JP2005222796A - Induction heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device capable of keeping an electric duty of electronic components constructing an inverter circuit below an allowable value. <P>SOLUTION: The induction heating device changes variable factors of a switching means 4a through a control circuit 7, so that an output value of a control object value detecting means 10 comes to a prescribed value; and constructed so that selection is made whether the variable factors of the switching means 4a should be changed in compliance with output values of an input voltage detection means 9 or not. By the above, the duty of the electronic components constructing the inverter circuit is kept below the allowable value against an abrupt variation of the power source voltage to be supplied to the inverter circuit caused by an abnormality of the power source, and the reliability of the inexpensive and user-friendly induction heating device with good operability can be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an induction heating device used as, for example, an induction heating cooker.

  A conventional induction heating apparatus will be described taking an induction heating cooker used in a general home, a restaurant, an office, or the like as an example.

In this type of induction heating cooker, one that varies the limit value of the control target of the inverter circuit (the input current to the inverter circuit, the voltage across the switching means, etc.) according to the voltage change of the AC power supply is known. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 9-245955

  However, in the conventional configuration, for example, when the limit value of the input current to the inverter circuit is varied according to the voltage change of the AC power supply, the voltage drop of the AC power supply corresponds to the voltage drop. Set the input current limit value for the minute to a smaller value. However, if the load operates at an operating point where the change width is insufficient, the maximum drive time ratio set by the rated value of the AC power supply is reached before reaching the input current limit value that has been reset to a small value. The drive time ratio control means performs an operation for increasing the drive time ratio. For this reason, if the AC power supply suddenly returns to the original voltage value in this state, the inverter circuit is connected to the maximum drive time ratio while the drive time ratio control means reduces the drive time ratio to the original state. The electric duty of the electronic parts, switching means, etc. constituting the inverter circuit exceeds the allowable value of the parts, and the worst is the destruction.

  In addition, as the output of equipment increases, the electrical responsibility of the electronic components that make up the inverter circuit also increases. To ensure a sufficient margin for the allowable value, the electronic components that make up the inverter circuit It is easiest to improve the tolerance of the electrical responsibility itself. However, there are problems in that the cost increases due to the deterioration of the manufacturing yield of the electronic components, and the increase in physical quantity is in a trade-off relationship with the increase in the allowable value of electrical responsibility. For example, in the case of an IGBT serving as a switching means, the conduction loss and the switching loss tend to increase with the improvement of the withstand voltage, which is an electrical duty, and the air flow rate of the cooling fan is used to sufficiently cool the loss. An increase in the size of the heat sink or the like, an accompanying increase in noise, and a decrease in heating efficiency may occur. The same applies to resonant capacitors. With the improvement of withstand voltage and allowable current, which are electrical responsibilities, film capacitors have difficulty in securing installation space due to an increase in the volume of parts accompanying the increase in film thickness. The cost increases due to the increase in quantity.

  The present invention solves the above-described conventional problems, and more reliably keeps the electrical responsibility of the electronic components constituting the inverter circuit below the allowable value with respect to changes in the power supply voltage, and is inexpensive and convenient to use. An object of the present invention is to provide an induction heating device with high reliability.

  In order to solve the conventional problem, the induction heating apparatus of the present invention varies the variable element of the switching means by the control circuit so that the output value of the control target value detection means becomes the first predetermined value. At the same time, whether to change the variable element of the switching means is selected according to the output value of the input voltage detection means.

  As a result, the electrical duty of the electronic components that make up the inverter circuit is kept below the permissible value against sudden fluctuations in the power supply voltage to the inverter circuit due to power failure, etc., and it is inexpensive, convenient and reliable. A highly efficient induction heating apparatus can be provided.

  The induction heating device of the present invention can more reliably keep the electrical duty of the electronic components constituting the inverter circuit below the allowable value with respect to changes in the power supply voltage.

  The first invention includes a heating coil and switching means, converts a direct current obtained by rectifying and smoothing an alternating current power source into a high frequency alternating current, supplies a high frequency current to the heating coil, and inductively heats an object to be heated; A control circuit for controlling the operation of the inverter circuit, the control circuit varying at least one of the variable elements of the conduction time, the driving cycle, or the conduction ratio of the switching means to the heated object. Drive means for controlling the induction heating output, input voltage detection means for detecting the voltage of the AC power supply, and control target value detection means for detecting a control target value corresponding to the induction heating output to the heated object. Then, the control circuit varies the variable element of the switching means so that the output value of the control target value detection means becomes a first predetermined value, and the input voltage detection By adopting an induction heating device that selects whether or not to change the variable element of the switching means according to the output value of the stage, it is possible to reduce the power supply voltage to the inverter circuit due to a power supply abnormality. On the other hand, it is possible to provide an induction heating device that keeps the electrical duty of the electronic components constituting the inverter circuit below the allowable value, is inexpensive, easy to use, and has high reliability.

  In the second invention, in particular, in the first invention, even when it is selected not to change the variable element of the switching means according to the output value of the input voltage detection means, the output of the control target value detection means Until the second predetermined value is reached, the variable element of the switching means can be changed, so that the electric power of the AC power supply is reduced at the time of low induction heating output in which the electrical duty of the electronic components constituting the inverter circuit is small. Without being affected by the power supply voltage fluctuation, the variable element of the switching means can be varied to obtain a desired induction heating output.

  According to a third invention, in particular, in the first invention, when the variable element of the switching means becomes a third predetermined value or more, whether to change the variable element of the switching means with respect to the voltage change of the AC power supply. By selecting it, the variable elements of the switching means can be varied without being affected by fluctuations in the power supply voltage of the AC power supply at the time of low induction heating output in which the electrical duty of the electronic components constituting the inverter circuit is small Therefore, when the variable element of the switching means becomes equal to or greater than the third predetermined value, it is selected whether to change the variable element of the switching means. Can be obtained.

  In particular, in the fourth invention, in any one of the first to third inventions, the control object value detection means is an input current detection means for detecting an input current to the inverter circuit, whereby the input to the inverter circuit is performed. The induction heating output of the heating coil can be controlled by varying the variable element of the switching means so that the output of the input current detection means corresponding to the current becomes the first predetermined value.

  In particular, the fifth invention is characterized in that, in any one of the first to third inventions, the control object value detecting means is a switching means both-end voltage detecting means for detecting a both-end voltage of the switching means. The induction heating output of the heating coil can be controlled by changing the variable element of the switching means so that the output of the voltage detection means across the switching means corresponding to the voltage becomes the first predetermined value.

  In a sixth aspect of the invention, in particular, in any one of the first to third aspects of the invention, the control object value detection means is a heating coil current detection means for detecting a current flowing in the heating coil, whereby a current flowing in the heating coil is determined. The induction heating output of the heating coil can be controlled by changing the variable element of the switching means so that the output of the heating coil current detection means corresponding to the above becomes the first predetermined value.

  In a seventh aspect of the invention, in particular, in any one of the first to third aspects of the invention, the control object value detection means is a switching means current detection means for detecting a current flowing in the switching means, so that the current flowing in the switching means The induction heating output of the heating coil can be controlled by varying the variable element of the switching means so that the output of the switching means current detection means corresponding to the above becomes the first predetermined value.

  In an eighth aspect of the invention, in particular, in any one of the first to third aspects of the invention, the inverter circuit includes a resonance capacitor that forms a resonance loop with the heating coil, and the control object value detection means is configured to obtain the voltage across the resonance capacitor. By using the capacitor both-end voltage detecting means to detect, by changing the variable element of the switching means so that the output of the resonance capacitor both-end voltage detecting means corresponding to the both-end voltage of the resonant capacitor becomes the first predetermined value. The induction heating output of the heating coil can be controlled.

  According to a ninth aspect of the invention, in particular, in any one of the first to third aspects of the invention, the inverter circuit includes a resonance capacitor that forms a resonance loop with the heating coil, and the current flowing through the resonance capacitor is controlled by the control target value detecting means. By using the capacitor current detection means to detect, heating is achieved by changing the variable element of the switching means so that the output of the resonance capacitor current detection means corresponding to the current flowing through the resonance capacitor becomes the first predetermined value. The induction heating output of the coil can be controlled.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
Hereinafter, the induction heating apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings, taking an induction heating cooker as an example.

  As shown in FIG. 1, an AC power supply (commercial power supply) 1 is rectified by a rectifier circuit 2 made of a bridge-connected diode and smoothed by a smoothing circuit 3 made of a choke coil 3a and a capacitor 3b.

  The inverter circuit 4 includes a heating coil 5, a switching means 4a, and a resonance capacitor 4b. The inverter circuit 4 converts a direct current obtained by rectifying and smoothing the alternating current power source 1 into a high frequency alternating current, and supplies the heating coil 5 with a high frequency current to cover the object such as a pan. The heating body 6 is induction-heated.

  The control circuit 7 that controls the operation of the inverter circuit 4 varies at least one of the variable elements of the conduction time, the driving cycle, or the conduction ratio of the switching means 4a to generate the induction heating output to the heated body 6. Driving means 8 for controlling, input voltage detecting means 9 for detecting the voltage of the AC power supply 1, and control target value detecting means 10 for detecting a control target value corresponding to the induction heating output to the heated body 6. Have.

  Then, the control circuit 7 varies the variable element of the switching means 4a so that the output value of the control target value detection means 10 becomes the first predetermined value, and the output of the input voltage detection means 9 Whether to change the variable element of the switching means 4a is selected according to the value. That is, the input voltage detection means 9 detects the voltage value of the AC power supply 1 and selects whether to change the variable element of the current switching means 4a, for example, the conduction time, according to the detected voltage of the AC power supply 1. To do.

  Here, the case where the control target value control means 10 in the present embodiment is an input current detection means for detecting an input current to the inverter circuit 4 will be described. In the control circuit 7, the output value (current value) of the control target value detection means 10 based on the input current to the inverter circuit 4 correlated with the induction heating output to the heated body 6 is a first predetermined value, for example, 14A, the variable element (for example, conduction time) of the switching means 4a is varied by the driving means 8 to change the high-frequency current supplied to the heating coil 5, and the high-frequency current generated from the heating coil 5 by this high-frequency current. The heated object 6 such as a pan is induction-heated by the magnetic flux. At the same time, the induction heating output to the heated body 6 can be controlled. In general, the induction heating output is controlled in a region where the input current to the inverter circuit 4 monotonously increases with respect to the variable element of the switching means 4a.

  On the other hand, the input voltage detection means 9 selects whether or not to change the variable element (conduction time) of the current switching means 4a according to the voltage of the AC power supply 1. The selection method is as follows.

  In the case of the heated body 6 operating at the operating point a of the characteristic A shown in FIG. 2, for example, when a voltage drop of 5% or less with respect to the rated voltage value of the AC power supply 1 is detected, switching is performed. By choosing to vary the conduction time of the means 4a, the driving means 8 changes the conduction time of the switching means 4a until the input current reaches the first predetermined value, 14A.

  Further, when a voltage drop of more than 5% with respect to the rated voltage value of the AC power supply 1 is detected and the operation is performed at the operating point aL of the characteristic AL, it is selected not to vary the conduction time of the switching means 4a, Even if the input current is not 14 A, the driving unit 8 operates at the operating point aL1 without changing the conduction time of the switching unit 4a.

  Further, when a voltage increase of 5% or less with respect to the rated voltage value of the AC power supply 1 is detected, it is selected not to change the conduction time of the switching means 4a, and the drive is performed even if the input current is not 14A. The means 8 does not change the conduction time of the switching means 4a.

  Further, when a voltage increase of more than 5% with respect to the rated voltage value of the AC power supply 1 is detected and the operation is performed at the operating point aH1 of the characteristic AH, it is selected to change the conduction time of the switching means 4a. The drive means 8 changes the variable element of the switching means 4a until the input current reaches 14A and operates at the operating point aH.

  By such selection, the conduction time of the switching means 4a can be appropriately limited according to the fluctuation range of the rated voltage value of the AC power supply 1. Therefore, since the control target value after the voltage of the AC power source 1 fluctuates can be made smaller than or equal to the input current when the voltage of the AC power source 1 is the rated value, the voltage level of the AC power source 1 can be changed. The electrical duty of the electronic components constituting the inverter circuit 4 can be made smaller than or equal to the electrical duty of the electronic components constituting the inverter circuit 4 when the voltage of the AC power supply 1 is at the rated value.

  In addition, when the voltage of the AC power supply 1 is instantaneously decreased, the voltage returns to the AC power supply 1, that is, when an instantaneous power failure and instantaneous power failure occur, and when operating at the operating point a of the characteristic A, the voltage of the AC power supply 1 is When the voltage drops by more than 5%, for example, 10%, during this reduced period, the conduction time of the switching means 4a is larger than when the AC power supply 1 is at the rated voltage, and operates at the operating point aL of the characteristic AL. Thereafter, the AC power supply 1 instantaneously returns to the rated voltage value, and this change is detected by the control circuit 7 through the control target value detection means 10 so that the conduction time of the switching means 4a is reduced in the drive means 8. To output and control various signals. That is, the switching means 4a tries to return the conduction time when the alternating current power supply 1 is at the rated voltage, and until the alternating current power supply 1 returns to the rated voltage, the switching means 4a is at the rated voltage. 4a operates at the operating point a1 while the conduction time is long. However, since the conduction time of the switching means 4a is not changed according to the voltage value of the AC power supply 1 detected by the input voltage detection means 9, the voltage of the AC power supply 1 is rated. Immediately after returning to, the operating point a is restored. For this reason, the electrical duty of the electronic component which comprises the inverter circuit 4 can be suppressed below to an allowable value.

  Here, in the voltage fluctuation range of 5% or less with respect to the rated value of the voltage of the AC power supply 1, it is selected that changing the conduction time of the switching means 4a is the detection variation of the input voltage detecting means 9. Avoiding the situation where the desired induction heating output cannot be obtained or the heating performance deteriorates due to inadvertent change of the conduction time of the switching means 4a due to erroneous detection due to noise or disturbance noise It is because it is doing.

(Embodiment 2)
Next, the induction heating apparatus in Embodiment 2 of this invention is demonstrated.

  In the present embodiment, the difference from the first embodiment is that even if it is selected not to change the variable element of the switching means 4a according to the output value of the input voltage detection means 9, the control target value is also selected. The variable element of the switching means 4a is variable until the output of the detection means 10 reaches the second predetermined value.

  That is, even when the output value of the input voltage detection means 9 exceeds 5% of the rated voltage and it is selected not to change the variable element of the switching means 4a, the control target value detection means 10 (input current detection means) ) Until the output reaches a second predetermined value, for example, a value corresponding to the input current 7A, the variable element (conduction time) of the switching means 4a is varied.

  Thereby, while the inverter circuit 4 starts to operate and gradually increases the variable element of the switching means 4a from the low input current, or the output of the control target value detection means 10 sets the first predetermined value small, For example, when 5A is used instead of 14A, the variable element of the switching means 4a, which is a region where the electrical duty of the electronic components constituting the inverter circuit 4 is small, is a low induction with a third predetermined value, for example, 10 μs or less. At the time of heating output, it is possible to obtain a desired induction heating output by varying the variable element of the switching means 4a without being difficult to control the induction heating output due to the influence of the power supply voltage fluctuation of the AC power supply 1. .

(Embodiment 3)
Next, the induction heating apparatus in Embodiment 3 of this invention is demonstrated.

  In the present embodiment, the difference from the first embodiment is that when the variable element of the switching means 4a exceeds the third predetermined value, the variable element of the switching means 4a is changed with respect to the voltage change of the AC power supply 1. It is to select whether to change.

  That is, when the variable element (conducting time) of the switching means 4a becomes a third predetermined value, for example, 10 μs or more, it is selected whether to change the variable element of the switching means 4a with respect to the voltage change of the AC power supply 1. To do. That is, until the variable element of the switching unit 4a reaches a third predetermined value, for example, 10 μs, the variable element of the switching unit 4a is always allowed to change regardless of the fluctuation of the AC power supply 1. As a result, the induction heating output of the heated body 6 is generally controlled in a region where the input current monotonously increases with respect to the variable element of the switching means 4a. While gradually increasing the variable element of the switching means 4a from the input current, or when the output of the control target value detection means 10 is set to a small first predetermined value, for example, 5A instead of 14A, At the time of low induction heating output in which the electrical duty of the electronic components constituting the inverter circuit 4 is small, it is not affected by the power supply voltage fluctuation of the AC power supply 1 and it becomes difficult to control the induction heating output. The variable element can be varied to obtain a desired induction heating output.

  In each of the first to third embodiments described above, a description has been given of a configuration including one power component that constitutes the inverter circuit 4 such as the switching means 4a, the resonant capacitor 4b, and the heating coil 5, but these are described. Even if it is configured by combining a plurality, the same effect is obtained. Further, although the control target value detection means 10 is described as the input current detection means to the inverter circuit 4, a physical quantity correlated with the induction heating output to the heated body 6, for example, the voltage across the switching means 4a is detected. Switching means both-end voltage detecting means, heating coil current detecting means detecting current flowing through the heating coil 5, switching means current detecting means detecting current flowing through the switching means 4a, capacitor both-end voltage detecting the voltage across the resonance capacitor 4b Needless to say, the same applies to the detection means, the capacitor current detection means for detecting the current flowing through the resonance capacitor 4b, and the like. Furthermore, the control of the induction heating output to the heated body 6 is not limited to the conduction time of the switching means 4a depending on the configuration of the inverter circuit 4, etc., but at least one of the variable elements of the conduction time, the driving cycle, or the conduction ratio. You can change one. Further, the selection of whether or not to change the variable element of the switching means 4a with respect to the voltage fluctuation range of the AC power supply 1 may be appropriately changed according to the behavior of the inverter circuit 4 with respect to the voltage fluctuation of the AC power supply 1. Furthermore, the voltage detected by the input voltage detecting means 9 may be any physical quantity that changes linearly corresponding to the AC power supply 1.

  As described above, the induction heating apparatus according to the present invention reduces the electrical duty of the electronic components constituting the inverter circuit to the voltage of the AC power supply approximately equal to or less than the rated voltage even with respect to the voltage fluctuation of the AC power supply. In addition to induction heating cookers and induction heating rice cookers that have already been put to practical use, it can also be used for heating equipment such as electric water heaters, electric irons, dishwashers and water heaters that can be used for induction heating. Further, the present invention can be applied to other electric devices using an inverter circuit, a microwave oven, a refrigerator, a washing machine, and the like.

The block diagram of the induction heating apparatus in Embodiment 1-3 of this invention Characteristic diagram showing the relationship between the conduction time of the switching means of the induction heating device and the input current to the inverter circuit

Explanation of symbols

1 AC power (commercial power)
DESCRIPTION OF SYMBOLS 2 Rectifier circuit 3 Smoothing circuit 4 Inverter circuit 4a Switching means 4b Resonance capacitor 5 Heating coil 6 Heated object 7 Control circuit 8 Drive means 9 Input voltage detection means 10 Control object value detection means (input current detection means)

Claims (9)

An inverter circuit that includes a heating coil and switching means, converts a direct current obtained by rectifying and smoothing an AC power source into a high-frequency alternating current, supplies a high-frequency current to the heating coil, and inductively heats the object to be heated; A control circuit that controls the induction heating output to the object to be heated by varying at least one of the variable elements of the conduction time, drive cycle, or conduction ratio of the switching means. Drive means, input voltage detection means for detecting the voltage of the AC power supply, and control target value detection means for detecting a control target value corresponding to the induction heating output to the object to be heated, by the control circuit The variable element of the switching means is varied so that the output value of the control target value detection means becomes a first predetermined value, and the output value of the input voltage detection means Flip, the induction heating device so as to select whether to change the variables of the switching means. Even when it is selected not to change the variable element of the switching means according to the output value of the input voltage detection means, the switching means until the output of the control target value detection means reaches the second predetermined value. The induction heating apparatus according to claim 1, wherein the variable element is variable. 2. The induction heating apparatus according to claim 1, wherein when the variable element of the switching means becomes a third predetermined value or more, it is selected whether to change the variable element of the switching means with respect to the voltage change of the AC power supply. . The induction heating apparatus according to any one of claims 1 to 3, wherein the control target value detection means is an input current detection means for detecting an input current to the inverter circuit. The induction heating apparatus according to any one of claims 1 to 3, wherein the control target value detection means is a switching means both-end voltage detection means for detecting a voltage across the switching means. The induction heating apparatus according to any one of claims 1 to 3, wherein the control target value detection means is a heating coil current detection means for detecting a current flowing through the heating coil. The induction heating apparatus according to any one of claims 1 to 3, wherein the control target value detection means is a switching means current detection means for detecting a current flowing through the switching means. The inverter circuit includes a resonance capacitor that forms a resonance loop with a heating coil, and the control target value detection unit is a capacitor both-end voltage detection unit that detects a voltage between both ends of the resonance capacitor. Induction heating device. 4. The inverter circuit according to claim 1, wherein the inverter circuit includes a resonance capacitor that forms a resonance loop with the heating coil, and the control target value detection unit is a capacitor current detection unit that detects a current flowing through the resonance capacitor. Induction heating device.

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