JP4176491B2 - Electromagnetic induction heating cooker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic induction heating cooker that uses an inverter circuit to supply a high-frequency current to an induction heating coil to heat a cooking pan by electromagnetic induction, and in particular, the temperature of a top plate installed on the upper surface of the induction heating coil. It is related with the electromagnetic induction heating cooking appliance which has the function which can measure and can discriminate | determine whether the cooking pan is heated appropriately.
[0002]
[Prior art]
FIG. 5 is an overall configuration diagram of a conventional electromagnetic induction heating cooker.
[0003]
In FIG. 5, IH indicates an electromagnetic induction heating cooker, PB indicates a pan that is induction heated by the electromagnetic induction heating cooker IH, and the electromagnetic induction heating cooker IH includes a top plate PL formed of ceramics or the like, and a spiral. An induction heating coil HL that is wound in a circular shape and has a blank in the center, a coil base CB that supports the induction heating coil HL, and a temperature detection unit TD for detecting the heating temperature of the pan PB, , And a high frequency power supply HS for supplying a high frequency current to the induction heating coil HL.
[0004]
In order to detect the heating temperature of the pan PB through the top plate PL, the temperature detection unit TD holds a temperature sensor element such as a glass-sealed thermistor (not shown) and the temperature sensor element. A sensor holder that is installed between the sensor holder and the coil base CB, and a coil spring for contacting the temperature sensor element to the lower surface of the top plate PL via the sensor holder, and induction heating. The magnetic flux from the coil HL is composed of a lead wire such as a jumet wire of the temperature sensor element and a copper ring that serves as a magnetic shield so as not to interlink with the magnetic coil spring.
[0005]
From the above, a nonmagnetic conductor, for example, a hollow copper ring, installed on the side surface around the temperature sensor element, can have a magnetic shielding action against the magnetic flux from the induction heating coil HL. As a result, the error of the measured value of the heating temperature of the pan can be reduced. However, a complicated fixing stop for contacting the top plate PL is required.
(See Patent Document 1)
[0006]
The cooking device of prior art 2 is a cooking device that heats and cooks the cooked product by heating a pan containing the cooked product by gas combustion means. This cooking device includes temperature detecting means for detecting the outer surface temperature of the pan and heating control means for gas combustion means for heating the pan. The temperature detection means is set on the gas combustion means and detects the outer surface temperature of the pan without contact with the pan. Then, the control means sets a temperature suitable for heating the cooked food, and subtracts a steady deviation obtained corresponding to the outer surface temperature of the pan detected by the temperature detecting means from the outer surface temperature. By calculating the temperature of the cooked food in the pan, the calculated temperature is compared with the set temperature, and if the calculated temperature is equal to or lower than the set temperature, the amount of combustion gas supplied to the gas combustion means is increased. When the calculated temperature exceeds the set temperature, the supply amount of the combustion gas to the gas combustion means is decreased. As a result, the food can be cooked at a temperature suitable for the food.
(See Patent Document 2)
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-100466 [Patent Document 2]
Japanese Patent Laid-Open No. 8-178295
[Problems to be solved by the invention]
In order to measure the temperature of the top plate, a thermistor element, a thermostat or the like is used, and the temperature is measured by directly contacting the lower surface of the top plate. However, a complicated fixing stop for contacting the top plate is required. Further, since the temperature of the top plate is detected at a single point, there is a problem in the accuracy of the measured temperature.
[0009]
[Means for Solving the Problems]
The invention of claim 1 includes a resonant capacitor, an induction heating coil that forms a series resonance with the resonant capacitor, a rectifier circuit that rectifies a commercial AC power source and converts it into a DC voltage, and a DC voltage of the rectifier circuit as an input. An inverter circuit that supplies a high-frequency current to the induction heating coil; a power calculation circuit that calculates an input power of the inverter circuit and outputs a power calculation signal; a power setting circuit that outputs a predetermined power setting signal; A differential amplifier circuit that differentially amplifies a power calculation signal and the power setting signal, a control processing circuit that controls an output frequency of the inverter circuit according to the differential amplification signal of the differential amplifier circuit, and an internal cooling And a top plate installed close to the top surface of the induction heating coil, and a pan is placed on the top surface of the top plate for heating. In magnetic induction heating cooker,
A non-contact temperature sensor for detecting the temperature of the lower surface of the top plate in a non-contact manner and outputting a temperature sensor signal; and when the value of the temperature sensor signal exceeds a predetermined normal temperature rise limit value, A fan control circuit for increasing the number of revolutions to moderate the temperature rise of the pan, and the inverter circuit when the value of the temperature sensor signal exceeds a predetermined second temperature rise limit value higher than the normal temperature rise limit value A power limiting circuit for attenuating the value of the power setting signal for controlling the output of the inverter, and the inverter when the value of the temperature sensor signal exceeds a predetermined temperature rise limit value higher than the second temperature rise limit value An electromagnetic induction heating cooker comprising a temperature protection circuit that cuts off an output of the circuit.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an electrical connection diagram of an electromagnetic induction heating cooker according to the present invention. FIG. 3 is an overall configuration diagram of the electromagnetic induction heating cooker shown in FIG. 1.
[0012]
In FIG. 1, the rectifier circuit DR1 rectifies the output of the commercial AC power source and converts it into a DC voltage, and the smoothing capacitor C1 smoothes the voltage converted into DC.
[0013]
The input current detection circuit ID detects an input current value and outputs an input current detection signal Id, and the input voltage detection circuit IV detects an input voltage value and outputs an input voltage detection signal Iv.
[0014]
The switching element TR1 and the switching element TR2 are switching elements that form a half-bridge type inverter circuit, and for example, MOSFETs or IGBTs are used. The induction heating coil HL forms a series resonance with the resonance capacitor C2 and the resonance capacitor C3. The top plate PL is installed close to the upper surface of the induction heating coil HL, and is heated by electromagnetic induction with a pan PB. When the heating start signal Ts of the heating switch TS is input, the fan drive circuit FD outputs a fan drive signal Fd that rotates at the normal rotation speed. The blower fan FA rotates the fan at a normal rotational speed when the fan drive signal Fd is input.
[0015]
The switching element drive circuit SD performs PFM control that modulates the pulse frequency with a constant pulse width ratio according to the value of the control processing signal Sc from the control processing circuit SC, and controls the switching element TR1 and the switching element TR2. Drive alternately.
[0016]
The power calculation circuit SA inputs the input current detection signal Id and the input voltage detection signal Iv and calculates the input power of the inverter. The power setting circuit PC sets a predetermined power setting signal Pc.
[0017]
The non-contact temperature sensor NC is installed at a predetermined position in the center of the induction heating coil HL on the lower surface of the top plate PL shown in FIG. 3, and the non-contact temperature sensor NC includes two high-precision thermistors and infrared absorption. An infrared ray film is used to convert infrared rays emitted from the top plate PL into heat, and this heat is measured with a detection thermistor. The other thermistor measures ambient temperature for temperature compensation, The outputs of the two thermistors are calculated to accurately detect the temperature around the central portion of the top plate PL and output it as a temperature sensor signal Nc.
[0018]
The temperature detection determination circuit TA sets a predetermined second temperature rise limit value T2 less than the temperature rise limit value T3 shown below, and calculates the value of the temperature sensor signal Nc and the second temperature rise limit value T2. In comparison, while the value of the temperature sensor signal Nc exceeds the second temperature rise limit value T2, the temperature detection determination signal ta is output.
[0019]
The power limiting circuit OA is formed by a resistor R1, a resistor R2, a resistor R3, a first analog switch AS1, an operational amplifier OP1, and an operational amplifier OP2. The power limiting circuit OA operates as an attenuation circuit. When the temperature detection determination signal ta is input and the analog switch AS1 is turned on, the resistor R3 and the resistor R1 are connected in parallel, and the value of the normal power setting signal ( For example, when 1/2) is attenuated, the power setting signal Pc is decreased and output as the power limit signal Oa, and the temperature detection determination signal ta is not input and the analog switch AS1 is cut off, the value of the power setting signal Pc is decreased. Output without
[0020]
The differential amplifier circuit CO differentially amplifies the power limit signal Oa and the power calculation signal Sa, and outputs the value of the differential amplified signal ΔI. The control processing circuit SC starts operation when the heating start signal Sc is input from the heating switch TS, performs calculation according to the value of the differential amplification signal ΔI, and when the value of the differential amplification signal ΔI is large The value of the control processing signal Sc is decreased, and conversely, when the value of the differential amplification signal ΔI is small, the value of the control processing signal Sc is increased.
[0021]
When the value of the control processing calculation signal Sc input from the control processing circuit SC is small, the switching element drive circuit SD increases the frequency of the PFM control to increase the impedance of the resonant tank including the induction heating coil HL and the resonant capacitors C2 and C3. The value is increased to reduce the current flowing through the induction heating coil HL. Conversely, when the value of the control calculation signal Sc is large, the current flowing through the induction heating coil HL is increased by lowering the frequency of the PFM control and decreasing the impedance value of the resonant tank to increase the current flowing through the induction heating coil HL. Take control.
[0022]
The temperature protection circuit TP sets a predetermined temperature rise limit value T3 that is equal to or greater than the second temperature rise limit value T2, compares the value of the temperature sensor signal Nc with the temperature rise limit value T3, and compares the temperature sensor When the value of the signal Nc exceeds the temperature rise limit value T3, the temperature protection signal Tp is output. When the temperature protection signal Tp is input, the control processing circuit SC prohibits the output of the control processing signal Sc and cuts off the output of the inverter circuit.
[0023]
FIG. 4 is a temperature characteristic diagram during operation around the center of the top plate PL of the present invention. The operation of the present invention will be described with reference to FIG.
[0024]
When the electromagnetic induction heating cooker IH activates the heating switch TS, it starts heating according to the value of the power setting signal Pc set by the power setting circuit PC. When the heating is normal, the central portion of the top plate PL As shown in FIG. 4, the ambient temperature is controlled within a normal temperature range.
[0025]
At time t = t1 shown in FIG. 4, when the water in the pan PB evaporates and empty cooking occurs, a rapid load fluctuation occurs, and the temperature of the top plate PL that is in contact with the pan PB rises rapidly. To do. When the temperature further rises and at time t = t3, the temperature detection determination circuit TA outputs the temperature detection determination signal ta when the value of the temperature sensor signal Nc exceeds the second temperature increase limit value T2.
[0026]
When the temperature detection determination signal ta is input to the power limit circuit OA, the power limit circuit OA reduces the power setting signal to a predetermined value and outputs the power limit signal Oa. The differential amplifier circuit CO differentially amplifies the power limiting signal Oa and the multiplication processing signal Sa, and outputs a value of the differential amplified signal ΔI. At this time, the value of the differential amplification signal ΔI increases and the value of the control processing calculation signal Sc decreases.
[0027]
When the value of the control processing calculation signal Sc decreases, the switching element drive circuit SD increases the frequency of the PFM control to increase the impedance value of the resonant tank, thereby reducing the value of the current flowing through the induction heating coil HL. The temperature rise after the time t = t3 shown is suppressed.
[0028]
Even if the power setting signal is reduced, the temperature rise of the top plate PL cannot be suppressed, and when the value of the temperature sensor signal Nc exceeds the temperature rise limit value T3 at time t = t5 shown in FIG. The circuit TP determines that the temperature is abnormal and outputs a temperature protection signal Tp, prohibits the operation of the control processing circuit SC, and cuts off the output of the inverter circuit.
[0029]
In order to return the electromagnetic induction heating cooker IH, the temperature protection signal Tp is canceled when the temperature of the top plate PL decreases and becomes lower than a predetermined protection release temperature T4 (not shown) that is lower than the temperature rise limit value T3, By starting the reset circuit RS shown in FIG. 1, the control processing circuit SC becomes operable, and heating of the pan PB is started.
[0030]
[Example 2]
FIG. 2 is an electrical connection diagram of the electromagnetic induction heating cooker according to the second embodiment. In the figure, the same reference numerals as those in the electrical connection diagram of the electromagnetic induction heating cooker of the present invention shown in FIG.
[0031]
The fan control circuit FP starts operating when the heating start signal Ts is input, sets a predetermined normal temperature rise limit value T1 that is less than the second temperature rise limit value T2, and sets the value of the temperature sensor signal Nc. Is smaller than the normal temperature rise limit value T1, the blower fan FA is rotated normally, and it is determined that the abnormal temperature rise continues when the value of the temperature sensor signal Nc exceeds the normal temperature rise limit value T1. Then, the value of the fan control signal Fp is increased and output (for example, twice the normal drive signal Fd), and the number of rotations of the blower fan FA is increased to enhance the cooling inside the electromagnetic induction heating cooker.
[0032]
FIG. 4 is a temperature characteristic diagram during operation around the center of the top plate PL of the second embodiment. The operation of the present invention will be described with reference to FIG.
[0033]
When the electromagnetic induction heating cooker IH activates the heating switch TS, it starts heating according to the value of the power setting signal Pc set by the power setting circuit PC. When the heating is normal, the central portion of the top plate PL As shown in FIG. 4, the ambient temperature is controlled within a normal temperature range.
[0034]
At time t = t1 shown in FIG. 4, when the water in the pan PB evaporates and empty cooking occurs, a rapid load fluctuation occurs, and the temperature of the top plate PL in contact with the rapid temperature rise of the pan PB is also To rise.
[0035]
If the temperature sensor signal Nc exceeds the normal temperature rise limit value T1 at time t = t2 when the temperature rise cannot be suppressed, the fan control circuit FP determines that an abnormal temperature rise has occurred and the fan The value of the control signal Fp is increased to increase the rotational speed of the blower fan FA, and the cooling inside the electromagnetic induction heating cooker is strengthened to suppress the temperature rise of the pan PB or the top plate PL.
[0036]
Further, when the temperature rises and the value of the temperature sensor signal Nc exceeds the second temperature rise limit value T2 at time t = t4, the output of the inverter circuit is reduced by reducing the power setting signal to a predetermined value. To suppress the temperature rise.
[0037]
【The invention's effect】
In order to measure the temperature of the top plate, the temperature is measured by directly contacting the top plate using a thermistor element or thermostat. In the present invention, the non-contact temperature sensor is used to contact the top plate. Eliminates the need for complicated fixing stops. Further, the thermistor element or thermostat has a problem of accuracy because the temperature of the top plate is detected at a single point. However, the temperature of the top plate can be measured in a relatively wide range by using a non-contact temperature sensor. Therefore, the accuracy of the measurement temperature of the top plate can be greatly improved.
[Brief description of the drawings]
FIG. 1 is an electrical connection diagram of an electromagnetic induction heating cooker according to the present invention.
FIG. 2 is an electrical connection diagram of the electromagnetic induction heating cooker according to the second embodiment.
FIG. 3 is an overall configuration diagram of an electromagnetic induction heating cooker according to the present invention.
FIG. 4 is a temperature characteristic diagram during operation around the central portion of the top plate of the present invention.
FIG. 5 is an overall configuration diagram of a conventional electromagnetic induction heating cooker.
[Explanation of symbols]
AS analog switch CB coil base CO differential amplifier circuit C1 smoothing capacitor C2 resonant capacitor C3 resonant capacitor DR1 rectifier circuit FA blower fan FD fan drive circuit FP fan control circuit HL induction heating coil HS high frequency power supply ID input current detection circuit IH electromagnetic induction heating Cooker IV Input voltage detection circuit NC Non-contact temperature sensor OA Power limiting circuit OP1 First amplifier circuit OP2 Second amplifier circuit PC Power setting circuit PB Pan PL Top plate RS Reset circuit R1 Resistor R2 Resistor R3 Resistor SA Power calculation circuit SC Control processing circuit SD Switching element drive circuit TA Temperature detection discrimination circuit TD Temperature detection part TP Temperature protection circuit TS Heating switch TR1 Switching element TR2 Switching element Fd Fan drive signal Fp Fan control signal Id input Current detection signal Iv Input voltage detection signal Nc Temperature sensor signal Oa Power limit signal Pc Power setting signal Sa Power calculation signal Sc Control processing signal Ta Temperature detection determination signal Tp Temperature protection signal Ts Heating start signal ΔI Differential amplification signal T1 Normal temperature rise Limit value T2 Second temperature rise limit value T3 Temperature rise limit value

Claims (1)

A resonant capacitor; an induction heating coil that forms a series resonance with the resonant capacitor; a rectifier circuit that rectifies a commercial AC power supply to convert it into a DC voltage; and a high-frequency current in the induction heating coil using the DC voltage of the rectifier circuit as an input An inverter circuit that supplies power, a power calculation circuit that calculates an input power of the inverter circuit and outputs a power calculation signal, a power setting circuit that outputs a predetermined power setting signal, the power calculation signal and the power setting A differential amplifier circuit for differentially amplifying a signal; a control processing circuit for controlling an output frequency of the inverter circuit in accordance with a differentially amplified signal of the differential amplifier circuit; a blower fan for cooling the interior; and the induction An electromagnetic induction heating cooker comprising: a top plate installed close to the top surface of the heating coil; and a pan placed on the top plate for heating Oite,
A non-contact temperature sensor for detecting the temperature of the lower surface of the top plate in a non-contact manner and outputting a temperature sensor signal; and when the value of the temperature sensor signal exceeds a predetermined normal temperature rise limit value, A fan control circuit for increasing the number of revolutions to moderate the temperature rise of the pan, and the inverter circuit when the value of the temperature sensor signal exceeds a predetermined second temperature rise limit value higher than the normal temperature rise limit value A power limiting circuit for attenuating the value of the power setting signal for controlling the output of the inverter, and the inverter when the value of the temperature sensor signal exceeds a predetermined temperature rise limit value higher than the second temperature rise limit value An electromagnetic induction heating cooker comprising a temperature protection circuit that cuts off an output of the circuit.

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