JP2003045637A - Induction heating cooker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply maximum power by reducing the possibility that an inverter circuit is broken when a load is suddenly changed during heating, while at the same time preventing a decrease in the power supplied to the load when the load is shaken during the heating. SOLUTION: The induction heating cooker is provided with a protection means 14 which issues a command to shift to a protection state if determining that the current value of a heating coil 5 detected by a coil current detection means 12 has exceeded a first set value (i1), and a control means 13 which limits the maximum value of the on time of a switching element 8 according to the command to shift to the protection state, so as to shift to the protection state in which the inverter circuit 9 is protected. The induction heating cooker is also provided with a protection state canceling means 15 which issues a command to cancel the protection state if determining that the current value of the heating coil 5 detected by the coil current detection means 12 is equal to or less than a second set value (i2). The control means 13 releases the inverter circuit 9 from the protection state according to the command to cancel the protection state.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for protecting an induction heating cooker, particularly an inverter circuit. 2. Description of the Related Art In an induction heating cooker, a switching element is turned on and off at a high frequency to supply a high-frequency current to a heating coil.
A magnetic flux is generated by the high-frequency current, and an eddy current is generated in a load such as a pan made of a magnetic material such as iron or stainless steel close to the heating coil through the magnetic flux, and the load is heated by the heat generating action of the load itself. Things. In a conventional induction heating cooker, when a load is suddenly changed from a magnetic material pot to a non-magnetic material pot in a normal heating state, an excessive current flows through an inverter circuit including a switching element. As a preventive measure, a method of shifting the inverter circuit from a normal heating state to a protection state has been adopted. [0004] An example of this prior art will be described with reference to the drawings. FIG. 3 is a circuit block diagram of a conventional induction heating cooker. In FIG. 1, an AC power supply 1 is supplied to a rectifier circuit 2, the rectifier circuit 2 converts the power supply 1 into a DC power supply, and a smoothing capacitor 3 further smoothes the DC power supply. The smoothed DC power is supplied to a resonance circuit 6 formed by the heating coil 5 and the resonance capacitor 4. In this state, a load 1 of a magnetic material such as iron is applied.
When the heater 6 is placed on a top plate (not shown) above the heating coil 5 and heating is started, the control means 13 grasps the signals from the primary current detecting means 11 and the coil current detecting means 12 while controlling the operating means ( In order to control the switching element 8 in accordance with the level of the heating power set by the heating unit (not shown), a signal is output to the drive unit 10 and on / off control of the switching element 8 is performed at a high frequency via the drive unit 10. The switching element 8 is turned on and off at a high frequency to generate a high-frequency resonance current in the resonance circuit 6, ie, the heating coil 5, and is mounted on a top plate (not shown) above the heating coil 5. Power is supplied to the load 16 to heat it. At this time, the control means 13
Means for operating the electric power supplied to the load 16 (not shown)
The heating time of the load 16 is controlled by changing the on-time of the switching element 8 so that the heating power level matches the heating power level set in step (1). The operation when the load 16 is replaced during the heating will be described. The load 16 is suddenly moved from a pot made of a magnetic material such as iron to SU.
When the pot is replaced with a nonmagnetic one such as S304, the current flowing through the heating coil 5 increases rapidly. This is detected by the coil current detection means 12, and when the protection means 14 determines that the current value has exceeded the first set value (i1), the protection means 14 issues a protection state shift command to shift to the protection state to the control means 13. The control means 13 shifts to a protection state for protecting the inverter circuit 9 according to the protection state shift command. The protection state limits the maximum value of the ON time of the switching element 8 to limit the flowing current. When the control means 13 starts protection of the inverter circuit 9, the timer means 17 starts time measurement, and the protection state is maintained for a certain time. After the lapse of the predetermined time, the timer means 17 issues a protection state release command. The control means 13 releases the inverter circuit 9 from the above-mentioned protection state and returns to the normal heating state by the protection state release command. Next, a description will be given of the operation when cooking is performed by shaking the load 16 such as a pan to perform, for example, stir-fry cooking during heating. When the load 16 swings back and forth or up and down during heating to move the load 16 away from the heating coil 5, the load impedance of the inverter circuit 9 increases, so that the current hardly flows, and the current is supplied to the load 16. Although the power to be supplied decreases, the control unit 13 controls to increase the on-time of the switching element 8 because the control unit 13 tries to maintain the supplied power. At this time, if the load 16 is quickly moved so as to approach the heating coil 5, the load impedance of the inverter circuit 9 becomes small, and the control means 13 tries to maintain the power supplied to the load 16, so that the switching element 8 is turned on. Control the time to return to the original length. However, when the load 16 comes directly above the heating coil 5, it may not be time to return the ON time of the switching element 8 to the original short time, and the load 16 may remain long.
The long on-time of the switching element 8 means that the current flowing through the switching element 8, that is, the inverter circuit 9 is large, and in the worst case, the inverter circuit 9 may be destroyed. In order to prevent the inverter circuit 9 from being destroyed, when the protection means 14 determines that the current value of the heating coil 5 detected by the coil current detection means 12 has exceeded the first set value (i1), the protection state transition command is issued. Is issued to the control means 13. In response to the protection state transition command, the control means 13 transitions the inverter circuit 9 to the protection state, restricts the maximum value of the ON time of the switching element 8, and restricts the flowing current. When the control means 13 starts protection of the inverter circuit 9, the timer means 17 starts measuring time, and the protection state is maintained for a certain time. After the lapse of the predetermined time, the timer means 17 issues a protection state release command. The control means 13 releases the inverter circuit 9 from the above-mentioned protection state and returns to the normal heating state by the protection state release command. As a similar known example, Japanese Patent Application Laid-Open No. H11-111
No. 440, for example. [0017] However, such a method for protecting an induction heating cooker has the following problems. When the load 16 made of a magnetic material is suddenly replaced with the load 16 made of a non-magnetic material during heating, the timer circuit 17 shifts the inverter circuit 9 to a protection state, and the current flowing through the inverter circuit 9 is limited. Thus, although abrupt destruction can be prevented, when the protection state by the timer means 17 is released within a predetermined time, a phenomenon occurs in which a large current flows through the inverter circuit 9 when the protection state is released. Then, this current is detected, the protection state is restored, and these phenomena are repeated to cause a problem. In other words, the protection state → protection state release (large current) → protection state → protection state release (large current)... Repeatedly occurs at regular time intervals, causing the temperature of the inverter circuit 9 to rise,
Eventually it can lead to destruction. When cooking is performed by shaking the load 16 such as a pan back and forth or up and down during heating, the inverter circuit 9
Although the protection state is executed for a certain period of time, the average current flowing through the heating coil 5 is reduced, and the power supplied to the average load 16 is reduced. The problem of becoming smaller was inherent. The present invention has been made to solve the above problem, and reduces the possibility of breaking down the inverter circuit 9 when the load 16 is suddenly replaced during heating.
The load 16 when the load 16 is shaken during heating or the like.
The purpose of the present invention is to prevent a decrease in power supplied to a vehicle and to supply the maximum power. According to the present invention, there is provided a heating coil for heating a load, and switching for generating a high frequency resonance current in the heating coil by being turned on and off at a high frequency. An inverter circuit formed by elements and the like; a coil current detecting means for detecting a current flowing through the heating coil; and a determination that the current value of the heating coil detected by the coil current detecting means has exceeded a first set value (i1). A protection means for issuing a protection state transition command, an input circuit and the like by controlling the ON time and the like of the switching element, and a maximum value of the ON time of the switching element by the protection state transition command and the inverter circuit. In the induction heating cooker provided with a control means for shifting to a protection state for protecting the When the current value of the heating coil is determined to be equal to or less than the second set value (i2), a protection state release unit for issuing a protection state release command is provided, and the control unit switches the inverter circuit from the protection state by the protection state release command. It is to cancel. DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, according to the present invention, the current value of the heating coil detected by the coil current detecting means is equal to the first value.
When it is determined that the set value (i1) has been exceeded, a protection unit that issues a protection state transition command, an input power and the like are controlled by controlling the ON time of the switching element, and the switching element is switched by the protection state transition command. In the induction heating cooker provided with control means for limiting the maximum value of the ON time and shifting to a protection state for protecting the inverter circuit, the current value of the heating coil detected by the coil current detection means is set to a second set value ( i2) Protected state releasing means for issuing a protected state releasing command when it is determined as follows, and the control means releases the inverter circuit from the protected state in response to the protected state releasing command. This reduces the possibility of breaking the inverter circuit when the load is suddenly replaced during heating, and at the same time, prevents a decrease in the power supplied to the load when the load is shaken during heating. The maximum power is supplied. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing one embodiment of the present invention. Referring to FIG. 1, reference numeral 1 denotes an AC power supply having a rectifier circuit 2 connected to both ends thereof, one end of a smoothing capacitor 3 connected to a positive terminal of the rectifier circuit 2, and another end connected to a negative terminal of the rectifier circuit 2. To form a DC power supply. Reference numeral 4 denotes a resonance capacitor, two of which are connected in series, and one end of which is connected to the high voltage side (+ of the rectifier circuit 2) of the DC power supply.
Terminal part. The same applies hereinafter. ), And the other end is connected to the low voltage side of the DC power supply (-terminal of the rectifier circuit 2; the same applies hereinafter), and two series connection points are connected to the heating coil 5 described later.
Is connected to the first terminal. A heating coil 5 heats a load 16 to be described later when a high-frequency resonance current flows. Reference numeral 6 denotes a resonance circuit formed by the two resonance capacitors 4 and the heating coil 5. Reference numeral 7 denotes a snubber capacitor, two of which are connected in series, one end of which is connected to the high voltage side of the DC power supply, the other end of which is connected to the low voltage side of the DC power supply, and two series connection points. Is connected to the second terminal of the heating coil 5. Reference numeral 8 denotes a switching element having an antiparallel diode, two of which are connected in series, one end of which is connected to the high voltage side of the DC power supply, and the other end of which is connected to the low voltage side of the DC power supply. , Two series connection points are connected to the second terminal of the heating coil 5. The gates of the two switching elements 8 are connected to the output of the driving unit 10 described later. The switching element 8 generates a high-frequency resonance current in the heating coil 5 by being turned on and off at a high frequency. Reference numeral 9 denotes an inverter circuit formed by the switching element 8 and the like. Specifically, it is formed by two switching elements 8 and two snubber capacitors 7. Reference numeral 10 denotes a drive unit, which connects this input unit to the output unit of the control means 13 described later, and connects the output unit to the switching element 8.
Connected to the gate section. Reference numeral 11 denotes a primary current detecting means, which is installed so as to detect a current flowing between the power supply 1 and the rectifier circuit 2, that is, a primary current, and has its output connected to the input of the control means 13 to be described later. . Numeral 12 denotes a coil current detecting means which is installed so as to detect a current flowing through the heating coil 5, and has an output part connected to an input part of the control means 13 to be described later. Numeral 13 denotes a control means which connects the input part to the primary current detecting means 11 and the coil current detecting means 12, connects the output part to the driving part 10, and turns on the switching element 8 through the driving part 10. And the like to control the input power and the like, and limit the maximum value of the ON time of the switching element 8 by a protection state shift command described later to shift to the protection state where the inverter circuit 9 is protected. The inverter circuit 9 includes a switching element 8
By limiting the maximum value of the ON time, the flowing current is limited and the current is protected from excessive current. The control means 13 includes a protection means 14 for issuing a protection state shift command and a protection state cancellation means 15 for issuing a protection state cancellation command. Numeral 14 denotes a protection means, which is built in the control means 13 and when the current value of the heating coil 5 detected by the coil current detection means 12 is judged to exceed the first set value (i1), a protection state shift command is issued. Emits. Numeral 15 denotes protection state releasing means,
When the current value of the heating coil 5 detected by the coil current detecting means 12 is determined to be equal to or less than the second set value (i2), a protection state release command is issued. The control means 13
In response to the protection state release command, the inverter circuit 9 is released from the protection state and returned to the normal heating state. Reference numeral 16 denotes a load, such as a pan made of a magnetic material such as iron or stainless steel, which is placed on a top plate (not shown) above the heating coil 5 and heated. The overall operation of the above configuration will be described. An AC power supply 1 is supplied to a rectifier circuit 2. The rectifier circuit 2 converts the power supply 1 into a DC power supply, and a smoothing capacitor 3 further smoothes the DC power supply. The smoothed DC power supply
It is supplied to a resonance circuit 6 formed by the heating coil 5 and the resonance capacitor 4. In this state, the load 1 of the magnetic material such as iron
When the heater 6 is placed on a top plate (not shown) above the heating coil 5 and heating is started, the control means 13 grasps the signals from the primary current detecting means 11 and the coil current detecting means 12 while controlling the operating means ( A high-frequency signal corresponding to the level of the heating power set by the controller (not shown) is output to the drive unit 10, and the inverter circuit 9, that is, the switching element 8 is turned on and off via the drive unit 10. The switching element 8 is turned on and off at a high frequency to generate a high-frequency resonance current in the resonance circuit 6, that is, the heating coil 5, and is mounted on a top plate (not shown) above the heating coil 5. Power is supplied to the load 16 to heat it. At this time, the control means 13
The heating time of the load 16 is controlled by changing the ON time of the switching element 8 so that the power supplied to the load 16 matches the level of the heating power set by the operation means (not shown). The operation when the load 16 is replaced during the heating will be described with reference to FIGS.
FIG. 2 is a diagram showing the state control of the inverter circuit according to one embodiment of the present invention, in which the current value of the heating coil 5 and the state of the inverter circuit 9 are shown with their time axes coincident. The load 16 is suddenly moved from a pot made of a magnetic material such as iron to SU.
When the pot is replaced with a nonmagnetic one such as S304, the current flowing through the heating coil 5 increases rapidly. This is detected by the coil current detection means 12, and when the protection means 14 determines that the current value has exceeded the first set value (i1), the protection means 14 issues a protection state shift command to shift to the protection state to the control means 13. The control means 13 shifts the inverter circuit 9 to the protection state according to the protection state shift command. In the protection state, the switching element 8
Is controlled so that the current flowing through the heating coil 5, that is, the current flowing through the switching element 8, is reduced. When the protection state release unit 15 determines that the current value of the heating coil 5 detected by the coil current detection unit 12 is equal to or less than the second set value (i2), the protection state release unit 15 issues a protection state release command. Since the load impedance of the material pot is sufficiently small, the switching element 8
Does not fall below the second set value (i2). Therefore, the protection state releasing means 15 does not operate, and the protection state of the inverter circuit 9 is continued, and the protection state → protection state release (large current) → at regular time intervals as in the prior art.
Since the protection state → protection state release (large current)... Does not occur repeatedly, the inverter circuit 9 is heated to the maximum level with respect to the load 16 without destruction. Next, a description will be given of the operation in the case where the load 16 such as a pan is shaken to cook, for example, a stir-fry dish during heating. The following will also be described with reference to FIGS. When the load 16 is swung up and down or up and down during heating to change the load impedance and the control means 13 controls the switching element 8 to increase the on-time, the current of the heating coil 5 increases, When determining that the current value of the heating coil 5 detected by the current detection means 12 exceeds the first set value (i1), the protection means 14 issues a protection state transition command to the control means 13. Control means 13
The protection circuit shifts the inverter circuit 9 to the protection state by this protection state shift command to prevent the inverter circuit 9 from being destroyed. In the protection state, when the load impedance changes and the control means 13 controls the ON time of the switching element 8 to be short, the current of the heating coil 5 decreases, and the heating coil detected by the coil current detection means 12 When it is determined that the current value of No. 5 has fallen below the second set value (i2), the protection state release means 15 issues a protection state release command. Since the control means 13 quickly releases the inverter circuit 9 from the protection state by the protection state release means, a normal current larger than that in the protection state flows through the inverter circuit 9. As described above, even when cooking is performed while shaking the load 16 such as a pot, the maximum power can be supplied without reducing the power supplied to the load 16. As described above, the induction heating cooker according to the present invention, when it is determined that the current value of the heating coil detected by the coil current detecting means has exceeded the first set value (i1). A protection unit that issues a protection state transition command, and controls the input power and the like by controlling the ON time and the like of the switching element, and limits the maximum value of the ON time of the switching element according to the protection state transition command to operate the inverter circuit. When the current value of the heating coil detected by the coil current detecting means is determined to be equal to or less than the second set value (i2) in the induction heating cooker provided with control means for shifting to the protection state to be protected, the protection state release command Is provided, and the control means releases the inverter circuit from the protection state in response to the protection state release command. Accordingly, when the load is suddenly changed from a pot made of a magnetic material such as iron to a pot made of a non-magnetic material such as SUS304,
Since the inverter circuit is released from the protection state as needed, there is no repetition of the protection state → protection state release (excessive current) → protection state → protection state release (excessive current)... Therefore, maximum heating of the load is continued without breaking the inverter circuit. Further, during cooking, for example, in order to perform stir-fry cooking, the inverter circuit is quickly released from the protection state even when cooking is performed by swinging the load of a pot or the like up and down or up and down. The maximum power can be supplied without reducing the power supply. Usually, since the control means is constituted by a microcomputer, the protection state canceling means can be constituted by a program, so that it can be implemented without increasing the cost. As described above, according to the present invention, it is possible to obtain the effect of improving the reliability and performance of a product without increasing the cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit block diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing state control of an inverter circuit according to one embodiment of the present invention. FIG. 3 is a circuit block diagram showing a conventional example. [Description of Signs] 5 Heating coil 6 Resonant circuit 8 Switching element 9 Inverter circuit 12 Coil current detecting means 13 Control means 14 Protecting means 15 Protected state releasing means 16 Load 17 Timer means

Claims (1)

1. A heating coil for heating a load, and a switching element for generating a high-frequency resonance current in the heating coil when turned on and off at a high frequency. Inverter circuit (9) formed by
A coil current detecting means (12) for detecting a current flowing through the heating coil (5); and a current value of the heating coil (5) detected by the coil current detecting means (12) is a first set value (i1). When it is determined that it has exceeded, the protection means (14) for issuing a protection state shift command, the input power and the like are controlled by controlling the ON time and the like of the switching element (8), and the switching element (8) is controlled by the protection state shift command. ), A control means (13) for limiting the maximum value of the ON time to shift to a protection state for protecting the inverter circuit (9). When it is determined that the current value of the coil (5) is equal to or less than the second set value (i2), a protection state release unit (15) for issuing a protection state release command is provided. Induction cooking device, characterized in that to release the inverter circuit (9) from the protected state by decree.