JPH0644510B2 - Induction heating cooker - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to improvement of an induction heating cooker, and even when the property of an object to be cooked is different, appropriate heating is performed to quickly obtain an appropriate cooking temperature. The present invention relates to an induction heating cooker that is controlled to be controlled.

[Prior Art] FIG. 3 is a circuit diagram of a conventional induction heating cooker disclosed in Japanese Patent Laid-Open No. 61-230288, and FIG. 2 is a block diagram thereof. In the figure, 1 is a cooking container such as a fryer, 2 is an object to be cooked such as tempura oil, 3 is an upper plate on which the cooking container 1 is placed, 4 is a heating coil for inductively heating the cooking container 1, and 5 is The temperature detection unit uses a thermistor or the like, and is provided on the lower surface of the upper plate 3 to indirectly detect the temperature of the cooking container 1. A temperature setting unit 6 sets a temperature required for cooking and gives an instruction to the control circuit, which is operated and set by the user. Reference numeral 7 is a control circuit, 8 is a frequency conversion circuit, and 9 is a commercial power source. The frequency conversion circuit 8 receives electric power from the commercial power supply 9, outputs high frequency electric power according to the output signal from the control circuit 7, and supplies the high frequency electric power to the heating coil 4. Due to the change in the high-frequency magnetic flux generated by the heating coil 4, heat is generated in the cooking container 1 and the cooking target 2 is heated.

Next, the control means and operation of the heating or cooking temperature in the conventional induction heating cooker will be described for the case of cooking tempura, for example. In FIGS. 2 and 3, the tempura oil 2 is put in the frying pan 1 and placed on the upper plate 3, the temperature of the temperature setting section 6 is set, and the power source 9 is turned on. Then, the frequency conversion circuit 8 generates high-frequency AC power and supplies the high-frequency AC power to the heating coil 4, and the change in magnetic flux by the heating coil 4 causes the tempura pan 1
And the tempura oil 2 is heated and the temperature rises. The temperature is detected by the temperature detector 5 and input to the control circuit 7. The control circuit 7 compares the temperature input signal from the temperature detection unit 5 with the temperature set in the temperature setting unit 6, and when the detected temperature reaches or approaches the set temperature, instructs the frequency conversion circuit 8 to do so. Turns off or reduces heating power.

However, since the temperature sensing part such as the thermistor of the temperature detecting part 5 is attached to the lower surface of the upper plate 3, the temperature of the pan 1 or the tempura oil 2 cannot be directly detected and is indirect. It takes time for the temperature of 1 to be transmitted to the temperature detection unit 5. That is, there is a delay in tracking the temperature change. In particular, during heating after the start of cooking, as shown in FIG. 10, the temperature detected by the temperature detection unit 5 cannot follow the rapid temperature rise of the temperature of the pan or the frying oil, and the oil temperature and the temperature detected. There is a big difference between and. If the above-mentioned control is performed with this as it is, there is a danger that the oil temperature reaches the ignition temperature and the ignition occurs before the detected temperature reaches the set temperature.

Therefore, as shown in FIG. 11, the heating output P that is half the maximum heating output PMAX from the start of heating to the predetermined time t _1.
The heating output is set to 1/2 and the heating output is set to the maximum heating output P after avoiding a sudden temperature rise and allowing the detected temperature to follow the oil temperature.
A control means is employed in which heating is performed as MAX, and the heating output is stopped when the detected temperature reaches the temperature set by the temperature setting unit 6. With this control means, as shown in FIG. 10, it is possible to prevent an extremely large difference between the oil temperature and the detected temperature, and the oil temperature reaches the oil ignition temperature before the detected temperature reaches the set temperature. We try to prevent inconveniences such as fire accidents.

[Problems to be Solved by the Invention] Since the control means of the conventional induction heating cooker is configured as described above, the occurrence of a fire accident can be prevented. However, for example, when the amount of tempura oil is normal or high, the rising rate of the oil temperature is not rapid, so the detected temperature can follow without making a large difference, and when the detected temperature reaches the set temperature, the oil temperature Is not very hot and there is no risk of fire accidents. Nevertheless, as shown in FIG. 11, since heating is performed at half the heating output for a predetermined time, there is a problem in that the rise in oil temperature is delayed by that amount and cooking takes time.

The present invention has been made to solve the above problems. For example, when the amount of oil in tempura oil is small, the heating output is limited to cause the oil temperature to rise too high and cause oil ignition. An object of the present invention is to provide an induction heating cooker capable of preventing such a situation and heating in the normal tempura cooking with the maximum heating output so as not to delay the oil temperature rise.

[Means for Solving the Problems] In the induction heating cooker according to the present invention, the control circuit for controlling the heating output provides the detection temperature input from the temperature detection unit with the change rate of the detection temperature and the predetermined time. The predicted temperature is calculated by adding the product, and the predicted temperature is compared with the set temperature. If the predicted temperature is less than or equal to the set temperature, the maximum heating output is obtained. When the predicted temperature exceeds the set temperature, the set temperature is detected. The heating output is determined so as to obtain the modified reduced heating output determined according to the difference from the temperature, and the control signal is output.

[Operation] The control circuit of the induction heating cooker according to the present invention calculates the predicted temperature by adding the product of the change rate of the detected temperature and the predetermined temperature to the detected temperature, and compares the predicted temperature with the set temperature. Control heating output. Therefore, when the amount of cooking target is small and the rate of temperature increase is large, the detected temperature is considerably lower than the temperature of the cooking target due to the tracking delay, but the predicted temperature is the temperature change rate (temperature rising rate). Is calculated as a high temperature. Since the heating output is controlled by the predicted temperature calculated to be high, it is possible to prevent the cooking target from becoming excessively hot.

Further, when the amount of the cooking target is large and the rate of temperature increase is small, the temperature detection unit has a small follow-up delay, and the detected temperature is not much different from the temperature of the cooking target. At this time, the predicted temperature is also calculated from the detected temperature to a value that is not too high because the temperature change rate is small. Therefore, the predicted temperature, which is not too high, is compared with the set temperature to control the heating output, and the maximum heating output is operating for a long time, so the set temperature is quickly reached and the cooking time is not delayed. To be done. When the predicted temperature exceeds the set temperature, the heating output is determined and the control signal is output so that the corrected reduced heating output is set according to the difference between the set temperature and the detected temperature. The proper heating output is achieved, and it is prevented that the temperature becomes excessively high.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. First
The drawing is a flowchart of the control operation performed by the control circuit of the induction heating cooker according to the embodiment of the present invention. 2 and 3 are a block diagram and a circuit diagram, respectively, of the induction heating cooker. 4 and 5 are explanatory diagrams of calculation of predicted temperature, FIG. 6 is a graph of heating output with respect to a control signal from the control circuit,
FIG. 7 is a diagram showing an example of gain, FIG. 8 is a diagram showing temperature changes when the properties of the cooking object are different, and FIG. 9 is a diagram showing changes in heating output corresponding to FIG.

In FIGS. 2 and 3, 1 is a cooking container such as a frying pan, 2 is a cooking object such as frying oil, and 3 is a cooking container 1.
An upper plate on which is mounted, 4 is a heating coil for generating magnetic flux, 5 is a temperature detection unit such as a thermistor, 6 is a temperature setting unit, 7 is a control circuit, 8 is a frequency conversion circuit, and 9 is a commercial power supply.
The control circuit 7 has a built-in microcomputer, and the set temperature set by the user in the temperature setting section 6 and the temperature detecting section 5 are set.
The detected temperature detected by is input, processing such as conversion and calculation is performed to determine the heating output, and a command is output to the frequency conversion circuit 8. The frequency conversion circuit 8 converts the frequency according to the command output from the control circuit and sends high-frequency power to the heating coil 4, the heating coil 4 generates a magnetic flux that changes at a high frequency, and the pan 1 and the tempura oil 2 are generated by induction heating. To heat.

Next, the operation of the control circuit 7 that determines the heating output and outputs the control signal to the frequency conversion circuit 8 will be described. In FIG. 1, when the power is turned on and the heating is started, the control circuit 7 also starts to operate, and the control output for commanding the frequency conversion circuit 8 is output as the maximum value V _H. As shown in FIG. 6, the heating output P corresponding to the maximum value V _H of the control output is the maximum heating output PMAX, and the frequency conversion circuit 8 performs frequency conversion to generate the maximum heating output and heats the power. Send to coil 4. On the other hand, the control circuit 7 stores the detected temperature signal input from the temperature detection unit 5 as a value at a predetermined time interval Δt such as 10 seconds. The predicted temperature is calculated from this detected temperature. The predicted temperature is the temperature obtained by adding the product of the rate of change of the detected temperature and the predetermined time to the detected temperature at that time. For example, if the predetermined time is 60 seconds and the above-mentioned time interval is 10 seconds, as shown in FIG.
If only the next temperature change rate is taken, T = T ₀ + 6 × ΔT ₀ , and as shown in FIG. 5, if the secondary temperature change rate is taken, T = T ₀ + 6 × {ΔT ₀ − ( ΔT ₁ −ΔT ₀ )}. However, T is the predicted temperature, T ₀ is the temperature detected at the calculation point in time, △ T ₀ is the temperature change rate, the current detection temperature T ₀ 10
It is the difference (T ₀ −T ₁ ) from the previous temperature T ₁ detected a second before. ΔT ₁ is the difference (T ₁ −T ₂ ) between the previously detected temperature T ₁ and the _two- preceding detected temperature T ₂ detected 20 seconds ago, and (ΔT ₁ −Δ
T ₀ ) represents the second-order temperature change rate.

Therefore, the former equation is T = T ₀ + 6 × (T ₀ −T ₁ ) T = 7 × T ₀ −6 × T ₁ , and the latter equation is T = T ₀ + 6 × (2T ₀ −3T ₁ + T ₂ ) becomes _{T = 13 × T 0 -18 ×} T 1 + 6 × T 2.

The predicted temperature calculated in this way indicates the temperature after a predetermined time (60 seconds) estimated from the current temperature and the state of temperature change, as shown in FIG. 4 or FIG. In fact, as shown in FIG. 8, when the temperature rises rapidly, the detection temperature of the temperature detection unit has a large follow-up delay with respect to the change in the temperature of the oil to be cooked, so a large correction amount is added to the detection temperature. Further, when the temperature rise is gentle, it is better to consider that the present actual oil temperature is estimated by adding a small correction amount.

Next, the calculated predicted temperature is compared with the set temperature, and if the predicted temperature does not exceed the set temperature, it returns to the original state and 1
After 0 seconds, the predicted temperature is calculated again from the detected temperature, and the same operation as above is repeated. If the predicted temperature exceeds the set temperature, the control output is corrected and output so as to reduce the heating output. The decreasing rate may be 100% or a predetermined amount, but in this embodiment, as shown in FIG.
The gain G is set for the value of the difference between the set temperature and the detected temperature, and the gain G is set as the correction ratio of the control circuit output.
The control output is modified by this gain G and output to the frequency conversion circuit 8, and the heating output is reduced.

As shown in FIG. 7, the gain G is set to be small when the difference between the set temperature and the detected temperature is small, and is set to be large when the difference is large, so that the amount of tempura oil is small as shown in FIG. If the temperature rise is rapid in (a), the difference between the predicted temperature a is set point t _a the set temperature the temperature exceeds the detection temperature T _a is large, in FIG. 7, the gain G is set larger, The reduction rate of the heating output becomes large, and the heating output P _a becomes low as shown by the line a in FIG. On the other hand, when the amount of oil is large and the temperature rise in FIG. 8 is gentle (b), at the time t _b when the predicted temperature b exceeds the set temperature, the difference between the set temperature and the detected temperature T _b is The heating output P _b is small and not so low as shown by the line b in FIG. 9. This is because if the temperature rises rapidly, it is necessary to reduce the heating output to prevent the temperature from rising too high, and even if the heating output is low, the temperature rise can be obtained. In this case, even if the heating output is large, there is no risk of the temperature rising too much, and a relatively large heating output is required until the set temperature is obtained.

In addition, in FIG. 1, the temperature detection and the calculation of the predicted temperature are
For example, it is repeated every 10 seconds, and if the predicted temperature exceeds the set temperature and is corrected so as to reduce the heating output, or after the correction is repeated and the predicted temperature becomes equal to or lower than the set temperature, the heating output is changed. Although it is necessary to increase the number, illustration of the operation is omitted. In that case, the flow chart as shown by the broken line may be set so that the maximum control output is V _H, and thereafter, the normal ON / OFF control may be performed.

If the time interval of 10 seconds for calculating the predicted temperature is shortened to, for example, 5 seconds, more precise control can be obtained. If the predetermined time of 60 seconds is increased to 120 seconds, for example, the coefficient for multiplying the temperature change rate is 12 instead of 6.
Therefore, the oil temperature rise is controlled earlier, which is more advantageous in preventing oil ignition.

The gain graph shown in FIG. 7 is an example, and may be set so that appropriate control can be obtained depending on the detection characteristics of the temperature detection unit 5 and the heating output characteristics with respect to the control circuit output shown in FIG. .

[Effects of the Invention] As described above, according to the present invention, the predicted temperature is calculated according to the tendency (rate of change) of the temperature rise, and the control output is corrected to control the heating output. Regardless of the nature of the above, since an appropriate heating output is automatically given, there is an effect that an overheating is prevented and an induction heating cooker in which the temperature rise is not delayed can be obtained.

[Brief description of drawings]

1 to 9 show an embodiment of the present invention, FIG. 1 is a flowchart of heating control, FIG. 2 is a block diagram of an induction heating cooker, FIG. 3 is a circuit diagram, and FIG. 4 is a prediction. Calculation chart of temperature, FIG. 5 is calculation chart of higher predicted temperature, FIG. 6 is a relational chart of heating output with respect to control output, FIG. 7 is a diagram showing an example of gain, and FIG. 8 is different in oil amount FIG. 9 is a diagram showing an increase in the oil temperature and a predicted temperature with respect to the case, and FIG. 9 is a diagram showing changes in the heating output in the case of FIG. FIG. 10 is a diagram showing the oil temperature and the detected temperature of the conventional induction heating cooker, and FIG. 11 is the 10th diagram.
It is a figure which shows the heating output in the case of a figure. In the figure, 1 is a cooking container, 2 is an object to be cooked, 3 is an upper plate, 4 is a heating coil, 5 is a temperature detection unit, 6 is a temperature setting unit, 7 is a control circuit, and 8 is a frequency conversion circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masamitsu Kawashima, Masamitsu Kawashima, 3-18-1, Oka, Shizuoka-shi, Shizuoka Mitsubishi Electric Mechatronics Software Co., Ltd. Shizuoka branch office (72) Inventor, Mitsuru Murata 3 Oga, Shizuoka-shi, Shizuoka No. 18-1 Mitsubishi Electric Mechatronics Software Co., Ltd. Shizuoka Branch (56) References JP-A-61-216293 (JP, A) JP-A-62-69484 (JP, A)

Claims (1)

[Claims] 1. A heating coil for induction heating a cooking container, a frequency conversion circuit for supplying electric power to the heating coil, a temperature detection unit for detecting a temperature near the bottom of the cooking container, and a temperature setting for setting the temperature. And a control circuit having a built-in microcomputer, the control circuit inputs the set temperature of the temperature setting section and the detected temperature signal of the temperature detecting section, and outputs the control signal to the frequency converting circuit. In the induction heating cooker that controls the heating output, the control circuit calculates the predicted temperature by adding the product of the change rate of the detected temperature and the predetermined time to the detected temperature input from the temperature detection unit, The predicted temperature is compared with the set temperature, and if the predicted temperature is less than or equal to the set temperature, the maximum heating output is set. When the predicted temperature exceeds the set temperature, the maximum temperature is set according to the difference between the set temperature and the detected temperature. Induction cooking device, characterized in that the heating output is determined so as to the modified reduced heating output, and outputs a control signal.