. The inside of the cooking chamber (not shown) is preheated by pre-heat treatment or the like, the food is stored in the cooking chamber, and the food in the cooking chamber is heated and cooked with hot air containing steam. At this time, the steam generator 10 supplies steam into the cooking chamber so as to achieve a set steam amount under the control of the control device 43. The control device 43 controls the operation of the high-frequency current supply circuit 41 to supply a high-frequency current to the induction heating coil 31 so that the amount of steam set in the cooking chamber is set, and heats the heating rod 32a to generate a steam generation container. Steam is generated from the water in 21. Further, since the water in the steam generation container 21 is reduced by generating the steam from the steam generation container 21, the control device 43 controls the opening and closing of the water supply valve 28 based on the detected water level of the water level sensor 26. The water in the steam generation container 21 is controlled to be a water level between the lower limit water level L1 and the upper limit water level L2.

  When the high frequency current is supplied to the induction heating coil 31 by controlling the operation of the high frequency current supply circuit 41 by the control device 43, if the current value measured by the ammeter 42 becomes higher than the second threshold value, the control is performed. The apparatus 43 controls the output of the high-frequency current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31 to be reduced by 50% from the set output for 60 seconds (temporarily). When a high current state is maintained in the high frequency current supply circuit 41 (overcurrent is generated) due to the generation of a vapor film around the heating rod 32a in the steam generation container 21, the high frequency current By temporarily lowering the output of the high-frequency current from the supply circuit 41, the vapor film generated around the heating rod 32a in the steam generation vessel 21 disappears, and the heating rod 32a is replaced with surrounding water (hot water). The state where a high current is maintained in the high-frequency current supply circuit 41 (overcurrent is generated) is eliminated by heat exchange. As a result, abnormal heat generation of the high-frequency current supply circuit 41 can be prevented, and an error that the inside of the steam generation container 21 is empty despite the presence of water (hot water) in the steam generation container 21. Detection can be prevented. The control device 43 controls to return the output of the high-frequency current from the high-frequency current supply circuit 41 after reducing the output of the high-frequency current from the high-frequency current supply circuit 41 for 60 seconds.

  On the other hand, the high-frequency current from the high-frequency current supply circuit 41 becomes a high current (second threshold value) due to the generation of a vapor film around the heating rod 32a in the vapor generation vessel 21. Instead, water is not properly supplied into the steam generation container 21 due to a malfunction of the water level sensor 26 or the water supply valve 28, etc., and the heating rod 32a is heated in the steam generation container 21 so that it is overheated to the Curie temperature or higher. An overcurrent may occur in the high-frequency current supply circuit 41 due to the state. In this case, the control device 43 may control the output of the high-frequency current supplied from the high-frequency current supply circuit 41 to the induction heating coil 31 to be reduced by 50% from the set output for 60 seconds (temporarily). The high current state of the high-frequency current supply circuit 41 is not resolved, and the current value measured by the ammeter 42 continues to rise. When the current value measured by the ammeter 42 exceeds the second threshold value and becomes higher than the first threshold value, the control device 43 confirms that the heating rod 32a is in an overheated state exceeding the Curie temperature due to airing. It detects and controls so that supply of the high frequency current from the high frequency current supply circuit 41 to the induction heating coil 31 may be stopped. Thereby, the abnormal heat generation of the high-frequency current supply circuit 41 can be prevented, and the heating of the heating rod 32a in the steam generation container 21 can be stopped.

 DESCRIPTION OF SYMBOLS 10 ... Induction heating type steam generator, 21 ... Steam generation container, 31 ... Induction heating coil, 32 ... Heating body, 41 ... High frequency current supply circuit, 42 ... Ammeter, 43 ... Control apparatus.

Claims (1)

A steam generation container for storing a predetermined amount of water and generating steam;
An induction heating coil wound around the outer periphery of the steam generating container;
A heating element that is housed in the steam generation container and generates heat by supplying a high-frequency current to the induction heating coil;
A high-frequency current supply circuit for supplying the high-frequency current to the induction heating coil;
An ammeter for measuring the current supplied to the induction heating coil from the high-frequency current supply circuit current;
A control device for controlling the operation of the high-frequency current supply circuit to control the supply of the high-frequency current to the induction heating coil;
The control device has an overheated state in which the heating body has exceeded the Curie temperature when a measured current value measured by the ammeter exceeds a first threshold value set higher than an output-corresponding current value corresponding to an output. An induction heating type steam generator that controls the high frequency current supply circuit to stop the supply of high frequency current from the high frequency current supply circuit,
When the measured current value measured by the ammeter exceeds a second threshold value set higher than the output-corresponding current value and less than or equal to the first threshold value, the control device causes the high-frequency current supply circuit to An induction heating type steam generator controlled to temporarily reduce the output of the high frequency current supplied to the induction heating coil.

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